Herbicides were detected more frequently than insecticides. Seventeen of 23 pesticides detected in water were herbicides. The commonly used herbicide 2,4-D was found in 12 of 13 streams. Other herbicides--bromacil, DCPA, dicamba, dichlobenil, diuron, and MCPP---were found at five or more streams. The insecticide diazinon was found in six streams, and three other insecticides-- malathion, mevinphos, and propoxur--were detected in one or two streams. In general, more pesticides were detected in urban streams than in agricultural streams. Eighteen pesticides were detected in Mercer Creek, an urban stream, whereas 13 pesticide detections in Joe Leary Slough were the greatest number of pesticides found in an agricultural stream. Seven pesticides were detected exclusively in urban streams, five were found only in agricultural streams, and 11 were common to both. Few of these pesticides are used exclusively in urban or agricultural areas. Their occurrences probably reflect local application practices.
The graph below shows that 23 pesticides were detected at mostly small concentrations either as estimated or quantifiable values.
Click here for a graph of concentrations
of pesticides detected in water