Mercury and Selenium in Texas Seafood Shape the Safety of What We Eat

When Dr. Jessica Dutton, a marine ecotoxicologist, at Texas State University, steps onto a fishing pier or into a cleaning station along the Texas coast, she is not there for the catch of the day in the usual sense. Her prize is a sliver of fish muscle, a biological bookmark in the story of how two trace elements, mercury (Hg) and selenium (Se), interact in seafood that we consume.

When Dutton moved to Texas in 2015, she quickly noticed a gap in understanding. “At the time, there had only been a few studies investigating mercury concentrations in bay and offshore fishes, and no study had investigated selenium concentrations or calculated Se:Hg molar ratios and HBVSe values,” she said. “This was a knowledge gap that needed to be addressed.”

That realization set her on a course of research that began in 2016, when she started collecting samples and analyzing them for mercury. “Through the support of Texas Sea Grant,” she added, “I have been able to expand that research and include selenium as well.”

Mercury is a nonessential trace element that bioaccumulates in fish and shellfish and biomagnifies in estuarine and marine food webs. More than 80 percent of the Hg in fish muscle can be in the form of methylmercury (MeHg), a potent toxin that can affect the brain, cardiovascular system, and developing fetuses. Humans are primarily exposed to Hg through the consumption of contaminated seafood. 

State and federal agencies issue consumption advisories when Hg levels exceed established thresholds: 0.3 µg/g for the Environmental Protection Agency (EPA), 0.7 µg/g for the Texas Department of State Health Services (TDSHS), and 1.0 µg/g for the Food and Drug Administration (FDA).

Mercury advisories in the United States are issued based on Hg concentrations alone, but Se—an essential trace element—has an antagonistic relationship with Hg. Selenium can form a toxicologically inert Hg-Se complex. Scientists are investigating whether Se levels, expressed in Se:Hg molar ratios and Health Benefit Values (HBVSe), could be used as an additional seafood safety criterion. A Se:Hg molar ratio greater than 1:1 suggests that selenium may have a protective effect against mercury toxicity, whereas a ratio less than 1:1 indicates that selenium may not have a protective effect against mercury toxicity. A positive HBVSe suggests there may be health benefits from consuming that species, whereas a negative value indicates there may be health risks associated with its consumption.

Since 2016, Dr. Dutton and her team have collected muscle samples from 25 fish species such as greater amberjack, cobia and great barracuda at fishing tournaments and cleaning stations along the Texas coast. They recorded body length, calculated moisture content, measured mercury concentrations using a direct mercury analyzer and measured selenium concentrations using microwave acid digestion and ICP-MS analysis. The team then calculated Se:Hg molar ratios and HBVSe values to investigate differences in the values within and among species.

The result is what Dutton describes as “the largest dataset that I am aware of — over 4,000 samples — and all from one area, the Texas coast.” That scope is crucial for assessing seafood safety. “Before we can determine whether Se:Hg molar ratios and HBVSe values can be used in risk assessment, several large case studies are needed,” she explained. “For most species, there is large variability in the Se:Hg molar ratios and HBVSe values within and among body lengths, and therefore they may not yet be useful seafood safety criteria in risk assessment. Only future research will tell.”

The findings show that many popular offshore species have a high percentage of individuals exceeding federal and state mercury advisory levels. For example:

• Greater amberjack: mean Hg concentration 1.10 µg/g wet weight; 86.9% exceeded the TDSHS advisory level, 52.2% exceeded the FDA advisory level.
• Great barracuda: mean Hg concentration 0.89 µg/g wet weight; 65.2% exceeded the TDSHS advisory level, 31.8% exceeded the FDA advisory level.
• Cobia: mean Hg concentration 0.97 µg/g wet weight; 60.7% exceeded the TDSHS advisory level, 39.3% exceeded the FDA advisory level.

Although the mean Se:Hg molar ratio was greater than 1:1 in all three species, 2% of barracuda and 15.7% of cobia had a ratio less than 1:1, indicating that Se may not have a protective effect against Hg toxicity in all individuals within these species. Furthermore, 2% of great barracuda and 15.7% of cobia had a negative HBVSe, indicating there may be health risks associated with their consumption.

For Dutton, the importance of this research goes beyond data collection; it’s about helping Texans make informed seafood choices. “We are encouraged to consume fish because it’s high in protein and omega-3 fatty acids and low in saturated fat,” she said. “However, depending on the species you eat, you may be exposed to high concentrations of mercury. The goal of this project is to provide awareness, so people can make informed decisions about the type of seafood they consume.”

Dutton’s work extends beyond the lab to public outreach and education. Through the Texas Seafood Mercury Study, founded in 2022, she shares findings on Instagram (@hgtxseafood), a pocket-sized Hg in seafood consumption guide, and later this fall, through a multilingual website in English, Spanish and Vietnamese (www.texasseafoodmercurystudy.com)

The project has included collaborations with fishing tournaments, the Harte Research Institute, and Dartmouth College, involved seven graduate and four undergraduate students, and contributed to conference presentations, a thesis, and forthcoming publications. Dutton hopes that continued research and public engagement will lead to better-informed advisories and healthier choices for seafood consumers.