According to the National Park Service, up to 6,000 tons of sunscreen enter reef areas each year, resulting in concern about its potential environmental impact. As a relatively new area of research much more still needs to be done, but here are the scientific findings thus far.
What Are Sunscreens?
In order to understand their impact on the environment, one first needs to have a basic understanding of what sunscreens are. There are two types: chemical and physical. Chemical sunscreen agents such as oxybenzone (benzophenone-3) or avobenzone work by absorbing ultraviolet (UV) light, thereby reducing skin exposure. Physical sunscreens such as titanium dioxide, iron oxide, or zinc oxide, work by reflecting and scattering UV rays in addition to absorbing some of them.
Physical sunscreens can occasionally give an undesirable white cast when applied to the skin. Formulators can reduce the chalky appearance by decreasing the particle size, resulting in some physical sunscreen’s classification as nanoparticles, or compounds whose size is measured on the nanoscale (1 nanometer is one billionth of a meter). Nanoparticles are another potential area of environmental concern in which more research needs to be done because they act differently than larger sized materials.
Sunscreen enters aquatic environments by two primary routes: indirectly from wastewater treatment plants after it has been washed off by consumers at home, or directly washing off from recreational activities such as swimming. Because sunscreen agents are continually added to aquatic environments through these means, they can be considered a persistent pollutant. However, sunscreen concentration in water (either fresh or salt) can vary greatly. The rate at which sunscreen particles sediment or fall to the bottom of the body of water, rather than remaining in suspension, varies for each compound. Additionally, some compounds biodegrade faster than others (and some aren’t biodegradable). The concentration of the amount of sunscreen in water also typically increases with increasing population; one study that tested the composition of surface ocean water around 12 cities in 4 countries found that the highest concentration was around Hong Kong. The same study also found traces of sunscreen compounds in Arctic waters, indicating that these UV filters can even affect waters in which a comparatively very small number of people swim. Several studies of freshwater rivers, basins, and lakes have found sunscreen compounds in both the water and sediment.[7-9]
Effect On Marine Life
One study of German lakes and fish discovered that the concentration of sunscreen ingredients was higher in fish than in the water itself; this concentration was equivalent to the amount of DDT and PCB, banned toxic chemicals, also found in the fish. This high concentration is due to bioaccumulation, or the propensity of substances to build up in an organism faster than their body can excrete it, potentially resulting in toxic build up. In this case, bioaccumulation occurs largely due to the fact that most sunscreen agents are more lipophilic than hydrophilic; that is, they are more easily dissolved in fats and oils (inside the fish) than in water.
Once a sunscreen compound is present in an organism’s body at high enough concentrations, it can have many deleterious effects. In fish, various sunscreen agents have been found to be estrogenic, or able to mimic the hormone estrogen. This hormone effect can alter reproductive success.[10,11] However, the concentration of the culpable compound needs to be higher than typically observed in the environment. Nanoparticle physical sunscreen agents have been shown to cause DNA damage due to the production of reactive oxidative species, a type of free radical. The same study, which used sea urchin embryos, found that nanoparticle zinc oxide is a chemosensitizer, or a compound that increases the susceptibility of an organism to toxic compounds. This effect can occur at lower, nontoxic concentrations.
Sunscreen agents are a highly likely cause of coral bleaching. One study showed that in areas with high concentrations of sunscreen compounds coral bleaching was observed, while in nearby regions with low concentration no coral bleaching was observed. When we think of coral, we are actually thinking of two different organisms living together symbiotically. Coral bleaching occurs when zooxanthellae, a microscopic photosynthetic organism, leave their coral host resulting in the coral’s loss of color. Since most corals receive the bulk of their nutrients from these organisms, their departure typically results in the death of the coral. Chemical sunscreen agents, such as oxybenzone, have been proven to promote viral infection in coral resulting in bleaching. Oxybenzone has also been shown to be a genotoxicant, a compound that damages DNA, as well as a phototoxicant, meaning its negative effects are worsened with the addition of sunlight. These effects occur even at low concentrations. Coral bleaching from sunscreens is so concerning that popular tourist destinations Xcaret and Xel-ha in Mexico have banned the use of sunscreen products containing benzophenone, homosalate, octyl methoxycinnamate, octyl salicylate, octinoxate, oxybenzone, and butyl methoxydibenzoylmethane in 2007.
The Bottom Line
Sunscreen agents affect aquatic environments around the world but are of more acute concern in popular recreational areas. While these compounds are linked to coral bleaching, their effects on other organisms are either not understood well enough or only observed at artificially high concentrations. The biodegradation of sunscreens has not been studied adequately and often varies in different chemical environments (for example, salt water versus fresh water), and any degradation typically occurs over a longer period of time due to their UV-resistant nature. The sunscreen agents that can be degraded by sunlight often result in the formation of free radicals capable of damaging DNA. Based on the data researched, the environmental safety of sunscreen agents remains unclear.
However, this is no excuse to skip sun protection or sunscreen use. The following set of guidelines can help reduce the environmental impact of sunscreens:
- Sun protective clothing should be worn, such as sun protection rated clothing, dive skins or rash guards (also known as swim shirts or surf shirts). This will also reduce the amount of sunscreen needed (it should still be applied to any skin still left exposed, such as your face, hands, and feet).
- Please wait to rinse off your sunscreen until you are bathing instead of in the ocean, lake, or river. The waste water can be treated to reduce its environmental impact.
Raising awareness of this environmental concern is the first step towards understanding it further and searching for solutions.