Chapter VI.
Epidemiological and Population Studies III:
Uranium Miners & Mill Workers
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Summary:
Concern over the risk to health of uranium miners has been studied for over 60 years. In mining natural uranium (mostly U-238), the minor is exposed not only to uranium, but to many of the thirteen daughter isotopes, all radioactive, that appear in uranium’s decay chain. These include radium-226 and radon-222. In the process of breaking up rock deposits, radon, a gas, is released and inhaled.
Radon-222 is of particular concern because it is a gas and has a half-life of 3.8 days and the next four radioactive isotopes in the decay chain have half-lives measured in minutes. So when a radon atom decays, emitting one alpha particle, within minutes two additional alpha particles and two beta particles are also produced. This greatly amplifies the radiotoxicity of radon, and the product of these five decay steps is a radioactive isotope of lead, a heavy metal with a chemotoxicity vector as well. Thus when inhaling even minute quantities of radon, some of those radon atoms will statistically decay while deep in the miner’s lungs, changing from a gas (which would otherwise be exhaled) to a metal which becomes deposited within the lung tissue, and within minutes that deposited metal has undergone four more decay steps, further irradiating lung tissue, and ultimately becoming atoms of radioactive lead.
Uranium mill workers are also exposed to uranium, but in a much more concentrated form than uranium miners. Uranium ore contains many other minerals besides uranium, so the miner encounters uranium in a very dilute form. At the mill, this ore is treated chemically and pure uranium metal is extracted. The two main isotopes of uranium metal (as hexafluorides) are then partially separated at a uranium enrichment facility. This results in two uranium fractions. One, called enriched uranium, is enriched in the U-235 isotope, making it a useful fuel for nuclear power plants and for use in atomic weapons. The other fraction is essentially a left-over, waste product that is depleted in this isotope and is roughly 99.8% U-238. This is radioactive depleted uranium. Finally, there are the uranium fabrication facilities where DU munitions are manufactured.
Details:
In 1944, Lorenz (1) published a critical review of uranium miner’s lung cancer and concluded that radon by itself wasn’t the sole cause of the lung cancer. Twenty years later, Wagoner (2) reported on cancer mortality patterns in uranium miners and millers over a twelve year period and found no mortality increase among millers, but a nearly 50% mortality increase among miners, with a 10-fold increase in respiratory neoplasms. His study eliminated most suggested causes for this increase except exposure to airborne radiation. The following year, Wagoner (3) reported similar findings based on a much larger sample consisting of 3415 miners.
In 1992, Shields (8) reported increased birth defects among children of Navajo women living near uranium mine tailings and waste dumps near Shiprock, NM. Brugge (17) in 2002 published a review on the overall health affects of uranium mining among the Navajos.
In 1997,
In 1983, Allard (5)
studied skin exposure to radiation and provided a dose-related model that
compared well with actual measurements. West (4)
discovered a group of uranium mill workers who exhibited exceptionally long
retention of uranium in their lungs. In 1987, Dupree (6) reported statistically significant
higher mortality in 995 workers at a uranium processing plant in
Henderson (7) reported a study in workers’ exposure to DU in 1991 at an Oak Ridge facility that resulted in procedural changes to reduce exposure levels. In 1996, Loomis (11) presented a report on mortality rates at an Oak Ridge DU processing plant. McGeoghegan (15), (16) published two reports in 2000, the first reporting mortality studies of nearly 14,000 radiation workers from 1946 to 1995 at British Nuclear Fuel’s Springfield plant and the second on 3244 radiation workers from 1946 to 1995 at British Nuclear Fuel’s Capenhurst plant.
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1. Radioactivity and lung cancer: a critical review of lung cancer in the miners of Schneeberg and Joachimsthal, by E Lorenz, J. Nat. Cancer Inst. Vol. 5, 1944 (pp. 1-15).
Concludes that radon cannot be the sole cause of lung cancer in miners,
but may also include pneumoconiosis produced from dust in the mines, chronic
irritation caused by respiratory diseases, arsenic, radioactive substances and
perhaps hereditary susceptibility.
[Lorenz1944xxJNCIv5nxp1].
2. Cancer mortality patterns among U.S. uranium miners and millers, 1950 through 1962, by JK Wagoner, et al., J. Nat. Cancer Inst. Vol. 32, 1964 (pp. 787-801).
Report cancer mortality patterns for a group of US uranium miners and
millers, with comparison of age-race-cause specific mortality with that of the
general male population of the Colorado Plateau. Among white millers, there was
no difference in cause-specific mortality relative to general population. Among
white U miners with 5 or more years experience, there were 218 deaths compared
with 148.7 expected, with respiratory neoplasms about 10 fold higher (11 vs 1.1
expected). The excess neoplasms was not attributable to age, smoking,
nativity, heredity, urbanization, self-selection, diagnostic accuracy and prior
hard-rock mining or other ore constituents including silica dust. The
evidence implicates airborne radiation in the genesis of this increase in resp.
cancer among US U miners.
[Wagoner1964xxJNCIv32nxp787].
3. Radiation as the cause of lung cancer among uranium miners, by JK Wagoner, et al., New Engl. J. Med. Vol. 273, 1965 (pp. 181-188).
Studied 3415 underground, white U miners compared with general white
male population of the Colorado Plateau. Excess mortality attributed to
respiratory neoplasms (22 obs. v 5.7 expected). Conclude that airborne
radiation causes respiratory cancers. From dose-response relationship,
even when other factors, e.g., cigarette smoking are taken into
consideration. Conclude that pathology of U miners was unlike age-smoking-resident
matched control group, but was similar to that observed in factory workers
exposed to "radiomimetic" agent, mustard gas.
[Wagoner1965xxNEJMv273nxp181].
4. A comparison of uranium cases showing long chest burden retentions, by CM West, et al., Health Physics Vol. 12, 1966 (pp. 1545-1555).
This paper describes a small percentage of uranium industry workers who
have unusually slow clearance of uranium from lungs. The authors can't explain
the reason for this phenomenon.
[West1966xxHPv12nxp1545].
5. Beta dosimetry experiences at a depleted uranium metal fabrication facility, by DJ Allard, et al., Nuclear Metals, Inc., Concord, MA. Proc. Int. Beta Dosim. Symp., 1983 (pp. 509-531).
Extensive
evaluation via physical measurements and calculations is presented for 3
exposure scenarios, with emphasis on skin doses. The scenarios are compared
with actual experiences.
[Allard1983xxPIBDSp509].
6. Mortality among workers at a uranium processing facility, the Linde Air Products Company ceramics plant, 1943-1949, by EA Dupree,et al., Scandanavian J. of Work and Environmental Health Vol. 13, 1987 (pp. 100-107).
A mortality study of 995 white males employed at this U processing facility in western New York State compared with the white male population of the U.S. and also compared separately with white males in Erie and Niagara counties of New York State shows statistically increased standardized mortality ratios (SMR) for all causes (118), laryngeal cancer (447), all circulatory diseases (118), arteriosclerotic heart disease (119), all respiratory diseases (152) and pneumonia (217) [note, 100 would be the SMR if there is no difference in mortality between exposed workers and controls]. There was also a statistically signif increase in number of death above expected for laryngeal cancer (5) and pneumonia (17). [Note: although all investigators were affiliated with U.S. institutions, this work was published in a Scandanavian journal].
[Dupree1987xxSJWEHv13nxp100].
7. Evaluation of radiation exposure in metal preparation depleted uranium process areas, by MD Henderson, Oak Ridge Y-12 Plant, Oak Ridge, TN. Gov. Rep. Announce. Index (US) Vol. 16(8), 1991 (abstr. no. 19829).
Research
in DU operations at the Y-12 plant to assess the magnitude of nonuniform and
extremity exposures in order to reduce such exposures and design optimum
dosimetry protocol to assure compliance. As a result of the research,
operational changes were made that lowered the dose equiv. to the employees.
[Henderson1991xxGRAIv16n8p19829].
8. Navajo birth outcomes in the Shiprock uranium mining area, by LM Shields, et al., Health Physics Vol. 63, 1992 (pp. 542-551).
Statistically significant association between U operations and
unfavorable birth outcome was identified with the mother living near tailing or
mine dumps. Indicates birth defects increased significantly when either parent
worked in Shiprock electronics assembly plant. Authors indicate weak
association between birth outcomes and radiation exposure. No discussion
of possible chemical toxicity from living near mine tailings or mine dumps.
[Shields1992xxHPv63nxp542].
9. Diurnal urinary volume and uranium output in uranium workers and unexposed controls, by DW Madley, et al., Health Physics Vol. 67, 1994 (pp. 122-130).
[Madley1994xxHPv67nxp122].
10. Uranium dust exposure and lung cancer risk in four uranium processing operations, by EA Dupree, et al., Epidemiology Vol. 6, 1995 (pp. 370-375).
[Dupree1995xxEv6nxp370].
11. Mortality of workers at a nuclear materials production plant at Oak Ridge, Tennessee, 1947-1990, by DP Loomis, et al., American Journal of Industrial Medicine Vol. 29, 1996 (pp. 131-141).
[Loomis1996xxAJIMv29nxp131].
12. Unexpected rates of chromosomal instabilities and alterations of hormone levels in Namibian uranium miners, by R Zaire, et al., Radiation Res Vol. 147, 1997 (pp. 579-584).
Shows a much higher prevalence of cancer among open pit U miners in
Namibia rel to general population. Measured U excretion in urine,
neutrophil counts and serum levels of FSH, LH and testosterone, and chromosomal
aberrations in whole blood cells. Compared 75 non-smoking, HIV-negative
miners with 31 individuals with no occupational mining history. There was 6
fold increase in U excretion among miners, with reduction in testosterone
levels and neutrophil count. Also a 3 fold increase in chromosomal
aberrations in miners rel to controls. Cells with multiple aberrations
among miners, i.e., rogue cells, found for the first time among U miners.
Previously only found among acute radiation dose victims in Hiroshima and
Chernobyl.
[Zaire1997xxRRv147nxp579].
13. German uranium miner study - historica background and available histopathological material, by H Wesch, et al., Radiation Research Vol. 152, 1999 (pp. S48-S51).
Gives historical bkgd on the Erzgebirge area of Saxony in Germany where
many metal ores were mined. About 400,000 workers produced a total of
220,000 tons U during 1946-1990. Documents contain protocols for 28,975 autopsy
cases and about 400,000 slides collected from 1957-92, about 66,000 tissue
blocks, and 238 whole lungs. From autopsy cases, about 17,466 could be
identified as workers of uranium mining. Shows significantly higher
incidence of lung cancer in miners rel to area residents. No significant
difference for other solid cancers and leukemias.
[Wesch1999xxRRv152nxpS48].
14. Radon exposure and lung cancer risk: Czech cohort study, by L Tomášek, et al., Radiation Res Vol. 152, 1999 (pp. S59-S63).
Analyzed 2 main factors for radiogenic risk, time since exposure and
age at exposure. Find that increasing age at initial exposure to radiation in
mines results in less lung disease (lower risk).
[Tomasek1999xxRRv152nxpS59].
15. The mortality and cancer morbidity experience of workers at the Springfields uranium production facility, 1946-95, by D. McGeoghegan, et al., Westlakes Scientific Consulting Ltd, Cumbria, UK. david.mcgeoghegan@westlakes.ac.uk. J Radiol Prot. Vol. 20(2), June 2000 (pp. 111-37).
The results presented here are from the follow-up of the cohort of
workers ever employed at the Springfields site of British Nuclear Fuels plc
(BNFL) between 1946 and 1995. The main activity of the site is uranium fuel
fabrication and uranium hexafluoride production. The study cohort consists of
19454 current and former employees, 13 960 of which were classified as
radiation workers, and contains 479146 person-years of follow-up. The mean
follow-up period is 24.6 years. To the end of 1995 there have been 4832 deaths
recorded for this cohort, 3476 of which were amongst radiation workers and 1356
were amongst non-radiation workers. The standardised mortality ratios (SMRs)
for all causes were 84 and 98 for radiation workers and non-radiation workers
respectively. For all cancers the SMRs were 86 and 96 respectively. For cancer
morbidity the standardised registration ratios (SRRs) for all cancers were 81
and 81 respectively. Significant associations were noted for both mortality and
morbidity due to Hodgkin's disease and cumulative external dose. A strong
association was also noted for morbidity, but not mortality, due to
non-Hodgkin's lymphoma. These associations, however, are unlikely to be causal.
The excess relative risk estimates for cancer other than leukaemia and for
leukaemia excluding chronic lymphatic leukaemia are consistent with other
occupationally exposed cohorts and estimates from the high-dose studies.
[McGeoghegan200006JRPv20n2p111].
(PMID: 10877261 [PubMed - indexed for MEDLINE]).
16. The mortality
and cancer morbidity experience of workers at the Capenhurst uranium enrichment
facility 1946-95, by D McGeoghegan, et al., Westlakes Scientific
Consulting Ltd, Cumbria, UK. david.mcgeoghegan@westlakes.ac.uk. J Radiol Prot. Vol. 20(4), Dec. 2000
(pp. 381-401).
The results presented here contain the follow-up of the cohort of
workers ever employed at the Capenhurst site of British Nuclear Fuels plc or
its predecessors between 1946 and 1995. The main activity of the plant is
isotopic, 235U, enrichment of uranium. The study cohort consists of 12,540
employees and contains 334,473 person-years of follow up. This is a relatively
mature cohort, with a mean follow-up period of 26.7 years, that has been
exposed to low levels of radiation. The collective external radiation dose
received by the 3244 radiation workers was 31.95 person-sieverts, with mean
cumulative dose 9.85 mSv. To the end of 1995 there have been 3841 deaths
recorded for this cohort, 585 of which were amongst radiation workers. The
standardised mortality ratios (SMRs) for all causes were significantly low, 83
and 91 respectively, for radiation and non-radiation workers, indicating the
usual 'healthy worker' effect. The cancer mortality was less than that
expected, though not significantly so, with SMRs for all cancers of 88 and 97,
for radiation and non-radiation workers respectively. The cancer registration
rates were significantly low, with standardised registration ratios (SRRs) for
all cancers of 82 and 88, for radiation and non-radiation workers respectively.
An association between bladder cancer registrations and cumulative external
radiation exposure was noted when the cumulative external dose was lagged by 20
years.
[McGeoghegan200012JRPv20n4p381]. (PMID: 11140711 [PubMed - indexed for
MEDLINE]).
17. The history of uranium mining and the Navajo people, by D Brugge, et al., Amer. J. Public Health Vol. 92, 2002 (pp. 1410-1419).
Gives a good review of health risks from uranium mining and describes
health effects of U mining on Navajo people.
[Brugge2002xxAJPHv92nxp1410].
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