Monitoring Surface Waters of the San Joaquin River Basin for Selected Summer-Use Pesticides, 2002 (original) (raw)

The California Department of Pesticide Regulation (CDPR) collected weekly surface water samples at four monitoring sites in the San Joaquin basin (San Joaquin, Sbnislaus and Merced counties) between July 2 and September 30,2002. Samples were analyzed for the pyrethroid insecticides permethrin and esfenvalerate, the herbicides metolachlor and alachlor and their degradation products, and other selected herbicides and organophosphate (OP) insecticides. The results of this study will be used to aid in the development of priorities for future monitoring and/or mitigation efforts. Analytical concentrations are compared to aquatic toxicity benchmarks, including water quality criteria (WQC) established to protect aquatic organisms. Quantifiable pesticide concentrations are referred to as detections, while'the presence of analytes at concentrations too low to be quantified are termed "trace" concentrations. A total of 14 pesticides and pesticide degradation products were detected in 56 water samples. This total included five OP insecticides, six herbicides and three herbicide degradation products. The most commonly detected compounds were dimethoate, diuron, metolachlor, and two metoIachlor degradation products, metolachlor ethanesulfonic acid and metolachlor oxanilic acid (metolachlor ESA and metolachlor OXA, respectively). Dimethoate, diuron and metolachlor were detected at concentrations ,well below those 'expected to impact aquatic organisms. Metolachlor ESA.was detected in'nearly 60% of all samples and was present at trace concentrations in an additional 30% of samples.. Metolachlor OXA was detected in approximately 40% of all samples and was present at trace concentrations in an additional 3 5%'of samples. Aquatic toxicity data. are not available for the metolachlor degradation products; therefore, the significance of those detections could not be evaluated; ' ' Three insecticides (chlorpyrifos, diazinon and malathion) were each detected in at least one sample at concentrations exceeding established WQC. Chlorpyrifos was detected in about 5% of all samples, with trace concentrations in an additional 7%. WQC for chlorpyrifos range from 0.014 to 0.041 pg/L. While chlorpyrifos concentrations exceeded established WQC in three samples, the analytical chlorpyrifos reporting limit of 0.040 pg/L was greater than certain WQC so that some additional exceedances may have occurred. The detection frequency for diazinon was similar to that of chlorpyrifos. Diazinon WQC range from 0.05 to 0.09 pg/L; the detected diazinon concentration exceeded established WQC in one sample. Malathion was detected in one sample and found at trace concentration in one sample (< 2% of samples each). The single malathion detection exceeded the established WQC of 0.1 pg/L. The remaining detections (methyl parathion, simazine, hexazinone, norhurazon, prometryn, and alachlor ESA) were both infrequent and well below concentrations expected to impact aquatic organisms. There were no detections of the pyrethroid insecticides permethrin and esfenvalerate.