Institute of Environmental and Plant Protection, Chinese Academy of Tropical Agricultural Science, Haikou, Hainan 571101, China; National Agricultural Environmental Science Observation and Experiment Station, Danzhou 571737, China; Hainan Key Laboratory of Tropical Eco-Circular Agriculture, Haikou 571101, China.
School of Ecology and Environment, Zhengzhou University, Zhengzhou, Henan 450001, China.
Ecotoxicol Environ Saf. 2023 Nov 1;266:115593. doi: 10.1016/j.ecoenv.2023.115593. Epub 2023 Oct 17.
Vermicompost is a promising amendment for immobilization of cadmium (Cd) in soils; however, its effectiveness can be influenced by rhizosphere environment conditions, such as pH and the presence of low-molecular-weight organic acids (LMWOAs). In this study, a batch experiment was conducted to examine the characteristics of Cd adsorption by vermicompost at different pH (pH = 3, 5, and 7) and after the addition of different LMWOAs (oxalic acid; citric acid; malic acid). Furthermore, a series of morphology and structural analyses were conducted to elucidate the mechanisms of observed effects. The results showed that the adsorption capacity of vermicompost for Cd increased as pH increased, and chemisorption dominated the adsorption process. Changes in pH altered adsorption performance by affecting the -OH groups of alcohol/phenol and the -CH groups of aliphatics. Further, the addition of oxalic acid promoted Cd adsorption, and the effect was concentration dependent. Modifying the verimicompost surface with more adsorption sites might be the main reason. Conversely, citric acid and malic acid showed the ability to inhibit Cd adsorption by vermicompost. Citric acid caused a blocking effect by covering flocculent substances on the vermicompost surface while reducing surface adsorption sites by dissolving mineral components such as iron oxides. However, the action of malic acid did not appear to be related to changes in morphology or the structure of vermicompost. Overall, the results of this study partially explain the limited effectiveness of Cd immobilization within the rhizosphere by vermicompost, and provide theoretical support for regulating rhizosphere environments to improve the effectiveness of vermicompost immobilization of Cd.
蚯蚓粪是一种很有前途的土壤中镉固定化改良剂；然而，其有效性可能会受到根际环境条件的影响，例如 pH 值和低分子量有机酸 (LMWOAs) 的存在。在这项研究中，进行了批实验以研究在不同 pH（pH=3、5 和 7）和添加不同 LMWOAs（草酸；柠檬酸；苹果酸）后，蚯蚓粪对镉的吸附特性。此外，还进行了一系列形态和结构分析，以阐明观察到的效应的机制。结果表明，随着 pH 值的增加，蚯蚓粪对镉的吸附容量增加，化学吸附主导了吸附过程。pH 值的变化通过影响醇/酚中的-OH 基团和脂肪族中的-CH 基团来改变吸附性能。此外，添加草酸促进了 Cd 的吸附，且效果与浓度有关。通过为更多的吸附位点改性蚯蚓粪表面可能是主要原因。相反，柠檬酸和苹果酸表现出抑制蚯蚓粪对 Cd 吸附的能力。柠檬酸通过覆盖蚯蚓粪表面的絮状物质并通过溶解氧化铁等矿物成分来减少表面吸附位点，从而产生阻碍作用。然而，苹果酸的作用似乎与蚯蚓粪形态或结构的变化无关。总的来说，本研究的结果部分解释了根际中蚯蚓粪对 Cd 固定化效果有限的原因，并为调节根际环境以提高蚯蚓粪固定 Cd 的效果提供了理论支持。
