P.L. Wofford 1and P. Lee 2

1Cal/EPA, Department of Pesticide Regulation,
Environmental Hazards Assessment Program

2California Department of Food and Agriculture,
Chemistry Laboratory Services

December 1995

Environmental Hazards Assessment Program
Department of Pesticide Regulation
California Environmental Protection Agency
Sacramento, CA 95814-5624


The study described in this report was undertaken as a preliminary investigation to quantify the extent and magnitude of MCPA contamination in the Sacramento River Basin, and address concerns over concentrations of MCPA previously detected in the Sacramento River Basin. Because of high use on winter wheat and barley and decreased use of MCPA on rice during the summer, the study was directed toward the winter season.

The Environmental Hazards Assessment Program of the Department of Pesticide Regulation (DPR) monitored seven sites on waterways draining the Sacramento River Basin: including the Colusa Basin Drain, the Sacramento Slough, the Feather River, the Sacramento River. Sampling continued twice a week for eight weeks during the late winter through early spring of 1992. Samples were analyzed for MCPA, 2,4-D, and dicamba. Pesticide use reports and rainfall data were reviewed to formulate a possible explanation for contamination.

MCPA was detected in measurable amounts at only three sampling sites: the Colusa Basin Drain, the Sacramento Slough, and the Feather River with the highest level (0.52 ppb) in the Sacramento Slough. Eleven percent of all samples collected contained measurable amounts of MCPA. 2,4-D was detected on each sampling date from March 3 to April 7 and April 14, 1992. 2,4-D was detected at all sites, except the northern most Sacramento River site and the Feather River site. The highest number of positive detections and concentration (2.8 ppb) came from the Colusa Basin Drain sampling site. 2,4-D was detected in 20 percent of all samples collected for the duration of the study. Only two water samples, both collected from the Colusa Basin Drain site, contained detectable amounts of dicamba. Concentrations of 1.8 and 0.1 ppb were detected on March 6 and March 10, 1992, respectively.

Although MCPA, 2,4-D, and dicamba were present at various times and levels in waterways of the Sacramento River Basin, all of the detections were below any reported health concern levels. The contamination from the herbicides appears to coincide with rainfall events causing runoff from the fields to the waterways draining the Sacramento River Basin.