A Study Of Cadmium Ecological Security Forecasting And Early Warning In Agroecosystem Of The Chengdu Economic Region, Sichuan

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.