Cd元素在土壤–水稻系统中的富集和分布

Enrichment and Distribution of Cd Elements in Soil-Rice Plant System

摘要: 本文选取四川某地为研究区，配套采集了33套水稻土壤和水稻植株样本，分析测试了水稻籽实、茎、叶三部分以及对应土壤中Cd元素的含量；同时测试了土壤中Cd元素不同赋存形态的分量数据。通过对以上数据的分析处理，得出以下结论：该区域水稻中Cd元素超标率达到84.8%，最高达11.85 mg/kg，已经超过了国家食品卫生标准的59倍；从富集情况看，Cd从土壤迁移到水稻各部分迁移能力为籽实 > 茎 >叶；从土壤中Cd的相态来看，离子交换态和水溶态占全量的30.62%，碳酸盐结合态在弱酸性环境下容易释放出来被吸收，占比也达到了8.45%，对于水稻作物来讲，具有一定的安全威胁；从相态的变异系数来看，只有水溶态以及残渣态均超过了50%，尤其是水溶态，达到了152.5%，显示出这两种相态在土壤中分布不均匀；理论上，当样本数量增加到45个，籽实中Cd与土壤中水溶态相关性达到显著正相关；土壤中pH值与水稻茎、叶、籽实以及地上部分均呈负相关，与土壤中Cd含量显著正相关，结合土壤中Cd形态与pH和有机质的相关性分析，pH升高，碳酸盐结合态、腐殖酸结合态、铁锰结合态、强有机结合态均有较大程度的提高，水溶态降低；提高有机质含量有助于降低土壤中Cd活跃形态，同时降低地上部分中Cd含量。

Abstract: 33 sets of paddy soil and rice plants were sampled from a certain place of Sichuan province. Cadmium contents in these rice plant samples, including their rice seeds, stems, leaves, and their corresponding soil system have been analyzed and tested. Component data of cadmium elements in different forms have been screened as well. Based on the data mentioned above, the following conclusions can be drawn: 84.8% of cadmium contents in the rice plants samples were above the regulatory limits, and the maximum cadmium level reached 11.85 mg/kg, 59 times higher than the National Quality Standard for food. In terms of the enrichment, migration abilities of cadmium from soil to 3 parts of rice plants in descending order were: seeds, stem, and leaf. In terms of phase distribution, ion-exchangeable and water-soluble cadmium make up 30.62% of the total cadmium. Carbonate cadmium that was easily released and absorbed in weak acidic environment became security threats to the rice crops, accounting for 8.45%. The coefficient of variation of phase state showed that only the water-soluble and residua were more than 50% and cadmium in water soluble state was most impressive, up to 152.5%. It showed the two phases were not distributed uniformly in the soil. When the amount of samples increases to a certain extent, cadmium element in the rice seeds was directly proportional to the water-soluble. pH of soil was negatively correlated to rice stems, leaves, seeds and the aboveground and was positively correlated with cadmium content. A correlation analysis of cadmium phases, pH and organism showed that the carbonate, humate, iron-manganese and organic increased a lot as pH increased, while the water-soluble decreased as pH increased. The increase of organic matter content contributed to decrease active phases of cadmium in soil, and decreased cadmium content in the aboveground parts as well.