home edit2 whole TSD November 2002 PDF format - OEHHA

following relationship, where C(t 1 ) is the experimentally derived cumulative tumor incidence (25%) and
d(t 1 ) is the average daily dose at time t 1 (15 years):
B = [C(t 1 )/d(t 1 )] × [(t L /t 1 ) k ]
The factor k describes the relationship of time of exposure to potency, in this case k=1 because of the
assumption of linear proportionality. From this relationship, CDHS (1988) derived a cancer potency
value. Using the average daily dosing derived by Allen et al. (0.023 mg/kg-day) and the cumulative
incidence data described by IARC (1982), the calculated cancer potency was 50 (mg/kg-day) -1 with
upper and lower 95% confidence bounds of 130 and 16 (mg/kg-day) -1 derived from the confidence
bounds of the dose.
CDHS (1988) considers the Allen et al .(1987) estimation of daily urine concentration of 0.023 mg/l to
be the most useful for establishing exposure levels. Assuming 1.5 l/day urinary output, 70 kg body
weight, 240 work days per year, and average duration of exposure 11.46 yrs in a cohort of 56.5 yrs
average age, lifetime average exposure is 0.0044 mg/kg-day. Using the US EPA (1986, 1987, 1988)
methodology and the upper 95% confidence bound on incidence [p(t) = 0.68], the cancer potency is
5.0 E+2 (mg/kg-day) -1 .
A unit risk factor of 0.14 (µg/m 3 ) -1 was derived by OEHHA/ATES assuming a breathing rate of 20
m 3 /day, 70 kg body weight, and 100% fractional absorption of inhaled benzidine.
Table 2. Benzidine cancer potencies derived from Zavon et al. (1973).
Source of methodology
Potency
[(mg/kg-day) -1 ]
Upper 95%
confidence bound
[(mg/kg-day) -1 ]
US EPA (1986, 1987, 1988) 234 363
Allen et al.(1987) 160 600
IARC (1982) * 50 130
CDHS (1988) 500
* Estimate based on IARC methodology using the dosage estimation of Allen et al. (1987).
V. REFERENCES
Allen RC, Ship AM, Crump KS, et al. 1987. Investigation of Cancer Risk Assessment Methods: Vol.
1. Introduction and Epidemiology. Office of Health and Carcinoma Assessment, EPA, Washington
DC, EPA/600/6-87/0516 (NHS PB88-127113).
Bonser GM, Bradshaw L, Clayson DB and Jull JW. 1956. The induction of tumors of the
subcutaneous tissues, liver and intestines in the mouse by certain dyestuffs and their intermediates. Br J
Cancer 10:653-667.
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