In the Nordic countries there are restrictions in the use of wood preservatives based on chromium and arsenic. For above ground use, class AB according to the Nordic system, only copper based preservatives are allowed in Sweden. Thus several new preservatives, copper based or metal free are now used. They have been approved by the Nordic Wood Preservation Council after passing laboratory tests against pure cultures of basidiomycetes. Their long term effectiveness in practice is still in many cases unknown. To increase the knowledge about these new “class AB” preservatives a field trial was started in 1996 at SP Swedish National Testing and Research Institute and another one in 1998 at The Swedish University of Agricultural Sciences. Durability against wood destroying fungi, leaching of preservatives during exposure and loss off effect against basidiomycetes in pure cultures of brown rot fungi after exposure were tested. As references untreated Pinus sylvestris and CCA-treated wood were used. For the preservatives tested the leaching after 5 years was between 15 and 100 % of the original retention while the leaching from CCA was less than 15 % for copper, chromium and arsenic. The durability in ground exposure was very low for wood treated with metal free preservatives. The amount of copper in copper based preservatives has a great influence on the durability in field. In general, with a higher retention of copper, the better was the performance. Test of durability in pure cultures showed a dramatic loss of effect when samples have been exposed outdoor above ground for two years compared to samples maintained in a dark conditioning room.

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