An environmental aspect relating to leachability of CCA from hardwood and softwood poles in Bangladesh
A K Lahiry
Leachability of CCA and the service performance of 8 softwood and 5 heartwood poles in service after 5 to 17 years in Bangladesh have been studied. The study included determination of retention of CCA-C in outer 6 mm zones at groundline (GL) and above groundline (AGL) along with the observation of decay and conditions of soils. The mean leaching of CCA-C derived from retention differential at GL and AGL are not found to be statistically significant. The existing balances of CCA-C components in poles do not indicate any leaching loss occurred. Reductions in retention have been noted at GL of softwood poles and at AGL of hardwood poles. Among several possibilities the density of wood as well as wood species/types, levels of retention, conditions of soil are found to be the prime factors which may increase leaching/depletion of CCA from the GL of softwood poles and responsible for poor performance of hardwood poles. The levels of CCA retentions in hardwood poles are not found to be adequate and equivalent to the levels of softwood poles in use. The CCA retentions of softwood poles were found still well above the toxic threshold for decay in even the oldest poles. Remedial treatments at GL of CCA-C treated hardwood poles installed in Bangladesh have been found to be essential. Very good service conditions confirm no remedial treatment necessary for CCA treated softwood poles.