Microplastics are not only everywhere in the environment and even in us – they can also become a carrier for other pollutants. Researchers have found that the tiny plastic particles can accumulate toxic metals. The smaller the microplastic, the more metal attaches to it. If the particles are then ingested through food or drinking water, they release their metal load in the digestive tract.
Microplastics float in seas, lakes and rivers, pollute the soil and even fly around in the air. The small, only micrometer to millimeter large plastic particles from disintegrated plastic waste are now almost ubiquitous. Tests show that we humans also absorb these particles through the food chain and through drinking water. The health consequences of microplastics have not yet been clarified. However, another danger is becoming more and more apparent: the plastic particles can also accumulate, transport and release other pollutants.
Vehicle for arsenic, lead and co
It is already known that microplastics in water are increasingly colonized by pathogenic bacteria and can also accumulate organic pollutants. Lars Hildebrandt from the Helmholtz Center Hereon in Geesthacht and his colleagues have now investigated whether the same applies to dissolved metals. To do this, they first tested in the laboratory how well 55 different metals and semi-metals attach to plastic particles made of polyethylene and polyethylene terephthalate (PET). “With regard to the pollution of water with plastic, the two types of plastic we examined play an important role,” explains Hildebrandt. Because both are particularly common: Polyethylene is used, among other things, for plastic bags, PET for plastic beverage bottles.
The result: some of the metals showed rapid and high accumulation on the microplastic. These highly enriched elements included arsenic, iron, lead, chromium, tin and many rare earth metals, the team reports. Other metals and semi-metals such as copper, cobalt or cadmium, on the other hand, were only slightly or not at all attached to the plastic particles. “During the investigations, we found that the smaller the particles, the greater the enrichment,” says Hildebrandt. In addition, the polyethylene particles bound significantly more metals than PET.
Metal cargo is released again in the stomach
These observations raise the question of what happens to these deposited metals when a human or animal ingests the contaminated microplastic. To test this, the scientists put the enriched particles in solutions that simulated the chemical conditions of the digestive juices – for example in the form of a low – acidic – pH value. It turned out that even in a moderately acidic environment, the microplastic quickly released elements such as arsenic, lead, tin, tellurium, vanadium and the rare earth metals. At pH values such as those found in the human stomach, the particles released all of their elemental load into their surroundings.
“Our test setup in the laboratory was simplified and without model organisms. Nonetheless, the results provide important indications that microplastic particles, when they are absorbed by the body, act as a kind of Trojan horse for metals and that they can possibly be carried into organisms to a greater extent ”, draws Lars Hildebrandt. The microplastics could thus make a significant contribution to introducing potentially harmful metals and semi-metals into the food chain.
Source: Helmholtz Center Hereon; Technical article: Journal of Hazardous Materials Letters, doi: 10.1016 / j.hazl.2021.100035