Dephenolisation in soil

Extract

1. Two colorimetric methods of estimation of phenol and the cresols in soil have been developed,—one for small quantities down to 0·01 mgm. in 50 c.c. of the soil distillate, and the other for larger amounts of the substances.

2. It is found that, even by starting the distillation of the soil within 20 minutes of the application of phenol, a 100 per cent. recovery of the added phenol cannot be effected, except in the case of autoclaved or steamed soil. This instantaneous disappearance is followed by a further loss, slower and different in character.

Phenol and the three cresols disappear, with more or less ease, in all soils examined.

3. The slow disappearance is apparently largely brought about by micro-organisms which are capable of decomposing phenol. There appears, however, to be some non-biological action also, since the disappearance in unmanured soil poor in micro-organisms, besides being much slower than in manured soil, is altogether different in character.

4. Autoclaving the soil at 130° C. for 20 minutes destroys the cause or causes of disappearance altogether, but the action proceeds, although much more slowly than in untreated soil, in the presence of a considerable amount of toluene and mercuric chloride. Further support is thus given to the view that a non-biological action accompanies the biological decomposition.

5. Partial sterilisation by treatment with toluene which was evaporated before the addition of phenol increases the rate of loss, but steaming does not.

6. The disappearance takes place even in soil air-dried to 2·4 per cent. moisture, but it is extremely slow compared with the rate in normal soil.

7. By applying a number of successive doses of phenol to the same soil it has been found that each dose disappears at a higher rate than the preceding one. This is entirely in accordance with an action mainly biological in character. The same effect has been observed in the case of m-cresol.

8. Two types of bacteria have been isolated from soil which are able to decompose phenol in culture solutions containing mineral salts and phenol. A third type capable of decomposing m-cresol has also been isolated from soil. A detailed study of the isolated organisms is being made in the bacteriological laboratory.

9. The instantaneous disappearance of phenol occurred in all soils examined. Its cause appears to be non-biological, but its exact nature has not yet been elucidated. There is reason to believe that the loss varies with the clay content of the soil. The loss does not appear to be materially affected by the period of contact of phenol with the soil prior to distillation, and is presumably complete only when the soil (air-dry) has been uniformly moistened with steam. Up to a certain point the loss is proportional to the concentration of the phenol solution.

10. The factor causing the loss is destroyed by autoclaving the soil at 130° C. for half an hour or by steaming it at 100° C. for one hour.

The treatment of the soil with sulphuric acid (50 per cent. by volume) either before or after addition of phenol greatly augments the loss, which may amount to 90 per cent, in case of phenol and 96 per cent. in case of m-cresol. This loss is not affected by autoclaving the soil.

11. Thus there appear to be at least three processes whereby phenol disappears from soil: one biological, one instantaneous chemical or physical and a third slow, chemical or physical. The mechanism of these changes, however, has not been elucidated.

This work was carried out during my tenure of the Earl Grey Memorial Fellowship awarded me by the Council of Armstrong College to whom and also to the Lawes Agricultural Trust I wish to express my thanks for facilities for carrying out this work.

My best thanks are due to Dr E. J. Russell at whose suggestion the investigation was undertaken and under whose direction the work has been carried out: and to Mr. H. G. Thornton for assistance on the bacteriological side.