Bioassay-directed fractionation and chemical identification of mutagens inbioremediated soils

Soil from a Superfund site (Reilly Tar Site, St. Louis Park, Minnesota) con taminated with polycyclic aromatic hydrocarbons (PAHs) from creosote was tr eated with several bioremediation technologies including bioslurry (BS), bi opile (BP), compost (CMP), and land treatment (LT). These treatment technol ogies are being evaluated in pilot scale laboratory systems by the U.S. Env ironmental Protection Agency's National Risk Management Research Laboratory in Cincinnati, Ohio. To evaluate the genotoxicity and identify the mutagen s in the soil before and after the various treatments, fractionated extract s of five soils were bioassayed for mutagenic activity with a microsuspensi on modification of the Salmonella histidine reversion assay. Soils were ext racted by sonication using dichloromethane (DCM). The five extracts were fr actionated in triplicate (two for bioassay and one for chemical analysis) b y reverse-phase high-performance liquid chromatography (HPLC) using hexane/ DCM/methanol, and the fractions for bioassay were solvent-exchanged into di methyl sulfoxide by nitrogen evaporation. Forty HPLC fractions for each sam ple were bioassayed in strain YG1041 with and without exogenous liver metab olic activation. As shown in a companion paper, the mutagenicity oi two tre atments (BS and BP) was significantly greater than the mutagenicity oi the untreated soil. Mutagenic fractions (>500 revertants) were analyzed by gas chromatography/mass spectrometry (GC/MS). PAH analysis of the soils indicat ed that all treatments were effective in reducing the total PAH concentrati on (48-74%). Qualitative GC/MS analysis of the mutagenic fractions from the BS and BP treatments indicated that they contained azaarenes, which are mu tagens. The CMP and LT processes were the most effective and least toxic bi oremediation procedures based on mutagenic potency and chemical analysis. T his research demonstrated that the combination of bioassays and chemical an alysis provided a more accurate determination of toxicity in these complex environmental mixtures.