In a massive survey of rivers conducted in 72 countries, researchers found antibiotics in 66 percent of the 711 sites sampled. Many of the waterways most polluted by the drug were in Asia and Africa, where not much data had been available until now.

Environmental pollution caused by antibiotics is a factor in microbial drug resistance, which threatens public health.

People should be as concerned about the evolution of resistance abroad as they are about resistance in their own backyards, says William Gaze, a microbial ecologist at the University of Exeter Medical School in England, who was not involved in the research.

Even if rich countries decrease antibiotic contamination, drug-resistant microbes can travel from one side of the world to the other in people who travel, birds that migrate, or in the marketing of food and animals, he says. "It's a global problem and we need global solutions."

About a third of the sites surveyed last year contained no detectable level of antibiotics. But 66 percent, or 470 of the sites, tested positive for at least one of the 14 types of antibiotics tested.

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And nearly 16 percent, or 111 sites, contained concentrations considered unsafe, based on safety levels estimated by the AMR Industry Alliance, a global biotech and pharmaceutical coalition. The alliance set its safety limits based on levels that would neither kill algae in the environment nor promote resistance by killing susceptible bacteria.

"I wasn't expecting the degree of concentration we saw. This was quite revealing," says environmental chemist Alistair Boxall of the University of York in England, who conducted the research with York University colleague John Wilkinson. The two presented their results May 27-28 in Helsinki at a meeting of the Society for Environmental Toxicology and Chemistry .

The scale of the study is unprecedented, Boxall says. Previously, most research focused on North America, Europe and China, so Boxall and Wilkinson sent water collection kits to colleagues around the world and then tested samples from a total of 165 rivers for 61 drugs, including the 14 antibiotics.

Samples continue to come in and researchers plan to release more data in the future. "Ultimately, it would be nice if we could get samples from every country in the world," Boxall says.

Many sites of those found to have unsafe levels of antibiotics were contaminated with more than one of these drugs.

The most commonly found antibiotic was trimethoprim, used to treat urinary tract infections, which appeared at 43 percent of the sampled sites. Other antibiotics that occurred were sulfamethoxazole, ciprofloxacin and metronidazole. Some of the antibiotics the researchers looked for - including oxytetracycline, amoxicillin and cloxacillin - were not detected at any sites.

Samples from the Kirtankhola River in Bangladesh near the south-central city of Barisal contained the highest concentrations of antibiotics of any site surveyed. The level of metronidazole approached 40,000 nanograms per liter, or about 300 times the safe level. The commonly prescribed drug ciprofloxacin exceeded safe levels by a factor of eight.

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High concentrations of antibiotics were also found in river samples near the cities of Accra, Ghana; Nairobi, Kenya; Lahore, Pakistan; Lagos, Nigeria; and Nablus, Israel. The most contaminated sites in Europe were in an urban tributary of the Danube in Austria. And the most polluted river in the U.S. was found in North Liberty, Iowa, near many animal farms.

To find out how antibiotics were getting into waterways, researchers did some investigating. Google Street View showed that some contaminated sites are near pharmaceutical factories, which could be releasing discharge into waterways, researchers say.

Photos of several heavily polluted sites in Africa and Asia also showed trash piled up along riverbanks, as well as sewage haul trucks nearby, Boxall says.

River characteristics, such as the depth of the water, how fast it flows and whether a sampling site is located downstream of a city or hospital would also have an impact on drug concentrations, Boxall says.

Boxall, Wilkinson and their colleagues plan to test how antibiotics at the levels measured may affect algae and other organisms in the environment. The researchers hope their work will lead policymakers around the world to take action to curb antibiotic pollution.

ENGLISH ORIGINAL: Many of the world's rivers are flash with dangerous levels of antibiotics [Science News].