Herbicide Risk Assessments, Characteristics, and Effects Specialist Report

This report provides a summary of the Forest Service Risk Assessments prepared for each herbicide by Syracuse Environmental Research Associates, Inc. and information about the characteristics and effects of herbicides that may be used for this project. More detailed information can be found in literature cited in the EA as well as on national and regional Web sites managed by the USDA Forest Service and Web sites for other agencies and organizations including the Environmental Protection Agency (EPA) and The Nature Conservancy. This information was used during the environmental analysis. Information given here was obtained from the SERA risk assessments (SERA 2004, SERA 2007, SERA 2011, SERA 2012 and SERA 2014) and the Weed Control Methods Handbook: Tools & Techniques for Use in Natural Areas prepared by the Nature Conservancy (Tu, et al 2001).

Human Health Risk Assessment This discussion reviews the risks to people associated with herbicide application. The following referenced literature was used to analyze potential human health risks associated with herbicide application. Although the risk assessments consider aerial application of herbicides, this project does not propose such a use.

• The Risk Assessment for Herbicide Use in Forest Service Regions 1, 2, 3, 4 and 10 and on Bonneville Power Administration Sites (USDA FS 1992) (referred to as RAHUFS). This analysis was developed for the Forest Service specifically to address human health issues raised by use of herbicides. • Assessing the Safety of Herbicides for Vegetation Management in the Missoula Valley Region – A Question and Answer Guide to Human Health Issues, referred to as ASH (Felsot 2001). • Risk assessments completed by the Forest Service under contract with Syracuse Environmental Research Associates for glyphosate, chlorsulfuron, triclopyr, clopyralid, imazapyr, imazapic, metsulfuron methyl, picloram, aminoclopyrachlor, and aminopyralid.

Three levels of analyses were used in the risk assessment processes:

• Review of toxicity test data (i.e., acute, chronic, and sub-chronic) for herbicides proposed for use on the project to determine dosage that could pose a risk to human health. Toxicity test data on laboratory animals is available for herbicides proposed for use in this analysis. Most tests have been conducted under EPA pesticide registration/re-registration requirements for use in the United States. The EPA uses test data to determine conditions for use of herbicides in the United States. • Estimate of exposure levels to which workers (applicators) and general public may be exposed during treatment operations. These exposure levels tend to be very conservative, with the highest doses expected multiplied by a factor of 100 to provide margins of safety. • Determine potential health risks by comparing dose levels to toxicological thresholds developed by EPA.

Factors Affecting Hazard of Herbicides

Toxicity of Herbicides A comparison of toxicity for herbicides proposed for use in this project is shown in Table 10. Toxicological studies using animals typically involve purposeful exposure to dosages (per unit of body weight) required to cause an effect (i.e. tumors, changes in immunity, etc.) or to establish a Lowest Observed Effect Level, known as a (LOEL) or a No-Observed-Effect-Level (NOEL). This often requires administration of relatively high doses of a chemical in order to document an effect or lack thereof.

Acute Toxicity

Acute toxicity is measured by the LD50, defined as the dosage of toxicant expressed in milligrams per kilogram of body weight, which is lethal to 50 percent of animals in a test population within 14 days of administration (USDA FS 1992). Risk assessments for the herbicides proposed for use show that the likelihood of exposure at these acute levels is not plausible, even in an accidental spill scenario.

Subchronic and Chronic Toxicity There is considerable information on subchronic and chronic effects due to exposure to herbicides in controlled animal studies. The information suggests that the herbicides proposed for use by the Forests are not carcinogenic, and there is no evidence to suggest that the herbicides proposed for use would result in carcinogenic, mutagenic, teratogenic, neurological or reproductive effects based on anticipated exposure levels to workers and the public (SERA 2004, 2007, 2011, 2012 and 2014).

The Reference Dose (RfD) provides a measure of long-term exposure that could result in chronic toxic effects. Generally, the dose-response assessments used in Forest Service risk assessments adopt RfDs proposed by the EPA as indices of acceptable exposure. An RfD is a level of exposure that will not result in any adverse effects in any individual. The EPA RfDs are used because they generally provide a level of analysis, review, and resources that exceed those that are or can be conducted in support of most Forest Service risk assessments. In addition, it is desirable for different agencies and organizations within the Federal Government to use concordant risk assessment values.

The Reference Dose comparison is discussed in more detail with the exposure risks discussion later in this section.

Table 1. Herbicide Characteristics

Mutagenic and Acute oral LD50 for rats Herbicide Carcinogenic1 Reproductive2 (mg a.e./kg bw) Glyphosate E No >1,920 - >4,860 Chlorsulfuron E No >5,000 Triclopyr E No 590 - 700 Clopyralid E No 3,390 - 5,440 Imazapyr E No >5,000 Imazapic E No 5,000 Metsulfuron methyl E No >5,000

Mutagenic and Acute oral LD50 for rats Herbicide Carcinogenic1 Reproductive2 (mg a.e./kg bw) Picloram E No >1,153 Aminoclopyrachlor E No 1,120 - 2,490 Aminopyralid E No 5,000

1 EPA carcinogenicity classification based on daily consumption for a 70-year life span. D = Not Classifiable as to Human Carcinogenicity; E = Evidence of Non-Carcinogenicity 2 Unlikely that compound is mutagenic or would pose a mutagenic risk to humans at expected exposure levels. Source: SERA 2004, 2007, 2011, 2012, 2014.

Synergistic Interactions Concerns are occasionally raised about potential synergistic interactions of herbicides with other herbicides in the environment or when they are mixed during application (tank mixing). Synergism is a special type of interaction in which the combined impact of two or more herbicides is greater than the impact predicted by adding their individual effects. The RAHUFS (USDA FS 1992) addresses the possibility of a variety of such interactions. These include the interaction of the active ingredients in an herbicide formulation with its inert ingredients, the interactions of these herbicides with other herbicides in the environment, and the cumulative impacts of spraying as proposed with other herbicide spraying to which the public might be exposed.

As noted in various risk assessments, no guarantee can be made regarding the effects of a chemical being zero. Similarly, no guarantee can be made about the absence of a synergistic interaction between herbicides and/or other chemicals to which workers or the public might be exposed. For example, exposure to benzene, a known carcinogen that comprises 1 to 5 percent of automobile fuel and 2.5 percent of automobile exhaust, followed by exposure to any of these herbicides could result in unexpected biochemical interactions. Analysis of the infinite number of materials a person may ingest or be exposed to in combination with chemicals is not feasible. Risk assessments conclude, however, that the additive effect of Forest Service herbicide use lies below the background levels for many of these chemicals (SERA 2004, SERA 2007, SERA 2011, SERA 2012, SERA 2014).

Adjuvants and Other Ingredients

During commercial synthesis of some pesticides, byproducts can be produced and carryover into the product eventually formulated for sale. Occasionally byproducts or impurities are considered toxicologically hazardous, and their concentrations must be limited so that potential exposures do not exceed levels of concern (Felsot 2001).

The following discussion on adjuvants and other ingredients is taken in whole or part from SERA 2014:

U.S. EPA is responsible for regulating both the active ingredients (a.i.) in pesticide formulations as well as any other chemicals that may be added to the formulation. As implemented, these regulations affect only pesticide labeling and testing requirements. The term inert was used to designate compounds that are not classified as active ingredient on the product label. While the term inert is codified in FIFRA, some inerts can be toxic, and the U.S. EPA now uses the term Other Ingredients rather than inerts (http://www.epa.gov/opprd001/inerts/). For brevity, the following discussion uses the term inert, recognizing that inerts may be biologically active and potentially hazardous components.

Inerts cover an extremely broad range of compounds including carriers, stabilizers, sticking agents, or other materials added to facilitate handling or application. However, these inerts may be toxic to humans or other nontarget species. The U.S. EPA is responsible for the regulation of inerts and adjuvants in pesticide formulations. As implemented, these regulations affect only pesticide labeling and testing requirements. As part of this regulatory activity, U.S. EPA had classified inerts into four lists based on the available toxicity information: toxic (List 1), potentially toxic (List 2), unclassifiable (List 3), and nontoxic 1 (List 4). List 4 was subdivided into two categories, 4A and 4B. List 4A constituted inerts for which there was adequate information to indicate a minimal concern. List 4B constituted inerts for which the use patterns and toxicity data indicated that use of the compound as an inert is not likely to pose a risk. While the U.S. EPA/OPP no longer actively maintains these lists, references to this classification system is encountered in some of the older literature and these lists may be mentioned in some Forest Service risk assessments.

Any compound classified by U.S. EPA as toxic or potentially toxic must be identified on the product label if the compound is present at a level of 1% or greater in the formulation. All such compounds are considered explicitly in the risk assessment. If the compounds are not classified toxic, all information on the inert ingredients in pesticide formulations is considered proprietary under Section 10(a) of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). In that case, the formulators of the pesticide need not and typically do not disclose the identity of the inert or adjuvant.

Even if the identities of the inerts are known, the toxicity data available on inerts are often very limited. As discussed by Levine (1996), the testing requirements for inerts are less rigorous than the testing requirements for the pesticides (i.e., the active ingredients). Some standard sources are typically consulted for information on inerts, including the classifications on the U.S. EPA’s inerts lists, discussed above. In addition, many inert ingredients are also approved food additives and the listing of approved food additives compiled by Clydesdale (1997) is also consulted. If an inert is on List 4 (nontoxic), concern for the inert is reduced. Similarly, if the inert is an approved food additive, concern is also reduced, particularly if the compound is classified as GRAS (generally recognized as safe). Some inerts that are potentially toxic have been reviewed and evaluated by other governmental groups.

The potential risks associated with inerts may also be assessed by comparing any available toxicity data on the active ingredient – i.e., the pesticide alone without any added adjuvants or inerts – to the toxicity of the formulated product. All pesticide formulations must identify the percent active ingredient in the formulation.

In some rare cases – e.g., the Roundup formulations of glyphosate as discussed in SERA 6 (2011b) – very detailed information may be available on both the toxicity of the active ingredient, the toxicity of specific adjuvants, and the toxicity of the formulation. In such cases, very detailed chemical specific analyses can be and are conducted based on an assessment of toxicologic interactions.

Surfactants are also commonly used in herbicide formulations. Surfactants are added to herbicides to improve herbicide mixing and the absorption or permeation of the herbicide into the plant. Like dyes and other inert ingredients, there is often limited information on the types of surfactants used and the toxicity of surfactants, especially since the industry considers the surfactant to play a key role in the effectiveness of the herbicide formulations. Most knowledge of surfactants is kept as proprietary information and not disclosed.

This is not always the case. The handling of other ingredients in the risk assessment of glyphosate, however, is much different. The surfactants used in many glyphosate formulations may be of equal or greater concern to the risk assessment than the toxicity of glyphosate itself. Consequently, as justified by the available data, most subsections of the current Forest Service risk assessment on glyphosate are

subdivided into discussions of the toxicity of glyphosate, the toxicity of glyphosate formulations, and/or the toxicity of the surfactants.

POEA (polyoxyethyleneamine) (SERA 2011)

While a number of surfactants may be used in conjunction with glyphosate, the most important class of surfactants is the POEA (polyoxyethyleneamine) group. A specific POEA surfactant, designated as MON 0818, was originally used with glyphosate in Roundup formulations at a concentration of 15% (Wan et al. 1989). The surfactant was a complex mixture consisting of a tallow amine surfactant at a concentration of 75% and other unidentified components.

Given the lack of specific information about the composition of the surfactants used by the various suppliers of glyphosate formulations as well as any differences in surfactants which might be used by a single supplier for different formulations, potential differences between surfactant-containing formulations of glyphosate limit the hazard identification for some toxic effects.

In terms of acute toxicities, the uncertainties associated with differences in the composition of POEA or other surfactants used in glyphosate formulations is not a substantial concern. As discussed in the different subsections on acute toxicities, the U.S. EPA requires formulation testing and reviews the results of the tests. Although specific details about the individual studies are not available, the available information does not suggest that the potential for systemic toxicity after exposure to any of the various glyphosate formulations which contain surfactants is substantially different.

Impurities and Metabolites This discussion on impurities and metabolites is taken in whole or part from SERA 2014:

In many respects, impurities and metabolites are much less difficult issues than inerts and adjuvants. Impurities often occur in pesticides. Virtually no chemical synthesis yields a totally pure product. Thus, any technical grade pesticides will contain some impurities. To some extent, concern for impurities in technical grade pesticides is reduced by the fact that the toxicity studies on pesticides are often conducted with the technical grade product. Thus, if toxic impurities are present in the technical grade product, they are likely to be encompassed by the available toxicity studies on the technical grade product.

The assumption is generally made that studies on whole animals, such as those used to derive acceptable levels of exposure in humans, will encompass the toxicity of both the parent compound as well as any metabolites that formed in vivo. However, this does not apply to toxic metabolites that are formed in the environment. In such a case, the toxicity of the metabolite as well as exposures to the metabolite may need to be quantitatively addressed in the risk assessment (SERA 2014).

Hexachlorobenzene (HCB)

An exception to this general rule involves carcinogens, most of which are presumed to act by non- threshold mechanisms. Because of the non-threshold assumption, any amount of a carcinogen in an otherwise non-carcinogenic mixture may pose a carcinogenic risk. An example of this is the occurrence of hexachlorobenzene in two herbicides used by the Forest Service, clopyralid and picloram. For these herbicides, the risk assessments each included a full dose-response assessment, exposure assessment, and risk characterization for the potential carcinogenic effects of hexachlorobenzene.

HCB is ubiquitous and persistent in the environment. The major sources of general exposure for the public to HCB involve industrial emissions, proximity to hazardous waste sites, and the consumption of contaminated food. Virtually all individuals are exposed to HCB and virtually all individuals have

detectable concentrations of HCB in their bodies. Based on current concentrations of HCB in environmental media and food, daily doses of HCB (i.e., background levels of exposure) are in the range of 0.000001 (1×10-6) mg/kg/day. Based on the amount of HCB in clopyralid and the amount of clopyralid used in Forest Service programs, the use of clopyralid by the Forest Service will not substantially contribute to any wide-spread increase of ambient levels of HCB (SERA 2004).

All of the HQs for carcinogenicity associated with HCB as a contaminant in technical grade picloram are also below the level of concern. The highest HQ associated with HCB is 0.4, the upper bound for the consumption of contaminated fish by subsistence populations (SERA 2011).

Endocrine Disruption The endocrine system is critical to the health of an animal because it participates in the control of metabolism and body composition, growth and development, reproduction, and many of the numerous physiological adjustments needed to maintain constancy of the internal environment (homeostasis).

An endocrine disruptor is an exogenous agent (from outside of the body) that produces adverse effects on an organism or population of organisms by interfering with endocrine function (Kavlock et al.1996). The endocrine system is highly regulated to achieve hormone activities in amounts needed to respond to physiological demands. Endocrine disruption is a state of uncontrolled hormone action, in which hormone responses are absent or insufficient when needed, or occur inappropriately when they are not needed. These can result in abnormalities in growth and development, reproduction, body composition, homeostasis, and behavior. Endocrine disruptors are not considered to be a major cause of endocrine disorders in humans. However, a variety of inherited endocrine diseases are known to be caused by abnormalities in endocrine glands, hormone transport, or hormone receptors. Certain endocrine diseases are thought to be caused by autoimmune disorders in which the body attacks and destroys its own endocrine glands

Some important drugs are endocrine disruptors. Examples of these include thyroid blocking agents used in the treatment of hyperthyroidism (e.g., thiopropyluracil); corticosteroids used in the treatment of inflammation, and as diuretics in the treatment of edema and hypertension; estrogens used in female birth control and to manage symptoms of menopause; hypoglycemics used in the treatment of certain forms of diabetes mellitus; and various adrenergic agonists and antagonists used in the treatment of allergic reactions, asthma, heart disease, and hypertension (Hardman and Limbird1996). Endocrine-active agents are also in our diet, including iodine, needed for the production of thyroid hormone, and phytoestrogens, estrogenic compounds found in many edible plants. (SERA 2014).

Chemicals, other than our own hormones, can interact with components of the endocrine system. Scientists have discovered that many kinds of chemicals, including natural food biochemicals as well as industrial chemicals and a few pesticides, can mimic the action of the hormones estrogen or testosterone. Concern has also been expressed about potential effects on the thyroid hormone during early development (Felsot 2001).

A variety of short-term in vitro and in vivo tests have also been described that assess whether a chemical interferes with hormone availability (e.g., synthesis, secretion, transport in the bloodstream) or with the target tissue response (e.g., hormone receptor binding or postreceptor processing) (SERA 2014).

Positive in vitro tests, however, do not necessarily indicate that a substance would actually disrupt hormone functioning in a whole organism. In vitro screening tests are properly used to determine which chemicals should be subjected to a second type of test, the in vivo or “live animal” test. In vivo tests use whole animals that are fed various doses of chemical. In some cases, the chemical is injected beneath the

skin or directly into the body cavity. Developmental and reproductive toxicity studies with live animals over several generations are especially useful for determining if a substance adversely affects the endocrine system.

With one exception—the drug DES (diethylstilbesterol)—all chemicals that have been tested in vitro are thousands to millions of times less potent than the natural estrogen hormone (estradiol) (Felsot 2001). In the in vivo (live animal) studies to date, only a handful of chemicals, including natural food biochemicals, a few pesticides, and several industrial chemicals show endocrine disrupting effects (Felsot 2001). The in vivo experiments usually involve feeding pregnant rats or mice one or more doses of a chemical. With one exception, the drug DES, any effects that have been observed were in tests with doses at least thousands of times greater than environmental or dietary concentrations.

Potential for Exposure The following discussion on human health exposure was referenced from SERA 2014:

Exposure scenarios are developed for workers and members of the general public. For each group, two types of exposure scenarios are generally taken into consideration: general exposure and accidental/incidental exposure.

The term general exposure refers to human exposure resulting from the normal use of the chemical. For workers, general exposure involves the handling and application of the compound. These general exposure scenarios can be interpreted relatively easily and objectively. The exposure estimates are calculated from the amount of the chemical handled/day and the exposure rates for the worker group. Although each of the specific exposure assessments for workers involves degrees of uncertainty, the exposure estimates are objective in that they are based on empirical relationships of absorbed dose to pesticide use. For the general public the general exposure scenarios are somewhat more arbitrary and may be less plausible. For each pesticide, at least three general exposure scenarios are considered, including walking through a contaminated area shortly after treatment, the consumption of ambient water from a contaminated watershed, and the consumption of contaminated vegetation. These three scenarios are consistently used because one of them usually leads to the highest estimates of exposure. Additional scenarios discussed below may be considered for each of the individual compounds as warranted by the available data and the nature of the program activities.

Some, if not all, of these general exposure scenarios for the general public may seem implausible or at least extremely conservative. For example, in many cases compounds are applied in relatively remote areas and so it is not likely that members of the general public would be exposed to plants shortly after treatment. Similarly, the estimates of longer-term consumption of contaminated water are based on estimated application rates and monitoring studies that can be used to relate levels in ambient water to treatment rates in a watershed; however, in most pesticide applications, substantial portions of a watershed are not likely to be treated. Finally, the exposure scenarios based on longer-term consumption of contaminated vegetation assume that an area of edible plants is inadvertently sprayed and that these plants are consumed by an individual over a 90-day period. While such inadvertent contamination might occur, it is extremely unlikely to happen as a result of directed applications (e.g., backpack applications). Even in the case of boom spray operations, the spray is directed at target vegetation and the possibility of inadvertent contamination of cultivated or edible vegetation would be low. In addition, for herbicides and other phytotoxic compounds, it is likely that the contaminated plants would show obvious signs of damage over a relatively short period of time and would therefore not be consumed. All of the factors discussed above concerning general exposure scenarios for the general public have merit and must be considered in the interpretation of the risk characterization. Thus, the typical hazard to the general public may often be negligible because significant levels of exposure are not likely. For the

general public, the general exposures may be regarded as extreme in that they are based on very conservative exposure assessments and/or very implausible events. Nonetheless, these general exposure assessments are included because the risk assessment is intended to be extremely conservative with respect to potential effects on the general public, and to provide estimates regarding the likelihood and nature of effects after human exposure to pesticides. Accidental/incidental exposure scenarios describe specific examples of gross over-exposure associated with mischance or mishandling of a chemical. All of these exposure scenarios are arbitrary in that the nature and duration of the exposure is fixed. For example, the worker exposure scenario involving immersion of the hands is based on a 1-minute period of exposure but could just as easily be based on an exposure period of 5 seconds or 5 minutes. Similarly, the consequences of wearing contaminated gloves could be evaluated at 4 hours rather than at 1 hour. These scenarios are intended to provide an indication of relative hazard among different pesticides and different events in a manner that facilitates conversion or extrapolation to other exposure conditions.

Like the general exposure scenarios, the accidental exposures for the general public may be regarded as more extreme than those for workers. Three scenarios are included in each exposure assessment. They include direct spray, the consumption of contaminated water shortly after a spill, and the consumption of contaminated vegetation shortly after treatment. The direct spray scenario is clearly extreme. It assumes that a naked child is sprayed directly with a pesticide as it is being applied and that no steps are taken to remove the pesticide from the child for 1 hour. There are no reports of such incidents in the literature, and the likelihood of such an incident occurring appears to be remote. Nonetheless, this scenario and others like it are useful not only as a uniform comparison among pesticides but also as a simplifying step in the risk assessment. If the 'naked child' scenario indicates no basis for concern, other dermal spray scenarios will not suggest a potential hazard and need not be explored. If there is a potential hazard, other more plausible exposure scenarios may need to be considered. The other two accidental scenarios are similarly intended to serve as uniform comparisons among chemicals as well as a means of evaluating the need to explore additional exposure scenarios.

Typically, the level of exposure is directly proportional to the exposure parameters. The exposure associated with wearing gloves for 4 hours is 4 times the exposure associated with wearing contaminated gloves for 1 hour. Similarly, the general exposure scenarios for workers are based on an 8-hour work day. If a 4-hour application period were used, the hazard indices would be reduced by a factor of two. As another example, general exposure scenarios for both workers and the general public are linearly related to the application rate. Consequently, if the application rate were to double or vary by some other factor, the estimated exposure would double or vary by the same factor. Thus, the specific exposure parameters used in the risk assessment are selected to allow for relatively simple extrapolation to greater or lesser degrees of exposure.

Additional variability is taken into consideration by estimating exposure doses or absorbed doses for individuals of different age groups (i.e., adults, young children, toddlers, and infants). Children may behave in ways that increase their exposure to applied pesticides (e.g., long periods of outdoor play, pica, or imprudent consumption of contaminated media or materials). In addition, anatomical and physiological factors, such as body surface area, and breathing rates and consumption rates for food and water, are not linearly related to body weight and age. Consequently, the models used to estimate the exposure dose (e.g., mg/kg body weight/day) based on chemical concentrations in environmental media (e.g., ppm in air, water, or food) indicate that children, compared with individuals of different age groups, are generally exposed to the highest doses of chemicals for a given environmental concentration

In addition, label requirements for herbicide applications include time limits on worker re-entry to treated areas and standards to protect non-workers. These are summarized in Table 2.

Table 2. General Guidelines for Reentry into Areas Treated with Herbicides

Non-Worker Protection Restricted Entry Interval (REI) Herbicide (under Worker Protection Standards Standard, 40 CFR part 170)

Keep people and pets off treated areas Glyphosate until spray solution has dried. 4 hours

Do not enter or allow entry into treated Chlorsulfuron 4 hours areas until sprays have dried.

Do not enter or allow others to enter the Triclopyr 3 12 hours treated areas until sprays have dried

Do not enter treated areas until sprays have dried. For early entry to treated areas, wear eye protection, chemical- Clopyralid resistant gloves made of any 12 hours

waterproof material, long-sleeved shirt, long pants, shoes and socks.

Do not enter or allow others to enter the 12 hours Imazapyr 4SL treated areas without protective clothing until sprays have dried.

Do not enter treated areas without Imazapyr 2SL protective clothing until sprays have 48 hours dried.

Do not enter treated areas without Imazapic protective clothing until sprays have 12 hours dried.

Metsulfuron Not stated on label 4 hours methyl

Do not allow people or pets on Picloram treatment area during application, or until sprayed areas have dried. 12 hours

Long-sleeved shirt and long pants. Shoes Aminoclopyrachlor No entry until product has dried plus socks

Do not enter or allow entry into treated Aminopyralid 48 hours areas until sprayed have dried.

Note: Data obtained from herbicide product labels.

Herbicide Drift Spray drift is largely a function of droplet particle size, release height, and wind speed (Teske and Thistle 1999). Other factors that control drift to a lesser degree include the type of spray nozzle used, the angle of the spray nozzle, and the length of the boom. The largest particles, being the heaviest, would fall to the ground sooner than smaller sizes upon exiting the sprayer. Medium size particles can be carried beyond the sprayer swath (the fan shape spray under a nozzle), but all particles would deposit within a short distance of the release point. The physics of sprayers dictates that there would always be a small percentage of spray droplets small enough to be carried in wind currents to varying distances beyond the target area. Because the small droplets are a minor proportion of the total spray volume, their significance beyond the field boundary rapidly declines as they are diluted in increasing volumes of air (Felsot 2001).

Drift characteristics differ between pesticides. With herbicides proposed in this analysis, it is not critical to coat the entire leaf since some of the products can be absorbed by the plant roots and good efficacy can be achieved by larger droplets on leaves to the target plant. Therefore, herbicide drift can be intentionally reduced by generating larger droplets without reducing efficacy.

Spray nozzle diameter, pressure, amount of water in the tank mixture, and release height of the spray are important controllable determinants of drift potential by virtue of their effect on the spectrum of droplet sizes emitted from the nozzles (Felsot 2001; Teske and Thistle 1999). Meteorological conditions such as wind speed and direction, air mass stability, temperature and humidity and herbicide volatility also affect drift.

Commercial drift reduction agents are available that are designed to reduce drift beyond the capabilities of the determinants previously described. These products create larger and more cohesive droplets that are less apt to break into smaller particles as they fall through the air. They reduce the percentage of smaller, lighter particles that are the size most apt to drift off the treatment area.

Wind speed increases the concentration of drifting droplets leaving the treated area if the wind is adverse (blowing away from the release point in the treatment area). If the wind is favorable (blowing into the treatment area) drift can be reduced. Numerous studies have shown that over 90 percent of spray droplets land on the target area, and about 10 percent or less move offtarget, and that the droplets that move offtarget most typically deposit within 100 feet of the target area (Felsot 2001; Yates et al. 1978; Teske and Thistle 1999).

RAHUFS Drift Estimations The 1992 Risk Assessment for Herbicide Use in Forest Service Regions 1, 2, 3, 4 and 10 and on Bonneville Power Administration Sites (USDA FS 1992, referred to as RAHUFS), determined spray drift distances downwind of an application site for aerial, backpack, and ground-mechanical application equipment. The results of the RAHUFS spray drift analysis indicates “low” health risk to the public from ground and aerial (aerial application is not a consideration in this project) applied herbicides (USDA FS 1992). “Low risk” was defined in the study as drift from the herbicides that presents a less than one in a million systemic, reproductive or cancer risk. Spray drift from hand application equipment was found to be negligible.

AGDRIFT/Felsot Drift Estimations Felsot (2001) used the EPA/USDA FS AGDRIFT model to simulate herbicide sprays for several application scenarios, including a truck mounted spray boom set at two heights and a helicopter (aerial application is not a consideration in this project) at two heights. These simulations included crosswinds blowing at 10 and 6 mph. The model output was an estimated amount (percent of that applied) that deposited a defined distance from the edge of a spray swath. A spray deposition curve was developed to calculate a dose that a bystander could potentially receive if standing within the drift zone of an application. The whole body surface area was assumed exposed to a drifting spray (highly conservative), and the bystanders were assumed to be an adult weighing 70 kg and a child weighing 10 kg. Absorption of the depositing dose was assumed to be 10 percent. Calculations were made to determine the percentage of the depositing spray that a child could be exposed to on a daily basis over a 70-year lifespan and be within the EPA safety guidelines as defined by the RfD (i.e., the “safe dose”).

Herbicide Characteristics and Environmental Effects

Glyphosate Glyphosate is a nonselective foliar-applied herbicide. It controls virtually all annual and perennial weeds, but generally is most phytotoxic to annual grasses. Growth is inhibited soon after application followed by general foliar chlorosis and necrosis with 4-7 days for highly susceptible grasses and within 10-20 days for less susceptible species. Sub lethal rates inhibit seed head emergence and suppress vegetative growth of most perennial grasses (Shaner 2014).

Glyphosate inhibits the shikimic acid pathway in plants, which is involved in the production of essential aromatic amino acids. This inhibition leads to an inhibition or cessation of growth, cellular disruption, and, at sufficiently high levels of exposure, plant death. Glyphosate formulations may be applied by directed foliar, ground broadcast foliar, or aerial methods. In Forest Service Programs, the most common method of applying glyphosate is by backpack-applied directed foliar sprays. The formulations of glyphosate identified by the Forest Service contain the ammonium, dimethylamine, isopropylamine, or potassium salts of glyphosate. (SERA 2011).

Because of patent restrictions, all of the commercial formulations of glyphosate were produced only by Monsanto and included Accord, Rodeo, Roundup, and Roundup Pro (SERA 1996). By 2003, the year of the last Forest Service risk assessment (SERA 2003), glyphosate was no longer protected by patent, and 35 commercial formulations of glyphosate were registered for forestry applications, all of which contained the isopropylamine salt of glyphosate. Since 2003, the number of commercial formulations has increased substantially (SERA 2011).

Chlorsulfuron Chlorsulfuron is recommended for preemergent and early postemergent control of many annual, biennial, and perennial broadleaf weeds. Three formulations of chlorsulfuron are available in the United States: Telar® DF and Glean®, which are produced by Dupont, and Corsair ™, which is produced by Riverdale. Chlorsulfuron is used in Forest Service programs only for the control of noxious weeds. The most common methods of ground application for chlorsulfuron involve backpack (selective foliar) and boom spray (broadcast foliar) operations (SERA 2004).

The most common methods of ground application for Telar DF and Corsair involve backpack (selective foliar) and boom spray (broadcast foliar) operations. In selective foliar applications, the herbicide sprayer

or container is carried by backpack and the herbicide is applied to selected target vegetation (SERA 2004).

Mechanism of action is the inhibition of branched chain amino acid production by inhibition of the enzyme acetolactate. Growth of treated plants is inhibited within a few hours after application, but injury symptoms usually appear 1-2 weeks later (Shaner 2014).

Triclopyr Triclopyr is used in Forest Service programs primarily for conifer and/or hardwood release, noxious weed control, site preparation, and rights-of-way management. The most common application method for triclopyr is backpack (selective) foliar applications. Triclopyr may be used in hack and squirt applications. Hack and squirt applications are a form of cut surface treatment in which the bark of a standing tree is cut with a hatchet and the herbicide is applied with a squirt bottle. This treatment method is used to eliminate large trees during site preparation, conifer release operations, or rights-of-way maintenance Two forms of triclopyr are used commercially as herbicides: the triethylamine salt (TEA) and the butoxyethyl ester (BEE) (SERA 2011).

Triclopyr mimics an auxin growth hormone, which causes abnormal increases in protein biosynthesis leads to uncontrolled cell division and growth, which results in vascular tissue destruction (Shaner 2014).

The number of triclopyr formulations with labeled uses relevant to Forest Service programs continues to grow. When the initial Forest Service risk assessment on triclopyr was conducted, there were only two available formulations, Garlon 3A and Garlon 4 (SERA 1996). The Forest Service risk assessment conducted in 2003 covers six formulations, Garlon 3A, Garlon 4, Forestry Garlon 4, Pathfinder II, Remedy RTU, and Renovate 3. Currently, 19 formulations of triclopyr that might be used in Forest Service programs have been identified (SERA 2011).

Clopyralid Clopyralid is a selective herbicide used primarily in the control of broadleaf weeds. The Forest Service uses only a single commercial formulation of clopyralid, Transline. The Forest Service uses Transline almost exclusively in noxious weed control. Relatively minor uses include rights-of-way management, wildlife openings, and facilities maintenance. Transline is a liquid formulation of clopyralid that is manufactured by Dow AgroSciences and contains 40.9% clopyralid as the monoethanolamine salt and 59.1% inert ingredients. The most common methods of ground application for Transline involve backpack (selective foliar) and boom spray (broadcast foliar) operations. (SERA 2004).

Clopyralid controls many annual and perennial broadleaf weeds including Canada thistle, wild buckwheat, cocklebur, jimsonweed, ragweed spp., marsh elder and wild sunflower. Mode of action is similar to other auxin type herbicides (Shaner 2014)

Imazapyr Imazapyr is a nonselective herbicide used to control a variety of grasses, broadleaf weeds, vines, and brush species. In Forest Service programs, imazapyr is used primarily in the Southern United States for noxious weed control, conifer release, and site preparation. Imazapyr may also be used to control aquatic macrophytes (SERA 2011)

Imazapyr works by the inhibition of branched chain amino acid production by inhibition of the enzyme acetolactate synthase (ALS) or acetohydroxy acid synthase (AHAS) (Shaner 2014).

While imazapyr formulations can be used in pre-emergence applications, the most common and effective applications are post-emergent when the vegetation to be controlled is growing vigorously. The most common methods of ground application involve backpack (selective foliar) and boom spray (broadcast foliar) operations. Cut surface treatment methods may also be used in Forest Service programs involving imazapyr (SERA 2011).

Imazapic Imazapic is used in the control of grasses, broadleaves, and vines, and for turf height suppression in non- cropland areas. The Forest Service will typically use imazapic in noxious weed control and rights-of-way management. The Forest Service may use two commercial formulations of imazapic, Plateau and Plateau DG. Both of these formulation contain the ammonium salt of imazapic as the active ingredient. Plateau is a liquid formulation that contains imazapic (22.2%) at a concentration of 2 lbs per gallon and Plateau DG is a dispersible granule formulation that contains the ammonium salt of imazapic (70%). Imazapic may be applied by directed foliar, broadcast foliar, or aerial (Plateau only) methods. Imazapic may be applied by directed foliar, broadcast foliar, or aerial (Plateau only) methods. The most common method of application in Forest Service programs will involve broadcast foliar applications (SERA 2004).

Imazapic works in a similarly to Imazapyr by the inhibition of branched chain amino acid production by inhibition of the enzyme acetolactate synthase (ALS) or acetohydroxy acid synthase (AHAS) (Shaner 2014).

Metsulfuron methyl Metsulfuron methyl is a selective pre-emergence and post-emergence sulfonyl urea herbicide used primarily to control many annual and perennial weeds and woody plants. Only one commercial formulation of metsulfuron methyl, Escort® XP, is in Forest Service programs. Escort XP is manufactured by Du Pont as a dry flowable granule. The composition of the product is 60% metsulfuron methyl and 40% inert ingredients. Metsulfuron methyl is used in Forest Service programs primarily for the control of noxious weeds. Minor uses include conifer release and rights-of-way management (SERA 2004).

The most common methods of ground application for Escort XP involve backpack (selective foliar) and boom spray (broadcast foliar) operations. In selective foliar applications, the herbicide sprayer or container is carried by backpack and the herbicide is applied to selected target vegetation (SERA 2004).

Metsulfuron methyl behavior in plants is similar to Imazapyr and Imazapic. Growth of treated plants is inhibited within hours after application, but injury symptoms usually appear more than one or two weeks later. Meristematic areas gradually become chlorotic and necrotic, followed by a general foliar chlorosis and necrosis (Shaner 2014).

Picloram Picloram is a herbicide used in the control of a number of broadleaf weeds and undesirable brush. Picloram is used in Forest Service programs primarily for the control of noxious weeds. Rights-of-way management is a minor use for picloram. Tordon K and Tordon 22K are the formulations of picloram currently used by the Forest Service. Both formulations are produced by Dow AgroSciences as a liquid containing the potassium salt of picloram (24.4% w/v). This is equivalent to a concentration of 2 lb a.e./gallon. The remaining 75.6% of the formulation consists of inerts, including a polyglycol polymer (SERA 2011).

The most common application methods for Tordon involve backpack (selective foliar), boom spray (broadcast foliar), and aerial applications. Picloram is a systemic herbicide that is registered for the postemergent control of broadleaf weeds and woody plants (SERA 2011).

Picloram is a systemic, ambi-mobile growth-regulator herbicide. Symptoms of Picloram injury are typical of other auxin-type herbicides, and include epinastic bending and twisting of stems and petioles, stem swelling (particularly at nodes) and elongation, and leaf cupping and curling (Shaner 2014).

Aminocyclopyrachlor Aminocyclopyrachlor is a new herbicide developed by DuPont™, which the U.S. EPA granted a conditional registration for the control of broadleaf weeds and woody vegetation. Because aminocyclopyrachlor is effective in controlling leafy spurge (Euphorbia esula), the Forest Service anticipates its use in vegetation management programs. Based on the distribution of leafy spurge, the Forest Service may use aminocyclopyrachlor in most areas of the United States, except the southeast. The greatest use of aminocyclopyrachlor is anticipated in northwestern states, particularly Idaho, Wyoming, Montana, and North Dakota. Aminocyclopyrachlor is labeled for numerous weeds, particularly terrestrial and riparian invasive and noxious weeds (SERA 2012).

The active ingredients in aminocyclopyrachlor formulations include either the acid form, or the potassium salt, or the methyl ester. DuPont™ is not commercializing formulations containing the methyl ester of aminocyclopyrachlor. Based on the available EPA product labels, it seems likely that the Forest Service may use DuPont™ Method® 50SG (acid) and DuPont™ Method® 240SL (potassium salt) to control leafy spurge as well as other noxious and invasive weeds. Various methods may be used to apply aminocyclopyrachlor formulations, including ground or aerial broadcast, directed foliar (including spot treatments), and various cut surface treatments, specified as cut stubble or cut stump on the product labels (SERA 2012).

Aminocyclopyrachlor is a systemic, ambi-mobile growth regulator herbicide. As the compound translocates and accumulates in meristematic tissue it causes uneven cell division and growth resulting in death of susceptible plant species (Shaner 2014).

Aminopyralid Aminopyralid is a new selective systemic herbicide that has been developed for the control of broadleaf weeds in rangeland, non-crop areas, and grazed areas. The most likely uses of aminopyralid will involve applications to forest and rangelands, rights-of-way, and developed recreational areas such as campgrounds, picnic areas and trails. Application methods have and will likely continue to include backpack (selective foliar), hydraulic spray, and aerial applications. Formulations include Milestone and Milestone VM. Both of these formulations contain the triisopropanolamine (TIPA) salt of aminopyralid (40.6 % w a.i./v, equivalent to 21.1% a.e. or 2 lbs a.e./gal). These formulations contain no inert ingredients other than water and triisopropanolamine (SERA 2007).

Aminopyralid has a similar mode of action as aminocyclopyrachlor. Aminopyralid provides a broad spectrum of broadleaf weed control. Within hours or days of application, aminopyralid causes symptoms such as thickened, curved and twisted stems and leaves, cupping and crinkling of leaves, stem cracking, narrow leaves with callus tissue, hardened growth on stem, and or enlarged root and proliferated growth (Shaner 2014).