镉(Cd)是我国农田土壤首要污染物,在南方一些地区稻米Cd超标严重,土壤Cd风险评估十分必要.采用长沙某地稻田土壤—糙米Cd点对点数据,通过生物富集系数(BCF)和Burr-Ⅲ物种敏感性分布(SSD)方程,构建了基于稻米食品卫生标准(GB2762-2012)和保护95%稻米品种的土壤Cd限值(HC5),探讨了HC5与土壤性质参数的量化关系和预测模型,并与我国土壤环境质量标准(GB15618-1995/2008)进行了比较.结果表明,pH、有机质(OM)和土壤全镉(TCd)对HC5影响显著,分别可控制HC5变异的62.2%、19.4%和18.3%.基于土壤pH和OM(TCd)的两因子模型能对HC5较为准确地预测,决定系数R2可达0.817(0.802).土壤pH、TCd与HC5呈正相关,而OM与之呈负相关.随着数值的增大,TCd和OM对HC5的影响降低,而pH影响相对稳定.本研究可为科学合理地进行稻田土壤风险管控及产地土壤环境质量基准研究提供一定依据.%[Objective]Cadmium(Cd)is the major pollutant in farmland soils of China,especially in South China,where the rice produced in certain areas is very high in over limit rate. It is,therefore, essential to perform soil Cd risk assessment and explore for major pathways of the food chain getting exposed to Cd pollution. Based on the point-to-point data of Cd in the soil and brown rice of a certain tract of paddy field in Changsha,the Food Health Standard for Rice(GB 2762-2012)and the research target of protecting 95% of the bio-species in the ecosystem,a threshold value for soil Cd was worked out using the biological concentration factor(BCF)and SSD(species sensitivity distribution)equations,quantitative relationships of HC5(hazardous concentrations)with soil properties and their prediction models discussed and studies done to compare the threshold value with the criteria for Cd in the Standard for Soil Environment Quality of China.[Method]Some foreign research institutions and scholars usually use BCF as an important parameter in assessing effect and variety of the pollutant,and HC5 as the concentration of a substance in soil being toxic to 5% of bio-species in the ecosystem,in other words,protecting 95% of the bio-species in the ecosystem. HC5 is the scientific basis for setting up soil environmental quality standards. In the present study,HC5 for Cd in soil was derived using the species sensitivity distribution method and the concept of BCF based on point-to-point field data from paddy soils. Prediction models for Cd crop safety thresholds based on soil properties were also developed and a function of soil physicochemical properties established.[Result]Results show that soil pH is the main soil factor affecting soil Cd food safety thresholds,and followed by organic matter (OM)content and total Cd(TCd),explaining 62.2%,19.4% and 18.3% of the variation of HC5 in paddy soil,respectively. The two-factor(soil pH and OM)prediction models can predict Cd crop safety thresholds quite accurately with determination coefficients(R2)ranging from 0.802 to 0.817,while the three-factor (soil pH,OM and TCd)prediction models are more accurate than the two-factor ones. With rising soil pH or TCd,HC5 increases in value,but the trend varies significantly. When the number of factors rises from two to three,the influence of TCd on HC5 decreases in degree,while the effect of pH does not vary much. In the test range,OM and HC5 show a certain negative relationship between the two. Soil Cd food safety thresholds vary with soil physical and chemical properties. The variation may lead to the the problem of insufficient protection and excessive protection at the same time,when the thresholds are used for controlling total Cd content by a single stage. In this study,a dynamic and quantitative food safety threshold model for Cd in soil was established.[Conclusion]The prediction models developed in the present study prove that quantitative relationships exist between soil properties and risk thresholds. And all the findings in this study are beneficial to developing and implementing soil specific,scientific and reasonable risk control of Cd in paddy soil and formulating regional soil environmental quality standards.
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