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Uranium Toxicity

(last updated 26 July 2011)

Contents:

> See also:


INTRODUCTION

Uranium presents both chemical and radiological hazards. Risk assessments must address both types of hazards, therefore.

Unfortunately, there are some problems with the comparison of these hazards:


INHALATION

Inhalation: Chemical toxicity

(see also: Uranium Biokinetics Calculator)

The study [ATSDR1999] reviews all published data on animal studies known on uranium toxicity:

In another review [Jacob1997], performed for the German Federal Environmental Agency, another study performed by [Stokinger1953a] on rats is used: The rat study showed slight impacts to the kidneys at uranium resorption rates of 2.6 g per kg per day. This rate corresponds to uranium concentrations of 40 g per m3 in air. Applying a number of safety and conversion factors, the authors obtain a "tolerable" level of 0.07 g/m3 uranium in air.

Inhalation of uranium
(based on chemical toxicity)
TAC
[g/m3]
[ATSDR1999] intermediate duration, soluble0.4
[ATSDR1999] intermediate duration, insoluble8
[ATSDR1999] chronic, soluble0.3
[Jacob1997]0.07
TAC = Tolerable Air Concentration

 

Inhalation: Radiological Hazard

(see also Uranium Radiation Exposure · Uranium Radiation Individual Dose Calculator)

Inhalation of uranium for workers
(based on radiological hazard)
insoluble soluble
Dose fact.
[mSv/mg]
ALI
[mg]
DAC
[g/m3]
Dose fact.
[mSv/mg]
ALI
[mg]
DAC
[g/m3]
natural uranium with progeny 0.4247.616.5 0.345921
pure natural uranium 0.210034.7 0.0131520530
enriched natural uranium (3.5%) 0.67629.610.3 0.044450159
depleted natural uranium (0.2%) 0.11018363.4 0.00732740950
recycled uranium 0.653110.8 0.041486169
enriched recycled uranium (3.5% equiv.) 2.807.152.5 0.17611439
depleted recycled uranium (0.2%) 0.17311640 0.0111750610
ALI = Annual Limit on Intake based on 20 mSv/a
DAC = Derived Air Concentration based on 20 mSv/a, breathing rate of 1.6 m3/h, working time of 1800 h/a
Short-lived decay products included
Based on ICRP68 dose factors for 1 m AMAD, initial enrichment to 3.5%, burnup of 39 GWd/tHM, storage time of 5 years after unload

Inhalation of uranium for the public
(based on radiological hazard)
insoluble soluble
Dose factor
[mSv/mg]
ALI
[mg]
DAC
[g/m3]
Dose factor
[mSv/mg]
ALI
[mg]
DAC
[g/m3]
natural uranium with progeny 0.701.420.18 1.60.630.08
pure natural uranium 0.224.50.58 0.01374.59.4
enriched natural uranium (3.5%) 0.751.340.17 0.04522.32.8
depleted natural uranium (0.2%) 0.128.31.05 0.007513417
recycled uranium 0.711.410.18 0.08112.31.6
enriched recycled uranium (3.5% equiv.) 3.10.3240.041 0.42.490.32
depleted recycled uranium (0.2%) 0.195.270.67 0.01285.111
ALI = Annual Limit on Intake based on 1 mSv/a
DAC = Derived Air Concentration based on 1 mSv/a, breathing rate of 0.9 m3/h, continuous exposure
Short-lived decay products included
Based on ICRP72 dose factors for adults, initial enrichment to 3.5%, burnup of 39 GWd/tHM, storage time of 5 years after unload

Note:
The new ICRP68/ICRP72 new window dose factors used here show significant differences from those in ICRP60/61 new window: The new inhalation dose factors for uranium and thorium are about a factor of 4 lower, and for actinium a factor 2 lower.

 

Inhalation: Current Standards

U.S. NRC Occupational Annual Limits on Intake (ALI's) for Inhalation
Unatural (soluble): 1 Ci (= 37000 Bq, equiv. to 1.5 g)
Unatural (insoluble): 0.05 Ci (= 1850 Bq, equiv. to 74 mg)
(10 CFR 20, App. B external link, 1991)
These values are based on a committed effective dose equivalent of 5 rems (50 mSv).

U.S. NRC Occupational Derived Air Concentrations (DAC's)
Unatural (soluble): 5.0E-10 Ci per ml of air (= 18.5 Bq/m3, equiv. to 0.74 mg/m3)
But, to address the chemical toxicity, the following tighter criterion is defined, in addition to the radiological one:
Unatural (insoluble): 2.0E-11 Ci per ml (= 0.74 Bq/m3, equiv. to 29.5 g/m3)
(10 CFR 20, App. B external link, 1991)

U.S. Occupational Safety and Health Administration (OSHA) regulations
Permissible Exposure Limit - Time Weighted Average:
soluble uranium: 0.05 mg/m3
insoluble uranium: 0.25 mg/m3 (!)
(29 CFR 1910 Subpart Z Table Z-1 external link, 1997)


ORAL INGESTION

Ingestion: Chemical Toxicity

(see also: Uranium Biokinetics Calculator)

The "minimal risk" level for intermediate-duration ingestion proposed by [ATSDR1999] is an oral uptake of 2 g of uranium per kg body weight per day. This is based on adverse effects observed by [Gilman1998b] with rabbits at uptakes of 0.05 mg per kg per day.

[Jacob1997] proposes a "tolerable" uptake of 0.7 g per kg per day. This value is based on adverse effects observed by [McDonald-Taylor1992] with kidneys of rabbits at resorption rates of 3.2 g U per kg and day.

The World Health Organization (WHO) has established a Tolerable Daily Intake (TDI) for uranium of 0.6 g/kg body weight per day [WHO1998, WHO2003]. This is based on adverse effects observed by [Gilman1998a] with kidneys of rats at uptakes of 60 g U per kg per day.

With [Zamora1998], for the first time, a study on the effects of chronic ingestion of uranium with drinking water on humans is available. It finds that kidney function is affected by uranium uptakes considered safe in the publications based on animal studies:
"A study was conducted of the chemical effects on the human kidney induced by the chronic ingestion of uranium in drinking water. Subjects were divided into two groups: The low-exposure group, whose drinking water was obtained from a municipal water system and contained < 1 g uranium/L, and the high-exposure group, whose drinking water was obtained from private drilled wells and contained uranium levels that varied from 2 to 781 g/L." These levels caused uranium intakes in the range of 0.004 to 9 g per kg body weight and day.
From the study's conclusions:
" The present investigation suggests that long-term ingestion of uranium by humans may produce interference with kidney function at the elevated levels of uranium found in some groundwater supplies."
"These observed effects may represent a manifestation of subclinical toxicity which will not necessarily lead to kidney failure or overt illness. It may, however, be the first step in a spectrum which with the chronic intake of elevated levels of uranium may lead to progressive or irreversible renal injury."

In a more recent larger study on humans [Kurttio2002], nephrotoxic effects of uranium in drinking water were found even for low concentrations - without a clear threshold. The authors conclude that "... our results suggest that the safe concentration of uranium in drinking water may be within the range of proposed guideline values of 2-30 g/L".

In another study with people who consumed drinking water with elevated uranium concentrations [Kurttio2005], the same authors found some indication that, in addition to kidneys, bone may be another target of chemical toxicity of uranium in humans.

Based on the higher uranium resorption in humans rather than experimental animals, [Konietzka2005] assumes a Tolerable Daily Intake of 0.2 g/kg body weight per day and recommends a safe concentration in drinking water of 10 g/L for lifetime exposure.

Ingestion of uranium
(based on chemical toxicity)
TDI
[g/(kg·d)]
ALI
[mg]
DDWC
[g/l]
[ATSDR1999]251.2102
[Jacob1997]0.717.936
[WHO1998]0.615.331
[Konietzka2005]0.25.110
TDI = Tolerable Daily Intake
ALI = Annual Limit on Intake based on 70 kg body weight
DDWC = Derived Drinking Water Concentration based on 500 l/a

For a discussion of the combined effects of ingested uranium, cyanide, fluoride, and/or nitrate, see [ATSDR2004].

 

Ingestion: Radiological Hazard

(see also Uranium Radiation Exposure · Uranium Radiation Individual Dose Calculator)

Ingestion of uranium for the public
(based on radiological hazard)
Dose factor
[mSv/g]
ALI
[mg]
DDWC
[g/l]
natural uranium with progeny31.731.563
pure natural uranium1.238131630
enriched natural uranium (3.5%)3.98251500
depleted natural uranium (0.2%)0.7114102820
recycled uranium3.89257515
enriched recycled uranium (3.5% equiv.) 16.760120
depleted recycled uranium (0.2%) 1.089231850
ALI = Annual Limit on Intake based on 1 mSv/a
DDWC = Derived Drinking Water Concentration based on 1 mSv/a, 500 l/a
Short-lived decay products included
Based on ICRP72 dose factors for adults (these don't make a distinction for solubility), initial enrichment to 3.5%, burnup of 39 GWd/tHM, storage time of 5 years after unload

 

Ingestion: Current Standards

WHO provisional guideline for drinking-water quality:
30 g of uranium per litre
This value is derived from epidemiological studies on populations exposed to high uranium concentrations and is based on the consumption of 2 litres of drinking water per day [WHO2011]. (see also Issues)
This value supersedes the earlier 2 g/l provisional guideline, which was based on animal studies and 10% allocation of the TDI to drinking water [WHO1998], the 9 g/l provisional guideline, which was based on 50% allocation of the TDI to drinking water [WHO2003], and the 15 g/l provisional guideline, which was based on 80% allocation of the TDI to drinking water [WHO2004]. (see also Issues)

Health Canada - Interim maximum acceptable concentration (IMAC) for uranium in drinking water:
20 g per litre
(see also Issues)

U.S. EPA - Rule on Radionuclides in Drinking Water:
Maximum contaminant level for naturally occuring uranium: 30 g per litre
EPA determines a safe level of 20 g/L, assuming that an adult with a body mass of 70 kg drinks 2 liters of water per day and that 80% of exposure to uranium is from water. For cost considerations, however, EPA established a standard of 30 g/L rather than 20 g/L. (65 FR 76707, 7 Dec 2000)
(see also Issues)

U.S. EPA - Preliminary Remediation Goal (PRG) for Superfund:
2.22 g per litre for U-238 in tap water
(see also Issues)

U.S. EPA - Groundwater Standards for Remedial Actions at Inactive Uranium Processing Sites:
Maximum Concentration Limit for combined uranium-234 and uranium-238: 30 pCi/l (1.11 Bq/l)
(Where secular equilibrium obtains, this criterion will be satisfied by a concentration of 0.044 milligrams per liter (0.044 mg/l = 44 g/l). For conditions of other than secular equilibrium, a corresponding value may be derived and applied, based on the measured site-specific ratio of the two isotopes of uranium.)
(40 CFR Part 192 external link (PDF-format); 60 FR 2854, 1995)

U.S. NRC Occupational Annual Limits on Intake (ALI's) for Oral Ingestion:
Unatural: 10 Ci (= 14.8 g)
(10 CFR 20, Appendix B external link, 1991)

California Public Health Goal for Uranium in Drinking Water (not a regulatory standard):
0.5 g per litre
(Public Health Goal for Uranium in Drinking Water external link, Office of Environmental Health Hazard Assessment, August 2001 )

German drinking water standard
10 g per litre
(Trinkwasserverordnung external link (PDF), view here)

German standard for bottled water designated suitable for preparation of baby food
2 g per litre
(Mineral- und Tafelwasser-Verordnung external link (PDF))

Australian Drinking Water Guidelines:
the concentration of uranium in drinking water should not exceed 0.02 mg/L (= 20 g/L)
(ADWG 1996, updated September 2001 external link)


ECO-TOXICITY

 

Eco-toxicity: Current Standards

Australian and New Zealand Guidelines for Fresh and Marine Water Quality:
A freshwater low reliability trigger value of 0.5 g/L was calculated for uranium using an AF (assessment factor) of 20 on limited chronic data. No marine data were available to calculate a guideline value. This should only be used as an indicative interim working level.
(Environment Australia: The National Water Quality Management Strategy (NWQMS) external link, Vol. 2, Ch. 8, 2000)


REFERENCES

> See also the following review draft reports:

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