Effect of humic acid on leaching of CCA from treated wood

It is known that organic acids are effective at extracting chromated copper arsenate (CCA) components from wood, so the effect of natural humic acids on leaching was studied in the laboratory and in poles in service. Comparative analysis of poles of similar ages was done between those in wet, boggy sites and dry sites. Laboratory leaching studies done according to American Wood Preservers' Association (AWPA) Standard E-11-97 indicated that relatively high concentrations (1,000 to 10,000 ppm) of humic acids increase the leaching of chromium and copper from CCA-C treated wood, and that copper was most affected. They also showed that leaching with natural water samples resulted in higher leaching of all components than leaching with distilled water. Evaluation of CCA component retentions and mass balances in the 5-mm surface of poles in service showed that copper and arsenic were leached significantly from the portions of the poles in contact with water in wet sites. Arsenic losses increased more with pole age compared to the other components. Chromium leaching did not appear to be affected by location in the pole or by site. Although regression analysis showed that the concentration of CCA components in water near poles in wet sites increased with higher natural humic acid concentrations and lower water pH, CCA component levels and mass balances in the wood surface in contact with water in service did not confirm that these factors increased surface leaching.