Hundreds of rivers across the world have been contaminated by 'dangerous' levels of antibiotics, according to a new study.
The study, led by the University of York, looked for 144 commonly-used antibiotics in samples from major global rivers from 72 countries across the world including the Danube, Mekong, Seine, Thames, Tiber, and Tigris.
They found antibiotics in 65 percent of the rivers - with concentrations exceeding 'safe levels' (as defined by AMR Industry Alliance, which aims to tackle antimicrobial resistance) by up to 300 times in some samples.
The findings have worried scientists because drug pollution is one of the main ways bacteria can become medicine-resistant. In addition, there is also the possibility of contaminated water entering both drinking supplies and the food chain.
Among the antibiotics found in the water were trimethoprim - which is primarily used to treat urinary tract infections, metronidazole - which is used to treat skin and mouth infections, and ciproflaxacin - used in the treatment of respiratory, urinary and skin infections.
The areas which most exceeded safety limits were Asia and Africa, but the levels found in Europe, North America, and South America meant antibiotic contamination is a 'global problem'.
High-risk sites were regularly next to wastewater treatment systems, waste dumps, or sewage dumps, according to the study.
'Scale of the problem'
Dr. John Wilkinson, who coordinated the monitoring work, said no other study had been done on this scale.
"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. We know very little about the scale of problem globally," he added.
"Our study helps to fill this key knowledge gap with data being generated for countries that had never been monitored before."
'Eye-opening and worrying'
Professor Alistair Boxall, of the York Environmental Sustainability Institute, said: "The results are quite eye opening and worrying, demonstrating the widespread contamination of river systems around the world with antibiotic compounds.
"Many scientists and policymakers now recognize the role of the natural environment in the antimicrobial resistance problem. Our data show that antibiotic contamination of rivers could be an important contributor.
"Solving the problem is going to be a mammoth challenge and will need investment in infrastructure for waste and wastewater treatment, tighter regulation and the cleaning up of already contaminated sites."