“There is a very small testosterone-like effect with one salt molecule,” said Max Lambert, who led the study.

“But if you’re dumping lots and lots of salt on the roads every winter that washes into these ponds, it can have a large effect.

“The health and abundance of females is obviously critical for the sustainability of any population because they’re the ones that make the babies, so if you have a population that is becoming male-based, the population might be at risk.”

The researchers created a series of water treatments containing varying levels of road salt, reducing the proportion of female frogs reared in the 500-liter tank by one in ten.

“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,” said Mr Lambert.

Rick Relyea, who co-authored the study, added: “The potential consequences to amphibian populations are interesting, including the continual masculinzation of frog populations for many generations in habitats contaminated with high concentrations of road salt, which could potentially affect the abundances of frogs in these habitats.”