Le matériau bois a depuis longtemps fait l'objet de traitements fongicides ou insecticides dont l'impact sur les sols après lessivage constitue un réel problème écologique. À ce jour, l'essentiel des études sur la dégradation de ces produits toxiques a été mené à partir des micro-organismes isolés en laboratoire. La présente étude a cherché à affiner les connaissances concernant ces microorganismes, en particulier les champignons lignivores dégradant les polluants in situ, pour lesquels peu de données sont en fait disponibles. En vue de dépolluer des bois traités, la capacité des micro-organismes lignivores issus de sols forestiers tropicaux de la Guyane et de la Réunion pour dégrader des biocides toxiques a été évaluée. Il s'agit du pentachlorophénol (PCP) et des composés à base de cuivre chrome arsenic (CCA). Le suivi de la dégradation d'éprouvettes de pin rouge, Pinus resinosa, montre que le sol de Guyane est plus performant que celui de la Réunion en termes d'activité microbienne vis-à-vis de ces deux biocides. Une différence significative de la perte de masse des éprouvettes de pin rouge traitées au CCA et au PCP peut aller du simple au double (respectivement 18 % et 30 %). Ces résultats confirment que le CCA est moins lessivable et moins dégradable par les microorganismes de ces sols que le PCP. D'après le barème des pertes de masse en essais de laboratoire, ces bois ainsi traités seraient classés peu durables après trois ans de mise en contact avec le sol, alors que le traitement est prévu comme très durable.
Wood-decay white-rot and brown-rot fungi have a major economic impact on commercial and manufactured tropical and temperate woods. The aim of this study was to design a molecular method, coupled with polymerase chain reaction (PCR) and DNA sequencing, to enable early identification of various forms of fungal decay in various types of wood. The resulting tool could be used to certify the healthiness of commercial woods and also to make more efficient use of chemicals and thus reduce their negative environmental impact. Sapwood plates of Distemonanthus benthamianus,Fagus sylvatica, Lophira alata, Pinus sylvestris, and Pycnanthus angolensis were incubated in vitro in the presence of Fibroporia vaillantii, Coniophora puteana, Gloeophyllum trabeum, Pycnoporus sanguineus, and Trametes versicolor according to the EN 113 standard method. Average mass losses ranging from 2.6% to 25.0% indicated that all wood samples had been actually infected and enabled us to test the reliability of our method. PCR products were obtained in 24 of 25 combinations, and DNA sequences were obtained in 21 of the 24 fungal PCR products. DNA sequences obtained from infected wood were compared with sequences from pure strains, thus confirming the identity of the infecting strains with 100% similarity for an average of 412 bp.
Materials and Methods Water solutions of albumin borate composed by a solution of 5% boric acid and 1% albumin solution both in water, applied premixed but not reacted to have still a single treatment were used to treat the wood specimens. 10replicate Pinus syIvestris sapwood specimens for each test of dimensions 50 x 25 x 15 mm were treated under 15 minutes vacuum at -I Bar followed by 120 minutes at atmospheric pressure. The treated specimens were then dried at 103~ for 8 hours to cause gelation of the proteins within the timber. The durability of these specimens against fungal attack was evaluated according to European Norm EN 350-1 for a period of 16 weeks and evaluated by average mass loss of the specimens. Twenty of the same type of treated specimens were also tested for 6 months for resistance to termite attack according to European Norm EN 117: while this norm prescribes insects of the Reticulitermes santonensis species we used the more aggressive Heterotermes indicola species. A value rating between 0 (= no attack) and 4 ( = complete destruction of the specimen) is then assigned to the specimens after 6 months exposure to termites. The results are shown in the table 1.
ResultsThe results of normalised biological tests of resistance of albumin borate treated wood to fungal attack from temperate zones white-rot (Coriolus versicolor and Lentinus squarrosulus), tropical zones white-rot (Pycnoporus sanguineus) as well as to brown rot fungat species shown in the table, in addition to the results already reported previously for other brown-rot and softrot fungal species indicate that protein borates are compounds of wide applicability as non-toxic wood preservatives. Such a conclusion is confirmed also by the resistance of wood specimens treated with albumin borate to termite attack under normalised test conditions.
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