Are some examples of pesticide trends evident in ground water?
Ground water responds more slowly than streams to changes in pesticide use—taking years and even decades for changes in quality to occur. A persistent pesticide or degradate can remain in ground water long after its use has been discontinued because of the slow rates of ground-water flow and the resulting long residence time of water and contaminants in ground-water flow systems. This is evident from a number of studies in different parts of the country. For example, bromacil remained at detectable levels in ground water in parts of Florida for several years after it was not longer used, and dieldrin, which is no longer used, was still detectable at concentrations greater than its human-health benchmark in 73 wells sampled by NAWQA.
