Exposure trial at tropical marine sites of pyrethroid/creosote mixtures as wood preservatives: Preliminary results
S M Cragg
Pinus sylvestris sapwood blocks measuring 25 x 25 x 200 mm³, impregnated using a Lowry or Rüping pressure treatment cycle with solutions of permethrin, cypermethrin or deltamethrin in BS144 creosote, have been exposed at marine sites in Australia, Papua New Guinea, the U.K. and Singapore. The effectiveness of these solutions in preventing marine borer attack is being compared with the efficacy of creosote alone, creosote/CCA double treatment, pyrethroids alone and no treatment. Blocks at the tropical sites have been installed in the intertidal zone in areas where the crustacean borer, Sphaeroma is active. Teredinids (shipworms) of several species are very numerous at these sites and the bivalve borer, Martesia, is present. Limnona colonies were found in untreated blocks at the sites in Papua New Guinea and Australia. The results of inspections after exposure periods of up to 26 months at the tropical sites are summarised in this report. Untreated sample blocks failed rapidly to borers, particularly teredinids. Pyrethroids alone reduced the level of crustacean borer attack and to a lesser extent, teredinid attack. All blocks treated with creosote-containing solutions have so far not been attacked by borers or degraded significantly by micro-organisms. Soft-rot and bacterial degradation occurred in untreated blocks and blocks treated with pyrethroids alone. Settlement by barnacles and serpulid worms appears to be inhibited by the creosote/CCA double treatment, but there is no evidence of long-term inhibition of barnacle or serpulid settlement by pyrethroid-containing solutions, whether with creosote or without. Samples at the site in the UK are exposed to teredinid attack. No inspections have yet been carried out at this site.