Common sources of mercury, with bioaccumulation in fish

This figure shows some common sources of mercury, the conversion to toxic methylmercury, and the outline of EPA consumption recommendations for certain types of fish based on mercury levels. Mercury from coal-fired power plants and other sources travels through the atmosphere and water. Methylmercury is formed from inorganic mercury by the action of microbes that live in aquatic systems (ie, lakes, rivers, wetlands, and the open ocean), and particularly sediments. Methylmercury can enter the aquatic food chain and is increasingly concentrated (bioaccumulated) at each step on that chain. Large old predators (eg, sharks and pike) or scavengers (eg, halibut), hold the greatest concentrations of mercury. The mercury is particularly problematic during development, so these limits here are designed to protect women, who might become pregnant, and children aged 12 years or younger. (Source: Bretwood Higman, 2009. Creative Commons Attribution 3.0 Unported [CC BY 3.0] license, creativecommons.org/licenses/by/3.0.)