Plastic has a backbone of carbon and an attached hydrogen, with chemicals forming a non-covalent bond with it. A non-covalent bond means that the chemicals just sit on the carbon backbone. e.g. for PFAS (Per- and Polyfluoroalkyl Substances), the fluorine is attracted to the carbon molecule, and just sits on it.
Plastic has 16,000 chemicals that can be attached to it. The chemicals are known to be CARCINOGENS (cause cancer), NEUROTOXICANTS (cause brain diseases) and 1,000 of them are labeled as ENDOCRINE DISRUPTORS.