Over time, plastic waste decomposes into microplastics, defined as plastic particles less than five millimeters in diameter. These can be ingested by fish and marine invertebrates such as crustaceans, including those intended for human consumption. Therefore, potential health impacts may occur due to the chemicals associated with these plastic particles, but also due to the presence of pathogens that adhere to their surface. It is this last point that has been studied in detail by researchers at the University of California, Davis.
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Parasites that bind to microplastics
In the review Scientific reportsexplain how human-produced plastic waste, whose microparticles can travel to Antarctica, contributes to the transmission of terrestrial microbial species to the marine environment, which can have serious consequences for both the health of marine life as for the human health it feeds on. about him.
For example, the parasite Toxoplasma gondii The cause of toxoplasmosis, which is commonly found in cat feces, has already infected many ocean species, killing sea otters and endangered species such as Hector’s dolphins and Hawaiian monk seals. This suggests that terrestrial germs may now reach previously saved regions and ecosystems. Nearly a third of the world’s population is believed to carry this parasite (after ingesting contaminated food or water); if the infection is asymptomatic in individuals without immunodeficiency, it is especially dangerous for the fetus.
The researchers also studied the parasites Cryptosporidium parvum i Enteric garden, responsible for cryptosporidiosis and giardiasis respectively: two gastrointestinal diseases that can be fatal in young children and immunocompromised people; these pathogens were chosen because they have been recognized by the World Health Organization as underestimated causes of shellfish-related diseases. These protozoa have also been shown to be persistent in seawater and have been reported as widespread contaminants in commercial seafood worldwide.
Parasite count in the surrounding seawater (pastel colors) and associated with 500 μm polyethylene microbeads (A) or 800-1200 μm polyester microfibers (B) (dark colors). Credits: E. Zhang et al., Scientific reports (2022)
Scientists have examined whether or not these three species of parasites could be associated with polyethylene microbeads (found in certain cosmetics, such as scrubs) and polyester microfibers (clothing and fishing nets) present in the ocean. His experiments showed that parasites adhere more to the microspheres, but these two types of plastic are quite capable of transporting germs. The number of parasites present in plastics increased over time.
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Benthic fauna directly impacted by the phenomenon
In fact, each type of plastic impacts marine ecosystems differently depending on whether it floats or sinks. Microplastics floating on the surface can travel long distances and spread pathogens far away from their terrestrial sources. At the same time, sinking plastics carry microbes into the benthic environment, which hosts organisms attached to the ground or skimming the seabed (zooplankton, clams, mussels, oysters and other shellfish); these animals feed by filtration, they are more likely to absorb both plastic and germs.
A piece of polyester microfiber seen under a microscope surrounded by parasites T. gondii (blue dots) and G. enterica (green dots). Credit: Karen Shapiro / UC Davis
The impact of large plastic debris on marine life is well established: many animals are found dead with their stomachs full of plastic. On the other hand, the direct or indirect consequences of the ingestion of microplastics by marine organisms remain to be clarified. This study is the first to shed light on the ability of microplastics to mediate the transport and destination of biological contaminants of terrestrial origin.
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” We are altering natural food webs by introducing this artificial material that can also introduce deadly parasites. “Karen Shapiro, an infectious disease expert at UC Davis School of Veterinary Medicine and co-author of the study. But the problem is just as important for humans: microplastics can increase the bioavailability of pathogens by increasing probability of ingestion by lower trophic species such as shellfish, which humans easily consume.
” This is really a problem that affects both humans and animals. He stressed the importance of a “health” approach that requires collaboration between human, wildlife and environmental disciplines. We all depend on the ocean environment recalls Emma Zhang, a student at UC Davis School of Veterinary Medicine. Obviously, we can contribute in several ways to reducing the impact of microplastics on the ocean, starting with reducing their production at source. Researchers mention in particular the use of filters in washing machines and dryers, to retain microfibers, but also bioretention cells and other technologies for treating rainwater and industrial discharges.