The serene, majestic bottlenose dolphins that swim off the Florida Everglades are contaminated with mercury – the highest levels ever documented in the entire species – and it’s killing them. And because the dolphins are a sentinel species that provide a glimpse into the health of both ecosystems and humans, the discovery means it’s likely that people living in the area are also affected. 
A study published in 2015, for example, found elevated mercury levels in dolphins in the Indian River Lagoon; it further discovered that these levels of mercury “accurately reflected high amounts in the nearby human population.” 
Tracking the Mercury
Florida International University (FIU) marine ecologist and co-author Jeremy Kiszka believes the mangroves that line the coast and form countless islands are at least one source of the high levels of mercury. Mangroves are “trees and shrubs that have adapted to life in a saltwater environment,” according to the Florida Keys National Marine Sanctuary.
The sanctuary’s website notes that there are about 80 species of mangrove trees and that:
“Mangrove forests stabilize the coastline, reducing erosion from storm surges, currents, waves, and tides. The intricate root system of mangroves also makes these forests attractive to fishes and other organisms seeking food and shelter from predators.”
The blame for the mercury had always been placed on smoke stacks and fertilizers used in farming, which had led to declines in birds in the past, as well as to repeated health warnings about eating fish. However, aggressive cleanup efforts have helped reduce mercury levels.
“I would love to answer this absolutely critical question. I understand it’s frustrating. We don’t know where it’s coming from. OK, potentially the mangroves, but there could be other sources.”
Mangroves are known to trap mercury and filter it into the water, but the researchers were shocked to find such high amounts in the bottlenose dolphins. 
“I couldn’t believe those levels because that’s the highest ever recorded. It raises a lot of other questions.”
Another source could be the approximately 55,000 metric tons of agricultural waste that is illegally dumped into the Everglades every year. The waste contains sulfur that mixes with the mercury dumped into the area. Together, they create methylmercury, a substance that is neurotoxic to both fish and humans. It’s especially dangerous to pregnant women. 
The research team studied dolphins in Florida Bay, Whitewater Bay, Joe River, and other areas in Everglades National Park. These dolphins have likely had high mercury levels for a long time, possibly with no ill effects on the population. Kiszka notes, however, that such a conclusion lacks supportive data and is speculative. The research on the Everglades dolphins was a baseline study. 
The researchers write in the journal Environmental Pollution:
“Additional organic pollutants were examined as part of the study, including pesticides and other compounds. Some were found in the various populations of bottlenose dolphins throughout the southern tip of Florida, but mercury was found in much more alarming concentrations in the waters of the Everglades.” 
FIU researchers plan on expanding the study to include alligators and bull sharks, to give them insight into how mercury is potentially affecting the marine environment. Kiszka explained:
“Expanding to other species in the Everglades will definitely help to understand the pathways. We’re trying to put together the many different pieces to understand what makes those animals or ecosystems more susceptible to high mercury. There’s a lot of work to be done.”
Prolonged exposure or exposure to high levels of methylmercury can cause the following potentially fatal ailments in humans:
- Loss of peripheral vision
- A “pins and needles” sensation in the hands and feet, and around the mouth
- Lack of coordination of movements
- Impaired hearing, speech, and walking
- Muscle weakness 
Methylmercury exposure in the womb can have a negative impact on children’s cognitive thinking, memory, attention, language, fine motor skills, and visual spatial skills.
 Miami Herald
 Miami New Times
Julie Fidler is a freelance writer, legal blogger, and the author of Adventures in Holy Matrimony: For Better or the Absolute Worst. She lives in Pennsylvania with her husband and two ridiculously spoiled cats. She occasionally pontificates on her blog.