FIU says Dolphins’ mercury levels high

Dolphins in the Everglades and the Indian River Lagoon are sending us a warning about how mercury accumulates in their bodies and ours.

A study published by Florida International University scientists in the scientific journal Environmental Pollution in October found bottlenose dolphins in the Everglades, particularly along the northeastern shore of Florida Bay, had the highest levels of mercury concentration ever recorded: an average of 11 parts per million. That’s like a pinch of salt in 20 pounds of potato chips.

The discovery echoed research by scientists at Florida Atlantic University’s Harbor Branch Oceanographic Institute in 2012 that found mercury levels in Indian River Lagoon dolphins that weren’t much lower.

“We had levels of 7.0 (parts per million),” said Adam Schaefer, a Harbor Branch research professor who studies diseases in wildlife. “The Everglades is a primary location for mercury accumulation, and the conditions in the lagoon are very similar. So it makes sense our mercury levels are comparable.”

Dolphins are a “sentinel species,” Schaefer said. “High levels of mercury in dolphins shows that there are high levels of mercury in animals throughout the food chain. Dolphins are telling us there is mercury throughout lagoon species and throughout Everglades species.”

The Harbor Branch researchers followed their dolphin study in 2014 by finding high levels of mercury in people who live along the Indian River Lagoon and eat fish from there. Hair samples from 135 residents showed those who ate seafood three times a week were three times as likely to have more than 1 part per million of mercury in their systems, the limit the federal Environmental Protection Agency recommends for human health. People who had seafood daily were four times as likely to exceed the threshold, researchers found.

The mercury typically doesn’t kill dolphins or humans, said Jeremy Kiszka, an FIU marine scientist who co-authored that school’s study, but it can affect their livers, kidneys, immune systems and their ability to reproduce.

“It doesn’t kill on its own so much as make you susceptible to diseases that you normally could fight off,” Schaefer agreed.

Where does mercury come from? It literally falls from the sky.

Smokestacks at coal-fired generators send mercury into the sky, where it accumulates in clouds and falls back to earth in rain hundreds or thousands of miles away.

“Because of prevailing weather patterns, a lot of mercury falls on South Florida,” Schaefer said.

At sites like the lagoon and the Everglades, the mercury finds favorable conditions to accumulate.

A 2011 study by Melodie Naja of the Everglades Foundation found the use of sulfates as a fungicide and fertilizer enhancer in fields north of the Everglades boosted mercury growth in the Everglades.

The mercury also accumulates naturally, Kiszka said. Water in mangrove ecosystems, such as the Everglades and Indian River Lagoon, contains a lot of organic matter that promotes the growth of bacteria that absorb and hold the mercury.

The FIU study found pesticides and other compounds in dolphins from the Everglades to the lower Florida Keys, but mercury levels were much lower in dolphins in the Keys, which don’t have agricultural runoff.

“We know the mercury has both humaninduced and natural sources, as well as a combination of the two,” Kiszka said. “We can hypothesize that (the high mercury levels) are the result of long-term agriculture, but the specific sources are still unknown.”

The FIU research team, which also includes scientists from the University of Liège in Belgium, the University of Gronigen in the Netherlands and the Tropical Dolphin Research Foundation in Virginia, plans to expand the study to examine mercury contamination in sharks, alligators, fish and other animals.