Assessment of metal inhibition of reductive dechlorination of hexachlorobenzene at a superfund site
1998
Jackson, W.A. | Pardue, J.H.
Laboratory studies were conducted to identify easily measured parameters that would predict the potential for metal inhibition in sediments co-contaminated by heavy metals and hexachlorobenzene (HCB) at the Petro Processors Superfund site. Metal inhibition was investigated using HCB-contaminated sediment and a range of added metal concentrations (1-1,000 mg/kg). Cadmium, Cu, Pb, and Zn all caused inhibition of HCB reductive dechlorination and methane production with inhibiting concentrations of Cd and Pb equivalent to those found in portions of the site. In the second phase of studies, laboratory experiments investigated the relationship between Cd and Pb availability on the kinetics of HCB degradation. Cadmium and Pb affected both dechlorination rates and lag times. In addition, Cd affected the appearance of lower chlorinated benzene metabolites. Inhibition of HCB dechlorination was well correlated to ratios of acid-volatile sulfide (AVS) to simultaneously extractable metals (SEM) and water-soluble Cd. Only treatments with a measurable concentration (>6 micrograms/L) of free, uncomplexed Cd exhibited inhibition. Lead inhibited HCB dechlorination at all concentrations tested (10-1,000 mg/kg) and inhibition did not correlate to either water-soluble Pb concentrations or AVS/SEM ratios. For both Cd and Pb, methane production was less sensitive to metals than HCB dechlorination, making production of methane a poor indicator of inhibition. Measurement of free, uncomplexed Cd was the best predictor of Cd inhibition while no suitable indicators were found for Pb. These results demonstrate the importance of metal bioavailability on the inhibition of reductive dechlorination.
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