Tracing the Biotransformation of Polycyclic Aromatic Hydrocarbons in Contaminated Soil Using Stable Isotope-Assisted Metabolomics

Biotransformation of organic pollutants may result in the formation of oxidation products that are more toxic than the parent contaminants. However, tracing and identifying those products, and the metabolic pathways involved in their formation, are still challenging within complex environmental samples. We applied stable isotope-assisted metabolomics (SIAM) to polycyclic aromatic hydrocarbon-contaminated soil collected from a wood treatment facility. Soil samples were separately spiked with uniformly ¹³C-labeled fluoranthene, pyrene, or benzo[a]anthracene at a level below that of the native contaminant and incubated for 1 or 2 weeks under aerobic biostimulated conditions. Combining high-resolution mass spectrometry and automated SIAM workflows, we propose chemical structures of metabolites and metabolic pathways in the soil. Ring-cleavage products, including previously unreported intermediates such as C₁₁H₁₀O₆ and C₁₅H₁₂O₅, were detected originating from fluoranthene and benzo[a]anthracene, respectively. Sulfate conjugates of dihydroxy compounds were found as major metabolites of pyrene and benzo[a]anthracene, suggesting the potential role of fungi in their biotransformation in soils. A series of unknown N-containing metabolites were identified from pyrene, but their structural elucidation requires further investigation. Our results suggest that SIAM can be successfully applied to understand the fate of organic pollutants in environmental samples, opening lines of evidence for novel mechanisms of microbial transformation within such complex matrices.