The Tiny but Toxic Ingredient in Your Sunscreen
The report, published in the journal Environmental Science and Technology, found that nanomaterials—nano-zinc oxide used in most sunscreens and some toothpastes and beauty products—make sea urchin embryos much more vulnerable to other environmental toxins. Nano-copper oxide found in boat paint has the same effect. Previous studies have shown that nanomaterials in sunscreens can harm phytoplankton, which are eaten by small fish, shrimp, and whales.
Nanomaterials are tiny chemical compounds about 100,000 times smaller than the diameter of a human hair. The microscopic particles can enter the body through the skin, ingestion, or inhalation.
“Both of these nanomaterials are nontoxic to cells at low levels,” said coauthor Gary Cherr, a professor and interim director of the UC Davis Bodega Marine Laboratory. “But even at low levels, where these kind of materials are not toxic to the embryos themselves, they can act as what we call chemosensitizers.”
Researchers took white sea urchin embryos, which are highly sensitive to toxic materials, and exposed them to various amounts of nano-zinc and nano-copper oxides.
Embryo cells expel toxins through a series of tiny pumps. But when nanomaterials inside the cells begin to dissolve, they overtax the pumps and allow other harmful environmental chemicals to enter the cells and remain there.
“It’s kind of like a doorway where people are crowding through to get out, but a certain group of people are stuck inside and can’t get out while the crowd is there, and they’re the ones that are toxic,” Cherr said.
The results can be devastating.
“If you expose them to a concentration of one of these other toxic chemicals, you might have 50 percent of the cells developing normally and 50 percent dying or being abnormal,” Cherr said. “And then you add nanomaterials, and suddenly that goes down to only 10 percent developing normally.”
At higher levels, the nanomaterials themselves can halt embryo development.
The tiny particles are not just harmful to sea urchins.
“Embryos and larvae from a variety of different marine and aquatic organisms all have a significant amount of these pumps that protect them from environmental chemicals,” Cherr said. “We assume they would be affected in the same way.”
Such chemosensitization may also be affecting adult fish, Cherr added, because their gills contain large concentrations of the detoxifying pumps.
Zinc oxide has been used in sunscreens for generations, but the nano-zinc formula was only introduced in the past decade, Cherr said. It has largely replaced the chemical para-aminobenzoic acid, which can act as an endocrine disrupter and affect hormones in fish.
The nano-zinc in sunscreen, even in waterproof products, washes off into the water when sunbathers go for a swim.
Several studies are now under way in Europe to determine how much nano-zinc enters the water. “In some places there are tens of thousands of bathers in shallow coves in the summertime,” Cherr said. “There are some early indications that [nano-zinc levels] could be quite significant.”
Some new “green” sunscreens contain no nano-zinc oxide, Cherr noted, and concerned consumers should check the label if they want to avoid contributing to the problem.
Nano-copper oxide, meanwhile, was introduced to boat paint over the last few years. Copper prevents the accumulation of mussels and barnacles on the bottom of boats.
Traditional copper-based paint for boats sheds more of the toxic metal than the nano-copper formula, which does not have to be applied to boat bottoms as often. But nano-copper also causes chemosensitization in sea urchin embryos. Scientists are now trying to develop copper-free paint formulas.