Morphology-dependent degradation and fragmentation of PVC microplastic particles influence their transport in saturated quartz sand columns

Abstract

Since microplastics are an obstinate pollutant in terrestrial environments, posing a risk to the subsurface soil matrix and entering inland waters via erosion pathways, it is necessary to understand their transport behaviours. The morphological descriptors used to characterize microplastic particles are usually highly subjective. This study explores the transport and retention behaviour of 125 – 200 μm Polyvinyl chloride (PVC) plastic fragments in saturated quartz sand (1.6 – 2.0 mm) columns. Retention profiles at different ultrapure water flow rates (2.0 – 3.5 ml/min) were compared and analysed. At the beginning and end of each column test, the microplastic particles were scrutinized, identified, and quantified by light microscopy. Each particle was characterized by dimensionless 3D morphological descriptors that can describe any particle shape. The results showed that the transport distance of microplastic particles increased with decreasing diameter of the microplastic particles. PVC microplastic particles, whose morphology was more 1-dimensional, were more susceptible to degradation and fragmentation within the column, promoting migration. Microplastic degradation into fragments appeared to play an important role in improving the movement of particles. This study offers initial indications of infiltration depths and morphology-dependent fragmentation of secondary microplastics in coarse sand, outlining the limitations of 2D projected images conventionally used to study the transport of microplastics.