PRESERVATIVE LEACHING FROM SOFTWOODS SUBMERGED IN IRISH COASTAL WATERS AS MEASURED BY ATOMIC-ABSORPTION SPECTROPHOTOMETRY

Preservative leaching from treated timber submerged in the sea, although an accepted phenomenon, has not been monitored or quantified closely until the recent International Research Group on Wood Preservation (IRG) worldwide marine trial (Leightley 1987). Results of an Irish marine trial are reported here. Test blocks of Irish-grown Pseudotsuga menziesii (Douglas fir) and Pinus contorta (lodgepole pine) were treated by vacuum-pressure impregnation with three concentrations of a CCA preservative (Tanalith CT 106) and submerged in the sea off the west coast of Ireland for varying periods of time up to 72 weeks. The loss of preservative components (Cu, Cr and As) was measured at 12 week intervals using atomic absorption spectrophotometry (AAS). All elements were leached from treated blocks; maximum levels of leaching reached after 72 weeks submergence were 14% for copper, 27% for arsenic and 7% for chromium from treated Douglas fir blocks and 37% for copper, 36% for arsenic and 22% for chromium from treated lodgepole pine test blocks. The extent of elemental losses was related to the wood species, size of test block, duration of submergence, characteristics of the site of submergence and the concentration of preservative used. Some evidence is also provided that the role of arsenic in preservative salts may be diminished in marine situations.