The amendments to the List Rule (63 FR 640; January 6, 1998) added exemptions from threshold determination for regulated substances in gasoline that is in distribution or related storage for use as fuel for internal combustion engines, and for regulated substances in naturally occurring hydrocarbon mixtures prior to processing.  Do these exemptions apply to regulated toxic substances as well as regulated flammable substances?

No. The exemption from threshold determination for regulated substances in gasoline or in naturally occurring hydrocarbon mixtures applies only to regulated flammable substances.  These exemptions are codified at 40 CFR Section 68.115 (b)(2), which specifically relates to "concentrations of a regulated flammable substance in a mixture."  Any regulated toxic substance (e.g., hydrogen sulfide) which is present in gasoline or in naturally occurring hydrocarbon mixtures must be considered when determining whether a threshold amount of that substance is present in a process at a stationary source.