Microplastic contamination is widespread across invertebrate taxa frequently consumed by terrestrial vertebrates

Little is known about the contamination of terrestrial food webs by microplastics. We conducted community-level assessments of invertebrates at 51 sites in England, sampling four trophic levels and six taxonomic groups. We hypothesized that plastic contamination would be most common in herbivores and detritivores, owing to the accumulation of microplastics in soil and plant material. A total of 581 samples, comprising pooled individuals from the same site and species, were digested using hydrogen peroxide and subsequently examined by micro-Fourier transform infrared microscopy. Plastic was found in 11.8% (95% CI 9.3%, 14.6%) of the samples, including all tested taxonomic groups and trophic levels, regardless of life history traits or dietary habits. The highest prevalence of plastic-positive samples was in Opisthopora (earthworms; 29.4%) and Stylommatophora (snails and slugs; 24.1%). Herbivores and detritivores were the trophic groups with the highest proportion of plastic-positive samples (15.4% and 10.2%, respectively). Although the prevalence was lower in carnivores, these animals ingested significantly larger microplastics when compared with other trophic levels. The most abundant polymers were polyester, polyethylene, polypropylene, nylon, and polyacrylamide. Polyester was present across all taxonomic groups and trophic levels, along with varying amounts of other polymers. The lack of correspondence between soil samples and invertebrate samples highlights the requirement to survey a range of invertebrates as well as soil to gain a full insight of the level of contamination in each site to ensure that the correct conclusions are drawn.