Around 22 million tonnes (24.2 million tons) of salt is thrown onto sidewalks and highways across the US each year in an attempt to de-ice the roads. No doubt, it makes your winter commute a lot safer. But unfortunately, it's also having a peculiar effect on frogs.
Naturally occurring chemicals found in the salts can change the sex of frogs during development, thereby screwing up the healthy sex ratios in their populations, according to ecologists from Yale School of Forestry & Environmental Studies. The study was recently published in the Canadian Journal of Fisheries and Aquatic Sciences.
"Many scientists have studied similar effects from exposure to pharmaceuticals and pesticides, but now we're seeing it from chemicals found in common road salt," said lead author Max Lambert, a doctoral student at Yale, in a statement.
The researchers say that the salt has a "masculinizing" effect that results in a sex reversal during the early development of the frogs. They hypothesized the strange phenomenon could be caused by molecules, such as sodium, which could bind the receptor in cells and mimic the effects of testosterone or estrogen.
"There is a very small testosterone-like effect with one salt molecule. But if you're dumping lots and lots of pounds of salt on the roads every winter that washes into these ponds, it can have a large effect,” Lambert explained.
They tested out their ideas through an experiment involving a series of 500-liter (110 gallons) water tanks, with varying levels of road salt, then introducing a frog population. Before the introduction of salt, the population had a female-heavy population, but when the salt was introduced the portion of females dropped by 10 percent.
“So you're not only seeing fewer females but smaller females that may not be able to produce as many eggs. And the eggs are probably going to be lower quality," Lambert added.
The researchers concluded that if road salt was affecting amphibians in a sub-lethal way, their study could pave the way for more research into how other aquatic species may also be being affected by road salts.