Evaluation of the protective means of some wood preservatives by means of accelerated tests

IRG/WP 232

I A Petrenko

In site conditions of the eastern site in the forest-steppe part of the Krasnovarsk region, the relative effectiveness of a series of wood preservatives was obtained by means of field tests. To obtain a more accurate evaluation of the protective qualities of these accelerated tests were carried out in laboratory conditions. In 9 boxes filled with non-sterile soil taken from the site, 72 samples of pine wood (in sizes of 20x20x30 and 20x20x5 mm³) soaked in copper naphthenate, pentachlorophenol and the compound FHM-7751 in three different concentrations were placed. In 3 boxes decay was mainly due to fungi causing limited rotting. In the other 6 boxes the soil was infected with the basidiomycete fungi Hymenochaete sp. and Coniophora cerebella in order to obtain more reliable results of the protective properties of the wood preservatives. Uniform distribution of infection was insured by placing cubes of wood infected with a pure culture of the fungi under test between the faces of two adjacent samples. Tests were carried out in an air temperature of 20-24°C with a relative air humidity of 70-80%. Soil humidity relative to its absolute dry weight was maintained at 30%. The decay of wood was measured by weight loss. Duration of tests was from 1 to 3.5 years. The advantage of the method used lies in the uninterrupted action of micro-organisms in the course of a long period while in field tests samples are subjected to attack only during the short Siberian warm period of the year. Moreover in field tests the samples do not always find themselves in the fungus infected zone and the decay is caused by imperfect fungi having only a moderate effect. A drawback of this method is the isolation of the sample as a result of which the soil zone around the treated samples is deprived of the influx of new micro-organisms, while available micro-organisms find themselves in severe conditions which become worse with the increase in the concentration of the wood preservative. As in field tests the accelerated tests have shown pentachlorophenol (PCP) to give the best protection. Samples after 6 months in the soil and with an absorption of 3 kg/m³ begin to be attacked by staining fungi, non-spore carrying bacteria and spore yeasts. With an absorption of 8 kg/m³ the samples are practically immune to micro-organisms. Analysis carried out a year after placing the samples in the soil has shown the samples to be in a good condition whether they have been treated with the maximal or minimal dose of PCP. The condition of the samples in analogous when subjected to the action of not only fungi causing moderate decay but also the basidiomycete fungus Hymenochaete sp. Samples treated even with minimal doses of wood preservative showed no signs of decay while the weight of untreated samples fell by 74 and 92% according to size. In non-sterile soil, together with fungi causing soft rotting, there develops to a sufficient extent mycelium of the basidiomycete fungus Lentinus lepideus. Nevertheless, after 2.5 years of accelerated tests, and in spite of the fairly high development of Lentinus lepideus in the soil, the condition of treated samples corresponded to a preservation (durability) index 100. The treated samples were immune to mycelium of Lentinus lepideus even in spite of the fairly strong attack at the beginning of the test by ammonia-forming bacteria and wood-staining fungi. Tests with Coniophora cerebella were the longest (3-5 years). Visual inspection showed decay of controls only. Treated samples, irrespective of the amount of PCP used, showed no signs of decay or weight loss. The results of accelerated tests agree with field tests. But sometimes there are found on the surface of samples mycelium and white well-branched wafts (fans) of Hymenochaete sp. The appearance of hymeno-mycetes seems to indicate their adaptation to PCP and the beginning of decay. Much attention is now given to the study of the reduced effect of PCP due to the adaptation of micro-organisms. The weakening of the protective action of wood preservatives leads also to their depletion in the wood while in service. The study of the microflora of samples in laboratory and field conditions has shown that in both cases bacterial flora predominates in the process of decay of wood treated with PCP. It is represented by spore-carrying as well as spore-free forms. With the increase of wood preservative loadings the spore-free forms predominate. The species composition of fungal flora has little variety on wood samples treated with PCP. The species resistant to it are, in field tests, Trichoderma lignorum and Fusarium sp.


Keywords: ACCELERATED TESTS; AGAR TESTING; CONIOPHORA PUTEANA; FIELD TEST; COPPER NAPHTHENATE; PCP; SOIL; WORT-AGAR MEDIUM

Conference: 73-06-19/22 Messilä, Finland


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