Cui Yuying, Wu Qingru, Liu Kaiyun, Wang Shuxiao, Wang Xun, Jiang Tao, Meng Bo, Wu Yurong, Guo Jia
State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China.
State Environmental Protection Key Laboratory of Sources and Control of Air Pollution Complex, Beijing 100084, China.
ACS Environ Au. 2022 May 2;2(4):324-335. doi: 10.1021/acsenvironau.1c00061. eCollection 2022 Jul 20.
Rice grain consumption is a primary pathway of human mercury exposure. To trace the source of rice grain mercury in China, we developed a rice paddy mercury transport and transformation model with a grid resolution of 1 km × 1 km by using the unit cell mass conservation method. The simulated total mercury (THg) and methylmercury (MeHg) concentrations in Chinese rice grain ranged from 0.08 to 243.6 and 0.03 to 238.6 μg/kg, respectively, in 2017. Approximately, 81.3% of the national average rice grain THg concentration was due to atmospheric mercury deposition. However, soil heterogeneity, especially the variation in soil mercury, led to the wide rice grain THg distribution across grids. Approximately, 64.8% of the national average rice grain MeHg concentration was due to soil mercury. In situ methylation was the main pathway via which the rice grain MeHg concentration was increased. The coupled impact of high mercury input and methylation potential led to extremely high rice grain MeHg in partial grids among Guizhou province and junctions with surrounding provinces. The spatial variation in soil organic matter significantly impacted the methylation potential among grids, especially in Northeast China. Based on the high-resolution rice grain THg concentration, we identified 0.72% of grids as heavily polluted THg grids (rice grain THg > 20 μg/kg). These grids mainly corresponded to areas in which the human activities of nonferrous metal smelting, cement clinker production, and mercury and other metal mining were conducted. Thus, we recommended measures that are targeted at the control of heavy pollution of rice grain by THg according to the pollution sources. In addition, we observed a wide spatial variation range of MeHg to THg ratios not only in China but also in other regions of the world, which highlights the potential risk of rice intake.
食用大米是人类接触汞的主要途径。为追踪中国大米汞的来源，我们采用单位网格质量守恒法，开发了一个网格分辨率为1千米×1千米的稻田汞迁移转化模型。2017年，中国大米中模拟的总汞（THg）和甲基汞（MeHg）浓度分别为0.08至243.6微克/千克和0.03至238.6微克/千克。全国大米平均THg浓度约81.3%归因于大气汞沉降。然而，土壤异质性，尤其是土壤汞含量的变化，导致各网格大米THg分布差异较大。全国大米平均MeHg浓度约64.8%归因于土壤汞。原位甲基化是大米中MeHg浓度增加的主要途径。高汞输入和甲基化潜力的共同影响导致贵州省部分网格以及与周边省份交界处的大米中MeHg含量极高。土壤有机质的空间变化对各网格的甲基化潜力有显著影响，尤其是在中国东北地区。基于高分辨率的大米THg浓度，我们确定0.72%的网格为THg重度污染网格（大米THg>20微克/千克）。这些网格主要对应有色金属冶炼、水泥熟料生产以及汞和其他金属开采等人类活动区域。因此，我们根据污染源提出了针对性控制大米THg重度污染的措施。此外，我们观察到不仅在中国，而且在世界其他地区，MeHg与THg的比值在空间上变化范围也很大，这凸显了食用大米的潜在风险。
