基于DGT和化学提取法研究浙西北地质高背景区土壤镉生物有效性

Cadmium Bioavailability Based on Diffusive Gradients in Thin Films Technique and Conventional Chemical Extraction in High Geological Background Soil Area of Northwestern Zhejiang Province,China

地质高背景区相较于人类活动引起的土壤镉污染影响范围更广,在区域尺度上对生态系统和人类健康构成危害。土壤镉生物有效性是决定其生物可利用性、生物毒性的关键因素,因此探寻可行的土壤镉生物有效性评价方法对污染农用地安全利用和风险管控具有重要的理论和实际意义。DGT技术、单一提取法、连续提取法和土壤溶液法常用于测定土壤有效镉,但已有研究成果主要基于同种土地利用类型土壤的室内盆栽实验,难以代表自然污染土壤中的复杂情况。为探明各土壤重金属有效态提取技术对地质高背景区不同土地利用类型土壤Cd生物有效性评估效果,本文以浙江西北部土壤Cd高地质背景区水田土壤-水稻籽实和旱地土壤-小白菜样品为研究对象,实验应用DGT技术、单一提取法(0.01mol/L氯化钙提取)、连续提取法(七步连续提取)和土壤溶液法评价土壤中镉生物有效性。结果显示:①研究区水田和旱地土壤Cd平均含量分别为1.07mg/kg和0.73mg/kg,显著高于浙江和全国土壤平均水平,Cd的异常富集主要与浙西北地区广泛分布的黑色岩系有关。②相较于碳酸盐岩区,黑色岩系区土壤中Cd的生物有效组分占比较高,水田和旱地土壤Cd的活动系数(MF)高达59.9%和51.8%,Cd易在土壤-作物系统中发生迁移富集;③植物体内镉含量Cd-P与不同方法测定的有效镉含量均呈显著正相关,但Cd-P与DGT技术测定的有效镉含量相关性优于其他三种方法,水田土壤测得的有效Cd与水稻籽实相关关系:C_(soln)>C_(DGT)>C_(Cacl_(2))>C_(F_(1)+F_(2)+F_(3)),旱地土壤测得的有效Cd与小白菜相关关系:CDGT>C_(Cacl_(2))>C_(F_(1)+F_(2)+F_(3))>C_(soln)。综合比较不同土壤有效Cd测定方法的优缺点,DGT技术可以模拟植物体对Cd的动态吸收过程,更能准确地反映土壤Cd生物有效性,预测作物Cd含量水平,这与已有研究成果一致。此外,本文研究成果表明DGT技术评价土壤Cd生物有效性,不仅适用于人为污染区,也可应用于地质高背景区。

BACKGROUND:High geochemical background has a greater impact on soil Cd pollution than human activities and is more detrimental to the environment and human health on a regional level.Research shows that the bioavailability of Cd in soil is the key factor to determine its bioavailability and biotoxicity,so it is of great theoretical and practical significance to find an effective method to evaluate the bioavailability of Cd in soil for the safe use and risk control of contaminated agricultural land.Single extraction methods with relatively simple operation and relatively low cost and sequential extraction methods providing morphological distribution feature information,are the most common methods for evaluation of heavy metals bioavailability in soil.In general,the available amount of soil heavy metals obtained by chemical extraction methods can better reflect the level of plant absorption than the total amount.However,chemical extraction methods have some drawbacks,including differences between the extraction principle and crop absorption process,a lack of universality in the extracts,redistribution and re-adsorption during the extraction process,and most notably,the failure to take into account dynamic changes in heavy metal concentrations in the root environment.Diffusive gradients in thin-films(DGT)technique is a new biomimetic in-situ sampling technique,which has been widely used to assess the bioavailability of various elements in soil,water,sediment and other environmental media in recent years.The process of DGT absorbing target elements is similar to plants absorption,which can better reflect bioavailability.However,existing research results using DGT to evaluate soil Cd pollution is mainly based on indoor pot experiments.Exogenous addition of heavy metals to contaminated soil not only has high bioavailability,but also reduces the sensitivity of soil pH and other factors to the bioavailability of heavy metals in soil,which does not accurately represent the complex situation in naturally contaminated soil.It is not clear whether the results of DGT can accurately reflect the bioavailability of soil Cd in high geological background areas.In order to confirm whether DGT technology can effectively evaluate the bioavailability of soil Cd in high geochemical background areas when compared to existing chemical extraction methods,80 sets of paddy soil-rice and 20 sets of dry soil-bok choy samples were collected in the black shale area of Northwest Zhejiang Province.The DGT technology,0.01mol/L CaCl_(2)extraction method,seven-step extraction method and soil solution method were used to evaluate the bioavailability of Cd in soil.Inductively coupled plasma-mass spectrometry(ICP-MS)was used to determine Cd content and available Cd in soil and crop.Soil pH was determined by potentiometry(POT),and soil organic matter(OM)was determined by oxidation combustion potentiometry(POT).The migration and accumulation characteristics of Cd in a soil-crop system were analyzed.The evaluation effects of different bioavailability evaluation methods were compared by the correlation between available Cd and crop Cd content.