Some of the world’s waterways exceed antibiotic concentrations considered ‘safe’ — by up to 300 times, the first global study on this subject reports.

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The researchers found meaningful concentrations of 14 common antibiotics across 65% of the sites they analyzed (the survey looked at rivers in 72 states across six continents). In many cases, these concentrations exceeded the values laid down in international safety guidelines.

By far the most concentrated offender was Metronidazole, which is used to treat bacterial infections including skin and oral infections. In one site in Bangladesh, it exceeded safe concentration values by a factor of more than 300.

Drugs, rivers, rock and roll

“The results are quite eye opening and worrying, demonstrating the widespread contamination of river systems around the world with antibiotic compounds,” Alistair Boxall, a scientist at the York environmental Sustainability Institute, said in a statement.

The research team compared drug concentrations retrieved from 711 locations around the world to ‘safe’ levels recently established by the AMR Industry Alliance. Depending on the antibiotic, these levels range from 20-32,000 nanograms per liter (ng/l). The AMR Industry Alliance is a grouping of more than 100 “biotech, diagnostics, generics and research-based pharmaceutical companies and associations” that aim to “provide sustainable solutions to curb antimicrobial resistance”, their website reads. The safety levels they set are meant to stop, or at least stifle, the development and spread of antibiotic resistance in pathogenic and non-pathogenic bacteria.

The team sent test kits to 92 partners across the world, who retrieved samples from local river systems. The samples were then frozen and shipped back to the University of York for testing. Some of the most iconic rivers in the world, including the Chao Phraya, Danube, Mekong, Seine, Thames, Tiber, and Tigris, were analyzed.

Which makes the team’s findings all the more worrying. On one hand, these antibiotics are very wide-spread in natural waterways. Safety limits were most frequently exceeded in Asia and Africa, but Europe and the Americas also have some waterways plagued by unsafe levels of antibiotics. The antibiotic seen most often was Trimethoprim, which was detected at 307 of the 711 sites tested. Trimethoprim is primarily prescribed for urinary tract infections. Ciprofloxacin, which is used to treat a number of bacterial infections, was the compound that most frequently exceeded safe levels, surpassing the threshold in 51 places.

On the other hand, the sheer concentrations the team found at some sites are nothing short of baffling. In the River Thames and one of its tributaries in London, the researchers detected a maximum total antibiotic concentration of 233 ng/l, which is over the safety limit, but not immensely so. At one site in Bangladesh, however, the concentration was 170 times higher.

Sites in Bangladesh, Kenya, Ghana, Pakistan, and Nigeria exceeded safety limits by the highest degree. In Europe, that ‘honor’ fell to one site in Austria, which boasted the highest antibiotic levels of all sites the team studied on the continent. High-risk areas tended to form around wastewater treatment systems, waste or sewage dumps, and in some areas of political turmoil, including the Israeli and Palestinian border.

Dr. John Wilkinson, from the Department of Environment and Geography, who coordinated the monitoring work, says that this study has a lot to teach us, because no other study on the subject had been done on this scale.

“Until now, the majority of environmental monitoring work for antibiotics has been done in Europe, N. America and China. Often on only a handful of antibiotics. We know very little about the scale of problem globally. Our study helps fill this key knowledge gap with data being generated for countries that had never been monitored before.”

“The results are quite eye opening and worrying,” adds Professor Alistair Boxall, Theme Leader of the York Environmental Sustainability Institute, “demonstrating the widespread contamination of river systems around the world with antibiotic compounds. Many scientists and policy makers 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.”

So can we solve the problem? The good news is that yes, yes we can. The bad news is that it’s going to be a very hard task, a “mammoth challenge” in Prof. Boxall’s words. We need tighter regulation, we need to develop and build better infrastructure for waste and wastewater treatment, and we’ll also have to clean the sites that are already contaminated.

The findings of this study were presented during two sessions at the annual meeting of the Society of Environmental Toxicology and Chemistry (SETAC) in Helsinki on 27 and 28 May.