The condition, after 31 years' exposure, of pine stakes treated with ammoniacal copper-based preservatives

Pinus sylvestris is sapwood stakes were treated with various copper - conta ining waterborne and oilborne preservatives and exposed in ground for 31 ye ars at Walpeup, Australia. Most of the waterborne preservative treatments c ontained basic copper carbonate and one or more of the following additives: arsenic pentoxide, pyridine, sodium pentachlorophenate, tannin and benzoic , boric, chromic, salicylic and sorbic acids. Basic copper carbonate and su lphate, at 0.95 kg m(-3) of copper, protected the stakes from significant s ubterranean termite attack at a site in Australia providing a moderate term ite hazard. Three additives (arsenic pentoxide at 0.95 kg m(-3), sodium pen tachlorophenate at 0.93 kg m(-3) and fluoride at 0.9 kg m(-3)) significantl y improved the efficacy of basic copper carbonate when used at retentions o f 1.7 to 2.0 kp m(-3) of copper. The six waterborne preservative combinatio ns that performed best (i.e. rating greater than 6.5 out of 8) against both the termite and decay hazards over the 31 year period contained basic copp er carbonate (at least 1.79 kg m(-3) of copper) plus arsenic pentoxide (at least 0.92 kg m(-3)). Three of the six combinations also contained chromic acid. The oilborne preservative combination performing best contained basic copper carbonate (1.33 kg m(-3)) and pentachlorophenol (6.64 kg m(-3)) in tall oil. A treatment containing a similar amount of pentachlorophenol in t all oil, but no basic copper carbonate was significantly less effective. Ot her treatments containing basic copper carbonate and pentachlorophenol in t all oil or the copper compound with sodium pentachlorophenate in oil emulsi on per formed well. The implications of these results for the current gener ation of copper-based preservatives are discussed.