College of Chemistry and Environmental Science, Hebei University, Baoding 071002, China.
Agriculture University of Hebei, Baoding 071002, China.
Sci Total Environ. 2018 Jun 15;627:553-560. doi: 10.1016/j.scitotenv.2018.01.267. Epub 2018 Feb 2.
Cadmium (Cd) contamination in soil is a global environmental pollution issue. Nanohydroxyapatite (NHAP) has been used in soil remediation to immobilize cadmium in contaminated soils. However, the effect of acid rain on the export of cadmium from topsoil and its behavior in deep soil and leachate is unclear. In this study, column experiments and development of parsimonious model were performed to estimate Cd leaching behavior from topsoil and environmental risk of groundwater after 0.5% NHAP remediation. Four leaching events were performed and total Cd, different fractions of Cd determined by sequential extraction procedure and pH were determined for each leaching. The results show that with the export of Cd in topsoil, the total Cd concentration in soil at different depths had the following vertical distributions: 0-5 cm > 5-10 cm > 10-15 cm > 15-20 cm. NHAP treatment increased the soil pH and decreased Cd leaching loss by 56.45% compared to the control, and the results fit the parabolic diffusion model. With sequential extraction it was observed that NHAP application increased the residual fraction of cadmium in soil. After leaching, there was a positive correlation between soil pH and Cd concentration with regards to the exchangeable, reducible, oxidizable and residual Cd fractions. The parabolic diffusion model showed that Cd-contaminated soil with NHAP remediation is harmless to humans after sufficient remediation duration, whereas the resultant concentrations from the CK treatment could be toxic. The results indicate that nanohydroxyapatite could significantly reduce the bioavailability of cadmium and the environmental risk. However, the release of Ca and P from the dissolution of NHAP should be carefully studied as this will impact the mobilization of Cd or colloid Cd, and high leaching of P may result in P-induced eutrophication risk.
土壤中的镉（Cd）污染是一个全球性的环境污染问题。纳米羟基磷灰石（NHAP）已被用于土壤修复，以固定污染土壤中的镉。然而，酸雨对表土中镉的浸出及其在深层土壤和淋出液中的行为的影响尚不清楚。在这项研究中，进行了柱实验和简约模型的开发，以估计 0.5% NHAP 修复后表土中镉的浸出行为和地下水的环境风险。进行了四次浸出实验，每次浸出后都测定了总镉和顺序提取程序测定的不同镉形态以及 pH 值。结果表明，随着表土中镉的浸出，不同深度土壤中的总镉浓度呈现以下垂直分布：0-5cm＞5-10cm＞10-15cm＞15-20cm。与对照相比，NHAP 处理增加了土壤 pH 值，减少了 56.45%的镉浸出损失，结果符合抛物线扩散模型。通过顺序提取发现，NHAP 的应用增加了土壤中镉的残留分数。浸出后，土壤 pH 值与可交换态、可还原态、可氧化态和残留态镉分数之间呈正相关。抛物线扩散模型表明，经过足够的修复时间，NHAP 修复的镉污染土壤对人类是无害的，而 CK 处理的结果可能是有毒的。结果表明，纳米羟基磷灰石可以显著降低镉的生物可利用性和环境风险。然而，应该仔细研究 NHAP 溶解过程中 Ca 和 P 的释放，因为这会影响 Cd 的迁移或胶体 Cd，而 P 的高浸出可能导致 P 引发的富营养化风险。
