Etidronic acid (HEDPA) is a bisphosphonate used in detergents, water treatment, cosmetics and pharmaceutical treatment. Target: Others Etidronic acid (HEDPA) is a chelating agent and may be added to bind to or counter the effects of substances such as arsenic, iron, or other metal ions that can occur in the presence of some soaps. Etidronic acid also acts to retard oxidation of fatty acids. For clarification, a chelator, or chelating agent is a binding component added to many cosmetics, beauty products, and water softeners to form multiple bonds with a single metal ion and neutralize it.