What concentration?
[link|http://www.who.int/ionizing_radiation/pub_meet/en/Report_WHO_depleted_uranium_Eng.pdf|WHO Report] (.pdf) on DU in Kosovo, p.7:
In addition to U235, U234 and U238, the mission was confronted with questions on the presence of plutonium or other radioactive chemicals in the munitions. KFOR informed the mission that it did not exclude the possibility that traces of plutonium could be present in depleted uranium. This is because the enrichment of some natural uranium, from which depleted uranium is a waste by-product, occurred at a production facility that had been used previously for the processing of spent fuel rods from nuclear reactors. The production facility had not been completely cleaned and cross-contamination could have been possible.
According to NATO (referring to a statement placed on the Internet on 18 January 2001) it "has long been established that there may be trace elements of U236 and plutonium in depleted uranium." The presence of plutonium was addressed in a report of the US Department of Defense (2000), which also contains comments on the possible presence of trace elements of other materials in depleted uranium. The report concludes that depleted uranium \ufffdmay contain trace levels (a few parts per billion) of transuranics (neptunium, plutonium and americium). Tests on samples of DU showed that transuranic contamination added 0.8% to the radiation dose from DU."
With regard to the presence of U236 in Kosovo, UNEP has mentioned (UNEP press release,16 January 2001) that "along with the more commonly expected isotopes, one of the laboratories has reported finding 0.0028% of U236." The UNEP press release says the \ufffdcontent of U236 in depleted uranium is so small that the radio-toxicity is not changed compared to DU without U236." Consequently, it has been concluded that detection of U236 indicates part of the depleted uranium originates from reprocessed uranium.
It would appear that the presence of the U236 isotope led to the scientific deduction that plutonium may also be present. At a meeting immediately prior to the commencement of the WHO mission in Kosovo, UNEP informed the team that the laboratory had not reported detecting any plutonium in their samples. After the mission returned from Kosovo, UNEP announced (press release, 16 February 2001) that traces of Pu239 and Pu240 were found in four penetrators. UNEP advised that the content of the plutonium found is very low and does not have any significant impact on overall radioactivity.
Oh, and there was plutonium in the soil, worldwide, before DU started being used. E.g. [link|http://www.davistownmuseum.org/cbm/RadxPlutonium.html|this] article from Nature from 1973.
I don't think Pu in DU is a significant (i.e. measurable) risk. YMMV.
Cheers,
Scott.
