Leachability and efficacy of CCA, creosote and two durable hardwood extracts in Ceiba pentandra (L.) Gaertn.-treated stakes against termite attack

Abstract

Leaching affects chemical potency of treated wood in service and has generated environmental and health concerns. Attempts to supplant inorganic preservatives with those from organic sources are achievable but their leaching potential is worth-ascertaining. Leaching resistance of two notable conventional preservatives (i.e., CCA and creosote) was compared with that of extracts from two durable hardwoods (i.e., Erythrophleum suaveolens bark and Azadirachta indica seed extracts) in pressure-treated Ceiba pentandra stakes (500 × 50 × 25 mm). Seventy treated stakes each were subjected to leaching in distilled water in the laboratory. Ten replicates were removed every 48 h and the water changed until 336 h. Decay resistance of the leached stakes was then assessed after 5 years of field exposure using visual durability ratings, mass and hardness losses. Ten non-leached treated stakes served as controls. Chemical retention was greater for stakes treated with water-borne preservatives (i.e., the extracts and CCA) than with creosote. Resistance of extract-treated stakes to bio-deterioration for all the durability parameters decreased as leaching periods lengthened. Inorganic preservative components leached and showed less mass losses in a more consistent fashion than their extract-treated counterparts, especially A. indica. This study shows that chemical discharge from treated stakes should not be overlooked by the wood treatment industry. Larger treated woods for outdoor construction would leak fewer chemicals than stakes under laboratory conditions, field exposure of the stakes simulates their service performance.