River systems around the world are coursing with over-the-counter and prescription drugs waste which harms the environment, researchers have found.

If trends persist, the amount of pharmaceutical effluence leaching into waterways could increase by two-thirds before 2050, scientists told the European Geosciences Union conference in Vienna on Tuesday.

“A large part of the freshwater ecosystems is potentially endangered by the high concentration of pharmaceuticals,” said Francesco Bregoli, a researcher at the IHE Delft Institute for Water Education in the Netherlands, and leader of an international team that developed a method for tracking drug pollution “hotspots”.

A large number of drugs – analgesics, antibiotics, anti-platelet agents, hormones, psychiatric drugs, antihistamines – have been found at levels dangerous for wildlife.

Endocrine disruptors, for example, have induced sex changes in fish and amphibians.

Bregoli and his team used a common anti-inflammation drug, diclofenac, as a proxy to estimate the presence and spread of other medications in freshwater ecosystems.

Both the European Union and the US Environmental Protection Agency have identified diclofenac as an environmental threat. Veterinary use of it has driven a sub-species of vultures on the Indian subcontinent to the brink of extinction.

More than 10,000km of rivers around the world have concentrations of diclofenac above the EU “watch list” limit of 100 nanograms a litre, the new research found.

“Diclofenac emissions are similar to any of thousands of pharmaceuticals and personal care products,” said Bregoli.

Global consumption of diclofenac tops 2,400 tonnes a year. Several hundred tonnes remain in human waste, and only a small fraction – about 7% – of that is filtered out by treatment plants.

Another 20% is absorbed by ecosystems, and the rest go into oceans.

Bregoli and his team developed a computer model to predict current and future pharma pollution based on criteria such as population densities, sewage systems and drugs sales.

They compared the results to data gathered from 1,400 spot measurements of diclofenac toxicity taken from around the world. Most of the data points were in Europe and North America.

Pollution levels are likely to be substantially higher in much of Latin America, Africa and Asia where less than a quarter of waste water is treated, and with technology unable to filter out most pharmaceuticals.

Technology alone cannot solve the problem, said Bregoli.

“We need a substantial reduction in consumption,” he said.

In other research presented at the conference, scientists found that the rapid expansion of sewage systems in large urban areas has sharply raised river pollution because much of it is not adequately treated.

“In 2000, sewage was a source of pollution in about 50% of the rivers in the world,” said Maryna Strokal, a scientist at Wageningen University and Research in the Netherlands.

“By 2010, sewage was a source of pollution in almost all rivers worldwide.”

Antibiotics and chemicals waste is also driving the evolution of drug-resistant bacteria, UN Environment warned in a study in December.

Between 70% and 80% of all antibiotics consumed by humans and farm animals – thousands of tonnes – find their way into natural environments, it said.