Metronidazole is an antibiotic commonly prescribed to treat infections such as pelvic inflammation or other vaginal diseases. It can cause side effects that include seizures, numbness, and diarrhea, and should not be used while pregnant or during breastfeeding. It’s perfectly safe—provided it’s taken as prescribed.
A combination of wastewater treatment leaks, human and animal waste, and runoff from drug manufacturers, however, has led to one river in Bangladesh showing concentrations of metronidazole 300 times greater than the “safe” level. A new study, presented on May 27 at the Society of Environmental Toxicology and Chemistry conference in Finland, revealed that hundreds of other rivers are also contaminated with antibiotics, often at unsafe levels. In total, researchers found antibiotics at more than 450 testing sites across 72 countries—65% of the 711 sites tested. Some 111 of the sites with antibiotics had unsafe levels, and the most concerning locations were in Asia and Africa. At one site in Kenya, antibiotic levels were so high that all fish had perished.
Beyond its impact on wildlife, the pollution may allow antibiotic-resistant superbugs to flourish, and could in turn usher in a global health emergency that would put millions at risk. Through repeated exposure to antibiotics, bacteria mutate and evolve, developing resistance to medicines that would ordinarily save lives.
“It’s quite scary and depressing,” researcher Alistair Boxall, who is an environmental scientist at the UK’s University of York, told the Guardian. “We could have large parts of the environment that have got antibiotics at levels high enough to affect resistance.”
London’s Thames was found to be contaminated by five different kinds of antibiotics, including nearly four times the safe level of clarithromycin, which is prescribed for infections like pneumonia and bronchitis. Overdoses of the drug may result in abdominal pain, vomiting, nausea, and diarrhea. The Danube, which flows from Germany through 10 countries to the Black Sea, was found to be Europe’s most polluted river. Some 8% of European sites showed antibiotic levels beyond safe limits.
The study is the largest of its kind, with sampling kits flown out across the world, frozen, and then couriered back to York-based researchers Boxall and John Wilkinson. “We know very little about the scale of problem globally,” Wilkinson said in a statement. ”Our study helps fill this key knowledge gap with data being generated for countries that had never been monitored before.”