NOAA's status and trends mussel watch program: Chlorinated pesticides and PCBs in oysters (Crassostrea virginica) and sediments from the Gulf of Mexico, 1986-1987

Chlorinated pesticides and PCBs were analyzed in more than 590 oyster and sediment samples collected during 1986 and 1987, the first 2 years of the NOAA's Status and Trends Mussel Watch Program established to monitor the current status and temporal trends of these contaminants in the Gulf of Mexico. Chlorinated hydrocarbons in oysters and sediments presented similar distribution patterns; however, their concentrations in oysters were several times higher than the concentration detected in the surrounding sediments. Alpha-chlordane, trans-nonachlor and dieldrin were the most abundant non-DDT pesticides in both types of sample. The major fraction of DDT related compounds measured in oysters and sediments was DDD. Based on average PCB concentrations, penta-, hexa-, and tetrachlorobiphenyls were preferentially accumulated by oysters as compared to the average sediment composition. Although this study was designed to avoid known point-sources of contaminant inputs, the measured concentrations were, in general, within the range of concentrations previously reported for the Gulf of Mexico. After the first 2 years of this program, the geographical distribution of chlorinated hydrocarbons in oysters and sediments is well defined. In contrast, the temporal trends at the different sites are not clear. Continued sampling will allow the identification of long-term trends in concentrations of chlorinated hydrocarbons in the Gulf of Mexico.