<p>Diners who are partial to salmon should avoid most farm-raised varieties, which often contain dangerous levels of cancer-causing contaminants, according to a major new international study that compared commercially bred salmon with their wild counterparts.</p>
<p>The orange-fleshed fish can harbor so many toxic substances that salmon eaters in the San Francisco area should ration their intake to one eight-ounce farmed salmon steak every two months, the researchers found. The two-year study, published today in the journal Science, found that farm-raised salmon has about 10 times the level of environmental toxins of wild fish -- largely because the farmed variety are fed other fish harvested from waters close to sources of industrial runoff.</p>