Trace metal pollution in soil and wild plants from lead–zinc smelting areas in Huixian County, Northwest China

Abstract

Pollution of trace metals was evaluated in the soil and plant samples collected from lead–zinc smelting areas in Huixian of Northwest China. The soil samples from the arable lands surrounding the smelting sites contained high levels of Cd, Pb, and Zn, which were 6.59–237, 3.27–218 and 0.375–2.38 times respectively above the background values in the study areas, indicating a certain extent of spreading of trace metal pollution. The main causes to the dispersion of pollution were proposed to be the continuous wastewater irrigation and wind transport of dust. The geo-accumulation index (Igeo) revealed that Cd and Pb were heavy pollutants. The correlation analysis proved a correlation between soil properties and individual metal, suggesting the significant effect of soil properties on trace metal pollution. A two step sequential extraction showed that heavy metals were poorly labile under natural conditions. However, extraction with complexing agent generated significant amounts of metals, suggesting they were potentially mobilizable. The levels of Cu, Cd, Pb, and Zn in aerial parts of typical plants ranged from 0.048 to 19.9, 0.122 to 8.17, 11.1 to 48.6, and 0.646 to 85.8mgkg−1, respectively. The accumulation ability changed in an order as: Cd>Zn>Cu>Pb and a high level was detected in maize (Cd), ainsliaea (Cd), goosegrass herb (Zn), and poplar (Zn). Pb and Cd were potentially risky to local inhabitants. Apparently, some effective measures may be necessary to treat trace metal pollution in soil and to reduce metal translocation from soil to edible crops.