Cal. Health & Safety Code § 108500

For the purposes of this article, an art or craft material shall be presumed to contain an ingredient that is a toxic substance causing chronic illness if the ingredient, whether an intentional ingredient or an impurity, is 1 percent or more by weight of the mixture or product, or if the department determines that the toxic or carcinogenic properties of the art or craft material are such that labeling is necessary for the adequate protection of the public health and safety.