Packaging, toys, cars, furniture... look everywhere we find some object made of plastic materials. There is such a quantity and variety, and sometimes they are so small, that we ingest them, inhale them and they come into contact with our body through the skin. The new issue of the collection What do we know about? (CSIC-Catarata) deals with micro and nanoplastics, those fragments from plastic products that have not been recycled and end up in the environment. The director of the Institute of Agrochemistry and Food Technology (IATA-CSIC), located in the scientific-academic area of the Science Park of the University of Valencia (PCUV), Amparo López-Rubio and CSIC researchers M. Victoria Moreno-Arribas, Cinta Porte and M. Auxiliadora Prieto explain their properties, how they become part of ecosystems and the routes of human exposure to these particles.
In the book Micro and nanoplastics, women scientists also describe existing studies on contamination by micro and nanoplastics, the known real risks and point out the gaps that still exist regarding their presence, exposure, potential effects and regulation. "Although we still have more questions than answers, the evidence accumulated in recent years clearly points to the fact that micro and nanoplastics are not harmless," say the authors.
Microplastics (MP) are fragments with a size of less than 5 millimeters, while nanoplastics (NP) include particles with sizes smaller than 1 micron, that is, one thousand times smaller than 1 millimeter. In terms of origin, a distinction is made between primary microplastics, which are already produced in small formats and added to products such as fertilizers, cosmetics or detergents, and secondary microplastics, which come from articles such as bags, toys or clothing and are progressively fragmented by the action of air, sun and water into smaller and smaller pieces.
It has been shown that contamination by microplastics is extremely persistent, almost impossible to eliminate once released, and accumulates progressively in the environment. The structure of these materials means that they are able to absorb or adsorb pollutants from the environment and transport or release them, so that they act as vectors for the distribution of toxins, pests or even pathogenic microorganisms
According to the researchers, the greatest concern about these materials, which are invisible to the human eye, stems from their ubiquity-they have been found virtually everywhere on the planet where they have been sought-and from the fact that they are not biodegradable. "Microplastic contamination has been shown to be extremely persistent, almost impossible to eliminate once released, and to accumulate progressively in the environment". In addition, "the structure of these materials makes them capable of absorbing or adsorbing pollutants from the environment and transporting or releasing them, so that they act as vectors for the distribution of toxins, pests or even pathogenic microorganisms," they warn.
And all this happens because of our 'addiction' to plastic. Its versatility, durability and low cost are some of the properties that have made it one of the most used materials. It is estimated that more than 8 billion tons of plastics have been produced since the mid-twentieth century, equivalent to over one ton per person on earth. However, not all plastics are used in the same way and do not have the same environmental impact. The CSIC experts point out that a plastic intended for the electrical sector, with a long service life and excellent insulating properties, is not the same as so-called single-use plastics, mainly used in packaging. The latter rapidly add to the huge amount of waste generated each day and are the main source of pollution. In fact, packaging accounts for more than 40% of total plastic consumption worldwide.
Recent studies show that the entry of plastics into terrestrial ecosystems is in the range of 10-40 million tonnes per year, or 3-10 times more than it is estimated to reach seas and oceans. In the case of terrestrial ecosystems, the authors point to agricultural practices such as the use of encapsulated fertilizers and plastics for soil coating, as well as irrigation with contaminated water as important sources of inputs of PM and NP into the soil. Another route is plastic waste dumps, where ultraviolet radiation, moisture or erosion fragment the material and spread to new areas by wind or even animals.
In aquatic ecosystems the presence of plastics has already iconic images such as the spectacular garbage island of the North Pacific, but these formations are only the tip of the iceberg. "It is estimated that 85% of the plastic entering the oceans remains hidden under water, accumulated in sediments at great depths," explain the authors. And that ocean litter proliferates in such a way that even the World Economic Forum predicts that by 2050 oceans could contain more tons of plastic than fish.
It is estimated that 85% of the plastic entering the oceans remains hidden under water, accumulated in sediments at great depths. Ocean litter proliferates in such a way that even the World Economic Forum predicts that by 2050 oceans may contain more plastic than fish
Plastics come into contact with organisms and can enter them. Plastic particles have been reported in more than 1,300 aquatic and terrestrial species including fish, mammals, birds and insects. If we look at fish, it has been described that they can accumulate higher levels of microplastics from contaminated prey than directly from water, highlighting the role of the food chain in their accumulation. In exposure studies, the smallest particles have been observed to accumulate in deep tissues such as liver, brain and muscle, while the largest particles are mainly found in gills, stomach and intestine. Particles smaller than 100 nanometers (nm) can penetrate into cells, which can cause effects such as oxidative stress or DNA damage.
Despite progress, one of the main challenges for the scientific community is to identify and quantify micro- and nanoplastics in ecosystems. The experts, with many hours of laboratory work behind them, point out that the analytical procedure involves manipulating very small particles, extracting them from very complex environmental matrices and accurately identifying the type of polymer, size and shape. "This is particularly difficult in the case of nanoplastics because their physical and chemical behaviour differs from that of larger particles," they say.
By the mouth, by the nose, and also by the skin. The human body is potentially continuously exposed to small plastic particles, either through the marine and terrestrial organisms we ingest, carriers of microplastics, or through both tap and bottled drinking water, to give just a couple of examples. These sources of exposure through ingestion are not exclusive, and also add to other routes such as the inhalation of air and dust, which involves not only the entry of particles but chemical pollutants that they can carry. The third 'channel' to penetrate our organism is contact with the skin. In this case, the researchers point out that it would be the nanoparticles, especially the smaller ones, which could cross the skin barrier.
In addition to the presence of MP and NP in food and beverages, it is important to consider bioaccessibility, that is, the fraction of particles and chemical compounds that can actually be released during digestion and absorbed by the body. The authors point out that not only plastic particles themselves, but also chemical additives such as plasticizers and flame retardants can be a source of dietary exposure. "The problem is that these compounds are not firmly attached to the plastic and can come off over time, especially when heating food or during digestion," they clarify.
What happens when plastic particles enter our bodies? Are they easily absorbed or eliminated? Can they accumulate in organs and tissues? Answering these questions is very difficult, because MP and NP have multiple forms, a wide range of sizes and are presented as complex mixtures that generate complicated combined effects to study.
Plastic particles have so far been detected in various human tissues and fluids, including blood, lung, liver, kidney, spleen, placenta, intestine, colectomy samples, sputum, semen, breast milk and faeces, among others. Available data suggest that the intestine is one of the main sites of accumulation, although it remains a challenge to accurately quantify particles, especially the smallest ones, in feces. "Ingestion is considered a very important route of exposure, but it is not yet clear to what extent and under what conditions PM and NP can be absorbed significantly by the human body". It is known that, "throughout the digestion process, these particles can interact with various molecules present in the digestive system such as digestive enzymes, bile salts, organic and inorganic compounds, forming on their surface a biological or (eco)corona, that it could change the way in which they are recognised by the body’s cells and, consequently, alter their biological behaviour and potential toxicity,' the researchers say.
The study of the impact of PM and NP on intestinal microbiota is an emerging line of research due to its possible relationship with alterations in intestinal and systemic health. A pioneering study conducted by the CSIC within the European project PlasticsFatE showed that polyethylene terephthalate (PET) microplastics modify the human colon microbiota during simulated gastrointestinal digestion. Other recent research has shown that, in addition to PET, exposure to PM from other polymers can also alter the composition of the gut microbiome, even in disease contexts, with a decrease in beneficial bacteria and an increase in pathogens and antibiotic-resistant microorganisms. Beyond these effects, the possible role of the intestinal microbiota in the biotransformation or elimination of these particles from the organism is also investigated, which could modulate their bioavailability and toxicity.
Do not miss the day "Women in Science" that we organize from the PCUV and in which participates Amparo López (IATA)
Although many unknowns still remain, current studies reflect a growing interest by the scientific community and regulatory bodies in better understanding the fate and effects of PMs and NPs on the human body. Among the challenges in this area, CSIC scientists point out that it is essential to have integrated tools that allow prioritizing the most relevant types of particles, improve the methods for detecting them, establish comparable standards between studies, and more accurately assess the potential risks to human health.
There is also a lot to be done in terms of prevention: from drastically reducing the production and consumption of single-use plastics to improving water and waste treatment technologies. The role of governments is also crucial, although the outlook for the moment is not very positive. On 15 August, the negotiations for an international treaty against plastic pollution sponsored by the United Nations (UN) failed again during the meeting of the Intergovernmental Negotiating Committee (INC5-2) and are suspended without consensus. "There are so many science-based strategies that can be followed, but the next steps are already in the hands of international negotiators," the scientists claim.
Source: IATA