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A Critical Evaluation of in Vitro Radioactive Phosphorus Additions for Estimating Soil Deposits¹

Department of Food Science and Technology, University of California, Davis

ABSTRACT

The results of 240 determinations show that soils labeled with in vitro additions of radioactive phosphorus are well suited for use in studies of cleaning phenomena. Discs were cleaned under varying conditions of time, temperature, and hydroxide ion concentration. The correlation coefficients for each set of 40 discs were highly significant. The correlation between the per cent decrease in radioactivity and the per cent decrease in the weight of the soil film for the combined data was calculated at 0.906. The fact that these data do not agree with material recently presented by others (13) is at least partly explained by a difference in the nature of the soil films used.

Milk labeled with C¹⁴ following jugular infusion of C¹⁴ propionate was found to be unsatisfactory for cleaning studies. This was ascribed to the heterogeneity of the film, the nonuniformity of this type of labeling, and the necessity that cleaning be stopped short of completion, so the relation between a given variable and cleaning can be ascertained.

The use of radioactive bacteria, harvested from a P³² broth, was investigated within a limited range. While the correlation between soil removal and weight removal appears satisfactory, the method is more involved than in vitro additions, and offers no apparent advantage.

¹ This investigation was supported in part by Research Grant No. RG 6778 from the National Institutes of Health, Public Health Service.