典型喀斯特地区土壤-作物系统镉的富集特征与污染评价

Characteristics of Cadmium Enrichment and Pollution Evaluation of a Soil-Crop System in a Typical Karst Area

为了研究喀斯特地区Cd在表层土壤和农作物中的富集特征及影响因素,为土地安全利用提供理论依据,选择在重庆市黔江区中部采集表层土壤样品360件、深层土壤样品7件、85件水稻样品和73件玉米样品(配套采集根系土样),分析了土壤及农作物中Cd的含量、土壤中TFe2O3、Mn、有机质(C_(org))、Se等含量和土壤pH.基于地统计法分析了表层土壤Cd的空间分布特征及富集原因,并对土壤及农作物进行了安全评价.结果表明,表层土壤Cd空间分布不均匀,且表层富集明显,表层土壤Cd含量受到成土母质和人为活动的控制,表层富集主要受到铁锰氧化物和有机质(C_(org))的影响.土壤Cd以无污染和轻度污染为主,部分区域存在强生态风险,污染区主要位于二叠系地层分布区,土壤Cd污染主要受到地质背景的控制.大宗农作物均存在一定程度的Cd轻微-重度污染,水稻的日均建议消耗量的限值为0.87 kg·d^(-1),玉米为1.53 kg·d^(-1).Cd的生物有效性受到土壤酸碱度和土壤Se含量的影响,酸性条件下Cd生物有效性高,土壤高Se区农作物较安全.建议在水田乡二叠系出露区种植Cd低累积作物,或通过调节土壤酸碱度,控制Cd的污染风险,实现土地安全利用.此外,优先选择在土壤高Se区种植农作物.

In order to study the characteristics and factors influencing Cd accumulation in surface soils and crops in karst areas,and to provide a theoretical basis for safe land use,360 surface soil samples,7 deep soil samples,and 85 rice samples were collected from central Qianjiang District,Chongqing.The samples and 73 corn samples(corresponding to root-zone soil samples),were analysed to determine the content of Cd,TFe2O3,Mn,organic matter(C_(org)),Se,and pH.Based on geostatistical analyses,the spatial distribution and Cd enrichment of the surface soils were determined and a safety evaluation for the soil and crops was carried out.The results showed that the spatial distribution of Cd in the surface soil was uneven,with the surface layer showing significant enrichment.This pattern was controlled by the soil parent material and human activities.The enrichment of surface layer was mainly affected by iron manganese oxides and organic matter(C_(org)).Soil Cd was mainly found at‘non-polluted’and‘lightly polluted’levels,although some areas present strong ecological risks.The main contaminated area occurs in association with Permian strata,demonstrating a geological control on soil Cd pollution.Slight-to-severe Cd pollution was identified in bulk crops;the recommended daily consumption limit for rice is 0.87 kg·d^(-1)and corn is 1.53 kg·d^(-1).The bioavailability of Cd is affected by soil pH and Se content.Under acidic conditions,Cd bioavailability is high,and crops in areas with high soil Se are safer.It is recommended that crops with low Cd accumulation are planted in the Permian outcrop area of Shuitian Township,or alternatively,soil pH should be adjusted to control the risk of Cd pollution and ensure safe land use.In addition,planting crops in areas with high soil Se content is preferable.