Field application of pure polyethylene microplastic has no significant short-term effect on soil biological quality and function

Abstract Plastics are now widespread in the natural environment. Due to their size, microplastics (MPs; defined as particles  0.05) on the soil bacterial community diversity (as measured by amplicon sequencing of bacterial 16S rRNA gene), the size and structure of the PLFA-derived soil microbial community, or the abundance and biomass of earthworms. In addition, metabolomic profiling revealed no dose-dependent effect of MP loading on soil biogenic amine concentrations. The growth and yield of wheat plants (Triticum aestivum L., cv. Mulika) were also unaffected by MP dose, even at extremely high (≥1000 kg ha−1) loading levels. Nitrogen (N) cycling gene abundance before and after N fertiliser application on the MP loaded experimental plots showed relatively little change, although further experimentation is suggested, with similar trends evident for soil nitrous oxide (N2O) flux. Overall, we illustrate that MPs themselves may not pose a significant problem in the short term (days to months), due to their recalcitrant nature. We also emphasise that most MPs in the environment are not pure or uncontaminated, containing additives (e.g. plasticisers, pigments and stabilisers) that are generally not chemically bound to the plastic polymer and may be prone to leaching into the soil matrix. Understanding the effect of additives on soil biology as well as the longer-term (years to decades) impact of MPs on soil biological and ecological health in the field environment is recommended.