Depth distribution of polychlorinated biphenyls in soils of the Yangtze River Delta region, China

Depth distribution of polychlorinated biphenyls (PCBs) in soil is important to assess transport of PCBs in soils and its associated environmental risks. Forty-four typical soil profiles representative of three dominant soil groups (Udic Luvisols, Gleyic Cambisols and Stagnic Anthrosols) in the Yangtze River Delta region were selected. A total of 169 pedogenetic horizon samples were collected and analyzed for PCB depth distribution of PCB concentrations and patterns. The relationship between PCB concentrations and soil properties in the topsoil is also discussed. The results indicate that PCBs are detected in all sampled horizons and its concentration ranges from 0.46 ng g− 1 to 73.5 ng g− 1 in topsoil and from 0.46 ng g− 1 to 116.4 ng g− 1 in subsoil. PCBs tend to accumulate in the subsoil of Gleyic Cambisols while Udic Luvisols and Stagnic Anthrosols show the highest concentrations in the topsoil. PCB pattern is dominated by 5Cl-CB and 4Cl-CB on average in topsoil, accounting for 45% and 21% of the total PCB concentration, respectively. Proportion of low-chlorinated PCBs (3Cl-CB and 4Cl-CB) increases with depth in Udic Luvisols and Stagnic Anthrosols. In contrast, proportions of 5Cl-CB and 6Cl-CB with the PCB concentration increase from topsoil to subsoil in Gleyic Cambisols. Less volatile PCB concentrations are positively correlated with soil organic matter contents (r = 0.362, p < 0.01). Humic acid and humic–mineral complex are assumed to contribute to PCB sorption based on their close correlation with PCBs in the soils.