Genotoxicity Assessment of Wood-Preserving Waste–Contaminated Soil Undergoing Bioremediation

Abstract

Bioremediation represents one of the most cost-effective technologies for treatment of petroleum hydrocarbons in contaminated surface soils. A major concern for regulatory agencies when evaluating bioremediation is how to determine acceptable levels for residual organics in soil. Although guidelines have been developed for some organics in soil, limited information is available to define acceptable levels of the metabolites of biological degradation. The products of oxidative degradation are likely to be more water soluble and may also be more toxic. The purpose of the current study was to monitor changes in compound concentration and genotoxicity in soils undergoing bioremediation. The site selected for this study was a former wood-preserving site in the northwestern United States. Soil samples were collected over a 4-year period from two 6075-m 2 land treatment units. Conditions for biodegradation were enhanced by the addition of water and nutrients, as well as by frequent tilling to add oxygen. Due to the location of the facility, the temperature was conducive to a more rapid rate of biodegradation for approximately 6 months per year. Soil samples were collected using a grid system and solvent extracted. Polycyclic aromatic hydrocarbons were quantified in soil extracts using gas chromatography-mass spectrometry (GC/MS), and genotoxicity measured using the Salmonella/microsome assay. After 2 years of treatment, concentrations of total and carcinogenic polycyclic aromatic hydrocarbons (PAHs) were reduced to approximately 10% the concentration in the untreated soil. However, the mean weighted activity of the untreated soil was 293 net revertants per g soil, whereas the extracts of soil collected after 2 years induced a mean weighted activity of 325 net revertants per g soil. Thus, although biodegradation clearly reduced the concentration of total and carcinogenic PAHs in the surface soils, the results from the genotoxicity bioassay indicate that there was a lag in the reduction of mutagenicity in treated soils.

Evaluating the Effects of Bioremediation on Genotoxicity of Polycyclic Aromatic Hydrocarbon-Contaminated Soil Using Genetically Engineered, Higher Eukaryotic Cell Lines

“…6, 9 In some studies toxicity decreased as treatment progressed, 12-14, 29, 30 while in other studies there was either no reduction or even a substantial increase in toxicity following bioremediation. 15, 31-33 Increases in toxicity might be caused by formation of toxic metabolites or increased bioavailability of native toxins over the course of bioremediation. 31 …”

“…Bioremediation is an established technology to remove PAHs from contaminated soil and sediment . However, some researchers have advised caution about bioremediation because the removal of the monitored PAHs during bioremediation of contaminated soil or sediment might not correspond to a reduction in health risk. , In some studies, toxicity decreased as treatment progressed, − ,, whereas in other studies there was either no reduction or even a substantial increase in toxicity following bioremediation. ,− Increases in toxicity might be caused by formation of toxic metabolites or increased bioavailability of native toxins over the course of bioremediation …”

Improving Polycyclic Aromatic Hydrocarbon Biodegradation in Contaminated Soil Through Low-Level Surfactant Addition After Conventional Bioremediation

“…Overall, the genotoxicity of remediated soil will depend both on the remaining parent compounds (including PAHs and other contaminants) and the formation or removal of any products of incomplete microbial metabolism. Reduction of parent-PAH concentrations does not always correspond to a reduction in genotoxicity (Hughes et al, 1998;Gillespie et al, 2007;Lemieux et al, 2009;Hu et al, 2012). Because second-stage treatment made the soil less cytotoxic, but more genotoxic, it is possible that surfactant treatment causes transformation of cytotoxic compounds that are not genotoxic themselves into genotoxic products.…”

Nontarget Analysis Reveals a Bacterial Metabolite of Pyrene Implicated in the Genotoxicity of Contaminated Soil after Bioremediation

“…Bioremediation is an accepted technology for PAH-contaminated soil, but like other remediation methods its efficacy is evaluated only on the basis of removal of the regulated compounds rather than on broader measures of risk. For example, bioremediation of PAH-contaminated soil can have little effect on , or actually increase − the soil’s genotoxicity, despite extensive removal of the EPA-regulated PAHs.…”