The main focus of this project is to determine the extent of PCB dechlorination and degradation by indigenous sediment microorganisms from the St. Lawrence River. A comparison of the congener pattern in sediments to the original Aroclor discharged showed that in situ reductive dechlorination of sediment PCBs has taken place, however the extent and pattern of dechlorination varied between sites. This project looks to develop techniques to degrade PCBs in sediment by enhancing anaerobic dechlorination and combining it with aerobic biodegradation.
This project involves conducting comparative laboratory incubation studies of sediment from the General Motors (GM) and Reynolds sites to determine if the differences between those two sites are due to microbial community composition, microbial competence or sediment composition, what determines the end point of in situ dechlorination at each site, how to accelerate in situ biotransformation, and the extent of detoxification of these sediments by dechlorination.
In this project we are determining the dechlorination potential in sediments using both Aroclor and single congener assays, and the microbial biomass and community characteristics with phospholipid, fatty acid, 16S rRNA hybridization and MPN techniques. We will also assess the threshold concentration for dechlorination which may set the residual PCB levels.
The project also looks at factors limiting the rates and degree of degradation. At this time, the project has found strong evidence that the limit to dechlorination is not due to PCB bioavailability but the inability of the present microbial consortium to further dechlorinate the accumulating daughter congeners.
This project also examines how to maintain and enhance dechlorination activities in dredged sediments. Dredging and encapsulation are commonly used to remediate contaminated sites and the most heavily contaminated sediments at the GM site will also be dredged soon. Our studies of dredged Hudson River sediments showed that dechlorination ceased at an early stage after encapsulation and the sediments no longer harbored dechlorinating organisms. Using a simulated disposal facility in the laboratory, we will determine the time course of change in dechlorination activity and microbial community structure and also how dechlorination activity is affected by various conditions including moisture content and organic matter.
Finally, this project is examining how to degrade dechlorination products with indigenous aerobic microorganisms. Aerobic cultures from surface sediment layers are being tested for their ability to degrade the products of anaerobic dechlorination. The degradation characteristics and optimum conditions for degradation are being determined. This project is also determining whether aerobic degradation can be induced in these sediments without inoculating isolates.
