Every single one contained mercury, but there were wide fluctuations in levels between cans — even those in the same brand. Three cans contained so much mercury that researchers said they should not be eaten at all.

James Rogers, the watchdog's director of food safety research, said: 'From can to can, mercury levels can spike in unpredictable ways that might jeopardize the health of a fetus.' The mercury levels Consumer Reports found were within FDA standards, which say pregnant people can eat canned tuna in limited quantities.