【作者】 汤奇峰；

【导师】 张本仁； 杨忠芳；

【作者基本信息】 中国地质大学（北京） ， 地球化学， 2007， 博士

【摘要】 土壤镉(Cd)污染问题自首次报道以来,就因为Cd极大的生理毒害性而引起了人们的极大关注。研究表明,土壤Cd经作物富集,并由食用而被人体摄入是引起人体健康危害的主要途径。随着工业化、城市化的进程加快,土壤表层Cd大量增加,对生态系统的安全已经构成一定危害。因此对土壤Cd的生态安全性进行预警研究具有重要意义,同时这也是一项跨学科、具有挑战性的重要课题。本文在查阅大量文献的基础上,提出了一套较为完整的土壤重金属生态安全预警模式,系统地阐述了生态安全及预警的基本理论和内容,明确了生态风险评价-预测-预警一系列较为合理的研究步骤,并综合运用地球化学、生态学、统计学等对四川省成都经济区农田系统Cd的生态安全性进行了未来趋势预测、预警。结果表明,成都经济区重金属Cd、Pb生态风险较高,Cd的风险指数在各地均超过1,是全区生态风险最高的重金属。农作物籽实Cd含量主要受控于土壤Cd和pH值,与土壤Cd成正比而与土壤pH成反比,土壤Cd含量增加或(和)土壤酸化均能造成作物Cd污染。土壤Cd通量研究表明,土壤表层Cd含量会持续增加,年均增长0.006 mg/kg。对大气干湿沉降和化肥的研究表明,土壤酸化速度明显,pH值年均降低0.02。参照不同的食物安全标准对作物籽实Cd含量危险程度进行的预警研究,对研究区的生态安全性水平进行了划分,目前红色警告区域约占0.7%,黄色预警、浅绿合格、深绿安全区域分别约占3%、15%和81%;未来数十年研究区警告、预警区域逐步扩大,而合格、安全区域大幅缩小,潜在生态风险显著增高。针对土壤Cd含量增加和土壤酸化问题提出了相应治理对策。本论文在解决实际问题和研究方法等方面都取得了新的进展,并为区域Cd污染的环境决策提供了科学依据。研究证明,通过对作物重金属进行生态风险评价能够较好的判断不同重金属的生态危害程度,便于挑选具有严重危险性的元素进行进一步的预警研究;土壤-作物体系元素迁移机理的研究揭示了两者之间的关联性,重金属相关方程的建立为预测作物Cd含量奠定了基础;通量研究和土壤酸化研究虽然可能存在不足之处,但是它们分别对土壤Cd和pH值的变化趋势进行了较好地预测;预警研究的分级标准较为合理,对成都经济区的生态安全性水平进行了较好划分,未来趋势令人担忧,土壤治理势在必行。更多还原

【Abstract】 The heavy metal cadmium (Cd) has been on the focus of attention since the first Cd pollution issue was reported, due to its vital physiological hazard. Studies appoint that oral intake of Cd-enriched crops is the main reason for human Cd risk. With the rapid progress of industrialization and urbanization, topsoil Cd content is greatly increasing, which has been inflicting stress onto the security of ecosystem. Hence, it is of great importance to study the early warning of soil Cd to ecosystem, which is also an interdisciplinary study with challenge.On the basis of volumes of reference work, a relatively integrated early warning model was put forward, the basic fundamentals of ecological security and early warning were systematically expounded, and a series of research steps, including ecological risk assessment, forecasting and early warning, were definitized. Accordingly, forecasting and risk assessment of cropland Cd in the Chengdu Economic Region (CER) of Sichuan was studied, with methodologies in disciplines of geochemistry, ecology, statistics and etc. Both cadmium and lead have relatively high risk in the CER, and Cd is the most dangerous heavy metal with risk index more than 1 all over the area. Cd concentration of crop grain is mostly controlled by both Cd concentration and pH value of soil, in direct ratio to soil Cd concentration and inverse ratio to soil pH value. Soil Cd concentration increase or/and soil acidification would result in crop Cd pollution. Cd flux in soil was studied and it shows that the topsoil Cd concentration would augment continuously with an annual increase of 0.006 mg/kg. The soil acidification is obviously rapid, with an annual decrease of 0.02, due to both atmospheric deposition and fertilization. Early warning of Cd in crop grain, based on different security standards of food, partitions the study area into plots of variant security levels, marked by colors of red, yellow, jade-green and bottle-green, indicating levels of warning, pre-warning, qualification and safety, respectively. At present, each plot of the 4 levels covers 0.7%, 3%, 15% and 81% of the whole area. However, the proportion of red and yellow plots would escalate and the green plots would shrink within decades. Some feasible measures are proposed to deal with the soil Cd increase and soil acidification.The study made new progress both in solving practical problems and in studying research approaches, and provided scientific foundations for decision-making of environmental management. Ecological risk assessment of heavy metals in crop grain works well in judging the risk levels of different heavy metals, and helps choose thehigh risk elements to carry out the future research of early warning. Element transportation in soil- crop system has its intrinsic relevancy, and thus the correlative equation of Cd has been established between soil and crop, making it possible to forecast the crop Cd concentration. The study of Cd flux and soil acidification accomplishes forecasting the Cd concentration and pH value of soil, although there might be insufficiencies. The classification of warning standards is reasonable and distinguishes the different levels of security, informing that the coming future is worrying and measures of remediation should be taken.更多还原