CFTR and cystic fibrosis: In a recent study of 100 adults in Bangladesh – a country with among the highest arsenic exposure in the world – water and toenail arsenic concentrations were higher among adults with increased sweat conductivity (a marker for elevated sweat chloride concentrations), and those with the highest sweat conductivity did not have CFTR mutations consistent with a genetic diagnosis of cystic fibrosis.24 This finding in humans supports the hypothesis that arsenic induces CFTR degradation, as was seen in experimental models, and that CFTR degradation may be a mechanism of arsenic toxicity.