Federal study shows high mercury level in dolphins in the Southeast United States

The skin on dolphins throughout the Southeast is laden with mercury, a new federal study shows. That could spell trouble for us as well, biologists warn.

We eat the same fish they do. And like us, when dolphins consume too many fish high in mercury, it stunts their ability to think, reproduce and even survive.

"I'd say those levels are on the high end," Colleen Bryan, a research biologist at the National Institute of Standards and Technology in Charleston, South Carolina, said of mercury levels NIST found in Florida, especially near the Panhandle.

NIST's study, published recently in the Toxics , can inform state and federal authorities evaluating mercury exposure risk to humans and which geographic areas should be further explored.

"It's a starting point for questions … for different epidemiology toxicologists," said Bryan, one of the study's lead authors.

What did the study show?

NIST's study found the following:

• The highest average mercury levels were in dolphins in St. Joseph Bay in Gulf County — 14,193 nanograms per gram (ng/g) in skin.
• Second highest levels were in dolphins near the Everglades — 10,916 ng/g.
• Third highest levels were in Choctawhatchee Bay in Okaloosa and Walton counties — 7,333 ng/g.
• By comparison, the authors cited 2007 levels in the Indian River Lagoon — 2,206 ng/g.
• The lowest levels were in Charleston, South Carolina, the authors noted, citing previously published studies — 509 ng/g.

Why was mercury so high in St. Joseph Bay dolphins?

Mackenzie Griffin, the study’s lead author and now a biologist at the National Oceanic and Atmospheric Administration, said industrial activities may be partially responsible, according to a NIST press release. She also said that the bay isn’t routinely flushed out by fresh water from other waterways, which would help reduce mercury levels.

Why is mercury higher in the Everglades?

Mangroves leaves absorb mercury in the atmosphere and then fall into the water, rotting and releasing the toxin. The waterlogged, low-oxygen, high-bacteria peat soils there are ideal for converting chemical mercury into its more dangerous form.

Drainage for farming, development and other mixed land uses caused a two-third reduction in the quantity of peat, releasing about 28 metric tons of mercury into the southern Florida environment over about 133 years, according to a study earlier this year by Florida Gulf Coast University.

How much mercury is released into South Florida yearly?

Up to 1.4 tons per year, the FGCU study found. The largest source of mercury entering the Florida environment is from combined atmospheric sources, including Saharan dust, aerosols, sea spray and ocean flux/evasion.

The FGCU study found the following other large yearly mercury contributors include: waste-to-energy incinerators (450 pounds); medical waste and crematory incinerators (352 pounds); and cement plant stack discharge (332 pounds).

Minor emissions include fuel emissions from motorized vehicles, gas emissions from landfills and asphalt plants. No data are available on controlled fires in the Everglades in sugar farming.

How did NIST do their study?

NIST analyzed 175 skin samples from bottlenose dolphins in the Southeast between 2005 and 2019. The scientists measured mercury in dolphin skin, which directly relates to a harmful form of mercury in their other tissues and organs.

Does NIST's study draw any conclusions about human risk?

No. The study drew no conclusions about Florida and Georgia residents’ mercury levels or the potential health risks to humans. But it cited previous research led by Florida Atlantic University that found a link between high mercury levels in dolphins in the Indian River Lagoon and humans living in the area.

Should I still eat fish?

Yes. Fish is part of a healthy diet. The U.S. Environmental Protection Agency says, “for most people, the risk from eating fish and shellfish is not a health concern.”

Should some temper fish consumption?

Yes. EPA also says “some groups of people, such as pregnant people, children, the elderly or those with weakened immune systems, are at a greater health risk of adverse health effects. Additionally, some individuals are at a higher risk for adverse health effects simply because they eat a lot of fish.”

Why is mercury bad?

In dolphins and other mammals, mercury toxicity can lead to reproductive failure, behavioral changes and even death, according to a statement last year from the Minamata Convention on Mercury, a 2017 global agreement informed by the scientific consensus on mercury.

What levels of mercury are safe in dolphins?

Biologists aren't sure, nor do they know what levels might have been before so many people populated coastal regions.

Where does the mercury come from?

Some occurs naturally, but mercury pollution results mostly from burning fossil fuels and industrial processes such as mining, cement production and chemical manufacturing.

More than half the mercury fallout on Florida comes from emissions outside of the state, studies show, especially from coal burning. Mercury rains out of the sky from power plants, wildfires and industry as far away as China. It sprinkles into the lagoon and St. Johns River, making its way into the aquatic food chain.

Mercury from power plants and other sources also collects into a toxic "hot spot" the size of Alabama located 180 miles offshore of Brevard, where frequent thunderstorms pull the toxic metal from the sky.

"Dolphins can effectively represent regional trends and reflect large-scale atmospheric mercury input and local biogeochemical processes," NIST researchers concluded.

Florida's current mercury advisories, visit the Florida Department of Health's website here .

Contact Waymer at (321) 261-5903 or jwaymer@floridatoday.com. Follow him on X (Twitter) at @JWayEnviro.

This article originally appeared on Florida Today: Federal study shows high mercury level in dolphins in the Southeast United States