The EPA reference dose (RfD) is defined as the amount of mercury a person, including sensitive subpopulations, can be exposed to on a daily basis over a lifetime without appreciable risk of effects.

The EPA RfD is 0.1 µg mercury per kg body weight per day. When using the mercury calculator at GotMercury.Org, this value (adjusted for a week of exposure) is the value to which your mercury levels are being compared.

This level corresponds to a blood mercury level of 5.8 ug/L or 5.8 parts per billion (ppb) mercury. Blood mercury levels below this value are considered to be without appreciable risk by the EPA.

For hair, the mercury level that corresponds to the RfD is 1 part per million (ppm).

A study by Turtle Island Restoration Network (TIRN) of mercury levels in swordfish found that 68% of the swordfish samples were above the FDA Action Level of 1 part per million mercury and 16% were over 2 parts per million (twice the FDA's Action Level). The average mercury concentration was 1.38 parts per million, which is 38% higher than the FDA Action Level.

The FDA has set an "action level" of 1 part per million (ppm) for seafood. Ironically, the FDA fails to take action when fish in grocery stores or restaurants exceed the "action level" value.

In 2004, a study found that the number of infants that are potentially exposed to dangerous levels of mercury in the womb was 630,000 children in the U.S. annually. This was double the previous estimates and was determined from mercury levels in umbilical cords, which contain mercury levels 1.7 times higher than those of the mother's blood level. Based upon this data, far more babies are being exposed to the reference dose than previously thought.