Heavy steel poisoning from eating fish oil dietary supplements is enormously unlikely, because heavy metals (mercury, lead, nickel, arsenic, and cadmium) selectively bind with protein within the fish flesh in preference to accumulate inside the oil.
However, other contaminants (PCBs, furans, dioxins, and PBDEs) is probably discovered, specifically in less-subtle fish oil supplements.
Throughout their history, the Council for Responsible Nutrition and the World Health Organization have published acceptability requirements regarding contaminants in fish oil. The most stringent present day well known is the International Fish Oils Standard. Fish oils which might be molecularly distilled beneath vacuum normally make this maximum-grade; degrees of contaminants are said in components consistent with billion in keeping with trillion.