((a)) ** Taxable substance** For purposes of this subchapter—

((1)) ** In general** The term “taxable substance” means any substance which, at the time of sale or use by the importer, is listed as a taxable substance by the Secretary for purposes of this subchapter.

((2)) ** Determination of substances on list** A substance shall be listed under paragraph (1) if—

((A)) the substance is contained in the list under paragraph (3), or

((B)) the Secretary determines, in consultation with the Administrator of the Environmental Protection Agency and the Commissioner of U.S. Customs and Border Protection, that taxable chemicals constitute more than 20 percent of the weight (or more than 20 percent of the value) of the materials used to produce such substance (determined on the basis of the predominant method of production).

((3)) ** Initial list of taxable substances**

((4)) ** Modifications to list** The Secretary shall add to the list under paragraph (3) substances which meet either the weight or value tests of paragraph (2)(B) and may remove from such list only substances which meet neither of such tests.

((b)) ** Other definitions** For purposes of this subchapter—

((1)) ** Importer** The term “importer” means the person entering the taxable substance for consumption, use, or warehousing.

((2)) ** Taxable chemicals; United States** The terms “taxable chemical” and “United States” have the respective meanings given such terms by section 4662(a).

((c)) ** Disposition of revenues from Puerto Rico and the Virgin Islands** The provisions of subsections (a)(3) and (b)(3) of section 7652 shall not apply to any tax imposed by section 4671.