A widely used pesticide could be placing frog populations in danger by diminishing their ability to reproduce properly.

Not only does exposure to the chemical linuron – a potato herbicide – reduce male frog fertility, it skews the sex ratios of growing tadpoles significantly towards females.

As frog populations are already under global threat of extinction, scientists are concerned that disrupting their natural reproduction could further hasten their decline.

The devastation pesticides have caused to insect populations has been well documented, with German scientists warning of an “ecological Armageddon” when they found numbers had plummeted by 75 per cent in the country’s nature reserves.

Knock-on effects further up the food chain are thought to be behind the disappearance of many bird species from the European countryside.

But pesticides can have toxic effects on other animals too, and there has been a distinct lack of research into their effects on amphibians such as frogs, toads and newts.

To improve this situation, ecotoxicologist Dr Cecilia Berg of the University of Uppsala and a team of Swedish and British researchers set out to investigate the effects of linuron in the West African clawed frog.

A common lab species, the clawed frogs were followed through their entire life cycle in Uppsala’s environmental toxicology lab.

The scientists exposed tadpoles to concentrations of the pesticide similar to those that have been measured in natural environments.

They found that the tadpoles grew ovaries substantially more than they grew testicles, an effect the team attributed to the endocrine disrupting – or hormone disrupting – properties of linuron, which could hinder production of testosterone.

After following the frogs through the adulthood, the researchers found that once they had developed fully the male frogs exposed to the chemicals as tadpoles were less fertile and had certain feminine characteristics.

British mammals’ fight for survival Show all 11 1 /11 British mammals’ fight for survival British mammals’ fight for survival The Mammal Society’s assessment of Britain’s mammal populations is the first such review in over 20 years. The results reveal winners and losers, and highlight some of the key threat’s facing the country’s wildlife such as habitat loss, invasive species and the spread of diseases. British mammals’ fight for survival Hedgehogs Populations of the much-loved insectivore may have declined by as much as 73% Richard Bowler British mammals’ fight for survival Greater mouse-eared bats Only one of these flying mammals has been recorded in the whole country, in a railway tunnel in West Sussex Andrew Harrington British mammals’ fight for survival Rabbits Despite being a common sight across the countryside, rabbits have decreased in number by nearly 10% Danni Thompson British mammals’ fight for survival Black Rats Though not generally considered threatened animals, black rats number have collapsed in recent years due largely to pest control measures. However their far more common cousins, the brown rats, are thriving. Tim Melling British mammals’ fight for survival Red Squirrels Though it is difficult to measure changes in squirrel numbers, their range has shrunk considerably due largely to the spread of squirrel pox virus by invasive grey squirrel Alistair Marsh British mammals’ fight for survival Wildcats There has been a marked decline in wildcat populations, with only around 200 left in Scotland Rachel Profit British mammals’ fight for survival Badgers Due to legal protections badgers have recovered from past persecution and the density of their setts (holes) has increased by over 100% in recent decades Phil Mumby British mammals’ fight for survival Otters The banning of persistent organic pesticides has had a positive population effect on otters Allan Chard British mammals’ fight for survival Fallow Deer The 2018 review estimates a population size of fallow deer almost three times the size of that estimated in the 1995 review – a positive trend that is seen in other deer species. James Shooter British mammals’ fight for survival Eurasian Beavers These aquatic mammals were nearly extinct in Europe at the start of the 20th century, but their reintroduction to the UK have been largely successful Paul Scott

"The results show that pesticides with this mechanism of action can cause permanent damage, such as reduced fertility in frogs exposed at the tadpole stage,” said Dr Berg. “This supports previous research showing that endocrine-disrupting substances in the environment may negatively impact amphibians.”

Scientists are concerned that chemicals leaching from farmland into ponds where amphibians lay their eggs could tamper with the reproduction of wild populations.

While linuron is not licensed for use in the UK – or in Sweden where the study was carried out – it is widely used in other parts of the European Union (EU) and North America.

The results of the study will therefore be crucial in shaping future policy decisions about pesticides in the EU and beyond.

“The European Commission is currently taking several measures to improve pesticide risk assessment,” said Dr Berg. “A new report from the European Food Safety Authority (Efsa), for instance, points to the need to assess the risks of pesticide use to amphibians – something that isn't being done today.”

In April the EU voted for a permanent ban on three pesticides after Efsa ruled that they posed a significant threat to wild bees and honeybees.

With global animal diversity on a downward trajectory, amphibians have already been hit particularly hard, and the additional pressure of widespread pesticide use could add to their burden.

Scientists think around 40 per cent of amphibian species are endangered, with habitat loss, climate change and pollution all taking their toll on these vulnerable animals.