Biodegradation of Pyrene in Soil Microcosms: Identification of a Toxic Intermediate

Abstract

Pyrene is a polycyclic aromatic hydrocarbon (PAH) compound that was a regulated pollutant that limited the rate of bioremediation of wood preservative contaminated soil at the Champion International Superfund Site in Libby, Montana. The half-life of pyrene in soil at field scale may extend beyond one year depending on environmental conditions. The environmental fate of pyrene and other PAHs affected by naturally occurring soil microbes is important in the development of monitoring and bioremediation strategies, and in protecting drinking water supplies originating from groundwater resources threatened by leaching of PAHs. Mycobacterium sp. KMS was isolated from vadose zone soil at the Libby site and was shown to transform more than 60% of 14 C pyrene added to soil microcosms to carbon dioxide within 38 days at 28 0 C. In this study, Pyrene fate was monitored in four soil matrices: an uncontaminated Kidman soil, a site boundary soil (BD), the BD soil with the addition of Mycobacterium sp. KMS, and mercuric chloride poisoned BD soil. The amount of extractable pyrene was relatively constant over the experimental period in Kidman and poisoned soil microcosms, whereas the amount of extractable pyrene decreased with time in BD soil and decreased rapidly in the inoculated BD soil. High-performance Liquid Chromatography (HPLC), Liquid Chromatography Mass Spectrometry (LC/MS) and Nuclear Magnetic Resonance (NMR) spectroscopy analyses showed the formation of a major metabolite, pyrene-4,5-dione (PYRQ) in the BD soil microcosms with and without Mycobacterium sp. KMS inoculation. PYRQ was also identified in solvent extracts of site soil. PYRQ demonstrated a response in the aqueous Microtox® toxicity assay. It can be further degraded in inoculated and uninoculated BD soil, but it accumulates in other systems. The production of PYRQ and its possible release into environment may present a potential risk.