Speciation Characteristics and Risk Assessment of Soil Heavy Metals from Puding Karst Critical Zone, Guizhou Province

Abstract

The Community Bureau of Reference (BCR) sequential extraction method was used to analyze the distribution and chemical fractions of soil heavy metals (i.e., Cd, Cr, Zn, Fe, Ni, and Mn) under different land uses from the Puding karst critical zone, and the bioavailability and potential ecological risk of these heavy metals were evaluated. The results showed that the Fe, Zn, Cr, and Ni mainly were mainly concentrated in residual fractions and not likely to be absorbed by organisms, whereas the available fractions of Cd and Mn were in higher concentration, which retained strong potential migration and bioavailability. The richer organic matter in Puding soil might have promoted the transformation of oxidizable speciation of Fe, Ni, Cr, and Cd. The oxidizable forms of Fe, Mn, and Ni tended to accumulate in macro-aggregate soil. The risk assessment of RAC and RSP showed that the Puding karst soil was at slight ecological risk, and most heavy metals (except Cd) were at low risk to the ecological environment. Among the five land use types, the environmental risk of Cd in cropland and abandoned farmland was higher, which was mainly related to the input of Cd caused by fertilization, spraying pesticides, and other agricultural activities.