A wood preservative includes injectable particles comprising one or more sparingly soluble copper salts. The copper-based particles are sufficiently insoluble so as to not be easily removed by leaching but are sufficiently soluble to exhibit toxicity to primary organisms primarily responsible for the decay of the wood. Exemplary particles contain for example copper hydroxide, basic copper carbonate, copper carbonate, basic copper sulfates including particularly tribasic copper sulfate, basic copper nitrates, copper oxychlorides, copper borates, basic copper borates, and mixtures thereof. The particles typically have a size distribution in which at least 50% of particles have a diameter smaller than 0.25 &mu；m, 0.2 &mu；m, or 0.15 &mu；m. At least about 20% and even more than 75% of the weight of the particles may be composed of the substantially crystalline copper salt. Wood or a wood product may be impregnated with copper based particles of the invention.
