The invention is directed to a sustained release system, to a method for preparing a sustained release system, and to a material for construction comprising said sustained release system.The sustained release system of the invention comprises a microcapsule, said microcapsule comprising an encapsulation material and an amount of one or more metal chelate complexes encapsulated by said encapsulation material of 10 wt.% or more, based on the total weight of matrix material and metal chelate complex together, wherein said one or more metal chelate complexes have one or more free coordination sites.
