地块尺度重金属污染风险耕地安全利用区划方法

耕地安全利用是保证粮食安全，实现生态文明建设的重要举措之一.为解决污染风险耕地安全利用与修复治理过程中技术措施选择盲目的问题，在重庆市黔江区鹅池镇采集表层土壤样品244件和水稻-根系土样品100套，在分析土壤和水稻中Cd、Hg、Pb、As和Cr这5种重金属含量及土壤中氧化物、有机质和pH等指标的基础上，利用多元回归和地统计分析法建立预测模型，并为地块赋值，结合地块中土壤和水稻中重金属全量、土壤重金属有效态及土壤pH，给出相应的地块尺度耕地安全利用建议.结果表明，研究区土壤以酸性和强酸性为主，Cd超过土壤污染风险筛选值和管制值的比例分别为33.61%和2.05%，Cd有效态占比为60%，水稻Cd超标率为28%，研究区存在明显Cd的生态风险.土壤Cd有效态主要受到土壤Cd全量和pH的影响，水稻中Cd的富集主要受到土壤有机质、Mn和CaO含量的影响.区划结果显示，研究区土壤以优先保护类为主，占比为59.30%；安全利用类占比为40.44%，其中安全利用（IAa）、安全利用（IAb）、安全利用（IBa）、安全利用（IIAa）、安全利用（IIAb）、安全利用（IIBa）占比分别为19.49%、8.01%、1.43%、7.04%、1.41%和3.06%；严格管控类占比为0.26%.该方法将土壤及农产品的安全风险相结合，并针对性给出安全利用建议，为因地制宜地开展受污染耕地安全利用工作提供了方法参考.

Zoning and Safe Utilization Method of Heavy Metal Contaminated Cultivated Land at Block Scale

The safe use of arable land is one of the important measures to ensure food security and to realize the construction of ecological civilization. In order to solve the problem of blindly selecting technical measures in the process of safe use and restoration of pollution-risk cultivated land, 244 surface soil samples and 100 sets of rice-root soil samples were collected in Echi Town, Qianjiang District, Chongqing. Based on the contents of five heavy metals of Cd, Hg, Pb, As, and Cr, as well as soil oxides, organic matter, and pH and other indicators, a prediction model was established using multiple regression and geostatistical analyses, and the plots were assigned values, combined with the soil and soil in the plots. The total amount of heavy metals in the rice, the available content of heavy metals in the soil, and the pH of the soil guided suggestions for the safe use of cultivated land at the corresponding plot scale. The results showed that the soil in the study area was mainly and strongly acidic. The percentages of Cd exceeding the soil pollution risk screening value and control value were 33.61% and 2.05%, respectively. The effective content of Cd accounted for 60%, and the Cd exceeding rate of rice was 28%. There was an obvious ecological risk of Cd in the study area. The available Cd content of the soil was mainly affected by the total amount of soil Cd and pH. The enrichment of Cd in rice was mainly affected by the content of soil organic matter, Mn, and CaO. The zoning results showed that the priority protection category of the soil in the study area accounted for 59.30%; the safe use category accounted for 40.44%, of which safe use (IAa), safe use (IAb), safe use (IBa), safe use (IIAa), safe use (IIAb), and safe use (IIBa) accounted for 19.49%, 8.01%, 1.43%, 7.04%, 1.41%, and 3.06%, respectively; and strict control accounted for 0.26%. This method combined the safety risks of soil and agricultural products and aided formation of specific recommendations for safe use, which provided a method of reference for the safe use of contaminated farmland in accordance with local conditions.