time (more than 30 minutes) an increased level of mercury vapor is released. Vapor levels will return to normal approximately 90 minutes following chewing cessation. This contributes to a daily mercury exposure for those with amalgam filling. According to one dental textbook, eating seafood once a week raises urine mercury levels to 5 to 20 µg/L, which is equivalent to two to eight times the level of exposure that comes from numerous amalgam fillings. Neither exposure has any known health effect. Scientists agree that dental amalgam fillings release elemental mercury vapor, but studies report different amounts. Estimates range from 1 to 3 micrograms (µg) per day according to the FDA. The effects of that amount of exposure are also disputed. Newer studies sometimes use mercury vapor analysis instead of the standard exposure test. Because this test was designed for factories and large enclosures, Consumer Reports has reported that this is not an accurate method of analysis for the mouth. It is less reliable, less consistent, and tends to greatly exaggerate the amount of mercury inhaled. Moreover, it is argued this test additionally exaggerates the amount of mercury inhaled by assuming that all the mercury vapor released is inhaled. This assumption was reviewed by the U.S. Department of Health and Human Services and not found to be valid. Their research review found that most of the mercury vapor released from amalgam fillings is mixed with saliva and swallowed, some part is exhaled, and the remaining fraction is inhaled. Of these amounts, it is important to note that the lungs absorb about 80% of inhaled mercury. A study conducted by measuring the intraoral vapour levels over a 24-hour period in patients with at least nine amalgam restorations showed that the average daily dose of inhaled mercury vapour was 1.7 μg (range from 0.4 to 4.4 μg), which is approximately 1% of the threshold limit value of 300 to 500 μg/day established by the WHO, based on a maximum allowable environmental level of 50 μg/day in the workplace. Critics point out that: (1) the workplace safety standards are based on allowable maxima in the workplace, not mercury body burden; (2) the workplace safety numbers are not applicable to continuous 24-hour exposure, but are limited to a normal work day and a 40-hour workweek; and (3) the uptake/absorption numbers are averages and not worst-case patients (those most at risk). A test that was done