Biological effectiveness of didecyl dimethyl ammonium tetrafluoroborate (DBF) against basidiomycetes following preconditioning in soil bed tests

Evaluation of wood preservatives in soil-contact tests is becoming an important issue since detoxification of wood-protecting compounds by fungi and bacteria found in soil may decrease the resistance of treated wood. In this study, the decay resistance of wood treated with didecyl dimethyl ammonium tetrafluoroborate (DBF), a recently developed quaternary ammonia compound, was evaluated in both soil bed and laboratory decay resistance tests. Small specimens (5×10×100 mm³) of DBF-treated and untreated sugi sapwood were subjected to decay in laboratory soil bed tests (DIN ENV 807 (2001)) followed by Basidiomycetes tests (DIN EN 113 (1996)). Exposure in field soil and compost soil substrates was used to observe the effects of wood degrading and other soil-inhabiting micro-organisms on the decay resistance of the specimens. Soil bed tests showed that DBF-treated wood specimens at 7.7 kg/m³ retention level (1% DBF solution concentration) showed better performance compared to 0.01 and 0.1% DBF treatments. The 7.7 kg/m³ retention level was also effective to protect the wood specimens against Coniophora puteana and Coriolus versicolor in Basidiomycetes tests. It is concluded that detoxification of wood preservatives in soil contact is an important factor to determine protective properties of treated wood in ground contact applications. Further experiments with larger specimens are needed to observe the performance of DBF-treated wood at higher retention levels in field above ground and ground contact tests.