Why Copper

Copper is an essential micronutrient for most living cells. In larger doses though, the copper ion demonstrates activity as an algaecide, bactericide, fungicide, insecticide, and moldicide. Presently copper compounds are used for algal control, wood treatment, antifouling pigments, and crop fungicides (Richardson 1997). The fungicidal properties of copper were recognized in the 1700s, and copper-based preservatives have been widely and successfully used for more than a century. Although borates and organic biocides are gaining importance, copper remains the primary biocide component used today to protect wood used in ground contact or fully exposed to the weather (Lebow et al. 2004). Copper is needed against this challenge since very few organic molecules (other than creosote and penta) possess activity towards soft rot fungi (Hughes 2004). The volume of wood products treated with copper-based preservatives grew exponentially during the 1970s and 1980s and remains high today. Copper compounds also have advantages: it is relatively easy to create waterborne formulations; it is easy to analyze and determine penetration in wood, and copper slows photodegradation by UV radiation and water (Archer and Preston 2006). The focus on copper-based preservatives has increased following concerns about environmental effects of chromium and arsenic and resulting restrictions on the use of chromated copper arsenate (CCA). Much of the early work on copper-based formulations forms the basis for the ammoniacal and amine copper-based systems currently in the marketplace as CCA replacements (Preston et al. 1985). These formulations include quats or azoles as co-biocides. Recently micronized copper formulations with the same co-biocides have come into use. The drawbacks on use of copper compounds include: copper tolerance exhibited in a number of fungal species, possible corrosivity to metal fasteners and aquatic toxicity (Archer and Preston 2006). This paper presents a discussion on copper issues such as the mode of action, problems of copper tolerance, replacements for CCA, the latest micronized formulations and environmental effects of copper-based preservatives.