• Relationship to ambient water quality criteria
• Use of aquatic life benchmarks
• OPP aquatic life benchmarks
• Footnotes
• Definitions
• References

Relationship to Ambient Water Quality Criteria

Both OPP and EPA's Office of Water (OW) have responsibilities for evaluating aquatic toxicity data to assess the ecological effects of chemicals in surface water. Effects assessments under both program offices are developed with high quality data pursuant to parallel but somewhat different rigorously peer-reviewed assessment methods.

• OW uses aquatic toxicity data to develop ambient water quality criteria that can be adopted by states and tribes to establish water quality standards under the Clean Water Act. Criteria are available for roughly 16 pesticides. Procedures for deriving the criteria are described in Guidelines^a, and require, for acute criteria, that data be available for at least 8 families.

• OPP uses aquatic toxicity data in ecological risk assessments for large numbers of pesticide registration decisions under FIFRA. OPP's procedures for effects assessment are described in the Overview Document ^b; and rely, at a minimum, on data for the most sensitive tested effects concentration for each taxon.

• Both the OW and OPP methods assess and characterize effects to protect aquatic communities.

The table below provides aquatic toxicity benchmarks, a reference for the most recent risk assessment conducted by OPP for each pesticide, and ambient water quality criteria, if available.

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Use of Aquatic Life Benchmarks

EPA worked initially with the USGS to identify aquatic ecotoxicity benchmarks values from risk assessments developed by EPA for individual pesticides during the recently completed re-registration program. The Overview Document and ecological risk assessments developed for individual pesticides provide useful information for understanding how these ecotoxicity benchmarks were developed and the uncertainties associated with each benchmark. Comparing a measured concentration of a pesticide in water with an aquatic life benchmark can be helpful in interpreting monitoring data, and to identify and prioritize sites and pesticides that may require further investigation.

These aquatic benchmarks are extracted from the most recent publically available OPP risk assessment for the pesticide and are based on the most sensitive aquatic toxicity data of the distribution for each taxa. Benchmarks, developed for baseline risk assessments, are estimates of the concentrations below which pesticides are not expected to harm aquatic life. OPP may further refine a risk assessment based on the full distribution of toxicity data for a given species, using point estimates, species sensitivity distribution approaches, or probabilistic methods.

OPP and OW are actively working together to harmonize the high quality, peer-reviewed scientific approaches that now underlie both programs. A harmonized approach will result in consistent tools and approaches for all stakeholder communities to use in ensuring the protection of aquatic ecosystems.

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Footnotes

• ¹ Benchmark = Toxicity value x LOC. For acute fish, toxicity value is generally the lowest 96-hour LC50 in a standardized test (usually with rainbow trout, fathead minnow, or bluegill), and the LOC is 0.5.

• ² Benchmark = Toxicity value x LOC. For chronic fish, toxicity value is usually the lowest NOEAC from a life-cycle or early life stage test (usually with rainbow trout or fathead minnow), and the LOC is 1.

• ³ Benchmark = Toxicity value x LOC. For acute invertebrate, toxicity value is usually the lowest 48- or 96-hour EC₅₀ or LC₅₀ in a standardized test (usually with midge, scud, or daphnids), and the LOC is 0.5.

• ⁴ Benchmark = Toxicity value x LOC. For chronic invertebrates, toxicity value is usually the lowest NOAEC from a life-cycle test with invertebrates (usually with midge, scud, or daphnids), and the LOC is 1.

• ⁵ Benchmark = Toxicity value x LOC. For acute nonvascular plants, toxicity value is usually a short-term (less than 10 days) EC₅₀ (usually with green algae or diatoms), and the LOC is 1.

• ⁶ Benchmark = Toxicity value x LOC. For acute vascular plants, toxicity value is usually a short-term (less than 10 days) EC50 (usually with duckweed) and the LOC is 1.

• ⁷ An acute-to-chronic ratio was used to calculate the chronic endpoint and benchmark, which may underestimate chronic toxicity.

• ⁸ Although the underlying acute toxicity value is greater than or equal to the chronic toxicity value, the acute benchmark is lower than the chronic benchmark because acute and chronic toxicity values were multiplied by LOC values of 0.5 and 1, respectively.

• ⁹ Original toxicity values are in micrograms of acid equivalents per liter. For 2,4-D and 2,4-DB, the toxicity values selected were the lowest available values for the acid or salt forms. For MCPA, acute toxicity values were the lowest for the acid, salt or ester forms, and chronic toxicity values were the lowest of the acid and salt forms. For Dicamba the toxicity values were the lowest of the acid or salt forms. (Selection was consistent with risk quotients in the cited USEPA references.)

• ¹⁰ The acute toxicity values were the lowest of the acid, salt or ester forms, and the chronic toxicity values were the lowest of the acid and salt forms of triclopyr. (Selection was consistent with risk quotients in the cited USEPA reference.)

• ¹¹ Toxicity values and benchmarks apply to permethrin. If monitoring data represent only the cis isomer of permethrin in water, comparison with benchmarks may underestimate potential toxicity.

Generic footnotes

• Empty cells indicate that acceptable aquatic toxicity values are not available.

• Benchmarks preceded by a "greater-than" symbol (for example, >265,000) were derived from a "greater-than" value and may overestimate toxicity.  Conversely, benchmarks preceded by a "less-than" symbol (for example, <1,500) were derived from a "less-than" value and may underestimate toxicity.

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Definitions

• CCC = Criterion continuous concentration

• CMC = Criterion maximum concentration

• EC₅₀ = 50 percent effect concentration

• LC₅₀ = 50 percent lethal concentration

• LOC = level of concern

• NOAEC = no-observed-adverse-effects concentration

• µg/L = microgram per liter

• — = no benchmark available

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References

^aStephan, C.E, D.I. Mount, D.J. Hanson, J.H. Gentile, G.A. Chapman, and W.A. Brungs. 1985. Guidelines for Deriving Numerical National Water Quality Criteria for the Protection of Aquatic Organisms and Their Uses. EPA PB85-227049.

^bU.S. EPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide Programs. Office of Prevention, Pesticides, and Toxic Substances. Office of Pesticide Programs. Washington, D.C. January 23, 2004.

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