Evaluating the potential of modified wood for use in marine environments using a short-term laboratory bioassay
L M S Borges, S M Cragg, M van der Zee
Chemically modified wood may be an alternative to preservative treated timber for marine structures. In this study a screening laboratory test using the wood-boring isopod crustacean Limnoria quadripunctata was used to assess the durability of chemically modified Pinus sylvestris, Pinus radiata and Picea sp. Most of the treatments used a combination of one of two of types of the resin dimethyloldihydroxyethyleneurea (DMDHEU) and phosphobutane tricarboxylic acid (PBTC). Untreated Pinus sylvestris sapwood was used as a non-durable comparison. Small test sticks from different types of modified wood were prepared and leached in seawater for 8 days prior to the experiment. A wood stick with a Limnoria and 4 ml of seawater was placed in each 12mm diameter well of a cell culture chamber. The number of faecal pellets produced by the animals was measured under these forced feeding conditions, and activity and mortality was recorded. With some treatments, no faecal pellets were produced, with others more faecal pellets were produced than with untreated Pinus sylvestris. Non-production of faecal pellets was sometimes due to mortality, but in some treatments there were also evidence of antifeedant effects as there was no evidence of acute toxicity Limnoria. However, some moribund animals were observed in these treatments and there was significant reduction in the number of pellets produced, so chronic toxicity may be suspected. The Arkofix type of DMDHEU gave significantly higher protection against borers than DMDHEU NG. A dose-dependent suppression of pellet production by PBTC was also detected.