Charged polymeric webs, such as electret webs, include a thermoplastic resin and a charge-enhancing additive. The charge-enhancing additive is a dual-function charge-enhancing additive that enhances the charge of the electret and also has anti-microbial properties. The additives are substituted-benzimidazole or substituted-benzothiazole compounds. The electret webs may be a non-woven fibrous web or a film. The electret webs are suitable for use as filter media.