Salting roads and pavements during winter damages frog populations by turning would-be females into males, a major new study warns.

Naturally occurring chemicals used in de-icing substances find their way into ponds, where the amphibians breed, and change the sex of young frogs during early development.

Experts at Yale University in the US found that gritting can reduce the number of female frogs by 10pc in a given area, as well as harming the quality and size of their eggs.

The scientists say the practice could threaten the sustainability of frogs in the wild and may also be harming other aquatic species.

Each year more than two million tonnes of salt are spread on Britain's motorways, trunk and main roads alone during icy conditions to give people and vehicles better grip.

Numbers of the common frog have already suffered huge declines - thought to be around 80pc - over the past 20 years due to outbreaks of ranavirus, which causes them to bleed to death.

The new research, published in the 'Canadian Journal of Fisheries and Aquatic Sciences', concluded that salt had a "masculinising" effect that triggered a "sex reversal" mechanism during the early life of the frog.

The researchers believe that sodium binds to the amphibian's receptor cells, mimicking the actions of testosterone or estrogen and altering the ultimate sex of the frog.

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

Irish Independent