2023-07-03 09:30:17
A new Ifremer study shows that natural microfibers are not as innocuous as one might think. They have impacts on oysters. Consequently, the release of all anthropogenic fibers and not just synthetic fibers should be better regulated.
According to scientific studies, approximately 2 million tons of synthetic and natural microfibers are released into the oceans each year. It has been estimated that 35% of the microfibers that end up in the marine environment come from washing machine effluents. Of new results published by Ifremer in the journal Environmental Pollution, in collaboration with the CNRS and the universities of Western Brittany and Le Mans, show that synthetic and natural fibers have effects on the metabolism of cupped oysters.
Scientists have observed that natural fibers cause inflammation of the digestive walls of these filtering organisms and affect their immune system more significantly than synthetic fibers. The reason: their roughness. Camille Détrée carried out this study during a post-doctorate in the Marine Environmental Sciences Laboratory (Ifremer/CNRS). Now a lecturer at the University of Caen, she explains these results to us.
Engineering Techniques: What was your modus operandi for this study?
Credits: Camille Détrée
Camille Detree: We were interested in the effect of natural and synthetic microfibers on the cupped oyster, Crassostrea gigas. We tested three natural fibres: cotton, wool and organic cotton. They are generally presented as biodegradable and less impactful for the environment and we wanted to verify this. We also tested three synthetic microfibers, similar to microplastics: acrylic, polyester and nylon.
We exposed our oysters for four days to an environmental concentration of 10 microfibers per liter to find out if a short exposure could have an impact. This corresponds to the average concentration found in the six ocean basins. We also tested a very high concentration of 10,000 microfibers per litre. This “disaster scenario” was carried out to identify the major biological functions of the oyster that could be affected.
We thus evaluated their ingestion capacity and the effects on digestion, the inflammatory response, the immune system and more generally the response to stress. For this, we evaluated the presence of microfibers in the digestive gland and in the faeces, and used biomarkers of the major functions of the oyster. Finally, we focused on the chemical compounds associated with these fibers.
What differences have you observed between synthetic and natural fibres?
We have prepared our own fibers from balls to have average lengths of 100 µm for diameters of 20 to 30 µm. Oysters filter particles between 2 and 200 µm, we wanted to ensure that the microfibers would be bioavailable. We then explored the effect of each polymer and each natural fiber independently of each other.
It has been seen that the natural microfibers tested have a greater effect on digestion and inflammation than the synthetic microfibers. We have done roughness tests on these microfibers: natural microfibers are more than 2 to 10 times rougher than synthetic ones, so they can cling to the walls of the digestive gland and gills and generate inflammation.
But beware, this absolutely does not mean that plastic is better than natural. This means that under our conditions, the natural microfibers had more effect on the biomarkers tested. If you take another wool or another cotton, you may have a different roughness, different additives and therefore different effects. We have also seen that polyester generated more stress in exposed oysters than in unexposed organisms.
Did you observe a difference in effects between the two concentrations tested?
We did not see any difference between the concentrations of 10 and 10,000 microfibers per liter of water. This means that the current concentration is sufficient to disturb the digestion of oysters. This is not dramatic in the context studied, but it raises questions about chronic exposure and the consequences that this can have in the long term.
How can this lack of difference be explained? It is assumed that there was a behavioral response of the oyster, probably at the level of the amount of filtration or at the level of the valve opening between the mediums slightly and strongly contaminated with microfibers.
What do these results mean for you?
What we really want to highlight is that the problem is general: we must take an interest in all anthropogenic debris. Natural fibers are processed, they are no longer really natural. Rather, we suggest a reduction in overall consumption and we invite to favor the second hand. A 2016 publication by the University of Plymouth showed that it is during the first four to five washes that new clothes will release the majority of microfibers. If there is a limitation of buying new, you greatly decrease the release of microfibers.
In the environment, cotton takes just over 270 days to degrade to 75%. On the synthetic, we are at 4% over the same period. It will stay for decades, compared to less than a year for cotton. This still suggests that synthetic materials are more bioavailable than natural microfibers.
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