Abstract:A paddy field is typical constructed wetland, where mercury (Hg) is easily methylated to methylmercury (MeHg). Due to long-term wastewater irrigation, a large area of farmlands, including paddy fields in Tianjin City, has been seriously contaminated with Hg. There is therefore an important question to be answered in our understanding as to the characteristics of total Hg (THg) and/or MeHg accumulations in rice from wastewater-irrigated areas and risk assessment for evaluation Hg exposure for the population by rice consumption. In this study, a field survey of mercury pollution in 29 paddy fields (soil and rice) from wastewater-irrigated areas around north discharged river in Tianjin city was conducted to evaluate the health risks of mercury to residents by rice consumption. The results showed that: 1. THg and MeHg concentrations in surveyed paddy fields were (367.04 ± 129.36) μg/kg and (0.87 ± 0.77) μg/kg, respectively, where the total mercury content of back soil was 73μg/kg. Analyses of the distribution of Hg species in different parts of rice plants from selected sampling locations shown that grain contained the lowest THg concentrations (12.80 ± 5.14) μg/kg, followed by stem 10%), followed by root > stem > leaf. This suggests that rice grain may preferentially accumulate MeHg compared to other parts of the plant. Observations clearly show that MeHg in the paddy soil could be more easily taken up and transferred to rice grain compared to THg. The probable weekly intake (PWI) of THg and MeHg for an adult population based on 60kg body weight (bw) in studied wastewater-irrigated area was 0.068~1.25 μg/(kg·bw) and 0.0095~0.49 μg/(kg·bw), respectively, which were all well below reference dose established by WHO (FAO) or U.S EPA. However, it was clearly manifest that there is a great concern of MeHg exposure risk for rice consumption around some highly Hg-contaminated areas. There were positive and significant correlations between soil MeHg concentrations and soil THg concentration, or clay contents in the collected soil samples. Similarly, significant positive correlations were also found between MeHg concentrations in brown rice and soil THg concentrations, or soil MeHg concentrations and soil clay contents. This study highlights the potential health risks of MeHg associated with cultivation and consumption of rice on the wastewater-irrigated areas.