The Environmental Working Group (EWG) uses the FDA’s own scientific guidelines for what constitutes a safe dose of mercury to calculate the maximum amount of tuna you can safely eat each week and not exceed what the FDA considers a safe exposure level. The site has a calculator to determine the safe amount for you. Note that EWG recommends that women of childbearing age and children under 5 not eat albacore tuna at all, because a significant portion of albacore tuna has very high mercury levels. People eating this tuna will exceed safe exposure levels by a wide margin.
http://www.ewg.org/tunacalculator
