California Clarifies Scope of Prop 65 Listing for Soluble Nickel Compounds

California's Office of Environmental Health Hazard Assessment (OEHHA) has issued an important clarification of the scope of last year's listing of "soluble" nickel compounds as reproductive toxins under Proposition 65. As previously reported, last October, OEHHA added “Nickel (soluble compounds)” to the Prop 65 reproductive toxin list, a move that begged the question of where to do draw the line between "soluble" and "insoluble" nickel compounds. California has now answered that question:

For purposes of Proposition 65, Nickel (soluble compounds) are defined to be compounds of nickel with solubility in water of greater than 0.1 moles per liter (mol/L) at 20oC. This definition is consistent both with the discussion by the DARTIC that led to the listing of Nickel (soluble compounds) (available at and OEHHA’s prior definition of soluble nickel compounds in the 2012 document, “Nickel Reference Exposure Levels: Nickel and Nickel Compounds; Nickel Oxide” (available at
OEHHA's October 2018 decision to limit the listing to only "soluble" nickel compounds -- and not expand the listing to metallic nickel and insoluble nickel compounds -- is significant for industries that produce nickel-containing metal alloys, such as stainless steel, as well as companies that use such materials to manufacture consumer and industrial products. The new clarification helps demonstrate further that these types of metal alloys do not contain or expose individuals to soluble nickel compounds.