Is road salt changing sex ratios in frogs?
Female frogs may be mutating into males, potentially endangering the population. The culprit? Something motorists rely to keep their roads ice-free during the frigid winter months.
According to new research from Yale University and Rensselaer Polytechnic Institute, exposing frogs to sodium chloride, or road salt, commonly used to de-ice paved surfaces, may have a “masculinizing effect” on would-be female frogs during their development.
The study, published in the Canadian Journal of Fisheries and Aquatic Sciences, showed that the female population of a group of tadpoles exposed to the salt dropped by about 10 percent by the time the amphibians had transformed into frogs.
“Females are the ones who make the babies,” he said. “So when the population is more male, that’s usually a problem.”
For the experiment — conducted at the Rensselaer Aquatic Lab in Troy, N.Y. — researchers filled 500-liter tanks with water and varying levels of both road salt, and “leaf litter,” or fallen leaves, from maple and oak trees. They found that the sodium chloride effectively masculinized the developing frogs. This happens when a element, such as sodium, binds to a receptor in cells and mimics a sex hormone, such as testosterone or estrogen, essentially changing the creature’s gender.
Researchers also found that oak leaf litter has a feminizing effect on the frogs, but Lambert said it’s minimal compared to the masculinizing effect of the salt.
The research wasn’t shocking to Jenny Dickson, a wildlife biologist with the state Department of Energy and Environmental Protection. It’s long been known that chemical runoff into water habitats can affect the gender development of reptiles and amphibians, and this is just another example, she said.
It’s unclear how far-reaching the effects of this phenomenon might be, but “it certainly is a serious concern,” Dickson said.
Frogs can help control certain insect populations, including mosquitoes, Dickson said.
“If there’s a reduction in the frog population, that can have an impact on the ecological services they provide,” she said.
About 22 million metric tons of road salt are applied to roads in the United States each year. In Connecticut, Department of Transportation spokesman Kevin Nursick said, over a recent five-year period, the state used an average of about 150,000 tons of road salt a year. However, he also pointed out that the DOT is the smallest user of road salt in the state, behind both the private sector and the various cities and towns.
Nursick said the state tries to be judicious in how much salt it uses but, right now, there isn’t a better de-icing alternative.
“Salt isn’t perfect,” he said. “But pound for pound, no one else has a material that’s effective and affordable, with a lower impact on the environment.”
Lambert said researchers are testing various road-salt products to see if they have less of an impact on frog populations. In the meantime, he agreed that options are limited.
“You can’t just stop salting roads at wintertime,” he said. “It’s a safety hazard.”