Mercury in fish can be a serious health concern and deter people from eating such a lean and healthy protein. Why is there mercury in fish in the first place, and are there some that are worse for you than others?
For starters, mercury is a metal that exists naturally in the environment and it is toxic. We also accidentally help add it to the environment through various manufacturing processes and through burning fossil fuels. Other common sources are through forest fires, weathering of rocks containing mercury, or even volcanos! When mercury combines with water, it becomes methylmercury.
Once it is in the water, it starts negatively impacting the aquatic life. It infects everything and impacts the entire food chain. It contaminates the bacteria and other food sources that herbivorous fish eat. It also finds its way into the plankton and invertebrates that other fish eat. This, in turn, means that the food sources of piscivorous fish (the fish that eat other fish) contain methylmercury as well. And every single time a fish eats something containing methylmercury, it is absorbed into the new fish. Since methylmercury has a half life of nearly three and a half months in aquatic life, and it accumulates every single time a food source is contaminated, creatures higher up on the food chain are especially susceptible to very high levels of methylmercury – much, much higher than what is in the water around them.
And I’m not just talking fish, either. Birds absorb the methylmercury in fish and shellfish if it is part of their diet. Other sea animals like otters are exposed the same way. The same thing goes for people, too. Pretty much the only way people can be exposed to methylmercury is through eating contaminated fish or other aquatic food sources. It can cause serious kidney or cardiovascular damage, as well significant birth defects if a woman is pregnant or becomes pregnant while methylmercury is in her bloodstream – and the half-life in humans is nearly three months! In other words, it’s something you really want to avoid.
So, how do you know what fish to avoid eating? The question is how high up the food chain it is. Tilefish from Mexico, swordfish, marlin, shark, bigeye tuna, and some types of mackerel, are essentially top of the food chain and therefore very high in methylmercury.
Knowing this information shouldn’t scare you off of fish altogether, however. There are plenty of options that are OK to eat, especially if you eat them in moderation. Safer choices are scallops, clams, tilapia, salmon, and pollock. The older and larger a fish, the more methylmercury you can assume it has. Also, the higher the omega-3 fatty content in the fish, the less methylmercury it seems to have. As an added bonus, omega-3s are very good for you, too!
If you want to learn more about this, check out the Environmental Defense Fund’s Seafood Selector, which can tell you how many meals you can eat containing fish per week and remain under accepted methylmercury levels.