Environmental Engineering Reference
In-Depth Information
where NL is the California Notii cation Level (in mg/L); BW is the adult body weight (in kg);
R
is the
de minimis
level for lifetime excess individual cancer risk;
q
1
*
human
is the CSF (in [mg/kg d]
−1
), the
upper 95% coni dence limit on the cancer potency slope calculated by the linearized multistage
(LMS) model and the potency estimate, which is converted from animal to human equivalent by using
(body weight ratio)
3/4
scaling; and
V
day
(in L/d) is the daily volume of water consumed by an adult.
The California NL for the carcinogenic effects of 1,4-dioxane is calculated on the basis of a
carcinogenic potency of 1.4
10
−2
(mg/kg d)
−1
as described below (Cal EPA, 1998).
California OEHHA selected the cancer potency [
q
1
*
human
] of 0.027 (mg/kg d)
−1
calculated for the
combined incidence of hepatocellular adenomas and carcinomas in female mice in the 1978 National
Cancer Institute study for 1,4-dioxane (NCI, 1978; described in Chapter 5). The study used an inter-
species scaling power of 2/3 as recommended by USEPA's 1986 Cancer Risk Assessment guidelines
and shown in Equation 6.2a. The currently recommended interspecies scaling power is 3/4, as
shown in Equation 6.2b (USEPA, 1986, 1992b, 1996a).
×
2
1/3
L
BW
(6.2a)
Ê
ˆ
Ê
ˆ
animal
human
q
*
=
q
*
¥
¥
,
Á
˜
Á
˜
1
human
1
animal
D
BW
Ë
¯
Ë
¯
animal
3
1/4
L
BW
Ê
ˆ
Ê
ˆ
animal
human
q
*
=
q
*
¥
¥
,
(6.2b)
Á
˜
Á
˜
1
human
1
animal
D
BW
Ë
¯
Ë
¯
animal
where
L
is the life span (in weeks) and
D
is the experimental duration (in weeks). In 1989, OEHHA
derived a cancer potency [
q
1
*
human
] of 0.027 (mg/kg d)
−1
by using Equation 6.2a, as shown in Equation
6.3 (Cal EPA, 2007c):
2
1/3
104
70
Ê
ˆ
Ê
ˆ
q
*
=
0.0014
¥
¥
=
0.027.
(6.3)
Á
˜
Á
˜
1
human
90
0.035
Ë
¯
Ë
¯
OEHHA derived a new cancer potency value [
q
1
*
human
] of 0.014 (mg/kg d)
−1
by using the scaling
power of 3/4, as shown in Equation 6.4:
3
1/4
104
70
Ê
ˆ
Ê
ˆ
(6.4)
q
*
=
0.0014
¥
¥
=
0.014.
Á
˜
Á
˜
1
human
90
0.035
Ë
¯
Ë
¯
The IRIS database uses data from the drinking water study by NCI (1978) and derives a cancer
potency of 0.011 (mg/kg d)
−1
, on the basis of the incidence of squamous cell carcinoma of the nasal
turbinates in male rats.
*
To calculate the NL,
70
¥
10
-
6
NL
=
=
2.5
m
g/L
ª
3
m
g/L,
(6.5)
-
2
1.4
¥
10
¥
2
where BW
=
70 kg is taken as the default adult male human body weight),
R
=
10
−6
is the default
de
minimis
lifetime excess individual cancer risk, the CSF used is
q
1
*
human
=
1.4
×
10
−2
(mg/kg d)
−1
, and
the default daily water consumption
=
2 L/d.
*
Hoch-Ligeti and Argus (1970) and Argus et al. (1973); see Chapter 5.
Search WWH ::
Custom Search