PCBS IN LAKE-SUPERIOR, 1978-1992 - DECREASES IN WATER CONCENTRATIONS REFLECT LOSS BY VOLATILIZATION

Polychlorinated biphenyl (PCB) water concentrations in Lake Superior from 1978 to 1992 have been compiled in order to determine long-term trends. Based on the concentrations of the same 25 PCB congeners from surface water samples collected between 1980 and 1992, SIGMAPCBs have decreased with a first-order rate constant of 0.20 yr-1. The concentration of SIGMAPCBs in 1980 based on 82 congeners was approximately 2.4 ng/L, by 1992 the concentration had decreased to 0.18 ng/L, indicating a loss of approximately 26 500 kg of PCBs from Lake Superior during this 12-yr period. PCB concentrations in dated sediment cores collected in 1986 and 1990 indicate that the sediments have accumulated approximately 4900 kg of PCBs since 1930 when PCB production began in the United States. A mass balance of PCBs in Lake Superior for 1986 predicts that volatilization, not sedimentation, is the dominant loss process of PCBs from the lake. Net volatilization of PCBs from Lake Superior is estimated to be approximately 1900 kg in 1986, while the loss due to burial in the sediments was approximately 110 kg. A congener-specific first-order rate constant model predicts sedimentation to be a minimal loss process in Lake Superior and volatilization to dominate. The pseudo-first-order rate constants for volatilization and sedimentation of SIGMAPCB are predicted by the rate constant model to be -0.24 and -0.004 yr-1, respectively. The model estimated PCB inputs in 1986 of 500 kg.