Effect of Dry Soil Aggregate Size on Microplastic Distribution and Its Implications for Microplastic Emissions Induced by Wind Erosion

Microplastics (MPs) have become a problematic pollutant in different environments. Dry soil aggregates may have a remarkable influence on the emissions of MPs from surface soil due to wind erosion. Here, we sampled surface soils and monitored wind erosion events to investigate the number of MPs distributed in different dry soil aggregate sizes and the implications for MP emissions induced by wind erosion. Of the MPs in soils, 35% (453.49 ± 187.62 kg–1) were associated with soil aggregates and 65% (848.69 ± 412.04 kg–1) were dispersed. Only 38% of all fiber and 27% of all nonfiber MPs were associated with soil aggregates. The abundances of <2.5 mm fibers and <0.5 mm nonfibers decreased exponentially with an increase in aggregate size. With an increase in the abundance of microfibers associated with soil aggregates, the total organic matter and nitrogen contents increased while the mean soil particle size decreased. The MP size distributions for different soil aggregate size fractions showed sigmoid trends similar to those described by logistic models. The aggregate stability and wind speed were inversely and positively correlated with microfiber enrichment, respectively, in wind-blown sand and dust. This study provides the first insights into the number distribution of MPs in different dry soil aggregate fractions.