Selenium
Se·Affects brain, liver, skin,
An essential trace nutrient that becomes neurotoxic and dermatologic above the EPA limit of 0.05 mg/L. High-selenium groundwater is common in parts of the western United States.
Se
EPA limit
0.05 mg/L (MCL)
Most at risk
Well users in seleniferous soil regions (Great Plains, Rocky Mountain West), residents near coal-mining or coal-ash sites
Found in
City water · Well water · Industrial areas
AquaOx filters
YesKDF-55 + activated carbon
What it does to you
Health effects
Selenium is a paradox: an essential trace nutrient at low doses (the body needs about 55 µg per day for thyroid and antioxidant function), but neurotoxic and dermatologically damaging at chronic intakes only modestly above the EPA MCL.
The classic chronic-toxicity syndrome is selenosis: hair loss, brittle and discolored nails, garlic breath odor, fatigue, peripheral neuropathy (numbness and tingling in hands and feet), and a characteristic dermatitis. Long-term high exposure damages the liver and the nervous system.
Acute high-dose selenium poisoning causes severe gastrointestinal distress and, at extreme doses, cardiac failure. The 50 µg/L MCL is set well below any acute-effect threshold but accounts for cumulative chronic exposure across food and water.
Where it comes from
How it gets into your water
Selenium enters drinking water primarily through natural geological dissolution. Seleniferous soils and rocks are common across the Great Plains and Rocky Mountain West, particularly in parts of South Dakota, Wyoming, Colorado, Nebraska, Kansas, and the Dakotas. Groundwater moving through these formations picks up dissolved selenium.
Irrigation drainage in selenium-rich agricultural regions (most famously the Kesterson Reservoir crisis in California's Central Valley in the 1980s) concentrates selenium in surface water and shallow groundwater.
Industrial sources include coal mining and coal-ash disposal (selenium is a trace component of coal), metal refining, glass manufacturing, and electronics manufacturing.
Natural geological deposits
Seleniferous soils in the Great Plains and West
Coal mining and coal-ash waste
Leaches from unlined disposal ponds
Irrigation drainage in seleniferous regions
Concentrates in evaporation ponds
Glass and electronics manufacturing
Process discharge from semiconductor production
Find out for yourself
Is it in your water?
Selenium is included in the standard inorganic package every utility tests and reports on their Consumer Confidence Report. Most municipal supplies run well below the 0.05 mg/L MCL.
Private well owners in the western United States, particularly in seleniferous-soil regions, have substantially higher background selenium risk. If your well is in South Dakota, Wyoming, Nebraska, Colorado, or the western Dakotas, request a selenium test as part of your inorganic panel.
Residents downstream of coal-fired power plants or active coal-ash disposal sites should also test specifically for selenium, since coal-ash leachate is one of the most consistent sources of waterborne selenium contamination.
The fix
How AquaOx filters it
AquaOx's KDF-55 copper-zinc media reduces selenium through redox chemistry, with the alloy converting soluble selenium ions into insoluble forms that get trapped in the filter bed. The activated carbon stages add adsorption capacity for residual selenium compounds.
For wells with documented high natural selenium (above 0.025 mg/L in your inorganic panel), AquaOx recommends pairing the whole-house system with a point-of-use reverse osmosis unit at the kitchen sink. RO membranes reject selenium to well below the EPA MCL and give you a dedicated barrier for drinking and cooking water.