Sunscreens, while vital for protecting our skin from UV radiation, contain compounds that are not necessarily innocuous for the environment. A group of scientists studying the waters around the Spanish island of Majorca has recently shown that these chemicals do accumulate in the sea and may have toxic effects on marine organisms. Surprisingly, sunscreens were also found to contain large amounts of nutrients, which could disrupt the natural balance of aquatic ecosystems.
Credit: Flickr / earthlydelights
Scientists in Spain have found that chemicals in sunscreen constitute a source of water pollution, both by their toxicity to phytoplankton and by adding nutrients to the ecosystem that may encourage harmful algal blooms. Marine chemist Antonio Tovar-Sánchez of the Mediterranean Institute for Advanced Studies (IMEDEA) in Majorca, Spain, explains that the question is of particular importance locally, as his island receives ten million sunblock-coated visitors annually who come for its beaches. But sunscreen is already among the fastest growing products globally(1). Estimates say that, in 30 years, 75% of the world’s population will live along the coast. That adds up to a lot of sunblock potentially washing off into the sea, but until now, little attention has been given to what the consequences might be.
Based on knowledge of the ingredients listed on the back of your sunblock bottle, Dr. Tovar-Sánchez and colleagues decided to address the question in an article published recently in PLOS ONE (available on MyScienceWork). “Titanium dioxide (TiO2) is a chemical used by wastewater treatment plants as an oxidizer,” he says, “and there’s tons of it in your sunscreen.” TiO2 reflects and scatters UV radiation, and so was recommended in the past to protect skin from the sun. When it was later found to cause cancer, a method was developed to coat the compound in silicate, making it safe for human use. However, in the water, this protective silicate layer breaks down. This begged the question of what consequences sunscreens might have on the environment.
Sampling the sea
The scientists took samples of water from two densely populated beaches on Majorca, and one control area, a pristine beach hardly used by anyone. They collected samples over 24 hours but, to avoid contamination, the researchers themselves could not use sunscreen. The team ended up “completely pink,” Tovar-Sánchez remembers.
Two types of seawater samples were taken and analyzed. The surface microlayer was collected with a glass plate sampler – a pane of glass dipped into the sea to which drops of this very thin surface layer, along with any oily sunblock components, adhere. The subsurface layer, at a depth of 1 to 5 cm, was collected with a pump. All samples were tested in the lab for their chemical content, while commercial sunscreens were analyzed for their effects on one marine organism, a species of phytoplankton, and for the presence of nutrients.
Photo: Antonio Tovar-Sánchez
Sunscreen pollution & toxicity
Four of the principal compounds used in sunblock products(2) were found in these waters, particularly concentrated on the surface, as many of these chemicals are insoluble in water. Levels were highest between 12pm and 6pm, corresponding to the peak number of beachgoers and the peak of sunblock application. At midday, the concentrations of these sunscreen components in the surface microlayer exceeded background levels by 60 to 90%. They were even detected at the little-used control beach, indicating how water moves around the island, spreading pollutants.
Thirteen commercial sunscreens were tested for toxicity at different concentrations using the common Mediterranean phytoplankton, Chaetoceros gracilis. Sunblocks were acutely toxic only at levels higher than those found in the seawater samples, but growth of the phytoplankton was inhibited even at very low concentrations. The most toxic sunscreen was a spray form. The researchers believe this could be explained by the greater number of water-soluble compounds in solar sprays; these components are more accessible for uptake by phytoplankton and, thus, more toxic.
“Huge amounts of nutrients”
As a matter of routine, the researchers also analyzed commercial sunscreens for the presence of nutrients, like phosphates and ammonium. Antonio Tovar-Sánchez says that they didn’t expect to find any, but were proved wrong: the sunblocks examined contained “huge amounts of nutrients.” Their addition to aquatic ecosystems, as occurs with agricultural runoff containing fertilizers, has been seen to cause algal, or phytoplankton, blooms (eutrophication). A given nutrient will affect one or another species of these microorganisms, favoring its growth and changing the balance within the community. For environmental reasons, “you can’t use phosphate in soaps,” Dr. Tovar-Sánchez points out, “but sunscreens have a lot. They should also be considered a source of pollutants.”
Protecting people and the environment
The results of this study indicate the toxicity of UV-filtering sunscreen compounds on one kind of phytoplankton (and a resistant one at that, according to Dr. Tovar-Sánchez.) Now, the effects on other species and how these chemicals may accumulate in the food chain need to be investigated. Antonio’s team is currently studying the effects of titanium dioxide on plants, for example. The chemical is insoluble and will sink to the bottom where it can affect vegetation that grows 2 to 5 meters below the surface.
As for the unexpected nutrient content, a pharmaceutical company producing sunscreen wouldn’t, or couldn’t, tell the researchers where this came from. “They probably don’t know,” Antonio believes. “We think they come from fragrances, but sunscreen has a hundred ingredients,” and producers may buy them without knowing their exact composition.
Since publishing the paper, Tovar-Sánchez says the big issue for him has become the public’s concern. “People are very worried about the environment, but they think, ‘What are we supposed to do? We have to use sunscreen.’ The only thing I know is we have to work together—scientists and companies—to find a balance between protecting the environment and healthy humans.” For starters, we humans could try to avoid the beach when the sun is at its strongest, reducing the need for sunscreen along with the risk of a painful, pink burn.
1- Nielsen Executive News Report from Nielsen Global Services (2007) What’s Hot around the Globe: Insights on Personal Care Products. (p. 14)
2- Benzophehone 3 (BZ-3), 4-methylbenzylidene camphor (4-MBC), TiO2 and ZnO