Credit: Stephanie Backhouse

Fish Quick to Recover From Mercury
By Phil Berardelli
ScienceNOW Daily News
17 September 2007

The bad news about mercury pollution is that it's harmful, widespread, and has been going on for decades. The good news is that if emissions of mercury can be limited, its concentration in fish and other creatures will decline in relatively short order. That's what a team of researchers has found during a years-long controlled experiment on a large lake ecosystem in Canada.
Mercury is one of the most toxic materials affecting the environment. As early as the mid-18th century, it was used in everything from hatmaking to dentistry. Now the biggest source of emissions in the United States is the smokestacks of coal-burning power plants. They have been depositing mercury in lakes and other aquatic ecosystems, where bacteria transform it into a dangerous form called methylmercury. This becomes even more concentrated through the food chain, finally reaching humans when they eat fish.

To study the effects of mercury, a team of researchers added an inorganic and much less toxic form of mercury to a lake and its watershed in western Ontario, artificially increasing mercury input sixfold. Since the beginning of the 7-year experiment, the team has regularly measured mercury levels in the food chain and in its top predator, the northern pike. Reporting online this week in the Proceedings of the National Academy of Sciences, the researchers reveal that their experiment, called METAALICUS, found that almost all of the mercury absorbed by the pike population came from the amounts they added to the lake's surface. A small additional amount accumulated from the watershed. Based on the fact that most environmental mercury enters lakes at their surface, the team concludes that restricting or removing mercury from power-plant emissions should result in a decontamination of the pike population within a few years.

"There's a lot of other circumstantial evidence supporting this conclusion," says biogeochemist and co-author John Rudd of R & K Research Inc. in Salt Spring Island, British Columbia. The levels of mercury in the ecosystem "may not go down in exactly the same way" as they accumulated, he says, "but they will go down." Rudd says the next phase of the experiment is to stop adding mercury to the lake and observe how quantities in the lake inhabitants change.

The researchers have done a "superb job" of detailing the changes in mercury in the lake system, says aquatic toxicologist James Wiener of the University of Wisconsin, La Crosse. In particular, he says, the study shows how readily mercury can accumulate within the bodies of fish, which reinforces health concerns about the consumption of contaminated fish by humans. Moreover, he says, the work "demonstrates the probable effectiveness of reducing emissions."