The invention relates to a compatibilizing dispersant used in a slurry composition comprising a strongly cationic component and a strongly anionic component. More specifically, the invention relates to stable aqueous slurries comprising suspended particles of sparingly soluble salts, oxide, and/or hydroxides of copper and/or zinc. The slurry further comprises a quaternary amine compound present in a biocidally effective amount when the slurry is used in a manner that provides the sparingly soluble copper and/or zinc containing particles in a biocidally effective amount. The slurry further comprises an effective amount of a dispersant having a large non-ionic component.