In a study with possible implications for the oceans and human health, scientists reported elevated mercury levels in dolphins in the southeastern US, with the highest levels found in dolphins in Florida’s St. Joseph and Choctawhatchee Bays.
Dolphins are considered a ‘guardian species’ for the oceans and human health because, like us, they are high on the food chain, live long lives and share certain physiological traits with humans. Some staples of their diet, such as spotfish, doomfish, weakfish and other small fish, are most vulnerable to mercury pollution and are also eaten by humans.
The study, which appeared in the journal Toxic gasses, did not draw any conclusions about the mercury levels of residents of Florida and Georgia or the potential health risks to humans. However, it cited previous research from a different group of researchers that found a link between high mercury levels in dolphins in Florida’s Indian River Lagoon and people living in the area.
“As a sentinel species, the bottlenose dolphin data presented here can guide future studies to evaluate mercury exposure in human residents” in the Southeast and other potentially affected areas in the United States, say the study authors in Toxic gasses wrote.
According to the U.S. Environmental Protection Agency (EPA), fish is part of a healthy diet and “for most people, the risk of eating fish and shellfish is not a health concern.” But the agency also says that “some groups of people, such as pregnant people, children, the elderly, or people with weakened immune systems, are at greater health risk for adverse health effects. In addition, some individuals are at greater risk of adverse outcomes.” health effects simply because they eat a lot of fish.”
In marine mammals such as dolphins, mercury poisoning 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 based on the scientific consensus on mercury.
Although some mercury occurs naturally in the environment, mercury pollution largely results from the combustion of fossil fuels and industrial processes such as mining, cement production and chemical production.
Bacteria in the water convert mercury into methylmercury, which is then ingested or eaten by small fish. It is then passed through the food chain to species that consume these fish, such as dolphins.
For the study Toxic substances, The scientists analyzed 175 skin samples collected from bottlenose dolphins between 2005 and 2019.
The samples were collected from multiple estuaries in Florida and Georgia, including St. Joseph, Choctawhatchee and Biscayne Bays in Florida and the Skidaway and Turtle/Brunswick and Sapelo Island estuaries in Georgia. The scientists measured mercury in the skin of dolphins, which is directly related to the methylmercury in their other tissues and organs.
“NIST has been involved in dolphin health assessment and biopsy studies since 2002,” said Colleen Bryan, research biologist and co-author of the study. “We have helped standardize testing protocols and collection and storage methods so that all measurements taken are highly accurate and comparable between studies.”
The researchers found that mercury levels in St. Joseph Bay, where dolphins averaged 14,193 nanograms of mercury per gram (ng/g) in their skin, were the highest they had measured.
In an interview, Mackenzie Griffin, lead author of the study and now a biologist with the National Oceanic and Atmospheric Administration (NOAA), said industrial activities may be partially responsible for the levels in St. Joseph Bay. She also said the bay is not routinely washed away by the influx of freshwater from other waterways, which would help lower mercury levels.
In their study, the authors cited previously published studies by others showing that dolphins in the Charleston, South Carolina area had the lowest average levels – 509 ng/g – while dolphins in the Florida Coastal Everglades had the highest – 10,916 ng/g . /G.
According to NIST’s Bryan, Charleston Harbor benefits from tidal currents that wash away mercury when the tide recedes.
In the Everglades, the leaves of the mangrove trees absorb the mercury in the atmosphere and then fall into the water, decomposing and releasing the toxin. The boggy, oxygen-poor peat soils provide a rich habitat for the bacteria that convert the chemical into methylmercury.
“Our research adds to other studies that have consistently shown elevated levels of mercury in dolphins in the Southeast,” says Bryan. “We hope this will lead to a better understanding of what is happening in our oceans.”
The following agencies and institutions contributed to Toxics research: NOAA, the National Marine Mammal Foundation, the Marine Science and Nautical Training Academy, Savannah State University in Georgia, Florida International University, the University of Miami and the Sarasota Dolphin Research Program.
