Influence of soil minerals on the rates and products of abiotic transformation of carbon tetrachloride in anaerobic soils and sediments

Rates and products of abiotic mineral-mediated carbon tetrachloride (CT) transformation were measured in microcosms prepared from natural soils and sediments that were incubated under iron-reducing and sulfate-reducing conditions, then sterilized to inhibit microbial activity. For one set of microcosms, the rate of CT disappearance was correlated with the concentration of weakly bound (MgCl ₂ extractable) Fe(II) in an experiment in which CT was repeatedly spiked into the microcosms. When pooling the results from all microcosms, however, there was no statistically significant positive correlation between CT transformation rate and the concentration of weakly bound Fe(II) or any other mineral species. There was, however, a statistically significant negative correlation between CT transformation rate and the concentration of Cr(II) extractable sulfur (CrES). Evidence from X-ray photoelectron spectroscopy in a related model system containing a mixture of FeS and pyrite ("aged FeS") showed that the decline in CT disappearance rate corresponded to a decrease in the abundance of FeS and an increase in the abundance of pyrite at the mineral surface. For aged FeS, the yield of chloroform (CF) also decreased as the abundance of pyrite at the surface increased, and there was an inverse relationship between the yields of CF and CS ₂.