Cod Liver Oil - pure enough?

Some brands of CLO claim to have "non-detectable" amounts of mercury, pesticides. etc... is it still ok to consume it? I don't eat tuna or any other seafood because of pollutants, so I am sceptical about CLO.

I don't trust most claims of purity as they don't usually make sense to me. I mean, like they would throw out a day's batch of CLO if they found traces of mercury or PCB's? I doubt it. Surely the shift manager at the processing plant would get fired. Have they EVER "detected" levels in the fish they process? I doubt it. And I doubt all of the fish they catch are pollutant free, so it doesn't add up.

And wouldn't the cod's liver contain more pollutants than the fat and muscles, since the liver filters the stuff out of the blood? And what is "non-detectable"? By who's standards?

Anyway... is CLO safe enough to take on a daily basis?