Association of black carbon with polycyclic aromatic hydrocarbons and heavy metals in urban topsoils and environmental implications

Abstract

Black carbon (BC) was quantified in the surface soils (0–10 cm) of Xuzhou, China, to examine the relationships with contents of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs). BC contents in Xuzhou urban soils varied from 1.7 to 169.5 mg/g with a mean of 32.8 mg/g. These results showed that BC showed a substantial build-up in Xuzhou surface soils. The various PAH ratios pointed to a domination by pyrogenically formed BC in soils. BC showed significant positive correlations with PAHs except for benzo(b)fluoranthene (BbF), indicating that soil BC is an important factor controlling the concentrations of PAHs in soils. The concentrations of Pb, Cu, Zn, Cd and Ni were determined by inductively coupled plasma–mass spectrometry. Similar to the PAHs, significant correlations between HMs and BC were found, suggesting that HMs investigated in this study are likely to be strongly retained by BC present in soils. These results show that BC represents a long-term carbon sink, and confers the concurrent benefit of immobilising PAHs and HMs in soils.