Q3: What is the source of the methylmercury that is found in fish and shellfish?
A3: Certain types of bacteria change inorganic mercury that exists in the
environment to methylmercury.
Certain types of bacteria that live in an aquatic environment (e.g. Desulfovibrio
desulfuricans LS) take up inorganic mercury and change it to methylmercury.
The methylmercury thus produced is gradually accumulated in fish and shellfish
through the food web of aquatic animals, i.e., from plankton to small fish,
and then to carnivorous fish.