The interactions of a chlorinated hydrocarbon insecticide among the water, sediments and biota in an estuarine system

Abstract

Water sediment and biota collected from the San Antonio Bay estuarine system were analyzed for residues of the chlorinated hydrocarbon insecticides dieldrin, DDT, DDD, and DDE by electron-capture gas-liquid chromatography. Analyses indicated a relatively low level of contamination, in the parts per billion range, of this area. Of the residues detected, those of DDE were the most common in biological samples. Blue crabs, as a group, had a greater incidence of contamination (dieldrin, 32%; DDTs, 94%) than any of the other organisms sampled. The incidence of insecticide residues in oysters (dieldrin, 25%; DDTs, 60%) and clams (dieldrin, 31%; DDTs, 68%) were comparable. Penaeid shrimp showed a lesser incidence of contamination than the other groups (dieldrin, 26%; DDTs, 13%). Laboratory experiments were conducted to assess various interactions among dieldrin, sediments and selected biota of the San Antonio Bay estuarine system. It was determined that sediments collected from San Antonio Bay and the Aransas Refuge shore rapidly adsorbed up to 80% of the dieldrin in a seawater solution to which they were exposed. These contaminated sediments desorbed only insignificant amounts of dieldrin (10-12%) when resuspended in clean saltwater. Bivalved molluscs, Rangia cuneate and Crassostrea virginica, were shown to accumulate dieldrin residues to levels of 12-23% of the initial dieldrin content of the sediment when exposed in a flowing seawater system. Rangia clams accumulated dieldrin directly from seawater to levels of up to 3517 times ambient when exposed to a dieldrin-seawater solution. A log-log plot of exposure concentration versus the resulting content of dieldrin in Rangia tissues demonstrated a linear relationship for uptake over the concentration range of 5.00 to 500 ug/L.