Small ( < 5 mm) fragments of plastic waste, or microplastics, are an emerging contaminant with unknown impact on aquatic and soil systems. One potential avenue for microplastics transport to the environment is the land application of biosolids from wastewater treatment plants to agricultural fields. A field study was conducted to assess the short-term fate of microplastics added to soils during biosolid land application. Biosolids from a local wastewater treatment plant were applied to six 1 meter square test plots using both surface application and incorporation into the upper soil layer. The test plots were then watered at varying rates over a four-week period to simulate natural rainfall and produce surface runoff. Analysis of microplastic concentrations in site runoff and soil cores were determined using Nile red staining after extraction from the samples. Microplastics concentrations in site runoff were affected by biosolid application method, with greater initial loss of microplastics from plots with biosolids incorporation. Rainfall intensity, however, did not have a consistent effect. Changes in microplastic size and shape profiles before and after the rainfall events show evidence of microplastic migration from the surface layer to 15 cm depth in the soil column over the study period. These results provide important data on microplastics fate and transport in agricultural systems that could affect the decision to land apply biosolid materials.
