Transport of Sediment-Bound Organochlorine Pesticides to the San Joaquin River, California

Charles R. Kratzer

American Water Resources Association, 32nd Annual Conference and Symposium, Ft. Lauderdale, Florida, September 22-26, 1996, oral presentation.

Abstract:
Suspended sediment samples were collected in west-side tributaries and the mainstem of the San Joaquin River during the irrigation season (June 1994) and during a winter storm (January 1995) and were analyzed for 15 organochlorine pesticides. The study objective was twofold: (1) to determine the occurrence and concentration of organochlorine pesticides attached to suspended sediment, and (2) to compare transport between irrigation season and winter storm runoff.

Eight sites were sampled once during the irrigation season; 17 total samples were collected at 12 sites during the winter storm. Sample volumes ranged from 5 to 140 liters. Samples were dewatered using a continuous-flow centrifuge followed by a high-speed laboratory centrifuge. Sample dry weights ranged from 0.7 to 53.6 grams for analysis of organochlorine pesticides. Detection levels varied depending upon the amount of sample collected.

Ten organochlorine pesticides were detected during the winter storm; seven during the irrigation season. The most frequently detected organochlorine pesticides during both sampling periods were DDE (detected 100% of the time), DDT (100%), DDD (96%), dieldrin (80%), toxaphene (80%), and chlordane (76%). At the eight sites in common between sampling periods, total DDT (sum of DDD, DDE, and DDT) concentrations ranged from 71 to 617 ug/kg during the irrigation season (median 258 ug/kg); and 54 to 406 ug/kg during the winter storm (median 211 ug/kg). Suspended sediment concentrations ranged from 50 to 2,530 mg/L during the irrigation season (median 489 mg/L); and 419 to 13,750 mg/L during the winter storm (median 3,590 mg/L). The ratio of storm to irrigation season streamflows at the eight sites ranged from 1.2 to 113. On a load per day basis, the transport of organochlorine pesticides was much greater during the winter storm than during the irrigation season.