Quantifying the risk
If we assume, for the moment, that the EPA limits represent a “true” assessment of the risk of cancer from PCBs, what, then, is that risk?
According to the EPA, if PCB levels in raw fish tissue are 24 48 parts per billion, then consumption of eight ounces per month over a lifetime of 70 years would increase one’s risk of cancer by one in 100,000.
As Hites et al. found an average of approximately 36 parts per billion in farm-raised salmon, then it would appear that one should restrict oneself to one meal per month — as the authors of the study recommend.
The immediate problem with these figures is that Hites et al. conducted their analysis with the skin on the fillets. This ensured that the highest possible residues were found, given that PCBs accumulate in fatty tissue. Yet cooking reduces the PCB levels in fish by 30 to 50 percent, and thus either significantly reduces the risk of cancer or enables you to eat more farm-raised salmon than the authors claim. And of course, you can simply avoid eating the skin.
The second point is whether a one in 100,000 lifetime risk of cancer is really a risk worth worrying about. According to the EPA’s calculations, such a risk would result in approximately 3,000 cases of cancer in the U.S. population (currently 300 million) over seventy years if, that is, everyone ate at least eight ounces of raw farm-raised salmon per month at current PCB levels.
By any measure, this is an extremely small risk — and it is one that is getting smaller and smaller given ongoing measures by the salmon industry to reduce PCB levels farmed salmon by changing salmon feed. By way of contrast, the Centers for Disease Control (CDC) recorded 700,142 deaths from heart disease in 2001; and the Harvard Center for Risk Analysis currently puts your odds of dying from heart disease at one in 397.
Given the growing body of evidence showing that omega-3 fatty acids confer substantial benefits in the fight against heart disease, the benefits of eating salmon — one of the best sources for omega-3 fatty acids — would appear to vastly outweigh any possible cancer risk from PCBs.