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In the case of uranium absorption across the respiratory tract (AFL), the relative absorption rate was assumed to be 1 (100%). There is little information available to estimate how uranium adsorbed to soil particulates would be absorbed across the respiratory tract. Consequently, AFL was assumed to be 1 (i.e., equal to the absorption rate in the oral toxicological studies). It is possible that the relative rate of uranium absorption across the respiratory tract could have conceivably been greater than across the gastrointestinal tract in the toxicological studies. Nevertheless, it is noted that the inhalation route is considered to be a relatively minor route of exposure and, thus, although this lack of route-specific data is not desirable, it is not expected to have a large impact on the data. In the case of uranium absorption across the skin (AFS), the relative absorption factor was assumed to be 0.05 (5%). There is little information available to estimate how uranium in soil would be absorbed across the skin. Some guidance suggests that a rate of 5% would be a reasonably conservative value (MDEP, 1995). Other guidance suggests lower values (e.g., ORNL [2005] recommends a value of 0.1%) as absolute absorption factors. However, it is important to note that the ORNL value is a generic default assumption for metals in general and is not specific for uranium. A variety of researchers contacted by these authors have suggested that this default assumption should not be applied to uranium. For the purposes of this assessment, a relative absorption factor of 0.05 (i.e., 5%) was used. It is noted that this was a relatively insensitive parameter in the development of the PSQGHH.