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石灰能否同时固定稻田中的砷和镉?

Can simultaneous immobilization of arsenic and cadmium in paddy soils be achieved by liming?

机构信息

School of Geographical Sciences, Hunan Normal University, Changsha, 410081, China.

Key Laboratory of Environmental Heavy-Metal Contamination and Ecological Remediation, Hunan Normal University, Changsha, 410081, China.

出版信息

Environ Sci Pollut Res Int. 2023 Jun;30(29):73677-73687. doi: 10.1007/s11356-023-27536-7. Epub 2023 May 17.

Abstract

Liming acidic paddy soils to near-neutral pH is the most cost-effective strategy to minimize cadmium (Cd) accumulation by rice. However, the liming-induced effect on arsenic (As) (im)mobilization remains controversial and is called upon for further investigation, particularly for the safe utilization of paddy soils co-contaminated with As and Cd. Here, we explored As and Cd dissolution along pH gradients in flooded paddy soils and extracted key factors accounting for their release discrepancy with liming. The minimum As and Cd dissolution occurred concurrently at pH 6.5-7.0 in an acidic paddy soil (LY). In contrast, As release was minimized at pH < 6 in the other two acidic soils (CZ and XX), while the minimum Cd release still appeared at pH 6.5-7.0. Such a discrepancy was determined largely by the relative availability of Fe under overwhelming competition from dissolved organic carbon (DOC). A mole ratio of porewater Fe/DOC at pH 6.5-7.0 is suggested as a key indicator of whether co-immobilization of As and Cd can occur in flooded paddy soils with liming. In general, a high mole ratio of porewater Fe/DOC (≥ 0.23 in LY) at pH 6.5-7.0 can endow co-immobilization of As and Cd, regardless of Fe supplement, whereas such a case is not in the other two soils with lower Fe/DOC mole ratios (0.01-0.03 in CZ and XX). Taking the example of LY, the introduction of ferrihydrite promoted the transformation of metastable As and Cd fractions to more stable ones in the soil during 35 days of flooded incubation, thus meeting a class I soil for safe rice production. This study demonstrates that the porewater Fe/DOC mole ratio can indicate a liming-induced effect on co-(im)mobilization of As and Cd in typical acidic paddy soils, providing new insights into the applicability of liming practice for the paddy soils.

摘要

将酸性稻田土壤调至接近中性 pH 是使水稻最小化积累镉 (Cd) 的最具成本效益的策略。然而,石灰引起的砷 (As) (不)迁移的效果仍然存在争议,需要进一步研究,特别是对于同时受到 As 和 Cd 污染的稻田土壤的安全利用。在这里,我们探索了淹水稻田土壤中 pH 梯度下 As 和 Cd 的溶解情况,并提取了关键因素,这些因素解释了它们在石灰作用下释放的差异。在酸性稻田土壤(LY)中,最小的 As 和 Cd 溶解同时发生在 pH 6.5-7.0 处。相比之下,在另外两种酸性土壤(CZ 和 XX)中,As 的释放在 pH<6 时最小,而最小的 Cd 释放仍出现在 pH 6.5-7.0。这种差异主要取决于在溶解有机碳 (DOC) 的强烈竞争下,铁的相对可用性。建议在 pH 6.5-7.0 处的孔隙水 Fe/DOC 摩尔比作为一个关键指标,用于判断在淹水稻田土壤中石灰作用下是否可以发生 As 和 Cd 的共固定。一般来说,在 pH 6.5-7.0 处,孔隙水 Fe/DOC 的摩尔比高(LY 中≥0.23)可以赋予 As 和 Cd 的共固定,而无需补充 Fe,而在其他两种铁/碳摩尔比较低的土壤中(CZ 和 XX 中为 0.01-0.03)则不会出现这种情况。以 LY 为例,在 35 天的淹水孵化过程中,引入水铁矿促进了土壤中不稳定的 As 和 Cd 形态向更稳定形态的转化,从而满足了安全水稻生产的 I 类土壤标准。本研究表明,孔隙水 Fe/DOC 摩尔比可以指示石灰对典型酸性稻田土壤中 As 和 Cd 共(不)迁移的诱导效应,为石灰应用于稻田土壤提供了新的见解。

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