Microcosm experiments to assess the effects of temperature and microbial activity on polychlorinated biphenyl...

Increased polychlorinated biphenyl (PCB) loadings from sediment to the water column under low-flow conditions during late spring and summer months have been observed in the Grasse River (Massena, NY) and other PCB-contaminated rivers in the United States. Temperature appears to be an important factor affecting this phenomenon, as increased sediment temperature leads to increased microbial and bioturbator activity as well as increased rates of diffusion and desorption. Laboratory-scale sediment microcosms were developed and used to study with fine-scale resolution the effects of temperature and microbial activity on PCB transport in river sediment. Over the time course of these experiments, with the extraction procedures used, irreversible sorption of each congener to sediment was observed and increased with aging of the sediment. Temperature-dependent transport was observed for PCB congeners 2,4,5-trichlorobiphenyl (BZ29), 2,5-dichlorobiphenyl (BZ9), and 2-chlorobiphenyl (BZ1) in Grasse River sediment and a synthetic sediment system. The fastesttransport of the congeners occurred in biologically active Grasse River sediment followed by biologically inactive (autoclaved) Grasse River sediment, and synthetic sediment. The increased transport in biologically active sediment demonstrated the importance of microbial activity, in particular gas bubble generation, in PCB transport in near-surface sediments.