Not an authority but the rule of thumb is the larger and older fish the higher the toxin levels.
Canned white tuna consists of albacore, a large species of tuna that accumulates moderate amounts of mercury. EDF recommends that both adults and children limit their consumption of canned white tuna to less than once per week.
Canned light tuna usually consists of skipjack, a smaller species with approximately one-third the mercury levels of albacore. Most people can safely eat canned light tuna once per week, but EDF recommends that young children (ages 0-6) limit their consumption of canned light tuna to less than once per week.
