TEMPORAL DISTRIBUTION OF INSECTICIDE RESIDUES IN FOUR

Several studies have indicated that certain pesticides are present in California rivers at levels which could be harmful to aquatic life. Generally, these studies have been conducted during certain seasons, but not year-round. Since year-round pesticide concentration data was limited for many California rivers having significant amounts of agricultural runoff, water was collected weekly from one sampling site along each of four rivers for a one-year period. This study was a cooperative effort between the Department of Pesticide Regulation (DPR) and the California Department of Fish and Game (CDFG). The portion conducted by DPR was an investigation of organophosphate, carbamate, and endosulfan residues in surface waters of four rivers: the Sacramento, Merced, Salinas and Russian Rivers. In addition to pesticide residue quantification by DPR, samples were tested for toxicity and ammonia concentration by CDFG on a bimonthly basis. Monitoring began on the Sacramento River in November 1993, followed by the Merced River in June of 1994 and by the Salinas and the Russian River