Annals of Occupational Hygiene Advance Access originally published online on July 13, 2006
Annals of Occupational Hygiene 2006 50(6):639; doi:10.1093/annhyg/mel038
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LETTERS TO THE EDITOR |
Reply
We appreciate Dr Mage's clarification on two points within our article (Geer et al., 2004). First, as indicated by Dr Mage, we did attribute dermal absorption factors (DAFs) of 1, 3, and 10% to Griffin et al. (1999), Nolan et al. (1984)/EPA (1999) and Krieger (1995), respectively. Dr Mage correctly identifies the attribution of 10% to Krieger (1995) as an error. The correct reference (also cited within our article) should be Krieger et al. (2000). In this work, Krieger et al. do not actually derive or measure a DAF of 10%, but, rather, they justify it for use in their analysis (Table 5) based on the unpublished work of Thongsinthusak, 1991. Dr Mage is correct that Nolan et al. (1984) do provide a mean DAF estimate of 1.28%. However, we cite and use the 3% value conservatively adopted by EPA based on the work of Nolan et al. Our justification for the use of a 3% DAF is not only based on these references but also on our own findings of a DAF in the range of 3–10% (our Figure 3). In fact, contrary to Dr Mage's suggestion that ‘usage of 3% for a DAF is very likely to lead to a gross over prediction of the amount entering the body,’ our results suggest that the 3% value underestimates the actual amount absorbed via the skin.We do not view, nor did we mean to imply, the differences or variability in DAFs as ‘experimental error’ but rather as inter-study variability due to methodological differences including the time course of exposure and biomarker measurement. This is acknowledged in our current discussion where we state, ‘dermal exposure estimates may be prone to uncertainty due to differences in pesticide metabolism in the worker attributable to DURATION and rate of exposure’. Accordingly, this first point of clarification by Dr Mage does not in any way alter our results or conclusions but does provide a point of clarification to our discussion.
Dr Mage's second point is that we should have adjusted our dose estimates by the worker's body weight to provide an appropriate metric for comparison with EPA's reference dose. As stated in our introduction, the focus of our research was to ‘provide improved understanding of worker exposure and methods of assessment as a fundamental basis for health protection’. Therefore, it was outside the scope of this paper to do as Dr Mage suggests and estimate risk. Our work is intended to provide the exposure assessment underpinning support for such an analysis. For purposes of our stated goal, estimates in units of mg per day provide the appropriate metric.
The Johns Hopkins Bloomberg School of Public Health Baltimore, MD, USA
Formerly with the Johns Hopkins Bloomberg School of Public Health and now at The Ohio State University School of Public Health Columbus, Ohio, USA E-mail: tbuckley{at}sph.osu.edu
Received May 21, 2006;
REFERENCES
Geer LA, Cardello N, Dellarco MJ, et al. (2004) Biomarker-based evaluation of whole body dosimetry for estimating worker chlorpyrifos exposure. Ann Occup Hyg 48:683–95.
Griffin P, Mason H, Heywood K, et al. (1999) Oral and dermal absorption of chlorpyrifos: a human volunteer study. Occup Environ Med 56:10–3.
Nolan RJ, Rick DL, Freshour NL, Saunders JH. (1984) Chlorpyrifos: Pharmacokinetics in Human Volunteers. Toxicology and Applied Pharmacology 73:8–15.[CrossRef][Web of Science][Medline]
US EPA Office of Prevention, Pesticides and Toxic Substances. Replacement of Human Study Used in Risk Assessments, Report of the Hazard Identification Assessment Review Committee. 2 June 1999.
Krieger RI. (1995) Pesticide exposure assessment. Toxicol Lett 82/83:65–72.
Krieger RI, Bernard CE, Dinoff TM, Fell L, Osimitz TG, Ross JH, Thongsinthusak T. (2000) Biomonitoring and whole body cotton dosimetry to estimate potential human dermal exposure to semivolatile chemicals. J Expo Anal Environ Epidemiol 10:50–7.[CrossRef][Web of Science][Medline]
Thongsinthusak T. Determination of dermal absorption of chlorpyrifos. Department of Pesticide Regulation, California Environmental Protection Agency. Memorandum to Malcom Black, 2 August 1991.
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