污灌区稻田汞污染特征及健康风险评价

选择天津北排污河灌区作为研究区域,调查了土壤和水稻总汞和甲基汞的含量及分布特征,评估污灌区稻米食用汞暴露风险,并对污灌区土壤-稻米甲基汞的影响因素进行了初步分析.结果表明,1.调查的29个污灌区稻田,土壤总汞含量为(367.04 ± 129.36) μg/kg,显著高于区域土壤Hg背景值73 μg/kg,甲基汞含量为(0.87 ± 0.77) μg/kg;水稻各部位总汞含量依次为稻叶 > 稻根 > 稻茎 > 稻米,稻米总汞含量为(12.80 ± 5.14) μg/kg,甲基汞含量依次为稻米 > 稻根 > 稻茎 > 稻叶,稻米对甲基汞具有很强的富集能力,甲基汞含量为(2.09 ± 1.20) μg/kg,甲基化率均值超过10%.污灌区稻米总汞每周摄入量为0.068~1.25μg/(kg·bw),甲基汞每周摄入量为0.0095~0.49μg/(kg·bw),污灌区稻米总汞及甲基汞暴露对居民健康风险总体仍在安全阈值内,但个别汞污染较严重地块甲基汞暴露风险值得高度关注.土壤甲基汞含量仅与土壤总汞含量及黏粒含量的相关性达到显著性水平,稻米甲基汞含量与土壤总汞含量、土壤甲基汞含量、稻米总汞含量及黏粒含量的相关性达到显著性水平.

Pollution characteristics and risk assessments of mercury in wastewater-irrigated paddy fields

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.