Heavy metal pollution in air-water-soil-plant system of Zhuzhou City, Hunan Province, China

The sources, distribution and mobility of heavy metals in Zhuzhou City, Hunan Province, China were systematically studied based on environmental monitoring data and random sampling from fields and markets. The significant positive correlations between some pairs of heavy metals (total Cd-Hg, total Cu-Pb) within the Zhuzhou section of the Xiang River may indicate that they are coming from the same pollution sources with similar pollution channels and removal patterns in the water bodies. Heavy metals from wastewater partly settled in the sediment after entering the Xiang River, which caused an inconsistent change in heavy metal concentrations over time in the middle and lower parts of the Xiang River. There was no significant difference in total Pb and Zn in topsoil between years in the period 1990-1997, which showed the balance between input and output. Heavy metals accumulated mainly in the topsoil with little downward movement. Heavy metals in the vegetables and rice were higher than the edible standard and background value to some degree with minor exceptions. The maximum heavy metal level observed divided by the acceptable level was in the order of Cd > Pb > Cu > Zn. Significant positive correlations were only found between cabbage uptake and total soil content for Hg, Pb and Cd, with no significant correlation for the other elements. The plant uptake of a heavy metal was somewhat influenced by the co-existence of other elements.