There are several methods by which a "chemical" (a term of art) can be listed under California's Proposition 65. See, for example, http://www.rmkb.com/index.cfm/publications/publication-details/?pkid=253 (pp. 3-5).
In California Chamber of Commerce v. Brown, 2011 Cal. App. LEXIS 694 (6/6/11), plaintiff challenged the methods listed in Section 25249.8(a) of the California Health & Safety Code. The plaintiff, not unreasonably, argued that this method is no longer operable and applied only to the creation of the initial Proposition 65 list.
The Court held that the statute ambiguous. In an opinion that reviews in detail the various theories related to statutory interpretation, the Court decided it was appropriate to review the ballot materials and other interpretive aids, and concluded that the listing method in § 25249.8(a) applied to revisions of the list and that the three listing methods set forth in § 25249.8(b) were additional methods which OEHHA could use.
The Court also held that the § 25249.8(a) method included the listing of reproductive toxins identified on the current American Conference of Governmental Industrial Hygienists (ACGIH) list. Section 25249.8(a) embraced substances identified by reference in Lab. Code, § 6382(b)(1), and substances identified additionally by reference in § 6382(d). Section 6382(d), in turn, referred to any substance within the scope of the federal Hazard Communication Standard in 29 C.F.R. § 1910.1200, which in turn referenced the ACGIH list in § 1910.1200(d)(3)(ii). Because the ACGIH list identified the hazards associated with each chemical, those subject to listing under § 25249.8(a) could be readily identified.