Tuna sushi in 20 Manhattan stores and restaurants contained high levels of mercury, according to testing commissioned by The New York Times. In five establishments, fish mercury levels were so high that the seafood could legally be removed from the market. According to a 2007 survey, New Yorkers’ blood mercury levels are three times the national average. Recently, mercury has been linked not only to neurological problems but to cardiovascular disease. So skimp on that sushi, New Yorkers — and that goes for the rest of you, too.