Observations on a Possible Method of Predicting Soil-Block Bioassay Thresholds By Distillation Characteristics of the Weathered Creosotes

Decay by a test organism was stopped consistently by about the same amount of residual creosote boiling below 355?C. regardless of the amount or kind of creosote in the blocks originally. The average residual creosote below 355?C. in 14 creosotes was 2.34 lbs./cu.ft. of wood. This figure was rounded upward to the nearest half point, and it was assumed that in general 2.5 lbs./cu.ft. of residual creosote below 355?C. following weathering indicates the threshold for a creosote assuming Madison 534 as the test organism. As an illustration of the application of the 2.5 lb. criterion, the Bell Laboratories bioassay data for the creosotes 6003 and 6006, including the calculated residual material below 355?C., are listed. Blocks treated with these oils were weathered for 60 days outdoors. For creosote 6003, the actual threshold in soilblock test for Madison 534 fell between 5.6 and 6.7 lbs./ cu.ft. By interpolation, the 2.5 lbs. of residual below 355?C. fell at a treatment threshold of 6.1 lbs./cu.ft.–within the same range as determined by bioassay. In the case of creosote 6006, the actual soil-block threshold was between 5.8 and 7.9 lbs./cu.ft. The estimated threshold by interpolation, using the minimum of 2.5 lbs. of residual creosote below 355?C., was 6.5 lbs.–firmly in the range found by bioassay. The results of many soil-block bioassays of creosotes indicate that the threshold obtained with test organism Madison 534 correlates with the amount of creosote boiling below 355?C. which is present after weathering, viz., at the time the blocks are placed in test. It also appears that estimated thresholds based on a criterion of 2.5 lbs. of residual creosote below 355?C. in each cubic foot of wood, duplicate reasonably well the actual thresholds obtained in the soilblock test. The results indicated that creosote thresholds can be estimated in terms of Madison 534 by determining the initial retention which assures 2.5 lbs. of material below 355?C remaining in the blocks after a 60-day outdoor weathering, and that a creosote could be evaluated in about 3 instead of 6 months.

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