BACTERIAL MUTAGENICITY OF SOIL EXTRACTS FROM A BIOREMEDIATION FACILITY TREATING WOOD-PRESERVING WASTE

Bioremediation is gaining acceptance as a viable alternative for remediating contaminated soils at Superfund sites. However, it has the potential for resulting in the production of intermediate breakdown products which may be more toxic and soluble than the parent compound. This study was designed to monitor the mutagenic activity of contaminated soils from an abandoned wood preserving facility undergoing bioremediation in an intensively managed land treatment unit (LTU). Sample collection included two waste samples, twelve soil samples from the LTU, one on-site control soil sample, and one off-site control sample. Samples were sequentially extracted with methylene chloride and methanol, and the residues from these extractions were dissolved in dimethyl sulfoxide for testing with the Salmonella/microsome assay (Ames test). Each extract was tested using strain TA98 with and without metabolic activation, and the results were used to measure the bacterial mutagenicity which is an indicator of the carcinogenic potential. Although chemical analysis had suggested that biodegradation had reduced the concentration of toxic organics to below method detection limits, the results of bioassay testing detected mutagenic chemicals still present in both lifts of soil in the LTU. The weighted activity (revertants per gram of soil) of the soil from the upper lift which had been in the LTU for only five weeks exceeded two times the background, whereas the weighted activities of soil samples from the lower lift which had been in the LTU for three months were within background values for this site. These data indicate that three months of remediation in an intensively managed LTU is sufficient to reduce the weighted activity of contaminated soil from this facility to near background levels.