Heavy metals in paddy soil-rice systems of industrial and township areas from subtropical China: Levels, transfer and health risks

The levels, transfer factors and health risks of selected metals were investigated in paddy soil-rice systems of industrial and township areas from subtropical China. The mean concentrations of cadmium (Cd), lead (Pb), arsenic (As) and mercury (Hg) in paddy soils were 1.08, 52.8, 19.5 and 0.20 mg.kg(-1) (dry weight), respectively. The concentrations of Cd from ca. 99% of the soil samples and 68.9% of the rice grain samples in the study region were above the allowable limits according to the current standards. The concentrations of Cd and Pb in paddy soil from industrial areas were significantly higher than those from township and clean areas, however, these situations did not happen for Cd and Pb concentrations in rice grains. The mean of transfer factors of Cd was 0.742, which was the highest of all selected metals. The soil pH and transfer factors of Cd were analyzed separately in groups of 0.1 pH unit interval. Piecewise means of the log Cd transfer factors kept around -0.10 between soil pH 4.3 and 6.3, whereas linearly decreased by a factor of 1.80 with the increase of soil pH from 6.4 to 7.7. The high hazard index values and cancer risk values were found in our study area, indicating a high non-carcinogenic and carcinogenic health risk from consumption of rice grains.