The ECVAM International Validation Study on In VitroTests for Acute Skin Irritation: Selection of Test Chemicals

The ECVAM-funded skin irritation validation study (SIVS) was initiated in 2003,with the aim toevaluate whether the EpiDerm™, EPISKIN™and the SIFT alternative methods were able to reliably identify skinirritant and non-irritant chemicals, and could therefore be candidates for replacing the rabbit Draize test forskin irritation. The primary goal of the study was to evaluate the predictive capacity of the assays with regardto the EU classification system, which employs the risk phrases,“R38”,for skin irritants,and “no label” fornon-irritants. A secondary objective was the retrospective analysis of the data,to assess whether the in vitrotests would be able to discriminate between strong irritants (category 2), mild irritants (category 3) and non-irritants (no category), as defined by the OECD and United Nations proposal for a Globally Harmonised System(GHS) for the classification and labelling of dermal irritancy. A Chemicals Selection Sub-Committee (CSSC) wasappointed to identify test chemicals to be used in the SIVS, forwhichexisting, high quality in vivodata wereavailable,with which to correlate the in vitromeasurements. Since chemicals from the European Centre forthe Ecotoxicology and Toxicology of Chemicals (ECETOC) database of reference chemicals for skin irrita-tion/skin corrosion had been extensively used in preceding studies, the CSSC made use of novel sources forpotential test chemicals. The first source of chemicals screened was the New Chemicals Database (NCD),which is the central archive within the EU notification scheme for ‘new’ commercial chemicals. Data regis-tered in the NCD originate from standard assays, submitted in compliance with the legislation which regu-lates the marketing of industrial chemicals, and are subject to quality assurance by the competent authoritiesof the EU Member States. In addition, to obtain ‘existing’ chemicals which were readily available from majormanufacturing and/or distribution sources, additional databases were surveyed,such as the Toxic SubstanceControl Act (TSCA) database maintained by the US Environmental Protection Agency (EPA),and the ECETOCdatabase, with the exclusion of the chemicals used in the previous optimisation and prevalidation phases. Atotal of approximately 3500 chemicals from the NCD and 1600 from the additional databases were screened.Pre-determined selection criteria were applied, primarily to ensure the quality of the in vivodata and the prac-ticability of their use in testing. Overall, the number of chemicals fulfilling the CSSC selection criteria wasfound to be limited, particularly in the case of GHS category 2 chemicals. However, a total set of 60 chemi-cals were selected and proposed to the Management Team of the SIVS for independent coding and supplyto the participating laboratories. The selected chemicals: i) represented statistically justified sample sizes fordistinguishing R38 from no-label chemicals; ii) provided a balanced representation of the three GHS cate-gories,to allow for the post hocevaluation of the performance of the assays for that classification system;and iii) acknowledged,to a certain degree,the large prevalence known to exist for chemicals which haveoedema and erythema scores of 0.The selected chemicals represented a variety of molecular structures, func-tional chemical groups, and effect and use categories, as well as a wide range of physico–chemical proper-ties. They represented a challenging set of chemicals,relevant to current industrial commerce, with which tovalidate the alternative methods.