Erosion assay

FIGURE 37.1 Effect of moisturizer treatment on sodium hydroxide erosion time of xerotic leg skin, (a) Marked improvement of alkali resistance after treatment with a water-in-oil emulsion for four weeks (p <. 0001). (b) Slight but significant improvement after treatment with a lotion containing 12% lactic acid (p <. 01). Erosion assays were performed before and after treatment on four adjacent spots per leg. Data shown as box plots. Statistical analysis was performed with the paired Mest. 

Kolbe, L., Kligman, A.M., and Stoudemayer, T., The sodium hydroxide erosion assay a revision of the alkali resistance test, Arch. Dermatol. Res., 290, 382, 1998. 

The principle of the human skin model test is that the test material is apphed topically for up to 4h to a three-dimensional human skin model, comprising at least a reconstructed epidermis with a functional stratum comeum (outermost layer of the skin). The human skin models can come from various sources, but they must meet certain criteria. Corrosive materials are identified by their abdity to produce a decrease in cell viabdity (as determined, e.g., by using a dye reduction assay) below defined threshold levels at specified exposure periods. The principle of the test is in accordance with the hypothesis that corrosive chemicals are able to penetrate the stratum comeum (by diffusion or erosion) and are sufficiently cytotoxic to cause cell death in the underlying cell layers. 

In a small test group of only five subjects erosion times of the dry skin of the calves were determined before and after four weeks of treatment with either a water-in-oil cream or a 12% lactic acid lotion (Figure 37.1). The assay was performed on four adjacent spots per leg. Spot-to-spot variation was on average less than one minute. In the majority of subjects erosions formed within two minutes. Erosion times on the legs treated with the water-in-oil cream were strongly increased, whereas the opposite legs, treated with the lactic acid lotion showed only slight improvement. This is not unexpected since alpha-hydroxy acids are known for their keratolytic activity which will weaken the... 

The Kettle Point Formation subcrops in southwestern Ontario. It is up to 60 m thick, with organic carbon values usually in the range 5%-16% and Fischer Assay oil yields up to 70 1/t (17 gal/ton). The organic matter is dominantly kerogen of marine origin and has attained only an immature thermal maturation stage. A particularly rich upper zone is present over much of the subcrop area and its thickness seems to be controlled by post-Kettle Point erosion. Although studies are still preliminary, especially for the Devonian shales, the Kettle Point Formation appears to have the most potential for shale oil production in southern Ontario. 

The principle of the assay is in accordance with the hypothesis that corrosive chemicals are those that are able to penetrate the stratum comeum (by diffusion or erosion) and are sufficiently cytotoxic to cause cell death in the underlying cell layers. 

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