Aquatic microplastics, not necessarily a problem

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Tiistai 25.8.2020 klo 18:18 - Mikko Nikinmaa

Indigestible fibers are considered to be good for you. Such fibers enter your alimentary canal and pass through it without any changes, nothing is taken up in the gut. However, they help in the motility of the gut, and some materials, which are indigestible to us, can be utilized by gut microbes. Regardless, if material is going through your gut without anything taken up, it is inert and if its dimensions are such that it is easily transferred through the gut, cannot be considered harmful. The same is true for all animals.

So, fibers are good for you. If I changed the word fiber to microplastic, then people would start screaming about terrible poisons. Headline news almost everywhere in the world feature every once in a while stories about how these terrible microplastics are found in fish and other seafood, and can therefore be transferred to you. But if the dimensions are correct, the microplastics can be just like any other inert material going through the alimentary canal. Many plastics are nowadays made such that they meet foodstuff packaging requirements. If these plastics are broken down or if microbeads are produced from such plastics, they are completely harmless. We have been drinking water and soft drinks in plastic bottles for tens of years without being poisoned by microplastics, although every time we drink, we digest microplastics. So, in principle, microplastics are not a problem, if the material is foodstuff quality.

Microplastics can, however, be a problem. First, there are many types of plastics, some of which contain toxic components. Currently, about half of all the microplastics entering water are particles from tire wear. With the current traffic situation, there is very little one can do to this type of contamination. This is in contrast to microplastics in wastewater treatment plants, where more than 95 % of plastics are retained. The tire plastics have toxic components. Second, most of the toxic compounds are hydrophobic. Therefore, they adsorb on plastic particles, and will easily diffuse to organisms through the hydrophobic lipid gut walls. In this case it is not the microplastics themselves which are toxic, but the toxic compounds that have found their way to the environment. By stopping the release of these toxicants also the toxicity of microplastics would disappear.

The problem is that by focusing on microplastics in the aquatic environment, one is not addressing the real questions: decreasing road traffic (thus decreasing tire wear particles), decreasing toxicant release (thus decreasing toxicant adsorption and transfer into organisms) and completely stopping the use of toxic compounds in plastics.     

Avainsanat: plastic pollution, aquatic toxicology

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