The importance of microplastic particles in the ecosystem, both as they might effect ecological systems and human health, is the subject of great deal of new research, and is one of more rapidly developing areas of of knowledge related to environmental concern. Once thought of as mainly a problem in the oceans (related to the now famous “Pacific Garbage Patch“) it is now understood that microplastic particles are also common in the terrestrial ecosystem and the part of the food chain we eat.

Sources of microplastic particles include wearing down of tires, the use of synthetic textiles, road paint, the coatings and pain used on boats, and personal care products (roughly in that order) as well as “city dust,” a ‘generic name given to a group of nine sources” including the soles of footwear, synthetic cooking utensils, building paint, cleaning supplies, etc, all with small individual contributions but collectively about 24% of the microplastic particle pollution observed in the ocean. (See this.)

The effects of microplastic particles may be more related to size and shape of the particles, rather than toxicity. (But all these factors matter.) Microplastic particles are mostly made of carbon. Normally carbon gets spread around the environment as part of the photosynthetic segment of the carbon cycle. Microplastic particles now exist in what has become known of as the “plastic cycle.” (See this and this.) Since the nature of microplastic routed carbon is different than “natural” carbon, direct and indirect effects on ecology can occur. Soil structure can be affected (including the spaces where air or water may be trapped in soil). Microplastics in soil can benefit plants, because soil density is lowered, so root growth is easier. However, where microplastics make up a large proporation of fill, plant growth is reduced (see this).

Note that the carbon in microplastic particles is fossil carbon, which prior to the manufacture of the plastic was mostly trapped in petroleum or coal, which in turn is mostly out of the short and medium term carbon cycle. Moving carbon from the long term cycle (which involves processes like continents being subjected into the mantle of the Earth, to be belched out later from volcanoes or added to spreading sea floors) into the short and medium term cycle (such as the cycle affected by human activity to cause global warming) may be important.

Microplastic particle contamination has been associated with changes in the immune system, the spread of antibiotic resistant bacteria (in part because bacterial microfilms that cover microplastic particles may favor, or at least contain, resistant forms), and microplastic particles have been found all over the place. Microplastic particles can be a vector moving chemicals between parts of the ecosystem.

See “Microplastic in terrestrial ecosystems” for a fuller review of the effects of microplastic particles in soils and other parts of the ecosystem. It is pretty complex.

We may tend to think of microplastic particles as being a problem because we use plastic containers, which can break down into micro particles. That is true. For example, using polypropylene bottles in the preparation of infant formula releases microplastic particles into the formula itself. But a lot of microplastic particles are introduced directly into the environment because we make and use those small sized particles in a range of applications including agriculture and cosmetics. As a rule where the material being used is less solid, the degree to which it is soluble and thus the ease with which it enters the environment increases. This could allow regulations to be focuses more stridently and more quickly on areas of plastic use and production that have the most effect.

Microplastic particles can be taken in to cells by a process called “internalization” or “endocytosis” (synonyms) (see abstract below). There is evidence that “fresh” microplastic particles are not easily taken in but once exposed to the environment for a while, the surface of the microplastic particles changes, allowing internalization to happen more easily. The effects of the microplastic on the inside of the cell is understudied, but could in some cases be a problem. Microplastics may decrease cellular activity and increase reactive oxygen species, which in turn has potentially serious health effects.

Is this hopeless? Possibly. Can we stop using plastics? Maybe. Can the environment sequester microplastic particles (and thus carbon) naturally? Sometimes and maybe. Developing nations contribute hugely to plastic pollution due to a lack of solid waste infrastructure. Developed nations like the US have a great plastic waste infrastructure, but use so many plastics that the contribution from these countries is still huge (see this). We shed microplastic particles through many activities from feeding one’s baby to driving to the store to buy more forumla.

The fact that microplastic particles are something we ingest, breath in, our that our cells engulf is not itself a novelty. The gas and liquids we exist among are normally full of particles. Many of these particles are polymers, like plastic, but natural (pollen, skin cells, etc.). The problem with microplastic particles isn’t so much that they exist, but that they exist and are subtly, or sometimes dramatically, different than what is normally there, and what we thus normally adapt to. Also, microplastic particles may create a different distribution than what would normally occur (like the frequency in baby formula?). The challenge is to figure out where microplastic particles matter most, and then figure out ways of addressing those problems first and fast. This will also involve figuring out if the best solutions (which is a function of how well the solution works and how likely it is to get it to happen) is a change in specific policies or regulations, or changes in individual behavior. And, of course, we must be cognizant that changes to avoid or reduce microplastic particles do not result in some other negative effect.

This is just a rough, preliminary look at microplastic particles. I tried to include a wide selection of links to recent works, but I’m afraid many may be behind paywalls. But, you should be able to find a lot more by CLICKING HERE.

Additional Info and Resources:
Machado, Et Al. 2018. Impacts of microplastics on the soil biophysical environment. Environ. Sci Technol 52(17)

Abstract: oils 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.

Ramsperger et al. 2020 “Environmental exposure enhances the internalization of microplastic particles into cells” Science Advances 6(50)
Abstract: Microplastic particles ubiquitously found in the environment are ingested by a huge variety of organisms. Subsequently, microplastic particles can translocate from the gastrointestinal tract into the tissues likely by cellular internalization. The reason for cellular internalization is unknown, since this has only been shown for specifically surface-functionalized particles. We show that environmentally exposed microplastic particles were internalized significantly more often than pristine microplastic particles into macrophages. We identified biomolecules forming an eco-corona on the surface of microplastic particles, suggesting that environmental exposure promotes the cellular internalization of microplastics. Our findings further indicate that cellular internalization is a key route by which microplastic particles translocate into tissues, where they may cause toxicological effects that have implications for the environment and human health.

Rilling and Lehman. 2020. Microplastic in terrestrial ecosystem. Science.

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