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The Toxicologist - Society of Toxicology

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data provided insight into how the feedback control mechanisms embedded in the<br />

HPG axis mediate these changes. As this work progresses we will obtain a refined<br />

understanding <strong>of</strong> how adaptive responses within the HPG axis <strong>of</strong> fathead minnows<br />

affect DRTC behaviors for fadrozole. This work was reviewed by the U.S. EPA and<br />

approved for publication but does not necessarily reflect Agency policy.<br />

731 APPLICATION OF A HUMAN PHYSIOLOGICALLY-<br />

BASED PHARMACOKINETIC MODEL TO EVALUATE<br />

BENZENE BLOOD LEVELS FOR PUBLIC HEALTH<br />

CONCERN.<br />

D. A. Fowler 1 , R. R. Worley 1 ,J. S. Wheeler 1 , C. Welsh 1 ,D. M<strong>of</strong>fett 1 and J.<br />

Fisher 2 . 1 Agency for Toxic Substances and Disease Registry, CDC/ATSDR/NCEH,<br />

Atlanta, GA and 2 National Center for Toxicological Research, U.S. FDA, Jefferson, AR.<br />

ATSDR recently evaluated exposure to benzene and related petroleum VOCs in<br />

two neighborhoods located near petroleum refineries and a major interstate. Each<br />

resident provided a blood sample that was analyzed for benzene levels and smoking<br />

biomarkers. We used a human physiologically-based pharmacokinetic (PBPK)<br />

model for benzene (multi-route, multi-compartment, developed in Berkeley<br />

Madonna simulation s<strong>of</strong>tware) to model possible exposure scenarios resulting in<br />

measured benzene blood levels and evaluate the public health significance <strong>of</strong> those<br />

benzene blood levels. Measured benzene blood concentrations were an order <strong>of</strong><br />

magnitude higher in smokers relative to non-smokers. Because benzene is rapidly<br />

metabolized, benzene blood concentrations predominantly reflect recent exposures<br />

preceding blood collection. We modeled peak and steady state inhalation <strong>of</strong> benzene<br />

resulting in the observed benzene blood levels. By doing so, we were able to<br />

evaluate PBPK predicted inhalation exposures that could result in the measured<br />

benzene blood concentrations with respect to health guidelines. Our comparative<br />

analyses included ATSDR’s chronic inhalation minimal risk level (MRL) and the<br />

Benchmark Concentration lower bound estimate (BMCL). Measured benzene<br />

blood levels in non-smokers correspond to modeled exposures that were below<br />

ATSDR’s chronic inhalation MRL and do not suggest a public health hazard.<br />

Blood from smokers had higher levels <strong>of</strong> benzene that correlated with smoking biomarkers,<br />

suggesting an elevated benzene blood level association with smoking.<br />

<strong>The</strong>se elevated benzene levels correspond to modeled exposures above the MRL<br />

and near the BMCL, suggesting a health concern for smokers. This model application<br />

demonstrates the combined use <strong>of</strong> a human PBPK model and biomonitoring<br />

data in enhancing exposure analysis and public health decision-making.<br />

732 CHARACTERIZATION OF STRAIN- & DOSE-<br />

DEPENDENT ROUTES OF ELIMINATION FOR<br />

BENZENE & ITS METABOLITES IN 4 MOUSE STRAINS.<br />

G. A. Knudsen 1 , R. K. Kuester 1 , M. L. Cunningham 2 , J. E. French 2 and I. G.<br />

Sipes 1 . 1 Medical Pharmacology, University <strong>of</strong> Arizona, Tucson, AZ and 2 National<br />

<strong>Toxicology</strong> Program, National Institutes <strong>of</strong> Environmental Health Sciences, Research<br />

Triangle Park, NC.<br />

Benzene & its metabolites are eliminated in the urine, feces or expired-air, in a<br />

dose-dependent manner. To characterize the strain- & dose-dependent routes <strong>of</strong><br />

elimination for benzene, four strains were selected based on data from previously<br />

reported PK studies in 18 isogenic strains: C57BL/6J (reference), NZW/LacJ (high<br />

blood, marrow AUC), PWK/PhJ (highest marrow AUC) & FVB/NJ (lowest blood,<br />

marrow AUC). In C57BL/6J, elimination patterns were similar for doses 0.1-10<br />

mg/kg (3-5% expired, 4-7% feces, 70-88% urine); at 100 mg/kg, 30% was expired<br />

while 66% micturated. At 1,000 mg/kg, 70% <strong>of</strong> the dose was expired with the remainder<br />

recovered in urine. In all doses tested (0.1-100 mg/kg), elimination in<br />

NZW/LacJ, PWK/PhJ, & FVB/NJ mice was similar to C57BL/6J mice, with few<br />

exceptions. All strains <strong>of</strong> mice eliminated the majority <strong>of</strong> administered [14C] radioactivity<br />

in the urine (NZW/LacJ: 80-88%; FVB/NJ: 75-85%; PWK/PhJ: 70-<br />

77%). Fecal recovery for NZW/LacJ was similar to C57BL/6J (3-7%), while<br />

FVB/NJ mice eliminated more on average (7-11%). Doses recovered in feces were<br />

highest in PWK/PhJ (9-13%); however, at the highest dose, recovery was 4%. In<br />

C57BL/6J, NZW/LacJ, & FVB/NJ, expired [14C] benzene did not change significantly<br />

over the low doses (3-7%). In PWK/PhJ, a 10 mg/kg dose resulted in significantly<br />

more expiration <strong>of</strong> the dose when compared to the same dose in FVB/NJ &<br />

NZW/LacJ (p

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