Pinus radiata sapwood treated to approximately 10 kg/m³ with Tanalith NCA or Tanalith C-type CCA preservatives was ground to a fine powder and samples were then leached with solutions of calcium chloride, calcium nitrate, magnesium nitrate, or a mixture of potassium di-hydrogen orthophosphate and di-potassium hydrogen orthophosphate, at 0.03M-1.00M solution concentrations. Leached wood samples were then analysed for copper content (%) and the results compared with those from unleached or de-ionised water-leached samples. Inorganic salt solutions caused enhanced copper leaching relative to de-ionised water and copper leaching increased with salt solution concentration at a rate dependent on each leaching solution type. Tanalith NCA-treated wood was more susceptible to copper leaching than Tanalith C-treated wood where both were exposed to the same leaching solution concentration of calcium or magnesium salts. In contrast, there was no consistent difference in copper leaching between Tanalith NCA and Tanalith C-treated wood exposed to phosphate solutions. It can be concluded that horticultural soils containing relatively high concentrations of calcium, magnesium, potassium and phosphorus will present a greater leaching hazard to CCA-treated wood than pastoral soils of lower ionic status. At the recommended concentrations of these elements in horticultural soils, the involvement of calcium salts in preservative leaching may be particularly significant. Phosphate ions have limited mobility in soil solutions and are therefore less likely to be involved in leaching processes.

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