A survey on polycyclic aromatic hydrocarbon concentrations in soil in Chiang-Mai, Thailand

Soil samples were collected at 30 sampling sites along roadsides in the city of Chiang-Mai, Thailand, in February 1996, and concentrations of 16 polycyclic aromatic hydrocarbons (PAHs) were determined. The distribution of PAH concentration in the soil samples was almost lognormal for all PAHs. Concentrations of pyrene (Py) and fluoranthene (Fluor) were the highest, followed by those of benzo[ghi]perylene and coronene (Cor). Since PAH concentrations were highest on the roadside where the traffic density was high, vehicles were the main determinants of PAH concentration in soil in Chiang-Mai. Significant correlations among PAH concentrations were found for almost all PAHs. PAH profiles in the air were different from those in the soil. For example, relative benzo[a]pyrene (BaP) concentration in the soil was significantly lower than that in the air. Relative concentrations of Fluor, Py, chrysene, and Cor in the soil were considerably higher than those in the air, due presumably to their difference in photochemical reactivities and in sources. The sampling of soil has advantages relative to that of air: 1) collection of soil is easy; 2) it needs no special equipment and electricity; 3) it takes little time; and 4) it can be collected anywhere. Therefore, PAH analysis in soil was useful as a proxy-screening tool for air pollution levels with consideration of compositional differences between soil and air samples.