What are the characteristics and limitations of the NAWQA assessment of potential effects?
There are several complexities and limitations. The potential for effects on humans, aquatic life, or wildlife may either be under or over estimated by benchmark comparisons in specific situations—the screening-level results are primarily intended to identify and prioritize needs for further investigation. • Most of the water-quality benchmarks are estimates of no-effect levels, such that concentrations below the benchmarks are expected to have a low likelihood of adverse effects and concentrations above a benchmark may have adverse effects, with the likelihood increasing as the concentration increases. • The presence of pesticides in streams or ground water at concentrations that exceed benchmarks does not indicate that adverse effects are certain to occur. Conversely, concentrations that are below benchmarks do not guarantee that adverse effects will not occur, but indicate that they are expected to be negligible. • Some compounds analyzed by NAWQA do not have water-quality benchmark
