Ann. occup. Hyg., Vol. 46, No. 6, pp. 559-560, 2002
© 2002 British Occupational Hygiene Society
Published by Oxford University Press
Letters to the Editor |
Excluding Exposure Data of Very Poor Quality Is a Core Principle for Regulatory Risk Assessment
Department of Chemical Exposure Assessment, TNO Chemistry, PO Box 360, 3700 AJ Zeist, The Netherlands
Received 24 April 2002;
In a recent issue of this journal, Money and Margary (2002) proposed some thoughtful guidelines for exposure assessment in regulatory risk assessment. Their structured approach acknowledges that currently available exposure data are of very variable quality (Northage and Marquart, 2001). We firmly underline their plea for a hierarchy in available exposure information sources, with a higher weight assigned to data with a lower level of uncertainty. The level of confidence an assessor has in the available exposure information should play an important role in the resultant risk assessment process. Moreover, the classification of data into different uncertainty categories should aid the assessor when conflicting exposure results are reported. Hence, a transparent system quantifying heterogeneity in data quality is crucial if one wants to arrive at consistent risk assessments.
The approach of Money and Margary largely coincides with and was to some extent complementary to our decision tree for data quality evaluation published in the same issue (Tielemans et al., 2002). However, we question their statement that all exposure information sources should be considered as being potentially useful in the risk assessment process. On the contrary, it is our opinion that not all exposure information meets even the minimum requirements for incorporation in the exposure assessment process and the exclusion of such data should be the starting point for a transparent and robust exposure assessment. In our paper we defined minimum requirements for four different aspects, i.e. available occupational hygiene information, variability and precision issues, internal validity and external validity. We consider data sources to be unacceptable if very basic requirements are not fulfilled for these aspects. In these cases, the level of uncertainty or bias related to exposure data is in our view difficult to interpret in even a broad sense.
In order to evaluate the quality of data in current European Union risk assessments of existing substances, we conducted a small-scale inventory of exposure data. One exposure assessor of our department evaluated data quality of 40 measurement series selected out of five Risk Assessment Reports (RARs). A second researcher also evaluated 20 of these sources in order to study agreement between assessors. The data classification was done according to both a strict and a lenient interpretation of our decision tree (Tielemans et al., 2002). The former implies a rigid adherence of the assessor to the rules of the decision tree. Any non-compliance to the decision rules results in exclusion of the data. The latter refers to an approach that leaves more room for subjective assessment tailored to the specific exposure assessment situation. Table 1 describes the results of our inventory. It is a striking finding that 80% of the information sources were excluded when a strict classification was applied. A lenient approach also yielded exclusion of several measurement series (12.5%), although most ratings shifted towards supplementary information (80%). It should be noted that in both approaches only a small percentage of sources resulted in sufficient information. The percentage agreement between both assessors was 85 and 70% for a strict and lenient approach, respectively. This difference is in accordance with expectation, since a less rigorous approach relies to a larger extent on subjective judgement.
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The outcome of our analysis clearly illustrates the contrast between a rigorous evaluation that dismisses most data as useless and a lenient approach that allows most data to be incorporated into the risk assessment process. It can be learned from this inventory that a large part of the investigated data is hampered by a poor documentation of occupational hygiene information, low precision or questionable validity. A scientifically rigorous assessment would classify these data as being of very little relevance. We agree with Money and Margary that, as a result of the paucity of good-quality data, one has to employ a pragmatic or lenient approach in risk assessment. The emphasis should be on including and synthesizing as much as possible of the available exposure information in the assessment process. The decision tree should therefore not be used to dictate rigid rules but may be seen as a reference point, which facilitates a consistent evaluation of the level of uncertainty in existing data.
Yet, a pragmatic interpretation of the decision tree still requires the exclusion of data if minimum requirements are not met. The implication of even this limited survey is that some data are of such poor quality that they should be rejected. Such data sources do not provide information and only add noise to the assessment process or, even worse, may be seriously misleading. The cautious exclusion of such data enhances a consistent interpretation and weighting of the remainder of the exposure information in the assessment process. We therefore consider the exclusion of very poor data to be a core principle in maintaining the integrity of exposure assessment and by extension risk assessment.
REFERENCES
Money CD, Margary SA. (2002) Improved use of workplace exposure data in the regulatory risk assessment of chemicals within Europe. Ann Occup Hyg; 46: 279–85.
Northage C, Marquart H. (2001) Occupational exposure information needs for regulatory risk assessment of existing chemicals. Appl Occup Environ Hyg; 16: 315–8.[Medline]
Tielemans E, Marquart H, de Cock J, Groenewold M, van Hemmen J. (2002) A proposal for evaluation of exposure data. Ann Occup Hyg; 46: 287–97.
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