Microplastics, tiny pieces of plastic less than five millimeters long, are becoming a ubiquitous pollutants. In addition, they can make other contaminants more harmful.
Studies suggest that, on their own, these small fragments are potentially harmful, and it is unclear what effect they might have on contaminants that cling to them. Now, a study in ACS’s Environmental Science & Technology Letters shows that, when attached to microplastics, UV filters used in products like sunscreens can make metallic chromium more toxic.
Because microplastics can accumulate other environmental contaminants on their surfaces, such as heavy metals or organic molecules, they could pose an even bigger problem to wildlife, plants, or humans than originally thought.
Previous research has shown that heavy metals can easily stick to microplastics and that this combination could potentially harm aquatic life. But beyond simply adhering to other contaminants, microplastics and the cocktail of substances they contain could interact with each other, altering their chemical properties.
For example, certain metals, such as chromium (Cr), can adopt different oxidation states while on the surfaces of microplastics. And while Cr(III) is relatively safe, Cr(VI) is toxic.
So Kelvin Sze-Yin Leung of Hong Kong Baptist University and his team wanted to investigate, for the first time, how the oxidation state of Cr might change when attached to microplastics, and how this might be affected by a contaminant. common organic: UV filter molecules.
The researchers created mixtures of microplastic chromium and polystyrene particles with and without benzophenone-type UV filters. The team found that microplastics could add even more Cr in the presence of a UV filter. In addition, the oxidation state of Cr was higher in the mixtures containing the filters.
Finally, the team tested whether this increased oxidation state translated into environmental toxicity for a population of microalgae. Microalgal growth was inhibited when exposed to the mixture containing the filter molecule, suggesting that Cr was now in its most toxic form. According to the researchers, this means that microplastics can help transform pollutants into a more harmful form, an interaction not previously tested.
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