By Verlin Cory Stephens and Jeffrey R. Deacon, U.S. Geological Survey, Box 25046, MS 415, Denver Federal Center, Lakewood, CO, 80225

Abstract

Bed-sediment and fish-tissue samples were collected in the Upper Colorado River Basin in Colorado, during August and October 1995, to determine the occurrence and distribution of pesticides. Bed sediment was sampled at 16 sites and analyzed for 32 organochlorine compounds. Fourteen of these sites also were sampled for fish tissue and analyzed for 27 organochlorine compounds. Organochlorines were detected more often in fish tissue than in bed sediment. DDE was the most frequently detected compound in fish tissue and was detected at 12 of the 14 sites at low concentrations (range of 5.7-700 ug/kg; median 110 ug/kg). DDE was the only compound detected in bed sediment and was detected at 4 of the 16 sites (range of 2.4-5.3 ug/kg; median 3.2 ug/kg). Chlordane, Dacthal, total PCB and other forms of DDT also were detected in fish tissue at low concentrations at five sites. Organochlorine compounds that were detected in bed-sediment at concentrations higher than reporting limits were detected only near agricultural land-use sites. Organochlorine compound-concentrations in fish tissue were highest and more frequently detected in the agricultural land-use setting, but also were detected in forest, range, and mixed land-use settings. These data provide complimentary lines of evidence in understanding the complexities of contaminant fate and distribution, the subsequent long-term effects on sediment and biota, and contaminant association with land-use settings.

KEY TERMS: organochlorines; pesticides; bed sediment; fish tissue; Colorado.

¹Hydrologists, U.S. Geological Survey, Water Resources Division, Colorado District, MS 415, Box 25046, Denver Federal Center, Denver Co. 80225-0046, Phone:(303) 236-2101, ext. 226, Fax: (303) 236-4912, e-mail: cory@usgs.gov, jrdeacon@usgs.gov.