珠江三角洲铊在水稻籽实-根系土间迁移及人体健康风险评价

Thallium(Tl)Migration Between Rice Grains and Root Soils and an Assessment on Human Health Risk in the Pearl River Delta

铊(Tl)是一种典型的剧毒重金属元素,其环境行为及人体健康效应日益得到广泛关注,土壤Tl富集会对土壤环境、农作物生长及人体健康造成严重的危害性。珠江三角洲作为土壤重金属富集的典型区域,当前研究主要聚集于Cu、Cd、Pb和As等元素,而对土壤Tl的地球化学特征及其影响因素、生物富集能力及人体健康效应评价的研究较少。本文以珠江三角洲3种成土母质分布区的243套水稻籽实及其根系土样品为研究对象,揭示了水稻根系土Tl含量、生物富集特征及其影响因素,并采用美国环保署(US EPA)推荐的人体健康风险评价模型对研究区土壤Tl的人体非致癌健康风险进行评价。结果表明:水稻根系土Tl含量显著高于我国和广东省土壤Tl含量背景值,18.1%的水稻根系土Tl含量超过加拿大Tl环境质量标准值及瑞士农业土壤Tl标准值(1×10^(-6))。酸性岩浆岩与第四纪沉积物分布区水稻根系土Tl超标率明显高于陆源碎屑岩。水稻根系土Tl含量表现出与K_(2)O、Al_(2)O_(3)、Pb和Zn含量显著相关。综合分析认为珠江流域硫化物矿床风化剥蚀及开采活动是导致下游平原区土壤Tl等重金属元素富集的主要原因。全区20件水稻籽实Tl含量的平均值为0.35×10^(-3),均远低于德国食品安全规定的Tl可食用标准值,水稻籽实Tl生物富集系数主要与根系土Na_(2)O、Zn和Pb含量显著相关。每个样点的HQ值分级结果显示,研究区68%的儿童有中等健康风险,46%的成人有中等健康风险,儿童健康风险显著高于成人。

Thallium(Tl)is a typical toxic heavy metal element,and its environmental behavior and effects on human health recently have attracted more attentions.However,only a few studies have been conducted previously on the geochemical characteristics,influencing factors,biological enrichment capacity,and assessment on human health risk of soil Tl in the river delta.Totally,243 samples of rice grains and root soils from three parent material areas in the Pearl River Delta were collected and measured.The concentrations,bio-concentration characteristics,and influencing factors of the Tl in the root soil were futher investigated.A human health risk assessment model recommended by the United States Environmental Protection Agency(USEPA)was used to evaluate the human non-carcinogenic health risk.The results show that the Tl concentration in the root soil is significantly higher than the values of Chinese soil background and Guangdong soil background.18.1%of rice root soil samples exceed the standard values of Canadian Tl environmental quality and the Swiss agricultural soil Tl(1×10^(-6)).The excess rate of Tl in the root soil in quaternary sediments and acid magmatic rocks is significantly higher than that in terrigenous clastic rocks.The Tl concentration in root soil is closely correlated with the K_(2)O,Al_(2)O_(3),Pb,and Zn contents.The main reason for the enrichment of soil Tl and other heavy metal elements in the lower Pearl River plain is due to the weathering denudation and mining activities of sulfide deposits in the Pearl River catchment.The average Tl concentration of rice grains is 0.35×10^(-3),which is far lower than the edible standard value of Tl in German food safety regulations.The bioconcentration coefficient of Tl in rice grains is closely correlated with the contents of Na_(2)O,Zn,and Pb in the root soil.HQ values of each sample show that 68%of children had moderate health risk;46%of adults have moderate health risks,indicating children have significantly higher health risks than adults in the study area.