National Water-Quality Assessment (NAWQA) Program

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Water-Quality Benchmarks for Pesticides

Water-quality benchmark is defined as a threshold value against which measured concentrations can be compared to help assess the potential effects of pesticides on water quality in a hydrologic system.

The USGS National Water-Quality Assessment (NAWQA) Program uses water-quality benchmarks in screening-level assessments—in which site-specific estimates of pesticide exposure (concentrations or concentration statistics determined from measurements of pesticides in various media at NAWQA sampling sites) are compared to water-quality benchmarks. This is similar in concept to USEPA screening-level assessments, which USEPA uses in early stages of risk assessments to evaluate the potential impact of pesticides to non-target organisms.

Screening-level assessments are not a substitute for either risk assessments, which include many more factors (such as additional avenues of exposure), or site-specific studies of effects. Rather, comparisons of measured or estimated concentrations with water-quality benchmarks provide an initial perspective on the potential for adverse effects, as well as a framework for prioritizing additional investigations that may be warranted. Concentrations that exceed a benchmark do not necessarily indicate that adverse effects are occurring—they indicate that adverse effects may occur and that sites where benchmarks are exceeded may merit further investigation. (See Characteristics and Limitations of Screening-Level Assessments)

Types and sources of water-quality benchmarks

This site provides:

Water-quality benchmarks used to analyze pesticide compounds in NAWQA samples, 1992–2001

Searchable online database for Health-Based Screening Levels

Contact: Lisa Nowell
lhnowell@usgs.gov, (916) 278-3096

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Page Last Modified: Tuesday, 04-Mar-2014 14:44:17 EST