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Modeled estimates of chlorpyrifos exposure and dose for the Minnesota and Arizona NHEXAS populations

Journal of Exposure Science & Environmental Epidemiology volume 11, pages 253–268 (2001)Cite this article

Abstract

This paper presents a probabilistic, multimedia, multipathway exposure model and assessment for chlorpyrifos developed as part of the National Human Exposure Assessment Survey (NHEXAS). The model was constructed using available information prior to completion of the NHEXAS study. It simulates the distribution of daily aggregate and pathway-specific chlorpyrifos absorbed dose in the general population of the State of Arizona (AZ) and in children aged 3–12 years residing in Minneapolis–St. Paul, Minnesota (MSP). Pathways included were inhalation of indoor and outdoor air, dietary ingestion, non-dietary ingestion of dust and soil, and dermal contact with dust and soil. Probability distributions for model input parameters were derived from the available literature, and input values were chosen to represent chlorpyrifos concentrations and demographics in AZ and MSP to the extent possible. When the NHEXAS AZ and MSP data become available, they can be compared to the distributions derived in this and other prototype modeling assessments to test the adequacy of this pre-NHEXAS model assessment. Although pathway-specific absorbed dose estimates differed between AZ and MSP due to differences in model inputs between simulated adults and children, the aggregate model results and general findings for simulated AZ and MSP populations were similar. The major route of chlorpyrifos intake was food ingestion, followed by indoor air inhalation. Two-stage Monte Carlo simulation was used to derive estimates of both inter-individual variability and uncertainty in the estimated distributions. The variability in the model results reflects the difference in activity patterns, exposure factors, and concentrations contacted by individuals during their daily activities. Based on the coefficient of variation, indoor air inhalation and dust ingestion were most variable relative to the mean, primarily because of variability in concentrations due to use or no-use of pesticides. Uncertainty analyses indicated a factor of 10–30 for uncertainty of model predictions of 10th, 50th, and 90th percentiles. The greatest source of uncertainty in the model stems from the definition of no household pesticide use as no use in the past year. Because chlorpyrifos persists in the residential environment for longer than a year, the modeled estimates are likely to be low. More information on pesticide usage and environmental concentrations measured at different post-application times is needed to refine and evaluate this and other pesticide exposure models.

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Acknowledgements

The authors thank Dr. P. Barry Ryan of Emory University, the principal investigator of this project, for his support and technical guidance.

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Authors and Affiliations

  1. Department of Mathematics and Statistics, Western Michigan University, Kalamazoo, 49008, Michigan, USA

    ROBERT J BUCK

  2. U.S. Environmental Protection Agency, Office of Research and Development, National Exposure Research Laboratory, MD-56, Research Triangle Park, North Carolina, 27711, USA

    HALÛK ÖZKAYNAK

  3. Genetics Institutes, Inc., 35 Cambridge Park Drive, Cambridge, 02140, Massachusetts, USA

    JIANPING XUE

  4. U.S. Environmental Protection Agency, Office of Research and Development, National Exposure Research Laboratory, 12201 Sunrise Valley Drive, 555 National Center, Reston, 20192, Virginia, USA

    VALERIE G ZARTARIAN

  5. U.S. Environmental Protection Agency, Office of Research and Development, National Center for Environmental Assessment, 8601D, U.S. EPA Headquarters, Ariel Rios Building, 1200 Pennsylvania Avenue, N.W., Washington, 20460,, District of Columbia, USA

    KAREN HAMMERSTROM

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Correspondence to HALÛK ÖZKAYNAK.

Additional information

The U.S. Environmental Agency, through its Office of Research and Development, funded and collaborated in the research described here under NHEXAS Cooperative Agreement No. CR822038-1 with Harvard University. It has been subjected to Agency review and approved for publication. Mention of trade names or commercial products does not constitute an endorsement or recommendation for use.

Appendix A

Appendix A

The equation for inhalation potential dose accounts for correlations between inhalation rates, dermal surface areas, and body weights ( CARB, 1993; Phillips et al., 1993):

where ADD ijk is the inhalation daily potential dose (μg/kg/day), Cijk is the concentration in a microenvironment (ng/m 3), IR ijk is the average inhalation rate in the microenvironment (l/min/m 2 surface area), EF ijk is the fraction of time spent in the microenvironment, SA i/BW i is the ratio of skin surface area to body weight, and CF is a units conversion factor.

The equation for ingestion of soil is:

where IR ijk is the combined soil and dust ingestion rate (mg/day), FS i is the fraction of the total that is soil, and Cijk is the concentration of chlorpyrifos in the soil or dust. The equation for ingestion of dust is:

Modeling ingestion of food is more complicated because of the wide variety in possible foods that may be eaten and the differences in chlorpyrifos concentrations in the various foods. In the chlorpyrifos exposure model, potential dose from ingestion of chlorpyrifos in food is calculated by:

where LI ijk is the chlorpyrifos dietary intake rate (μg/day) for individual i.

For dermal uptake of compounds in soil or dust, the length of exposure is commonly defined as the number of exposure events per day without regard to the length of time an individual is exposed ( U.S. EPA, 1992a). Event duration is difficult to measure and is incorporated into absorbed dose as part of the absorption factor. An event is defined as the time from which contact is made with soil in an environment, such as a garden, to the time it is washed off. The cumulative amount of soil adhering to skin during multiple contacts with soil is reflected in the soil adherence factor in the equation. The potential dose equations for dermal exposure to chlorpyrifos in soil and dust, respectively, are:

where Cijk is the chlorpyrifos concentration in soil (μg/g), SF i is soil-to-skin adherence factor (mg/cm 2−event), DF i is dust-to-skin adherence factor (mg/cm 2−event), FR i is the fraction of skin surface area exposed, and EF i is the event frequency (events/day).

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BUCK, R., ÖZKAYNAK, H., XUE, J. et al. Modeled estimates of chlorpyrifos exposure and dose for the Minnesota and Arizona NHEXAS populations. J Expo Sci Environ Epidemiol 11, 253–268 (2001). https://doi.org/10.1038/sj.jea.7500164

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