Effect of Microplastics on Pore Structure of Sandy Loam Soil: Study Using X-ray Computed Tomography

Abstract

【Background】 Microplastic particles are an emerging pollutant found in almost all ecosystems including soils. Its impact on soil function is multifactual, and this paper investigates the change in pore structure of soil contaminated by microplastic particles. 【Method】 Sandy loam soil samples with (treatment) and without (CK) contaminated by 2% of polypropylene microplastics were taken from different depths in soil columns. They were then scanned using x-ray Computed tomography. The pore structure in each sample was analyzed. 【Result】 The polypropylene microplastics significantly affected pore structure of the soil. 3D visualization revealed that the pores in the non-contaminated soil were more uniformly distributed and well connected compared to the contaminated soil. In contrast, pores in the contaminated soil were highly fragmented and less connected. The porosity of pores identified by the image was 4.98% and 3.79% for the CK and the treatment, respectively. The number of pores and distribution of pore volume varied with soil depths in soil column contaminated by microplastic particles. In the 0~4 cm soil layer, the total number of pores in the treatment was 73.02% lower than that in the CK. The difference in the number of pores between CK and the treatment increased gradually with the increase in soil depth. The average volume of pores in the CK and treatment was 1 709 mm3 and 1 235 mm3, respectively, with CK containing more large pores than the treatment. The microplastics also influenced the pore morphology in that with the increase in soil depth, the pore rounding rate in the CK tended to stabilize and the pores were close to round. The average equivalent diameter of the pores in the treatment was greater than that in the CK, and increased gradually with the increase in soil depth. 【Conclusion】 Polypropylene microplastics not only reduced the porosity of the sandy loam soil, it also affected the number and morphology of the pores at different soil depths.

Keywords

• computed tomography technique
• microplastics
• soil pore structure
• three-dimensional visualization