【作者】 李秀娟；

【导师】 靳孟贵；

【作者基本信息】 中国地质大学 ， 地下水科学与工程， 2010， 硕士

【摘要】 中国地质调查局先后在长江流域的四川、重庆、湖北等9个省及直辖市进行了调查,结果发现从长江源头的沱沱河直至长江入海口、沿江及两岸平原区出现宽度达几十至数百公里贯穿全流域的镉等重金属异常带。“五毒之首”的镉元素是一种危险的有害物质,在环境系统中迁移较为活跃,是作物极易富集的重金属元素之一,不仅会导致作物减产和品质下降,而且会通过食物链进入人体,严重威胁着人体健康。黄石市位于湖北省东南部、长江中游南岸,是我国中部地区重要的原材料工业基地和国务院批准的沿江开放城市、长江经济开发带的重要支点、武汉城市圈的副中心城市和鄂东区域经济龙头。黄石市郊沿江冲积农田主要种植蔬菜和粮食,其镉含量及上面生长的作物(主要为蔬菜)是否受到Cd的污染,是否符合国家食品卫生标准,这方面的报道比较少,特别是该区土壤对镉的吸附特征、土壤水中镉的含量及土壤镉的生物有效性方面的研究几乎没有。因此,本文以黄石为例,研究土-水-作物系统中镉的分布特征,探讨土壤镉的生物有效性,为在研究区合理布局种植结构、建设无公害蔬菜以及镉的污染防治提供科学依据。通过实地调查,在黄石沿江典型地段的作物地及下陆区杨家畈蔬菜生产基地用无锈钢铁铲采集表层土壤样36个,同时用土壤水分计(MPM-160, Australia)测定土壤含水量；用麻花钻钻取剖面7个,分别在距土壤表层20、40、60、80、120、160cm处采集土样；在对应采集了表层土样的14个点埋置自制陶土头式土壤水取样器28根(每个点2根),野外定期用真空泵抽取其中的土壤水；并在采集了表层土样的相应点采集成熟的作物样,有高粱、玉米、辣椒等,都分为根、茎、可食部分(本文主要指果实)。室内测定分析了所有土样、土壤水样和作物样中镉的全量；用tessier连续浸提法测定了22个表层土样不同形态的镉含量,用常规分析方法对其基本物理化学性质,如土壤pH、有机质、颗粒组分、阳离子交换量等进行了测定分析；并选取4个土样作为代表,进行了镉的吸附-解吸实验。参照国家土壤环境质量二级标准和大冶有色金属冶炼厂附近A层土壤的背景值尝试评价了土壤镉富集和污染程度；研究了土壤中镉赋存形态分布及其与土壤理化性质的关系；分析了土壤镉的静态吸附、解吸特征及影响因素；讨论了不同作物对土壤中镉的吸收富集及同一作物不同部位镉的分配情况；探讨了土壤镉的生物有效性；依据国家标准食品中镉限量值及国际辐射防护委员会(International Commission Radiological Protection, ICRP)推荐的最大可接受风险水平和我国居民平均食物消费结构评价了这些农产品对于当地人群的潜在健康风险,初步提出了研究区镉危害的一些预防措施。主要研究结论如下：1.研究区36个表层土壤样的镉含量均高于国家土壤环境标准的二级标准值,为轻度-重度污染(异常)。黄石下陆区杨家畈蔬菜生产基地土壤镉在表层(0-20cm)有明显累积现象,随着深度增加,镉含量递减,深度大于2米时降至1mg/kg以下。2.研究区土壤中各形态镉平均含量为残渣态>铁锰氧化物结合态>碳酸盐结合态>有机质结合态>可交换态。生物不可利用态镉和生物潜在可利用态镉含量较高,可利用态镉含量很低。交换态镉与有机质结合态镉关系最密切,土壤总镉的增加在一定程度上会造成可交换态镉含量的增加,会显著影响残渣态镉及铁-锰氧化物结合态含量。对研究区土壤总镉含量及不同形态镉含量影响显著的环境因子主要是土壤pH、有机质含量和粘粒含量。3.研究区潮土对镉的吸附等温线均可用Langmuir方程、Freundlich方程和Temkin方程来描述,总体看Langmuir方程拟合效果更佳。解吸镉的数量随吸附量的增加而增加。在实验条件下,Cd的吸附和解吸过程都可分成两个阶段,40min之前的快反应和60min之后的慢反应。土壤对镉的吸附很大程度上受到土壤有机质含量、阳离子交换量、土壤粘粒和粉粒所占比例的控制。研究区土壤对镉的吸附潜力较大。4.不同作物对镉的吸收富集能力不同,同一作物的不同部位对镉的富集能力也存在较大差异。空心菜和茄子、辣椒等茄果类蔬菜较易富集镉,而高粱、玉米等粮食类作物和豆类作物不易富集镉。作物不同部位Cd的总体分布特征为根部>茎部>可食部分。镉在作物内的总体迁移能力为根部一茎部>茎部一可食部分。研究区作物中空心菜、辣椒和茄子已受到污染,存在轻微的健康风险,其他蔬菜和粮食类作物都较为安全,不存在健康风险。5.研究区土壤水中镉含量很低,基本上小于国家农业灌溉水标准中的镉限定值5μg／L。土壤水中镉,浅部比深部稍高；少雨秋季比多雨夏季高；下陆杨家畈蔬菜生产基地土壤水中的镉含量(如SW0314 7.67μg／L)大于黄石沿江作物地土壤水中的镉含量(如SW03070.60μg／L)。6.作物根部和茎部吸收的镉主要与土壤可交换态镉、铁锰氧化物结合态镉、碳酸盐结合态镉和土壤总镉的含量密切相关,而可食部分的镉含量与土壤各形态镉相关性不明显,与土壤水中镉的含量显著正相关。表明土壤水的镉具有较高的生物有效性,土壤总镉含量只能初步指示镉的生物有效性大小,土壤可交换态镉、铁锰氧化物结合态镉和碳酸盐结合态镉含量是研究区镉生物有效性大小的重要指标。7.研究区土壤镉异常已经对研究区作物的安全造成了一定影响,建议有关部门予以高度关注并采取有效应对措施,如严格规范工矿企业的排放标准,鼓励农民多施用有机肥料少用废水进行灌溉等等。更多还原

【Abstract】 China Geological Survey conducted investigations in 9 provinces and municipalities along the Yangtze River such as Sichuan, Chongqing, Hubei and so on, and found that there was abnormal belt of cadmium and other heavy metals with width of tens to several hundred kilometers through the whole drainage basin, from the Tuotuo River to the Yangtze River estuary and in the plains along the Yangtze River. As"the first of five evils", cadmium is a dangerous harmful substance, it migrates actively in the environment system, is one of the highly enriched heavy metals in crops. It not only leads to decreased crop yields and quality, but also comes into the human body through the food chain, which is a serious threat to human health.Huangshi City located in the southeast of Hubei Province and the south bank of the midstream of the Yangtze River, is an important raw material industrial base in Central China and the open city approved by State Council, an important fulcrum of economic development zone along the Yangtze River, deputy central city of Wuhan city circle and economic leader of eastern regional of Hubei province. In alluvial farmland along the Yangtze River in the outskirts of Huangshi City, the main crops are vegetables and grains. Reports about if the soils and growing crops (mainly vegetables) are subject to Cd contamination and meet the national food hygiene standard are relatively little, especially the adsorption characteristics of cadmium in the soil of the area, the content of cadmium in soil water and cadmium bioavailability of the soil are hardly researched. Therefore, taking Huangshi City as an example in this paper, we studied distribution characteristics of cadmium in soil-water-crop system, explored and discussed the bioavailability of Cd in the soil, provided scientific basis for citizens in Huangshi City on rational layout of planting structure, pollution-free vegetables construction and cadmium contamination prevention.Through field investigation, in farmlands of typical section along the Yangtze River and Yang Jiafan vegetable production base of Huangshi City, we collected 36 surface soil samples with a rust-free steel blade, measured soil water content using soil moisture meter (MPM-160, Australia) at the same time; digged 7 soil profiles with a twist drill, sampled the soil at the depth of 20,40,60,80,120,160 cm from the soil surface respectively; embedded 28(two for one site) homemade soil water samplers of pottery clay head type at the corresponding 14 sites collected surface soils, sampled soil water with vacuum extraction regularly in field; and collected mature crops like sorghums, maizes, hot peppers, etc, at the corresponding sites collected surface soils, which were divided into roots, stems, edible parts (here mainly refer to the fruits). Indoor cadium contents of all soil samples, soil water samples and crop samples were measured and analyzed; with tessier sequential extraction method, the contents of different speciations of cadmium of 22 surface soil samples were determined, with conventional analysis methods their basic physical and chemical properties, such as soil pH, organic matter, particle composition, cation exchange capacity, etc, were determined and analyzed; and selected four soil samples as representative for the cadmium adsorption-desorption experiment. Levels of cadmium accumulation and contamination were assessed according to national soil environmental quality standard and the background value of Cd in A layer of the soil near Daye Nonferrous Metal Smelter; studied distribution characteristics of speciations of cadmium in the soil and the relationship with the soil properties; analyzed static adsorption-desorption characteristics of cadmium of the soils and their influence factors; discussed about the absorption and accumulation of the cadmium of different crops and distribution characteristics of the cadmium in different parts of them; explored and discussed about Cd bioavailability in the soils; evaluated the potential risk of these crops to local people health according to the limited value of cadmium in national food hygiene standard, maximum acceptable level of risk recommended by International Commission Radiological Protection and the average consumption structure of these agricultural products of Chinese residents, preliminaryly putted forward some preventive measures against cadmium harm for the study area. The main conclusions are as follows:1.The cadmium contents of 36 soil samples in the study area are all above second-level standard value of the national soil environment standard, appeare mild to severe contamination (abnormity). Cadmium is significantly accumulated in surface soils (0-20cm) of Yang Jiafan vegetable production base in Huangshi City, with the depth increase, the content of cadmium decrease, when the depth is more than 2 meters, the content of cadmium is lower than 1mg/kg.2.The average contents of different speciations of cadmium in the soils of the study area follow the order of residual>Fe-Mn oxides bound>carbonate bound>organic bound>exchangeable. The contents of speciations of cadmium which are unavailable and potentially available to biology are relatively high, while that of the available speciation is very low. Exchangeable Cd and organic bound Cd are closely related, with the increasing in total cadmium of the soil, the content of exchangeable cadmium increases to a certain extent, and it significantly influences the contents of residual cadmium and iron-manganese oxides bound cadmium. The environmental factors that significantly influence the content of total cadmium and different speciations of cadmium are mainly soil pH, organic matter content and clay content.3.Cd adsorption isotherms of the soils in the study area all can be described by Langmuir equation, Freundlich equation and Temkin equation, overall Langmuir equation fits better. With the quantity of adsorbed cadmium increased,desorbed cadmium is also increased. Under the experimental conditions, Cd adsorption and desorption process can be divided into two stages, the fast reaction stage before 40min and the slow stage after 60min. The content of Cd adsorbed by the soil are mianly controlled by organic matter content, cation exchange capacity, soil clay and silt. The potential ability to adsorb Cd of the soil in the study area is relatively strong.4.Accumulation ability of cadmium of different crops are different, that of different parts of the same crop are also quite different. Water spinaches and eggplants, hot peppers and other fruit vegetables are easy to accumulate cadmium, while sorghums, corns and other grain crops and legumes are not. In general, the contents of Cd in different parts of crops follow the order of roots>stems>edible parts. The overall migration ability of cadmium in crops are roots-stems> stems-edible parts. Water spinaches, peppers and eggplants in the study area, have been contaminated, which have slight health risk, other vegetables and grain crops are relatively safe, having no health risk.5.The content of cadmium in soil water of the study area is very low, basically less than the limited value 5ug/L of national agriculture irrigation standard. Cadmium in soil water appear that the cadmium content of the deep is slightly higher than the shallow; in dry autumn higher than in rainy summer; in Yang Jiafan vegetable production base higher (for instance SW0314 7.67μg/L) than in farmlands along the Yangtze River (for instance SW0307 0.60μg/L).6.The contents of cadmium absorbed by crop roots and stems are closely related to that of exchangeable cadmium, iron-manganese oxides bound cadmium, carbonate bound cadmium and total cadmium in the soil, while the contents of cadmium in edible parts are not that related to all the speciations of cadmium in the soil, but are significantly positively correlated to cadmium in soil water. It showes that cadmium in soil water has a relatively high bioavailability, total cadmium content of the soil is just initial indicator of the cadmium bioavailability, exchangeable cadmium, iron and manganese oxides bound cadmium and carbonate bound cadmium are important indicators of cadmium bioavailability in the study area.7. Cadmium abnormity in the soil of the study area has influenced the safety of crops to some degree, it is recommended that relevant departments pay high attention to and take effective countermeasures to control the food safety in the area, such as setting up strict emission standards for industrial and mining enterprises, encouraging farmers to use more organic fertilizer and less wastewater for irrigation and so on.更多还原