Mercury contaminates watersheds around Lake Superior, and naturally-occurring bacteria convert this mercury into its most toxic form - methylmercury. Scientists have known for many years that these toxic transformations occur in wetlands and lake sediments: studies in Michigan's Upper Peninsula documented similar transformations in groundwater. Researchers from UW-Madison worked on a team that found that methylmercury levels in the watershed of the Tahquamenon River were elevated during periods when most of the water was coming from groundwater, not surface runoff.
The findings of this research suggest that the methylation process occurs amidst the rocks and gravel at the bottom of streams and in the sandy landscape that underlies coniferous forests in the Upper Peninsula. However, these findings are not specific to just Lake Superior and the Upper Peninsula: they confirm the importance of groundwater as a source of methylmercury to watersheds around the Great Lakes.Medical News Today
