The effect of aging time on the distribution of pyrene in soil particle-size fractions

•We studied the distribution of pyrene in soil particle-size fractions with aging time.•The concentration of pyrene in unsterilized bulk soils decreased over time.•The ratio of pyrene in size fraction to that in bulk soil was similar over time.•Pyrene associated with different soil size fractions has similar biodegradability.•Pyrene might be adsorbed on the external surface of soil particles in 90 days.

The effect of aging time was studied on the extractability with acetone of pyrene (PYR) from whole soil and soil particle-size fractions (clay, fine silt, coarse silt, fine sand and coarse sand) with and without soil microbial activity. Soil microbial activity was inhibited or not with sodium azide (NaN3). In NaN3-amended soil, the extractable PYR decreased rapidly over the first 15 days and then stabilized from 15 to 90 days; in nonamended soil, the extractable PYR decreased continuously over the 90 day aging period presumably due to biodegradation. In nonamended soil, the concentration of PYR in particle-size fractions also decreased gradually with aging time, however, the percentages of PYR in particle-size fractions relative to total PYR in bulk soils were similar at 0, 7, 30 and 90 days of aging. These results indicate that the PYR in different particle-size fractions had similar bioavailability. Comparing our results with those of other studies suggests that the PYR in soil was probably still at an initially rapid sorption phase of the external surface adsorption over the 90 day aging period.