Evaluation of creosote fortified with synthetic pyrethroids as wood preservatives for use in the sea. Part 1: Efficacy against marine wood boring molluscs and crustaceans

Scots pine (Pinus sylvestris) wood samples were treated with creosote, CCA plus creosote, creosote fortified with different concentrations of the synthetic pyrethroids permethrin, cypermethrin and deltamethrin, and these synthetic pyrethroids in white spirit. Replicate treated and untreated samples were exposed in the sea for 59 months at three tropical sites in Australia and Papua New Guinea, and for 44 months at a fourth site in Singapore where populations of teredinids, pholads, limnoriids and sphaeromatids were known to be present. Untreated samples were destroyed by marine borers after ∼2 years. Samples treated with synthetic pyrethroids in white spirit were very severely damaged or destroyed by the end of the trial, while the samples treated with creosote fortified with synthetic pyrethroids ranged from very slight to moderate attack. Teredinid and limnoriid infestation of samples treated with all the creosote-containing preservatives was almost totally absent at all sites; pholad and sphaeromatid damage was very slight to moderate. The most promising combination treatment against pholads and sphaeromatids was creosote fortified with deltamethrin.