Where is Selenium Most Commonly Found? A Guide to Natural Sources

January 12, 2026 •

4 min read

Selenium is a naturally occurring essential trace mineral that is found unevenly distributed in the Earth's crust. Its presence and concentration vary significantly across different regions, with the amount in plant-based foods depending heavily on the mineral content of the soil in which they are grown. In contrast, animal products tend to have more consistent selenium levels due to regulated dietary intake in livestock.

Quick Summary

The most common sources of selenium include a variety of foods like Brazil nuts, seafood, meat, and grains, alongside its presence in soils and water. The mineral's concentration is highly dependent on geographical location, impacting local agricultural products and human dietary intake.

Key Points

Brazil Nuts are Supreme: A single ounce of Brazil nuts can deliver an extremely high dose of selenium, though levels vary between individual nuts and regions.
Soil is the Source: The fundamental presence of selenium in food is determined by the soil composition; plants absorb it, and animals then consume those plants.
Geographic Hotspots: High-selenium soils are found in specific areas, such as the Great Plains of the US, while other areas like the Pacific Northwest are known for low soil concentrations.
Seafood is Consistent: As a dietary source, fish and shellfish provide a more consistent level of selenium than many plants, as animal diets are often regulated.
Industrial Production: The majority of commercially produced selenium is a byproduct of refining other metals, primarily electrolytic copper.
Plant Accumulators: Certain plants, known as hyperaccumulators, can contain significantly higher levels of selenium, especially when growing on seleniferous soils.
Organic vs. Inorganic: Selenium in food is primarily organic (selenomethionine), which is highly bioavailable, while supplements often contain inorganic forms like selenite or selenate.

The Primary Dietary Sources of Selenium

For humans, the most common way to acquire selenium is through a balanced diet. The selenium content of foods is directly tied to the soil composition of the region where it is produced, though this is more pronounced in plant-based foods. Brazil nuts, for example, are renowned for their exceptionally high selenium concentration.

Seafood and Meats

Seafood is an excellent source of selenium, with some fish and shellfish containing a high concentration of the mineral. Organ meats like beef liver are also particularly rich in selenium.

Fish: Yellowfin tuna, cod, and sardines are notable sources.
Shellfish: Shrimp and crab contain significant levels.
Meats: Pork chops, beef steak, and chicken all contribute to dietary selenium intake.

Plant-Based Foods

The selenium in plant-based foods is highly variable. Plants absorb selenium from the soil, where it is converted into organic forms like selenomethionine.

Brazil Nuts: These nuts are the most potent natural source of selenium, though levels can fluctuate based on the specific tree and soil.
Grains: Bread, pasta, and cereals are major dietary contributors, particularly in regions with selenium-rich soil.
Other Vegetables: Some plants, like garlic and onions, can accumulate selenium more effectively than others.

Distribution of Selenium in Soils

Geographical location is a critical factor in determining where selenium is found. There are significant regional differences in soil selenium content, which in turn impacts the local food supply.

High-Selenium Regions: Soils in the Great Plains of the central and west-central United States are known for being rich in selenium. This is often linked to the weathering of sedimentary rocks from the Cretaceous period. This abundance can lead to high selenium concentrations in locally grown crops, which can be beneficial or, in excessive amounts, toxic to livestock.

Low-Selenium Regions: Conversely, certain areas have very low selenium levels in the soil, leading to deficiencies in local plants and animals. Areas affected include:

The Pacific Northwest and Northeast of the United States.
Parts of Eastern Canada.
Countries such as New Zealand and Finland (which addressed the issue through fertilizer fortification).

Selenium in Industrial Byproducts and Water

Beyond biological systems, selenium is also recovered from industrial processes and is present in certain water sources. Commercially, the element is most often obtained as a byproduct of electrolytic copper refining, where it is found in the anode mud.

Fossil Fuels and Smelting

Coal: Coal combustion releases selenium into the environment. Historically, very high concentrations have been found in coal from specific regions.
Refining: Smelting and refining of metals like copper, lead, and zinc also contribute to environmental selenium.

Water Sources

The concentration of selenium in water is highly variable, depending on the source. In general, surface and ocean waters tend to have very low levels, while some groundwater and springs in seleniferous regions can contain higher, potentially toxic, amounts. This is influenced by natural weathering of rocks and human activities like agricultural runoff.

Comparison of Selenium Sources


Source Type	Examples	Selenium Content	Availability Factor	Key Consideration
Dietary (Plant)	Brazil Nuts, Grains, Some Vegetables	Highly Variable	Dependent on local soil selenium levels	Can be a primary source, but regional differences impact potency.
Dietary (Animal)	Seafood, Meats, Eggs	Generally Consistent	Reliable, as livestock feed is often fortified.	High-protein sources often contain more selenium.
Geological (Soil)	Sedimentary rock formations	Highly Variable	Determines agricultural availability	Alkaline, well-aerated soils have more plant-available selenium.
Industrial	Copper refining, Fossil fuel combustion	Byproduct of processing	Used for specific manufacturing needs	Can be a source of environmental pollution.
Water	Springs, Rivers, Groundwater	Variable, mostly low	Generally not a primary dietary source	Higher concentrations can be localized and potentially toxic.

Conclusion

Selenium is a ubiquitous element, but where it is most commonly found depends largely on whether the context is nutritional or geological. For human health, dietary sources like Brazil nuts, seafood, and grains are the most common and accessible, though their specific selenium content is influenced by geographical soil variations. Geologically, selenium is naturally concentrated in certain sedimentary rocks and is a byproduct of metal refining and fossil fuel combustion. The uneven global distribution of selenium highlights the importance of dietary awareness, especially for those living in low-selenium regions, while also pointing to the need for careful industrial management to prevent environmental contamination.

Key Takeaways

Brazil Nuts are a Top Source: A single ounce of Brazil nuts can provide several hundred micrograms of selenium, making them the richest known dietary source.
Soil Dictates Plant Content: The selenium level in plants, including major crops like wheat, is highly dependent on the mineral content of the soil they are grown in.
Seafood is Reliably High: Fish and shellfish are reliable and protein-rich sources of selenium, with levels less affected by regional variations than plant-based foods.
Geographic Variation is Significant: Regions like the Great Plains of the US are known for high soil selenium, while the Pacific Northwest and certain European countries have very low levels.
Industrial Byproduct: Commercially, most selenium is recovered as a byproduct of copper refining and is also present in fossil fuels.
Essential but Toxic: While essential in small amounts for human health, excessive selenium can be toxic, a condition known as selenosis.
Organic vs. Inorganic: In foods, selenium is typically found in organic forms like selenomethionine, whereas in supplements, inorganic forms like selenite and selenate are common.

Frequently Asked Questions

Brazil nuts contain the highest concentration of selenium per serving, with one ounce providing several times the daily recommended intake.

The amount of selenium in plant-based foods, such as vegetables and grains, is directly influenced by the selenium content of the soil they are grown in. Animals, however, maintain more consistent tissue levels through homeostatic mechanisms.

No, selenium in dietary supplements often comes in inorganic forms like sodium selenite and sodium selenate, while selenium in food is primarily in organic forms like selenomethionine.

Yes, excessive intake of selenium, particularly from supplements, can be harmful. This condition, called selenosis, can lead to hair loss, brittle nails, and other adverse effects.

Regions with low soil selenium include the Pacific Northwest and Northeastern United States, as well as countries like New Zealand and Finland, though the latter has taken steps to fortify its soil.

Commercially, selenium is recovered as a byproduct during the refining of other metals, particularly copper. The combustion of fossil fuels also releases selenium into the environment.

No, the ability to absorb selenium varies by plant species. Some plants, known as hyperaccumulators, can store very high levels of the mineral, while others take up very little.