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Organochlorine Residues in Sediment Cores of a Midwestern Reservoir¹

ABSTRACT

Organochlorine residues detected in sediment core samples collected from Rock Reservoir, Iowa, in early 1981 were < 5 µg/kg dry weight for dieldrin (1,2,3,4,10,10-hexachloro-exo-6,7-epoxyl,4,4a,5,6,7,8,8a-octahydro-1,4-endo, exo-5,8-dimethanophthalene), p,p'-DDE (1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene), p,p'-DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane), and < 16 µg/kg for PCB's (polychlorinated biphenyls). The mean concentration of PCB residues (13 µg/kg) was higher than that of the three insecticides (dieldrin, 2.9 µg/kg; DDE and DDD, 2.4 µg/kg each). Concentrations of organochlorine contaminants in sediments were higher at the upper and lower ends of the reservoir than at midreservoir locations. Deposition of organochlorine residues did not correlate well with either clay or organic composition of the sediment. A mechanism not related to clay-organic sediment appears to be influencing accumulation of organochlorines in the upper end of the reservoir. In the river channel, dieldrin levels were higher than at loations on either side of the channel, while no variation due to transect location was noted for DDE, DDD or PCB's. Dieldrin concentrations were highest in surficial sediments, whereas those of PCB's, DDE, and DDD were highest near the bottom of core samples. An estimated 53 kg of PCB's, 17 kg of dieldrin, 14 kg of DDD, and 9.3 kg of DDE were present in the top 7.5 cm of sediment over Red Rock Reservoir's 3600 ha.

Key Words: polychlorinated biphenyls • dieldrin • DDT • pesticides • impoundment

¹ Journal Paper J-10775 of the Iowa Agriculture & Home Economics Experiment Station, Ames, IA. Project no. 2465. Financed by a grant from the U.S. Department of Defense Army Corps of Engineers, and made available through the Engineering Research Institute, Iowa State University, Ames, IA 50011.

² Res. Associate, Center for Environ. Studies, Arizona State Univ., Tempe; Wyoming Cooperative Fish & Wildlife Res. Unit, Univ. of Wyoming, Laramie; and U.S. Dep. of Energy, Ames, Iowa, respectively.

Received for publication October 6, 1982.