Elizabeth Donovan, Senior Biologist Rosanna Louie‐Juzwiak, Risk Assessment Process Leader Environmental Risk Branch III Environmental Fate and Effects Division

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D.C. 20460

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION September 3, 2020

PC Code: 053001 MEMORANDUM DP Barcode: 456133

SUBJECT: Metaldehyde: Draft Ecological Risk Assessment for Registration Review

FROM: Katherine Stebbins, Biologist Sarah Hafner, Ph.D., Chemist Environmental Risk Branch III Environmental Fate and Effects Division

REVIEWED Jessica L. O. Joyce, Physical Scientist BY: Elizabeth Donovan, Senior Biologist Rosanna Louie‐Juzwiak, Risk Assessment Process Leader Environmental Risk Branch III Environmental Fate and Effects Division

THROUGH: Dana Spatz, Branch Chief Environmental Risk Branch III Environmental Fate and Effects Division

TO: Rachel Eberius, Chemical Review Manager Nicole Zinn, Team Leader Kevin Costello, Branch Chief Risk Management and Implementation Branch 2 Pesticide Re‐evaluation Division

The Environmental Fate and Effects Division (EFED) has completed the draft ecological risk assessment in support of the Registration Review of the molluscicide, metaldehyde.

Draft Ecological Risk Assessment for the Registration Review of Metaldehyde

Metaldehyde; CAS No: 108‐62‐3

USEPA PC Code: 053001

Prepared by: Katherine Stebbins, Biologist Sarah Hafner, Ph.D., Chemist

Reviewed by: Jessica L. O. Joyce, Physical Scientist Elizabeth Donovan, Senior Biologist

Approved by: Dana Spatz, Branch Chief Environmental Risk Branch III Environmental Fate and Effects Division Environmental Fate and Effects Division Office of Pesticide Programs United States Environmental Protection Agency

Table of Contents

1 Executive Summary ...... 3 1.1 Overview ...... 3 1.2 Risk Conclusions Summary ...... 3 1.3 Environmental Fate and Exposure Summary ...... 5 1.4 Ecological Effects Summary ...... 5 1.5 Identification of Data Needs ...... 6 2 Introduction ...... 7 3 Problem Formulation Update ...... 8 3.1 Mode of Action for Target Pests ...... 9 3.2 Label and Use Characterization ...... 9 3.2.1 Label Summary ...... 9 4 Environmental Fate Summary ...... 12 5 Ecotoxicity Summary ...... 15 5.1 Aquatic Toxicity ...... 15 5.2 Terrestrial Toxicity ...... 18 5.3 Incident Data ...... 20 6 Analysis Plan ...... 24 6.1 Overall Process ...... 24 6.2 Modeling ...... 25 7 Aquatic Organisms Risk Assessment ...... 25 7.1 Aquatic Exposure Assessment ...... 25 7.1.1 Monitoring ...... 26 7.2 Aquatic Organism Risk Characterization ...... 26 7.2.1 Aquatic Plants: ...... 26 8 Terrestrial Vertebrates Risk Assessment ...... 27 9 Terrestrial Invertebrate Risk Assessment ...... 28 9.1 Bee Exposure Assessment ...... 28 9.2 Bee Tier I Exposure Estimates ...... 31 9.3 Bee Risk Characterization (Tier I) ...... 32 9.3.1 Tier I Risk Estimation (Contact Exposure) ...... 32 9.3.2 Tier I Risk Estimation (Oral Exposure) ...... 32 9.4 Bee Risk Characterization – Additional Lines of Evidence ...... 33 10 Conclusions ...... 34 11 Literature Cited ...... 34 12 Referenced MRIDs ...... 39 Appendix A. ROCKS table...... 50 Appendix B. BeeRex Modeling Inputs/Outputs ...... 52 Appendix C. Endocrine Disruptor Screening Program (EDSP) ...... 56 Appendix D. Potential Exposure from Consumption of Pellets (USEPA, 2014 Assessment) .... 57

1 Executive Summary

1.1 Overview Metaldehyde is a systemic molluscicide for controlling terrestrial slugs and snails. Metaldehyde is registered in the United States for use on a variety of agricultural crops including: artichokes, berries, brassica crops, leafy vegetables, citrus, clover, cole crops, field and sweet corn, herbs, ginseng, grasses grown for seed/ forage/ fodder, onion, peas/beans, soybeans, prickly pear cactus pads, taro, tomato, vetch, ornamental sod farm (turf), Christmas tree plantations, and watercress. Non‐agricultural uses include: golf course turf, non‐agricultural cultivated areas/soils, ornamentals, ornamental lawns and turf, and as a wide area/general outdoor treatment for state and federal invasive mollusk eradication programs.

This Draft Risk Assessment (DRA) examines the potential ecological risks associated with labeled uses of metaldehyde to non‐target organisms that are not listed as Federally threatened or endangered species (referred to as “non‐listed”). The risk assessment takes a streamlined approach to focus on the taxa of primary risk concern based on previously completed risk assessments, and also taxa for which additional data have become available. New data are available for assessing risk to bees and for updating the risk for aquatic plants (using exposure values from previous assessments). The only models required for this streamlined assessment were for assessing risk to bees (BeeREX and AgDRIFT). Risk conclusions for all other aquatic and terrestrial organisms are summarized in this document based on previous risk assessments.

1.2 Risk Conclusions Summary

Terrestrial Vertebrates The primary risk from metaldehyde exposure is for birds (surrogates for reptiles and terrestrial‐ phase amphibians) and mammals. Numerous uses were assessed for granular metaldehyde products in 2013, 2014, and 2016 and the greatest risk is from direct consumption of the granular bait. Summarizing from previous assessments, the risk for granular consumption is 2 based on the median lethal dose per sq. ft. (LD50/ft ) analysis. As reported in USEPA, 2016, there is a potential for risk to birds and mammals as the RQ values exceed the Levels of Concern (LOCs). Risk Quotients (RQs) exceed the acute risk level of concern (LOC) of 0.5 for small birds and mammals (avian RQs: 3.6‐18.2, mammalian RQs: 0.79‐3.97). The RQ values also exceed the acute risk LOC for medium‐size birds (RQs 0.57‐2.9) and mammals (RQs 0.42‐2.1). To further investigate the acute risk to birds and mammals, the number of bait granules (pellets) that an animal must ingest to reach the LD50 dose was estimated. This analysis found that a small bird and a small mammal would need to consume 8 and 37 pellets, respectively, to reach the LD50. Based on these results, there is a potential that small birds or mammals feeding on treated pellets will exhibit signs of acute toxicity (e.g., mortality, neurotoxicity). Additionally, there are several bird and mammal mortality incidents to support the likelihood of acute adverse effects from granular bait consumption.

For chronic risk, a similar analysis relating the number of pellets to reach the endpoint concentrations found that the Bobwhite Quail (Colinus virginianus) could reach exposure levels that cause adverse effects by consuming only 3 pellets (3 pellets to reach the LOAEC for reduced egg hatching; effects at all treatment levels‐NOAEC not established). For mammals, the exposure for a small mammal (e.g., deer mouse; Peromyscus maniculatus) would reach the chronic mammalian NOAEC with consumption of 11 pellets.

While the ecological assessments typically focus on wild animals, of note is that the dog is the most sensitive mammal tested throughout the entire mammalian toxicity dataset (USEPA, 2016). Thus, the higher sensitivity for dogs, in conjunction with the continued incidents of domestic pet (dog) mortalities (151 since 2010), is another line of evidence for acute risk to domestic (and wild) mammals from consumption of the granular bait.

Aquatic Organisms Acute and chronic RQ values for fish and aquatic invertebrates were below their respective LOCs for all of the uses assessed in 2013 and 2014 including the highest exposure scenario for use on taro. These results indicate that metaldehyde uses have minimal risk to fish and aquatic invertebrates. However, five incident reports describe adverse effects to fish in residential ponds following application of products (residues not confirmed) of slug and snail bait containing metaldehyde. This raises uncertainty that metaldehyde slug and snail bait may be hazardous to fish under some circumstances, possibly from direct oral ingestion of the bait.

Terrestrial Invertebrates For acute exposure to adult honey bees (Apis mellifera), the endpoint is non‐definitive (e.g., the acute oral LD50 greater than 87 µg a.i./bee), thus, RQs are not calculated. However, when comparing the estimated environmental concentrations (EECs) to the highest dose tested, the foliar rate of 2 pounds of active ingredient per acre (lbs a.i./A) produces EECs within the range of the highest tested concentration; thus, there is uncertainty for acute risk to bees at the 2 lb a.i./A rate (for foliar applications). There would be no LOC exceedances for the soil applications. Acute contact toxicity is also based on a non‐definitive endpoint and using a similar comparison to the highest test concentration as a proxy, there would be no LOC exceedances based on contact exposure. Additionally, data are not available for assessing the toxicity to adult bees on a chronic exposure basis. Chronic risk to larval honey bees (based on reduced adult emergence) is identified for the range of the foliar rates with RQs ranging from 2.1‐5.1 (LOC=1). Risk from applications to soil is below the LOC. Of the limited uses with foliar sprays, only the non‐ agricultural/mollusk eradication uses (e.g., parks, golf courses, rights‐of‐way) would be potentially attractive to pollinators. There is also a potential for spray drift exposure to adjacent attractive areas from the limited foliar uses.

Plants The terrestrial plant toxicity values did not exceed the maximum application rates in the 2013 and 2014 assessments, indicating minimal risk to terrestrial plants. Likewise, the likelihood of adverse effects on non‐vascular and vascular aquatic plants is low after incorporating the newly

4 submitted non‐vascular studies (RQs 0.01‐0.04 compared to LOC of 1.0 after using the highest EECs from the previous 2013 assessment).

1.3 Environmental Fate and Exposure Summary Based on submitted laboratory data, metaldehyde is considered very mobile in soil based on FAO classification system (FAO, 2000), having adsorption coefficients (KF) ranging from 0.1‐0.44 L/kg with corresponding organic carbon partition coefficient (KOC) values between 14.6‐55.7 L/KgOC. Two field studies in California demonstrate metaldehyde mobility in soil with leaching to 6‐12” in one study and 24‐36” in another. Based on Goring et al. (1975), metaldehyde is also expected to be moderately persistent with an aerobic half‐life of 67 days and anaerobic half‐life of 222 days in soil. Acetaldehyde is the only major transformation product but is not expected to result in exposure to organisms due to high volatility. Conversely, metaldehyde has a Henry’s Law constant (2.43 x 10‐8 atm‐m3/mol) and vapor pressure (1.1 x 10‐5 torr) that suggest volatilization is not a major transport route. Metaldehyde is stable to hydrolysis and photolysis (aqueous and soil) under typical environmental conditions. Therefore, the major routes of dissipation for metaldehyde are through runoff, leaching, and aerobic degradation.

1.4 Ecological Effects Summary Aquatic Metaldehyde is classified as slightly toxic to freshwater fish (Rainbow Trout 96‐hr [Oncorhynchus mykiss] LC50 = 69 mg a.i./L) and no more than slightly toxic to freshwater invertebrates (waterflea [Daphnia magna] 48‐h LC50 >77.6 mg a.i./L) on an acute exposure basis. Based on a supplemental acute study with the estuarine/marine invertebrate [Eastern oyster (Crassostrea virginica)], the 96‐hr EC50 based on shell deposition is 12.9 mg a.i./L, classifying it as moderately toxic, and making the oyster the most sensitive invertebrate species on an acute exposure basis. An open literature study reports a slightly more sensitive LC50 value of 7.4 mg a.i./L for the Pacific oyster (Crassostrea gigas). Metaldehyde is classified as practically nontoxic on an acute basis to estuarine/marine (E/M) fish and crustaceans, with LC50/EC50 values exceeding 100 mg a.i./L. A 21‐day chronic toxicity test with freshwater fish resulted in a NOAEC value of 37.5 mg a.i./L, based on a 42% reduction in body weight. No chronic toxicity data are available for E/M fish or invertebrates. Toxicity testing of metaldehyde with aquatic plants indicated that vascular aquatic plants (duckweed) with an EC50 > 105 mg a.i./L, are less sensitive than non‐vascular plants where cyanobacteria (Anabaena flos‐aquae) has an EC50= 22.1 mg ai/L.

Terrestrial Based on the available data, metaldehyde is moderately toxic to birds (LD 50=190 mg a.i./kg‐bw) and mammals (LD 50=398 mg a.i./kg‐bw) on an acute exposure basis. Chronic exposure to the Mallard Duck (Anas platyrhynchus) resulted in a 23% reduction in the hatchability of eggs at the lowest dietary concentration tested (49 mg a.i./kg‐diet). Therefore, a definitive NOAEC could not be established in the study (i.e., NOAEC <49 mg a.i./kg‐diet). In contrast, a test with the Northern Bobwhite Quail did not detect any statistically significant chronic effects with dietary

concentrations up to 497 mg a.i./kg‐diet. As reproductive effects in the mallard were observed at dietary concentrations much lower than those which cause acute toxicity, reproduction impairment of birds may be a concern.

For mammals, the two ‐generation reproduction study with the laboratory rat resulted in parental (9% mortality and hindlimb paralysis) and juvenile effects (slight bodyweight reductions) at the highest concentration of 2,000 mg a.i./kg‐diet (NOAEL = 65 mg a.i./kg‐bw; NOAEC = 1000 mg a.i./kg‐diet). Dogs were noted to be the most sensitive for neurotoxic effects with a chronic NOAEL of 10 mg/kg/day (LOAEL of 30 mg/kg/day based on deaths and atrophy of testes/prostate and clinical signs of neurotoxicity observed at 90 mg/kg/day starting on the first day of exposure).

Metaldehyde is classified as practically non‐toxic to the adult honey bee on both and an acute oral and contact exposure basis (acute contact 48‐hr LC50 of >113 μg a.i./bee; oral LD50 >87 μg a.i./bee). For bee brood (i.e., larvae and pupae), chronic toxicity data are available and the only affected endpoint was adult emergence (13% reduction). The NOAEL and LOAEL were 5.3 and 13 µg ai/larva/day, respectively.

For terrestrial plants, the EC25 is >1.1 lb a.i./A in both the vegetative vigor and seedling emergence tests.

1.5 Identification of Data Needs The acute larval and chronic adult‐ (Tier I) honey bee data have not been submitted. A waiver request for these data was previously reviewed and the decision was to reassess the need for additional data after the chronic larval test was reviewed. In this assessment, the value of obtaining the acute larval toxicity test is low considering the low mortality observed (2‐6% across the treatments) in the early/larval stage of the chronic larval test. In contrast, the submission of a chronic adult toxicity test would be of high value to provide a better understanding of the risk from exposure to foliar applications.

Table 1‐1. Summary of Risk Quotients (RQs) for Taxonomic Groups from Current Uses of Metaldehyde. Risk Exposure RQ Exceeding the LOC Additional Information/ Taxa Quotient Duration for Non‐listed Species Lines of Evidence (RQ) Range1 Acute <0.01‐0.03 No Freshwater Fish Chronic <0.01‐0.02 No Estuarine/ Marine Acute ‐‐ No Data Fish Chronic ‐‐ Based on use on grasses‐highest RQs from Freshwater Acute 0.02‐0.08 No previous taro assessment (USEPA, 2013). Invertebrates Chronic <0.01‐0.01 No Not Estuarine/ Marine Acute ‐‐ Calculated Invertebrates Chronic No Data ‐‐ 6

Risk Exposure RQ Exceeding the LOC Additional Information/ Taxa Quotient Duration for Non‐listed Species Lines of Evidence (RQ) Range1 Newly assessed‐Using EECs from USEPA, Aquatic plants Acute 0.01‐0.04 No 2013. Granular/pelleted risk: A small mammal would need to consume approximately 37 pellets to reach the LD thus, acute risk to Acute 0.3‐3.97 Yes (from 2016) 50, small mammals is possible. Domestic pet Mammals incidents reported (within the 2010‐current time period/ after mitigation). RQ not Chronic NOAEC reached with 11 pellets. Chronic calculated for Yes (from 2016) Based on 9% mortality and paralysis at the granular LOAEC. A small bird would need to consume 8 pellets Acute 0.04‐18.2 Yes (from 2016) to reach the LD50, thus, risk is indicated for consumption of pellets. Incidents reported. Birds RQ not Chronic LOAEC reached from consuming <3 Yes Chronic calculated for pellets. LOAEC based on a 23% reduction in (from 2016) granular egg hatching at the lowest dose tested. Not Risk from metaldehyde applications to soil is Acute Adult calculated low (no LOC exceedances). Of the limited ‐‐ uses with foliar sprays, only the non‐ag/ Terrestrial Chronic Adult No data mollusk eradication uses (e.g., parks, golf Invertebrates2 Acute Larval No data courses, rights of way) would be potentially Foliar: 2.1‐5.1 Yes (foliar) Chronic Larval attractive to pollinators. Granular risk is Soil: 0.02 No (soil spray) assumed to be low.

Not Metaldehyde is predicted to pose minimal Terrestrial Plants ‐ ‐‐ calculated risk to terrestrial plants.

Levels of Concern (LOC):  Terrestrial Vertebrates: Acute=0.5; Chronic=1.0  Terrestrial Invertebrates: Acute=0.4; Chronic=1.0  Aquatic Animals: Acute=0.5; Chronic=1.0  Terrestrial and Aquatic Plants: 1.0 1RQs reflect exposure estimates for parent metaldehyde and maximum application rates allowed on labels. 2RQs for terrestrial invertebrates are applicable to honey bees (Apis mellifera), which are also a surrogate for Apis and non‐Apis bees. Risks to other terrestrial invertebrates (e.g., earthworms, beneficial arthropods) are only characterized when toxicity data are available.

2 Introduction

This DRA examines the potential ecological risks associated with labeled uses of metaldehyde on non‐listed non‐target organisms. Federally listed threatened/ endangered species (“listed”) are not evaluated in this document. The DRA uses the best available scientific information on the use, environmental fate and transport, and ecological effects of metaldehyde. The general risk assessment methodology is described in the Overview of the Ecological Risk Assessment Process in the Office of Pesticide Programs (“Overview Document”) (USEPA, 2004a). Additionally, the process is consistent with other guidance produced by the Environmental Fate

7 and Effects Division (EFED) as appropriate. When necessary, risks identified through standard risk assessment methods are further refined using available models and data. This risk assessment incorporates the available exposure and effects data and most current modeling and methodologies.

3 Problem Formulation Update

The purpose of problem formulation is to provide the foundation for the environmental fate and ecological risk assessment being conducted for the labeled uses of metaldehyde. The problem formulation identifies the objectives for the risk assessment and provides a plan for analyzing the data and characterizing the risk. As part of the Registration Review (RR) process, a detailed preliminary Problem Formulation (USEPA, 2016; DP 429206) for this DRA was published to the docket in March 2016. As summarized in the preliminary Problem Formulation based on previous risk assessments, potential risks associated with the use of metaldehyde include risks to birds and mammals from ingestion of the granular products (pellets). Since the preliminary Problem Formulation, new data are available for an additional bird (a passerine). In addition to avian toxicity data, data for aquatic non‐vascular plants are available and this DRA provides an update to include risk quotients (RQs) using the relevant exposure estimates from past assessments. Previous assessments did not quantify risk to bees so the focus of this assessment is on assessing the risk to bees.

The following newly submitted data are available for assessing risk to birds and non‐vascular aquatic plants: o Avian Acute Oral Study with the House Sparrow (Passer domesticus; MRID: 50603505) o Non‐vascular Aquatic Plant: Freshwater Diatom (Navicula pelliculosa) Toxicity (MRID: 50756602 o Non‐vascular Aquatic Plant: Marine Diatom (Skeletonema costatum) Toxicity (MRID: 50756601 o Non‐vascular Aquatic Plant: Cyanobacteria (Anabaena flos‐aquae) Toxicity (MRID: 50756603) o Non‐vascular Aquatic Plant: Freshwater algae (Raphidocelis subcapitata formerly Pseudokirchneriella subcapitata) Toxicity (MRID: 50603301)

The additional avian study resulted in a higher toxicity endpoint than the current endpoint (i.e., less toxic than to the Bobwhite Quail); thus, the new data have no impact on risk conclusions (i.e., no change to RQ). The new data for the aquatic non‐vascular plants are used in this DRA (adding to the aquatic plant conclusions of low risk).

The following data are available for assessing risk to bees: o Honey bee acute contact with adult bees (MRID: 50603502) o Honey bee acute oral with adult bees (MRID: 50603503 o Honey bee chronic oral toxicity study with bee larvae (MRID: 50964301) These new data are described in more detail in the effects characterization (Section 5).

3.1 Mode of Action for Target Pests

Metaldehyde is a systemic molluscicide for controlling slugs and snails. Slugs and snails are exposed to metaldehyde through contact of the snail’s foot and/or through stomach action after ingestion. Metaldehyde stimulates the mucus‐producing cells to overproduce mucus, thus causing secretion of large quantities of slime by the snail leading to irreversible destruction of mucus cells, followed by desiccation and death.

Several mechanisms of toxicity in non‐target organisms have been proposed for metaldehyde and its degradate acetaldehyde, which is formed at very low pH in the stomach. In mammals, it has been proposed that metaldehyde acts at the ỿ‐aminobutyric acid (GABA) receptor complex, leading to convulsions (Sparks et al. 1996). Acetaldehyde has been shown to act as a releasing factor for 5‐hydroxytryptamine (5‐HT) and noradrenaline (NA) (WHO, 1995). It also competitively inhibits biogenic amine oxidation which, in turn, decreases 5‐hydroxyindoleacetic acid (5‐HIAA), a metabolite of 5‐HT by competitively inhibiting 5‐HT‐oxidation (WHO, 1995). Incident data show that metaldehyde exposure is associated with seizures in dogs.

3.2 Label and Use Characterization

3.2.1 Label Summary Metaldehyde is formulated in 23 Section 3 end‐use products and 6 Special Local Need (SLN) products as granular, pelleted/tableted and ready‐to‐use liquid formulations. Application equipment includes aerial equipment, applicator rolls, granule applicators, ground equipment, hand dispersal, hand‐held sprayers, hose‐end sprayers, product containers, shaker cans, sprayers, sprinkler cans, sprinkler irrigation, and squeeze applicators. Metaldehyde products are most often formulated as granules or pellets that serve as solid bait for snails and slugs. Granular and pelleted products are generally applied to the soil surface using a granular spreader or by manual dispersal, or by aircraft with an aerial granular broadcaster. Liquid products are not approved for aerial application. There is one pelleted/tablet aerial use (Oregon SLN‐OR110016) for Christmas tree plantations.

For the bee risk assessment, the liquid formulation (EPA Reg. No.: 71096‐4) is the primary focus. For the majority of the use sites, the liquid application is targeting the soil around the plant/crop rather than direct spray to the foliage. Application to plant parts is prohibited except for the following: to grass (grown for seed and forage/hay), for application to watercress, and for uses specified under State and Federal invasive eradication operations. These uses may also result in spray drift exposure off site. Table 3‐1 provides a summary of the labelled uses.

Table 3‐1. Summary of the Maximum Labeled Use Patterns for Metaldehyde. Max Single Max # Max Annual App App App MRI Use Site Form Rate App/yr Rate Comments Target Type Equip (d) lbs ai/A * lbs ai/A/yr* Directed/ Artichokes G/L Soil Ground 1 6 per cc [12] 18 Banded Directed/ Berries G/L Soil Ground 0.8 3 [2.4] 14 Banded Directed/ Strawberries G/L Soil Ground 1 6 [6] 14 Banded Directed/ Citrus G/L Soil Ground 1 6 [6] 14 Banded Not Directed/ Clover (grown for seed) G/L Soil Ground 0.8 2 [1.6] 10 allowed in Banded CA Celery, rhubarb, chard, Directed/ G/L Soil Ground 1 4 per cc [8] 21 fennel, etc. Banded SLN OR110016; Aerial Christmas Tree Directed/ Ground G Soil 1 3 [3] 14 application Plantation/Landing site Broadcast /Aerial over the top only in Spring. Directed/ Ginseng G/L Soil Ground 1 6 [6] 21 Banded Directed/ Peas and Beans G/L Soil Ground 1 3 per cc [6] 7 Banded Directed/ Prickly pear cactus G/L Soil Ground 0.8 3 [2.4] 30 Banded Directed/ Tomato G/L Soil Ground 1 3 per cc [6] 14 Banded Lettuce, Cole Crops, and the following Leafy Greens Directed/ (broccoli, Brussels G/L Soil Ground 1 3 per cc [6] 14 Banded sprouts, cabbage, cauliflower, Kale, spinach etc.) Directed/ Mint G/L Soil Ground 1 4 [4] 21 Banded Directed/ Corn (field and sweet) G/L Soil Banded; Ground 1 4 [4] 7 perimeter Use not Directed/ Soybean G/L Soil Ground 0.4 3 [1.2] 7 allowed in Banded all states

Directed/ Beets (garden) G/L Soil Ground 1 2 [2] 14 OR, WA, ID Banded only

Max Single Max # Max Annual App App App MRI Use Site Form Rate App/yr Rate Comments Target Type Equip (d) lbs ai/A * lbs ai/A/yr* Directed/ OR, WA, ID Hops G/L Soil Ground 1 4 [4] 14 Banded only Directed/ OR, WA, ID Rutabaga/Turnip G/L Soil Ground 1 2 [4] 14 Banded only Directed/ Sugarbeet G Soil Ground 0.8 4 [4] 14 Banded Directed/ Grown in Taro G Soil Ground 1 7 [7] 35 Banded Hawaii Directed/ Vetch G Soil Ground 0.8 4 [4] 14 Banded OR SLN Directed/ OR, WA, ID Wheat G/L Soil Banded; Ground 1 2 per cc [4] 14 only Broadcast Foliage/ Watercress G/L Broadcast Ground 2.0 2 per cc [8] 14 Plant

Ornamentals G/L Soil Broadcast Ground 1 6 [6] 21 Soil; Grass (grown for seed, 14‐ G/L Foliage/ Broadcast Ground 0.77 4 [4] forage and hay) 21 Plant Non‐Ag Uses for Eradication programs (Premises/area, fallow Soil; land, railroad, pipeline, G/L Foliage/ Broadcast Ground 2.0 6 [12] NS roadways, seaports, Plant parks, golf course and other non‐crop areas) L=liquid; G=granular; MRI = Minimum retreatment interval; cc=crop cycle; NS=not specified * Information is provided for number of apps per cc and Year. Annual maximum rate is not specified and is calculated from the single rate and number of apps per year. Some crops have more than one CC per Year.

Usage Summary

Based on market usage data from 1998‐2018, agricultural usage of metaldehyde has fluctuated over time. During recent years (2014‐2018), metaldehyde usage averaged 20,000 lbs per year (USEPA, 2020). Citrus crops account for the highest usage, with an average of 10,000 pounds for oranges and 5,000 pounds each for lemons and tangerines. Non‐agricultural usage survey data are available for usage on for rights of way, golf course turf, fallow land, and residential gardens (USEPA, 2020). These non‐agricultural insecticide usage surveys did not indicate usage of metaldehyde, thus, use of metaldehyde is likely to be low, although, use below the reporting threshold may be occuring. The degree of metaldehyde use under the mollusk eradication use is unknown.

Residues of Concern The only major degradation product of metaldehyde in the submitted environmental fate studies is acetaldehyde, while paraldehyde is also formed in minor (<10%) amounts. Acetaldehyde has very high volatility and low boiling point (20 °C); accordingly, most was recovered from fate studies in volatilized form and not in soil. Therefore, acetaldehyde is expected to dissipate rapidly once formed, limiting potential exposure (D429206). As such, metaldehyde is the only residue of concern assessed. Fate data have not been submitted for either degradate. Therefore, the only residue of concern for assessing ecological risk is parent metaldehyde.

4 Environmental Fate Summary

Table 4‐1 summarizes the physical‐chemical properties of metaldehyde. Metaldehyde is classified as mobile based on measured organic carbon‐normalized sorption coefficient (Koc) values and the Food and Agriculture Organization of the United Nations classification system (FAO, 2000) and may be transported to surface water via spray drift and runoff or to groundwater via leaching. High mobility is supported by leaching observed in some terrestrial field dissipation studies in which leaching was observed up to 36 in depth in the soil. While it may be found in both water and sediment, the octanol‐water partition coefficient (KOW) and organic‐carbon normalized soil‐water distribution coefficient (KOC) values are much lower than the values that would trigger the need to conduct a separate sediment exposure assessment 1 (40 CFR Part 158.630). Compounds with a log KOW of three and above are generally considered to have the potential to bioconcentrate in aquatic organisms. Based on log KOW’s ranging from ‐ 2.96 to ‐1.76, bioconcentration of metaldehyde is not a primary concern. A Henry’s Law constant of 2.43x10‐8 atm‐m3/mol and vapor pressure of 1.1‐3.1x10‐5 torr suggest that volatility of metaldehyde is possible, but not a major route of dissipation in the environment.

Table 4‐1. Summary of Physical‐Chemical, Sorption, and Bioconcentration Properties of Metaldehyde. Parameter Value1 Source/Study Classification/Comment Molecular Weight 176.2 ‐‐ (g/mole) Water Solubility Limit EpiSuite™ 45,360 at 25°C (mg/L) Highly soluble

Vapor Pressure at 25°C Product Chemistry 1.1 x 10‐5 (torr) Some volatility

1 Sediment data may be required if the soil‐water distribution coefficient (Kd) is ≥ 50 L/kg, KOCs are ≥1000 L/kg‐ organic carbon, or the log KOW is ≥ 3 (40 CFR Part 158.630). Sediment data may also be requested if there may be a toxicity concern. 12

Parameter Value1 Source/Study Classification/Comment Henry’s Law Constant Estimated1 from vapor pressure and 2.43 x 10‐8 at 20°C (atm‐m3/mole) water solubility at 20°C. Log Dissociation Not expected to ionize in natural No dissociation between pH 1 ‐12 Constant (pKa) waters. Octanol‐water 0.12 MRID 44641702 and EpiSuite™ Partition Coefficient

(log Kow) (unitless)

Soil‐Water Distribution Soil/Sediment KF KFOC Coefficients (K in L/kg‐ d Sand 0.103 41.2 soil) Sandy loam soil 0.223 55.7 MRID 41228001, 41675101 Organic Carbon‐ Silt loam soil 0.175 14.6

Normalized Clay loam soil 0.436 33.5 Distribution Mean 0.234 36.25 Coefficients (Koc in L/kg‐organic carbon) CV 61% 47% Species BCF Depuration Fish Bioconcentration 8.7x edible, 20x No depuration MRID 42430001 Factor (BCF) ‐‐ inedible, 14x in 21 days whole CV=Coefficient of Variation 1All estimated values were calculated according to “Guidance for Reporting on the Environmental Fate and Transport of the Stressors of Concern in Problem Formulations for Registration Review, Registration Review Risk Assessments, Listed Species Litigation Assessments, New Chemical Risk Assessments, and Other Relevant Risk Assessments” (USEPA, 2010a).

Metaldehyde is degraded by aerobic metabolism in soil (half‐life 67 days in one soil) and more slowly by anaerobic metabolism in soil (half‐life of 222 days in one soil). Metaldehyde is stable to hydrolysis at pH 5, 7, and 9 and stable to aqueous and soil photolysis. No aerobic or anaerobic aquatic metabolism studies have been submitted.

Table 4‐2 summarizes representative degradation half‐life values from laboratory degradation data for metaldehyde. Acetaldehyde is a major transformation product (>10% of applied radioactivity [AR]) resulting from the aerobic soil degradation of metaldehyde while paraldehyde is a minor product. However, due to the high volatility and low boiling point of acetaldehyde, exposure is expected to be minimal.

Table 4‐2. Summary of Environmental Degradation Data for Metaldehyde. Representative Half‐life Source/Study Study System Details (days) Classification/Comment MRID 41114701 Abiotic Hydrolysis pH 5, 7, 9 Stable Acceptable MRID 41337401 Aqueous Photolysis 25°C Stable Acceptable MRID 41507701 Soil Photolysis 25°C Stable Acceptable MRID 41546001 Acceptable Sandy loam soil, 25°C 67.2 For modeling purposes, Aerobic Soil Metabolism multiply single value by 3x to account for uncertainty (201 days)1 Anaerobic Soil MRID 41507702 Sandy loam soil, 25°C 222 Metabolism Acceptable Not submitted, use 2x Aerobic Aquatic aerobic soil metabolism ‐‐ ‐‐ Metabolism input for modeling purposes (402 days)1 Not submitted, use 3x anaerobic soil Anaerobic Aquatic ‐‐ ‐‐ metabolism input for Metabolism modeling purposes (666 days)1 1 This assessment relies on modeling from previous assessments using these inputs.

A summary of terrestrial field dissipation data is provided in Table 4‐3. Dissipation half‐lives in reviewed terrestrial field dissipation studies are several months indicating the potential for high persistence. Additionally, the leaching depth was up to 36 in which is consistent with a low Koc and supports the analysis that metaldehyde has the potential to leach to groundwater in some environments. While field dissipation studies are designed to capture a range of loss processes; laboratory studies are designed to capture loss from one process (e.g., hydrolysis, aerobic metabolism, etc.). Thus, the degradation/metabolism values from laboratory studies are not directly comparable to the dissipation values from the field studies; however, it is informative to have some understanding of how the laboratory data compare to the loss rates in the field dissipation studies. Acetaldehyde was not measured in either field study due to high volatility and difficulty developing analytical methods.

Table 4‐3. Summary of Terrestrial Field Dissipation Data for Metaldehyde. Deepest Core Source/Study System Details Half‐life (observed) in Which ROC Classification/Comment Found (in) Sandy loam soil, 1.6 lb a.i./A 4‐6 months 6‐12 MRID 42287001 applied, CA Loamy sand soil, 1.6 lb a.i./A 2‐4 months 24‐36 MRID 42345901 applied, CA

5 Ecotoxicity Summary

Ecological effects data are used to estimate the toxicity of metaldehyde to surrogate species. The ecotoxicity data for metaldehyde and its associated products have been reviewed previously in multiple ecological risk assessments (USEPA,2013; 2015; 2016) and in a preliminary Problem Formulation for Registration Review (USEPA, 2016, DP Barcode: 429206). These data are summarized in Section 5.1 and Section 5.2. Various studies with terrestrial invertebrates, aquatic plants, and a passerine were received since the preliminary Problem Formulation was issued in 2016; the results of these studies are described briefly in this section. Another source of information is any data submitted for the Endocrine Disruptor Screening Program, although, no such data are available at this time for metaldehyde (see Appendix C for details on the program). Table 5‐1 and Table 5‐2 summarize the most sensitive measured toxicity endpoints available across taxa. These endpoints may not capture the most sensitive toxicity endpoint for a particular taxon but capture the most sensitive endpoint across tested species for each taxa. All studies in this table are classified as acceptable or supplemental. Non‐ definitive endpoints are designated with a greater than or less than value. Values that are based on newly submitted data are designated with an N prefix associated with the master record identification (MRID) number in the tables.

5.1 Aquatic Toxicity

Based on available acute toxicity data, metaldehyde is classified as slightly toxic to freshwater fish on an acute exposure basis, (Rainbow Trout 96‐hr LC50 = 62 mg a.i./L) and no more than slightly toxic to freshwater invertebrates (daphnid 48‐h LC50 >77.6 mg a.i./L). Metaldehyde is classified as practically nontoxic on an acute exposure basis to estuarine/marine (E/M) fish and crustaceans, with LC50 or EC50 values exceeding 100 mg a.i./L.

Metaldehyde has greater toxicity to mollusks than crustaceans. A supplemental toxicity study of shell deposition with the Eastern oyster (Crassostrea virginica) yielded a 96‐hr EC50 of 15 mg a.i./L. A supplemental toxicity study from the open literature (His and Seaman, 1993) reports similar acute toxicity based on lethality to embryos of the Pacific oyster, Crassostrea gigas (LC50 = 7.4 mg a.i./L). Putchakayalla and Ram (2000) found that metaldehyde significantly (p<0.05) increased the mortality of zebra mussels (Dreissena polymorpha) at 100 mg a.i./L, while having no significant effects at 20 mg a.i./L. Together these reports indicate that metaldehyde is slightly to moderately toxic to bivalves. Metaldehyde is assumed to be highly toxic to snails and slugs (gastropods) as they are the target species of this pesticide.

Metaldehyde has also been found to have relatively low toxicity to fish and crustaceans on a chronic exposure basis. A 21‐day chronic toxicity test with freshwater fish yielded a NOAEC value of 37.5 mg a.i./L based on a 42% reduction in body weight observed at 72.3 mg a.i./L. A life‐cycle toxicity test with the freshwater invertebrate D. magna did not detect any statistically significant effects after 21 days of exposure at concentrations up to 90 mg a.i./L. No chronic toxicity data are available for E/M fish or invertebrates. Based on the available acute data, E/M fish and crustaceans do not appear to be more sensitive than freshwater species, and therefore 15 chronic toxicity to saltwater fish and crustaceans is not expected to be greater than to freshwater species. However, since mollusks have been shown to be more sensitive to metaldehyde than crustaceans, chronic toxicity to freshwater and E/M mollusks is likely to be greater than that measured in D. magna (water flea).

Testing with the vascular aquatic plant duckweed resulted in a non‐definitive toxicity endpoint (i.e., EC50 >105 mg a.i./L). The following non‐vascular plant studies were submitted for Registration Review, with Cyanobacteria (Anabaena flos‐aquae) as the most sensitive (EC50= 22.1 mg ai/L).

New Studies Submitted for Registration Review

Non‐Vascular Plant: 96‐Hour Toxicity Test with the Cyanobacteria (A. flos‐aquae)‐ (MRID 50756603). In this test, percent inhibition of algal cell density as compared to the control ranged from ‐33 to 97%. After 96 hours, the most sensitive endpoint was area under the growth curve (i.e., biomass) with NOAEC and IC50 values of 11.8 and 22.1 mg ai/L, respectively, based on mean‐measured concentrations. This study provides the most sensitive endpoint for use in risk assessment for non‐vascular plants.

Non‐Vascular Plant: 96‐Hour Toxicity Test with Freshwater Diatom (Navicula pelliculosa) Toxicity (MRID: 50756602). In this test, percent inhibition of cell density in treated algal cultures compared to the control ranged from 0 to 6%. After 96 hours, the only statistically significant endpoint was reduced yield. The NOAEC and IC50 were 45.7 and >93.7 mg ai/L, respectively, based on mean‐measured concentrations.

Non‐Vascular Plant: 96‐Hour Toxicity Test with Marine Diatom (Skeletonema costatum) Toxicity (MRID: 50756601). In this test, inhibition of cell density in the treated algal culture as compared to the control ranged from ‐10 to 9%. After 96 hours, the most sensitive endpoint was area under the growth curve (i.e., biomass), with a NOAEC of 47.9 mg ai/L, based on reviewer‐calculated mean‐measured concentrations. The IC50 value for all endpoints was >96.1 mg ai/L, based on mean‐measured concentrations.

Non‐Vascular Plant: 96‐Hour Toxicity Test with Freshwater algae, (R. subcapitata formerly P. subcapitata) Toxicity (MRID: 50603501). In this test, the percent growth inhibition in the treated algal cultures relative to the negative control ranged from ‐15 to 37%. After 72 hours, the most sensitive endpoint was the area under the growth curve (biomass), which had an IC50 value of 199 mg ai/L. The area under the curve and the cell density endpoints were both statistically different from controls at the 176 mg ai/L test level, setting the NOAEC at 88.2 mg ai/L.

Table 5‐1. Aquatic Toxicity Endpoints Selected for Risk Estimation for Metaldehyde. Test MRID or Study Toxicity Value in mg Substance Test Species ECOTOX No./ Comments Type a.i./L (% a.i.) Classification Freshwater Fish (Surrogates for Vertebrates)

Acute TGAI 96‐h LC50 = 69 mg a.i./L 42044004 ‐‐

22‐weeks NOAEC = 37.5 mg a.i./L Oncorhynchus mykiss LOAEC =72.3 mg a.i./L Rainbow Trout based on 20% mortality 46909101 Chronic TGAI ‐‐ and 42 and 12% reductions in bodyweight and length, respectively. Estuarine/Marine Fish (Surrogates for Vertebrates) Cyprinodon 96‐h LC >123 mg Acute TGAI variegates 50 47623001 ‐‐ a.i./L Sheepshead Minnow

Estuarine/Marine fish chronic toxicity study not available; Chronic value using ACR (acute‐to‐ Chronic ‐ chronic ratio) approach could not be determined because a definitive acute toxicity endpoint was not available for estuarine/marine fish.

Freshwater Invertebrates (Water‐Column Exposure) Daphnia magna 48‐h LC >77.6 mg Acute TGAI 50 42044005 ‐‐ Water flea a.i./L NOAEC = 73.9 mg a.i./L Chronic Daphnia magna TGAI LOAEC > 73.9 mg 46909102 Water flea ‐‐ a.i.*/L Estuarine/Marine Invertebrates (Water‐Column Exposure) Americamysis bahia 96‐h LC >112 mg Acute TGAI 50 ‐‐ Mysid shrimp a.i./L 47623002 Crassostrea virginica 96‐h LC = 12.9 mg Acute TGAI 50 ‐‐ Eastern oyster a.i./L 48009001 Estuarine/Marine invertebrate chronic toxicity study not available; chronic value using ACR Chronic ‐‐ approach could not be determined due to non‐definitive value for acute freshwater invertebrate (D. magna). Aquatic Plants and Algae Lemna gibba EC >105 mg a.i./L Vascular TGAI 50 48143102 ‐‐ Duckweed NOAEC = 105 mg a.i./L Cyanobacteria Non‐ 9‐d EC = 22.1 mg ai/L TGAI (Anabaena flos‐ 50 N‐50756603 ‐‐ vascular NOAEC = 11.8 mg ai/L aquae) TGAI=Technical Grade Active Ingredient; a.i.=active ingredient >Greater than values designate non‐definitive endpoints where no effects were observed at the highest level tested, or effects did not reach 50% at the highest concentration tested (USEPA, 2011). < Less than values designate non‐definitive endpoints where growth, reproductive, and/or mortality effects are observed at the lowest tested concentration.

5.2 Terrestrial Toxicity

Based on the available data, metaldehyde is moderately toxic to birds and mammals on an acute exposure basis. A chronic toxicity test with Mallard Ducks resulted in reduced hatchability of eggs at test concentrations as low as 49 mg a.i./kg‐diet (the lowest concentration tested). Therefore, a definitive NOAEC could not be established in the study (i.e., NOAEC <49 mg a.i./kg‐ diet). In contrast, a test with the Northern Bobwhite Quail did not detect statistically significant effects at dietary concentrations up to 497 mg a.i./kg‐diet. As reproductive effects in the mallard were observed at dietary concentrations much less than those which cause acute toxicity, reproductive impairment of birds may be a concern. Chronic dietary exposure of mammals resulted in parental (mortality and paralysis; 9%) and juvenile bodyweight reductions (~6‐9%) observed at 2000 mg a.i./kg‐diet (NOAEL = 65 mg a.i./kg‐bw; NOAEC = 1000 mg a.i./kg‐ diet). For terrestrial plants, a vegetative vigor study reported minor effects to one species, and the seedling emergence study found no significant adverse effects to plants exposed up to the application rate of 1 lb a.i./A, thus, the EC25 values are >1 lb a.i./A.

New Studies Submitted for Registration Review

An Acute Oral Toxicity Study with the House Sparrow Using a Sequential Testing Procedure (MRID 50603505). In this test of passerines, signs of toxicity included a loss of coordination, lower limb weakness, minor muscle fasciculation, and convulsions. No regurgitation was observed during the study and the 14‐day‐acute oral LD50 is 351 mg ai/kg‐bw, thus, metaldehyde is classified as moderately toxic to the house sparrow (Passer domesticus) on an acute oral basis. This LD50 endpoint is higher (less toxic) than the quail value of 190 mg a.i./kg‐ bw, therefore, there is no change to the current assessment endpoints.

Terrestrial Invertebrates Since the preliminary Problem Formulation, a subset of the honey bee Tier 1 toxicity data have been submitted for metaldehyde and the studies are briefly described below.

Acute Contact Toxicity Test with the Honey Bee (MRID 50603502; Acceptable) The acute contact 48‐hr LD50 for adult bees is >113 µg a.i./bee with no mortality or sublethal effects following contact exposure. Based on these data, metaldehyde is classified as practically non‐toxic to bees on an acute contact exposure basis.

Acute Oral Toxicity Test with the Honey Bee (MRID 50603503; Acceptable) In this test, the 48‐hour acute oral LD50 was empirically determined to be >87 μg a.i./bee. No sublethal effects were observed in any of the control or treatment groups. Based on these data, metaldehyde is classified as practically non‐toxic to bees on an acute oral exposure basis.

Chronic Toxicity with Honey Bee Larvae (MRID 50964301; Acceptable) In this test, the most sensitive endpoint and only affected endpoint was adult emergence (13% reduction). The NOAEL and ED50 were 5.3 and >13 µg ai/larva/day, respectively.

Table 5‐2. Terrestrial Toxicity Endpoints Selected for Risk Estimation for Metaldehyde. Test MRID or ECOTOX Study Type Substance Test Species Toxicity Value1 Comments No./ Classification (% a.i.) Birds (Surrogates for Terrestrial Amphibians and Reptiles) Observational NOAEL < 140 mg a.i./kg‐bw based on mortality, transient Coturnix japonica 41553201 Acute Oral TGAI LD = 190 mg a.i./kg‐bw reduced food Japanese quail 50 (Supplemental) consumption, and transient weight loss.

Observational NOAEC < 1,000 mg a.i./kg‐diet Sub‐acute Anas platyrhynchos 14‐days 41553204 based on reduced TGAI dietary Mallard Duck LC50 =2,668 mg a.i./kg‐diet (Supplemental) activity, reduced body weight, and clinical signs of toxicity 22‐weeks NOAEC < 49 mg a.i./kg‐diet Anas platyrhynchos based on 23% reduction of 42867902 Chronic TGAI ‐‐ Mallard duck egg hatching at all test (Supplemental) levels.

Mammals 00131435, Rattus Norvegicus Acute Oral TGAI LD = 398 mg a.i./kg‐bw 00131969 ‐‐ Rat 50 (Acceptable) NOAEC = 1000 mg a.i./kg‐ diet NOAEL: 65 mg a.i./kg‐bw per day) Chronic (2‐ LOAEL = 2000 mg a.i./kg‐ Rattus Norvegicus 42823101 generation TGAI diet based on parental ‐‐ Rat (Acceptable) reproduction) mortality and paralysis (9%), and decreased pup body weights and bodyweight gains (reductions ~6‐9%). Terrestrial Invertebrates Acute contact Honey Bee N‐50603502 TGAI LD >113 µg a.i./bee ‐‐ (adult) (Apis mellifera L.) 50 (Acceptable) Acute oral Honey Bee N‐50603503 TGAI LD >87 µg a.i./bee ‐‐ (adult) (Apis mellifera L.) 50 (Acceptable) Chronic oral No Data (adult) Acute oral No Data (larval)

Test MRID or ECOTOX Study Type Substance Test Species Toxicity Value1 Comments No./ Classification (% a.i.) NOAEL = 5.3 Chronic oral Honey Bee LOAEL = 13 µg a.i./larvae N‐50964301 TGAI (larval) (Apis mellifera L.) based on a 13% reduction (Acceptable) in emergence. Foliage No Data Residue Semi‐field study or full No Data field study) Terrestrial and Wetland Plants 48555402; 48633501 21‐d EC >1.0 lbs a.i./acre (Supplemental for Seedling 25 TEP Various species 21‐d NOAEC = 1.0 lbs sugar beet; Emergence a.i./acre Acceptable for other test species)

*Wheat – 5.4% decrease in dry height was 21‐d EC >1.1 lbs a.i./acre 25 statistically significant,

although the biological 21‐d NOAEC Vegetative 48555401 significance is TEP Various species <1.1 lbs a.i./acre for Vigor (Acceptable) questionable. wheat* Lettuce – 11% decrease 1.1 lbs a.i./acre for other in dry weight which was test species not significantly different than controls TGAI=Technical Grade Active Ingredient; TEP= Typical end‐use product; a.i.=active ingredient N Studies submitted since the Problem Formulation was completed are designated with an N associated with the MRID number. 1 NOAEC and LOAEC are reported in the same units. >Greater than values designate non‐definitive endpoints where no effects were observed at the highest level tested, or effects did not reach 50% at the highest concentration tested (USEPA, 2011). < Less than values designate non‐definitive endpoints where growth, reproductive, and/or mortality effects are observed at the lowest tested concentration.

5.3 Incident Data

The Incident Data System (IDS) is an OPP database that houses incidents that have been attributed to the use of pesticides. A query of this database was conducted on June 29, 2020, to identify all reported ecological incidents (those involving non‐target wild animals and plants) that were linked to use of metaldehyde. Many of the incidents were recently summarized in EFED’s preliminary Problem Formulation of February 2016 (DP 429206). Table 5‐3 provides a summary of the wildlife incidents for birds, mammals, and fish. One consideration is that there were mitigation measures that were implemented as part of the 2006 metaldehyde Reregistration Eligibility Decision (RED). Advisory statements were added to prohibit use for

20 domestic applications unless domestic animals (and children) were excluded from the treated area until the material is no longer visible and also the addition of a bittering agent to deter accidental consumption (for residential uses).

Summary There are six reported fish kill incidents attributed to metaldehyde. Five involved a product containing metaldehyde as the only active ingredient while one involved a product containing metaldehyde and carbaryl. In all of the cases, application of granular or “mini‐pellet” products metaldehyde near a residential pond resulted in fish in the pond becoming displaying sublethal effects or dying. The circumstances of these incidents suggest that runoff likely washed some of the applied granules or pellets into the pond, where they were eaten by fish. Calumpang et al. (1995) observed fish dying in a rice paddy after application of pelleted metaldehyde bait and suggested that the fish may have been eating the floating pellets. See Appendix D for a previous analysis on pellet exposure/consumption.

The IDS contains one incident involving birds for a product containing metaldehyde alone. Incident (I018436‐004), reports two birds were found dead in a yard after a granular product (Ortho® Bug‐Geta Snail and Slug Killer, 71096‐7‐239) was applied, but there was no evidence (i.e., residue analysis) to link the deaths to metaldehyde exposure, thus, the certainty is noted as “possible”. Also, since this incident occurred prior to the implementation of risk mitigation measures that were prescribed in the 2006 metaldehyde RED, this incident may not reflect risk of current use patterns. For mammals, three calves in Scotland were purportedly poisoned (I024836‐047), when they consumed bait from a container that was disposed of improperly. Incidents to domestic animals are discussed in the next section.

Two incidents of plant damage have been recorded in IDS (I023832‐017 and I024179‐368). These incidents were assigned a certainty level of “possible.” Both incidents were associated with Bug‐Geta Plus, a product that contains carbaryl as well as metaldehyde. These incidents do not provide strong evidence that metaldehyde itself is phytotoxic.

5‐3. Ecological Incident Data for Birds, Mammals, and Fish (2000‐present). Product and Incident Certainty Year Additional Active Legality Use Site Species Magnitude/Other Notes Number Index Ingredients Birds and Mammals Two birds were found dead in a Ortho® Bug Geta yard after a granular product I018436‐ 2006 Snail and Slug Registered Possible Residential N/R was applied, but there was no 004 Killer evidence to link the deaths to metaldehyde exposure. Three calves in Scotland apparently were poisoned I024836‐ 2011 N/R Misuse Probable Field Calves when they consumed bait from 047 a container that was disposed of improperly.

A dog allegedly exposed to the I010216‐ K‐GRO SNAIL AND Highly product. The dog experienced 2000 Undetermined Residential Dog 001 SLUG BAIT Probable severe seizures and moderate tremors.

I010216‐ K‐GRO SNAIL AND A dog was exposed to the 2000 Undetermined Probable Residential Dog 002 SLUG BAIT product resulting in seizures.

Two domestic dogs (pet) may have died from eating Correy's I024855‐ Corrys Slug and 2012 Undetermined Possible Residential Dog Slug and Snail Bait (a.i. 001 Snail Bait metaldehyde and carbaryl) that was placed outside. Fish I018734‐ Slug® Clear Product was used on plants 2001 Registered Possible Garden N/R 002 minipellets surrounding a garden pool. A caller reported Bug‐Geta Snail and Slug Killer (active I018734‐ Bug‐Geta Snail ingredient metaldehyde) 2003 Undetermined Possible N/R N/R 003 and Slug Killer caused a fish kill in her pond. Product applied 3 feet from the pond. Mortality after storm.

Application of product with I018436‐ metaldehyde and carbaryl 2004 4622 Undetermined Possible Pond N/R 001 around a pond. Fish injury/ mortality reported.

Application of metaldehyde I018436‐ 2004 N/R Undetermined Possible N/R N/R next to a pond allegedly caused 005 mortality to 19 fish Metaldehyde product applied I018436‐ to area 5‐m distance from 2006 N/R Undetermined Possible N/R N/R 006 pond caused mortality to 50 fish. Metaldehyde was used to treat the plants in a greenhouse. Catfish, Plants were transferred to I021896‐ Deadline® Force koi, 2010 Registered Unlikely Greenhouse pond. Owner notice rapid and 001 11 Slug & Snail mosqui total fish kill one month after tofish transfer of treated plants to the pond; ~150 fish affected. N/R =not reported/specified

Aggregate Database Additional metaldehyde incidents are recorded in the Aggregate Summary Module, a database that stores counts of minor wildlife incidents that pesticide registrants report in quarterly

22 aggregated incident reports. This database also contains reports on domestic animal incidents. Results of a query of this database on 7/1/2020 shows additional domestic animal mortality and domestic animal (moderate severity) incidents beyond those which were summarized in EFED’s preliminary Problem Formulation report of February 2016 (DP 429206). Updated counts of aggregated incidents are given in Table 5‐4.

Twelve aggregated fish/wildlife incidents have been reported for snail and slug bait products that contain metaldehyde. More than half of these were for products that contained only metaldehyde, indicating that metaldehyde exposure may be hazardous to non‐target animals. EPA does not have information on the species that were affected in minor wildlife (WB) incidents, but based on other incident data, they likely involve either fish or terrestrial wildlife vertebrates that consumed the slug and snail bait. Wildlife incidents reported in the UK to the British Wildlife Incident Investigation Scheme (WIIS) and summarized in the WIIS Quarterly Reports include some incidents involving metaldehyde poisoning of wild birds (mallards) and mammals, including badgers and foxes.2

Incidents have been reported for “other nontarget”, which are typically incidents of mortality of arthropods. However, the incidents involved products that contain carbaryl, an insecticide that is highly toxic to arthropods on an acute exposure basis. Therefore, the aggregate incidents do not give any indication that metaldehyde alone is hazardous to arthropods (including bees). Three minor plant incidents were reported.

A large number of domestic animal incidents have been reported since 2010, including 151 cases involving the death of an animal (Table 5‐4). The majority of incidents were from products containing metaldehyde as the only active ingredient. Metaldehyde snail and slug bait is known to be a hazard to pets, particularly dogs, which eat bait granules or pellets that are placed around the home, or that eat the product after tearing into or opening the package container (USEPA 2006). The RED of 2006 imposed requirements for several revisions to labels of residential‐use products containing metaldehyde with the intention to mitigate the risk to pets. For example, the RED prohibits use unless you can exclude domestic animals from the area until it is no longer visible, additionally, a bittering agent is also required for the residential uses. Many domestic animals and several fish/wildlife incidents have been reported for snail and slug bait products that contain only metaldehyde. While these incidents have been reported for products with residential uses, it is uncertain how they may or may not reflect risk from products with agricultural uses.

2 Wildlife Incident Investigation Scheme (WIIS), http://www.pesticides.gov.uk/guidance/industries/pesticides/topics/reducing‐environmental‐impact/wildlife 23

5‐4. Metaldehyde‐ Aggregate Incidents from the Incident Data System (IDS) from 2010‐ present. Incidents for Incidents for Products Exposure/Severity Products Containing Incident Type Code Containing Only Metaldehyde and Metaldehyde Carbaryl Fish and Wildlife, Minor WB 7 5 Plant Damage, Minor PB 2 0 Other Non‐Target ONT 0 1 Domestic Animal, Mortality DA 147 4 Domestic Animal, Severe DB 62 1 Symptoms Domestic Animal, Moderate DC 797 35 Symptoms Aggregate Query Date Range: January 1, 2010‐July 1, 2020

6 Analysis Plan

6.1 Overall Process

This assessment uses a weight‐of‐evidence approach that relies heavily, but not exclusively, on a risk quotient (RQ) method. The RQs are calculated by dividing an estimated environmental concentration (EEC) by a toxicity endpoint (i.e., EEC/toxicity endpoint). This is a way to determine if an estimated concentration is expected to be above or below the concentration associated with the toxicity endpoint. The RQs are compared to regulatory levels of concern (LOCs). The LOCs for non‐listed species are meant to be protective of community‐level effects. For acute and chronic risks to vertebrates and aquatic invertebrates, the LOCs are 0.5 and 1.0, respectively, and for aquatic and terrestrial plants, the LOC is 1.0. The acute and chronic risk LOCs for bees are 0.4 and 1.0, respectively. In addition to RQs, other available data (e.g., incident data) can be used to help understand the potential risks associated with the use of the pesticide.

This streamlined assessment relies on previous conclusions when possible and the exposure considerations are briefly outlined below to capture the overall approach. Exposure estimations throughout the assessments considered the following routes:

 For granular and pelleted products, the primary exposure route to terrestrial animals was expected to be from direct consumption of the granules or pellets.

 For liquid spray products, the primary route of exposure is expected to be from consumption of contaminated plants and invertebrates. Plants would be exposed by direct foliar spray as well as by root uptake. Note, for the liquid formulation, the product label instructs the user to spray the soil around the crops (except for application on grass for seed, watercress, taro and mollusk eradication sites). However, this application does not prevent direct application on the foliage of weeds which then serves as a foliar substrate for

dietary exposure to terrestrial animals. There is a potential for spray drift, for the non‐ directed foliar sprays (e.g., the applications for grass grown for seed, watercress, taro, and to the mollusk eradication sites).

 Secondary exposure from animals consuming the target species (slugs and snails) or nontarget species (e.g., insects) that feed on the metaldehyde product is possible (but not assessed).

 Aquatic animals and plants are expected to be exposed primarily from exposure of residues in the ambient water. For products applied as a liquid spray, mechanisms of transport to aquatic habitats include direct spray, spray drift, leaching to ground water, and runoff. For granular and pelleted products, mechanisms of transport would include inadvertent direct application to water (primarily with aerial application), leaching to ground water, and transport of dissolved residues in runoff. Aquatic animals could also be exposed by direct consumption of granules or pellets that are transported to water by runoff (Calumpang et al. 1995).

6.2 Modeling

The primary model used in this assessment is the BEEREX model. The specific models used in this assessment are discussed further below. (Table 6‐1)

Table 6‐1. List of the Models Used to Assess Risk.

Exposure Environment Taxa of Concern Exposure Pathway Model(s) or Pathway Media Spray contact and Bees and other ingestion of residues Terrestrial Contact BeeREX version 1.0 terrestrial in/on dietary items as a Dietary items invertebrates result of direct application Movement through AgDRIFT version 2.1.1 (Spray All All air to aquatic and Spray drift drift) Environments terrestrial media

7 Aquatic Organisms Risk Assessment

7.1 Aquatic Exposure Assessment

This streamlined assessment for including the new aquatic plant data is relying on the highest EECs from the 2013 assessment (USEPA, 2013) for Taro and Turf (Table 7‐1). Surface water concentrations were generated for grasses using the Generic Estimated Environmental Concentration (GENEEC; version 2) model and for wetland taro using the Pesticide Flooded Application Model (PFAM) (version 0.70). These uses have the highest EECs and will be used for

25 screening the risk to plants without further modelling. While the use of the peak EEC has been replaced with the 1‐day average under current practice, the peak values from the 2013 assessment will be used in this streamlined assessment as they are conservative and provide an adequate screen for aquatic exposure.

Table 7‐1. Estimated Environmental Concentrations (EECS) For Assessing Risk to Aquatic Plants (from Previous Assessment). Crop Estimated Environmental Concentration (µg/L) (annual applications, app. rate, retreatment interval) Peak 21‐Day Average 60‐Day Average Grasses (4 apps, 1.6 lb a.i./A, 14 d) 321 318 312

Taro (11 apps, 1.36/1.53 lb a.i./A, 21 d) (1958 / 2364)1 9102 8943 8653 1 The first value represents the 90th percentile of the daily peak metaldehyde concentration of the water from the simulated field that is discharged once annually. The second value represents the 90th percentile daily peak concentration in the water overflowing from the field into the pond after a rain event. 2 This is the estimated peak concentration in the standard farm pond based on the mass of pesticide in manual release water discharged annually (1,958 µg/L or 40.11 lbs of metaldehyde) diluted into the standard pond (20x106 liters). 3These values represent the 90th percentile 21‐ or 60‐day average concentration of metaldehyde in the standard pond. Concentrations were calculated using the following equation: [metaldehyde]= peak concentration/‐k*(exp(‐ ‐1 k*time‐1)/time, where the peak concentration=910 µg/L; ‐k=7.18E‐5 hr =t1/2= 402 days; time = 504 hours (21 days) or 1440 hours (60 days).

7.1.1 Monitoring There have been no updates to the available monitoring data since the last assessment (USEPA, 2016). Metaldehyde is not an analyte in the following databases and sources as of July 2020:

 Water Quality Portal (USEPA et al.)3  California Environmental Data Exchange Network (CEDEN) (State Water Resources Control Board, 2015)4  California Department of Pesticide Regulation Surface Water Database5 (CADPR, 2020)

7.2 Aquatic Organism Risk Characterization

7.2.1 Aquatic Plants:

Based on the new data for aquatic non‐vascular plants, the RQs range from 0.01‐0.04. Therefore, the risk to aquatic plants from the use of metaldehyde is expected to be low.

3 https://www.waterqualitydata.us/ 4 http://www.ceden.org/ 5 http://www.cdpr.ca.gov/docs/emon/surfwtr/surfdata.htm 26

Table 7‐2. Aquatic Plant Risk Quotients (RQs) for Non‐listed Species. Risk Quotients 1‐in‐10 Year Peak* EEC Use Sites Vascular Non‐vascular (µg/L) EC50 >105,000 µg a.i./L EC50 = 22,100 µg a.i./L Grasses 321 Not Calculated 0.01 Taro 910 Not Calculated 0.04 The level of concern (LOC) for risk to non‐listed plants is 1. The toxicity endpoints listed in the table are those used to calculate the RQ. *Using peak from previous assessment.

8 Terrestrial Vertebrates Risk Assessment

This assessment relies on the previous risk estimates and conclusions from past assessments as there are no new data to alter the previous conclusions. A summary of the assessment findings from USEPA, 2016 is included here and for further details refer to the original document. Given 2 that metaldehyde is applied as pelleted formulation, the rates were modeled using the LD50/ft concept with no incorporation. This approach estimates risk for one application and does not account for chronic exposure. Some uses have broadcast applications which distribute the pellets evenly over the entire field, and the majority are applied as banded applications which are concentrated in the rows in the space between the plants (Table 3‐1). For banded applications, the input variables for T‐REX include row spacing, band width, and percent soil incorporation. Since metaldehyde bait is always applied without soil incorporation, the soil incorporation depth was set to zero. The estimated maximum band width was calculated by subtracting an estimated plant width from the estimated row spacing. To make the assessment conservative, estimated plant widths were based on young plants early in the growing season. The banded applications at 1 lb a.i. /A result in the highest EECs due to the concentration of pellets within the band. For example, a broadcast application of metaldehyde at 1.0 lb a.i./A is 10.41 mg a.i./ft2. For the crops with banded application, the application rate is concentrated within the bands between the rows, and therefore is concentrated by a factor of the band width divided by the row width [e.g., the estimated exposure for the minimum band width for beet (3 inches) is 10.41 x (15/3)] = 52.05 mg a.i./ ft2.

8‐1. Sample of Input Parameters for T‐REX (used in USEPA, 2016) for Granule Applications of Metaldehyde in Various Crops. 1 Maximum Single Crop Row Plant Width Band Width Application Crop Application Rate Spacing (inches) (inches) Method (lb a.i./A) (inches) Min. Max. Min. Max. Beets, garden 1.0 Banded 15 4 12 3 11

Rutabaga 1.0 Banded 24 6 12 12 18

Turnips 1.0 Banded 18 4 12 6 14

Wheat 1.0 Broadcast N/A N/A N/A N/A N/A

Hops 1.0 Banded 96 24 36 60 72 1 Band widths were estimated by subtracting the estimated plant width by the maximum typical row width. 27

Summary of Risk to Birds and Mammals from Granular Products (Risk driver from past assessments) There is the potential for risk to birds (surrogates for reptiles and terrestrial‐phase amphibians) and mammals as the RQ values exceed the acute risk LOC of 0.5. The RQs exceed the acute risk LOC for small birds and small mammals (avian RQs: 3.6‐18.2, mammalian RQs: 0.79‐3.97). The RQ values also exceed the acute risk LOC for medium‐size birds for all of the assessed uses (RQs 0.57‐2.9) and for medium‐sized mammals (RQs 0.42‐2.1). Chronic RQ values could not be calculated for birds and mammals, as there currently is no methodology to quantify potential risk from exposure to pesticides formulated as granules/pellets.

To further investigate the acute risk to birds and mammals, the number of granules that an animal must ingest to reach the LD50 was estimated. This analysis found that a small bird and a small mammal would need to consume 8 and 37 pellets, respectively, to reach the LD50. Based on these results, acute risk to acute small bird feeding in a treated area is likely; whereas, acute risk to small mammals is possible but is less certain.

A similar analysis for chronic risk found that the bobwhite quail could reach the concentration that resulted in reductions in egg hatchability by consuming only 3 pellets. For mammals, the NOAEC is reached for the deer mouse via approximately 11 pellets a day. This is equivalent to consuming 0.13 g of pellets, which comprises approximately 3.4% of the mouse’s daily food ingestion rate. Chronic risk to mammals appears to be somewhat smaller than for birds but cannot be ruled out.

While the ecological assessments typically focus on wild animals, of particular note, is that the dog is the most sensitive of the mammals for which there are data. In a chronic toxicity study (MRID 46378401), the NOAEL is 10 mg/kg/day (LOAEL of 30 mg/kg/day based on deaths and atrophy of testes/prostate and at 90 mg/kg/day, clinical signs of neurotoxicity were observed in all dogs on the first day of exposure and throughout the first week). The continued incidents of domestic pet (dog) mortality (151 since 2010‐ see Table 5‐4), suggests the previous mitigation efforts may not be effective.

9 Terrestrial Invertebrate Risk Assessment

9.1 Bee Exposure Assessment

The list of crops to which metaldehyde is applied is listed in Table 9‐1 (USDA, 2018) along with the United States Department of Agriculture (USDA) pollinator attractive data to identify which crops may represent direct exposure to pollinators on the field. Off‐field assessments are conducted for foliar sprays regardless of whether the crop is attractive or not. Metaldehyde is generally applied as granules around the base of the plants or as a liquid targeting the soil. Bees (both Apis and non‐Apis) may be exposed on the field to a variety of crops. Off‐ field exposure is only in the limited situations where foliar applications are permitted (i.e., grass grown for seed, watercress (not a pollinator attractive crop), and the non‐agricultural sites for mollusk eradication. 28

9‐1. Summary of Information on the Attractiveness to Bees of Registered Use Patterns for Metaldehyde. Bumble Solitary Require Acreage App Honey Bee Bee Bee bees for Use Site/ Location Form in the Notes Target Attractive?1,2 Attractiv Attractive? pollinati U.S. e? 1, 2 1, 2 on Y (pollen & Harvested prior to Artichokes G/L Soil Yes1 Yes1 Yes 7,000 nectar)1 bloom Y (pollen & Uses managed Berries‐Blueberry G/L Soil Yes2 Yes2 Yes 77,700 nectar)1 pollinators Y (pollen & Berries‐Strawberry G/L Soil Yes1 Yes1 No 58,190 nectar)1 Variable‐ some Y (pollen & Citrus G/L Soil Yes1 Yes1 No 613,000 bees brought to nectar)2 groves for honey Only a small % of 28,506 acreage is grown Y (pollen & Yes‐ seed White, Clover (grown for seed) G/L Soil Yes1 Yes2 for seed. nectar)2 prod. Red and Harvested prior to Crimson bloom. Only a small % of acreage is grown Y (pollen & Yes‐ seed for Celery G/L Soil Yes1 Yes1 nectar)1 prod. seed. Harvested prior to bloom.

N/AV N/AV Does not use Ginseng G/L Soil Yes No ‐‐ managed bees. Y (pollen & Acreage is for Peas and Beans G/L Soil Yes1 N/AV No 77,200 nectar)1 snapbeans Prickly pear cactus G/L Soil N/AV N/AV N/AV N/AV May be grown in N (Pollen, glasshouses, with Tomato G/L Soil Yes1 Yes1 Yes ‐‐ Nectar) bumble bees for pollination Exposure is

Lettuce and Leafy limited to when G/L Soil Y (Pollen, Yes Yes Yes Greens ‐‐ crop is grown for Nectar) seed. Exposure is limited to when Y (Pollen, Brassica Crops G/L Soil Yes Yes Yes crop is grown for Nectar) ‐‐ seed. Harvested before bloom. Peppermint oil is produced from Y (Pollen1, vegetative growth Mint G/L Soil Yes2 Yes1 No 68,800 Nectar2) without flowering or seed production.

Bumble Solitary Require Acreage App Honey Bee Bee Bee bees for Use Site/ Location Form in the Notes Target Attractive?1,2 Attractiv Attractive? pollinati U.S. e? 1, 2 1, 2 on Wind pollinated, but can N (nectar) & 87,668,0 Corn (field and sweet) G/L Soil Yes1 Yes1 No be visited during Y (pollen1) 00 pollen shedding Bee pollination is not required, but Y (nectar & 76 soybean is used Soybean G/L Soil Yes1 Yes1 No pollen)1 million by some beekeepers for honey production N (nectar) & Hops G/L Soil No No No 35,224 Y (pollen1) Vicia faba. Not Yes‐Vicia 77,200 harvested prior to Succulent Bean G/L Soil Y (Pollen, Yes Yes faba; (Snap) bloom. Does not Nectar) 1 No snap Broad use managed bees. Only a small % of acreage is grown Y (nectar)1 & 1,154,20 for Sugarbeet G Soil NV Yes1 Yes N (pollen) 0 breeding. Managed pol. for breeding. Taro G Soil N/AV N/AV N/AV N/AV Y (nectar1 & Vetch G Soil Yes2 Yes2 No 3,441 pollen2) 45 Wheat G/L Soil No No No No million Foliage Watercress G/L / N/AV N/AV N/AV N/AV Plant Soil Ornamentals G/L Assumed Assumed Assumed ‐‐ ‐‐

Wind pollinated, Soil; source of pollen Grass (grown for seed, Foliage N (nectar) & 35 only when no G/L No No No forage and hay) / Y (pollen1) million other forage Plant sources are available. 1 attractiveness rating is a single “+”, denoting a use pattern is opportunistically attractive to bees. 2 attractiveness rating is a double “++” denoting a use pattern is attractive in all cases. N/AV=no data Shaded crops are of lower attractiveness or exposure (e.g. harvested before bloom).

9.2 Bee Tier I Exposure Estimates

Contact and dietary exposure are estimated separately using different approaches specific for different application methods. The BeeREX model (Version 1.0) calculates default (i.e., high end, yet reasonably conservative) EECs for contact and dietary routes of exposure for foliar, soil, and seed treatment applications. See Appendix B for a sample output from BeeREX for metaldehyde. Additional information on bee‐related exposure estimates, and the calculation of risk estimates in BeeRex can be found in the Guidance for Assessing Risk to Bees (USEPA et al., 2014). In cases where the Tier I RQs exceed the acute risk LOC of 0.4 or chronic risk LOC of 1.0, discussed below, estimates of exposure may be refined using measured pesticide concentrations in pollen and nectar of treated crops (provided measured residue data are available), and further calculated for other castes of bees using their food consumption rates as summarized in the White Paper to support the Scientific Advisory Panel (SAP) on the pollinator risk assessment process (USEPA, 2012c).

This assessment used the following strategy to bin the uses by rate and application target (soil vs foliar; Table 9‐2). Of the limited uses with foliar sprays, only the ornamentals/non‐ agricultural/eradication uses would be potentially attractive to pollinators. In contrast, many of the soil‐applied uses are attractive to pollinators.

9‐2. Use Parameters for Assessing Risk to Honey Bees (Apis mellifera). Max Single App Use Site/ Location Form Rate Target lbs ai/A Soil; Grass (grown for seed, forage and hay) G/L 0.8 Foliage Berries, clover, cactus G/L Soil 0.8 Artichoke, strawberry, citrus, celery, ginseng, peas and beans, tomato, lettuce, cole crops, G/L Soil 1 brassica, mint Ornamentals G/L Soil 1 Watercress G/L Foliage 2.0 Non‐Ag Uses for Eradication programs Soil; (Premises/area, fallow land, railroad, pipeline, G/L Foliage 2.0 roadways, seaports, parks, golf course and other

non‐crop areas) G=granule; L=liquid

9.3 Bee Risk Characterization (Tier I)

9.3.1 Tier I Risk Estimation (Contact Exposure)

On‐Field Risk Since an exposure potential for bees is identified for many crops, (predominately on the treated field), the next step in the risk assessment process is to conduct a Tier 1 risk assessment. By design, the Tier 1 assessment begins with (high‐end) model‐generated (foliar and soil treatments) or default (seed treatments) estimates of exposure via contact and oral routes. For contact exposure, only the adult (forager and drones) life stage is considered since this is the relevant life stage for honey bees (i.e., since other bees are in‐hive, the presumption is that they would not be subject to contact exposure). Furthermore, toxicity testing protocols have only been developed for acute contact exposures. Effects are defined by laboratory exposures to groups of individual bees (which serve as surrogates for solitary non‐Apis bees and individual social non‐Apis bees).

Metaldehyde contact exposure resulted in a non‐definitive (i.e., greater than) LC50 value (LD50= >113 µg a.i./bee), thus, RQs were not calculated. In order to gain a better understanding of the risk, when comparing the highest foliar EEC (using the 2 lb a.i./A rate) to the highest tested concentration, the exposure would need to be 10 times higher to reach the highest concentration tested. Therefore, contact exposure poses low risk to adult honey bees.

9.3.2 Tier I Risk Estimation (Oral Exposure)

On‐Field Risk For oral exposure, the Tier 1 assessment considers just the caste of bees with the greatest oral exposure (foraging adults). If risks are identified, then other factors are considered for refining the Tier 1 risk estimates. These factors include other castes of bees and available information on residues in pollen and nectar which is deemed applicable to the crops of interest. These exposure data may have been collected on surrogate crops (e.g., phacelia, buckwheat, alfalfa) which are known to be attractive sources of both pollen and nectar for bees).

For acute exposure to adult honey bees, the endpoint is non‐definitive (e.g., LD50 greater than 87 µg a.i./bee), thus, RQs are not calculated. However, when comparing the estimated exposure values to the highest tested doses, the foliar rate of 2 lbs a.i. per acre results comparable doses that potentially exceed the acute risk LOC of 0.4. Therefore, there is uncertainty in the potential for acute risk at this rate for foliar applications.

Additionally, data are not available for assessing the chronic toxicity of metaldehyde to adult bees. Chronic risk to larval stage honey bees is identified for the range of the foliar rates with RQs ranging from 2.1‐5.1 (LOC=1). The RQ values from metaldehyde applications to soil are below the LOC. A summary of the available RQs for adult foragers and larval worker honey bees are provided in Table 9‐3.

Table 9‐3. Tier 1 (Default) Oral Risk Quotients (RQs) for Adult Nectar Forager and Larval Worker Honey Bees (Apis mellifera) from BeeRex (ver. 1.0) Max. Unit Dose Oral Dose Bee Acute Oral Chronic Use Pattern Single (μg a.i./bee (μg Caste/Task RQ1,2 Oral RQ3 Appl. Rate per 1 lb a.i./A) a.i./bee) Adult nectar 32 25.6 Proxy= 0.30 No data Lowest Rate‐ 0.8 lb forager Foliar a.i./A Larval 13.6 10.9 No data 2.1 worker Adult nectar 32 64 Proxy=0.74 No data Highest rate 2.0 lb forager Foliar a.i./A Larval 13.6 27.2 No data 5.1 worker Adult nectar NA NA Proxy<0.01 No data Highest rate 2.0 lb forager Soil a.i./A Larval NA NA No data 0.02 worker 1 Based on a 48‐h acute oral LD50 of > 87 µg a.i./bee for adults, thus, using highest test concentration as a proxy (MRID 50603502); no acute toxicity data for larval bees. 2 Bolded RQ value exceeds (or potentially exceeds) the acute risk level of concern (LOC) of 0.4 or chronic risk LOC of 1.0. 3 Based on a 22‐d chronic NOAEL of 5.3 µg a.i./bee/d for larvae (MRID 50964301); no chronic data for adult bees.

Off‐Field Risk In addition to bees foraging on the treated field, bees may be foraging in the fields adjacent to the treated fields. The AgDrift™ model was used to screen for the distance off the treated field where chronic RQs are expected to exceed the chronic risk LOC. The distances are shown in Table 9‐4.

Table 9‐4. Tier I Default Off‐site Distances (in feet) for Chronic Risk to Larval Worker Honey Bees Max. Oral Chronic Single Bee Dose Acute Oral Ground‐ Ground‐ Oral Appl. Caste/Task (μg RQ1,2 Low High RQ3 Rate a.i./bee) Larval 3.2 6.6 0.8 10.9 No data 2.1 worker Larval 6.6 16 2.0 27.2 No data 5.1 worker For Ag Drift model the Fraction of the applied is calculated as LOQ/RQ. For the low rate (1/2.1= 0.48); high rate (1/5.1=0.20) Based on Very Fine to Fine droplets. If using Fine to medium/coarse; all less the 5 ft off the field.

9.4 Bee Risk Characterization – Additional Lines of Evidence

Of the limited uses with foliar sprays, only the non‐agricultural/ mollusk eradication uses (e.g., parks, golf courses, rights‐of‐way) would be potentially attractive to pollinators. Usage data are not available to determine the intensity of use for all of these sites but for the sites that were

33 surveyed, usage was low. In contrast, many of the soil‐applied uses of metaldehyde are attractive to pollinators. The exposure via soil application is lower than foliar applications and there are no LOC exceedances for soil (or granular) applied metaldehyde, thus, for the majority of the pollinator attractive uses, risk to pollinators is low. According to the usage data, the majority of metaldehyde usage as a granular/pellet formulation is for citrus crops. There are also no reported incidents involving pollinators as a result of metaldehyde usage.

10 Conclusions

Given the uses of metaldehyde and the chemical’s environmental fate properties, there is a likelihood of exposure of metaldehyde to non‐target terrestrial and/or aquatic organisms. When used in accordance with the label, such exposure may result in adverse effects upon the survival, growth, and reproduction of non‐target terrestrial and aquatic organisms. Consistent with previous risk assessments (USEPA, 2016), there is a potential for direct adverse effects to birds and mammals from direct ingestion of granules. While there were no LOC exceedances for fish, several incidents have documented fish mortality that is likely the result of direct ingestion of granules. Risk to terrestrial invertebrates (e.g., pollinators) is identified for foliar uses, and below the LOC for soil applications. Risk estimates for all other taxa are below their respective LOCs. A more in depth summary of the risk conclusions are available in the Executive Summary Section 1.

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12 Referenced MRIDs Avian Single Dose Oral Toxicity MRID Citation Reference

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121700 Gibson, R. (1975) LC50 Study: ?Go West Meal Tested on Pheasants|. (Unpublished study received Aug 12, 1975 under 802‐507; prepared by Harris Laboratories, Inc., submitted by Chas. H. Lilly Co., Portland, OR; CDL:165010‐A) 121701 Taylor, R. (1974) ?Dietary LC50 Using Lilly's Go‐West Meal: Mal‐ lard Ducks|. (Unpublished study received Aug 12, 1975 under 802‐507; prepared by Harris Laboratories, Inc., submitted by Chas. H. Lilly Co., Portland, OR; CDL:165010‐B)

131976 Til, H. (1979) Prufung der Annahme und Vergallungswirkung mit sechs Meta‐ granulaten. (Unpublished study received Aug 19, 1983 under 6836‐90; prepared by Zentralinstitut fur Ernahrungsforschung, Neth., submitted by Lonza, Inc., Fair Lawn, NJ; CDL:251383‐C) 131977 Til, H.; Van Der Velde, A. (1978) Sub‐acute (8‐day) Dietary LC50 Study with Metaldehyde in Peking Ducks: Report No. R 5801. (Unpublished study received Aug 19, 1983 under 6836‐90; prepared by Centraal Instituut voor Voedingsonderzoek, Neth., submitted by Lonza, Inc., Fair Lawn, NJ; CDL:251383‐D) 131978 Til, H.; Van Der Velde, A. (1978) Sub‐acute (8‐day) Dietary LC50 Study with Metaldehyde in Japanese Quail: Report No. R 5800. (Unpublished study received Aug 19, 1983 under 6836‐90; prepared by Centraal Instituut voor Voedingsonderzoek, Neth., submitted by Lonza, Inc., Fair Lawn, NJ; CDL:251383‐E) 41437703 Til, H.; Van der Velde, A. (1978) Sub‐Acute (8 Day) Dietary (LC50) Study with Metaldehyde in Japanese Quail: Lab Project Number: B78/0851. Unpublished study prepared by Centraal Institut Voor Voedingsonderzoek. 13 p. 41437704 Til, H.; Van der Velde, A. (1978) Sub‐Acute (8 Day) Dietary Study with Metaldehyde in Peking Ducks: Lab Project Number: B78/0852. Unpublished study prepared by Centraal Institut Voor Voeding‐ sonderzoek. 12 p. 41553203 Til, H.; Van DerVeld, A. (1978) Sub‐Acute (8 Day) Dietary (LC50) Study with Metaldehyde in Japanese Quail: Lab Project Number: B78/0851. Unpublished study prepared by Centraal Institute Voor Voedingsonderzoek. 13 p. 41553204 Til, H.; Vander Velde, A. (1978) Sub‐Acute (8 Day) Dietary Study with Metaldehyde in Peking Ducks: Project Number: B78/08521. Unpublished study prepared by Centraal Instituut Voor Voedingson derzoek. 13 p. 42044002 Til, H. (1978) Sub‐Acute (8‐day) Dietary LC50 Study with Metaldehyde in Japanese Quail: Lab Project Number: 131977. Unpublished study prepared by Lonza Inc. 28 p. 42044003 Til, H. (1978) Sub‐Acute (8‐day) Dietary LC50 Study with Metaldehyde in Peking Ducks. Unpublished study prepared by Lonza Inc. 23 p. 71‐4 Avian Reproduction MRID Citation Reference

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50756602 Arnie, J.; Zhang, L.; Aufderheide, J.; et al. (2018) Metaldehyde: A 96‐ Hour Toxicity Test with the Freshwater Diatom (Navicula pelliculosa): Final Report. Project Number: 289P/108. Unpublished study prepared by EAG Laboratories. 154p. 850.4550 Cyanobacteria (Anabaena flos‐aquae) Toxicity MRID Citation Reference

50756603 Arnie, J.; Paz, T.; Aufderheide, J.; et al. (2018) Metaldehyde: A 96‐ Hour Toxicity Test with the Cyanobacteria (Anabaena flos‐aquae): Final Report. Project Number: 289P/109A. Unpublished study prepared by EAG Laboratories. 201p.

Appendix A. ROCKS table

Table A1. Chemical Names and Structures of Metaldehyde and its Transformation Products Final %AR Code Name/ Ref. Maximum Chemical Name Chemical Structure Study Type (study Synonym (MRID) %AR (day)A length) PARENT

Metaldehyde 2,4,6,8‐tetramethyl‐1,3,5,7‐ tetraoxocane

CAS No.: 108‐62‐3 Smiles Code: CC1OC(C)OC(C)OC(C)O1 Formula: C8H16O4 MW: 176.21 g/mol

MAJOR TRANSFORMATION PRODUCTS Acetaldehyde CAS No.: 75‐07‐0 Volatilized: Volatilized: Smiles Code: CC=O 11% (365 d) 11% (365 d) Formula: C2H4O Aerobic soil 41546001 MW: 44.05 g/mol Soil: Soil: 5% (~270 d) 4% (365 d) Vapor Pressure: Volatilized: Volatilized: 757.6 torr (20C) (NIOSH) 2% (30‐90 d) 2% (90 d) Aerobic 41507702 soil/anaerobic soil Soil: Soil: 7% (75 and 90 d) 7% (90 d) Paraldehyde CAS No.: 1499-02-1, 51289- 71-5, 123-63-7 Soil: Soil: Aerobic soil 41546001 Smiles Code: < 1% (~30 d) 4% (365 d) CC1OC(C)OC(C)O1

Final %AR Code Name/ Ref. Maximum Chemical Name Chemical Structure Study Type (study Synonym (MRID) %AR (day)A length)

Formula: C6H12O3 MW: 132.16 g/mol

Vapor Pressure: Aerobic Soil: Soil: 7.5 torr (20C) (NIOSH) 41507702 soil/anaerobic soil 1% (45 d) ND (365 d)

A Bolded values indicate a major degradate was formed or that a degradate is of toxicological significance. B ND means “not detected”.

Appendix B. BeeRex Modeling Inputs/Outputs

Screen for Soil Application Table 1. User inputs (related to exposure) Description Value Application rate 2 Units of app rate lb a.i./A Application method soil application Log Kow 0.12 Koc 36 Mass of tree vegetation (kg‐wet weight) 0.1 Are empirical residue data available? no Table 2. Toxicity data Description Value (µg a.i./bee) Adult contact LD50 113 Adult oral LD50 87 Adult oral NOAEL Larval LD50 Larval NOAEL 5.3

Table 3. Estimated concentrations in pollen and nectar Application method EECs (mg a.i./kg) EECs (µg a.i./mg) foliar spray NA NA soil application 1.028986843 0.001028987 seed treatment NA NA tree trunk NA NA

Table 4. Daily consumption of food, pesticide dose and resulting dietary RQs for all bees

Average Life Caste or task Jelly Nectar Pollen Total dose age (in Acute RQ Chronic RQ stage in hive (mg/day) (mg/day) (mg/day) (µg a.i./bee) days) 1 1.9 0 0 1.95508E‐05 #DIV/0! 3.69E‐06 2 9.4 0 0 9.67248E‐05 #DIV/0! 1.82E‐05 Worker 3 19 0 0 0.000195508 #DIV/0! 3.69E‐05 4 0 60 1.8 0.063591387 #DIV/0! 0.011998 5 0 120 3.6 0.127182774 #DIV/0! 0.023997 Larval Drone 6+ 0 130 3.6 0.137472642 #DIV/0! 0.025938 1 1.9 0 0 1.95508E‐05 #DIV/0! 3.69E‐06 2 9.4 0 0 9.67248E‐05 #DIV/0! 1.82E‐05 Queen 3 23 0 0 0.000236667 #DIV/0! 4.47E‐05 4+ 141 0 0 0.001450871 #DIV/0! 0.000274

Worker (cell cleaning and 0‐10 0 60 6.65 0.068581973 0.0007883 #DIV/0! capping) Worker (brood and queen 6 to 17 0 140 9.6 0.153936432 0.00176938 #DIV/0! tending, nurse bees) Worker (comb building, 11 to 18 0 60 1.7 0.063488488 0.00072975 #DIV/0! cleaning and food handling) Adult Worker (foraging for >18 0 43.5 0.041 0.044803116 0.00051498 #DIV/0! pollen) Worker (foraging for >18 0 292 0.041 0.300506347 0.0034541 #DIV/0! nectar) Worker (maintenance 0‐90 0 29 2 0.031898592 0.00036665 #DIV/0! of hive in winter) Drone >10 0 235 0.0002 0.241812114 0.00277945 #DIV/0! Queen Entire (laying 1500 525 0 0 0.005402181 6.2094E‐05 #DIV/0! lifestage eggs/day)

Table 5. Results (highest RQs) Exposure Adults Larvae Acute contact NA NA Acute dietary 0.00 No Data Chronic dietary No Data 0.02

Screen for Foliar Application (lower foliar rate) Table 1. User inputs (related to exposure) Description Value Application rate 0.8 Units of app rate lb a.i./A Application method foliar spray Log Kow 0.12 Koc 36 Mass of tree vegetation (kg‐wet weight) 0.1 Are empirical residue data available? no 0.001 Table 2. Toxicity data Description Value (µg a.i./bee) Adult contact LD50 113 Proxy Adult oral LD50 87 Proxy Adult oral NOAEL Larval LD50 Larval NOAEL 5.3

Table 3. Estimated concentrations in pollen and nectar Application method EECs (mg a.i./kg) EECs (µg a.i./mg) foliar spray 88 0.088 soil application NA NA seed treatment NA NA tree trunk NA NA

Table 4. Daily consumption of food, pesticide dose and resulting dietary RQs for all bees Average Life Caste or task in Jelly Nectar Pollen Total dose Chronic age (in Acute RQ stage hive (mg/day) (mg/day) (mg/day) (µg a.i./bee) RQ days) 1 1.9 0 0 0.001672 #DIV/0! 0.000315 2 9.4 0 0 0.008272 #DIV/0! 0.001561 Worker 3 19 0 0 0.01672 #DIV/0! 0.003155 4 0 60 1.8 5.4384 #DIV/0! 1.026113 5 0 120 3.6 10.8768 #DIV/0! 2.052226 Larval Drone 6+ 0 130 3.6 11.7568 #DIV/0! 2.218264 1 1.9 0 0 0.001672 #DIV/0! 0.000315 2 9.4 0 0 0.008272 #DIV/0! 0.001561 Queen 3 23 0 0 0.02024 #DIV/0! 0.003819 4+ 141 0 0 0.12408 #DIV/0! 0.023411 Worker (cell cleaning and 0‐10 0 60 6.65 5.8652 0.06741609 #DIV/0! Adult capping) Worker (brood 6 to 17 0 140 9.6 13.1648 0.15131954 #DIV/0! and queen

tending, nurse bees) Worker (comb building, cleaning 11 to 18 0 60 1.7 5.4296 0.0624092 #DIV/0! and food handling) Worker (foraging >18 0 43.5 0.041 3.831608 0.04404147 #DIV/0! for pollen) Worker (foraging >18 0 292 0.041 25.699608 0.29539779 #DIV/0! for nectar) Worker (maintenance of 0‐90 0 29 2 2.728 0.03135632 #DIV/0! hive in winter) Drone >10 0 235 0.0002 20.6800176 0.23770135 #DIV/0! Queen (laying Entire 525 0 0 0.462 0.00531034 #DIV/0! 1500 eggs/day) lifestage

Table 5. Results (highest RQs for the 0.8 lb a.i.rate) Exposure Adults Larvae Acute contact 0.019115 NA Acute dietary 0.30 No data Chronic dietary No data 2.05

For reference‐ Same analysis as above but for the 2 lb a.i. rate Table 6. Results (highest RQs for the 2.0 lb a.i.rate)

Exposure Adults Larvae Acute contact 0.047788 NA Acute dietary 0.74 No data Chronic dietary No data 5.13

Only exceedances based on the available data set are for chronic larval RQs ranging from 2.1‐ 5.1.

Appendix C. Endocrine Disruptor Screening Program (EDSP)

As required by FIFRA and the Federal Food, Drug, and Cosmetic Act (FFDCA), EPA reviews numerous studies to assess potential adverse outcomes from exposure to chemicals. Collectively, these studies include acute, subchronic and chronic toxicity, including assessments of carcinogenicity, neurotoxicity, developmental, reproductive, and general or systemic toxicity. These studies include endpoints which may be susceptible to endocrine influence, including effects on endocrine target organ histopathology, organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, reproductive loss, and sex ratios in offspring. For ecological hazard assessments, EPA evaluates acute tests and chronic studies that assess growth, developmental and reproductive effects in different taxonomic groups. As part of the Draft Ecological Risk Assessment for Registration Review, EPA reviewed these data and selected the most sensitive endpoints for relevant risk assessment scenarios from the existing hazard database. However, as required by FFDCA section 408(p), Metaldehyde is subject to the endocrine screening part of the Endocrine Disruptor Screening Program (EDSP).

EPA has developed the EDSP to determine whether certain substances (including pesticide active and other ingredients) may have an effect in humans or wildlife similar to an effect produced by a “naturally occurring estrogen, or other such endocrine effects as the Administrator may designate.” The EDSP employs a two‐tiered approach to making the statutorily required determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal systems. Chemicals that go through Tier 1 screening and are found to have the potential to interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 testing is designed to identify any adverse endocrine‐related effects caused by the substance, and establish a dose‐response relationship between the dose and the E, A, or T effect.

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between October 2009 and February 2010, EPA issued test orders/data call‐ins for the first group of 67 chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. A second list of chemicals identified for EDSP screening was published on June 14, 20136 and includes some pesticides scheduled for registration review and chemicals found in water. Neither of these lists should be construed as a list of known or likely endocrine disruptors. Metaldehyde is not on List 1. For further information on the status of the EDSP, the policies and procedures, the lists of chemicals, future lists, the test guidelines and Tier 1 screening battery, please visit our website7.

6 See http://www.regulations.gov/#!documentDetail;D=EPA‐HQ‐OPPT‐2009‐0477‐0074 for the final second list of chemicals. 7 Available: http://www.epa.gov/end

Appendix D. Potential Exposure from Consumption of Pellets (USEPA, 2014 Assessment)

Several ecological incidents have been reported of fish in small residential ponds being killed or harmed after slug and snail bait containing metaldehyde was applied on adjacent land. One possible explanation of the apparent risk to fish in these circumstances is that runoff is washing metaldehyde bait into the pond, and this created water concentrations that were much greater than those predicted based on transport of dissolved residues in runoff. To evaluate this hypothesis, we calculated the amount of product that would need to enter a small pond for the water concentration to reach the rainbow trout acute LC50 value of 69 mg ai/L. We assumed two pond sizes, 30 gallons and 100 gallons. Based on the active ingredient concentration of the product (0.03 lb ai/lb product or 13,600 mg a.i./lb product), we estimated that 0.57 pounds of product would need to wash into a 30 gallon pond, and 1.92 pounds of product would need to wash into a 100 gallon pond. Based on the information provided by the registrant that 1 pound product contains approximately 38,000 pellets, the number of pellets that would need to wash into a 30 and 100 gallon pond are 21,900 and 72,900, respectively. The probability of this large amount of product washing into a small pond seems very low. Therefore, the explanation that fish are being impacted by elevated metaldehyde concentrations in the water caused by bait pellets washing into the pond appears unlikely.

Another possible explanation of the fish incidents is that fish in the pond are readily eating pellets of metaldehyde bait that are washed in with runoff, resulting in a large oral dose. The hypothesis that the fish mistook the metaldehyde bait for food seems plausible since the reported fish kills have all been observed in residential fish ponds. The ornamental fish in these ponds are likely fed with pelleted fish food, and thus the slug and snail bait pellets, which are generally grain‐based, might resemble their normal food. If the fish ate the bait pellets, toxicity could have been caused by the large oral dose of metaldehyde, by the consumption of large amounts of inert ingredients in the bait, or by a combination of both.

The relevance of these fish kill incidents in ornamental fish ponds from residential uses to fish in natural aquatic environments from agricultural uses is uncertain. It is plausible that runoff may wash pellets applied to agricultural fields into natural fish habitats, but this may not occur as frequently or to the same extent as it does when residential users apply it near ornamental ponds. Also, wild fish may not feed on the pellets as readily as do fish in ornamental ponds that are regularly fed pelleted fish food.