Seasonal Fluctuations of Dieldrin Residues in the Tissues of the Marsh Clam, Rangia Cuneata, from a Texas Estuary

Abstract

The marsh clam, Rangia cuneata, was collected in Trinity Bay, Texas, in 1970 and 1971 and analyzed for residues of the chlorinated hydrocarbon insecticide, dieldrin, by gas-liquid chromatography. Analysis was carried out on ten individual clams randomly selected, shucked, and frozen. Recoveries of dieldrin from fortified clam tissue samples were above 85%. Clams collected in October and December 1970 had lower residues of dieldrin (mean and standard deviations were 7.9 plus or minus 1.5 ppb and 6.8 plus or minus 1.1 ppb, respectively) than those for February, April, and July (mean and standard deviations were 16.4 plus or minus 2.8 ppb, 16.6 plus or minus 1.4 ppb and 14.8 plus or minus 1.8 ppb respectively), or at least twice the fall values. These seasonal fluctuations in insecticide residues in tissue may be due to changes in river flow into the bay, with maximum tissue levels in months of large freshwater input. Also maturation of gonads and production of gametes in the spring and summer may cause higher whole body insecticide residue levels during these periods. (Buchanan-Davidson--Wisconsin)