Heavy metal distribution, translocation, and human health risk assessment in the soil-rice system around Dongting Lake area, China.

Heavy metals including copper (Cu), zinc (Zn), cadmium (Cd), chromium (Cr), lead (Pb), and arsenic (As) were investigated in 89 pairs of rice plant and paddy soils around Dongting Lake area, China. Rice plants and soils were collected with GPS device, and heavy metal contents in different rice plant tissues and soils were measured. The aim of the present study was to assess the heavy metal pollution and translocation in the whole soil-rice system, including the consequent human health risk for residents. According to the indices of average geoaccumulation (Igeo) of the studied elements, paddy soils in study area were moderately polluted by Cd, lowly polluted by Pb, and not polluted by Cu, Zn, Cr, and As. Considering the much higher concentrations of studied elements in roots than in other tissues of rice plants, a great mass of these elements was assumed to be confined in the roots. The low translocation factors from root to shoot (Tfroot-shoot) of all the studied heavy metals (0.04-0.74) underpinned this. The high translocation factors from soil to root (Tfsoil-root) of Cd (9.12), As (4.38), and Zn (2.05) indicated the high bioavailability of these heavy metals for rice plant. The health risk assessment using target hazard quotients (THQs) model indicated that Cd (5.17 for adults and 4.49 for children respectively) and As (3.61 for adults and 3.14 for children respectively) could cause human health risk both for adults and children. Further, given the rate of individual THQ values exceeding one, Cu might also be considered as a potential human health dangerous element in the study area. It was worth noting that as one of the main pollutants, Pb did not show human health risk through rice grain consumption due to its low Tf values in soil-rice system. However, the risk identification of As using comparisons of measured concentrations with risk screening value in Chinese paddy soil standard (GB15618-2018) was not consistent with the human health risk assessment result. This might indicate that site-specific risk screening values of As in China is in demand.