What do we know about how the terrestrial multicellular soil fauna reacts to microplastic?

The ubiquitous accumulation of microplastic particles across all global ecosystems comes along with the uptake into soil food webs. In this work, we evaluated studies on passive translocation, active ingestion, bioaccumulation and adverse effects within the phylogenetic tree of multicellular soil faunal life. The representativity of these studies for natural soil ecosystems was assessed using data on the type of plastic, shape, composition, concentration and time of exposure.Available studies cover a wide range of soil organisms, with emphasis on earthworms, nematodes, springtails, beetles and lugworms, each focused on well known model organisms. Most of the studies applied microplastic concentrations similar to amounts in slightly to very heavily polluted soils. In many cases, however, polystyrene microspheres have been used, a combination of plastic type and shape, that is easily available, but do not represent the main plastic input into soil ecosystems. In turn, microplastic fibres are strongly underrepresented compared to their high abundance within contaminated soils. Further properties of plastic such as aging, coating and additives were insufficiently documented. Despite of these limitations, there is a recurring pattern of active intake followed by a population shift within the gut microbiome and adverse effects on motility, growth, metabolism, reproduction and mortality in various combinations, especially at high concentrations and small particle sizes.For future experiments, we recommend a modus operandi that takes into account the type, shape, grade of aging and specific concentrations of microplastic fractions in natural and contaminated soils as well as long-term incubation within soil mesocosms.