Unsafe levels of antibiotics contaminate world's rivers: Study

Concentrations of antibiotics in some of the world's rivers exceed 'safe' levels by up to 300 times, according to a global study of some of the most iconic water bodies including Thames and Tigris.

Researchers from the University of York in the UK looked for 14 commonly used antibiotics in rivers in 72 countries across six continents and found antibiotics at 65 per cent of the sites monitored.

"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," said John Wilkinson, from the University of York.

"Our study helps fill this key knowledge gap with data being generated for countries that had never been monitored before," said Wilkinson.

Metronidazole, which is used to treat bacterial infections including skin and mouth infections, exceeded safe levels by the biggest margin, with concentrations at one site in Bangladesh 300 times greater than the 'safe' level.

In the River Thames and one of its tributaries in London, the researchers detected a maximum total antibiotic concentration of 233 nanograms per litre (ng/l), whereas in Bangladesh the concentration was 170 times higher.

The most prevalent antibiotic was trimethoprim, which was detected at 307 of the 711 sites tested and is primarily used to treat urinary tract infections.

The researchers compared the monitoring data with 'safe' levels recently established by the AMR Industry Alliance which, depending on the antibiotic, range from 20-32,000 ng/l.

Ciproflaxacin, which is used to treat a number of bacterial infections, was the compound that most frequently exceeded safe levels, surpassing the safety threshold in 51 places.

The team said that the 'safe' limits were most frequently exceeded in Asia and Africa, but sites in Europe, North America and South America also had levels of concern showing that antibiotic contamination was a "global problem."