What is known and unknown about the effects of plastic pollution: A meta‐analysis and systematic review

Abstract

As a consequence of the global ubiquity of plastic pollution, scientists, decision‐makers, and the public often ask whether macroplastics (>5 mm) and microplastics (<5 mm) have a realized ecological threat. In 2016, we conducted a systematic review of the literature and made a call for further research testing hypotheses about ecological effects. In the subsequent years, the amount of relevant research has risen tremendously. Here, we reassess the literature to determine the current weight of evidence about the effects of plastic pollution across all levels of biological organization. Our data spans marine, freshwater, and terrestrial environments. We extracted data from 139 lab and field studies testing 577 independent effects across a variety of taxa and with various types, sizes, and shapes of plastic. Overall, 59% of the tested effects were detected. Of these, 58% were due to microplastics and 42% were due to macroplastics. Of the effects that were not detected, 94% were from microplastics and 6% were from macroplastics. We found evidence that whether or not an effect is detected, as well as the severity and direction of the effect, is driven by dose, particle shape, polymer type, and particle size. Based on our analyses, there is no doubt that macroplastics are causing ecological effects, however, the effects of microplastics are much more complex. We also assessed the environmental relevancy of experimental studies by comparing the doses used in each exposure to the concentrations and sizes of microplastics found in the environment. We determined that only 17% of the concentrations used in experimental studies have been found in nature, and that 80% of particle sizes used in experiments fall below the size range of the majority of environmental sampling. Based on our systematic review and meta‐analysis, we make a call for future work that recognizes the complexity of microplastics and designs tests to better understand how different types, sizes, shapes, doses, and exposure durations affect wildlife. We also call for more ecologically and environmentally relevant studies, particularly in freshwater and terrestrial environments.

The Way of Macroplastic through the Environment

“…This makes it possible to consider the path of MaP through all areas of the aquatic, terrestrial, and atmospheric environment. In comparison to existing reviews or research articles of plastic waste and MaP in the environment (marine environments: [18,19]; freshwater environments: [20][21][22]; terrestrial environments: [23] or regarding ecological effects [24,25], this one looks at the whole life cycle and all environmental areas by determining all possible sources, pathways, and receptors (sinks).…”

Microplastics in aquatic organisms: Improving understanding and identifying research directions for the next decade

“…Although communication across research groups continues to increase, efforts to strengthen these connections are critical to improving the quality and comparability of research findings, eventually allowing for the meta-analyses that are necessary to accurately assess the hazard and risk of microplastics across freshwater and marine ecosystems (e.g., Bucci et al 2019). However, because the study of microplastics is still relatively nascent, one area that may most severely limit forward progress is the lack of standardized methodologies because this greatly limits researchers' ability to compare across studies.…”

“…However, because the study of microplastics is still relatively nascent, one area that may most severely limit forward progress is the lack of standardized methodologies because this greatly limits researchers' ability to compare across studies. Although communication across research groups continues to increase, efforts to strengthen these connections are critical to improving the quality and comparability of research findings, eventually allowing for the meta-analyses that are necessary to accurately assess the hazard and risk of microplastics across freshwater and marine ecosystems (e.g., Bucci et al 2019). Nevertheless, we are optimistic about these challenges, as we describe next.…”

Microplastic fibers affect dynamics and intensity of CO2and N2O fluxes from soil differently

“…An important process that has been under-researched in microplastic-affected soils is the emission of greenhouse gases 14 . Despite its potential importance, compared to other factors of global change, we have so far only scratched the surface in terms of assessing microplastic impacts on soil properties and processes in general [15][16][17][18] .…”

“…Initial evidence also pointed to soil physical properties being altered by microplastics 26 . We have evidence that microplastic can affect basic parameters including soil structure and bulk density 15 , and that the performance of biota can be altered, which has been shown, for example for earthworms 27 , microbes 28 , and for plant growth [29][30][31][32] . However, the only study to date on the effect of microplastics on the emission of climate-relevant trace gases from soils does not address the impact of soil physical properties on the greenhouse gas emission 28 .…”