Amid growing concerns about the spread of harmful mercury in plants and animals, a new study compared levels of the chemical in captive dolphins with dolphins found in the wild. The captive animals were fed a controlled diet, while the wild mammals dined on marine life that may carry more of the toxic metal.
Mercury is emitted as a gas from coal- and oil-fired power plants. Some makes its way into the ocean, where bacteria turn it into methylmercury, which moves up the food chain. Eventually, it turns up in the large fish that serve as dinner for wild dolphins. Once ingested, the heavy metal makes its way into the animals' bloodstream, where it can begin to damage the nervous system.
Public health officials are concerned about human consumption of mercury, particularly in a form called methylmercury, because it can damage the brain and other parts of the nervous system, especially in young children. Dolphins that ingest too much methylmercury can suffer similar harm (NOTE: Subscribers can still listen to this show).
The study found lower levels of mercury in the captive animals, particularly compared to wild dolphins tested off the Atlantic and Gulf coasts of Florida, a state that is in the path of mercury-laden fumes from power plants. The aquarium dolphins are fed smaller fish from North Atlantic waters, where mercury pollution is less prevalent.
Researcher Edward Bouwer says, "This is just one puzzle piece. What we'd like to do now is repeat this project with aquariums in other parts of the world. The goal is to get a clearer comparison of mercury-related health risks facing dolphins both in captivity and in the wild. This type of research can give us hints about how the type of diet and where it originated can affect mercury-related health problems in captive dolphins, compared to their cousins in the wild."