Impact of coplanar PCBs on microbial communities in anaerobic estuarine sediments

The toxicity of three coplanar PCBs on microbial communities of an estuarine sediment were assessed. Sediment slurries were amended with 2, 10 and 50 mg/L of 345-4 CB, 345-34 CB and 345-345 CB, respectively under anaerobic conditions. The fate and effects of these coplanar PCBs were studied over 250 days. Bacterial communities in sediment slurries were described by dehrdogenase activity and by bacterial populations deduced from the clone libraries. Dechlorination of 345-4 CB and 345-34 CB occurred at least after 100 days of incubation, but dechlorination of 345-345 CB was not observed over the entire incubation period. However, time profiles of dehydrogenase activity were similar in sediment slurries amended with 345-4 CB, 345-34 CB or 345-345 CB. After normalization of the effect of acetone we found that dehydrogenase activity was increased in sediment slurries amended with 50 mg/L, but were inhibited in those amended with 2 and 10 mg/L of coplanar PCBs. Extra addition of electron donors plus sulfate or sulfate could increase dehydrogenase activity significantly. The major microbial populations in the sediment slurries incubated with 2, 10, and 50 mg/L of 345-4 CB were -Proteobacteria, Chloroflexi, and epsilon-Proteobacteria, respectively. This study shows that (1) dechlorination of coplanar PCBs did not change their effects on microbial metabolic activities, (2) concentration of coplanar PCBs had effects on microbial metabolic activities and community composition, (3) extra addition of electron donors plus sulfate or sulfate could increase dehydrogenase activity significantly, but this did not always lead to higher dechlorination rates, (4) coplanar PCBs induced perturbations of sediment microbial communities in terms of population structures (but not always as an inhibition).