Arsenic
Arsenic is a contaminant of groundwater and rice, a proven cause of lung, skin and bladder cancer, and a driver of heart disease. It is also the one toxic metal where lowering exposure has been followed by fewer deaths — but that evidence comes from people drinking water at about ten times the safety guideline, not from the low levels most readers face.
If you drink from a private well, have it tested for arsenic, and if it is high, use a treatment system rated for the form of arsenic your test finds. Vary your grains rather than relying on rice.
Where it comes from
Arsenic is a toxic element found in groundwater. The main exposures are drinking water, especially from private wells, and rice. The World Health Organization's guideline for drinking water is 10 µg per litre.
Cancer and heart disease
The International Agency for Research on Cancer classes arsenic as a definite human carcinogen (Group 1), for lung, skin and bladder cancer.
For the heart, a dose-response meta-analysis found that each doubling of arsenic in drinking water raised the incidence of cardiovascular disease by about 9% and coronary heart-disease mortality by about 16%. Risk rose continuously from the 10 µg/L guideline upward with no evident threshold, though the evidence below the guideline itself is only suggestive.[1] A 2023 American Heart Association scientific statement reviewed arsenic, lead and cadmium together as cardiovascular risk factors; it is a literature review by a writing group, not a formal classification.[2]
Lowering exposure was followed by fewer deaths
Among 10,977 adults in Bangladesh followed to 2022, community well-switching cut average urinary arsenic from 283 to 132 µg per gram of creatinine, more than half. People whose levels fell below the median had about 57% lower cardiovascular mortality than those who stayed high, approaching the risk of people who had never been highly exposed.[3]
Two limits. This was a high-exposure group, with well water averaging around 100 µg/L, about ten times the guideline. And the switching was community-driven, not randomised, so it doesn't show the same payoff at the sub-10 µg/L levels most readers face.
Removing it from water
Reverse osmosis removes more than 95% of arsenic, but that figure is for the oxidised form, arsenate. Groundwater without much oxygen, which includes many wells, more often carries arsenite, which most treatment removes much less well unless it is first converted to arsenate (pre-oxidation). So test before buying, and pick a system rated for what the test finds. Filter choice is covered on Reverse osmosis and Water.
What to do
- Test a private well for arsenic (and lead).
- If it reads high, treat it with a system rated for the arsenic form in your water, which may mean pre-oxidation before reverse osmosis.
- Vary your grains rather than eating rice every day, and cook with clean water.
- Skip chelation and detox products; chelation is for diagnosed metal poisoning, under a physician.
How arsenic fits with other household and dietary toxins is on Environmental toxins.
Further reading
- Moon KA et al. A dose-response meta-analysis of chronic arsenic exposure and incident cardiovascular disease. Int J Epidemiol 2017.[4]
- Wu F et al. Arsenic Exposure Reduction and Chronic Disease Mortality. JAMA 2025.[5]
- Lamas GA et al. Contaminant Metals as Cardiovascular Risk Factors (AHA scientific statement). J Am Heart Assoc 2023.[6]