Selenium

Where It Comes From in New Mexico

In New Mexico, high levels of selenium in water primarily come from natural geological formations, specifically an ancient rock layer known as the Mancos Shale that covers large areas like the San Juan Basin.² When these rocks are exposed to oxygen and groundwater, selenium dissolves and leaks into the water supply.² Human activities heavily accelerate this process; agricultural irrigation washes selenium out of the soil into groundwater and drainage canals, while activities like oil drilling, mining, and abandoned uranium mills, like the former Shiprock mill site, can further stir up and release the mineral into the environment.²

Health Concerns

While low doses are essential for good health, drinking water with high levels of selenium over a short period can cause nausea, vomiting, and diarrhea.¹ Long-term exposure to high selenium levels leads to a dangerous condition called “selenosis.”¹ The main signs of selenosis include hair loss, brittle and deformed fingernails, severe fatigue, and numbness or odd sensations in the extremities.¹˒³ Over a lifetime, excessive selenium exposure can also cause severe damage to the kidneys, liver, and circulatory and nervous systems.³

How Climate Change Exacerbates Exposure Risks

In New Mexico's arid climate, droughts and high temperatures make selenium contamination worse through evaporation; as water evaporates, the selenium left behind becomes much more concentrated in the remaining water supply.² Natural disasters like wildfires can also worsen heavy metal contamination in general. For example, following the massive 2022 Calf Canyon/Hermits Peak Fire, studies found elevated levels of heavy metals in private drinking water wells in Mora County, an area already known for naturally high soil minerals.⁵

How to Mitigate Exposure Risks

If you rely on a private well, it is your responsibility to test and treat your own water to ensure it is safe, as the government does not regulate private wells.⁴

• Test your water: Have your well water tested by a certified laboratory to check for selenium and other heavy metals, especially if you live in rural areas with high geologic selenium levels.⁵

• Never boil the water: Boiling your water will not remove selenium; instead, it simply evaporates the water and leaves the selenium behind, making it even more concentrated and dangerous to drink.⁴˒⁵

• Filter your water: If your water tests high for selenium, you can install specialized water treatment systems in your home, such as point-of-use reverse osmosis or distillation systems, which are highly effective at removing more than 90 percent of selenium and other harmful metals.³˒⁴