To investigate the prediction of the long term emission of copper from preservative treated wood in a Use Class Class 3 scenario, treated boards were exposed vertically above ground to natural weather conditions. The study included two products; an amine copper ACQ-type formulation, air-dried after treatment to a 22 kg/m3 retention, and the same formulation which was hot oil vacuum dried after treatment. During a six year study period run-off emissates were continuously collected and their content of copper determined by chemical analysis at intervals. The total emission of copper was approximately 2 g/m2 exposed wood for the ACQ treated, air dried boards whereas the hot oil vacuum dried boards had a copper emission which was ten times lower at 0.2 g/m2 in total after six years. Approximately 50 % more leachate was collected from underneath hot oil dried boards, presumably due to increased water repellency of the oil treated surface; this is considered to be the reason for the reduced emission of copper. The prediction of long term emission after six years was possible from short term measurements after two years, using logarithmic extrapolation.

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