Occurrence and distribution of polycyclic aromatic hydrocarbons in organo-mineral particles of alluvial sandy soil profiles at a petroleum-contaminated site.

The occurrence and the distribution of 16 USEPA priority pollutants polycyclic aromatic hydrocarbons (PAHs) were investigated in two alluvial sandy soil profiles and in their four sizes of organo-mineral particles (<2 μm clay, 2-20 μm silt, 20-200 μm fine sand, and >200 μm coarse sand) beside a typical oil sludge storage site in eastern China. PAHs were mainly enriched in the surface soil (0-20 cm) and the concentrations declined in deeper soils, from 3.68 to 0.128 μg/g in profile 1 and 10.8 to 0.143 μg/g in profile 2 (dry wt.). The PAHs in the upper soil layers of this study site mainly came from combustion pollution, whereas in the lower soil layers petroleum contamination became the major source of PAHs. The content of different sized organo-mineral particles of this alluvial sandy soil decreased in the following order: fine sand>coarse sand>silt>clay. X-ray diffraction (XRD) results showed that all the different sized soil fractions of this study site were dominated by quartz, calcite and feldspar. The particle surface became smoother with size increasing as shown by scanning electron microscope (SEM) images. PAH concentrations varied largely in different sized soil fractions. The highest PAH concentration was associated with clay and decreased in the order: clay>silt>coarse sand>fine sand. Soil organic matter (SOM) content, mineral composition and particle surface characteristics were suggested as three main factors affecting the distribution of PAHs in different sized organo-mineral particles. This study will help to understand the distribution and transport characteristics of PAHs in soil profiles at petroleum-contaminated sites.