that agricultural chemicals were not staying on the fields, but were being washed into
streams and rivers and seeping into groundwater, came about with the development
of sensitive chemical testing procedures. These procedures did not become available
for organochlorine pesticides (such as DDT, DDE, aldrin, dieldrin, heptachlor, and
chlordane) until the late 1960s. The DDT problem was known before that time
largely because of bioaccumulation, resulting in detectable levels in animals high in
the food chain. In addition, Rachel Carson’s bookSilent Spring,released in 1962,
increased public awareness.
Today, pesticide levels in water are monitored routinely. Pesticide residues have
been found in groundwater, surface water, and rainfall. The EPA began to empha-
size groundwater monitoring for pesticides in 1979 following the discovery of
DBCP and aldicarb in groundwater in several states. DBCP and aldicarb are dan-
gerous because of their high toxicity. They are in the carbamate class and are nema-
tocides use to control nematodes or parasitic worms which live in water. DBCP
and aldicarb leach from agricultural soil into water. In 1985, thirty-eight states
reported that agricultural activity was a known or suspected source of groundwater
contamination within their borders.^23 Since then, several federal and state agencies
have developed programs to sample water resources and test for the presence of ag-
ricultural chemicals. Results published to date have shown that chemicals used in
agricultural production have been found in groundwater, sometimes at levels
exceeding the EPA’s drinking-water criteria.^24 Monitoring for pesticides in surface
water was frequent in the 1960s and 1970s as studies were conducted that led to
the banning of chlorinated hydrocarbon insecticides. Sampling in the 1980s and
1990s found that the four leading herbicides in use during that time—atrazine,
metolachlor, alachlor, and cyanazine—were frequently detected in surface waters in
agricultural regions.^25 The highest levels of contamination occurred after planting
and during the early part of the growing season. Most of the pesticides commonly
used presently and in the past have also been found in the atmosphere, including
DDT, toxaphene, dieldrin, heptachlor, organophosphorous insecticides, triazine herbi-
cides, alachlor, and metolachlor.^26 These airborne pesticides return to the ground with
rainfall and further contribute to water contamination. A recent survey by the U.S.
Geological Survey of pesticides in the nation’s waters concluded that pesticides were
common in surface and shallow groundwater in both urban and agricultural areas, but
investigators were not able to determine if contamination is lessening or worsening.^27Pesticides in the Aquatic EnvironmentAlthough certain characteristics of pesticides are well known, their final characteris-
tics after they reach a body of water are extremely difficult to estimate. It is necessary
to conduct both field studies and laboratory testing of soil and water environments.
Pesticide transport in soil and transfer to water together with probable impacts on
water quality are determined by conducting detailed field surveys and water residue
analyses.200 | Pesticides