According to the Environmental Working Group (EWG), farm-raised salmon has 16 times the polychlorinated biphenyls (PCBs) as wild-caught salmon. That’s because farm-raised salmon are often fed contaminated fish meal, which builds up in salmon’s fatty tissue.

Chilean-farmed fish had lower levels of toxins than fish raised in the U.S., Scotland, Canada and Norway. Those tested from Scotland had such high levels that the EWG recommended it be eaten no more than once per month.

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