Superfund Research Program

Bioremediation of PCB-contaminated Sediments in the St. Lawrence River

Project Leader: G-Yull Rhee (Wadsworth Center, New York State Department of Health)
Grant Number: P42ES004913
Funding Period: 1995 - 2000

Project-Specific Links

Final Progress Reports

Year:   1999 

A study of simulated dredged sediments spiked with Aroclor 1242 has shown that moisture content is crucial for continuing microbial dechlorination; in these sediments, the maximum level of dechlorination decreased with moisture content. There was a significant correlation between the maximum extent of dechlorination and the specific death rate of dechlorinating populations. This indicates that the underlying mechanism of the moisture-dependent maximum dechlorination is the moisture-dependence of the death rate.

Sediments dredged from the Hudson River and encapsulated at the Moreau containment site in 1978 showed that PCB dechlorination in these sediments was far less advanced than that in the river sediments collected from the same dredged site in 1991 and appeared to have stopped soon after dredging. Although dechlorinating microorganisms were still present, a restoration of the moisture content to an optimum level did not restart dechlorination. However, when inoculated with sediment microorganisms eluted from fresh river sediments, these moisture-optimized sediments showed further dechlorination. These results indicate that with the optimization of moisture level and selective enrichment of dechlorinating microorganisms, it may be possible to reduce the degree of chlorination in dredged sediments to levels which can be completely degraded through aerobic decomposition.

When sediment microorganisms eluted from Aroclor 1248-contaminated St. Lawrence River sediments were enriched with non-PCB haloaromatic compounds (chlorobenzoates, chlorophenols, chlorobenzenes) in PCB-free sediments, the enrichment of PCB-dechlorinating microorganisms was much greater with many of these compounds than with Aroclor 1248. When PCB-contaminated sediments were amended with these compounds, many of them enhanced the extent of dechlorination, many at the meta or both meta and para positions, and some at the para position. These results suggest that it may be possible to maximize dechlorination by enriching specific dechlorination competence using more readily degradable haloaromatic compounds.