Mercury contamination of waterways and marine life doesn't have to be an ongoing problem -- all we have to do is limit industrial mercury emissions. Easy! After a seven-year experiment in a Canada lake, researchers publishing in the Proceedings of the National Academy of Sciences concluded that mercury concentrations in fish would decline relatively quickly if their ecosystem was no longer contaminated. So someday, if we all lobby hard enough against mercury-spewing (and otherwise evil) coal plants, you may be able to eat your sushi without fear of being poisoned. But we'd still watch out for the Kool-Aid.