Why do some fish oil flog as "mercury free"?

Wouldn't any fish oil product sold contained by the US have to be free of mercury? I clutch Spring Valley brand fish oil from Walmart. It doesn't utter that it is mercury free, so it does concern me a little. What do you estimate?Why do some fish oil flog as "mercury free"?
However, nearly all fish and shellfish contain traces of mercury. For most associates, the risk from mercury by eating fish and shellfish is not a condition concern. Yet, some fish and shellfish contain higher level of mercury that may harm an unborn infant or young child's developing jittery system. The risks from mercury in fish and shellfish depend on the amount of fish and shellfish eat and the levels of mercury within the fish and shellfish. Therefore, the Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA) are advising women who may become pregnant, pregnant women, nursing mothers, and young-looking children to avoid some types of fish and eat fish and shellfish that are lower contained by mercury.
poison
Most fish have traces of murcury within it. If you eat it, thats fine, theres not plenty mercury to kill you. It is said that if you get through fish containing mercury that you should NOT eat it more than 3 times a week. Don't verbs though, its very frozen to get fish not containing mercury
The World Health Organization lately found unsafe (as if safe is possible) level of mercury contamination in weighty sea tuna, especially albacore tuna. Albacore tuna is a larger species of tuna than its cousins so more mercury is found contained by these kind of fish.
be concerned if you be allergic to mercury which many ethnic group are