Scientists have learned how microplastics in the oceans carry pathogens dangerous to humans

(ORDO NEWS) — The new study, according to its authors, is devoted to an unexplored area – the connection between plastic entering the oceans and water pollution by pathogens.

By polluting the oceans with microplastics – the smallest particles of plastic no more than five millimeters in length – we endanger not only marine life, but also ourselves.

As shown by a study by scientists from the University of California at Davis and the University of Nebraska (USA), pathogenic microorganisms travel from land in this way: in particular, the protozoa Toxoplasma gondii , Cryptosporidium parvum and Giardia enterica.

The World Health Organization considers them an underestimated cause of diseases that occur after eating seafood, such as shellfish.

Every year, millions of tons of plastic waste enter the Earth‘s hydrosphere. Over time, such debris breaks down into microplastics, which, as experts have already reported, penetrate the organisms of fish and marine invertebrates such as molluscs.

Subsequently, they end up on the shelves of stores and our tables with you. Although researchers are actively studying how microplastics affect the health of animals, we know much less about the similar consequences for humans.

Some previous studies have confirmed that plastic waste carries chemical pollutants (oil and petroleum products, pesticides, heavy metals, acids, alkalis, salts and synthetic surfactants). It is also known that unique communities of bacteria colonize the surfaces of debris and form their own ecosystem – the plastisphere.

Among other things, fungi and harmful species of algae “live” there. But the role of microplastics in the spread of pathogens, including zoonotic protozoan parasites, has remained poorly understood.

The authors of the new work studied the relationship of Toxoplasma gondii, which threatens toxoplasmosis , Cryptosporidium parvum , the causative agent of cryptosporidiosis , and Giardia enterica , parasitic in the small intestine of humans and some animals , provoking giardiasis , with microplastic surfaces.

In humans, Cryptosporidium and Giardia cause gastrointestinal illnesses that can be fatal in children and immunocompromised patients. T. gondii , in turn, cause lifelong infections due to encystation (existence in the form of a cyst ) in muscle and brain tissue.

When a person’s immunity declines later in life, the parasite can reactivate and lead to the development of dangerous toxoplasmosis. In pregnant women, T. gondii can cross the placenta and infect the fetus, causing fetal abnormalities or miscarriages.

“We conducted laboratory experiments to test the hypothesis that zoonotic protozoa are able to bind to microplastics in polluted seawater.

Next, we quantified and compared the relationship of protozoan parasites with two main types of microplastics – polyethylene microgranules with a size of 500 micrometers and polyester microfibers with a size of 800-1200 micrometers, ”the scientists write. Microbeads are often found in cosmetics and detergents, while microfibers are often found in clothing and fishing nets.

Experiments have shown that all three protozoan parasites are associated with the surfaces of the studied types of microplastics.

On microgranules, the number of microorganisms grew over time. The scientists observed a similar trend in the case of microfibers: the number of parasites associated with them increased from the first to the third day, with the exception of C. parvum . Moreover, in the surrounding sea water, their numbers decreased over the week.

Scientists have learned how microplastics in the oceans carry pathogens dangerous to humans 2
Fragment of microplastic fiber and pathogens with biofilm (shown in blue). T. gondii – blue dot, Giardia – green dot

“Although the difference in the number of parasites associated with microplastics and found in seawater may seem small, it must be taken into account that the total mass of microplastics occupied a much smaller volume in each experimental unit (bottle) compared to the volume of seawater.

When analyzing the concentration of parasites per gram of plastic, these microorganisms were several orders of magnitude higher compared to their concentrations per equivalent weight of the surrounding seawater in bottles.

Similarly, under natural conditions, microplastics in a body of water make up a relatively small fraction of the environment compared to the total volume of water in which they are suspended. Thus, the observation that these parasites can be associated with the surfaces of microplastics is an important discovery in itself, ”the researchers noted.

In a second set of experiments, they looked at how the type and size of microplastics affect the ability of these particles to bind to parasites.

As it turned out, the protozoan parasites preferred to inhabit the surface of microfibers rather than microgranules. Smaller particles were associated with fewer microorganisms, probably due to not too much surface area.

Although relatively “large” particles (microgranules 500 micrometers in size) did not always have large numbers of parasites associated with them.

Therefore, in addition to surface area, there are other factors for example, surface roughness, the chemical characteristics of the plastic, the composition of the biofilm that affect the association of pathogens with plastic.

According to scientists, their study once again shows how important it is to prevent microplastics from entering the oceans.

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