Modeling transfer of heavy metals in soil-rice system and their risk assessment in paddy fields

Many studies have been conducted on model transfer in soil-plant systems. However, relatively little information is available on modeling metal transfer in soil-rice system and associated risk assessment in real paddy fields. Based on a random sampling method from Nanxun, Shengzhou and Wenling in Zhejiang province, China, 15 pairs of rice and the corresponding soil samples were respectively collected for analysis of heavy metals and soil pH. The results showed that the accumulation ability of rice for different heavy metals was significantly different (p < 0.05), and was in the order of Cd > Zn > Cu > Ni > Cr > Pb. The relationships of heavy metals in rice with those in soil, along with soil pH, were well described by linear regression models. Except for Pb, the contents of most metals in rice were positively correlated with those of the soil. Soil pH was negatively correlated with the contents of Cd, Zn and Ni in rice, and positively correlated with Pb in rice; however, it had less effect on Cr and Cu. Based on risk reference dose (RfD), the risk assessment data indicated that the rice grown in Zhejiang paddy fields does pose some potential Cd and Cr contamination risk to food safety; rice in Shengzhou posed light Ni risk.