throughout the 1980s by some opposition groups and holistic dentists was the skin patch test for mercury allergies. As part of "prospecting for disease", Consumer Reports wrote that these groups had placed high doses of mercuric chloride on a skin patch which was guaranteed to produce irritation on the patient's skin and subsequent revenue for the person administering the test. The current recommendations for residential exposure (not including amalgam fillings already accounted for) are as follows: The ATSDR Action Level for indoor mercury vapor in residential settings is 1 µg/m3 and the ATSDR MRL (Minimal Risk Level) for chronic exposure is 0.2 µg/m3 According to the ATSDR, the MRL(Minimal Risk Level) is an estimate of the level of daily exposure to a substance that is unlikely to cause adverse non-cancerous health effects. The Action Level is defined as an indoor air concentration of mercury that would prompt officials to consider implementing response actions. It is a recommendation and does not necessarily imply toxicity or health risks. Breathing air with a concentration of 0.2 µg mercury/m3 would lead to an inhaled amount of approximately 4 µg/day (respiratory volume of 20m3/day). About 80% of inhaled mercury vapor would be absorbed. A 2003 monograph on mercury toxicity from the WHO concluded that dental amalgam contributes significantly to mercury body burden in humans with amalgam fillings and that dental amalgam is the most common form of exposure to elemental mercury in the general population, constituting a potentially significant source of exposure to elemental mercury. Estimates of daily intake from amalgam restorations range from 1 to 12.5 μg/day, with the majority of dental amalgam holders being exposed to less than 5 μg mercury/day. They also note that this will continue to decline as the number of amalgam restorations is declining. Health research As public pressure demands more research on amalgam safety, an increasing number of studies with larger sample sizes are being conducted. Those who are not opposed to amalgam claim that, aside from rare and localized tissue irritation, recent evidence-based research has continued to demonstrate no ill effects from the minute amounts of mercury exposure from amalgam fillings. A 2004 systematic review conducted by the Life Sciences Research Office, whose clients include the FDA and NIH, concluded, "the current data are insufficient to support an association between mercury release from dental amalgam and the various complaints that have been attributed to this restoration material."