Comparison of PBTK model and biomarker based estimates of the internal dosimetry of acrylamide

Estimates of internal dosimetry for acrylamide (AA, 2-propenamide; CASRN: 79-06-1) and its active metabolite glycidamide (GA) were compared using either biomarkers of internal exposure (hemoglobin adduct levels in rats and humans) or a PBTK model (Sweeney et al., 2010). The resulting impact on the human equivalent dose (HED, oral exposures), the human equivalent concentration (HEC, inhalation), and final reference values was also evaluated. Both approaches yielded similar AA HEDs and HECs for the most sensitive noncancer effect of neurotoxicity, identical oral reference doses (RfD) of 2 × 10−3 mg AA/kg bw/d, and nearly identical inhalation reference concentrations (RfC = 0.006 mg/m3 and 0.007 mg/m3, biomarker and PBTK results, respectively). HED and HEC values for carcinogenic potential were very similar, resulting in identical inhalation unit risks of 0.1/(mg AA/m3), and nearly identical oral cancer slope factors (0.4 and 0.5/mg AA/kg bw/d), biomarker and PBTK results, respectively. The concordance in estimated HEDs, HECs, and reference values from these two diverse methods increases confidence in those values. Advantages and specific application of each approach are discussed. Reference values derived with the PBPK model were part of this research, and do not replace values currently posted on IRIS: http://www.epa.gov/iris/toxreviews/0286tr.pdf.)