Comparing the microplastic content in biosolid-amended and non-amended agricultural soils

Biosolids have been identified as a major source of microplastics (MP) to the environment. While they have been heavily studied, the impacts biosolids have following their amendment to agricultural soils on the MP content of these soils is poorly understood. Eleven biosolid-amended and nine non-amended agricultural fields in Southern Ontario were sampled to compare the MP content between them. Biosolid-amended fields averaged 2441.82 ± 268.03 MP kg-1, while non-amended fields averaged 775 ± 50.97 MP kg-1. Additionally, MP abundance was correlated with the type of biosolid applied, with fields that received a single application of dewatered biosolids averaging 2412.14 ± 174.81 MP kg-1, whereas fields that received a single application of liquid biosolids averaged 1689.83 ± 225.81 MP kg-1. However, differences in MP abundance were primarily dictated by differences in application rate between dewatered and liquid biosolids. In addition to increasing overall MP content, biosolid amendments influenced MP composition. Biosolid amendment increased soil fibre content, as biosolids are rich in textile fibres derived from the laundering process. As a result, biosolid-amended soils primarily contained polyester, while unamended soils primarily contained polypropylene. Quantifying and characterizing MP content in biosolid-amended fields, and understanding how it differs from unamended fields, is crucial for accurately assessing the risks microplastics pose to terrestrial ecosystems.