Distribution patterns of polycyclic aromatic hydrocarbons among different organic carbon fractions of polluted agricultural soils

Differences in the distribution patterns of polycyclic aromatic hydrocarbons (PAHs) among soil organic matter pools may influence PAH mobility and bioavailability in the soil. Here, we studied the distribution of 15 USEPA priority PAHs in soil light fractions (LF), heavy fractions (HF) and three additional organic matter fractions (loosely combined humus (H1), stably combined humus (H2) and tightly combined humus (H3)) further separated from HF by fractionating the soil organo-mineral complexes. The contents of total PAHs in LF ranged from 51 676 to 618 651 μg kg− 1, far greater than in HF in which the range of values was 657 to 3869 μg kg− 1. Although the LF accounted for only 0.1 to 1.4% of the soil, they were associated with 17.9 to 64.1% of the PAHs present. The PAHs in HF were mainly associated with H3, ranging from 80.8 to 92.7% of the total amount of PAHs. The degree of enrichment of the different organic matter fractions decreased in the order of LF > H3 > H2 > H1. The environmental risks of PAHs associated with different organic matter fractions are also discussed.