Pesticide Transport and Bioconcentration Model

A pesticide transport and bioconcentration model has been developed and applied to Coralville Reservoir, Iowa, for the insecticide dieldrin. Two spatial configurations, a two compartment and an eight compartment model, provided essentially identical results. Dieldrin is strongly sorbed to suspended solids and approximately 40 percent of the inflow undergoes sedimentation, with approximately 50 percent flowing out the outflow and approximately 10 percent entering a large standing crop of fish. Being neutral and hydrophobic, dieldrin is bioconcentrated in proportion to the exposure concentration and oil content of the fish. Seventy four percent of the dieldrin in the water column resides in fish, 25 percent is dissolved, and less than 1 percent is adsorbed to suspended solids. Fish, sediment, and water residues are all declining in rough equilibrium and are tracking the declining input concentration. Average residues in bottom feeding fish have declined below the FDA action level of 0.3 ppm in wet, edible tissue.