376 Estimation of cutaneous squamous cell carcinoma incidence attributable to arsenic in U.S. water supplies

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Arsenic in water supplies potentially exposes millions of people to increased disease risk worldwide. Despite strengthened regulation, arsenic concentrations commonly found in U.S. water supplies may increase the incidence of cutaneous squamous cell carcinoma (cSCC). We estimated cSCC incidence attributable to arsenic in water supplies among U.S. non-Hispanic whites, a demographic with disproportionately high skin cancer incidence. We determined the number of people exposed to various concentrations of arsenic in water supplies by analyzing three datasets: urine samples from the National Health and Nutrition Examination Survey (2015–2016), public water supply data from the Environmental Protection Agency (EPA) Six-Year Review 3 (2006–2011), and private well user data from Ayotte et al. (2017). Among 743 representative patients, total arsenic concentrations in urine had a median (interquartile range) of 3.00 μg/l (2.25–4.02). Public water supplies serving 10 million out of 151 million non-Hispanic white users had detectable levels of arsenic. An estimated 1.6 million out of 33 million non-Hispanic white private well users had water arsenic concentrations above 10 μg/l (EPA limit for public water). These data were combined with published odds ratios for cSCC incidence with arsenic exposure, assuming that total arsenic concentrations in urine less than 4.76 μg/l do not affect cSCC risk. Based on urinary arsenic data, 32,512 out of 2,548,845 cSCCs annually in the U.S. are attributable to arsenic in water supplies. This estimate includes 26,228 cSCCs among public water users and 6,284 among private well users. Separately, water supply data suggest that at least 10,361 and 4,380 cSCCs are attributable to arsenic in public water supplies and in private wells, respectively. Overall, up to 1.3% of cSCC incidence in the U.S. may be attributed to arsenic in current water supplies. Thousands of cSCCs may be prevented by further restricting arsenic in U.S. water supplies.