Uranio empobrecido

7. What is known about uranium exposures?

• 7.1 Natural exposure is a relevant comparison
• 7.2 What happens to the DU in munitions?

7.1 Natural exposure is a relevant comparison

Uranium is among the 20 most abundant elements on earth and is present in a variety of minerals. Its relative abundance is similar to that of silver or gold and U is more abundant than tin, mercury and lead. The concentration of U in soil ranges from 0.05 to 10 mg/kg (UNSCEAR, 2000b, a). However, soil concentrations may reach up to 200 mg/kg in certain areas.
Natural U is present in concentrations from 0.01 μg/L to more then 1,500 μg/L in surface and ground water. Table 5 shows typical concentration ranges of natural U in different environmental matrices.

Matrix	Typical concentration range of natural U	References
Soil	0.3 – 11.7 mg/kg	(UNSCEAR, 1993)
Air	2.5 x 10-8 – 10-7 mg/m3	(NCRP, 1999)
Surface water	3 x 10-2 – 8.0 µg/L	(WHO, 2001)
Groundwater	3 x 10-3 – 2.0 µg /L	(Orloff et al., 2004; WHO, 2001)
River water	0.2 – 0.6 µg/L	(Palmer and Edmond, 1993)
Sea water	3.3 µg/L	(ATSDR, 1999)

Table 5. Uranium concentrations in environmental matrices.

Due to its widespread presence, natural U occurs also in human food and drinking water. In groundwater and in private wells used for drinking water abstraction, concentrations of U are highly variable, ranging from <0.1 up to 40 μg/L (UNSCEAR, 1993). Extremely high values (up to 12,400 μg/L) have been measured in groundwater in Finland and in other Nordic countries, linked to high concentrations of U in geologic formations (Karpas et al., 2005; Kurttio et al., 2005; NCRP, 1999).

The average daily intake of natural U in humans is estimated as 1 to 2 μg from food and 1.5 μg from drinking water (ATSDR, 1999; UBA, 2005; UNEP, 2001); ingestion with food represents the major source in areas with low concentrations of U in drinking water (Fisenne et al., 1987; Priest, 2001).

7.2 What happens to the DU in munitions?

A combination of DU fragments and aerosols is produced during the impact of a DU penetrator on an armoured target. The DU dust (aerosol) formed spontaneously ignites due to the pyrophoric properties of U. The proportion of DU present in a penetrator converted into an aerosol on impact on a hard target such as a tank usually is in the range of 10–30%, with a maximum of 70% (Capstone-Report, 2005; Harley et al., 1999). The aerosol is mainly deposited inside the tank hit. For particle characteristics in such aerosols, see table 6.

Table 6. Approximate aerodynamic equivalent particle size distribution of DU particles formed after impact of a DU penetrator (from a 105 mm round) in armour plates

Particle Aerodynamic Equivalent Diameter (micrometers)	Mass Percent in Size Range
<0.18	31
0.18 – 0.56	14
1.8-5.6	13
5.6-18.0	11
18-56	7
>56	9

DU ammunition easily penetrates even thick armour plates and DU particles formed in the impact are released both to the inside of the armoured vehicle and to its surroundings. The DU particles formed are rapidly deposited and are not easily re- suspended due to the high density of U-containing particles. The studies conducted so far have not identified the presence of DU nanoparticles (Cheng et al., 2009; Parkhurst and Guilmette, 2009b, a). Since a larger part of the particles are deposited to the limited space inside an armoured vehicle, the exposure to DU through inhalation of DU containing dust inside abandoned vehicles hit by DU ammunition is generally much higher than that to DU from the environment (Mitchel and Sunder, 2004).

After hit of a DU penetrator on a tank, a part of the DU released will be deposited on the soil surface as pieces of DU metal, fine fragments and as dust of DU oxides. The characteristics of DU particles in soil/sand from Kosovo and Kuwait contaminated during the Balkan conflict and the Gulf wars vary significantly depending on the release scenarios. Re-suspension of DU dust may occur, but DU exposure from this pathway is very low for the general population due to the low concentrations of DU involved and the high density of U-containing particles reducing potential for re-suspension (UNEP, 2003).

DU penetrators impacting in soft soil (e.g. sand or clay) may remain intact and penetrate for 50 cm to several meters into the soil. In soil, they are slowly oxidized and dissolved. The dissolution rate of DU fragments depends on soil conditions. It is estimated that DU penetrators deposited near the surface completely dissolve within 35 years (McLaughlin, 2005; UNEP, 2003). Once deposited, DU is transported from the penetrator surface into the surrounding environment through dissolution of U(VI) (Erikson et al., 1990), with subsequent interactions resulting in the formation of secondary U species in the sediment (Chazel et al., 1998; Danesi et al., 2003a; Handley-Sidhu et al., 2009a; Handley-Sidhu et al., 2009b; Lind et al., 2009; Mitchel and Sunder, 2004; Oughton and Kashparov, 2009). A review of the environmental chemistry of U is presented in Annex 2. In general, higher concentrations of DU are present in soil near deposited penetrators, but the DU will be slowly removed from the site of deposition and will add to the natural U background. Due to the comparatively high background, the small amounts of DU added are not expected to increase the total concentrations of U in larger areas.

Specific concerns have been raised regarding human and environmental exposure to DU in areas where DU ammunition has been used. A detailed assessment of such potential exposures has been performed in Kosovo (Danesi et al., 2003b; Salbu et al., 2003; UNEP, 2001), Serbia- Montenegro (McLaughlin et al., 2003), Bosnia and Herzegovina (UNEP, 2003), Kuwait (IAEA, 2003; Salbu et al., 2005) and Iraq (Gerdes et al., 2004; IAEA, 2009). Residues of DU ammunitions have also been detected in military proving grounds (Sowder et al., 1999). Concentrations of DU in areas with intensive use of DU ammunition in Kosovo varied from a few mg DU/kg soil at depths of 40 cm up to about 18,000 mg DU/kg soil close to the surface. Some small spots contained hundreds of thousands of DU particles in a few milligrams of soil. However, despite the reported huge variability in DU concentrations, in most (80%) of the soil (core) samples, 238U was lower than 100 Bq per kg soil (the lowest was 8.8 Bq per kg soil), even in locations with intensive use of DU ammunitions (Papastefanou, 2002) (table 7). Other studies did not observe the presence of DU in soil samples collected randomly all over Kosovo (Uyttenhove et al., 2002).

Table 7. Concentration of U in soil and water (minimum and maximum) from three UNEP and two IAEA surveys. N = number of investigated sites (IAEA, 2003, 2009; UNEP, 2001, 2002, 2003)

Kosovo

Bosnia Herzegovina

Serbia Montenegro

Kuwait

Iraq

min

max

n

min

max

n

min

max

n

min

max

n

min

max

n

U + DU in Water (mg/L)

2.4 E-5

1.6 E-3

11

nd

nd

10

1.4 E-5

3.6 E-3

5

1.3 E-3

9.5 E-3

3

nd

3.35 E-3

23

U + DU in soil (g/kg)

0.003

7.60

9*

0.0002

0.0045

13**

0.002

0.007

5

0.4

1.7

7

-

2.6

23

Very low concentrations of DU were detected in plant material (bark, lichens, mosses). DU was mostly absent in water samples (Di Lella et al., 2004; Popovic et al., 2008), with very low concentrations of DU detected only in a few samples. The detection limit in water was 0.22 mBq/L for U-238 and U-234 and 0.022 mBq/L for U235 and U-236 (Jia et al., 2006; Jia et al., 2004). In general, the concentrations of DU detected in environmental samples in areas with intensive use of DU ammunition, except for very localized hotspots, was much lower than DU concentrations predicted by scenarios based on assumed releases of DU from military activities and conservative assumptions. It should be noted that even soil concentrations of DU estimated with a conservative scenario (6 mg DU/kg) are within the typical concentration range of natural U in soil (UNEP/UNCHS, 1999).

Measurement of U excreted in urine is a sensitive method for directly determining human exposure to U (UBA, 2005). Urinary excretion of U is the most appropriate indicator of past exposures to U, whereas faecal excretion can only indicate a very recent exposure to U due to the rapid elimination of U with faeces. Urinary DU concentrations may therefore also be used to assess human exposures to DU. However, uncertainties in the relationship between urinary U concentrations and past exposures are considerable since many assumptions concerning aerosol size, U solubility, and transfer rates between different body compartments must be made. When determining DU exposure by measurement of total U in urine, natural U intake from food and water is an important confounder (Werner et al., 1997). To assess the contribution of DU to the total U intake, it is therefore necessary to measure the isotopic ratio U-235 /U-238 by mass spectrometry or apply specific radiological techniques (Ejnik et al., 2005; Jia et al., 2004; Schramel, 2002; Tresl et al., 2004; Werner et al., 1997). Urine biomonitoring using these techniques can then be applied to specifically assess human DU exposure both by oral intake and by inhalation to confirm the conclusions from the indirect exposure assessments using environmental concentrations of DU and exposure scenarios (Valdes, 2009).

Regarding human exposure to DU, most of the biomonitoring studies failed to detect the presence of DU in urine samples of both soldiers serving in the conflicts and in residents in areas where DU ammunition was used (Table 8).

			Urinary concentration [ng/L]		235U/238U
Region	Sample type	Year	Range	Mean	As determined by ICPMS	Reference
Germany, n = 1500	24 h urine	2001 -2003	6.5 – 21	11.5	na	(UBA, 2005)
USA, n = 2464	Spot urine		46 (95th)	8 (GM)	na	(NHANES, 2005)
Jordan, n = 60 given in microg/day			18 – 2647	135 (GM)	na	(Al-Jundi et al., 2004)
Italy, n = 38	Spot urine	1999	3 – 26	10	na	(Galletti et al., 2003)
Finland, n = 205			2647 (95th)	64 (GM)	na	(Karpas et al., 2005)
German peacekeepers in Kosovo (n = 1228) samples analyzed within one year after return to Germany	24 h urine	1999 – 2006	0.6 – 171.5	12.82 (GM)	0.007253 + 0.3 %	(Oeh et al., 2007a)
Kosovo residents living in area where DU was used, after conflict	24 h urine	2001-2002	2.92 – 266.81	Not given	0.007253 + 0.3 %	(Oeh et al., 2007b)
UK, n = 199, combat veterans from Gulf war	Spot urine		3.9 – 4.6 (95th)	3.9	0.0072358	(Bland et al., 2007)
UK, n = 24, involved in clean-up in Iraq	Spot urine		2.0 – 3.6 (95% CI)	2.7	0.0072463	(Bland et al., 2007)
UK, n = 22, medics deployed to Iraq	Spot urine		2.0 – 3.6 (95% CI)	4.2	0.0072411	(Bland et al., 2007)
UK, non-combat n = 96	Spot urine		3.4 – 4.6 (95% CI)	3.9	0.0072359	(Bland et al., 2007)
US, 1 700 US soldiers from Gulf war and after gulf war	24 h urine	2003 - 2008		10 + 1 based on a creatinine concentration of 0.9 g/L	Three samples gave isotopic signatures indicative of traces of DU	(Dorsey et al., 2009)
US, workers in plant producing DU, n = 5	Spot urine			79.6	0.00461	(Parrish et al., 2008)
US, residents near plant producing DU, n = 17	Spot urine			2.64	0.00720	(Parrish et al., 2008)
US, 28 soldiers involved in friendly fire incidents with DU-ammunition; 12 reference soldiers from 1992 Gulf war	Spot urine	1997-1999	16 – 180 in those exposed to DU in friendly fire; 11 – 79 in reference group	59 in those exposed to DU in friendly fire incidents, 15 in reference group, (medians)	Change of isotopic signature in samples from 10 of the 28 soldiers exposed to DU, and in one in reference group	(Gwiazda et al., 2004)
France, 154 soldiers serving in Gulf region and 54 in the Balkans	Spot urine	1999-2003			Not detected, detection limit < 10 mBq/L per isotope	(Cazoulat et al., 2008)

Due to the long half-life of U, spot urine samples could be used for exposure assessment.
The biomonitoring results show that the incorporation of DU in soldiers serving in Kosovo and Iraq and in residents of Kosovo is very low (Table 8). The ICP-MS method is very sensitive and can easily detect exposures to DU based on the ratio of the U isotopes 235U/238U. Even the presence of a low percentage of DU in the total U excretion can be detected. The sensitivity of the method is demonstrated by a significantly changed isotope ratio in workers in a DU-plant and also in some residents living in the vicinity of the plant (Parrish et al., 2008) either exposed through releases of DU from the plant into drinking water or in the air (Table 8) despite total U concentrations in urine in the normal range. The detection of DU in soldiers in friendly fire incidents during the 1st Gulf war, but without retained DU-shrapnel, also indicates that inhaled DU-aerosols formed after impact are taken up from the lung and that biomonitoring is appropriate to confirm past inhalation exposures to DU-aerosols.
In summary, general contamination with DU, even in areas of heavy fighting with documented intensive use of DU ammunition, is low or could not be demonstrated. This confirms the reliability of the exposure scenarios and the assessment based on environmental monitoring.