BMJ: Depl Ur w/o Incr CA risk

Gary Greenberg Gary.Greenberg at Duke.edu
Sun Jan 21 21:31:28 EST 2001


BMJ 2001;322:123-124 ( 20 January )

This author is (once) an OEM-L subscriber. 

There are already 5 rebuttals at the BMH website, probably more by the
time you read this message.

- Gary Greenberg

http://bmj.com/cgi/content/full/322/7279/123

Editorials

Depleted uranium and public health 

Fifty years' study of occupational exposure provides little evidence of
cancer

Depleted uranium, used in anti-tank weapons, provides a common thread
that links concerns about leukaemia and other health effects in
peacekeeping forces returned from the Balkans and worries about the
environmental impact of debris from weapons in this war-weary segment of
Europe. Unlike many agents that seem suddenly to prompt health
concerns,1 however, we know quite a lot about the health effects of
depleted uranium. 

Depleted uranium is derived from natural uranium mined from the earth's
crust. Uranium is composed of three radioactive isotopes, U238, U235,
and U234, which decay to other radioactive elements and ultimately to
stable non-radioactive isotopes of lead.2-4 Uranium isotopes emit
particles during decay, which possess high energy but are poorly
penetrating. Thus, uranium poses primarily an internal radiation hazard
to tissue in close proximity. 

Uranium is not very radioactive, owing to its isotopes' relatively long
half lives (105-109 years). These compare with radon, a prominent member
of the daughter progeny of the uranium decay cascade, which possesses a
half life of 3.8 days and a radiological activity 10 000 times
greater.2-4 Depleted uranium possesses only 60% of the radioactivity of
natural uranium, having been "depleted" of much of its most highly
radioactive U234 and U235 isotopes. 

Depleted uranium is also a heavy metal, like lead or arsenic, with
toxicity a function of route of exposure, particle solubility, contact
time, and rate of elimination. 2 5 Some of these chemical properties,
high density, and tensile strength, made depleted uranium an attractive
material for use in weapons. 

Though its first combat use was in the Gulf war of 1991, what we know
about depleted uranium's effects on human health did not begin there. A
sizeable store of knowledge has been gathered over the past 50 years in
studies of uranium miners, millers, and other processors worldwide. Two
recent reviews of uranium exposure and cancer risk address overall
cancer mortality and also lung, lymphoid, and bone cancer, those most
likely to be related to internal uranium exposure. The first, by the US
Centers for Disease Control and Prevention/Agency for Toxic Substances
and Disease Registry, concluded that "no significant differences in
cancer [of the lungs] was found between workers who are occupationally
exposed to uranium and control populations."2 A review of over 11
studies in uranium miners attributed an observed increase in lung cancer
to radon and its progeny and not to uranium. "There is no unequivocal
evidence that inhalation, oral or dermal exposure induces cancers in
humans." 6 7 Confounding exposures, often to more radioactive materials,
were cited. Long term animal studies with both natural and enriched
uranium had negative (nine studies) or equivocal (three studies) results
for carcinogenicity.2 

A second recent review of health effects of uranium authored by the US
National Academy of Sciences Institutes of Medicine evaluated existing
epidemiological studies more rigorously and gave relative weight to the
studies' strengths and weaknesses in their assessments. Regarding the
lung cancer risk, "the Committee concludes that there is
limited/suggestive evidence of no association between exposure to
uranium and lung cancer at cumulative internal dose levels lower than
200 mSv or 25 cGy."3 This roughly corresponds to the burden occurring
from a full year's exposure to a dusty indoor uranium workshop
environment.8 

For both lymphatic and bone cancer the committee concluded that there
was inadequate or insufficient evidence to determine whether an
association does or does not exist with uranium exposure. Most of the
studies cited did not show an excess, but there was also inadequate
evidence to dismiss the possibility.2 

Other evidence comes from a small surveillance study of (then 30 and now
60) US Gulf war veterans who were victims of friendly fire with depleted
uranium. About 15 of these veterans possess retained metal fragments of
depleted uranium in soft tissue and are excreting raised uranium
concentrations in their urine. None of these veterans has leukaemia,
bone cancer, or lung cancer.9 Thus, the argument for uranium being the
cause of leukaemia in peacekeeping forces is thin, notwithstanding the
short latencies implied, even by the standards of haematological
malignancies. 

The questions raised as to the connection between cancer and depleted
uranium are understandable, however. Having lived through the cold war
and beyond, we have all been sensitised to the fear of nuclear exchange,
and justifiably so. In addition, many of us, including those in the
medical community, have little familiarity with the dose-response curves
of health effects caused by radiation exposure. Experts in risk
communication tell us that lack of familiarity with a hazard heightens
the public perception of risk.10 In this context pronouncements about
background rates of disease observable in populations being
statistically expected fail. 

Certainly, attribution of disease to "expected" or background levels
should be a diagnosis of exclusion, and vigilance is warranted. However,
the information we have on cancer risk is not simply a theoretical
calculation, as some critics have suggested. Rather, there is both a
context in which to evaluate the evidence and a hierarchy of relative
weight to assign to types of evidence available for human risk
assessment. Heading that list are epidemiological studies of human
health effects, which do exist in this case. 3 6 7 

Regarding non-cancer health effects, and references made to Gulf war
illness, there is still no single candidate hazard which serves as its
unifying explanation, depleted uranium included. Indeed, Gulf war
illnesses is a more appropriate title for the groupings of symptoms made
by returning US veterans and recalled in the "Balkan syndrome" of
affected peacekeepers. The report into Gulf war syndrome of the
presidential advisory panel in 1996 stated that there was no evidence of
a connection between depleted uranium and Gulf war illnesses.11 

Some final prevention points still must be made. Strident efforts at
hazard communication training are in order for all serving in affected
areas in any rolemilitary or humanitarian. Similar efforts must be
undertaken for the affected local populations. Low radiation risk issues
aside, children should not be playing with depleted uranium penetrators
and environmental monitoring (of drinking water, for example) is
appropriate in highly affected areasat the very least for assurance
purposes. 

It is uncommon to have the benefit of 50 years of human epidemiological
evidence in managing any of the environmental or occupational public
health problems facing the global medical community today. We should use
that evidence in informing the public about their potential health risk
and, more positively, in guiding our prevention activities. 

Melissa A McDiarmid, professor of medicine. 

University of Maryland School of Medicine, 655 West Baltimore Street,
Baltimore, MD 21201-1559, USA



1. Beaumont P. British safety claims wilt as uranium panic grips NATO.
Observer 2001; 7 Jan. 

2. Agency for Toxic Substances and Disease Registry. Toxicological
profile for uranium. Washington, DC: US Public Health Service, 1999. 

3. Fulco CE, Liverman CT, Sox HC, eds. Gulf war and health. , Vol 1
Washington, DC: National Academy Press, 2000. 

4. McDiarmid MA, Squibb KS. Uranium and thorium. In: Bingham E, Cohrssen
B, Powell CH, eds. Patty's toxicology. New York: John Wiley,
2001:381-422. 

5. Eckerman KF. Limiting values of radionuclide intake and air
concentration and dose conversion factors for inhalation submersion and
ingestion. Washington, DC: Environmental Protection Agency, 1988. 

6. Kathren RL, Moore RH. Acute accidental inhalation of uranium: a 38
year follow-up. Health Phys 1986; 51: 609-619. 

7. Kathren RL, McInroy JF, Moore RH, Dietert SE. Uranium in the tissues
of an occupationally-exposed individual. Heath Phys 1989; 57: 17-21. 

8. Donoghue JK, Dyson ED, Hislop JS, Leach AM, Spoor NL. Human exposure
to natural uranium. Br J Ind Med 1972; 29: 81-89. 

9. McDiarmid MA, Keogh JP, Hooper FJ, Squibb KS, Kane R, et al. Health
effects of depleted uranium on exposed Gulf war veterans. Environ Res
2000; 82:168-180. 

10. Covello VT. Risk comparisons and risk communication: issues and
problems in comparing health and environmental risks. In: Kasperson RE,
Stallen PJM, eds. Risks to the public. Dordrecht: Kluwer, 1991:79-124. 

11. Presidential Advisory Committee on Gulf War Veterans' Illnesses.
Final report. Washington, DC: US Government Printing Office, 1996. 


-- 
Gary N. Greenberg, MD MPH    Sysop / Moderator Occ-Env-Med-L MailList
gary.greenberg at duke.edu     Duke Occupat, Environ, Int & Fam Medicine
OEM-L Maillist Website:                      http://occhealthnews.com


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