The invention relates to an additive of ZnO/Ag° with a bacteriostatic and fungistatic action in the production of plastic items based on resins such as polypropylene, polyethylene, polystyrene, high-impact polystyrene, polyurethanes, etc., especially for producing automotive products, electrical appliances, products for washing, for storing and conducting water, for packaging, etc. The additive is prepared by mixing nanometric silver concentrates and pre-treated zinc oxide with a polymer resin compatible with the target application as a vehicle, obtaining pellets of the additive in a ratio of between 10:90 and 90:10 in weight of ZnO/Ag° : vehicle. The additive is biologically effective at a ratio in the final product of between 0.01 and 0.5 wt. % of polymer mixture and does not have any negative effects on other properties of the polymer, such as the whiteness thereof.
