Ann. occup. Hyg., Vol. 46, No. 2, pp. 209-217, 2002
© 2002 British Occupational Hygiene Society
Published by Oxford University Press
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A Dirichlet Tessellation-based Sampling Scheme for Measuring Whole-body Exposure
Health and Safety Executive, Magdalen House, Stanley Precint, Bootle L20 3QZ; Health and Safety Laboratory, Broad Lane, Sheffield S3 7HQ, UK
Received 22 December 2000; in final form 22 October 2001.
Dermal sampling can be conducted using small pads or patches attached to various areas of the skin or clothing, or by using a whole-body coverall. Both techniques are recognized standardized methods for collecting chemicals. Patch sampling is simple to perform and inexpensive to analyse compared with an entire overall, but may require some user intervention. Extrapolation from a small sampled area to the total body area can lead to inaccurate estimates of total body exposure because of a lack of uniformity of deposition. Whole-body overall analysis eliminates the problems associated with using patches and gives a more accurate estimate of total body exposure. Therefore, if it were possible to measure the whole-body overall accurately and quickly, we would have a better assessment of dermal exposure. In this study we develop a working protocol using a standardized approach, to measure the contamination over an entire overall. The protocol takes into account size differences and establishes a reproducible pattern of sampling in order to map the distribution of contamination over each overall. The working protocol has been applied to 10 overalls collected from companies using copper-based biocides. A portable X-ray fluorescence spectrometer (PXRF) was used to measure the copper in the biocide. The exposure estimate from the PXRF results uses an averaging scheme based on the Dirichlet tessellation of the sampling locations. This allows unbiased estimates to be obtained from a complex sampling scheme that allocates more measurements to areas of high exposure. The Dirichlet tessellation method has been compared to the patch sampling method and the conventional total digestion of the entire overall method. Using the whole-suit digestion method as the benchmark, exposures ranged from 92.0 to 5848.5 mg. Mean absolute percentage errors (from the benchmark acid digestion of the whole suit) varied from ~20% for the Dirichlet-based PXRF method to 60% for the patch methods. The patch methods underestimated the true dermal exposure (–28 to –82% for acid digestion of the patches). Analysis of this data indicates that the Dirichlet PXRF method gives a more accurate estimate of whole-body contamination than the patch method. Furthermore, the 104 measurements give a much greater spatial resolution to the exposure data than analysis of the whole overall or patches by inductively coupled plasma-atomic emission mass spectrometry (ICP-AES). This detailed knowledge of the pattern of deposition on the body is of potential importance in chemical risk assessments.
Keywords: patch sampling; dermal; overalls; exposure; Dirichlet tessellation; portable X-ray fluorescence spectrometry
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