Underestimated and ignored? The impacts of microplastic on soil invertebrates—Current scientific knowledge and research needs

Abstract

The accumulation of plastics in the environment is a major problem in the Anthropocene. As most plastic is produced, used and discarded on land, ∼4–23 times more plastics are deposited in soils than in the oceans. However, there is far too little knowledge on the ecological consequences of plastic pollution, especially for soil ecosystems. Microplastics (<5 mm), whether derived from larger plastic pieces through physical, chemical and biological degradation or produced as primary particles, is of considerable interest, as they can be ingested by organisms at the basis of the trophic net and transferred to higher trophic levels. Nonetheless, although the assessment of microplastic effects on soil invertebrates is of undeniable relevance, most studies have focussed on nano- and microplastics in aquatic environments. This review examines the current state of knowledge regarding the effects of microplastics on soil invertebrates. As part of the soil biota, these organisms are of utmost importance for carbon cycling, respiration and biodiversity. Based on strict quality criteria, the data of 45 papers reporting ecotoxicological effects on soil invertebrates were analyzed, considering various test organisms and types of microplastic (in terms of polymer, shape and size). However, although different impacts were demonstrated, a deduction of general effect tendencies of microplastics in soils was difficult due to the scarcity of data and the use of diverse methodological setups. Moreover, almost all experiments were based on short-term single-species testing involving only a small number of species and single microplastic types. The review concludes with a discussion of the remaining knowledge gap and the needs for a standardized approach allowing an ecologically relevant risk assessment of the impacts of microplastic on invertebrates in terrestrial ecosystems.

Terrestrial Isopods Generate Microplastics from Low‐Density Polyethylene Without Effects on Survival

“…The majority of studies investigating the effects of plastics on soil invertebrates have focused on terrestrial oligochaetes and springtails (e.g., Eisenia fetida , Folsomia candida ; Moehrke et al, 2022). Current literature on soil invertebrates has measured a range of adverse effects including significant reductions in growth of Lumbricus terrestris and Eisenia fetida after exposure to polyethylene (PE) and polystyrene (PS) MPs, respectively (Huerta Lwanga et al, 2016; Jiang et al, 2020); a decrease in the number of juveniles produced by Enchytraeus crypticus (Lahive et al, 2019); and increased mortality for F. candida exposed to PE MPs (Ju et al, 2019).…”

Plastics in Agricultural and Urban Soils: Interactions with Plants, Micro-Organisms, Inorganic and Organic Pollutants: An Overview of Polyethylene (PE) Litter

“…According to He et al [22], 51.49% of papers on plastic litter from 2014 to 2018 focused on aquatic environments, compared to just 3.86% on soils. Approximately 4-23 times as much plastic is deposited in soils as there is in the world's marine environment, although little is known about the ecological effects, for instance on plant growth [23], of plastic litter on terrestrial ecosystems (soil) [24]. As an example, the biggest terrestrial biomes, i.e., dryland, cover 41% of the planet's terrestrial surface, supporting over 38% of the human population worldwide [16,25], and could be seriously threatened by an increasing concentration of MPs in the soil [16].…”