Microbial Removal of Atmospheric Carbon Tetrachloride in Bulk Aerobic Soils

Abstract

ABSTRACT Atmospheric concentrations of carbon tetrachloride (CCl 4 ) were removed by bulk aerobic soils from tropical, subtropical, and boreal environments. Removal was observed in all tested soil types, indicating that the process was widespread. The flux measured in field chamber experiments was 0.24 ± 0.10 nmol CCl 4 (m 2 day) −1 (average ± standard deviation [SD]; n = 282). Removal of CCl 4 and removal of methane (CH 4 ) were compared to explore whether the two processes were linked. Removal of both gases was halted in laboratory samples that were autoclaved, dry heated, or incubated in the presence of mercuric chloride (HgCl 2 ). In marl soils, treatment with antibiotics such as tetracycline and streptomycin caused partial inhibition of CCl 4 (50%) and CH 4 (76%) removal, but removal was not affected in soils treated with nystatin or myxothiazol. These data indicated that bacteria contributed to the soil removal of CCl 4 and that microeukaryotes may not have played a significant role. Amendments of methanol, acetate, and succinate to soil samples enhanced CCl 4 removal by 59%, 293%, and 72%, respectively. Additions of a variety of inhibitors and substrates indicated that nitrification, methanogenesis, or biological reduction of nitrate, nitrous oxide, or sulfate (e.g., occurring in possible anoxic microzones) did not play a significant role in the removal of CCl 4 . Methyl fluoride inhibited removal of CH 4 but not CCl 4 , indicating that CH 4 and CCl 4 removals were not directly linked. Furthermore, CCl 4 removal was not affected in soils amended with copper sulfate or methane, supporting the results with MeF and suggesting that the observed CCl 4 removal was not significantly mediated by methanotrophs.