FeSO4 Amendments Stimulate Extensive Anaerobic PCB Dechlorination

Anaerobic microbial reductive dechlorination of PCBs is important because it removes the chlorine substituents that block aerobic metabolism and it reduces PCB toxicity. Although this process occurs widely in nature, its extent is often limited to dechlorination of some of the chlorines in the meta positions of biphenyl. In this report we demonstrate the ability to achieve nearly complete meta plus para dechlorination of Aroclor 1242. This involves the additions of FeSO4 to PCB contaminated sediments and results in ∼90 mol % of the total PCBs being converted to aerobically degradable ortho-substituted monoand dichlorinated congeners. We propose that iron sulfate provides two mutually beneficial effects leading to its stimulation of anaerobic PCB dechlorination. Sulfate stimulates growth of sulfate reducing organisms responsible for PCB dechlorination, while Fe2+ reduces sulfide bioavailability and hence toxicity by forming the insoluble precipitate FeS. Ferrous sulfate is an inexpensive, innocuous compound which could be utilized to overcome factors limiting both the extent of in situ dechlorination as well as the implementation of sequential anaerobic/ aerobic biotreatment systems. In addition it is expected that the toxicities of Aroclors, and hence the risk they pose, will be substantially reduced at sites where PCBs have been extensively dechlorinated.