Influence of metabolites and co-contaminants on the biodegradation of polycyclic aromatic hydrocarbons in soils

Soils contaminated with potentially carcinogenic polycyclic aromatic hydrocarbons (PAH's) also contain complex mixtures of co-contaminants. These compounds combined with the specific attributes of their deposition and location may effect the natural attenuation process and risk estimation for contaminated sites. Work presented in the following document illustrates the complexity of interactions between parent PAH compounds and possible co contaminants. A series of solvent spiking and soil moisture conditions were investigated for their impact on microbial response. Degradation and fate of pyrene was monitored in field-wet and air-dry and rehydrated soils using dichloromethane, acetone, ethanol or toluene as spiking solvents. Soils subject to ethanol solvent spikes exhibited total elimination of pyrene mineralization capacity and dramatically increased solvent extractability of pyrene. Other solvent spikes showed high, and largely similar, levels of pyrene mineralization. Additional tests of microbial response to solvent spiking included glucose turnover, culturable heterotrophs and DNA extractability. Results indicate that choice of soil spiking protocols can alter the response of the microbial community and degradation of the target compound.; Simple aerobic soil microcosms were used to demonstrate the effect of identified PAH metabolic products on the rate, extent of degradation and final disposition of two high molecular weight PAH's. Data indicate that low concentrations of salicylic acid (50μg/g soil) have a mild stimulatory effect on mineralization of pyrene in soil. 4-hydroxybenzoic acid (4-HB) and protocatechuate have no effect on mineralization of pyrene. Pyruvate significantly inhibited pyrene mineralization. BAP mineralization was unaffected by salicylic acid and other compounds, but was inhibited by the presence of phenanthrene.; Toxicity, mobility and persistence of the oxidized metabolite pyrene-4,5-dione (P45D) were investigated in soil systems. Toxicity of P45D in saturated solution, as measured by Microtox, indicated an EC50 of 0.63 mg/L. Degradation of pyrene in the presence of P45D in spiked soil microcosms showed greatly reduced initial mineralization kinetics and significantly less total mineralization over 180 d. The presence of P45D had no effect on the mineralization and ultimate disposition of benzo[a]pyrene. Recovery of spiked P45D from soil microcosms indicated that 15 to 18% of the initial concentration of P45D could be solvent-extracted after treatment.