How do fish get contaminated by mercury?
It happens through the food chain. In the bottom sediments of rivers, lakes, and oceans, mercury undergoes methylation, a process carried out by bacteria in certain conditions. Small fish eat small snails, crawfish and insects that have eaten even smaller things containing methylmercury. Then larger predator fish, like bass, eat the smaller fish. Since bass are at the top of the freshwater food chain, they can build up methylmercury. Methylmercury then gets into the food chain and results in mercury exposure to persons who eat fish.
