Concentrations of chlorinated pesticides and PCBs in microlayer and seawater samples collected in open-ocean waters off the U.S. East Coast and in the Gulf of Mexico

Microlayer and surface seawater samples, collected during four surveys in 1985 and 1987 to open-ocean waters off the United States middle and south East Coast and in the Gulf of Mexico, were analyzed for selected chlorinated pesticides and polychlorinated biphenyls (PCBs). Analytes detected by gas chromatography-electron capture detection (GC-ECD) were confirmed by analysis with a different gas chromatographic column or detector or both. Of the 27 filter and filtrate microlayer samples collected during the surveys, only one contained pesticides or individual PCB congeners above method detection limits ranging from 0.1 to 1.0 ng 1 −1. Most PCB congeners and pesticides were not detected in any of the 24 open-ocean surface seawater samples, even at method detection limits of 0.5-3.0 pg 1 −1, which were achieved by processing 9001 of seawater. Lindane was detected at concentrations in the range of 0:01-0.15 ng 1 -1 in nearly every seawater filtrate sample taken off the Southeast Coast and in the Gulf of Mexico. Chlordane was the other pesticide found predominantly in Gulf of Mexico samples at concentrations of 0.004-0.034 ng 1 −1. Only a few sample contained very low concentrations of DDTs and their degradation products. No more than four to five individual PCB congeners were detected in any seawater sample; none of the samples possessed an Aroclor pattern. Previous literature on concentrations of pesticides and PCBs in open-ocean waters is reviewed. Most literature values for pesticides (almost exclusively DDTs and their degradation products) and PCBs in microlayer and surface seawater samples are 10–20 years old. Concentrations of PCBs and DDT identified in the earlier studies were significantly higher than their concentrations in samples collected in our 1985 and 1987 surveys. These observations may reflect an actual decline in PCB and DDT levels in the open ocean or improvement in analytical methods, including confirmation of analyte identities. In the earlier studies, PCBs and pesticides were determined by a single-column, single-detector analysis (i.e. GC-ECD): confirmation analysis of identified analytes was not performed.