High levels of mercury in fish such as tuna have been linked to heart and immune system damage, as well as fetal dangers. A new analysis by the Defenders of Wildlife (DW) cites canned tuna imported from Mexico and Ecuador as containing the highest mercury levels-- much higher than the federal limit.The tuna caught by companies in these southern countries are generally larger, older fish. They have higher levels of mercury because they have had more time to absorb the metal into their bodies, largely due to being at the top of the food chain. DW advises avoidance of eating canned tuna from these countries. However, DW did note that canned tuna imported from Asia contain the lowest mercury levels.
