(VCCEP) Tier 1 Pilot Submission for BENZENE - Tera

nursing events were assumed to occur each day, lasting 12 minutes each, with 115 mL of milk
ingested per nursing event, yielding a daily milk consumption of 0.92 L. Three individual nursing
events were assumed to occur during working hours and the remainder five nursing events
were assumed to occur after working hours. The nursing events that occurred during working
hours all occurred after the benzene blood concentrations had reached steady-state with the
workplace exposures and occurred at 2.1, 4.1 and 7.1 hours into the workday. The remaining
five nursing events occurred at 2, 5, 10, 13 and 15 hours post-work-shift. If the working day
were assumed to begin at 8:00 a.m., this would amount to nursing events occurring at 2:00
a.m., 5:00 a.m., 7:00 a.m., 10:00 a.m., 12:00 p.m., 3:00 p.m., 6:00 p.m., and 9:00 p.m.
All parameters for the PBPK model of benzene were obtained from Fisher et al. (1997), except
the metabolic rate constants for benzene which were obtained from Tardif et al. (1995). The
Fisher et al. (1997) model was reproduced successfully before using it to simulate the
lactational transfer of benzene according to the defined exposure scenarios. The human milk
concentrations for both the non-occupationally exposed mother (urban, typical and high-end)
and the occupationally exposed mother were calculated.
The parameters of the model and the simulations of lactational transfer are included in Appendix
B. The results of the model are summarized in Table 7.27 below.
Table 7.27: Modeled Benzene Concentrations in Human Milk using the Fisher et
al. (1997) Lactation Model
Scenario
Benzene VCCEP Submission
March 2006
Modeled Human
Milk Benzene
Concentration
(µg/L)
125
Mass Ingested (mg/day)
Urban, typical 0.02 0.000016
Urban, high-end 0.1 0.00012
Occupational, typical 1.5 0.0014
Occupational, high-end 5.3 0.0049
The results of the modeling for the nursing mother in an urban environment are consistent with
those measured by Fabietti et al. (2004) where the measured values ranged from 0.01 to 0.18
µg/kg. Although information regarding the mothers’ occupational exposures to benzene were
collected by Fabietti et al., it was not reported. However, given that the occupational exposures
are at least one order of magnitude higher than the ‘urban’ exposure scenario, it is reasonable
to predict human milk concentrations from occupationally exposed mothers that are an order of
magnitude higher.
Intakes of benzene in terms of mass per body weight for an infant were calculated and are
presented on Table 7.28 below.