Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

undeveloped sites in the Santa Ana Basin. Organochlorine compounds include DDT and
its breakdown product diphenyl dicloroethylene (DDE), and chlordane. Other
contaminants detected at high levels included trace elements such as lead, zinc, and
arsenic. According to Belitz et al. (2004), the biological community in the basin is
heavily altered as a result from these pollutants.
San Joaquin­Tulare Basin: NAWQA assessment
A study was conducted by the USGS in the mid-1990s on water quality within the San
Joaquin-Tulare basins. USGS detected 49 of the 83 pesticides it tested for in the
mainstem and three subbasins. Pesticides were detected in all but one of the 143
samples. The most common detections were of the herbicides simazine, dacthal,
metolachlor, and EPTC (Eptam), and the insecticides diazinon and chlorpyrifos. Twentytwo
pesticides were detected in 20% of the samples (Dubrovsky, Kratzer et al. 1998).
Carbaryl and methomyl were detected in all three subbasins, despite land use differences.
Carbaryl was detected in roughly 20% of samples from each subbasin, while methomyl
detections ranged from 5% to 25%. Further, most samples contained mixtures of
between 7 and 22 pesticides. Criteria for the protection of aquatic life were exceeded in
37% of samples of streams (Dubrovsky, Kratzer et al. 1998). Only seven pesticides
exceeded their criteria: diuron, trifluralin, azinphos-methyl, carbaryl, chlorpyrifos,
diazinon, and malathion. Forty percent of these exceedances were attributed solely to
diazinon. However, criteria do not exist yet for over half of the detected compounds
(Dubrovsky et al.1998).
Organochlorine insecticides in bed sediment and tissues of fish or clams were also
detected. They include DDT and toxaphene. Levels at some sites were among the
highest in the nation. Concentrations of trace elements in bed sediment generally were
higher than concentrations found in other NAWQA study units (Dubrovsky, Kratzer et al.
1998).
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