Global plastic pollution is a significant environmental and public health concern. A total of about 8.3 billion tons of plastic was produced from 1950 to 2015, and the production rate has increased, reaching 368 million tons in 2019. Plastics are resistant to chemical and biological degradation and therefore durable. There are currently at least 45 different types of plastic on the market and it is generally believed that large plastic polymers are inert and are not absorbed by the intestinal system due to their size, and therefore are excreted as such. However, upon entering the environment and/or biological systems, plastic breaks down into small particles through transformation processes and weathering, creating huge amounts of smaller plastic particles in the environment, including particles <1mm which are referred to as microplastics. It is estimated that around 250,000 tonnes of particles are released each year in the EU alone due to plastic breakdown.
As plastic continues to decompose in the environment, the percentage of fragments in the total mass of plastic waste is projected to reach 13% by 2060 and continue to increase. Secondary MPs are those generated from plastic polymers through normal weathering processes, including erosion, abrasion, photo-oxidation, and biological transformation. Polymers persist in the environment for hundreds to thousands of years. For example, PET plastic water bottles, disposable diapers, and Styrofoam foams are estimated to have environmental lifespans of 450, 500, and >5,000 years, respectively. Not only is pollution from microplastics a significant environmental concern, but plastic particles can also leach performance-enhancing additives when added to polymers during manufacturing. The water and land pollution caused by plastic additives has been widely documented.
Furthermore, microplastics can act as carriers for various other contaminants, as they sequester organic and inorganic pollutants from the surrounding environment. The ubiquitous exposure of humans to microplastics through inhalation of particles in the air and ingestion in dust, water and diet is well established. It is estimated that humans ingest tens of thousands to millions of MP particles per year, or on the order of several milligrams per day. Available information suggests that inhalation of indoor air and ingestion of plastic bottled drinking water are the main sources of exposure to MPs. Evidence is accumulating that baby bottles and medical devices can contribute to MP exposure in newborns and infants. Biomonitoring studies in human stool, fetus and placenta provide direct evidence of MP exposure in infants and children. Microplastics <20 μm have been reported to cross biological membranes.
Although plastics were once perceived as an inert material, exposure to MPs in laboratory animals has induced various forms of inflammation, immunological response, endocrine disruption, impaired lipid metabolism, and other disorders. While the exposure itself is a concern, they can also be sources of exposure to plastic additives and other toxic substances. Several studies have reported the ubiquitous presence of microplastics in various environmental matrices, including surface waters, sediments, wastewater, bottled water, selected food products and even among the ice of the North Pole and Antarctica. Not to mention their detection in seafood, honey, milk, beer, table salt and drinking water. There is preliminary evidence that given the small size of the particles, they not only release the additives but molecular portions of the polymer itself (nano-units) which can interact with proteins both inside and outside the cell.
A worrying fact is that these molecules target the receptors of sex hormones, thyroid and related to the metabolism of carbohydrates and fats (PPARs). In conjunction with the additives possibly released by the microplastics, the whole complex may well behave as a complete “endocrine disruptor” (EDC). This is what consumerism and the “hasty” lifestyle have brought about: opting to make everything out of plastic because it is lighter, it can be thrown away (“because it is inert for the environment”, as they said 40 years ago) and is more economy of glass and wood. Choosing plastic instead of wood was not a favor to avoid deforesting the planet: this still happens constantly today for the most varied reasons. Nor because a fragment of plastic doesn’t cut while shards of glass are dangerous. Not to mention that there is perhaps more sand in this world by weight than oil itself. And now, that we are aware of the damage done to the environment and to global health, we are trying to run for cover with recycling and sustainability.
- edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
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