This form of mercury is easily taken up by biota and bioaccumulates in their tissues. Unlike many other fish contaminants, such as PCBs , dioxin , and DDT , mercury does not concentrate in the fat, but in the muscle tissue. Thus, there is no simple way to remove mercury-contaminated portions from fish that is to be eaten. The local aquatic environment largely determines how much available mercury takes the accessible toxic for of methylmercury.
Research suggests that sulfur-using bacteria are a major source.