"there has been chatter": watch out, there is a commercial battle between farmed salmon (essentially European) and wild salmon (essentially N. American), in which we may hear allegations of high toxicity levels in one or the other kinds. Specifically, that farmed salmon concentrates toxins because the sea-bottom small fish etc used to make feed are polluted; wild salmon because the N. Pacific is polluted with industrial toxins from Asia. There may be truth in both, but there's probably a certain amount of commercial disinformation going on.