how to assess their toxicity in the laboratory?
Adults would ingest around 50,000 plastic particles per year, and babies more than a million per year. Plastic particles can be ingested through drinking or tap water, contaminated food (in direct contact with plastic packaging), ambient air containing microfibers (from textiles, for example) or even through skin in contact with hygiene products.
The toxic effects of these particles in humans are still unknown, but there are three main health risks: the diffusion of toxic chemical components such as additives (bisphenols, phthalates, metals); the release of harmful substances adsorbed by particles, which then act as vectors of environmental pollutants; physical damage directly caused by plastic debris (fragment, fibers, foam, microbead) causing lesions or obstruction in various organs. Several studies have shown effects at the cellular level, in particular increased inflammation, oxidative stress, cell death and disruption of energy metabolism.
The aquatic environment is the final receptacle for waste and contaminants linked to these “microplastics” (less than 5 millimeters in size) and is therefore particularly studied. At the beginning of September 2021, the number of plastic fragments floating on the surface of the oceans was estimated at 24.4 trillion, with an estimated weight of between 82,000 and 578,000 tonnes.
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For several years, more and more laboratories have been studying the toxic effects of plastic particles in marine and freshwater organisms – bacteria, fish, aquatic plants in particular – but the wide variety of characteristics of these particles such as their sizes, shapes, types of polymer (polyethylene, polypropylene, polystyrene, etc.) and added additives, make the effects difficult to disentangle. If we can assess the toxicity of these particles individually in each of these species, it will take a lot of time to test all the types of existing particles and the associated additives.[Plus de 80 000 lecteurs font confiance à la newsletter de The Conversation pour mieux comprendre les grands enjeux du monde. Abonnez-vous aujourd’hui]
Among the complementary or even alternative methods, cell culture, also called test in vitrocould be a promising tool to assess the toxicity of different plastic particles. This approach presents technical challenges and also limitations, especially to extrapolate the results to whole organisms… like humans.
The interest of cell culture to assess the toxicity of micro and nanoplastics
Scientists, who are used to working with animal models, face more and more ethical, economic and environmental challenges in their practices.
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Cell culture is mainly used to assess toxicity at the level of cells from certain organs, for example the liver or the lungs, and the mechanisms involved, under a wide variety of experimental conditions.
Currently, in vitro studies are being developed to determine the toxicity of contaminants in several aquatic organisms. This tool would have a powerful ethical interest because it would make it possible to respect the “3R principle”: replacing the use of animals by other experimental methods, reducing the number of animals used in experiments, and improving testing procedures. experimentation to reduce animal suffering.
The tests in vitro also allow to quickly pre-select the potential toxicity of chemicals before further analysis with tests liveand correlations between tests live and in vitro confirm that cell cultures could be an alternative method to animal experimentation.
The second advantage of cell culture is that it allows the assessment of many biological impacts, such as DNA damage or cell viability under different conditions, because the size scale of the assays is much smaller than the display of animals in aquariums – which also reduces costs.
Finally, it makes it possible to study the cellular mechanisms involved in toxicity, such as the production of reactive oxygen species linked to the increase in oxidative stress, which can induce the peroxidation of lipids and damage the membranes of cellular organelles, then potentially lead to cell death.
Thus, research has shown that all types of plastic particles have potentially harmful effects on cells with cytotoxicity, immunotoxicity and increased oxidative stress.
Difficulties of cell culture for ecotoxicological assessment
The first difficulty is the limited number of standardized cell lines available for aquatic organisms. Apart from commercialized lines concerning fish models, for other aquatic species, it is necessary to isolate cells and cultivate them in the laboratory before carrying out the tests. This requires a significant development period, the accuracy of which must be firmly established before any toxicity test. The origin of the cells is considered a limitation since the cells of certain organs are more difficult to maintain than others and require specific culture media.
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The composition of the culture medium also seems to play a role in the response of cells to microplastics, since the presence of certain compounds could induce changes in the physico-chemical properties of plastic nanoparticles and therefore their interaction with cells.
The limits of this approach
Despite its potential, the use of cell culture to study the toxicity of microplastics and nanoplastics is still in its infancy with a number of limitations.
For microparticles, an alternative approach using tissue or organ cultures seems to be more suitable as large particles will tend, livenot to penetrate cells and to interact with organs and tissues.
Furthermore, the use of cell cultures has a limit insofar as it does not make it possible to reproduce exactly the conditions of the cells in an entire organism. For example, isolated and cultured cells usually differ greatly from the corresponding cell type in an organism, which limits the value of data. in vitro to predict the toxic impact live.
Many works continue the study of the optimization of tests on cell cultures with in particular the use of culture media under conditions closer to those encountered. livefor example in three dimensions.
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