Do fish oil supplements contain contaminants?

Alexander Kofinas M.D.

Recent analyses of dozens of brands of fish oil supplements, including testing by, have not found significant levels of mercury or unsafe levels of PCBs, dioxins, or other contaminants—in inexpensive or pricey brands. This is not surprising, since mercury tends to accumulate in larger fish, and supplements are made from smaller species (such as anchovies or sardines) or algae (which supply only DHA). Moreover, mercury is water‐soluble and thus tends to accumulate in the flesh of the fish, not in the fat or oil. Finally, most supplements are processed to reduce levels of PCBs and other contaminants.