微塑料比表面积大、易于吸附污染物，是一类新兴污染物，在土壤中被广泛检出，可能对土壤中磷的环境行为产生影响。磷对土壤质量和土壤养分循环极为重要，同时土壤中磷的流失也是造成周边水体富营养化的重要因素。目前微塑料对土壤磷吸附特性的影响尚未形成统一认识，不同微塑料含量和粒径如何影响土壤磷吸附特性尚不明确，微塑料进入土壤后形成的微塑料-土壤体系的磷吸附机制还有待深入研究。为了探究微塑料对土壤磷吸附特性的影响及机制，选用聚苯乙烯微塑料（PS-MPs）作为微塑料样品，辽宁省某农田土壤作为供试土壤，对含有0.1-10%含量微塑料的土壤对磷的吸附动力学和吸附等温线进行测定和分析，并考察了3种不同粒径微塑料对土壤磷吸附量的影响。采用XRD表征吸附前后微塑料-土壤体系的晶体组成变化，采用FT-IR表征吸附前后微塑料-土壤体系的官能团变化，以探究微塑料对土壤磷吸附的影响机制。结果表明，磷在微塑料-土壤体系中的吸附过程可分为三个阶段，而吸附过程第一阶段液膜扩散阶段速率显著提升（p<0.05），使得微塑料-土壤体系磷吸附速率增加。与不含PS-MPs的土壤（qe=6.456mg/g）相比，添加质量分数为0.1%、0.5%、1%的PS-MPs显著降低了微塑料-土壤体系磷吸附容量（p<0.05），但添加5%、10% PS-MPs的微塑料-土壤体系吸附容量显著升高（p<0.05）。此外对48、150、250μm粒径PS-MPs的吸附实验表明，含有48μm PS-MPs微塑料-土壤体系对磷的吸附量最大，150μm次之，250μm最弱。通过对吸附前后微塑料-土壤体系的XRD与FT-IR图谱的比较，揭示了微塑料对土壤磷吸附的影响机制。土壤中含Si、Al、Ca的矿物是磷的吸附位点，但同时也会吸附微塑料，微塑料通过与磷竞争吸附位点，降低了微塑料-土壤体系对磷的吸附。由于微塑料也可直接吸附磷，因此当添加5%以上PS-MPs时，微塑料-土壤体系对磷的吸附量升高。此外，微塑料-土壤体系中微塑料的粒径减小，会使得低含量PS-MPs对土壤磷的抑制吸附作用减弱，高含量PS-MPs对土壤磷的促进吸附作用增强。这是由于微塑料粒径减小，微塑料-土壤体系总比表面积增大。因此，土壤微塑料污染会显著改变土壤对磷的吸附特性，且这种影响与微塑料的含量和粒径等因素密切相关。

As a new class of pollutants, microplastics have a large specific surface area and are easy to adsorb other pollutants. They are widely detected in soil and may affect the environmental behavior of phosphorus in soil. Phosphorus(P) plays an extremely important role in soil quality and nutrient cycling, and the loss of P from soil is also a major factor causing eutrophication of surrounding water. At present, there is no unified understanding of the effects of microplastics on soil P adsorption characteristics, and differences due to different content and particle size of microplastics is not clear. The mechanism of P adsorption in the microplastic-soil system formed after microplastics entering soil needs further study. In order to explore the effect and mechanism of microplastics on soil P adsorption, polystyrene microplastics (PS-MPs) were selected as microplastics samples, and soil from a farmland in Liaoning Province was sampled as the test soil. The P adsorption kinetics and adsorption isotherms of soil containing 0.1-10% microplastics were measured and analyzed. The effects of three different particle sizes of microplastics on soil P adsorption were investigated. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) were used to characterize the crystal compositions and functional groups of the microplastic-soil system before and after adsorption, to explain the effect mechanism of microplastics on soil P adsorption. The results showed that the adsorption process of P in the microplastic-soil system could be divided into three stages. In the first stage of the adsorption process, the rate of liquid film diffusion stage was significantly increased (p<0.05), and consequently increased the adsorption rate of P in the microplastic-soil system. Compared with the soil without PS-MPs (qe=6.456mg/g), the concentrations of 0.1%, 0.5% and 1% PS-MPs significantly reduced the P adsorption capacity of the microplastic-soil system (p<0.05). However, the P adsorption capacity of microplastic-soil system increased significantly with the concentrations of 5% and 10% PS-MPs (p<0.05). In addition, the adsorption experiments using PS-MPs with size of 48, 150, and 250 μm showed that the microplastic-soil system containing 48 μm PS-MPs had the highest adsorption capacity for P, followed by 150μm PS-MPs and 250μm PS-MPs. The XRD and FT-IR patterns of the microplastic-soil system before and after adsorption were compared to reveal the mechanism of the influence of microplastics on soil P adsorption. Minerals containing Si, Al and Ca in the soil were the adsorption sites of P and microplastics. Microplastics reduced the adsorption of P in the microplastic-soil system by competing with phosphorus for adsorption sites. Since microplastics can also directly adsorb P, the adsorption capacity of microplastic-soil system would increase when PS-MPs were more than 5%. In addition, the decrease of particle size of microplastics in soil would reduce the inhibitory effect of low content PS-MPs on soil P adsorption, and enhance the promoting effect of high content PS-MPs on soil P adsorption. This was due to the increase in the total specific surface area of the microplastic-soil system when the particle size of microplastics decreased. Therefore, microplastics pollution in soil can significantly change soil P adsorption characteristics, which is closely related to the content and particle size of microplastics.

国家自然科学基金项目（32001195）；国家重点研发计划（2019YFD1100501）