Previous Regional Tables used Inhalation Reference Doses (RfDi) and Slope Factors (SFI). Why does the new table use RfCs and IURs?
In the past, some regional tables converted RfCs to RfDs and IURs to SFIs for inhalation. This was initially done because risk equations once relied upon RfDs and SFIs in units of mg/kg/day and 1/mg/kg/day, respectively. However, as the inhalation guidance has evolved, RfCs and IURs, in units of mg/m3 and m3/ug respectively, have become the recommended toxicity factors. Please see Methods for Derivation of Inhalation Reference Concentrations (RfCs) and Application of Inhalation Dosimetry or PDF (409 pp, 21 MB) for more information. Also please see the FAQ concerning route-to-route extrapolation. • How were the toxicity values provided in IRIS on Chromium used to calculate Chromium Screening Levels? It is recommended that valent-specific data for Chromium be collected when Chromium is likely to be an important contaminant at a site, and when Cr6 may exist. In the absence of valent-specific data, screening levels for total Chromium are provided. For Chromium (VI) (Cr6), IRIS shows an air
In the past, some regional tables converted RfCs to RfDs and IURs to SFIs for inhalation. This was initially done because risk equations once relied upon RfDs and SFIs in units of mg/kg/day and 1/mg/kg/day, respectively. However, as the inhalation guidance has evolved, RfCs and IURs, in units of mg/m3 and m3/ug respectively, have become the recommended toxicity factors. Please see Methods for Derivation of Inhalation Reference Concentrations (RfCs) and Application of Inhalation Dosimetry or (PDF (409 pp, 20MB, About PDF)) for more information. Also please see the FAQ concerning route-to-route extrapolation.
