Are some examples of pesticide trends evident in streams?
Yes. NAWQA has only begun to look at trends, but early results provide an indication of what to expect. A first look at trends shows examples of both decreasing and increasing levels of certain pesticides in streams and ground water, showing responses to regulatory actions and reduced use. The most complete story of trends is the decline in concentrations of organochlorine pesticides that followed reductions in use during the 1960s and bans on uses in the 1970s and 1980s. Concentrations of total DDT in fish, for example, decreased rapidly from the 1960s through the 1970s and then more slowly during the 1980s and 1990s. Just as notable as the declines, however, is the finding that these persistent organochlorine pesticide compounds still occur at levels greater than benchmarks for fish-eating wildlife in many urban and agricultural streams across the Nation. The decline in organochlorine compounds will continue, but they have long half-lives and we can expect levels to occur above bench
