Michigan Administrative Code › Department - Environmental Quality › Air Quality Division › Part 2 - AIR USE APPROVAL › Section R. 336.1232 - Methodology for determining initial threshold screening level

Current through Vol. 24-12, July 15, 2024
Rule 232.
(1) The
				initial threshold screening level (ITSL) for each toxic air contaminant shall
				be determined as follows:
(a) If an inhalation
				reference concentration (RfC) can be determined from best available information
				sources, then the ITSL equals the inhalation RfC.
(b) If an ITSL cannot be determined under the
				provisions of subdivision (a) of this subrule and an oral reference dose (RfD)
				can be determined through best available information and data are not available
				to indicate that oral route to inhalation route extrapolation is inappropriate,
				then the ITSL is determined as follows:
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(c) If an ITSL cannot be determined under the
				provisions of subdivision (a) or (b) of this subrule and an occupational
				exposure level (OEL) exists for the toxic air contaminant, then the ITSL is
				determined as follows:
ITSL = OEL divided by 100
Where the OEL is the lowest value of either the national
				  institute of occupational safety and health (NIOSH) recommended exposure level
				  listed in the NIOSH pocket guide to chemical hazards or the time-weighted
				  average or ceiling threshold limit value listed in the TLVs and BEIs. The NIOSH
				  Pocket Guide to Chemical Hazards is adopted by reference in
				  R
				  336.1902. TLVs and BEIs. Threshold Limit Values for
				  Chemical Substances and Physical Agents, and Biological Exposure Indices, is
				  adopted by reference in
				  R
				  336.1902.
(d) If an ITSL cannot be determined under the
				provisions of subdivision (a), (b), or (c) of this subrule, then the ITSL may
				be determined from a 7-day, inhalation no observed adverse effect level (NOAEL)
				or lowest observable adverse effect level (LOAEL) as follows:
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Where:
UF = A value from 1 to 10 determined on a case-by-case basis,
				  considering type and severity of effect.
The ITSL may be determined on a case-by-case basis using
				  NOAELs or LOAELs from repeated dose studies other than 7-day
				  studies.
(e) If an ITSL
				cannot be determined under the provisions of subdivision (a), (b), (c), or (d)
				of this subrule, then the ITSL may be determined from a 7-day, oral, NOAEL or
				LOAEL as follows:
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Where:
WA = Body weight of experimental
				  animal in kilograms (kg).
IA = Daily inhalation rate of
				  experimental animal in cubic meters/day.
b = Absorption efficiency by the oral route of
				  exposure.
a = Absorption efficiency by the inhalation route of
				  exposure.
UF = A value from 1 to 10 determined on a case-by-case basis,
				  considering type and severity of effect.
The ITSL may be determined on a case-by-case basis using
				  NOAELs or LOAELs from repeated dose studies other than 7-day
				  studies.
(f) If an ITSL
				cannot be determined under the provisions of subdivision (a), (b), (c), (d), or
				(e) of this subrule, then the ITSL may be determined from an inhalation LC50
				that is 4 or more hours in duration as follows:
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Where:
LC50 = A calculated concentration of a chemical in air to
				  which exposure for a specific length of time is expected to cause death in 50%
				  of a defined experimental animal population.
(g) If an ITSL cannot be determined under the
				provisions of subdivision (a), (b), (c), (d), (e), or (f) of this subrule, then
				the ITSL may be determined from a 1-hour inhalation LC50 as follows:
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(h) If an ITSL cannot be determined under the
				provisions of subdivision (a), (b), (c), (d), (e) (f), or (g) of this subrule,
				then the ITSL may be determined from an animal oral LD50 as follows:
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Where:
LD50 = The dose of a chemical that has been calculated to
				  cause death in 50% of a defined animal population.
WA = Body weight of experimental
				  animal in kilograms (kg).
IA = Daily inhalation rate of
				  experimental animal in cubic meters/day.
(i) If an initial threshold screening level
				cannot be determined under the provisions of subdivision (a), (b), (c), (d),
				(e), (f), (g), or (h) of this subrule, then the initial threshold screening
				level = 0.1 ug/m3.