Abiotic and Biotic Dissipation in Natural Attenuation of Phenanthrene and Benzo[a]pyrene: A Systematic Quantification Study in Contrasting Soils

Natural attenuation represents a significant ecosystem function for mitigating the quantity and toxicity of polycyclic aromatic hydrocarbons (PAHs) through both abiotic and biotic dissipation processes. This study systematically investigated abiotic and biotic dissipation of phenanthrene (Phe) and benzo[a]pyrene (BaP) in four soils over 360 days, using CSIA to quantitatively analyze δ¹³C changes and demonstrate biodegradation. The results indicated that extractable Phe was primarily attenuated via biodegradation (65% - 81%), as revealed by CSIA, with the δ¹³C changes ranging from 2.06‰ to 4.20‰ across the four soil types. Only 17% -27% of Phe dissipated by forming Type II non-extractable residues (NERs), while its Type I NERs remained available for microbial utilization. Notably, the microbial genera Gemmatimonas and Sphingomonas emerged as key contributors to the biotic dissipation of Phe. Conversely, extractable BaP was predominantly attenuated through abiotic process (35% - 52%), particularly via the formation of Type I and Type II NERs, with a smaller fraction (6% - 17%) undergoing biotic dissipation. Although the changes in δ¹³C values for BaP were only 0.76‰ -1.06‰, the significant changes (p<0.05) supported the microbial degradation of BaP. Additionally, soil organic matter and pH influenced the extractable and residual Phe, whereas soil electrical conductivity and texture primarily affected BaP rather than Phe. These findings underscore the multiple dissipation mechanisms involved in the natural attenuation of PAHs in soils and offer valuable quantitative data for remediation strategies of PAHs-contaminated soils.