Fatbergs are a threat to human health because they are breeding grounds for superbugs immune to antibiotics, a new investigation has found.

The Telegraph reports that analysis of a 750m fatberg — a congealed mass of fat and discarded items — in a London sewer revealed strains of bacteria including E. coli and listeria, which are resistant to life-saving drugs.

Experts have warned that people could be exposed to the bugs if a blocked drain pushes sewage back up through domestic or commercial pipes. Normal antibiotics would prove useless against the virulent strains.

Antimicrobial-resistance is one of the gravest current threats to global health. Experts estimating it could kill 10 million people a year by 2050.

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Fatbergs are made of cooking oil and other items flushed into sewers. Photo / Mark Johnson
Fatbergs are made of cooking oil and other items flushed into sewers. Photo / Mark Johnson

The study by Thames Water and Channel 4 also found prohibited gym supplements in the fatberg, including the muscle-gain drugs hordenine and ostarine banned by the World Anti-Doping Agency, reports the Telegraph.

The banned drugs accounted for more than half the proportion of pharmaceuticals found in the sample, more than illegal recreational drugs such as cocaine and MDMA.

The fatberg was found under the South Bank in London and is believed to be the largest known example of the phenomenon in Britain, dwarfing the 250m Whitechapel fatberg, which was discovered last year.

Forensic analysis showed cooking fat made up the bulk of the berg, and typical items in it included cotton buds, wet wipes, condoms and nappies.

Fatbergs are believed to be the result of growing city populations where sewers are struggling to cope with changing habits.

Alex Saunders, waste networks manager for Thames Water, said: "We and other water companies are facing a constant battle to keep the nation's sewers free from fatbergs and other blockages."

About twice as much performance-enhancing drugs than illegal drugs such as cocaine were found in the 750m London fatberg. Photo / Mark Johnson
About twice as much performance-enhancing drugs than illegal drugs such as cocaine were found in the 750m London fatberg. Photo / Mark Johnson

Fatbergs typically build after fat sticks to the side of the pipe, which attracts items such as wet wipes and then more fat.

Tests in the Channel 4 investigation revealed some of the wet wipes found are marketed as flushable, even though they do not disintegrate in a sewer.

The Telegraph reports that dealing with fatbergs costs around £80 million ($157m) a year.

"For the sake of our sewer workers, please only flush the three Ps - pee, poo and toilet paper. Don't feed the fatberg," Saunders said.