Content, distribution, source and ecological risk of heavy metals in soils of Benggang areas in Southwest Fujian

Sixty-three surface (0-20 cm) soil samples were collected in two typical Benggang areas (BG₁ and BG₂) in Huangnikeng Benggang Group and an adjacent hillside without Benggang (CK) in Changting County of southwestern Fujian Province. The contents of seven heavy metals in those samples were measured, and each heavy metal’s source was identified by means of correlation and principal component analyses. Finally, the potential ecological risks of heavy metals were assessed on the basis of soil background values of Fujian Province and the second class standard of national soil environmental quality. The results indicated that the order of contents of heavy metals in the investigated soil was Zn (105.56 mg·kg^-1) > Pb (67.21 mg·kg^-1) > As (61.47 mg·kg^-1) > Cu (22.33 mg·kg^-1) > Cr (17.12 mg·kg^-1) > Ni (5.24 mg·kg^-1) > Cd (0.80 mg·kg^-1), the contents of Pb and Cd in both BG1 and BG2 were higher than those in CK, while those of Cu, Zn, Ni, Cr, As and Cd were opposite. The contents of Zn, Pb, As and Cd in BG1 were 1.12, 2.82, 8.68 and 13.33 times, BG2 were 1.11, 1.36, 11.22 and 16.67 times, and CK were 1.58, 1.60, 5.14 and 14.44 times the averages of soil background values in Fujian Province. Compared with the second class standard of national soil environmental quality (GB15618—1995), the contents of As in Benggangs and CK soils were 1.92 and 2.70 times, respectively, and the content of Cd was 2.31 and 2.60 times, respectively, the nation standard. From upper slope to bottom of slope in Benggang systems, the contents of Pb, Zn and Cd increased, Cu and Cr basically remained stable, while Ni decreased. From top to bottom of CK slope, Cu, Zn, Ni, Cr and Cd contents increased, and Pb content decreased slightly. As content in study region kept relatively consistent. According to heavy metals resources analysis with correlation and principal component analyses methods, Cu, Ni and Cr mainly came from parent materials, Zn was associated with livestock breeding probably, Cd and As originated from substrate weathering and mining of rare earth elements, and Pb were ascribed to compound pollution of bedrock mineralization, coal combustion, and exhaust emission on provincial highway (No. 205). The potential ecological risk coefficients of Cd and As were classified as ‘extreme strong level’ and ‘strong level’ respectively, and those of Cu, Zn, Ni, Pb, Cr were ranked as ‘slight level’ with soil background values in Fujian Province as reference; while only Cd was ranked as ‘strong level’ and others were in range of ‘slight level’, when the second class standard of national soil environmental quality was used as reference. The order of potential ecological risk index was BG₂>CK>BG₁. The proper measures would be suggested to control the severe contamination of Cd and As in this area.