Fish are a valuable food source, but many fish and seafood species—including tuna fish—are contaminated with toxic pollutants, like mercury, flame retardants or PCBs. Mercury and PCBs are especially toxic to the young, developing brain. PCBs were an industrial compound used in electrical equipment and phased out of production in 1979 due to their toxicity. PCBs persist in fatty tissue like breast milk and the fat of more oily fish species, including those that are also higher in "healthy" omega-3 fats. Though declining, PCB levels in fish are still high enough to trigger local advisories against eating fish from many contaminated lakes, rivers and streams. Mercury pollution is widespread, as is mercury contamination of locally-caught and commercial fish. Most human exposure to mercury and PCBs comes through eating fish. Yet advice from the federal government regarding fish consumption can be incomplete at best, and is often confusing. Federal agencies fail, for example, to monitor and issue warnings for PCB levels in seafood and other commercial fish. Our Smart Fish Guide offers advice for buying and eating fish that takes into account both mercury and PCB contamination, in addition to information about the sustainability of various fisheries due to overfishing and other practices. Our Smart Fish Calculator will help you estimate safe fish portions based on body weight.