In a study that attempted to duplicate humans’ exposure to arsenic throughout their entire lifetime, researchers at the National Institute of Environmental Health Sciences found significant increases in lung tumors in mice exposed to very low levels of arsenic, levels similar to those that humans might encounter (Waalkes MP et al. Arch Toxicol. doi:10.1007/s00204-014-1305-8 [published online July 9, 2014]).
Millions of people obtain their drinking water from private wells, for which there are no established standards. Arsenic levels in public drinking water cannot exceed 10 parts per billion (ppb), but researchers say that because of differing rates of metabolism between humans and rodents, mice must be exposed to greater concentrations of arsenic in drinking water than humans to achieve the same biological dose and similar health effect.
Hampton T. Arsenic at Low Levels Linked With Cancer in Rodents. JAMA. 2014;312(8):779. doi:10.1001/jama.2014.10967