Microplastics (plastics <5 mm, including nanoplastics which are <0.1 μm) originate from the fragmentation of large plastic litter or from direct environmental emission. Their potential impacts in terrestrial ecosystems remain largely unexplored despite numerous reported effects on marine organisms. Most plastics arriving in the oceans were produced, used, and often disposed on land. Hence, it is within terrestrial systems that microplastics might first interact with biota eliciting ecologically relevant impacts. This article introduces the pervasive microplastic contamination as a potential agent of global change in terrestrial systems, highlights the physical and chemical nature of the respective observed effects, and discusses the broad toxicity of nanoplastics derived from plastic breakdown. Making relevant links to the fate of microplastics in aquatic continental systems, we here present new insights into the mechanisms of impacts on terrestrial geochemistry, the biophysical environment, and ecotoxicology. Broad changes in continental environments are possible even in particle-rich habitats such as soils. Furthermore, there is a growing body of evidence indicating that microplastics interact with terrestrial organisms that mediate essential ecosystem services and functions, such as soil dwelling invertebrates, terrestrial fungi, and plant-pollinators. Therefore, research is needed to clarify the terrestrial fate and effects of microplastics. We suggest that due to the widespread presence, environmental persistence, and various interactions with continental biota, microplastic pollution might represent an emerging global change threat to terrestrial ecosystems.
Soils
are essential components of terrestrial ecosystems that experience
strong pollution pressure. Microplastic contamination of soils is
being increasingly documented, with potential consequences for soil
biodiversity and function. Notwithstanding, data on effects of such
contaminants on fundamental properties potentially impacting soil
biota are lacking. The present study explores the potential of microplastics
to disturb vital relationships between soil and water, as well as
its consequences for soil structure and microbial function. During
a 5-weeks garden experiment we exposed a loamy sand soil to environmentally
relevant nominal concentrations (up to 2%) of four common microplastic
types (polyacrylic fibers, polyamide beads, polyester fibers, and
polyethylene fragments). Then, we measured bulk density, water holding
capacity, hydraulic conductivity, soil aggregation, and microbial
activity. Microplastics affected the bulk density, water holding capacity,
and the functional relationship between the microbial activity and
water stable aggregates. The effects are underestimated if idiosyncrasies
of particle type and concentrations are neglected, suggesting that
purely qualitative environmental microplastic data might be of limited
value for the assessment of effects in soil. If extended to other
soils and plastic types, the processes unravelled here suggest that
microplastics are relevant long-term anthropogenic stressors and drivers
of global change in terrestrial ecosystems.
Microplastics
can affect biophysical properties of the soil. However,
little is known about the cascade of events in fundamental levels
of terrestrial ecosystems, i.e., starting with the changes in soil
abiotic properties and propagating across the various components of
soil–plant interactions, including soil microbial communities
and plant traits. We investigated here the effects of six different
microplastics (polyester fibers, polyamide beads, and four fragment
types: polyethylene, polyester terephthalate, polypropylene, and polystyrene)
on a broad suite of proxies for soil health and performance of spring
onion (Allium fistulosum). Significant
changes were observed in plant biomass, tissue elemental composition,
root traits, and soil microbial activities. These plant and soil responses
to microplastic exposure were used to propose a causal model for the
mechanism of the effects. Impacts were dependent on particle type,
i.e., microplastics with a shape similar to other natural soil particles
elicited smaller differences from control. Changes in soil structure
and water dynamics may explain the observed results in which polyester
fibers and polyamide beads triggered the most pronounced impacts on
plant traits and function. The findings reported here imply that the
pervasive microplastic contamination in soil may have consequences
for plant performance and thus for agroecosystems and terrestrial
biodiversity.
Summary
Microplastic effects in terrestrial ecosystems have recently moved into focus, after about a decade of research being limited to aquatic systems. While effects on soil physical properties and soil biota are starting to become apparent, there is not much information on the consequences for plant performance. We here propose and discuss mechanistic pathways through which microplastics could impact plant growth, either positively or negatively. These effects will vary as a function of plant species, and plastic type, and thus are likely to translate to changes in plant community composition and perhaps primary production. Our mechanistic framework serves to guide ongoing and future research on this important topic.
Microplastic pollution is increasingly considered to be a factor of global change: in addition to aquatic ecosystems, this persistent contaminant is also found in terrestrial systems and soils. Microplastics have been chiefly examined in soils in terms of the presence and potential effects on soil biota. Given the persistence and widespread distribution of microplastics, it is also important to consider potential evolutionary implications of the presence of microplastics in soil; we offer such a perspective for soil microbiota. We discuss the range of selection pressures likely to act upon soil microbes, highlight approaches for the study of evolutionary responses to microplastics, and present the obstacles to be overcome. Pondering the evolutionary consequences of microplastics in soils can yield new insights into the effects of this group of pollutants, including establishing ‘true’ baselines in soil ecology, and understanding future responses of soil microbial populations and communities.
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