Mercury decline in air may be mirrored in fish
New evidence supports the success of efforts to reduce the neurotoxic metal in fish.
After tracking the movement of distinctive mercury isotopes in a small ecosystem for 3 years, a team of 24 Canadian and U.S. researchers concludes that reducing the pollutant in the atmosphere will likely lead to substantial reductions in fish contamination within a decade or two. Fish are a primary source of toxic mercury loads in people.
From 2001 to 2003, the researchers added a different stable isotope of mercury to each part of a watershed in Canada's Experimental Lakes Area—the uplands, wetlands, and a lake. The added mercury simulated what is generated in many settings by atmospheric sources such as coal-fired power plants. The team regularly tracked the isotopes, which could be readily distinguished from ambient mercury, as they spread through the ecosystem.
The findings, which are the first synthesis results from a project called the Mercury Experiment to Assess Atmospheric Loading in Canada and the U.S. (METAALICUS), were published online in Proceedings of the National Academy of Sciences U.S.A. on September 27 (DOI 10.1073/pnas.0704186104). They provide some of the first evidence of exactly how mercury moves through a whole ecosystem.
The isotopes barely budged from the wetlands or uplands, but they moved within a month from lake water to sediment and zooplankton. Within 2 months, the seeded lake water isotope was lodged in several fish species in the form of toxic methylmercury.
Researchers observed substantial short-term decreases in methylmercury in biota such as zooplankton. These reductions closely tracked those of methylmercury in the ecosystem as changes in temperature, pH, and other factors temporarily curtailed the migration of mercury.
This evidence and parallel findings from more-limited studies led the researchers to conclude that mercury might move relatively quickly into and out of numerous fish species in various settings. They plan to continue monitoring the isotopes, which are no longer being added to the watershed, for several years to glean additional information.
