Contents and ecology risk assessments of heavy metals in different forest soils in West Guangdong

Objective  To understand heavy metal content characteristics and pollution conditions in different forest soils in west Guangdong, and provide a theoretical basis for their ecology risk assessments.

Method  Eucalyptus urophylla plantation, Pinus massoniana plantation, Cunninghamia lanceolata plantation, Acacia spp. plantation and broad-leaved mixed forest in West Guangdong were chosen to investigate heavy metal (Cu, Zn, Pb, Cd and Ni) contents in soil at the 0–20 cm depth. Single pollution index (P_i), Nemerow index (P_N) and Hakanson potential ecological risk index (RI) methods were used to assess heavy metal pollution conditions and potential ecological risks in different forest soils.

Result  Cd content was the lowest while Zn content was the highest in all studied forest soils, but they were all below soil background value of Guangdong Povince. The values of pH ranged from 3.62 to 6.42, presenting acidic. Both Cu content (16.06 mg·kg^–1) in P. massoniana plantation soil and Pb content (12.37 mg·kg^–1) in E. urophylla plantation soil were significantly higher than those in broad-leaved mixed forest soil (9.21 and 6.87 mg·kg^–1). The correlations among five heavy metal contents in plantations were significant. All P_i values in five forests were lower than 1, indicating no contamination. Both P_i and P_N ranks in five forests were as follows: P. massoniana plantation>C. lanceolata plantation>E. urophylla plantation>Acaciaspp. plantation>broad-leaved mixed forest. ExceptP. massonianaplantation, the pollution levels of all other forests were safe. The potential ecological risk assessment results of single and multiple heavy metals were slight risk. The potential ecological risk coefficients (E_i) of single heavy metal showed that Cd had the highest value while Zn had the lowest value. The results of RI showed that P. massoniana forest had the highest value and broad-leaved mixed forest had the lowest value.

Conclusion  The E_i method can more comprehensively reflect the soil heavy metal contamination. According to its assessment results, it is still a long-term and necessary measure to prevent and reduce heavy metal pollution caused by human.