The most widely available dietary source of EPA and DHA is cold water oily fish, such as salmon, herring, mackerel, anchovies and sardines. Oils from these fish have a profile of around seven times as much n−3 as n−6. Other oily fish, such as tuna, also contain n−3 in somewhat lesser amounts. Consumers of oily fish should be aware of the potential presence of heavy metals and fat-soluble pollutants like PCBs and dioxins, which are known to accumulate up the food chain. After extensive review, researchers from Harvard’s School of Public Health in the Journal of the American Medical Association (2006) reported that the benefits of fish intake generally far outweigh the potential risks. Although fish is a dietary source of n−3 fatty acids, fish do not synthesize them; they obtain them from the algae (microalgae in particular) or plankton in their diets.