Liu Hanyi, Ling Yun, Liu Na, Chen Ying, Wei Shiqiang
College of Resources and Environment, Department of Environment Science and Engineering, Southwest University, Chongqing, 400715, China.
Chongqing Key Laboratory of Agricultural Resources and Environment, Chongqing, 400715, China.
Environ Sci Pollut Res Int. 2022 Dec;29(58):88008-88017. doi: 10.1007/s11356-022-21751-4. Epub 2022 Jul 12.
Regulating soil pH becomes a crucial practice to alleviate cadmium (Cd) contamination. However, little is known about the threshold of soil pH for the safe production of rice at various soil Cd levels. In this paper, the relationships between soil pH values and the contents of available Cd extracted by calcium chloride (CaCl-Cd) in neutral and acidic soils were studied by mandatory acidification with H addition or neutralization with lime at various soil Cd levels. The results showed that the soil CaCl-Cd contents dramatically decreased with increasing soil pH, and a logarithmic function could well describe the relations of soil CaCl-Cd contents and soil pH at constant total Cd (CaCl-Cd model). The Cd contents in rice grain (grain-Cd) in relation to soil CaCl-Cd was further established through modified rice pot experiments. A model for the prediction of Cd content in rice grains (grain-Cd model) was set up, though which the grain-Cd content could be predicted based on soil pH and total Cd content. 122 data pairs of rice grain-Cd contents obtained at various soil total Cd contents and pH were employed from the literature to verify the reliability of the established model, approximately 95.08% of those data favorably located within the 1:1 line ± 0.5 unit area of the grain-Cd model. Notably, this model can be applied to determine the thresholds of soil pH at a specific Cd pollution level. For instance, to achieve a rice grain-Cd contents matching the Chinese national food safety limit of 0.2 mg kg, the soil pH thresholds were estimated to be 5.05, 5.70, and 6.02 at soil Cd contents of 0.3, 0.6, and 0.8 mg kg, respectively. In addition, the established model can also be used to estimate the health risk from rice in broad regions with various soil pH values and Cd contents.
调节土壤pH值成为缓解镉（Cd）污染的一项关键措施。然而，对于不同土壤镉水平下水稻安全生产的土壤pH阈值，人们了解甚少。本文通过在不同土壤镉水平下添加H进行强制酸化或用石灰中和，研究了中性和酸性土壤中土壤pH值与氯化钙提取的有效镉（CaCl-Cd）含量之间的关系。结果表明，土壤CaCl-Cd含量随土壤pH值升高而显著降低，对数函数能够很好地描述在总镉含量恒定的情况下土壤CaCl-Cd含量与土壤pH值的关系（CaCl-Cd模型）。通过改良水稻盆栽试验进一步建立了水稻籽粒镉含量（籽粒-Cd）与土壤CaCl-Cd的关系。建立了一个预测水稻籽粒镉含量的模型（籽粒-Cd模型），通过该模型可以根据土壤pH值和总镉含量预测籽粒-Cd含量。从文献中选取了122组在不同土壤总镉含量和pH值下获得的水稻籽粒-Cd含量数据对，用于验证所建立模型的可靠性，其中约95.08%的数据位于籽粒-Cd模型1:1线±0.5单位面积范围内。值得注意的是，该模型可用于确定特定镉污染水平下的土壤pH阈值。例如，为使水稻籽粒镉含量符合中国国家食品安全限量0.2 mg/kg，在土壤镉含量分别为0.3、0.6和0.8 mg/kg时，土壤pH阈值估计分别为5.05、5.70和6.02。此外，所建立的模型还可用于估算不同土壤pH值和镉含量的广大区域水稻的健康风险。
