稻田土壤Cd污染与安全种植分区:以重庆市某区为例

水稻对土壤中Cd的富集积累能力强，开展稻田土壤Cd污染与安全种植分区研究对于区域土地有效利用具有重要意义.在重庆市某区22个镇同步采集稻田土壤-水稻样品300套，测定土壤pH、Cd全量和有效态含量、糙米Cd含量，采用地累积指数、生物富集系数和单因子污染指数评价土壤Cd污染状况；结合土壤和糙米Cd污染指数进行水稻安全种植分区.结果表明，研究区稻田土壤总体偏酸性，Cd全量为0.09~1.60 mg ·kg^-1，超过风险筛选值的点位占35.0%；糙米Cd含量为0.002~0.808 mg ·kg^-1，超过食品安全限量值的点位占13.7%.Pearson相关分析表明，糙米Cd含量与土壤Cd全量、有效态Cd含量均呈极显著正相关（P<0.01）.污染评价显示，稻田土壤呈现明显的Cd累积，部分土壤表现为轻-中度污染；糙米对土壤Cd的富集系数为0.004~1.72.研究区稻田土壤总体为安全或基本安全，低风险区在南部、西部和东部均有分布；中高风险区面积较小，主要分散在8个地区.

Cd Pollution and Safe Planting Zoning in Paddy Soils: A Case Study in a District of Chongqing

Rice has a strong ability to accumulate Cd in soil, and it is of great significance to study Cd pollution and safe planting zoning in paddy soils. In this work, 300 sets of paddy soil-rice samples were simultaneously collected in 22 towns in a District of Chongqing, and soil pH, soil total and available Cd contents, and brown rice Cd contents were determined. Soil Cd pollution was assessed using the geoaccumulation index, bioconcentration factor, and the single-factor pollution index. Based on the Cd pollution indices of soil and brown rice, safe planting zoning for rice was determined. The results showed that the paddy soils were generally acidic, and total Cd contents ranged from 0.09 mg·kg^-1 to 1.60 mg·kg^-1, with 35.0% of sites exceeding the risk screening value. The Cd contents of the brown rice ranged from 0.002 mg·kg^-1 to 0.808 mg·kg^-1 and exceeded the food safety limit in 13.7% of cases. Pearson correlation analysis showed that the Cd content of brown rice was significantly positively correlated with soil total and available Cd (P<0.01). The pollution evaluation indicated that significant Cd accumulation occurred in the paddy soils, with some areas showing light-to-moderate pollution levels. The enrichment coefficients of rice to soil Cd ranged from 0.004 to 1.72. Overall, the paddy soils in the studied area were considered generally safe with respect to Cd pollution, with low-risk areas distributed in the south, west, and east, whereas some medium-high risk areas were detected in eight towns.