Herbicide Risk Assessments, Characteristics, and Effects Specialist Report
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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. 1 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 2 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. 3 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 non- toxic 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.