Survey of total mercury in some edible fish and shellfish species collected in Canada in 2002.

Total mercury was measured in the edible portions of 244 selected fish and shellfish purchased in Canada at the retail level. By species, average mercury concentrations ranged from 0.011 microg g(-1) for oysters to 1.82 microg g(-1) for swordfish. The predatory fish contained the highest concentrations of mercury: swordfish (mean 1.82 microg g(-1), range 0.40-3.85 microg g(-1)), marlin (1.43, 0.34-3.19 microg g(-1)), shark (1.26, 0.087-2.73 microg g(-1)), and canned, fresh and frozen tuna (0.35, 0.020-2.12 microg g(-1)). Levels of mercury in the fresh and frozen tuna contained a mean of 0.93 microg g(-1) (range 0.077-2.12 microg g(-1)) and were substantially higher than in the canned tuna (0.15, 0.02-0.59 microg g(-1)). In the canned tuna, mercury concentrations varied with subspecies, with the highest average concentrations being found in Albacore tuna (mean 0.26 microg g(-1), range 0.19-0.38 microg g(-1)) and the lowest (0.047, 0.025-0.069 microg g(-1)) in five samples for which the subspecies of tuna were not identified. Mean concentrations of mercury in swordfish and fresh and frozen tuna were up to three times higher than reported for the USA. Dietary intake estimations found that provided fresh and frozen tuna, marlin, swordfish or shark are consumed once a month or less, the dietary intakes of total mercury by women of child-bearing age, averaged over 1 month, would fall below the Joint FAO/WHO Expert Committee on Food Additives provisional tolerable weekly intake for total mercury. The current Canadian advisory to children and women of child-bearing age is to limit their consumption of fresh and frozen tuna, swordfish and shark to no more than one meal per month.