Heavy Metal Contamination in Farmed Fish

In a process known as “bioaccumulation”, fish ingest and store compounds in their flesh. This can include toxic chemicals like PCBs, PBDEs, dioxins, microplastics, and pesticides, and it can also include heavy metals like lead, mercury, arsenic, and cadmium. When we eat fish, the toxic compounds in their bodies transfer to our own.

Both wild fish and farmed fish accumulate heavy metals but the amounts vary with the type of fish and the waters they swam in. Research shows that traces of arsenic may be higher in farmed salmon than in wild, but cadmium may be higher in wild salmon than farmed.³ Mercury has been found in both farmed and wild fish,⁴ though in greater amounts in the wild.

The fish in UK supermarkets is imported from all over the world, so it is impossible to say which fish swam where, and it is impossible to know without testing each fish individually what heavy metals are in their bodies.

What we do know is that the optimal amount of heavy metal to ingest is zero because those heavy metals accumulate in our bodies, too, and are linked to diseases such as diabetes, cardiovascular diseases, cancer, and neurodegeneration.⁵ There are other, safer ways to get our omega-3s.