Current standardized methods are not well-suited for estimating in-service preservative leaching from treated wood products. This study compared several alternative leaching methods to a commonly used standard method, and to leaching under natural exposure conditions. Small blocks or lumber specimens were pressure treated with a wood preservative containing borax and copper hydroxide. The specimens were leached using scenarios involving short periods of immersion, simulated rainfall, or to a longer period of outdoor exposure to natural precipitation. When compared with lumber specimens exposed to natural precipitation, leaching from immersed small blocks overestimated losses of both copper and of boron, whereas immersion of lumber specimens underestimated losses of copper. Stirring during immersion, which is required by some standard methods, did not affect leaching. Simulated rainfall most closely simulated leaching during outdoor exposure, but is relatively complex and may be difficult to standardize. Leaching appeared to be directly related to the time that specimens had sufficient moisture to allow diffusion to occur. Further research is needed to better characterize moisture contents of wood products outdoors and develop methods that simulate those moisture conditions.
