Diazinon and chlorpyrifos in urban waterways in northern California, USA

Samples collected from urban streams in the cities of Sacramento and Stockt on, California, USA, during the precipitation season were analyzed for diaz inon and chlorpyrifos. Concentrations were determined with enzyme-linked im munosorbent assays specific for each pesticide. Two hundred thirty-one samp les from the two cities were analyzed for diazinon; 85% exceeded California Department of Fish and Came water-quality criteria for this pesticide. Chl orpyrifos was measured in 90 of the samples collected from Sacramento and S tockton: 80% exceeded the California Department of Fish and Game criterion for this pesticide. Thirty-six of 47 samples (76.6%) tested for toxicity pr oduced total mortality within 72 h with Ceriodaphnia dubia. Toxicity identi fication evaluations on selected samples confirmed that toxicity was primar ily due to one or both of these pesticides. Uses of diazinon and chlorpyrif os in urban areas include dormant sprays on fruit trees, professional lands cape and maintenance uses, and structural pest control. Pesticide concentra tions were lower in a catchment favoring commercial and industrial activiti es compared with a catchment receiving largely residential inputs. Aerial d rift from agricultural applications may play a role in storm-water concentr ations.