By Laura Elizabeth May
Green Right Now
The U.S. Geological Survey has released a study showing an increase in mercury emissions from human sources is affecting the fish population in the Pacific Ocean.
Scientists have predicted a 50 percent increase in mercury levels in the Pacific Ocean by 2050, if mercury emission rates continue as projected. Human contribution to mercury pollution includes coal burning power plants and waste incineration. The water sampled for this study — released May 1 — shows that the mercury levels in 2006 were already approximately 30 percent higher than the same samples in the 1990′s.
The paper presents the first evidence linking current atmospheric mercury deposition to methylmercury (the compound that mercury gets converted into) in Pacific Ocean fish. Scientists say it is plausible that a reduction in ocean mercury levels would follow if mercury emissions were decreased.
In the U.S., about 40 percent of all human exposure to mercury is from tuna harvested in the Pacific Ocean. Other previous studies have shown that 75 percent of human exposure worldwide to mercury is from the consumption of marine fish and shell fish. In 2004, the EPA and FDA released guidelines on fish consumption for pregnant women and children.
Many studies have been conducted involving mercury levels in freshwater; but less is known about mercury in marine environments. This study was one of the first to thoroughly analyze mercury levels in ocean waters, concluding that the methylmercury contamination could not just be from natural sources, as some have theorized.
According to the study, methylmercury is produced at mid-depth ocean waters from mercury that “originates from atmospheric fallout to the ocean surface”, and taken up the food chain by predators like tuna. For this study, scientist sampled Pacific Ocean water from 16 different sites. The results showed the increased mercury emissions were particularly high in off the coasts of Asia.
“It appears the recent mercury enrichment of the sampled Pacific Ocean waters is caused by emissions originating from fallout near the Asian coasts,” said USGS scientist and coauthor of the study David Krabbenhoft.
Don’t forget to read our story on How to shop for seafood before you head to the store.
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(Photo credit: NOAA)