Where is selenium found
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These studies suggest selenium is found in black rock series, certain plants, soils, deep-seated rocks, sediments, and industrial areas.
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Sources and Distribution of Selenium in the Environment
Selenium in Geological Formations
Selenium (Se) is a naturally occurring element found in various geological formations. It is commonly associated with sulfide minerals and is often found in deep-seated plutonic rocks where large magma bodies have cooled slowly. Selenium is also present in volcanic rocks, particularly basalts, and is enriched in surface waters that leach selenium from these volcanic materials. In Taoyuan County, China, selenium distribution is heavily influenced by the geological bedrock, with the highest concentrations found in the Lower Cambrian and Ediacaran black rock series. These geological formations are primary sources of selenium in the environment.
Selenium in Soils
The selenium content in soils varies significantly depending on the underlying geological materials. In Taoyuan County, soil selenium levels range from 0.18 to 7.05 mg/kg, with higher concentrations in areas with selenium-rich bedrock. In Northwestern Tanzania, selenium in soils ranges from 0.3 to 0.5 µg/g, influenced by the type of rock and the degree of weathering. Agricultural soils can also be deficient in selenium, which affects the selenium content in crops grown in these soils.
Selenium in Plants
Certain plants have the ability to accumulate high levels of selenium. For instance, the native legume Neptunia amplexicaulis in Central Queensland, Australia, is known to hyperaccumulate selenium, with foliar concentrations exceeding 4000 µg Se g-1. In Punjab, India, wheat and Indian mustard grown in selenium-rich soils show high selenium enrichment, particularly in the leaves, due to the uptake of selenate and organic selenium species from the soil. These plants also exhibit detoxification mechanisms, such as methylation, to manage high selenium levels.
Selenium in Water and Sediments
Selenium is also found in water and sediments, contributing to its distribution in aquatic ecosystems. In Lake Macquarie, Australia, sediments near industrial sources like smelters and power stations have significantly higher selenium concentrations compared to remote areas. Selenium in these sediments is bioavailable and accumulates in benthic organisms, which then transfer selenium through the food web to higher trophic levels, including fish.
Selenium in Agroecosystems
In agroecosystems, selenium cycles through the environment, being taken up by plants and soil microorganisms, which can convert it into volatile forms like dimethylselenide that enter the atmosphere and return with precipitation. The primary source of selenium in soils is the weathering of selenium-containing rocks, but secondary sources include volcanic activities, industrial dust, and selenium-containing fertilizers.
Conclusion
Selenium is widely distributed in the environment, with its presence in geological formations, soils, plants, water, and sediments. Its distribution is influenced by geological sources, soil characteristics, and human activities. Understanding the sources and distribution of selenium is crucial for managing its levels in the environment and ensuring adequate selenium intake for human and animal health.
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