Selenium in Drinking Water

Selenium is a metal found in natural deposits as ores containing other elements. At typical groundwater pH values (7.0 to 9.5) only anionic forms of selenious (Se IV) or selenic (Se VI) acid are found.


Contaminant  In Water As (pH = 7.0 to 9.5) Maximum Contaminant Level

Selenium (Se)

Selenate (Se2-)
Biselenite (HSeO3-)
Selenite (SeO32-)

US EPA:
MCL* = 0.05 mg/L
MCLG** = 0.05 mg/L

WHO† Guideline = 0.04 mg/L

Sources of Contaminant

Natural deposits
Releases from copper smelting

Potential Health Effects

Hair and fingernail changes
Damage to the peripheral nervous system
Fatigue and irritability

Treatment Methods

Activated alumina adsorption (85-95% reduction)
Strong base anion type I Cl- (60-95% reduction)
Distillation (>98% reduction)
Reverse osmosis (>90% reduction)

*Maximum Contaminant Level (MCL) — The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to MCLGs as feasible using the best available treatment technology and taking cost into consideration. MCLs are enforceable standards.

**Maximum Contaminant Level Goal (MCLG) - The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety and are non-enforceable public health goals.

WHO† - World Health Organization


Click here to open WQA's Technical Fact Sheet on Selenium.

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