232
Kidneys
The chief targets of uranium toxicity in the human body are the proximal convoluted tubules in the kidneys where bicarbonate uranium complexes degrade due to
secretion of protons (ATSDR 1999; Aschner and Jiang 2009). The model projects
average values of kidney retention and kidney concentration in members of public
as 2.39 μg and 7.72 ng g
−1
of kidney tissues, taking the total mass of both kidneys
as 310 g. As calculated by the hair model, the uranium concentration in the kidneys
at all times and for all water samples is less than the nephrotoxicity standard of
0.3 μg g
−1
. Nephrotoxic effects of uranium may include cell necrosis and tubule
degeneration, leading to elevated levels of glucosuria, proteinuria, B2-microglobulin,
BUN (blood urea nitrogen) and NPN (nonprotein nitrogen) (ATSDR 1999).
Skeleton
Ingested uranium is osteotropic as UO 2
2+
mimics Ca
2+
. In the present case study, the
mean value of uranium present on the cortical and trabecular bone surfaces is 1 and
1.27 μg, respectively. Moreover, the uranium contents in non-exchangeable cortical
and trabecular bone volume are 181.2 and 48.68 μg. These data agree with the
assumption in the ICRP biokinetic model for uranium that the removal of uranium
from the non-exchangeable bone volume is very low. The non-exchangeable compartment of the skeleton is indeed the most stable storehouse of uranium in the
human body.
Other Soft Tissue (OST)
OST includes the skin, muscle, subcutaneous fat and all other remaining soft tissues
not explicitly assigned a compartment in the hair model. Soft tissue compartments
ST0, ST1 and ST2 represent rapid (2 h), intermediate term (20 days) and tenacious
retention (100 years), respectively. OST has the second highest build-up of uranium
after cortical bone volume with magnitude ranging from 20.05 to 230.09 μg. 30%
of uranium from plasma is delivered to ST0 in the early circulation of soluble
uranium.
Urinary Bladder
Uranium may be taken up directly from plasma or indirectly from kidneys into the
bladder with transfer rates k 4 = 6.3 d
−1
and k 5 = 1.2 d
−1
, respectively, as reported in
the hair compartment model. The three main processes participating in urine formation are glomerular filtration, secretion from peritubular capillaries to nephrons and,
finally, the reabsorption from nephrons back to peritubular capillaries. 63% of uranium is excreted in urine via the bladder.
R. Mehra and S. Kaur
Kidneys
The chief targets of uranium toxicity in the human body are the proximal convoluted tubules in the kidneys where bicarbonate uranium complexes degrade due to
secretion of protons (ATSDR 1999; Aschner and Jiang 2009). The model projects
average values of kidney retention and kidney concentration in members of public
as 2.39 μg and 7.72 ng g
−1
of kidney tissues, taking the total mass of both kidneys
as 310 g. As calculated by the hair model, the uranium concentration in the kidneys
at all times and for all water samples is less than the nephrotoxicity standard of
0.3 μg g
−1
. Nephrotoxic effects of uranium may include cell necrosis and tubule
degeneration, leading to elevated levels of glucosuria, proteinuria, B2-microglobulin,
BUN (blood urea nitrogen) and NPN (nonprotein nitrogen) (ATSDR 1999).
Skeleton
Ingested uranium is osteotropic as UO 2
2+
mimics Ca
2+
. In the present case study, the
mean value of uranium present on the cortical and trabecular bone surfaces is 1 and
1.27 μg, respectively. Moreover, the uranium contents in non-exchangeable cortical
and trabecular bone volume are 181.2 and 48.68 μg. These data agree with the
assumption in the ICRP biokinetic model for uranium that the removal of uranium
from the non-exchangeable bone volume is very low. The non-exchangeable compartment of the skeleton is indeed the most stable storehouse of uranium in the
human body.
Other Soft Tissue (OST)
OST includes the skin, muscle, subcutaneous fat and all other remaining soft tissues
not explicitly assigned a compartment in the hair model. Soft tissue compartments
ST0, ST1 and ST2 represent rapid (2 h), intermediate term (20 days) and tenacious
retention (100 years), respectively. OST has the second highest build-up of uranium
after cortical bone volume with magnitude ranging from 20.05 to 230.09 μg. 30%
of uranium from plasma is delivered to ST0 in the early circulation of soluble
uranium.
Urinary Bladder
Uranium may be taken up directly from plasma or indirectly from kidneys into the
bladder with transfer rates k 4 = 6.3 d
−1
and k 5 = 1.2 d
−1
, respectively, as reported in
the hair compartment model. The three main processes participating in urine formation are glomerular filtration, secretion from peritubular capillaries to nephrons and,
finally, the reabsorption from nephrons back to peritubular capillaries. 63% of uranium is excreted in urine via the bladder.
R. Mehra and S. Kaur