Researchers in the US have found that even a very low exposure to arsenic can cause cancer in humans, "raising the possibility that no level of arsenic appears to be safe".
The study carried out at the National Toxicology Programme (NTP) Laboratory in the US found that mice exposed to low doses of arsenic in drinking water developed lung cancer.
"This is the first study to show tumour development in animals exposed to very low levels of arsenic, levels similar to which humans might be exposed," said Michael Waalkes, director of NTP.
Arsenic is present in the environment as a naturally occurring substance or due to contamination from human activity.
In this study, the concentrations given to the mice in their drinking water were 50 parts per billion (ppb), 500 ppb, and 5,000 ppb.
Fifty ppb is the lowest concentration that has been tested in an animal study, and researchers say that because of differing rates of metabolism mice need to be exposed to greater concentrations of arsenic than humans to achieve the same biological dose and similar health effects.
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The researchers used a model that duplicates how humans are exposed to arsenic throughout their entire lifetime.
"Although this is only one study, it adds to a growing body of evidence showing adverse health effects from very low exposures to arsenic, raising the possibility that no level of arsenic appears to be safe," said Linda Birnbaum, director of National Institute of Environmental Health Sciences.
The study appeared in the journal Archives of Toxicology.