May 12, 2009 -- Ocean fish can contain high levels of mercury, even though mercury levels in the seawater around them are extraordinarily low. Now, scientists have an explanation for what's going on. A new study in the Pacific Ocean suggests that algae at the water's surface absorb mercury from the atmosphere and then sink to mid-depths, where they decompose and release methylmercury, a highly toxic form of the metal that poisons both fish and the people who eat them. Mercury concentrations have increased in the Pacific by 30 percent in the last 20 years, the study found. And if emissions continue to rise as expected, the scientists predict another 50 percent jump by 2050. "We can now explain why large predatory fish in the open oceans have methylmercury in the first place," said Dave Krabbenhoft, a geochemist with the United States Geological Survey in Middleton, Wisc. "We don't have to scratch our heads anymore." Related Content:
Mercury is a byproduct of coal combustion, industrial waste and other human activities. It is also a powerful neurotoxin that can cause developmental problems in babies and heart disease in adults, among other health woes. More than 90 percent of methylmercury that gets into people in the United States comes from ocean fish and shellfish, especially tuna. Yet, compared to lakes, oceans haven't been studied much when it comes to mercury, and there hasn't been a clear explanation for how mercury gets from the air into ocean fish. One reason is that ocean waters contain such low amounts of methylmercury that scientists have struggled to collect reliable samples. Krabbenhoft and colleagues were the first to employ new, highly sensitive techniques to get water samples at 16 sites in the Pacific Ocean, form Alaska to Hawaii. At each site, the researchers analyzed samples every 100 meters (328 feet) or so, down to a depth of 1,000 meters. Get More NewsSpiders, Scorpions Among World's Oldest CreaturesMany creepy crawlies have been on Earth much longer than previously believed.Blood-Sucking Vampire Bats Sing DuetsWhite-winged vampire bats "harmonize" with separated roost mates.Oldest Hebrew Writing Possibly FoundAncient inscriptions on a 3,000-year-old pottery shard could make history.Rare, Prehistoric-Age Reptile Found in N.Z.A tuatara has been spotted on the New Zealand mainland for the first time in 200 years.Iceman Has No Living RelativesOetzi, the 5,300 year-old frozen mummy, left no living genetic legacy.SLIDE SHOW: Landscapes of TerrorWhat makes a place feel scary? There are scientific explanations.It's Official: People Are Warming the PolesHumans are conclusively to blame for polar warming, say scientists.Eight-Armed Animal Preceded DinosaursWhat may be one of Earth's first animals was no bigger than a coaster and had eight arms.Phoenicians Live on in People's GenesOne in 17 Mediterranean men may be descended from ancient Phoenicians.Pesticides, Fertilizers Linked to Frog DeclineA pesticide is found to promote parasites among amphibians.Hubble Telescope Taking Photos AgainThe Hubble Space Telescope is once again snapping stunning photos of the universe.Andean Mummy Hairs Show Hallucinogen UseScientists find direct evidence of hallucinogenic drug use among ancient Andeans.Opals on Mars Reveal Planet's Long Wet PastOpals found on Mars suggest the planet has been wet for much longer. |
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