Vertical distribution and sources of PAHs in different agricultural soil profiles: a case study in Jianghan Plain, Central China

Abstract

PAHs are one of the persistent organic pollutants (POPs) and widely distributed in nature. This study aimed to investigate the distribution and origination of polycyclic aromatic hydrocarbons (PAHs) in 3 different agricultural soil profiles (paddy, cotton and rape). The study found that 16 PAHs were all detected in 3 soil profiles, where the concentrations of ∑16PAHs ranged from 122.37-664.13ng/g in surface soil and 24.15-109.76ng/g in bottom soil. Compared to other areas, the concentrations were higher than most plains, but lower than several cities. The ∑16PAHs of naphthalene(Nap) counted the most in nearly every sample. The total concentrations of ∑16PAHs were higher in shallow soil and decreased sharply with the increase of depth, while those were smoothly distributed in paddy field (PF). The results showed that 3 soil profiles were all weakly alkaline (8 < pH < 9), and PAH concentrations in soil were linearly related with total organic carbon (TOC) at different depths except for the PF soil profiles. It was the flooded tillage method in PF that caused the different characteristics of distribution and physicochemical properties. There were high correlation between dissolved organic matters(DOM) and PAH concentrations in cotton field (CF). However, there were no correlations between concentrations of PAHs and other 3 properties (pH, clay miners). By the ratio method, PAHs were revealed mainly derived from combustion, and then petroleum.