Reduced pyrene bioavailability in microbially active soils

The influence of microbial activity on pyrene biodegradation and fate was assessed by quantifying the distribution of C-14-label and pyrene among soil organic matter fractions (SOM) in soils that contained varied microbial communities. A southern, hardwood forest soil was incubated with pyrene in aerated chambers for 9 months. Soil was incubated in three sets: soil alone, soil augmented with a pyrene-degrading community, and soil inhibited with sodium azide (NaN3). After 9 months, pyrene mineralization was observed only in the degrader-amended soil set. Most of the pyrene and [C-14]pyrene in the NaN3-amended soil set was recovered by solvent extraction (>75%). The [C-14]pyrene extracted from the NaN3-amended soil set was mineralized by a microbial community shown to mineralize pyrene. Extractable pyrene from nonamended soil and degrader-amended soil sets decreased with time due to biodegradation. Extracted label from these soils was not mineralized to the same extent as NaN3-amended soil. Nonextractable label in humic/fulvic acid and humin fractions was greater in these soils than in the NaN3-amended soil set. Pyrene degradation products were detected in biologically active soils by HPLC. Over time, the extractability of pyrene and pyrene products in biologically active soils decreased to a greater extent than NaN3-amended soil.