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Uranium presents both chemical and radiological hazards. Risk assessments must address both types of hazards. There are some problems with the comparison of these hazards. They are, 
insufficient data for chemical toxicitystandards for radiation doses and chemical toxicity not comparableresidual risk from chemical toxicity regarded acceptable usually is orders of magnitude lower than from radiation  
The inhalation of soluble forms of uranium in air produced the lowest observable adverse effect. From this figure, a "minimal risk" inhalation level for humans of 0.4 µg/m3 is derived.The inhalation of insoluble forms of uranium in air produced no observable adverse effect. From this figure, a "minimal risk" inhalation level for humans of 8 µg/m3 is derived. Inhalation of uranium for workers(based on radiological hazard)
|  |  | insoluble |  | soluble | 
|---|
 |  |  | Dose fact. [mSv/mg] | ALI [mg] | DAC [µg/m3] |  | Dose fact. [mSv/mg] | ALI [mg] | DAC [µg/m3] |  | natural uranium with progeny |  | 0.42 | 47.6 | 16.5 |  | 0.34 | 59 | 21 |  | pure natural uranium |  | 0.2 | 100 | 34.7 |  | 0.013 | 1520 | 530 |  | enriched natural uranium (3.5%) |  | 0.676 | 29.6 | 10.3 |  | 0.044 | 450 | 159 |  | depleted natural uranium (0.2%) |  | 0.110 | 183 | 63.4 |  | 0.0073 | 2740 | 950 |  | recycled uranium |  | 0.65 | 31 | 10.8 | 
 | 0.041 | 486 | 169 |  | enriched recycled uranium (3.5% equiv.) |  | 2.80 | 7.15 | 2.5 |  | 0.176 | 114 | 39 |  | depleted recycled uranium (0.2%) |  | 0.173 | 116 | 40 |  | 0.011 | 1750 | 610 |  
ALI = Annual Limit on Intake based on 20 mSv/aDAC = Derived Air Concentration based on 20 mSv/a, breathing rate of 1.6 m3/h, working time of 1800 h/aShort-lived decay products includedBased on ICRP68 dose factors for 1 µm 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 [µg/m3] |  | Dose factor [mSv/mg] | ALI [mg] | DAC [µg/m3] |  | natural uranium with progeny |  | 0.70 | 1.42 | 0.18 |  | 1.6 | 0.63 | 0.08 |  | pure natural uranium | 
 | 0.22 | 4.5 | 0.58 |  | 0.013 | 74.5 | 9.4 |  | enriched natural uranium (3.5%) |  | 0.75 | 1.34 | 0.17 |  | 0.045 | 22.3 | 2.8 |  | depleted natural uranium (0.2%) |  | 0.12 | 8.3 | 1.05 |  | 0.0075 | 134 | 17 |  | recycled uranium |  | 0.71 | 1.41 | 0.18 |  | 0.081 | 12.3 | 1.6 |  | enriched recycled uranium (3.5% equiv.) |  | 3.1 | 0.324 | 0.041 |  | 0.4 | 2.49 | 0.32 |  | depleted recycled uranium (0.2%) |  | 0.19 | 5.27 | 0.67 |  | 0.012 | 85.1 | 11 |  
Current Standards of Inhalation:ALI = Annual Limit on Intake based on 1 mSv/aDAC = Derived Air Concentration based on 1 mSv/a, breathing rate of 0.9 m3/h, continuous exposureShort-lived decay products includedBased on ICRP72 dose factors for adults, initial enrichment to 3.5%, burnup of 39 GWd/tHM, storage time of 5 years after unload. 
 
U.S. NRC Occupational Annual Limits on Intake (ALI's) for InhalationUnatural (soluble): 1 µCi (= 37000 Bq, equiv. to 1.5 g)Unatural (insoluble): 0.05 µCi (= 1850 Bq, equiv. to 74 mg) 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 µCi 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 µCi per ml (= 0.74 Bq/m3, equiv. to 29.5 µg/m3)0.2 mg uranium/m3 of air (for soluble uranium)0.045 mg natural uranium/m3 of air, if its decay products are present in equilibrium, as in ore dust prior to chemical separation of the uranium from the oreU.S. Occupational Safety and Health Administration (OSHA) regulationsPermissible Exposure Limit - Time Weighted Average: soluble uranium: 0.05 mg/m3insoluble uranium: 0.25 mg/m3 (!)  | 
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