Facts: This statement is wrong in two ways. First, the RfD is 0.1 micrograms of mercury per kilogram of body weight per day; it is an index of dietary mercury intake, not a level of mercury in blood. The latter is called the Reference Level. Second, the Reference Level in blood is 5.8 micrograms per liter, not 58 micrograms per liter. This error creates the impression that the EPA safe level is ten times higher than it actually is.
Sometimes the seafood lobby states outright that the “RfD” is 58 micrograms per liter, and sometimes they claim that it is 5.8 micrograms per deciliter. (Since a deciliter is one-tenth of a liter, this is the same as saying the limit is 58 micrograms per liter.) The use of the correct number (5.8 micrograms) with the wrong units (deciliters) is a more insidious error, and may be more likely to mislead those encountering it. It repeats the mistakes just described: It confuses the RfD, a measure of safe dietary intake, with the Reference Level, a measure of a safe mercury content in blood. And it overstates the actual Reference Level by a factor of 10.
Why would the seafood lobby consistently make such obviously incorrect statements on such an easily checked factual point? Sometimes they explain that they know the actual reference level is 5.8 micrograms per liter, but because “there is a 10-fold safety margin built into the RfD,” the actual “safe” level is 58 micrograms per liter. This claim is based on another major conceptual error. Frequently, however, they don’t explain, but simply assert flatly that the “safe” level as defined by the EPA is 58 micrograms per liter.
In early 2009, the seafood lobby tried briefly to inflate the true Reference Level by 100-fold. In challenging a reporter who had eaten a can of albacore tuna a day for 20 days and seen her blood mercury level rise from 4 to 17 micrograms per liter, to suggest that this increase was trivial, the National Fisheries Institute boldly asserted that “The EPA has deemed 580 micrograms per liter [emphasis added] to be a level of mercury in blood that approaches risk.” When this claim was exposed by another reporter, NFI did a quick about-face, claiming it had made a “decimal point error” in converting micrograms per deciliter to micrograms per liter. They then backtracked to their longstanding false claim that the safe level is 58 micrograms per liter.