Mortality verification of pinewood nematode from high temperature treatment of shavings

Ce rapport est disponible dans : EFSA Journal

Inglés. The European Commission requested the European Food Safety Authority (EFSA) to provide a scientific opinion on the report “Mortality verification of pinewood nematode from high temperature treatment of shavings” provided by the United States Department of Agriculture (USDA).The pinewood nematode, Bursaphelenchus xylophilus (Steiner and Buhrer) Nickle, is listed in Community plant health legislation and protective measures include a requirement that wood shavings of coniferous wood (except that of Thuja L.) originating in the United States (US) must be heat treated to achieve a minimum core temperature of 56 °C for at least 30 minutes.The USDA, through the United Kingdom (UK) Authorities, requested the recognition of an alternative treatment by the European Community. The request was supported by a report of an experiment entitled "Mortality verification of pinewood nematode from high temperature treatment of shavings" and additional explanatory information. This report (and additional explanatory information) presents a treatment process whereby wood shavings are exposed to high temperatures (398 °C) for a short time (3 minutes). The report was submitted to EFSA’s Scientific Panel on Plant Health for evaluation with regard to the reliability and effectiveness of the proposed treatment method, as an alternative to the current heat treatment requirement. A scientific opinion was requested to assist risk managers in considering the technical justification for derogation from the current treatment requirement for wood shavings of coniferous wood listed in Annex IV, Part A, Section 1, point 1.2 of the Council Directive 2000/29/EC[2].The Panel examined the report and supporting information in detail and based its conclusions on the following:* An analysis of the cited references, and the extent to which they support the statements made in the introduction and discussion sections of the USDA report;* Evaluation of the materials, methods and results presented in the report and* A statistical analysis performed by the Panel to test the hypothesis of a mortality estimate after the heat treatment lower than 100%.No comparison is made of the effectiveness and reliability of the proposed treatment method in relation to the current treatment requirement.The scope of this opinion is restricted to one species of Pinus “white pine” (Pinus strobus) as no wider species testing of other coniferous wood has been undertaken. Although the Panel is requested to consider the proposed treatment as an alternative to the current requirement for coniferous wood shavings, this extrapolation of the findings of the report cannot be made since no species other than white pine have been tested.According to the Panel, the references cited do not provide adequate evidence to support the effectiveness of the high temperature treatment proposed, are in some cases incorrectly interpreted and do not sufficiently validate the premise behind the treatment as stated in the USDA report. In particular, the relationship between lethal temperature and duration of exposure was not accurately established and no conclusion can, therefore, be derived about the appropriateness of the proposed temperature/time combination.The Panel considers that the accuracy of the results is difficult to assess due to missing data in the report for the control samples. The report claims that the treatment results in 100% mortality, but a statistical analysis is not included in the report to specify the statistical level of confidence supporting these results. The Panel performed a statistical analysis of the data provided in the USDA report and cannot exclude that the mortality estimate is lower than 99.85%.Uncertainties relating to the experimental design are identified by the Panel. These include:* The effect of the high temperature treatment alone, independent of the shredding process cannot be derived from this experiment.* After the shredding process, shavings are expelled onto a mesh conveyer, which allows dust and particles to fall before the material enters the dryer. The possibility of B. xylophilus contamination from untreated waste material is not discussed.* Only one temperature-time combination has been tested. Therefore the safety margins and reliability of routine operational application of the proposed high temperature treatment cannot be derived from this experiment. This is noted as particularly important in relation to the short exposure time of 3 minutes proposed.* A temperature of 115 °C is recorded at the end of the high temperature treatment. Thus, a continuous exposure to 398 °C for 3 minutes cannot be confirmed from the experiment described.The Panel considers that several elements of the experiment were also not adequately described:* The temperature of the wood shavings in the experiment is unknown. Further information on temperature measurement and placement of thermal sensors would enable more accurate evaluation of the temperature exposure over time.* A number of factors that may influence the results of the experiment are unknown. These include: the volume of the wood shavings relative to the air volume inside the dryer, the homogeneity of the distribution of the shavings in the dryer and wood moisture levels at the start of the treatment.* No information is provided to confirm the identity and the frequency of occurrence of the most resistant life stages of B. xylophilus in the treated samples. The storage conditions of the control samples are unknown, which may affect the natural mortality over time.The Panel agrees that there is potential for development of an alternative treatment protocol based on exposure of wood shavings to high temperatures for a short duration. The Panel however, does not consider that the evidence presented in this report demonstrates the effectiveness and reliability of the proposed temperature/time regime as an alternative to the heat treatment requirement for coniferous wood shavings set out in Annex IV Part A Section I Point 1.2. of Council Directive 2000/29/EC.