this is from their blurb on the costco site - suppossedly complies with standards stricter than FDA's for contaminents - >
PureGels® Omega-3 300/200 - For Your Knowledge: The raw material fish oil in our products complies with the CRN (Council for Responsible Nutrition) Voluntary Monograph for Omega-3 fatty acids obtained from fish, plant, or microbial sources. CRN established standards for mercury, heavy metals, PCB's, and dioxins more stringent than FDA, and equal to or more stringent than those set by EPA and the state of California (Proposition 65). Natural processes called molecular distillation and steam deodorization provide maximum purity of our Omega-3 fatty acids.
Nordic Naturals Ultimate Omega contains 70% pure Omega-3, and is purified through molecular distillation to ensure the absence of impurities including PCBs and heavy metals.