Microplastics in terrestrial ecosystems: Moving beyond the state of the art to minimize the risk of ecological surprise

Abstract

Microplastic (plastic particles measuring <5mm) pollution is ubiquitous. Unlike in other well‐studied ecosystems, for example, marine and freshwater environments, microplastics in terrestrial systems are relatively understudied. Their potential impacts on terrestrial environments, in particular the risk of causing ecological surprise, must be better understood and quantified. Ecological surprise occurs when ecosystem behavior deviates radically from expectations and generally has negative consequences for ecosystem services. The properties and behavior of microplastics within terrestrial environments may increase their likelihood of causing ecological surprises as they (a) are highly persistent global pollutants that will last for centuries, (b) can interact with the abiotic environment in a complex manner, (c) can impact terrestrial organisms directly or indirectly and (d) interact with other contaminants and can facilitate their transport. Here, we compiled findings of previous research on microplastics in terrestrial environments. We systematically focused on studies addressing different facets of microplastics related to their distribution, dispersion, impact on soil characteristics and functions, levels of biological organization of tested terrestrial biota (single species vs. assemblages), scale of experimental study and corresponding ecotoxicological effects. Our systematic assessment of previous microplastic research revealed that most studies have been conducted on single species under laboratory conditions with short‐term exposures; few studies were conducted under more realistic long‐term field conditions and/or with multi‐species assemblages. Studies targeting multi‐species assemblages primarily considered soil bacterial communities and showed that microplastics can alter essential nutrient cycling functions. More ecologically meaningful studies of terrestrial microplastics encompassing multi‐species assemblages, critical ecological processes (e.g., biogeochemical cycles and pollination) and interactions with other anthropogenic stressors must be conducted. Addressing these knowledge gaps will provide a better understanding of microplastics as emerging global stressors and should lower the risk of ecological surprise in terrestrial ecosystems.

Occurrence and distribution of micro/nanoplastics in soils and their phytotoxic effects: A review

“…On the other hand, some studies have shown the terrestrial system as a bigger reservoir for plastic accumulation as opposed to the aquatic system (Blasing & Amelung, 2018; Hurley & Nizzetto, 2018), and thus it is suggested that the terrestrial system can also act as a major sink of microplastics (Baho et al, 2021; Boots et al, 2019; David et al, 2018). About 79% of the plastic waste generated worldwide is disposed in landfills, which again indicates that soil can serve as a large sink for the accumulation of microplastics (Guo et al, 2020).…”

“…In this regard, it is worth mentioning that many studies have been done under environmentally unrealistic conditions which may be an obstacle to the understanding of their ecological relevance. Baho et al (2021) in a review study showed that many studies measuring toxicities of microplastics in plants have used microplastic concentrations with a range from 0.001% to 2% (w/w). As discussed in this review (Table 1) that different studies measuring the abundance of microplastics in soils have expressed concentrations as: numbers of items/unit weight of soil or number of particles per/unit weight of soil.…”

Rethinking the Connections between Ecosystem Services, Pollinators, Pollution, and Health: Focus on Air Pollution and Its Impacts

“…For the University of Reading, the most recent document is focused on productivity, biodiversity trade-offs, and farm income in agroforestry versus an arable system and concluded how a diversified farming system could improve farm income, but support from grants would reduce the initial negative cash flow [ 34 ]. For Sveriges lantbruksuniversitet, the most recent document is a review by Baho et al [ 35 ] on microplastics in terrestrial ecosystems by moving beyond the state-of-the-art to minimize the risk of ecological surprise.…”

Stakeholders' Perspectives on Microplastics in Sludge Applied to Agricultural Land

“…They were first reported in the Sargasso Sea (Carpenter and Smith, 1972) but it was not until much later that the issue began to attract widespread scientific and popular attention (Thompson et al, 2004). Much of the early focus was on marine systems, but more recently, attention has expanded to include freshwater (Wagner et al, 2014;Eerkes-Medrano et al, 2015;de Sá et al, 2018;Li et al, 2018) and terrestrial environments (Huerta Lwanga et al, 2016;de Souza Machado et al, 2018;Rillig and Lehmann, 2020;Baho et al, 2021). Microplastics are ubiquitous in the environment.…”

“…Terrestrial MPs originate from multiple sources including atmospheric deposition (Allen et al, 2019;Klein and Fischer, 2019), leaching from landfills (He et al, 2019), tire wear (Knight et al, 2020), breakdown of agricultural mulch (Huang et al, 2020;Zhang et al, 2020) and application of sewage sludge to agricultural land (Nizzetto et al, 2016a,b;Crossman et al, 2020). Despite multiple lines of evidence suggesting that terrestrial ecosystems are major MPs sinks, microplastic research in the terrestrial environment is still at an early stage (see, e.g., Baho et al, 2021 for a recent review).…”