广东典型镉污染稻田土壤镉的生物有效性测定方法及风险管控值初探

为探寻适合广东省典型镉（Cd）污染稻田土壤镉生物有效性测定方法及其管控阈值，以广东韶关、清远和广州三种典型Cd污染稻田土壤为供试土壤，系统比较了四种有效Cd提取方法（CaCl₂法、HCl法、EDTA法和DTPA法）对土壤Cd的浸提能力，并分析两个品种水稻对Cd的累积吸收量与土壤有效Cd含量的相关性，探讨糙米Cd超过食品安全标准时各测定方法的风险管控值。结果表明，四种化学提取剂对土壤Cd的提取能力大小依次为0.1 mol·L^-1 HCl>0.05 mol·L^-1 EDTA>0.005 mol·L^-1 DTPA>0.1 mol·L^-1CaCl₂；外源添加条件下土壤Cd有效性高，土壤总Cd和各提取态Cd均与糙米Cd极显著相关（P<0.01），四种有效Cd测定值与水稻Cd累积量的相关系数均超过0.9，其中CaCl₂提取态Cd与水稻Cd含量的相关性更强，但自然污染型土壤全Cd含量与水稻Cd累积量的相关性最弱；根据各方法测定值与糙米Cd相关性计算获得了广东Cd污染稻田的风险管控值。采用四种有效Cd测定方法评价广东酸性稻田土壤Cd的生物有效性优于土壤全Cd的方法，其中CaCl₂提取法测定的结果与稻米Cd含量相关性最高，进一步深入研究可确立基于0.1 mol·L^-1 CaCl₂提取态Cd含量的稻田Cd污染风险管控阈值。

Comparison of Cd bioavailability determination methods and the risk control value of Cd for typical Cd-contaminated paddy soils in Guangdong

This study aimed to find a suitable method for determining the bioavailability and risk control value of cadmium(Cd) in typical Cd-contaminated paddy soils in Guangdong to provide technical support for the safe use of these paddy fields. Four available Cd extraction methods(CaCl₂, HCl, EDTA, and DTPA) were used and systematically compared for three typical Cd-contaminated paddy soil samples collected from Shaoguan (SG), Qingyuan (QY), and Guangzhou (NC) in Guangdong. Correlation analyses were performed on the Cd accumulated in the plant parts of two rice varieties and the available Cd content in soil. In addition, the risk control values of Cd were determined for each extraction method based on the food safety standard(0.2 mg ·kg^-1) of Cd in brown rice. The results showed that the extraction capacities of the four chemical extractants for soil Cd were 0.1 mol·L^-1 HCl > 0.05 mol·L^-1 EDTA > 0.005 mol·L^-1 DTPA > 0.1 mol·L^-1 CaCl₂. When Cd was artificially added, soil Cd availability was high. Both the total Cd content and available Cd content of soil were significantly correlated with the Cd content of brown rice(P<0.01), and the correlation coefficients between the available Cd in soil(i.e., HCl-Cd, EDTA-Cd, DTPA-Cd, and CaCl₂-Cd) and the cumulative Cd uptake by rice all exceeded 0.9, with that between CaCl₂-Cd and Cd uptake by rice being the highest. However, for the naturally polluted soils, the correlation between the total Cd content of soil and the cumulative Cd uptake by rice was weaker than that between the available Cd content of soil and Cd uptake by rice. According to the correlations between the total or available Cd contents of soil and the Cd content of brown rice, method-dependent risk control values of Cd were determined for Cd-contaminated rice fields in Guangdong. Soil available Cd, HCl-Cd, EDTA-Cd, DTPA-Cd, and CaCl₂-Cd provided better indicators of Cd bioavailability in the acidic paddy soils in Guangdong than the total Cd content of soil. Among HCl-Cd, EDTA-Cd, DTPA-Cd, and CaCl₂-Cd, CaCl₂-Cd had the strongest correlation with the Cd content of rice. Further in-depth research should be conducted on the development of pollution risk control values of Cd in paddy soils based on CaCl₂-Cd.