User Guide to Thresholds and Classification - Environmental ...

160User Guide for Thresholds and Classifications11. Skin Corrosion and Irritation – Subclass 6.3 (8.2)11.1. General considerations11.1.1. Skin corrosion or irritation overviewSee section 9.6 in chapter 9, for definitions of the key terms used in this chapter.Several factors should be considered when determining the corrosive and irritant potential of substancesbefore testing is undertaken. Solid substances (powders) may become corrosive or irritant when moistenedor in contact with moist skin or mucous membranes. Existing human experience and data, including fromsingle or repeated exposure, and animal observations and data should be analysed first, as they giveinformation directly relevant to effects on the skin. In some cases enough information may be available fromstructurally related compounds to make classification decisions.Likewise, pH extremes like ≤ 2 and ≥ 11.5 may produce skin effects, especially when buffering capacity isknown, although the correlation is not perfect. Generally, such substances are expected to producesignificant effects on the skin.If a substance is highly toxic by the dermal route, a skin corrosion or irritation study on animals may not bepracticable, since the amount of test substance to be applied would considerably exceed the toxic dose, sowould result in the death of the animals. When observations are made of skin corrosion or irritation in acutetoxicity studies and are observed up through the limit dose, additional testing is not needed, provided thedilutions used and species tested are equivalent. In vitro alternatives that have been validated and acceptedmay also be used to help make classification decisions.Although information might be gained from the evaluation of single parameters within a tier, for example,caustic alkalis with extreme pH are considered skin corrosives, there is merit in considering the totality ofexisting information and making an overall weight-of-evidence determination. This is especially true whenthere is information available on only some parameters. Generally, primary emphasis should be placed onexisting human experience and data, followed by animal experience and testing data, followed by othersources of information, but case-by-case determinations are necessary.A tiered approach to the evaluation of initial information should be considered, where applicable (Table11.1), recognising that all elements may not be relevant in certain cases.Table 11.1: Tiered testing and evaluation of skin corrosion and irritation potentialStep Parameter Finding Conclusion1a Existing human or animal experience g CorrosiveClassify as corrosive aNot corrosive or no data1b Existing human or animal experience g Irritant Classify as irritant aJanuary 2012 EPA0109