EASEing into the Future

The current edition (2005 49) of the Annals of Occupational Hygiene presents
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,
the evaluation and further development of the EASE model, the validity of the
EASE dermal model and two papers on the validity of the inhalation model.

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. 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 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'. 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. 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 model gives considerable overestimates
of actual exposure.

Where does this leave us in the light of the proposed changes to the European
chemical supply legislation through REACH? There is still a need for
transparent, consistent, scientifically valid and practically relevant exposure
assessments. In the short term (if ever), it is not realistic to expect that
occupational exposures to chemicals will be described in all workplaces
throughout the EU. The validation studies reported in this issue and earlier
have highlighted weaknesses in the current model and make a clear case for the
need for improvements. HSE, CEFIC and The American Chemistry Council sponsored
a study carried out by the Institute of Occupational Medicine (IOM) to examine
the underlying structure and philosophy of the EASE model (version 2), to
provide a critical assessment of its utility and performance to date and to
make recommendations for the structure of a revised model.

Further information

AplusA-online.de - Source: Annals of Occupational Hygiene