Tens of tons of sunscreen end up in water every year – studies show that this has consequences for the living beings there. In some countries there are now bans on certain ingredients.

Summer, sun, bathing time: the higher temperatures lure people to the beaches and to the water. However, large quantities of sunscreen get into the water with the bathers – and UV filters and nanoparticles from creams, lotions and sprays can damage corals and other aquatic life.

More and more studies show such effects. Replacement solutions are in the works – but until then it’s up to the users themselves. Up to 14,000 tons of sunscreen end up in the sea every year, of which 4,000 to 6,000 tons end up on coral reefs, according to researchers at the US marine agency NOAA. It has not yet been conclusively clarified how this will affect the maritime environment. Above all, the included UV filters seem to give cause for concern.

The NOAA lists that the substances impair the growth of green algae, lead to defects in the young of mussels and damage the immune and reproductive systems of sea urchins. In dolphins, the substances could accumulate in cell tissue and be transmitted to the young animals, while in fish fertility could be reduced and genetic changes triggered.

danger to corals

Above all, however, UV filters pose a threat to corals – in addition to stressors such as rising sea temperatures. The chemical-organic filter oxybenzone in particular could damage the genetic material of the sensitive cnidarians and cause their larvae to become encapsulated in their skeleton and die , as a 2016 US study suggests.

Study results like this one prompted the US state of Hawaii to pass legislation banning the sale of sunscreens containing oxybenzone and octinoxate from 2021. Similar regulations apply in Key West in Florida, the Virgin Islands, the island state of Palau, Thai marine national parks, the Caribbean island of Bonaire and some holiday areas in Mexico.

How exactly corals are damaged by oxybenzone has now been worked out by a new US study, which is reported in the journal “Science”. Scientists from Stanford University used a coral and a sea anemone species for this purpose, to which they added oxybenzone in high concentrations in aquariums and then exposed them to different light irradiations. The astonishing effect: only the animals that were exposed to the simulated sunlight died.

“Oxybenzone makes sunlight toxic”

“It was strange to see oxybenzone making sunlight toxic to corals – the opposite of what it’s supposed to do,” said lead author William Mitch. In fact, like other chemical UV filters, oxybenzone is used as a sunscreen because it absorbs ultraviolet light that hits human skin and emits the light energy in the form of harmless heat. However, according to the researchers, the anemones and corals metabolize the filter in such a way that the resulting substance forms harmful radicals when exposed to sunlight. The filter is converted into a phototoxin.

The scientists also observed that the algae, which live in symbiosis with the corals and give them their colorful appearance, appear to protect their hosts by trapping the toxins produced from the oxybenzone. The spreading phenomenon of coral bleaching, together with oxybenzone in the water, could therefore have even more fatal consequences. Bleaching occurs when stressed corals shed their algal partners, exposing their bone-white skeleton. According to the study, such bleached corals are even more susceptible to oxybenzone.

In addition to oxybenzone, another chemical-organic filter is under discussion with octocrylene. According to studies, it is said to harm water fleas, ciliates and zebrafish by affecting their hormone balance, among other things. In addition, the water-insoluble substance is difficult to break down and could therefore accumulate in organisms.

UV filters widespread in water bodies

According to various studies, UV filters can now be found both in tropical coral reefs and in the Arctic Ocean – and also in the Baltic Sea: Kathrin Fisch from the Leibniz Institute for Baltic Sea Research Warnemünde carried out measurements on the German Baltic Sea coast in 2016 and found 30 nanograms of UV filters here per liter of Baltic Sea water; in the rivers that flow into the Baltic Sea, it was sometimes up to 836 nanograms per liter. Although these are small amounts, they could have a long-term effect on marine organisms. There is no nationwide monitoring of the pollution of water bodies by UV filters in Germany, nor are there defined upper limits for their quantities.

In response to the potential environmental risks of chemical UV filters, more and more manufacturers are offering “coral-safe” or “reef-friendly” mineral sunscreens. These contain zinc or titanium dioxide – the particles act like small mirrors on the skin that reflect the UV light. In order to minimize the annoying “whitening” of many of these products, some manufacturers are trying to reduce the size of the mineral pigments and rely on nano-sized particles. However, as Spanish researchers showed in 2014, these nanoparticles act as catalysts, causing sunlight to produce highly reactive hydrogen peroxide from water. This can harm microorganisms.

It’s better to apply less cream

Research is now being carried out into alternatives in which compounds from algae, seaweed and other sea creatures act as UV filters. Until these are ready for the market, the ecologically best protection against the sun is probably one that relies on less sunscreen without – in view of the risk of skin cancer – doing without it completely.

The consumer magazine “UMID” of the Federal Environment Agency recommends mineral filters in non-nano form and advises lying in the sun in the afternoon or early evening, staying in the shade and protecting yourself with appropriate clothing and showering at home with it fewer UV filters end up directly in the water.