Fish with the highest concentrations of mercury included catfish from remote blackwater streams in the South.
Mercury is not just in some fish, according to an in-depth study by the U.S. Geological Survey—it’s in all the fish the agency tested. In a first-of-its-kind study, the agency tested fish from 300 streams across the U.S. from 1998 to 2005. Every one of the more than a thousand fish collected, including bass, trout and catfish, contained mercury. A quarter of those tested had mercury levels surpassing the Environmental Protection Agency’s limit for safety.
The news is particularly disheartening to recreational fishers who enjoy eating their catch—especially those fishing more remote streams in places like Louisiana, Florida and Georgia where concentrations were the highest. The study not only highlights a serious public health concern—since mercury is a dangerous neurotoxin that can cause nervous system damage and learning disabilities in fetuses and small children—but also highlights the dangers of the country’s continued dependence on coal-powered electricity.
Coal is responsible for half the nation’s electricity, and the burning of coal is the main source of mercury contamination in the nation’s streams and waterways. According to the AP news story: "The mercury released from smokestacks here and abroad rains down into waterways, where natural processes [specifically, bacteria] convert it into methylmercury—a form that allows the toxin to wind its way up the food chain into fish." The highest concentrations of mercury, therefore, are found in the larger predator fish—such as shark, swordfish and tuna, and also, in the most recent study, bass and catfish—some of the nation’s favorite fish to eat.
Sources: AP; PBS; U.S. Geological Survey.