Selenium in Water

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Selenium is a mineral that gets into water from natural deposits, mining operations, and agricultural runoff. Low levels of selenium are essential to human health, but selenium is known to have serious health effects if found in elevated levels in drinking water.

This glossary discusses the important facts about selenium in water, including the causes of selenium contamination, the health risks of this mineral, and how to protect your family from selenium exposure.

❔ What is Selenium?

Selenium is a mineral and chemical element found in natural deposits of other elements. While selenium is a nutrient that the human body needs to survive, drinking excess selenium in water may lead to dangerous health effects.

💡 Selenium has a photoconductive action (meaning that its electrical resistance decreases with increased illumination) and a photovoltaic action (meaning that it converts light to electricity). These properties give the mineral a range of industrial uses.

The most common industrial use of selenium is in photocopier and electronic components. Selenium is also used to produce rubber, glass, textiles, metal alloys, petroleum, pigments, and solar cells.

In water, selenium is commonly found in three forms:

  • Selenate (Se2-)
  • Selenite (SeO32-)
  • Biselenite (HSeO3-)
In Water AsSe2-, HSeO3-, SeO32-
SourcesNatural deposits
Selenium discharge from mines and refineries
Industrial wastewater and agricultural runoff
Run-off from lead and copper refineries
Waste disposal sites
Contaminant Levels (MCLs)
US EPA: 0.05 mg/L, 0.05 mg/L (MCLG)
WHO Guideline: 0.04 mg/L
EWG: 0.03 mg/L
Potential Health RisksHair and fingernail loss
Changes in peripheral nerves
Decreased thyroid hormone production
Gastrointestinal disturbances
TreatmentsReverse osmosis
Activated alumina adsorption
Anion exchange

🩺 What are the Potential Health Effects of Selenium?

The majority of selenium compounds and selenium in food are absorbed effectively during digestion. However, selenium sulfide and elemental selenium aren’t absorbed properly by the GI tract.

Humans need selenium to survive – in fact, a selenium deficiency is just as dangerous as consuming too much selenium. The type and amount of selenium consumed affect our response to this mineral.

Short-term oral exposure to high levels of selenium may cause:

  • Vomiting
  • Nausea
  • Diarrhea

According to a CDC report, a high intake of selenium is associated with the following symptoms and health effects:

  • Gastrointestinal disturbances
  • Discoloration of the skin
  • Decayed teeth
  • Hair and fingernail loss
  • Skin lesions
  • Changes in peripheral nerves
  • Decreased thyroid hormone production

Thankfully, reports of selenium toxicity in drinking water are rare, and many people with symptoms make a full recovery after reducing their exposure to selenium.

Nausea after drinking water

🚰 How Does Selenium Get Into Drinking Water?

There are numerous ways that selenium gets into the earth, including:

  • Natural deposits
  • Selenium discharge from mines and refineries
  • Industrial wastewater
  • Agricultural runoff
  • Run-off from lead and copper refineries
  • Municipal waste disposal sites

Once in the earth, selenium can enter surface water and groundwater supplies through surface runoff, rain, snowfall, and soil seepage. As water flows over or through sedimentary rocks and soils containing selenium, some of the selenium dissolves into the water.

Selenium dust also gets into the air as a result of several industrial processes, including smelting (using heat to separate metals from their natural sources), burning coal and petroleum fuels, and refining other metals. Rainfall or snow carries selenium to the earth, where it is picked up by water supplies.

📉 Do Water Treatment Facilities Monitor Levels of Selenium in Drinking Water?

Yes, water treatment facilities monitor, test for, and use treatment technologies to remove selenium in public water systems.

There are several guidelines and regulations in place for selenium in public drinking water supplies:

  • Environmental Protection Agency (EPA) Maximum Contaminant Level: 0.05 mg/L (50 PPB)
  • EPA Maximum Contaminant Level OAL: 0.05 mg/L (50 PPB)
  • World Health Organization (WHO) Guideline: 0.04 mg/L

Your local public water supplier is legally obliged to stick to the EPA’s Maximum Contaminant Levels and maintain a maximum of 0.05 mg/L selenium in water. The EPA’s MCL is the maximum level of selenium, while the MCLG is the maximum amount of selenium that has no known health risk in water.

Not all facilities adequately reduce their levels of selenium to the EPA-deemed safe amount. According to a database produced by the Environmental Working Group (EWG), 56 utilities in 11 states serve more than 34,000 people water containing higher concentrations of selenium than recommended in the EPA health guidelines.

You may not feel comfortable drinking “safe” lower concentrations of selenium in your water, either. The EWG believes that the EPA’s Maximum Contaminant Level for selenium is too low, and proposes its own more stringent regulation of 30 PPB.

Person turning the faucet on

🔎 How Can I Tell if Selenium is in My Drinking Water?

Selenium doesn’t have a taste or smell in water, and is invisible to the eye. Very high selenium levels in water may have a garlicky odor. Generally, though, you won’t know by looking at, smelling, or tasting your water whether it contains this contaminant.

The only way to know how much selenium your water contains is to conduct a water test. The most effective way to test for selenium is with a laboratory test, which can detect different forms of this contaminant and compare these levels to national guidelines. A good lab report will also give information on the human health problems associated with selenium in your water sample, and the best selenium treatment methods for water.

If you want to test for other contaminants alongside selenium, consider buying a water testing package, which can detect a range of impurities that commonly occur together in water.

Water testing with tap score

👩🏽‍⚕️ How Can I Protect My Family from Selenium in Drinking Water?

The best way to protect your family from chronic exposure to selenium is to install a water treatment system that can reduce or remove this contaminant.

There are several drinking water treatment units that are capable of removing selenium from contaminated water:

  • Reverse osmosis – A reverse osmosis system is one of the most effective methods of selenium removal, removing up to 90 % on average, of the mineral from drinking water. The reverse osmosis process involves a sediment pre-filter, a carbon filter, a semipermeable membrane, and a post-carbon filter. The semipermeable membrane is capable of removing virtually all total dissolved solids from water. RO systems are most commonly installed as under-sink or countertop units.
  • Activated alumina adsorptionActivated alumina is a type of carbon filter that has been treated to give the media extra capabilities. This filter uses adsorption to grab onto selenium particles, pulling them out of water. This process removes between 85% and 95% of selenium. Activated alumina filters can be installed in point of entry or point of use filtration systems.
  • Distillation – A distiller purifies water by boiling and evaporation. Treated water from a distiller is almost 100% pure and contains virtually no contaminants. This process removes up to 98% of selenium found in drinking water. Most distillers are installed as countertop units and take several hours to produce a batch of purified water.
  • Anion exchange – While ion exchange is most commonly known for its water softening abilities, this process is moderately effective at reducing selenium, too. Anion exchange can reduce between 60% and 95% of selenium, depending on the concentration of sulfate in drinking water. Anion exchange systems are installed as point of entry water treatment systems.

If testing uncovers large quantities of selenium in your water, switch to bottled water temporarily while you compare selenium removal solutions.

Reverse osmosis system and distiller

⚠️ How Else Can I Be Exposed to Selenium?

Selenium in drinking water is one of the most common sources of exposure. Other ways you may be exposed to selenium are:

  • Consuming selenium in foods. Selenium occurs naturally in certain foods, including brazil nuts, seafood, poultry, eggs, grains, cereals, and dairy products.
  • Inhaling selenium dust in the air. You’re most likely to be exposed to high levels of selenium if you live near factories where selenium is processed or produced, or near coal-burning plants or hazardous waste sites.

Remember, selenium is an essential nutrient, and being deficient in this mineral may cause several health effects. We need about 55 micrograms of selenium daily, and the safe upper limit for this mineral is 400 micrograms a day. Overdosing on selenium is rare, and is only likely to happen if you abuse selenium supplements or your water supply contains an unnaturally high concentration of the mineral.

If you think you’ve been exposed to dangerously high levels of selenium, book an appointment with your doctor, who can conduct a blood or urine test to measure the selenium levels in your body.

📝 Where Can I Get More Information?

You can find more information about selenium in water, including sources of selenium and selenium’s health risks, in the links below.

  • Jennifer Byrd
    Water Treatment Specialist

    For 20+ years, Jennifer has championed clean water. From navigating operations to leading sales, she's tackled diverse industry challenges. Now, at Redbird Water, she crafts personalized solutions for homes, businesses, and factories. A past Chamber President and industry advocate, Jennifer leverages her expertise in cutting-edge filtration and custom design to transform water concerns into crystal-clear solutions.

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