220
Cancer risk
C
= ×
A R
(1)
In the above equation, A C represents the activity concentration of uranium (Bq L
−1
).
R is the risk factor (Bq
−1
L), a product of risk coefficient, r and per capita activity
intake, I. Since the specific activity of a radioelement determines its radio toxicity,
the choice of risk coefficients depends on the isotopic nature of uranium in water
along with its physic-chemical form (Guseva Canu et al. 2011). The cancer mortality risk coefficients (in Bq
−1
) for the three uranium isotopes
234
U,
235
U and
238
U are
6.1 × 10
−11
, 6.2 × 10
−11
and 7.5 × 10
−11
respectively, whereas cancer morbidity risk
coefficients (in Bq
−1
) are 9.5 × 10
−11
, 9.8 × 10
−11
and 7.5 × 10
−10
, taken in same
order.
3.2 Chemical Toxicity
The chemical toxicity of uranium is of relevance only after it enters the body. This
toxicity is a function of several environmental parameters. The key ones are carbonate concentration, because of the formation of soluble carbonate complexes, and
divalent cation concentration (Ca
2+
and Mg
2+
), because of their competitive interactions with the uranyl ion (UO 2
2+
) (Sheppard et al. 2005). The chemical/noncarcinogenic risk for uranium is quantified in terms of lifetime average daily dose (LADD)
and hazard quotient (HQ):
LADD
EPC IR IF
AT
=
× × ×
×
D
W
(2)
In the above expression, EPC is the exposure point concentration of uranium in
water (μg L
−1
), IR is ingestion rate (taken as 1.4 L day
−1
), IF is ingestion frequency
(365 days y
−1
), D is duration (taken as a lifetime of 69.89 y), AT is average time
(days) and W is the ideal body weight (68.831 kg) (ICRP 2014).
HQ
LADD
RD
=
(3)
where RD is the reference dose limit taken as 0.6 μg kg
−1
day
−1
(WHO 2004).
3.3 Age-Dependent Annual Ingestion Dose for Different Age
Groups
The dose received by a person is dependent on many parameters like:
(a) The volume or quantity of the contaminant inhaled or ingested
(b) The fraction of the contaminant reached the respiratory or GI tract
R. Mehra and S. Kaur
Cancer risk
C
= ×
A R
(1)
In the above equation, A C represents the activity concentration of uranium (Bq L
−1
).
R is the risk factor (Bq
−1
L), a product of risk coefficient, r and per capita activity
intake, I. Since the specific activity of a radioelement determines its radio toxicity,
the choice of risk coefficients depends on the isotopic nature of uranium in water
along with its physic-chemical form (Guseva Canu et al. 2011). The cancer mortality risk coefficients (in Bq
−1
) for the three uranium isotopes
234
U,
235
U and
238
U are
6.1 × 10
−11
, 6.2 × 10
−11
and 7.5 × 10
−11
respectively, whereas cancer morbidity risk
coefficients (in Bq
−1
) are 9.5 × 10
−11
, 9.8 × 10
−11
and 7.5 × 10
−10
, taken in same
order.
3.2 Chemical Toxicity
The chemical toxicity of uranium is of relevance only after it enters the body. This
toxicity is a function of several environmental parameters. The key ones are carbonate concentration, because of the formation of soluble carbonate complexes, and
divalent cation concentration (Ca
2+
and Mg
2+
), because of their competitive interactions with the uranyl ion (UO 2
2+
) (Sheppard et al. 2005). The chemical/noncarcinogenic risk for uranium is quantified in terms of lifetime average daily dose (LADD)
and hazard quotient (HQ):
LADD
EPC IR IF
AT
=
× × ×
×
D
W
(2)
In the above expression, EPC is the exposure point concentration of uranium in
water (μg L
−1
), IR is ingestion rate (taken as 1.4 L day
−1
), IF is ingestion frequency
(365 days y
−1
), D is duration (taken as a lifetime of 69.89 y), AT is average time
(days) and W is the ideal body weight (68.831 kg) (ICRP 2014).
HQ
LADD
RD
=
(3)
where RD is the reference dose limit taken as 0.6 μg kg
−1
day
−1
(WHO 2004).
3.3 Age-Dependent Annual Ingestion Dose for Different Age
Groups
The dose received by a person is dependent on many parameters like:
(a) The volume or quantity of the contaminant inhaled or ingested
(b) The fraction of the contaminant reached the respiratory or GI tract
R. Mehra and S. Kaur