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U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2008–5027

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Table 6. Aquatic-life benchmarks for pesticides and degradates detected in the lower Clackamas River basin, Oregon, 2000–2005.

[Pesticide concentrations in micrograms per liter (µg/L). Shaded values represent benchmark exceedances. USEPA OPP references available at http://www.epa.gov/oppefed1/ecorisk_ders/aquatic_life_benchmark.htm. Canada: CCME, Canadian Council of Ministers of the Environment (2003). NAS/NAE: National Academy of Sciences/ National Academy of Engineering (1973). Abbreviations: USEPA, U.S. Environmental Protection Agency; OPP, USEPA Office of Pesticide Programs; NAS/NAE, National Academy of Sciences/National Academy of Engineering; USGS, U.S. Geological Survey; HBSL, Health-Based Screening Levels; Sept., September; Oct., October; na, no benchmark available for these compounds; ds, downstream]

¹ Endosulfan includes endosulfan I and endosulfan II.

² The chronic benchmark is based on the acute toxicity value (which was lower than the lowest available chronic toxicity value), and therefore may underestimate chronic toxicity.

³ Because the underlying toxicity value is a “less-than” value (such as <1,500), this benchmark may underestimate toxicity.

⁴ 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.

⁵ During public comment on draft ambient water-quality criteria that are under development by USEPA, public comment noted an atypical distribution of the acute toxicity data for diazinon. If data from the second most sensitive study were used (U.S. Environmental Protection Agency, 2000b risk assessment), rather than the most sensitive study, then the benchmark would change from 0.1 to 0.4 µg/L.

⁶ 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. Selection was consistent with risk quotients in the cited USEPA references.

⁷ Because the underlying toxicity value is a “greater-than” value (such as >265,000), this benchmark may overestimate toxicity.

⁸ Benchmark applies to total DDT, so comparison with measured p,p´-DDE concentration may underestimate potential effects.

⁹ Carbaryl recoveries in some QA spike samples were as high as 304 percent. For more details, see the quality-control discussion in appendix A.

¹⁰ The diazinon benchmark concentrations are DEQ guidance values, rather than water-quality criteria. DEQ can, however, use these values in the application of Oregon’s Narrative Toxics Criteria (State of Oregon Administrative Rule 340-0033[1]).

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