Possibly less for mercury because of age, but I'm not sure even about that. Many of the Atlantic salmon that are sold cheap in the large Asian stores are frozen whole or fillet, smaller fish not like those on display at the counter. Not like the fish that escaped that are larger.
I can find info about virus testing, but nothing about testing Puget Sound Atlantics for toxics.
Here is info PCB's:


"Farmed salmon has much higher concentrations of persistent, bioaccumulative contaminants (polychlorinated biphenyls, dioxins, and several chlorinated pesticides) than wild salmon.11 Scientists have concluded that:

"Consumption of farmed salmon at relatively low frequencies results in elevated exposure to dioxins and dioxin-like compounds with commensurate elevation in estimates of health risk."

In a global assessment of farmed salmon published in the January 2004 issue of Science, 13 persistent organic pollutants were found. Some of the most dangerous are PCBs, strongly associated with cancer, reproductive and other health problems. PCB concentrations in farmed salmon were found to be eight times higher than in wild salmon. Those contamination levels are deemed safe by the Food and Drug Administration (FDA) but not by the Environmental Protection Agency (EPA). Researchers postulated that if EPA guidelines were applied to the farmed salmon they tested, recommendations would be to restrict salmon to no more than once per month."

http://articles.mercola.com/sites/articles/archive/2015/01/03/omega-3-levels-farmed-salmon.aspx