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:

• Available types of benchmarks by
• Sampling medium (drinking water, ambient surface water, bed sediment, whole fish, or edible fish tissue); and
• Beneficial use of the hydrologic system that the benchmark is designed to protect (human health, aquatic life, or wildlife).
• Links to original sources (web sites maintained by the agency or organization that issued the benchmarks), where possible.  These sources provide:
• Up-to-date benchmark values (because values available for a given type of benchmark may change over time).
• Information on the technical bases and underlying assumptions of benchmarks. The effective use of benchmarks in water-quality assessment requires an understanding of how the benchmarks were derived, as well as information about the specific hydrologic system being studied.

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

• The NAWQA Program used water-quality benchmarks in its national-scale analysis of pesticide concentrations measured in U.S. streams and ground water from 1992 to 2001, as described in USGS Circular 1291.
• This site provides the benchmark values (current as of December 2005) used to interpret pesticide data for USGS Circular 1291. For up-to-date benchmark values, users are directed to the original sources for each benchmark type (see Types and sources of water-quality benchmarks).

Searchable online database for Health-Based Screening Levels

• Health-Based Screening Levels (HBSL):
• Are non-enforceable benchmarks indicating concentrations of contaminants in water that may be of potential concern for human health;
• Were developed by the USGS in collaboration with USEPA and others using USEPA methodologies for establishing drinking-water guidelines and the most current, USEPA peer-reviewed, publicly available human-health toxicity information;
• Apply to unregulated contaminants in water (compounds without USEPA Maximum Contaminant Levels).
• This searchable online database:
• Contains HBSLs for pesticides and degradates, volatile organic compounds, semivolatile organic compounds, polychlorinated biphenyls, trace elements, major ions, and nutrients;
• Provides underlying toxicity information and procedure for computing HBSLs.

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