Contaminated sediments of lakes and oceans act as sources of chlorinated hydrocarbons for release to water and atmosphere

Abstract

Atmospheric transport is a major route for entry of chlorinated, aromatic hydrocarbons into aquatic ecosystems. Once in the water, the compounds are readily taken up by the biota and distributed in the food webs. Major fractions of the compounds are deposited in the sediment¹, and it had been thought that most persistent contaminants are inactivated in this way as a consequence of their lipophilic properties. However, results from recent laboratory studies^2,3 raise the possibility that aquatic sediments may not be the final sink for the substances but may rather act as a source through redistribution of the compounds to water and the atmosphere. Polychlorinated biphenyls (PCBs) may be regarded as ‘tracers’ for these contaminants in the ecosystem, and I studied the transport of PCBs from sediment to water and air in two artificial ponds in the field. The transport from the sediment followed a seasonal cycle; higher concentrations of PCBs in water and air were recorded in the summer and lower in the winter. PCB concentrations in the air over the ponds were positively correlated with PCB levels in the water. My results show that contaminated sediments may act as a source of chlorinated hydrocarbons released into the environment.