With respect to Document No: IRG/WP/246, and the recommendation that an economic leaching test can be based on a non-changing volume of water (500 ml/block), I would like to relate our experiences with this suggestion. Following 14 days of continuous immersion in de-ionized water it was found that blocks treated with moderate and above concentrations of a preservative gave no problems, but those blocks either having low chemical treatments or none (controls) produced a very healthy growth of slimy fungi and bacteria. Obviously these micro-organisms could be affecting the wood structure, should you wish to subsequently decay the blocks for biological toxicity evaluation. Also the micro-organisms could be degrading or otherwise modifying the preservative under evaluation. Under the old methods of "beaker leaching", with the water being changed daily, the growth of micro-organisms does not appear to be a problem. Any sugars leaching out into the water are removed within 24 hours and therefore the environment does not support their growth. The proposed method may be acceptable for leaching blocks containing a high retention of preservative (as reported in the paper), but as a method generally applicable to a concentration range of retentions, it does not seem to be acceptable. Obviously toxic agents could be added to the leaching water to prevent the growth of such micro-organisms, but this would have unpredictable effects on the wood-preservative-fungus complex under examination. I feel that this situation should be brought to the attention of the members of the IRG Working Group, since a non-biologist might not be aware of what has happened to his test and therefore present erroneous results.