Purpose

The role of microplastics (MPs), as vectors for coexisting contaminants, in affecting the adsorption and desorption behavior of cadmium (Cd) by regulating soil properties such as dissolved organic matter (DOM) is still under debate.

Methods

A 2-month incubation of soil contaminated with different sizes and concentrations of non-biodegradable polyethylene (PE) and three types of biodegradable MPs were conducted. Subsequently, three-dimensional excitation-emission matrix (3D-EEM) with fluorescence region integration (FRI) analysis of DOM and a batch experiment of Cd behavior on MP-contaminated soils were further conducted.

Results and discussion

Soil properties such as pH, ammonium nitrogen, and urease activity were significantly affected by MP properties. 3D-EEM analysis indicated that the microbial by-product substances and the humic acid–like substances were the major components of DOM in MP-contaminated soil, accounting for approximately 50%. Overall, Cd adsorption was decreased by higher MP concentration and larger size, and PE-contaminated soils had similar or higher adsorption capacities than soil with biodegradable MPs. MPs can decrease in Cd adsorption and increase in Cd desorption when compared to the control. Both the Langmuir and Freundlich models fitted well with Cd adsorption and desorption isotherms. Correlation analysis confirmed that the characteristics of DOM, such as the humification index values and major components, rather than other soil properties, contributed more to the adsorption behaviors of Cd on MP-contaminated soils.

Conclusion

Addition of MPs could mitigate soil Cd adsorption capacity, mainly due to the changes of soil DOM characteristics, which will enhance the mobility and risks of Cd to agricultural soil.

中文翻译：

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农业土壤中溶解性有机物成分与不可生物降解和可生物降解微塑料对镉吸附行为的相关性

目的

微塑料（MP）作为共存污染物的载体，通过调节溶解有机物（DOM）等土壤性质来影响镉（Cd）的吸附和解吸行为，其作用仍然存在争议。

方法

对被不同尺寸和浓度的不可生物降解聚乙烯 (PE) 和三种可生物降解 MP 污染的土壤进行了 2 个月的培养。随后，进一步进行了三维激发发射矩阵（3D-EEM）和DOM荧光区域积分（FRI）分析以及MP污染土壤上Cd行为的批量实验。

结果与讨论

MP 特性显着影响 pH、铵态氮和脲酶活性等土壤特性。3D-EEM分析表明，微生物副产物物质和腐植酸类物质是MP污染土壤中DOM的主要成分，约占50%。总体而言，较高的 MP 浓度和较大的尺寸会降低 Cd 吸附，并且 PE 污染的土壤与具有可生物降解 MP 的土壤具有相似或更高的吸附能力。与对照相比，MP 可以减少 Cd 吸附并增加 Cd 解吸。Langmuir 和 Freundlich 模型都很好地符合 Cd 吸附和解吸等温线。相关分析证实，DOM的特性，如腐殖化指数值和主要成分，而不是其他土壤特性，对MP污染土壤对Cd的吸附行为贡献更大。

结论

MPs的添加会降低土壤对Cd的吸附能力，主要是由于土壤DOM特性的改变，从而增强Cd对农业土壤的迁移性和风险。