MORE than a quarter of the world’s rivers are poisoned with over-the-counter and prescription drugs, according to new research by York academics.

The research involved monitoring rivers across the world and UK - including in York.

Concentrations have reached “potentially toxic levels” - endangering people, fish and other wildlife, say scientists.

Medications that target hormones, for example, have induced sex changes in marine animals.

Project co-leader Dr John Wilkinson, of the University of York, said: “Environmental exposure to active pharmaceutical ingredients (APIs) harms ecosystems and, potentially, human health through mechanisms such as antimicrobial resistance.

“We’ve known for over two decades now that they make their way into the aquatic environment where they may affect the biology of living organisms.

“But one of the largest problems we have faced in tackling this issue is that we have not been very representative when monitoring these contaminants, with almost all of the data focused on a select few areas in North America, Western Europe and China.”

The most comprehensive study to date looked at 258 rivers across the globe - including the Thames in London and the Amazon in Brazil.

It found pharmaceutical pollution is contaminating water on every continent. A total of 54 sampling locations were selected in the UK.

Drugs were detected in all - apart from four in remote Snowdonia in Wales. The most contaminated was the River Clyde in Glasgow.

Dr Wilkinson said: “Concentrations in the UK were in line with what we’ve observed more generally across Europe.”

The most frequently detected drug in British waterways was carbamazepine prescribed for epilepsy - found at 69 per cent of the sites.

Dr Wilkinson said: “There are 19.5 million people who live across the cities where we did monitoring work in the UK - London, Leeds, York, Glasgow, Northern Wales and Belfast.

“That’s nearly a third of the population.”

The world’s worst hit regions are the ones that have been analysed the least - sub-Saharan Africa, South America and parts of southern Asia.

Less than a quarter of waste water is treated - and technology is unable to filter out most pharmaceuticals.

There was a strong link with socio-economic status - with lower-middle income nations most vulnerable.

Local communities with an older average age and high unemployment and poverty rates were also more at risk.

Dumping of rubbish along banks and septic tank contents in rivers, poor drugs manufacturing and inadequate wastewater management were other key factors.

Over one-in-four sites contained pharmaceutical effluence that was likely harm the environment.

The chemical cocktails were a mix of drugs ranging from antibiotics to beta blockers, hay fever pills and anti-psychotics.

It’s hoped increased monitoring will lead to strategies that limit the effects.

The findings were published in the journal Proceedings of the National Academy of Sciences (PNAS).