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

Large urban centers are foci for contaminants. Contaminant levels in surface waters near
San Francisco, Oakland, and San Jose are highest. These areas are also where water
clarity is at its worst. Some of the most persistent contaminants (PCBs, dioxins, DDT,
etc.) are bioaccumulated by aquatic biota and can biomagnify in the food chain. Fish
tissues contain high levels of PCB and mercury. Concentrations of PCB were 10 times
above human health guidelines for consumption. Birds, some of which are endangered
(clapper rail and least tern), have also concentrated these toxins.
Santa Ana Basin: NAWQA assessment
The Santa Ana watershed is the most heavily populated study site out of more than 50
assessment sites studied across the nation by the NAWQA Program. According to Belitz
et al. (2004), treated wastewater effluent is the primary source of baseflow to the Santa
Ana River. Secondary sources that influence peak river flows include stormwater runoff
from urban, agricultural, and undeveloped lands (Belitz, Hamlin et al. 2004). Stormwater
and agricultural runoff frequently contain pesticides, fertilizers, sediments, nutrients,
pathogenic bacteria, and other chemical pollutants to waterways and degrade water
quality. The above inputs have resulted in elevated concentrations of nitrates and
pesticides in surface waters of the basin. Nitrates and pesticides were more frequently
detected here than in other national NAWQA sites (Belitz, Hamlin et al. 2004).
Additionally, Belitz et al. (2004) found that pesticides and volatile organic compounds
(VOCs) were frequently detected in surface and ground water in the Santa Ana Basin. Of
the 103 pesticides and degradates routinely analyzed for in surface and ground water, 58
were detected. Pesticides included diuron, diazinon, carbaryl, chlorpyrifos, lindane,
malathion, and chlorothalonil. Carbaryl was detected in 42% of urban samples, though it
generally did not exceed the standard for protection of aquatic life (Belitz et al. 2004).
Carbofuran was also detected, but did not exceed any water quality standards. Methomyl
was tested for but not detected. Of the 85 VOCs routinely analyzed for, 49 were
detected. VOCs included methyl tert-butyl ether (MTBE), chloroform, and
trichloroethylene (TCE). Organochlorine compounds were also detected in bed sediment
and fish tissue. Organochlorine concentrations were also higher at urban sites than at
216