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三峡库区高镉地质背景区镉的表生富集特征与环境效应
刘意章
导师肖唐付
2014
学位授予单位中国科学院研究生院
学位授予地点北京
学位名称博士
学位专业环境科学
关键词 污染 自然地质源 迁移富集 健康效应
摘要镉(Cadmium, Cd)是一种典型的有毒有害重金属元素,其在环境中的来源主要为人为源;但在高Cd地球化学背景区域,自然源占主导因素。因此,研究典型高镉地质背景区Cd的区域环境地球化学,对丰富和深化Cd的环境污染研究是很好的补充。本论文选择位于三峡库区的巫山县建坪地区为研究区,系统采集了研究区的环境和生物样品,对表生环境中Cd的分布特征、来源、富集和迁移特征、环境健康效应等进行了深入研究,取得了以下研究成果和认识: (1)研究区出露的岩石均富集Cd元素,为明显的高Cd地质背景区;碳质泥页岩(平均值2.0 mg/kg)、黏土岩(平均值29 mg/kg)和石煤(平均值25 mg/kg)富集最为显著;黑色岩系Cd的富集可能与沉积时大量生物质的带入和还原环境等因素有关,Cd等金属元素可能以硫化物的形式存在。岩石中Cd的风化淋滤迁移与金属硫化物的风化有较好耦合关系,其风化产酸过程加速了Cd的活化迁移。 (2)研究区水体中Cd的含量(0.05-0.36 μg/L)低于我国饮用水安全限值(5 μg/L),但Cd在水系沉积物中富集(4.23-9.18 mg/kg),这与Cd在水-沉积物系统的迁移特性和沉积物来源有关。长江沉积物中Cd含量(0.84-0.87 mg/kg)要明显高于其历史值和背景值。 (3)研究区土壤中Cd超常富集,远高于我国土壤相应背景值;且Cd分布特征与成土母岩具有很好的地球化学继承性。土壤中Cd的分布规律为表层耕作土(均值7.1 mg/kg)>深层土(均值2.6 mg/kg)>自然土(均值2.0 mg/kg),研究区土壤Cd的分布规律受母岩风化和重力流作用等多重影响。典型土壤剖面中Cd在表层相对富集,可能与其中较高的有机质含量和植物泵等因素有关。研究区土壤中Cd的富集可能与土壤中黏土矿物和铁氧化物的吸附作用,以及有机质的吸附/络合作用有关。土壤中Cd的来源主要为自然地质源,而煤矿开采等人类活动加剧了土壤中Cd的富集。表层耕作土的污染水平为中度污染,单项生态风险因子为“很强生态风险”级别;综合生态风险指数为“中等生态危害”级别,其中Cd为最主要的贡献源。 (4)受成土母质、元素来源等多重因素影响,土壤中Cd主要以残渣态(平均41%)、可交换态(平均21%)和可还原态(平均21%)存在;具有较高的生物有效性,可能与Cd的低分配系数有关。 (5)土壤中高Cd含量及其较高的生物有效性导致农作物中Cd的富集(平均0.68 mg/kg);由于相对较高的生物富集系数,白菜(均值3.57 mg/kg)和甘蓝(均值1.12 mg/kg)中镉含量高于其他农作物,且远高于我国食品安全限值;食用大米中Cd含量(均值0.04 mg/kg)处于安全限值范围内。对蔬菜、粮食和饮用水进行摄入量和健康风险因子计算表明,Cd具有高的健康风险(HRI=4.62),其主要贡献源为本地农作物的摄入。 (6)研究区人群尿Cd含量(均值4.3 μg/L)远高于对照区(均值0.61 μg/L)和某些工业区人群;尿Cd含量无明显性别差异,但与年龄具有很好的线性关系。分析表明该区域Cd的主要暴露途径为本地农作物的摄入和富Cd煤的室内燃烧。 (7)研究区碳质泥页岩和石煤为F的主要地质载体,土壤中F的含量(均值1136 mg/kg)也远高于我国背景值(480 mg/kg),水体中F含量(0.18 mg/L)属于安全范围。岩石和土壤中Cd与F无明显相关性,但土壤总Cd与HCl提取态F具有很好的线性关系,岩石风化淋滤过程中F与Cd迁移规律有很好的相关性。虽然Cd和F的致病机理不同,但两者的主要暴露途径均为本地农作物的摄入;结合尿样分析结果,研究区地方病可能为一种新型的Cd-F慢性中毒地方病。 综上所述,本论文对研究区的系统研究表明,研究区为典型的高Cd地质背景区,岩石的风化淋滤等作用使得大量Cd元素进入土壤并富集,由于Cd的高生物有效性,导致在农作物中富集,并通过食物链摄入对人体健康产生了危害。研究区除地氟病外,还应关注居民的长期Cd暴露问题。
其他摘要Cadmium (Cd) is a typical toxic trace metal that poses high environmental risk. Anthropogenic contribution is generally the major source of Cd pollution in the environment. However, natural source may dominate in areas with high Cd geochemical background. Such that research on naturally-induced Cd contamination is a helpful supplement for better understanding of Cd contamination and associated environmental impacts in the environment. This thesis aims to study the distribution pattern, sources, migration, accumulation, and environmental health effects of Cd in a rural area with high Cd geochemical background, from Jianping area in the Three Gorges region. The following findings have been obtained from the study. The local outcroped rocks contained elevated Cd content, pointing to high Cd geochemical background of the study area. Among them, carbonaceous mudstone, siltstone and shale (mean at 2.0 mg/kg), claystone (mean at 29 mg/kg) and stone coal (mean at 25 mg/kg) showed higher Cd contents. The enrichment of Cd in black rock series was probably attributable for the abundant biological materials introduced and the reducing environment during geological deposited. Cadmium and other metals may be existed as sulfides in rocks. Mobility of Cd during rock leaching process was coupled with weathering of the sulfides, and the consequent acidic solution accelerated Cd release. Cadmium contents (0.05-0.36 μg/L) in the local waters were much lower than the safety limits (5 μg/L) of drinking water in China, but it was enriched in the sediments (4.23-9.18 mg/kg) because of higher mobility in the water-sediment system and the source of sediment. Cadmium contents in the collected sediments of Yangtze River (0.84-0.87 mg/kg) were significantly higher than the historical and background values of Cd in the Yangtze River catchment. The local soils significantly enriched for Cd, and the Cd contents were much higher than the background value of Chinese soil. The element distribution in soils showed clear geochemical inheritance with parent rocks. The Cd contents in soils decreased in the order of arable soils (mean at 7.1 mg/kg) > subsoils (mean at 2.6 mg/kg) > natural soils (mean at 2.0 mg/kg), which was mainly constrained by the weathering of parent rocks and gravity flows. Cadmium in soil profiles showed relative enrichment in top soil, which was probably related to high soil organic contents and plants absorption. Enrichment of Cd in local soils was probably contrained by the adsorption effects of clay minerals and Fe oxides, or by the adsorption or complexation of organic materials, or both. Geogenic source was the dominated origin of Cd in the local soils, and the anthropogenic activities, such as coal mining, additionally aggravated accumulation of Cd in soils. Contamination of Cd in arable soils was within moderate level, and the single ecological risk factor was classified as strong ecological risk grade. The comprehensive ecological risk index for Cd graded to moderate ecological risk level, for which Cd was the major contributor. The dominated fractions of Cd in soils were composed of residual (mean at 41%), exchangeable (mean at 21%) and reducible (mean at 21%) fractions, which pointed to high bioavailability of Cd, probably due to low partition coefficient of Cd. Cadmium was significantly accumulated in the local food crops (mean at 0.68 mg/kg), due to the enrichment and high bioavailability of Cd in soils. Cadmium concentrations in Chinese cabbage (mean at 3.57 mg/kg) and green cabbage (mean at 1.12 mg/kg) were higher than other crops, significantly higher than safety limits of Chinese food, due to the higher biological accumulation factors. However, the Cd contents in the locally consumped rice (mean at 0.04 mg/kg) was relative low, compared to the safety limits. Assessment of daily intake and health risks of vegetables, grain and drinking waters indicated that Cd posed high health risk (HRI = 4.62), for which the intake of v
学科领域环境地球化学
语种中文
文献类型学位论文
条目标识符http://ir.gyig.ac.cn/handle/352002/5896
专题研究生_研究生_学位论文
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刘意章. 三峡库区高镉地质背景区镉的表生富集特征与环境效应[D]. 北京. 中国科学院研究生院,2014.
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