U.S. Geological Survey U.S. Geological Survey BACKGROUND: The U.S. Geological Survey's (USGS) National Water Quality Assessment (NAWQA) Program is designed to assess the nation's ground- and surface-water resources and to provide an understanding of the natural and human factors that affect the quality of these resources. Organochlorine pesticides are of particular interest in assessing water quality because of their persistence in the environment and established role in causing adverse environmental effects, such as reproductive dysfunction in wildlife.
Sampling sites were distributed throughout forest, agricultural, range, and urban land in three NAWQA study units in the Pacific Northwest: the Upper Snake River Basin, the Willamette River Basin, and the Central Columbia Plateau. Bed sediment samples were collected from 63 sites and fish from 56 sites; samples were analyzed for 33 organochlorine pesticides and total PCB.
FINDINGS:
· The total number of organochlorine compounds detected ranged from 9 to 16 for the three study units, depending on the media tested. The most commonly detected compound was the DDT isomer p,p'-DDE, other compounds detected included total PCB, dieldrin, various isomers of chlordane, lindane, and toxaphene.
· Although the same number of compounds was detected in bed sediment as in fish, there was a higher frequency of detection in fish; for example, in the Central Columbia Plateau, p,p'-DDE was detected in 94 percent of sites where fish were collected and 52 percent of sites where sediment was collected.
· Areas with agricultural and mixed land uses (agricultural and urban) had the greatest number and concentrations of compounds detected; the lowest number of compounds was associated with forest. The Central Columbia Plateau, which has the greatest percentage of agriculture among the three study units (62 percent), had 16 compounds detected; the Upper Snake (21 percent agriculture) and the Willamette River (22 percent agriculture) had 14 and 12 compounds detected, respectively.
· Fish from some sites had concentrations of total DDT, p,p'-DDE, toxaphene, dieldrin, or total PCB that exceeded the national criteria for the protection of fish-eating wildlife. A small percentage of bed sediment sites contained concentrations of p,p'-DDE, dieldrin, or lindane that exceeded the Canadian Probable Effect Levels for the protection of aquatic life (there are no U.S. guidelines for sediment quality).
CONCLUSIONS: The compounds detected and their concentrations reflect historical use because most of the pesticides (including PCBs) are no longer used. Agricultural soils serve as long-term reservoirs for many of these compounds, which enter surface waters primarily as a result of erosion. Reducing sediment runoff from agricultural fields should decrease the amount of these compounds entering surface waters.