Mercury pollution might not give fish three eyes, but it does make them
dangerous to eat. Image credit: True/Slant
Until 1970, mercury was not classified as a dangerous compound in the United States. Before the metal was regulated, it was used extensively in industry—especially in paper making and chemical refining processes. Much of this industry lined the banks of the Great Lakes and, before 1970, factories dumped the contaminant into the water.
Once there, the mercury worked its way up the food chain until it accumulated in fish in high enough concentrations that they became dangerous for human consumption. In the decades following the 1970 decision, concentrations of mercury have gone down, but a new study has found an alarming trend: the slow return of contaminated fish.
Image credit: alex_lee2001/Flickr
Looking at more than 5,800 fish samples collected between the late 1970s and 2007, researchers found that levels of mercury in Lake Erie fish decreased steadily until the 1990s. At that point, however, mercury began creeping up once again—in spite of decades-worth of efforts to reduce local sources of mercury pollution.
So, if local sources of mercury are decreasing, how can concentrations increase?
Answering this question, researchers concede, is not a simple task. Instead, the global nature of mercury pollution must be taken into consideration.
Even as local emissions have decreased, global emissions—especially those from China and Russia—have continued. The long-range spread of these emissions is a problem Lake Erie is now becoming an example of.
The introduction of non-native species, which may bring mercury from outside the region or process it differently, is also a possible source of the increase. Increased concentrations of mercury in fish, than, is in part the result of the arrival of an invasive mussel.
Regardless of the source, tracking the increase is important: As the largest body of fresh water on the planet, increases in the mercury concentrations in the Great Lakes can serve as an indicator of the regional, national, and even global presence of the pollutant.