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-m² 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.

KEYWORDS:

• biodegradation
• genotoxicity
• polycyclic aromatic hydrocarbons
• land treatment

Notes

∗Revertants = total TA98 revertants per plate (solvent control [DMSO = 44 ± 2(+S9)]).

∗∗Summary Response: (++) = no. revertants/plate > 2× the solvent control for 3 consecutive doses; + = no. revertants/plate > 2× the solvent control for 2 conseccutive doses; +/− = no. revertants/plate > 2× the solvent control for 1dose; − = no. revertants/plate < 2× solvent control at all doses.

∗Revertants = Total TA98 revertants per plate (solvent control [DMSO = 44 ± 4 (+S9)]).

∗∗Summary Response: (++) = no. revertants/plate > 2× the solvent control for 3 consecutive doses; + no. revertants/plate > 2× the solvent control for 2 consecutive doses; +/− = no. revertants/plate > 2× the solvent control for 1 dose; − = no. revertants/plate < 2× solvent control at all doses.

∗Revertants = Total TA98 revertants per plate less concurrent solvent control [DMSO = 43 + 6 (+S9)].

∗∗Summary Response: (++) = # revertants/plate > 2× the solvent control for 3 consecutive doses; (+) = # revertants/plate > 2× the solvent control for 2 consecutive doses; (+/−) = # revertants/plate > 2× the solvent control for 1 dose; (−) = # revertants/plate not > 2× solvent control at any dose.

^a

^b

^c n = 5.