Impact of low levels of arsenic in drinking water with incident urologic cancers in Washington state.

Arsenic is a known carcinogen that may contaminate human drinking water. Since 2000, regulations in the United States (US) have limited arsenic in the water to 10 parts per billion (ppb). However, evidence suggests that even low levels of arsenic may still increase the risks of bladder, prostate and kidney cancer. We performed an ecological study in Washington State (WA) to examine the relationship between low levels of arsenic in drinking water and incident urologic cancers. Average county-level arsenic levels in drinking water were estimated from public water systems in WA (2000-2018). Incident bladder, prostate and kidney cancer cases in WA (2014-2018) were ascertained from the Department of Health. Multivariable Poisson regression was conducted to estimate adjusted incidence rate ratios (aIRRs) for the associations between arsenic exposure and cancer risk. We found that average arsenic levels at the county-level were 3.8 ppb (SD 1.1). When comparing the highest (4.16-7.50 ppb) versus lowest (1.65-3.14 ppb) quartiles for arsenic levels in drinking water, the highest quartile was associated with an increased risk of bladder cancer (aIRR: 1.21, 95%CI 1.09-1.35), prostate cancer (aIRR: 1.20, 95%CI 1.12-1.29), with a suggestive positive association with kidney cancer (aIRR: 1.10, 95%CI 0.97-1.26). These findings demonstrate that low levels (<10ppb) of arsenic were associated with an increased risk of incident bladder and prostate cancer. Additionally, these data suggest that US drinking water standards may not adequately reduce the risk of cancer associated with low levels of arsenic exposure.