In a massive global study, led by researchers at the University of York, hundreds of rivers around the world have been tested for levels of common antibiotics. The study found 65 percent of all samples contained some concentration of antibiotics, with the worst cases showing levels more than 300 times higher than the generally accepted safe threshold.

The study is the first to coordinate such a broad global survey of the world's rivers, examining levels of 14 common antibiotics from 711 sites across 72 countries. John Wilkinson, one of the researchers coordinating this large project, suggests that alongside many regions never before monitored, this is the largest antibiotic survey ever conducted.

"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," says Wilkinson. "We know very little about the scale of problem globally."

The striking results found antibiotics in 65 percent of the 711 sites, and 111 samples revealed concentrations exceeding generally accepted safe levels. The majority of sites exceeding safe antibiotic concentrations were found in Africa and Asia, however, eight percent of sites sampled in Europe and 15 percent of sites sampled in North America were above safe limits.

Five different antibiotics were found in London's famous River Thames, while the Danube was Europe's most contaminated river. The most commonly found antibiotic was trimethoprim, used to treat urinary tracts infections and found in nearly half of all sampled rivers. One of the most polluted samples in the study came from a site in Bangladesh, revealing the presence of metronidazole at levels 300 times higher than the safe recommendation.

"The results are quite eye opening and worrying, demonstrating the widespread contamination of river systems around the world with antibiotic compounds," says Alistair Boxall, from the York Environmental Sustainability Institute.

A major concern following on from this research is the role this contamination may play in the ongoing evolution of antibiotic-resistant bacteria. Prior research has revealed the presence of antibiotic-resistant bacteria in UK waterways, and this new study suggests the broader global contamination of our waterways with antibiotics could be speeding up this potential crisis.

"Many scientists and policy makers now recognize the role of the natural environment in the antimicrobial resistance problem," says Boxall. "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."

The research is to be presented at upcoming annual meeting of the Society of Environmental Toxicology and Chemistry (SETAC) in Helsinki this week.

Source: University of York