June 23, 2024


Ocean: “environmentally friendly” sunscreen harms parasites

Foraminifera – single-celled organisms that live mostly in the sea – play an important role in the ocean ecosystem. However, tests have shown that she and her algae are damaged by the ingredients in the sunscreen. This also applies to sunscreens that are sold as “environmentally friendly”. Its remains are considered even more harmful to the health of protozoa, as environmental biologists have now discovered.

Because of their long-lived shells, foraminifera are important indicator fossils of past geological ages—but they are still an important part of the marine ecosystem today. Some of these unicellular marine organisms can ingest algae or cyanobacteria as symbionts. Thus they make a critical contribution to the marine carbon and nitrogen cycle in both deep and shallow waters.

Effects tested on symbionts

However, this important process, particularly in coastal areas and river deltas, can be affected by pollution from sunscreen residues. Michael Lintner of the University of Vienna and colleagues have now taken a closer look at the consequences of this contamination for foraminifera. The research team focused on the species Heterostegina depressa, which belongs to the larger foraminifera and hosts diatoms as symbionts. These provide their host with important substances such as sugar or glycerol and are therefore essential for their metabolic activity. The photosynthetic performance of these diatoms is greatly influenced by physical and chemical parameters and thus also by human contamination.

“In detail, we analyzed the potential effects of commercially available sunscreens on the activity of photosynthetic symbionts on H. depressa bacteria using fluorescence microscopy,” explains Lintner. Changes in the photosynthetic activity of diatoms can be traced microscopically. The research team selected four different sunscreens, two of which are sold as “traditional” and the other two as “environmentally friendly.” They also tested the effect of pure insole, which is often used as a UV blocker in sunscreens.

Damage to diatoms is also caused by ‘eco-friendly’ sunscreen.

The results showed that pure insulinisol caused a significant decrease in the photosynthetic activity of diatoms. The researchers note the same for conventional sunscreens, albeit to a lesser extent. According to the researchers, the reason traditional sunscreens affect the photosynthesis of Heterostegina depressa is that they also contain insole. It has long been known that this substance is stored in plant cells and therefore has a negative effect on the mechanisms of the cell. “Even the smallest concentrations strongly inhibit algae activity. Lintner and colleagues say the concentration of insuolisol in sunscreen is lower than the concentration of pure insulin that was tested.

However, the research team noted a sharp decrease in photosynthetic activity and a negative impact on the health of foraminifera even with sunscreens being sold as environmentally friendly. Compared to conventional sunscreens, the damage caused by these agents was greater, the team reported. Interestingly enough, eco-friendly sunscreens do not contain insulisol at all. So what then ensures that diatoms are inhibited in their photosynthetic activity?

“We hypothesize that metallic nanoparticles in particular such as titanium dioxide or zinc oxide from ‘environmentally friendly’ sunscreens are causing this effect,” Lintner and colleagues explain. “In the past decade, the use of titanium dioxide nanoparticles has increased dramatically. The nanoparticles are able to assemble and pose a potential danger to the organism.” Since titanium dioxide is the only mineral present in each of the tested sunscreens, the research team suspects that it is likely responsible for the toxic effects of the eco-friendly sunscreen. However, more studies are needed to prove this

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Source: University of Vienna; Specialized Articles: Scientific Reports, doi: 10.1038/s41598-022-06735-1