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DEGRADATION OF POLYNUCLEAR AROMATIC HYDROCARBONS UNDER BENCH-SCALE COMPOST CONDITIONS
Citation:
Potter, C., J. Glaser, L. Chang, J. Meier, M. Dosani, AND R. Herrmann. DEGRADATION OF POLYNUCLEAR AROMATIC HYDROCARBONS UNDER BENCH-SCALE COMPOST CONDITIONS. Environmental Science and Technology 33(10):1717-1725, (1999).
Description:
The relationship between biomass growth and degradation of polynuclear aromatic hydrocarbons (PAHs) in soil, and subsequent toxicity reduction, was evaluated in 10 in-vessel, bench-scale compost units. Field soil was aquired from the Reilly Tar and Chemical Company Superfund site in St. Louis Park, MN(Reilly soil) and brought to the U.S.Environmental Protection Agency Test and Evaluation Facility in Cincinnati, OH for a 12-week composting study. Five separate amendment conditions were applied in duplicate to Reilly soil to stimulate varying degrees of biomass growth. Amendments included standard nutrients (SN) adjusted to C:N:P=100:5:1, based on total organic carbon plus 1% cow manure, modified OECD nutrients adjusted to C:N:P=100:5:1 plus 1% cow manure, SN plus 1% activated sludge, SN plus 5% activated sludge, and SN plus 5% autoclaved sludge. All reactors contained 30% (w/w) corn cobs. All amendment conditions resulted in decreased concentrations of PAHs with two to four rings in their molecular structure. No reduction in concentrations of five-or six-ring PAHs occurred during the 12-week study. No significant differences resulted between the final concentrations achieved through any of the amendment conditions. Starting concentrations of total PAHs ranged from 1606 to 4445 mg/kg, and final concentrations ranged from 888 to 1556 mg/kg in the reactors. Contaminant concentration plateaus appeared in all treatment curves by the eighth week. Once a concentration plateau was attained, little further PAH removal occurred during the remaining treatment, and all treatments moved closer to a similar concentration plateau value. Therefore, percent removal of PAHs from Reilly soil correlated with starting PAH concentrations but not with final concentrations. Rates of removal of PAHs during the first 4 weeks of compost treatment correlated strongly with starting PAH concentration but did not correlate with reactor biomass concentration. Several toxicity bioassays in earthworms and plants were used to evaluate the efficacy of compost biomass to reduce toxicity of PAH-contaminated soil. Earthworms (Lumbricus terrestris and Eisenia fetida andrei) were exposed to contaminated soil mixed with artificial soil in 6% to 100% dilutions (w/w), and survival was assessed after 14 days. Seed germination and root elongation tests were evaluated in lettuce and oats, and genotoxicity (mitotic aberrations) testing was performed on Allium cepa (onion). Composting of PAH contaminated soil decreased toxicity to earthworms and oat roots but had no significant effect on lettuce root toxicity. Untreated soil evoked genotoxicity in the Allium assay. After composting, no significant genotoxicity was observed in Reilly soil. Two challenges for future research on compost treatment of soils contaminated with PAHs involve increasing the removal of five- and six-ring compounds and achieving total removal that plateaus at a lower level. Whether this can be achieved by optimizing compost biomass development is uncertain. Continued evaluation of the amount and physiological status of compost biomass may provide information on the long-term ability of composting to destroy large PAHs.