无机钝化剂对镉污染酸性水稻土的修复效果及其机制

以浙江南部重金属镉（Cd）轻度污染酸性稻田为对象，以当地应用最广泛的3种无机钝化剂（硅钙镁钾肥、钙镁磷肥和石灰）为材料，通过田间试验研究了不同用量（750、1500和2250 kg ·hm^-2）钝化剂阻控土壤酸化与稻米Cd积累的效果与化学机制.结果表明，3种钝化剂可有效地改良土壤酸化和降低水稻稻米Cd积累，施用2250 kg ·hm^-2硅钙镁钾肥、钙镁磷肥和石灰分别增加土壤pH值0.62、0.65和0.86单位，减少交换性酸总量67%、69%和78%，降低糙米镉含量73%、68%和77%.施用2250 kg ·hm²钝化剂可使Cd轻度污染稻田上种植水稻糙米中ω（Cd）低于0.2 mg ·kg^-1，达到国家食品安全标准；与对照比较，3种钝化剂均显著降低土壤中DTPA提取有效态镉含量，降低弱酸提取态（F1）和可还原态（F2） Cd含量，增加残渣态（F4） Cd含量；相关分析表明糙米Cd含量与土壤pH与交换性阳离子含量呈显著负相关，与DTPA-Cd、F1-Cd、F2-Cd和交换铝含量呈显著正相关.应用最小二乘路径模型分析了糙米Cd含量、Cd有效性和化学形态与土壤性质的关系，土壤交换性阳离子对糙米Cd含量、有效镉和水稻产量直接影响的路径系数分别为-0.566、-0.866和0.873，土壤pH主要通过直接影响有效镉而间接影响糙米镉含量.田间试验证明，这3种钝化剂是实现镉污染酸性水稻土水稻安全生产的有效技术，它们主要通过影响土壤交换性阳离子而直接影响土壤镉生物有效性，进而影响糙米中镉的积累，研究结果可为受污染耕地水稻安全生产和酸化土壤改良提供科学依据.

Remediation Effect and Mechanism of Inorganic Passivators on Cadmium Contaminated Acidic Paddy Soil

Cadmium (Cd) is one of the main pollutants in acidic paddy fields, and its accumulation in rice (Oryza sativa L.) and subsequent transfer to the food chain is an important environmental issue in China. In our field study, three types of inorganic passivators (silicon-calcium-magnesium-potassium fertilizer (SCMK), calcium magnesium phosphate fertilizer (CMP), and lime (L) at the rate of 750, 1500, and 2250 kg·hm^-2, respectively) were applied to acidic paddy soils polluted by the heavy metal Cd in southern Zhejiang province. The objective of this study was to reveal the effects and chemical mechanisms of passivators on soil acidification and Cd accumulation in rice. The field experimental results showed that the three passivators could effectively improve soil acidification and reduce Cd accumulation in rice grains. The application of 2250 kg·hm^-2 SCMK, CMP, and L increased soil pH by 0.62, 0.65, and 0.86 units; decreased exchangeable acidity by 67%, 69%, and 78%; and reduced the content of Cd in brown rice by 73%, 68%, and 77%, respectively. The application of 2250 kg·hm^-2 SCMK, CMP, and L reduced the content of Cd in brown rice planted on polluted paddy rice fields to lower than 0.2 mg·kg^-1, which reached the national food safety standard. Compared with the control, the application of SCMK, CMP, and L significantly (P<0.05) decreased the content of available Cd extracted by DTPA; decreased the contents of weak acid-extractable (F1) and reducible (F2) Cd; and increased the content of residual (F4) Cd. Correlation analyses indicated that Cd content in brown rice was significantly negatively correlated with soil pH and exchangeable cation content and significantly positively correlated with DTPA-Cd, weak acid-extractable (F1) and reducible (F2) Cd, and exchangeable Al contents. The partial least squares path model (PLS-PM) was used to analyze the relationship between the Cd content of brown rice, DTPA-Cd, and various chemical forms of Cd and soil properties. The direct path coefficients of soil exchangeable cations on Cd content in brown rice, available cadmium, and rice yield were -0.566, -0.866, and 0.873, respectively. Soil pH indirectly affected Cd content of brown rice mainly by directly affecting available Cd in soil. Field experiments demonstrated that the three passivators SCMK, CMP, and L were effective technologies for the safe production of rice in acidic paddy soils polluted by Cd. The possible mechanism for passivators reducing the bioavailability of Cd in soil and its accumulation in brown rice contributed to increased exchangeable cations in the soils. These findings could provide a scientific basis for the safe production of rice in acidic paddy soil polluted by heavy metals.