Effects of microplastic on water flow and contaminant transport in water-saturated sand

After decades of discovery of microplastic contamination over the world, effects of microplastic on organisms have been studied thoroughly, whereas ones on hydrological aspect are yet quite mentioned. As one of major microplastic sinks, soils are inevitable to face a number of microplastics; however, the movement of microplastic through soil and its consequence are still unknown. Then this research would be focusing on effects of microplastic contamination in soil sediment on hydraulic and transport parameters. Hydraulic conductivity (K), distribution coefficient (Kd), and dispersion coefficient (D) are the main parameters to be measured. The column experiment in column of diameter 7 cm and depth 20 cm of sand, half of which is contaminated with microplastic, together with bromide tracer solution (1000 mg/L) was chosen to be conducted for controllability, and replication. The total of 15 column experiments were conducted with microplastic contamination of microplastic in sand ranging from 5-20% by mass. Three size ranges of sand, 0.5-1.0, 1.0-2.0 and 2.0-4.0 millimeters, together with microplastic of size 0.25-0.5 and 0.5-1.0 millimeters, were used in the experiments. The result suggested that microplastic contamination has significantly affected hydraulic conductivity of the sand and dispersion of the solution. A relationship between hydraulic conductivity and dispersion coefficient, as well as one between distribution coefficient and dispersivity, was discovered. Those findings were mentioned in no prior theories. After each experiment, the movement, or migration, of microplastic was examined. The result suggested that there was no migration of microplastic to any other layers of sand.