Influence of contact time on extractability and degradation of pyrene in sons.

In this study, temporal changes in extractability of [C-14]pyrene were followed in two soils with differing organic matter contents under sterile and nonsterile conditions over 24 weeks. The nonsterile pasture soil was the only incubation to show significant loss of [C-14]pyrene-associated activity over the 24-week incubation. Sequential extraction using methanol:water (1:1), followed by 1-butanol and finally dichloromethane-Soxhlet showed changes in the relative proportions of extractability with increased soil-PAH contact lime. Significant decreases in methanol:water and l-butanol extractability were recorded over the 24-week incubation. The nonsterile pasture soil exhibited the greatest decrease in 1-butanol extraction. Significant nonextractable residues were formed with increased soil-pyrene contact time in all soils, with the largest increase found in the nonsterile pasture soil. These residues were investigated by the alkaline extraction of the humic material and saponification of the resultant humin. After 24-week soil-pyrene contact time, the bioavailability of the added [C-14]pyrene was assessed by bacterial mineralization. A comparison was made between bioavailability and the amount of C-14 activity extracted by the sequential scheme of solvents. Methanol:water significantly underestimated the bioavailable fraction, whereas 1-butanol overestimated the bioavailability of the [C-14]pyrene-associated activity.