Accumulation characteristics and potential risk of heavy metals in soil-vegetable system under greenhouse cultivation condition in Northern China

Abstract

Heavy metal pollution in greenhouse vegetable production system is a growing concern for public health. In this study, 87 soil and 72 vegetable samples were collected from greenhouse vegetable production systems in Shanxi province, Northern China, aiming to evaluate the accumulation characteristics and potential risk of heavy metals in soil-vegetable system under greenhouse condition. The results showed that Cd and Pb concentrations in 72.4% and 35.5% of the soil samples were higher, while all of As, Cr, Ni, Cu, Zn samples were lower than the Grade II value in Environmental Quality Standard for Soils (GB15618-1995). Nearly 99% of the total amount Pb existed in the form of residual and could not be absorbed by vegetables. The proportions of As, Cd, Zn in ionic form, bound to carbonates and the exchangeable fraction were 6.21, 13.71, and 13.47% respectively, and were relatively higher than other metals (Cr, Cu, Ni, Pb). The transfer factors (TF) of As, Cr, Ni, Pb were found to be higher in leaf and fruit vegetables than that in tuber vegetables. With a relatively low total concentration and high proportion of available form in soils, Cd showed relatively larger TF in three kinds of vegetables than other metals. The concentrations of Cr, Ni and Pb in three kinds of greenhouse vegetables exceeded the limit in national food safety standards. Especially, Ni in leaf and fruit vegetables showed significantly higher hazard quotient (HQ) than that in tube vegetables. Overall, leaf and fruit vegetables had a relatively higher hazard index (HI) than tube types, and exceeded 1, suggesting that there was larger potential health risk by ingestion of heavy metals through fruit and leaf vegetables. Thus, in order to avoid human body health endangered by heavy metals through the food chain, appropriate management measures should be implemented in greenhouse cultivation, especially tuber vegetables be cultivated instead of leaf and fruit types.