Q: Does OEKO-TEX Standard 100 cover zipper sliders and tape?
Standard 100 is organised around articles, and a zipper is a combination of materials: dyed tape, polymer teeth, metal hardware and sometimes a coating or lubricant. A certificate can cover the tape and teeth while excluding the metal parts, or cover the assembled zipper. What matters is that the certificate's article description names what you actually buy.
Metal components are assessed for extractable heavy metals and for the general residue parameters, while dyed tape carries the burden of colourant-related tests: azo dyes, allergy-inducing disperse dyes, chlorinated benzenes and the like. Nickel release is a separate legal question under REACH and is not answered by the Standard 100 certificate. Ask the supplier which parts and which product class the certificate covers, and get the appendix parameters for that class.
Verification is straightforward: the certificate names the applicant, the production site, the articles and the product class, and the label can be checked with the issuing body. Do not accept a certificate for a different colour or a different mill as covering your order.