When the summer heat is on it is hard to find a freshwater river or lake that doesn’t have recreationalists cooling off and having fun. Even in the cold headwaters of Montana, the rivers and lakes are filled with floaters, swimmers, boaters, and fisherman.
I had the opportunity to float several of Montana’s Rivers over the past weekend. The weather was exceptionally hot and dry which brought record numbers to cool off. I saw recreators of all ages enjoying relaxation and splash-time under a cloudless sky. During this adventure, my son jumped into the water from the drift boat and I noticed an oil sheen dispersing from his body. Of course, like most things I witness, I formulated a hypothesis about the oily sheen…The oily sheen is from my son’s sunscreen.
I am very conscious of the ill effects of certain chemicals in commercial sunscreen. However, his sunscreen was a somewhat “natural” product.
So, What About Everyone Else’s Oily Sheen?
Most of the people floating on the river for endless hours in the hot cloudless summer sun were likely wearing plenty of sunscreen that contained plenty of chemicals.
According to the Environmental Working Group’s website, the most common sunscreens on the market contain a combination of chemical filters. The most worrisome chemical is oxybenzone, added to nearly 65 percent of the non-mineral sunscreens in EWG’s 2017 sunscreen database.
Oxybenzone has been identified as a contributing cause to the bleaching of coral reefs as described in a recent Time magazine article. Coral reefs are exposed to oxybenzone primarily by sunscreen wash-off as people swim near them. Reefs can also be exposed through discharge of wastewater that contain the chemical from bathing wash-off and through urine. Oxybenzone is in urine because the body absorbs it.
What About Oxybenzone Toxicity to Freshwater Aquatic Life?
Oxybenzone is one of many pharmaceutical and personal care products that have not been extensively studied and do not have freshwater water quality standards. While freshwater lakes and rivers do not have coral reefs, they do have other very sensitive species such as freshwater mussels, clams, frogs, invertebrates, and fish. Studies show oxybenzone can trigger outbreaks of viral infection in coral reefs (Danovaro 2008) and can cause feminization of male fish (Kunz 2006). These studies were performed in saltwater but could correlate to sensitive freshwater ecosystems. This is purely speculative of course, I am not aware of any toxicity studies addressing freshwater species.
How Much Oxybenzone is Too Much Oxybenzone?
Researchers studying coral reefs found that oxybenzone can induce damage coral reefs at concentrations as low as 62 parts per trillion (Downs et al, 2015). To put this in perspective, beaches in Hawaii have oxybenzone levels higher than 700 parts per trillion early in the morning before swimmers even arrive. Other emerging research is showing that oxybenzone concentrations on nearshore reefs around the world are commonly between 100 parts per trillion and 100 parts per billion — well within the range of being a significant environmental threat (Downs et al, 2015).
On a very hot day, I would expect that there is a tremendous amount of oxybenzone entering freshwater environments by wash-off, urine and wastewater discharges. Is this enough to cause damage to freshwater ecosystems? Perhaps a good topic for a master’s thesis! Until more is known, I suggest caution not only for your own health when you buy sunscreen, but also for the potential for freshwater ecosystem damage.
What are the Alternatives?
Some sunscreens do not use oxybenzone. The most common replacement chemicals are zinc oxide and titanium dioxide. Niether of these chemicals absorb into the skin. Instead they create physical barriers to UV rays. Sunscreens that use zinc oxide or titanium oxide instead of oxybenzone are more expensive and require frequent re-application. Similar to oxybenxone there are no water quality standards for zinc oxide and titanium dioxide. Yet, I am not aware of any studies or evidence suggesting a risk to humans and aquatic life.
Danovaro R, Bongiorni L, Corinaldesi C, Giovannelli D, Damiani E, Astolfi P, et al. 2008. Sunscreens cause coral bleaching by promoting viral infections. Environmental health perspectives 116(4): 441-447.
Downs CA, Kramarsky-Winter E, Segal R, et al. Toxicopathological Effects of the Sunscreen UV Filter,Oxybenzone (Benzophenone-3), on Coral Planulae and Cultured Primary Cells and Its Environmental Contamination in Hawaii and the U.S. Virgin Islands. Arch Environ Contam Toxicol 2015 Oct 20. doi: 10.1007/s00244-015-0227-7.v
Kunz PY, Galicia HF, Fent K. 2006. Comparison of in vitro and in vivo estrogenic activity of UV filters in fish. Toxicol Sci 90(2): 349-361.