Sunscreen flours heavy metals into the sea

Bathers bring significant amounts of titanium, aluminum and lead into the water

Sunscreens are important to our health, but when bathing in the sea, they release potentially harmful metals and chemicals. © FiremanYU / iStock
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Invisible contamination: A typical bathing day in the Mediterranean can leach significant amounts of heavy metals and nutrients into the sea, a study reveals. Because these substances are released by the sunscreen rinsed in the water. On a normal beach, this can increase the titanium content in the water by 20 percent, that of aluminum by four percent. Lead, cadmium and phosphates are also released in small quantities.

In view of the consequences of sunburn and too much UV radiation, a good sun protection is indispensable for a beach holiday. These agents contain partly organic compounds, partly inorganic nanoparticles, which act as UV filters. The problem, however, is that some of these chemicals have hormone-like effects and may interfere with sperm function, studies suggest. Nanoparticles such as titanium dioxide are in turn suspected of damaging aquatic animals and perhaps even promoting intestinal inflammation in humans.

Aluminum, lead and cadmium

But there is another component of sunscreens: heavy metals. Because in addition to titanium from the titanium dioxide nanoparticles common sun creams also contain traces of aluminum, cadmium, copper, manganese, cobalt, nickel and lead. These metals are often bound to organic chemicals in the cream. Whether and how strongly they pass into the seawater during bathing, for example, was previously unclear.

This is what Araceli Rodriguez-Romero from the University of Cantabria in Santander and her colleagues have examined. For their study, they first determined in a laboratory experiment with fresh Mediterranean water how strong and fast the metals from a common sunscreen with a sun protection factor of 50 dissolve in seawater. Then they used a model to calculate what amounts of a typical Mediterranean beach would be released in a day.

Solar radiation favors solution

The result: in seawater, suntan lotion initially forms stable colloids hard-to-remove drops of organic chemicals with nanoparticles and metals. However, under the influence of UV light, these aggregates gradually release the metals, albeit sometimes with a delay of up to six hours, the researchers report. The highest release rates were found for aluminum, titanium, molybdenum and manganese. display

But what does this mean for the sea on a beach? For their model calculation, the scientists assumed that the number of bathers on a Mediterranean beach would be typical for a summer's day. The bathers spent an average of 18 grams of sunscreen this is half the recommended amount. A quarter of this sunscreen is washed off while bathing and gets into the sea water. The simulation then showed how the composition of the seawater in this section of the beach changes as a result.

Even a bathing day changes the seawater

The "beach model" revealed: Even a bathing day can significantly increase the content of some metals in beach water near the beach. "The highest increases we found at Titan at 19.8 percent, aluminum at four percent and lead at 0.2 percent, " report Rodriguez-Romero and her team. Copper, cobalt, manganese and cadmium also showed a clear increase, albeit only in the range of a few hundredths of a percent.

"But these trace metals play a biological key role in the ocean even at low concentrations, " explain the researchers. "Therefore, even tiny amounts of the dissolved concentrations of these metals could have an impact on the marine environment." For example, cadmium and lead already have a toxic effect on algae cells in the amounts released in the model. Aluminum is known to damage diatoms, and titanium is putting mussels under oxidative stress, studies show.

Ecological consequences still largely unknown

According to the researchers, sunscreens could have an impact on the marine environment, especially on heavily visited beaches. This is especially true when the beaches are in bays with little water exchange. So far, however, the effects of most of the metals studied here on marine organisms have hardly been studied, as they report. In view of the enormous tourist crowds that visited the beaches of the Mediterranean every summer, this was urgently needed.

"On the beaches of this sea millions of visitors enjoy every year, in 2016 alone there were more than 300 million tourists, " said Rodriguez-Romero and her team. If you then extrapolate the amount of sunscreen used and flushed into the water, this could have unrecognized biological consequences. (Environmental Science & Technology, 2019; doi: 10.1021 / acs.est.9b02739)

Source: American Chemical Society

- Nadja Podbregar