Effect of rapid redrying shortly after treatment on leachability of CCA-treated southern pine

The use of southern pine lumber treated with chromated copper arsenate (CCA) has grown tremendously in recent years. This is largely because CCA-treated wood products are clean and odorless, as well as durable. However, due to increased demand and for certain applications, redrying treated wood may be necessary. If kiln-drying is used to supply treated wood for this increased demand, it would be desirable to know how rapid redrying might affect leaching of preservative from the treated wood. In this study, small samples (25 by 25 by 29 mm) of southern pine were treated with CCA preservative to retentions of 4.0, 6.4, 9.6, and 40 kg/m3 (0.25, 0.4, 0.6, and 2.5 lb./ft.3). Samples were wrapped in plastic for 24 hours at room temperature and then either air-dried at 24?C (75?F) or kiln-dried at either 60?C or 82?C (140?F or 180?F). Leaching tests of CCA elements were performed by soaking 25-mm cube samples of treated wood in water up to 14 days, and the resulting leachates were analyzed for CCA elements. In general, wood kiln-dried at high temperatures produced higher amounts (in parts per million (ppm)) of leached elements than did the air-dried wood. Each successively higher preservative retention produced increasingly greater amounts of leached elements. However, when expressed as a percentage of the original, samples with higher preservative retentions retained a higher percentage of the chemical element after leaching. It should be noted that full-sized treated lumber in service probably would not produce proportionally as much leached elements as did these small samples because of the lower proportion of exposed surface and, except in marine or freshwater uses, they would not be continuously soaked in water for 14 days.

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