Copper naphthenate (CuN) has a long history in wood preservation and is recently finding increased usage as a treatment for wooden crossties and timbers. One of the principal reasons that CuN has gained market acceptance, in addition to its efficacy against decay fungi and wood-destroying insects, is its low mammalian toxicity and environmental impact. CuN is a well proven non-restricted use preservative, used extensively by utilities across the US when the environmental impact of their poles is a consideration. CuN was recently adopted by a Class 1 railroad to replace creosote in ties in several regions for both performance and regulatory reasons. This paper reviews the efficacy of CuN in laboratory and long term field tests, with an emphasis on the treated wood properties including permanence of preservative and conductivity. An update on the regulatory status of CuN is also given, including disposal options for treated wood. CuN is likely to increase in importance due to both economic and efficacy performance, and future disposal concerns with treated wood are also likely to increase its specification as a preferred preservative system for railroad, utility and highway structures.

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