Does mercury contamination outweigh the health benefits of eating fish?

For most adults, the risk of getting too much mercury or other contaminants from fish is generally outweighed by the health benefits of omega-3 fatty acids. The main types of toxins in fish are mercury, dioxins and polychlorinated biphenyls (PCBs). The amount of toxins depends on the type of fish and where it's caught.

Mercury occurs naturally in small amounts in the environment. But industrial pollution can produce mercury that accumulates in lakes, rivers and oceans, which turns up in the food fish eat. When fish eat this food, mercury builds up in the bodies of the fish.

Large fish that are higher in the food chain eat the smaller fish, gaining higher concentrations of mercury. The longer a fish lives, the larger it grows and the more mercury it can collect. Fish that may contain higher levels of mercury include:

• Shark
• Tilefish
• Swordfish
• King mackerel