Sunscreen Production of Hydrogen Peroxide in Coastal Waters

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Titanium dioxide

Many people use titanium dioxide as sunscreen. – but it may be harmful for the marine environment. Photo by Benjah-bmm27.

Sunscreen protects your skin, but what does it do to the fish and plants in the water?

According to new research, sunscreen creams, when released in coastal waters, could be dangerous for the marine environment.

This is because their components, titanium dioxide and zinc oxide, under sun irradiation, can form hydrogen peroxide, which can be harmful for some marine organisms.

Spanish scientists reported about worrying high level of hydrogen peroxide in Mediterranean waters.

Hydrogen Peroxide

Hydrogen Peroxide (H2O2) is a chemical compound with high reactivity. Because of this, it has several important applications; for instance, it can be used as a bleach or disinfectant.

At the same time, however, its high reactivity can cause damage to living organisms, such as plants and marine species.

In a marine environment, H2O2 can be formed from the reaction of ultraviolet light with organic matter and/or algae present in the waters.

Sunscreen for UV Protection

Ultraviolet (UV) radiations can be very dangerous for human health. Prolonged exposure to UV rays can, in fact, lead to DNA damage and illness such as skin cancer.

Generally, sunscreen creams are used to give UV protection. Sunscreens are chemicals which can absorb the UV light and stop it reaching the skin.

Although there are non-toxic sunscreens, (including a potential new sunscreen made from cod fish bones) titanium dioxide (TiO2) and zinc oxide (ZnO) are the most common inorganic sunscreens commercially available. They are produced in the form of powder or nanoparticles, and then added to an appropriate cream.

Problems with TiO2 and ZnO

Both titanium and zinc oxides are quite effective sunscreens, as they absorb over all the range of UV radiations. Their use, however, may cause other problems.

This is because both oxides are photoactive materials; this means that, when irradiated with light, they can generate reactive species, such as free radicals. These species can be dangerous for human skin, with similar effects to that caused by UV radiations.

Considering in particular TiO2, to try to reduce its photoactivity, a very thin protective coating of aluminum oxide can be applied on the surface of the powder. In this way, the material should generate less (or no) reactive species, without losing its good sunscreen properties.

Effect on the Marine Environment

Further than for human health, the use of TiO2 and ZnO also raised concern for the possible effects it can have on the environment; because of this, several studies were performed to try to establish the real threat that these sunscreens can pose.

Scientists from two Spanish institutes – the Mediterranean Institute for Advances Studies (IMEDEA-CSIC) and the Andalusian Institute for Marine Science (ICMAN-CSIC) – published very interesting results in this field, in the journal Environmental Science and Technology. They measured the formation of H2O2 caused by the presence of sunscreens in the water.

Reason for This Study

Decoded Science spoke to Mr. David Sánchez, PhD student who took part to the study, explaining the reason for this research.

“Today people are more aware of the dangers caused by UV light, so they tend to use sunscreens a lot. At the same time, there is an increasing number of tourists visiting Spanish Mediterranean beaches. Of course, this is something very good for the economy; at the same time, however, we have to see what can be the effects on the environment.

Because of this, we decided to see what was happening in these waters; in particular we wanted to see if sunscreens could cause the formation of H2O2.”

H2O2 Formation

According to Mr. Sánchez:

“H2O2 can be formed with a reaction between the reactive species generated by the sunscreens and other ions (H+, OH-, etc.) naturally present in the water.”

The researchers tested three different commercial sunscreens: One of the sunscreens contained TiO2 (sunscreen A), one contained ZnO (sunscreen B) and another one which contained none of the oxides (sunscreen C). They placed a fixed amount of each sunscreen (0.125 g/l) into marine water samples, under natural sunlight, and monitored the formation of hydrogen peroxide with time, from early morning to sunset.

“We saw that with both sunscreens A and B there was remarkable increase in the H2O2 concentration in correspondence with the hours of maximum solar radiation; with sunscreen C, on the other hand, the increase was much smaller. H2O2 content was particularly high with sunscreen A (TiO2), more than 270 mg/l. We observed this despite the presence of the protective aluminum oxide coating on the TiO2 surface, which was supposed to reduce the formation of the reactive species.

These data clearly show that the reactivity of these sunscreens could really be a problem.”

Hydrogen Peroxide could damage marine species. Photo by kconnor.

Hydrogen Peroxide could damage marine species. Photo by kconnor.

Field Sampling

As well as laboratory tests, Mr. Sánchez and coworkers also did some in-field sampling.

“After our simulation tests, we wanted to see what was the real situation in the sea waters; that’s why we decided to do some field sampling.” Mr. Sánchez explains.

They measured the concentration of H2O2 in Palmira beach, a semi-enclosed beach of Majorca island. They also monitored the quantity of titanium coming from TiO2 dissolved in the water; for both compounds the concentration was measured during a 24 hour period.

Results showed that during maximum solar radiation H2O2 concentration reached values as high as 8.5 mg/L; titanium concentration, on the other hand, was about 38 mg/L.

Sunscreen Dangers: Worrying Results

According to Mr. Sánchez:

“The H2O2 concentration we measured in Palmira beach could cause problems to the environment, as it could contribute to oxidative stress for coastal marine organisms. This value is higher than the H2O2 concentration in other waters, probably because we monitored an enclosed bay, poorly flushed by currents. In Spain, and generally in the Mediterranean sea, there are many bays with similar characteristics; therefore it is likely that H2O2 levels there are also high.

We are also concerned that, with further tourism development, this value could increase even more, and potentially cause even more problems.

This is an issue we should be aware of and keep in mind, to have tourism which is ecologically sustainable.”

Sunscreen Chemicals, Tourism, and Ecology

Although sunscreens can potentially prevent health problems for people, indications are that they could have a profound impact on the marine environment. Increased tourism, and the resulting increase in sunscreen in the water, could result in a toxic habitat for the very organisms the tourists are coming to see.

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