World’s rivers laced with unsafe concentrations of antibiotics

27 May 2019

Image: © Mahbubur Rahman/

Some of the world’s rivers have almost 300 times the safe limit of antibiotics, threatening both humans and fragile ecosystems.

One of the first global studies into the concentration levels of antibiotics in rivers has returned some truly worrying results. At a time when antibiotic resistance is on the rise due to extensive use by humans and in agriculture, some of the world’s rivers now have concentrations hundreds of times more than what would be considered a ‘safe’ level.

Researchers from the University of York were looking for 14 of the most common antibiotics across 72 countries in six continents, and found traces at 65pc of the monitoring sites. In Bangladesh, Metronidazole – used to treat skin and mouth infections – was found in concentrations 300 times greater than what could be considered safe.

By comparison, the Thames river in London showed an antibiotic concentration of 233 nanograms per litre (ng/l), 170 times less than what was found in Bangladesh. The private sector coalition created to prevent widespread antibiotic resistance, the AMR Industry Alliance, has deemed levels ranging from 20,000 to 32,000 ng/l as safe, depending on the antibiotic.

The most common type of antibiotic found was trimethoprim – used to treat urinary tract infections – which was detected in 307 of the 711 test sites. Ciprofloxacin – used to treat a number of bacterial infections – was most frequently found to have exceeded safe levels, surpassing the threshold at 51 test sites.

Nations that had the highest levels of antibiotics in their rivers included Bangladesh, Kenya, Ghana, Pakistan and Nigeria. Overall, the safe limits were exceeded in Asia and Africa, but sites in Europe, North America and South America also returned a number of cases, highlighting a global problem.

Sites at high risk of large concentrations were typically near wastewater treatment systems and other waste sites, but the researchers noted that areas of conflict – such as the Israeli-Palestine border – also showed high concentrations.

‘Results are quite eye-opening and worrying’

“The results are quite eye-opening and worrying, demonstrating the widespread contamination of river systems around the world with antibiotic compounds,” said Prof Alistair Boxall.

“Many scientists and policymakers now recognise the role of the natural environment in the antimicrobial resistance problem. Our data show that antibiotic contamination of rivers could be an important contributor.”

The findings were gathered as part of a major logistic challenge, where 92 sampling kits had to be flown across the globe and frozen samples then returned to the University of York.

Dr John Wilkinson, coordinator of the monitoring work, said this had never been done before.

“Until now, the majority of environmental monitoring work for antibiotics has been done in Europe, North America and China. Often on only a handful of antibiotics,” he said. “We know very little about the scale of problem globally.”

The findings are to be unveiled during two presentations at the annual meeting of the Society of Environmental Toxicology and Chemistry in Helsinki, Finland, today and tomorrow (28 May).

Colm Gorey was a senior journalist with Silicon Republic