The performance of CDDC (copper dimethyldithiocarbamate) and CCA (copper chrome arsenic) treated timber blocks was examined in a 1.5 year aquaria bioassay against the marine borers Limnoria tripunctata Menzies and Lyrodus pedicellatus (Quatrefages). Three timbers, southern yellow pine (SYP), Pinus radiata D. Don and Eucalyptus regnans F. Muell were treated with CDDC to retentions of 16, 32, 48 and 64 kg/m3 (1, 2, 3, 4 pcf), while CCA salt retentions were 8.1, 16.2, 32.5, 48.8 and 65.0 kg/m3. Water-treated controls of all timbers were heavily attacked by one or both marine borer species. There was also some surface softening of blocks due to microbial activity. CCA and CDDC treatments were generally similar in their effectiveness against L. tripunctata. However, CDDC was much more effective than CCA against L. pedicellatus. Only one block treated with CDDC showed any signs of L. pedicellatus attack, while nearly all CCA treated blocks were at least lightly attacked. CDDC treated blocks in aquaria with L. pedicellatus generally had greater mass loss than CCA treated blocks, probably due to the activities of marine soft rotting fungi and bacteria.

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