Cancer-causing 'forever chemicals' are leaching into water and soils around the world, a report has warned.
Chinese researchers reviewed a decade of research to study how the chemicals move into groundwater and soil.
The chemicals – PFAS – are man-made, spread in the atmosphere, and can now be found in rain and snow in the world's remotest places.
They are produced by industry and are extremely persistent in the atmosphere, the researchers warned.
PFAS is a collective name for perfluoroalkyl and polyfluorinated alkyl substances or highly fluorinated substances that have a similar chemical structure.
Read more: What are ‘forever chemicals’?
All PFAS are either extremely persistent in the environment or break down into extremely persistent chemicals, which has earned them the nickname 'forever chemicals'.
PFAS have been associated with a wide range of serious health problems, including cancer, learning and behavioural problems in children, infertility and pregnancy complications, increased cholesterol, and immune system issues.
The scientists, led by Xueyan Lyu, of Nanjing University of Information Science and Technology, write: "There are thousands of different PFAs compounds and only a few of them have been studied in detail."
This makes the job of tracing them difficult, the researchers said.
The team added that certain PFAS are more likely to pollute groundwater, due to their chemistry.
They write: "Generally PFAS with long carbon chains are retained in soils more strongly.
"Negatively-charged PFAS are more mobile in soil than neutral and positively charged PFAS and can thus readily pollute groundwater. Even more strongly sorbed PFAS can be a sustained source for groundwater pollution."
The researchers said that further research to understand what happens to these chemicals in subsurface environments would help to assess the risks of the chemicals – and develop new ways to clean up contaminated sites.
Earlier this year, a Stockholm University report warned that rainwater everywhere on Earth contains so much cancer-causing 'forever chemicals' that it should be classified as unsafe to drink.
As scientists have understood more about the toxicity of these chemicals, the guidelines for 'safe' levels have become more and more strict – meaning that rainwater would now be classified as 'unsafe'.
Levels of some harmful PFAS in the atmosphere are not declining, despite being phased out by the major manufacturer 3M two decades ago.
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