Every time you go for a swim, some of your sunscreen gets left behind.An estimated 25% of applied sunscreen washes off during recreational water activities, releasing some 5,000 tons annually in reef areas alone, according to a study in Environmental Health Perspectives. That’s equivalent to the weight of about 1,000 elephants, and many of those chemicals are toxic to corals. Some researchers argue that may be a low estimate, noting the experiment did not replicate the friction caused by swimming, which could cause more sunscreen to rub off.Coral reefs support about a quarter of all marine species despite covering just 0.1% of Earth’s oceans. Already under mounting pressure from warming waters, pollution, overfishing and coastal development, reefs face an additional threat from sunscreen chemicals that can damage coral larvae, trigger bleaching and disrupt growth. Scientists say it’s a smaller stressor than climate change, but one consumers can actually address.AdvertisementAdvertisementThe pollution doesn’t just come from swimming. Sunscreen chemicals can enter waterways when people shower, wash towels or urinate after beach trips. Sewage is the largest source of sunscreen contamination in oceans, as conventional treatment plants can’t effectively remove many UV filter compounds, studies show. The chemicals flow from wastewater facilities into rivers and ultimately the sea.Certain chemicals pose documented risks to reefsWhile sunscreen prevents sunburn and reduces skin cancer risk, not all formulas carry the same environmental footprint.The strongest evidence of harm centers on oxybenzone and octinoxate — two widely used chemical UV filters. A 2016 study published in Archives of Environmental Contamination and Toxicology found oxybenzone transforms coral larvae from healthy, mobile organisms into deformed, immobile ones. The chemical causes corals to expel the algae that provide much of their food and color, a stress response known as bleaching. Bleached corals are weakened, more vulnerable to disease and can starve or die if stressful conditions persist. Researchers also found oxybenzone damages DNA and triggers premature skeleton formation that can encase entire larvae. It can also cause corals to bleach at lower temperatures, worsening the effects of marine heat waves driven by climate change.The chemical proves toxic at concentrations as low as 62 parts per trillion — equivalent to one drop in six Olympic-sized swimming pools. At Hanauma Bay, a popular Hawaii snorkeling spot, nearly 2,600 daily visitors left around 412 pounds of sunscreen in the ocean each day, according to a 2017 study by nonprofit Haereticus Environmental Laboratory.AdvertisementAdvertisementScientists have growing concerns abo …
