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“The Quantitative analysis of Uranium Isotopes in the population of Port Hope, Ontario Canada” authored by Durakovic, Gerdes, and Zimmerman Prepared for the Municipality of Port Hope Program in Occupational Health and Environmental Medicine The Departments of Family Medicine and Public Health Sciences Executive Summary
This review of the document entitled “The Quantitative analysis of Uranium Isotopes in thepopulation of Port Hope, Ontario Canada” authored by Durakovic, Gerdes, and Zimmerman(DGZ) was prepared at the request of the Municipality of Port Hope. The goal was to assesswhether there are public health issues arising from the results of the study that require theattention of the authorities.
Uranium is present in soil, food and water throughout the world. In Port Hope there is alsoemission from industrial processes. The soluble portion of inhaled or ingested uranium movesinto the blood, and then passes through the kidneys into the urine. Uranium is a radioactive heavy metal with very low radioactivity. Its major toxicity is damage tothe kidneys. DGZ report that they obtained urine samples from nine subjects who were residentsof Port Hope. They present no detail about the subjects. In particular there is no mention ofwhether any of the subjects had occupational exposures to uranium. The urine samples wereanalysed by mass spectrometry to determine isotopic content. The results were presented inTables 1 and 2 of their paper. The authors report that the average concentration of uranium in the urine of the nine subjects was8.1 ng/L. Expressed in a different way, this is 8 parts of uranium per million million parts ofurine (or about 1 part uranium per 100 thousand million parts of urine). This tiny number is hardto conceptualize. The concentration is equivalent to dividing 1/3 of an aspirin tablet among allthe citizens of Canada and having each swallow their piece of aspirin with a litre of water.
Is the presence of uranium at an average concentration of 8.1 ng/L more than one finds elsewherein the world? DGZ state that they obtained control samples from residents of other parts ofOntario. In fact, there were only 2 control samples obtained, a number that is much too small tobe helpful given the known variability of urine uranium measurements in individuals. I wasunable to find reports of uranium sampling among other Canadians. Fortunately there are reportsof measurements made elsewhere. Scientists from the US Centers for Disease Control reportedthe results of a survey of uranium in the urine of a nationally representative sample of 500 USresidents. The average concentration of uranium in the urine of these 500 subjects was 11.0 ng/L.
In Europe, urine samples were collected from 24 male and 14 female occupationally unexposedsubjects, 20-50 years of age, living and working in the district of Rome, Italy. The meanconcentration was 10 ng/L. The average result in Port Hope was thus lower than the averagefound in the United States and in Italy. DGZ spend some time talking about depleted uranium. Most nuclear reactors (with the exceptionof the Candu) are designed to operate with above natural amounts of U235 in the core. Elaboratetechnology has been developed to separate this isotope from the chemically identical U238 whichcomprises over 99% of natural uranium. What is left behind is termed depleted uranium, that is,natural uranium with less than natural abundance of U235. Depleted uranium is indistinguishable to the body from natural uranium. Removal of U235 makes depleted Uranium less radioactive thannatural uranium. Since the decay energy of U235 is higher than that of U238, the radioactive decaysof depleted uranium are thus, on average, less energetic and less biologically damaging thanthose of natural uranium. One individual (Subject 3) had an isotopic ratio statisticallysignificantly different from natural uranium, consistent with intake of depleted uranium. Thisindividual thus has less U235 in their urine than the others. He/she would be thus expected to havefewer nuclear decays, and at a lower average decay energy, than subjects with the natural ratio ofuranium in their bodies. It cannot be argued that this is harmful.
In conclusion, I have reviewed the report authored by Durakovic, Gerdes, and Zimmerman. Themost important finding was that the average concentration of uranium in the urine of Port Hoperesidents, 8 ng/L, about 1 part uranium per 100 thousand million parts of urine, was similar to(actually less than) the average concentrations reported elsewhere in the world. I conclude thatthese results do not suggest any danger to the public health from uptake of uranium by residentsof Port Hope.
Introduction
This review of the document entitled “The Quantitative analysis of Uranium Isotopes in thepopulation of Port Hope, Ontario Canada” authored by Durakovic, Gerdes, and Zimmerman(DGZ) was prepared at the request of the Municipality of Port Hope. The goal was to assesswhether there are public health issues arising from the results of the study that require theattention of the authorities.
By way of introduction, I am an occupational and environmental physician with 29 years ofexperience in issues of human exposure to chemical, physical, and radioactive agents. For manyyears I was the representative of the Province of Ontario on the Committee of Medical Advisersto the Atomic Energy Control Board. Prior to entering medical school, I obtained a PhD inexperimental physics from Case-Western Reserve University in Cleveland, Ohio.
DGZ report that they obtained urine samples from subjects who were residents of Port Hope.
They present no detail about the samples. I presume that these were “spot” random samples ofvarying volume and concentration. They mention control samples from residents of other parts ofOntario. In fact, there were only 2 control samples obtained. This is woefully inadequate giventhe known variability of urine uranium measurements in individuals. The samples were analysedby mass spectrometry to determine isotopic content. The results were presented in Tables 1 and 2of their paper.
Uranium Isotopes
Before proceeding further it is useful to discuss uranium isotopes. Uranium appears in nature as avariety of species, differing by the number of neutrons in the atomic nucleus. The number ofprotons and electrons are identical among the various isotopes. The human body identifies atomsof uranium only by the number of electrons in the external shell, so as far as the human body isconcerned, all uranium atoms are the same. Their metabolism and distribution in the human bodyis identical. They differ internally but are externally indistinguishable to the human body in theirappearance, chemistry, and toxicity. The isotopes of uranium are labelled by their atomic weight, that is the sum of the numbers ofprotons (fixed at 92) and neutrons (variable). The major isotopes are U238 (99.27% relativeabundance in natural uranium), U235 (0.72% relative abundance ), and U234 (0.005% relativeabundance). There are several additional manmade isotopes which are produced in nuclearreactors, of which U236 is mentioned by DGZ. Uranium is radioactive, that is, over time it will split into 2 smaller atoms by emitting particles ofradiation or matter. Uranium is of very low radioactivity, a property measured by the “half-life”, the amount of time it takes for 50% of a sample of radioactive material to decay and change intosomething else. The shorter the half-life of ingested materials, the more the body will be bombarded by the emitted radiation. The longer the half life, the less frequent the bombardment.
With the exception of the very rare U234 , all of the isotopes of uranium have half-lives exceeding10 million years. In comparison, the half life of radioactive iodine used by doctors to treat thyroidcancer is 8 days. The Table below gives the relative abundances and half-lives of the uranium isotopes.
Table 1: Relative abundances and half-lives of the uranium isotopes The potential to cause radiological harm is related to the decay energy of the emitted radiation.
This is shown in Table 2 below. The decay energies of the isotopes are similar.
Table 2: Decay Energies of the uranium isotopes Decay Energy (Millions of Electron Volts) Depleted Uranium.
Most nuclear reactors (with the exception of the Candu) are designed to operate with abovenatural amounts of U235 in the core. Elaborate technology has been developed to separate thisisotope from the chemically identical U238. What is left behind is termed depleted uranium, thatis natural uranium with less than natural abundance of U235. Depleted uranium isindistinguishable to the body from natural uranium. Because U235 is an isotope whose half life is6 times shorter than U238, its removal makes depleted Uranium less radioactive than naturaluranium. Since the decay energy of U235 is higher than that of U238, the radioactive decays ofdepleted uranium are thus, on average, less energetic and biologically damaging than those ofnatural uranium.
The Concentration of Uranium in the Urine of Port Hope residents.
Uranium is a very common natural element, appearing in most soils in the world. It is present infoodstuffs and drinking water. It is thus ingested by everyone and appears as an excretion productin most people’s urine. In Port Hope, there is the additional possibility of intake from uraniumdusts emitted from industrial processes or wastes. This latter would be an inhalational pathway,and soluble compounds of uranium will be absorbed into the circulation and appear in the urine.
It is not possible from urinalysis to identify the route(s) of exposure. The important considerationis that, because of its low radioactivity, the major toxicity of uranium is its potential “heavymetal” toxicity to the kidney. This potential can be well assessed by measurements of theconcentration of uranium in urine.
Since uranium is ingested by everyone, it would be expected that it would be found in the urineof Port Hope residents. So, the important question is: Is the uranium concentration of the urine ofPort Hope residents higher than average? DGZ present the results of analysis of 2 non-Port Hope residents, as “controls”. Two comparison subjects is too few to be reliable as controls. DGZreport, for comparison purposes, that the total uranium concentrations in the urine of humans is1- 7 ng/L. This is incorrect. I have been unable to locate survey values for Canadians, so I willuse comparative values from American and European populations that have been published inthe medical literature.
Firstly, I reprint in Table 3 below the results of the measurements of uranium in urine (ng/L)reported by DGZ.
Table 3. Uranium concentrations in the Urine of Port Hope residents reported by DGZ The average concentration of uranium in the urine of the nine subjects was 8.1 ng/L. Expressedin a different way, this is 8 parts of uranium per million million parts of urine (or about 1 parturanium per 100 thousand million parts of urine). This tiny number is hard to conceptualize. Thistiny number is hard to conceptualize. The concentration is equivalent to dividing 1/3 of an aspirintablet among all the citizens of Canada and having each swallow their piece of aspirin with a litreof water.
Is the uranium concentration of the urine of Port Hope residents higher than average? A. American Survey
Ting and colleagues, from the Centres for Disease Control (CDC) in Atlanta, published theresults of a survey of uranium in the urine of 500 US residents (Ting et al. 1999). The Urinesamples were collected as part of NHANES III, a nationally representative sample of the USpopulation. The Table below gives the distribution of sample results.
Table 4: Percentile distribution of uranium concentrations in the urine of Americans (ng/L) Number of subjects (out of 9) with results at or less than US value Comparing the Port Hope results with the American survey, we find that the averageconcentration of Uranium in urine is lower than the US average, and that the distribution isshifted to the left, that is to lower concentrations.
Rome, Italy
Urine samples were collected from 24 male and 14 female occupationally unexposed subjects,20-50 years of age, living and working in the district of Rome, Italy (Galletti et al. 2003). Themean concentration found was 10 ng/L, similar to the Port Hope result.
CONCLUSION on Uranium Excretion
Based upon the results presented by DGZ, it can be concluded that residents of Port Hope haveurinary uranium concentrations similar to, or lower than, residents of the United States andRome, Italy. Depleted Uranium
DGZ have measured the isotopic ratios of uranium in the urine of the Port Hope residents. Asseen in Table 1, natural uranium has more U238 than U235: the ratio is 137.88:1. In any sample, ifsome of the U235 has been removed (depleted uranium) , then the ratio will increase above137.88. DGZ present the results of the determination of this ratio in the Port Hope urine samples.
Because there is statistical uncertainty about any measurement of radioactivity, they give theestimate with a measure of statistical uncertainty, the standard deviation (SD). From statisticstheory, we know that on 100 repeated measurements of any of these samples, one would find 95of them to lie between (Estimate - 2 sd) and (Estimate + 2 sd). Any result in which estimate ± 2sd excludes 137.88 is said to be significantly different from the natural ratio. We thus see that only one sample (Subject 3) has an isotopic ratio statistically significantly different from naturaluranium. This individual has less U235 in their urine than the others. He/she would be thusexpected to have fewer nuclear decays, and at a lower average decay energy, than subjects withthe natural ratio of uranium in their bodies. It cannot be argued that this is harmful.
U236 is a manmade isotope. It has a half-life of 23 million years and it’s decay energy is slightlyhigher than that of U238. Four subjects had detectable levels of U236 in their urine. The levels wereabout 1 millionth or less of the amount of U238, that is the average concentration was about onemillionth of a nanogram/L, that is 1 millionth of a thousandth part per million. Theseextraordinarily low concentrations do not represent a health hazard.
Summary by DGZ
Durakovic, Gerdes, and Zimmerman conclude their paper by stating that “our results provide thefirst objective analytical study of long-term contamination and possible association with adversehealth effects in the current population of Port Hope.” These comments are misleading. It is not possible to identify long term contamination from a
single urine specimen. The authors have merely demonstrated that their subjects have had uptake
of uranium into their bodies. But everyone ingests uranium, and the results of DGZ demonstrate
that the uptake of soluble uranium is less than the average in the United States. It is not possible
to make any comment about poorly soluble uranium from these analyses. Most importantly, the
authors have not demonstrated “a possible association with adverse health effects”. This was not
a health study, but a measurement of biological excretion.
CONCLUSION
Durakovic, Gerdes, and Zimmerman have importantly demonstrated that uranium excretion
among residents of Port Hope is not elevated in comparison to populations in the United
States and Europe.
There is no reason to expect any unusual pattern of health effects from
uptake of uranium among residents of Port Hope.
Reference List
Galletti M, D'Annibale L, Pinto V, Cremisini C. 2003. Uranium daily intake and urinaryexcretion: a preliminary study in Italy. Health Phys 85:228-235.
Ting BG, Paschal DC, Jarrett JM, Pirkle JL, Jackson RJ, Sampson EJ, Miller DT, Caudill SP.
1999. Uranium and thorium in urine of United States residents: reference range concentrations.
Environ Res 81:45-56

Source: http://porthope.ca/en/municipaldepartments/resources/HEALTH_CANADA_Finkelstein_review.pdf

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