R 336.1233 Methodology for determining initial threshold screening levels based on acute data.

Rule 233. (1) An ITSL based on acute data shall be determined by either of the following: From short-term studies, as follow: ITSL = POD X hours exposed UFh x UFA X UFL AT Where: POD = Point of Departure UFH = a value from 1 to 10 for average human to sensitive human extrapolation UFA = a value from 1 to 10 for animal to human extrapolation UFL = a value from 1 to 10 for LOAEL to NOAEL extrapolation AT = Averaging time of 1, 8 or 24 hours The POD is defined as the human equivalent concentration of any of the following: NOAEL = no observed adverse effect level LOAEL = lowest observed adverse effect level BMDL = 95% lower confidence limit on the benchmark dose (BMD) BMCL = 95% lower confidence limit on the benchmark concentration (BMC) The BMD or BMC value is derived according to the United States environmental protection agency benchmark dose technical guidance, adopted by reference in R 336.1902. “Human equivalent concentration” is defined as an exposure concentration for humans that has been adjusted for dosimetric differences between experimental animal species and humans to be equivalent to the exposure concentration associated with observed effects in the experimental animal species. If occupational human exposures are used for extrapolation, the human equivalent concentration represents the equivalent human exposure concentration adjusted to a continuous basis. (b) The ITSL may be determined on a case-by-case basis using a POD from repeated dose studies using any alternative methodology to assess acute health effects that can be demonstrated to the department to be more appropriate based on toxicological grounds and that is supported by the scientific data. (2) The averaging times to be used for an acute ITSL will be 1, 8, or 24 hours, as appropriate based on the data.