Distributions and risks of Cu, Cd, Pb and Zn in soils and rice in the North River Basin, South China

As the largest industrial and population centre in China, the Pearl River Delta is facing a growing threat of heavy metal pollution from local mining and power industries. This study investigates the distribution and potential health risks of copper (Cu), cadmium (Cd), lead (Pb) and zinc (Zn) in paddy soils and rice at four typical sites. The Nemerow synthetic pollution index (PN) of soils from Fogang, Dabao Mountain, Shaoguan and Lechang were 8.40, 9.10, 4.64 and 10.28, respectively, indicating serious pollution at all four sampling sites. The average concentrations of Cu, Cd, Pb and Zn in rice grains were 2.23, 10.98, 29.84 and 1.62 times their corresponding maximum allowable levels, indicating potential health risks to humans. Cd has greater bioavailability because of its high mobility from soil to roots, and its subsequent transfer to grains. Pb mainly accumulates in roots because of its lower translocation rate from roots to grains. The greatest health risk index for Cd and Pb for adults and children was at the Shaoguan site, probably due to pollution from atmospheric deposition. Cd and Pb had greater health risk indices than Cu and Zn at almost all sites, indicating a major health risk to local people.