Farmed-raised salmon contain more cancer-causing chemicals called PCBs than do salmon caught in the wild, according to a new study published in the journal Science.

The study, which obtained 700 filets of salmon from wholesalers and supermarkets from around the world, found that farmed salmon from Europe had the most PCBs, followed by North America and Chile.

Consumers should limit their consumption of farmed-raised Atlantic salmon to no more than one meal per month, the study warns.

“We are certainly not telling people not to eat fish…. We’re telling them to eat less farmed salmon,” said David Carpenter of the University at Albany, N.Y., one of the study authors.

The Food and Drug Administration disagrees with the study’s recommendations. The agency says the levels of PCBs found in farmed salmon are too low to be worrisome.

The high levels of PCBs found in farmed salmon result from the feed they are generally given, which consists of fishmeal and oil made from a few species of ocean fish.

(via The Associated Press)