Arsenic in Private Well Water — Natural Geological Contamination, EPA 10 ug/L MCL, Chronic Low-Dose Exposure Cancer Risk (Bladder, Lung, Skin) — water/air safety profile
High riskApproximately 43 million Americans rely on private wells not regulated by the Safe Drinking Water Act, and arsenic is among the most prevalent and dangerous contaminants in private well water.
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Approximately 43 million Americans rely on private wells not regulated by the Safe Drinking Water Act, and arsenic is among the most prevalent and dangerous contaminants in private well water. Arsenic occurs naturally in geological formations — arsenopyrite, scorodite, and arsenic-bearing iron oxides dissolve under certain pH and redox conditions, particularly in the western US, New England, and upper Midwest. The EPA maximum contaminant level (MCL) for arsenic in public water systems is 10 ug/L (reduced from 50 ug/L in 2006), but private wells are exempt from this standard. USGS surveys indicate that approximately 2.1 million domestic well users in the US are exposed to arsenic above 10 ug/L. Chronic low-dose inorganic arsenic exposure (>10 ug/L over decades) is definitively linked to bladder cancer (OR 2.7 at >50 ug/L), lung cancer (OR 3.1), and skin cancer (IARC Group 1 carcinogen), as well as cardiovascular disease, diabetes, and developmental neurotoxicity. The arsenic-cancer association has no established threshold — even exposures below 10 ug/L may carry incremental risk.
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Natural Contaminant
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Open in water View raw API dataReference data, not professional advice. Aggregates publicly available regulatory and scientific information. Why we built ALETHEIA →