U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Diazinon Concentrations and Transport in the Sacramento River and San Francisco Bay, California, February 1993

Abstract

Previous studies of pesticide concentrations in the Sacramento River suggest that narrow pulses of diazinon, a major dormant spray pesticide, are transported down the river following rainfall. A study in February 1993 followed these anticipated pesticide pulses down the Sacramento River and into San Francisco Bay. Water samples for pesticide analysis were collected daily at four sites in the river and bay. Three distinct pulses of diazinon were detected in the Sacramento River at Sacramento 1 to 3 days after rainfall. The load of diazinon in the Sacramento River in February was calculated to be 340 kilograms (active ingredient) or approximately 0.5 to 1.7 percent of the total diazinon applied to orchards in the Sacramento Valley in January and February. The diazinon pulse detected at Sacramento on February 12 was detected the next day at Rio Vista, 2 days later at Chipps Island (the boundary between the delta and San Francisco Bay), and 3 to 5 days later at Martinez (the western edge of Suisun Bay). Study results suggest that the transport of pesticides from the Sacramento River into San Francisco Bay is episodic and highly dependent on rainfall and flow conditions.