There are several factors that influence a pesticide’s potential to contaminate water:¥The ability of the pesticide to dissolve in water (solubility).
¥Environmental factors, such as soil, weather, season, and distance to water sources.¥Application methods and other practices associated with the pesticide use.Groundwater contamination is higher when there is no crop or a young crop. A
large, actively growing crop has the ability to reduce pesticide concentration through
a variety of mechanisms:
¥Larger plants consume more water from the soil and therefore reduce the ability
of a pesticide to migrate through the soil and enter streams or groundwater.¥Larger plants can collect precipitation that prevents pooling of water and run-
off from the area.
¥Root zones enrich the microbial community of the soil, which enhances biode-
gradation of the pesticide by bacteria.The Safe Drinking Water Act sets standards for drinking water and mandates the
EPA set Maximum Contamination Levels (MCLs) for a number of pesticides in pub-
lic water supplies. Private water supplies are not monitored or regulated by this act
and must be arranged privately. Since pesticides are most prevalent in agricultural
areas where most residents obtain their drinking waster from private sources, it is up
to the consumer or well owner to monitor contaminant levels.^28
Importance of Surface Waters
Streams and reservoirs supply approximately 50 percent of the nation’s drinking
water, primarily in urban areas. Streams, reservoirs, lakes, and downstream estuaries
are also vital aquatic ecosystems that provide important environmental and economic
benefits. Surface waters are particularly vulnerable to pesticide contamination because
runoff from most agricultural and urban areas, where pesticides are applied, drains
into streams. Pesticides may also enter streams through wastewater discharges, atmo-
spheric deposition, spills, and groundwater inflow. The uses and ecological signifi-
cance of surface water, combined with its vulnerability to contamination, make it
particularly important to understand the extent and significance of pesticides in this
part of the hydrologic system.^29
Significance to Water Quality
Under provisions of the Safe Drinking Water Act, the EPA established MCLs for
concentrations of certain chemicals in drinking water. Of the currently used
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