Where do fish, such as Pacific Ocean tuna, acquire their methylmercury?
A U.S. Geological Survey (USGS) scientist, David Krabbenhoft, and his university colleagues have discovered a new source of methylmercury entering the waters of the eastern North Pacific Ocean. Their study presents evidence linking current atmospheric mercury deposition to methylmercury in Pacific Ocean fish. According to the study mercury levels in 2006 were approximately 30 percent higher than those measured in the mid-1990s. In this study the scientists for the first time try to explain the formation of methylmercury in the North Pacific Ocean. Algae, which are produced in sunlit waters near the surface, die quickly and “rain” downward to greater water depths (called “ocean rain”). At depth, the settling algae are decomposed by bacteria and the interaction of this decomposition process in the presence of mercury results in the formation of methylmercury. Many steps up the food chain later, predators like tuna receive methylmercury from the fish they consume. One of the findings from
