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

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 interindividual 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.

Analysis of aggregate exposure to chlorpyrifos in the NHEXAS-Maryland investigation.

“…For example, we are not aware of empirical data on chlorpyrifos absorption following respiratory exposure. We assumed that 100% of inhaled chlorpyrifos is absorbed, following Hubal et al (4) and Byrne et al (18), whereas other investigators have assumed a 70% absorption efficiency for respiratory exposures (24,25). Human volunteers who ingested neat chlorpyrifos are estimated to have absorbed 70-90% of the administered dose (26,27).…”

Comparison of food consumption frequencies among NHANES and CPES children: Implications for dietary pesticide exposure and risk assessment

“…Thus, by design, such surveys are appropriate sources of data for national-scale, acute dietary exposure assessments. In the absence of alternative data, the national data are sometimes used as default inputs for estimating pesticide intakes for geographic cohorts (Buck et al, 2001) or for estimating chronic dietary exposures (Shurdut et al, 1998;Harris and Gaston 2004). Some researchers have even developed statistical methods for estimating longer-term intakes using the national data (Dodd et al, 2006).…”

Biologically based modeling of multimedia, multipathway, multiroute population exposures to arsenic

“…The magnitude of non-dietary arsenic intake from incidental soil/dust ingestion is estimated using age-specific empirical intake rate distributions fitted to available tracer element mass balance study results. The geometric means (GM) and geometric standard deviations (GSD) of the estimated soil and dust ingestion rates (mg/day) were obtained from Buck et al (2001):…”