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

17% of mainstem Yakima River samples at a screening level of 21 nanograms/liter
(Fuhrer et al. 2004). Carbofuran was screened for, but not detected. The assessment did
not screen for methomyl. The median and maximum number of chemicals in a mixture
was 8 and 26, respectively (Fuhrer, Morace et al. 2004). The herbicide 2,4-D, occurred
most often in the mixtures, along with azinphos-methyl, the most heavily applied
pesticide, and atrazine, one of the most aquatic mobile pesticides (Fuhrer, Morace et al.
2004). However, the most frequently detected pesticides in the Yakima River Basin are
total DDTs ,(DDT and its breakdown products, dichloro-diphenyl-dichloroethylene
(DDE), dichloro-diphenyl-dichloroethane (DDD)), and dieldrin (Johnson and Newman
1983; Joy 2002; Fuhrer, Morace et al. 2004). Nevertheless, concentrations of total DDT
in water have decreased since 1991. These reductions are attributed to erosioncontrolling
best management practices (BMPs).
Williamette Basin: NAWQA analysis
From 1991 to 1995, the USGS also sampled surface waters in the Willamette Basin,
Oregon. Wentz et al. (1998) reported that, of the 86 tested for, 50 pesticides and
pesticide degradates were detected in streams. Ten of the pesticides exceeded criteria
established by the EPA for the protection of freshwater aquatic life from chronic toxicity.
Carbaryl exceeded protective criteria in 17 of its 46 detections, while carbofuran
exceeded limits in three of 51 detections (Wentz et al. 1998). Atrazine, simazine,
metolachlor, deethylatrazine, diuron, and diazinon were detected in more than one-half of
stream samples. Methomyl was tested for but not detected. Forty-nine pesticides were
detected in streams draining predominantly agricultural land. About 25 pesticides were
detected in streams draining mostly urban areas. The highest pesticide concentrations
generally occurred in streams draining predominately agricultural land.
Snake River Basin: NAWQA assessment
The USGS conducted a water quality study from 1992-1995 in the upper Snake River
basin, Idaho and Wyoming (Clark, Maret et al. 1998). In basin wide stream sampling in
May and June 1994, Eptam [EPTC] (used on potatoes, beans, and sugar beets), atrazine
and its breakdown product desethylatrazine (used on corn), metolachlor (used on potatoes
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