The Impact of Microplastics on Soil Invertebrates ^†

As a result of plastic pollution and intentional use of plastics in agriculture, small plastic particles called microplastics (<1 mm) are commonly found in soils. This has raised many concerns on the possible effects of microplastics on soil physico-chemical properties, soil biota and the ecosystem services they provide [1,2]. Hazard assessment of microplastics on soil biota relies on using model terrestrial invertebrates, which are exposed to microplastics either by ingesting the soils or through body surface contact. In recent years, we have gathered considerable information regarding the effects of microplastics on key ecotoxicity test invertebrates: woodlice Porcellio scaber, mealworms Tenebrio molitor, springtails Folsomia candida, enchytraeids Enchytraeus cripticus and earthworms Eisenia andrei [3,4,5,6]. The organisms were exposed through soil or food spiked with environmentally relevant microplastic concentrations (0.005–5%) for typically 3–4 weeks. Microplastics were generated from various plastic materials, generating tire wear particles, textile fibres, polypropylene microplastics from disposable medical masks, low-density polyethylene fragments from packaging, low-density-polyethylene fragments milled from mulching films and starch blend polybutylene adipate-co-terephthalate mulching film fragments. A number of endpoints was followed: survival, reproduction, moult, growth, energy-related biomarkers and immune response. In general, our results show that tested microplastics are not lethal to tested invertebrates, but microplastic exposure can induce sublethal effects, such as alternation in reproduction, reduced growth, changes in metabolic activity and induction of immune response. We will present an overview of the various effects observed on different organisms and discuss how the responses differ between types of microplastics and whether plastics-associated chemicals might contribute to the observed effects.