EASEing into the Future

Abstract

In this edition of the Annals you will find five papers relating to the Estimation and Assessment of Substance Exposure (EASE) model. There are papers on: the history of the development of the EASE model (Tickner et al., 2005), the evaluation and further development of the EASE model (Creely et al., 2005), the validity of the EASE dermal model (Hughson and Cherrie, 2005) and two papers on the validity of the inhalation model (Cherrie and Hughson, 2005; Johnston et al., 2005). Other earlier studies have looked at the validity of the EASE model (Vincent et al., 1996; Devillers et al., 1997; ECETOC, 1997; Van Rooij and Jongeneelen, 1999; Mark, 1999 and Bredendiek-Kamper, 2001) The EASE model was first developed by the Health and Safety Executive (HSE) on behalf of the European Union (EU) in the early 1990s. EU legislation required evaluation of the health risk of new chemicals before they were placed on the market, and this required estimation of exposure during use. Obviously, there were unlikely to be exposure measurements available for new chemicals, and EASE was designed purely as a screening tool to assist the estimation. There is currently much interest in and discussion of the changes to the European chemical supply legislation (http://europa.eu.int/comm/enterprise/ reach/index.htm). This is reflected in the range of regulators, industry and academia supporting the work on EASE in this issue, including the UK HSE, the European Chemical Industry Council (CEFIC), The American Chemistry Council, the International Lead Zinc Research Organization (ILZRO) and the International Institute of Synthetic Rubber Producers. As EASE is the main model used for regulatory occupational exposure assessment in the EU, now is a good time to question whether or not the current model can be upgraded or whether a new model is needed to face the challenges in European regulatory risk assessment that are to come. The basis for the development of EASE was the conceptual model outlined by Devine (Devine, 1993). This model postulates that the concentration of a substance could be predicted by analogy with similar situations, provided that the judgements made were calibrated by reference to measured exposure data that was sufficiently comprehensive, precise and representative. The model is based on three parameters: the tendency to become airborne, the way in which the substance is used and the means of control. The first, MS-DOS, version of EASE was soon found to be too crude to produce useful predictions. The second, Windows, version was produced by HSE in 1997 and had been improved mainly by changing the software interface and fixing obvious deficiencies in the model structure. A third version was developed but was never distributed because problems arose during user trials. The developers ‘always considered that the EASE outputs should be regarded as broad estimates, being adapted by experienced occupational hygienists in light of experience and factors not covered by the scope of the model’ (Tickner et al., 2005). EASE was not designed to be an ‘all-singing all-dancing’ exposure prediction model, so we should not be surprised that it does not perform well as a method of predicting individual sampling results (Johnston et al., 2005). It was designed to be an aid to regulatory exposure assessment, to be used by experienced occupational hygienists, where no real exposure data were available. How far the current model meets this aim is discussed in detail in the papers presented. The general opinion seems to be that for inhalation exposure EASE tends either to predict close to the measured values or to over-estimate. The dermal *Tel: +44 151 951 4464; fax: +44 151 951 3595; e-mail: chris.northage@hse.gsi.gov.uk