PORTLAND — Farm-raised salmon contains more cancer-causing PCBs than wild fish and other common foods, according to a report released Wednesday by a public health advocacy group. The study, by the Environmental Working Group, tested 10 samples of farmed salmon bought in three U.S. cities, including Portland. Farmed salmon now makes up 80 percent of fresh salmon sold around the country. Opinions differ about whether the risk of polychlorinated biphenyls outweighs health benefits of eating seafood. The salmon tested by the Washington, D.C.-based group would be safe under U.S. Food and Drug Administration standards for fish sold in supermarkets. The...