IRS Adds Two Substances to List of Chemical Substances Subject to Superfund Excise Tax

The Internal Revenue Service (IRS) published a notice of determinations on June 26, 2026, that the list of taxable substances is modified to include the following two substances: chloro-isobutene-isoprene rubber and ethylene-propylene-dicyclopentadiene rubber. 91 Fed. Reg. 38778. Arlanxeo USA LLC and Arlanxeo Canada Inc., importers and exporters of the chemicals, submitted petitions requesting to add the chemicals to the list. The IRS states that according to the petition for chloro-isobutene-isoprene rubber, the taxable chemicals butylene, chlorine, and sodium hydroxide constitute 97.36 percent by weight of the materials used to produce this substance, based on the predominant method of production. According to the petition for ethylene-propylene-dicyclopentadiene rubber, the taxable chemicals ethylene and propylene constitute 98.80 percent by weight of the materials used to produce this substance, based on the predominant method of production. For purposes of the tax under Section 4671 of the Code, these additions to the list of taxable substances will be effective October 1, 2026. For purposes of refund claims under Section 4662(e) of the Code, the additions were effective April 1, 2023.