Selenium’s Toxic Trait: From Essential Nutrient to Coastal Threat for Louisiana’s Shellfish and Economy

Selenium is a trace element essential to human health, supporting immune function, thyroid regulation, and antioxidant defense. But this micronutrient has a narrow margin between benefit and harm. In small amounts, it’s vital; in excess, it becomes toxic, potentially causing organ damage and gastrointestinal distress. Because selenium can accumulate in the environment, its delicate balance must be closely monitored—not only in our diets but also across ecosystems, where even slight disruptions can pose serious risks to both ecological and public health.

This is where Associate Professor Achim Herrmann’s research comes in. At the intersection of geology, biology, and chemistry, Herrmann investigates how environmental shifts—particularly changes in atmospheric and oceanic oxygen levels—have shaped life on Earth in the past and could continue to do so in the future. His work focuses on modern sediments and trace elements that respond to oceanic changes, such as selenium, tracking how they move through sediment layers, accumulate in organisms, and make their way into the food chain.

"Especially here in Louisiana, with all the shellfish, fisheries, and oysters, we have to be mindful of how selenium behaves in the ocean and other environments," Herrmann explains. "To predict its future impacts, we first need to understand its current biogeochemistry”. 

One major concern is that, while selenium exists in very low concentrations in ocean water, it can accumulate in sediments. If released back into the water due to changes in oxygen levels, for example, it could form a selenium plume, potentially entering the food chain or triggering harmful algal blooms, posing risks to both human health and the economy.

Supported by an NSF Mid-Career Advancement grant, Herrmann’s research focuses on the biogeochemistry of selenium under changing environmental conditions. One key approach involves studying selenium isotopes—variations of the element with slightly different weights—that provide insights into past environmental changes, including shifts in oxygen levels and chemical reactions in water, sediment, and soil.  
Since scientists cannot sample ancient seawater directly, they use proxies—indirect indicators of past conditions—by analyzing modern calcareous organisms like corals and algae. This technique allows researchers to reconstruct past ocean oxygenation and better understand long-term environmental shifts.

Herrmann’s latest project will begin in the Florida Keys, where he will study how selenium moves from ocean water into calcareous organisms and limestone deposits, and whether it can re-enter the food chain through fish and shellfish. He then hopes to apply this method in Louisiana’s Gulf Coast and bayous to assess potential risks to local fisheries and ecosystems.

The project will involve collaboration with experts in selenium isotope geochemistry in Europe and scientists at Tulane University, where he will utilize a state-of-the-art Multicollector ICP-MS (Inductively Coupled Plasma Mass Spectrometry) system. This instrument breaks down water or rock samples into infinitely small ions, enabling scientists to precisely quantify selenium in the samples. By mastering this technique, Herrmann’s research will not only enhance our ability to predict selenium’s future behavior in marine ecosystems but also provide valuable insights into Earth's past. Understanding how selenium chemistry is linked to seawater oxygen levels can help scientists reconstruct historical ocean changes, offering a deeper perspective on how environmental processes evolve over time.  

His findings could contribute to better environmental management strategies, ensuring that the delicate balance of selenium in marine ecosystems is maintained—protecting both human and ecological health.