Tritium is created and released into the environment in far greater quantities from CANDU reactors than from other power reactors, such as the American "light-water" designs.
Like all radioactive substances, tritium is a carcinogen, a mutagen, and a teratogen. Laboratory work with mice and rats has clearly shown that tritium is particularly potent as a mutagen and teratogen.
The first document in this series was written in 1981 at the request of Marion Dewar (then Mayor of Ottawa) following a deliberate dump of 3500 curies of tritium into the Ottawa River upstream of Ottawa, with no warning to the population or to municipal authorities. The other documents in this series are verbatim excerpts from documents on tritium produced by various independent bodies.
Gordon Edwards, 1996.
VERBATIM EXCERPTS FROM
"Effects on Populations of Exposures to Ionizing Radiation" (1980)
Report of the Select Committee on Ontario Hydro Affairs
to the Select Committee on Ontario Hydro Affairs
from Annex H of the 1977 UNSCEAR Report
from Annex J of the 1977 UNSCEAR Report
WHO SHOULD DECIDE?
COMMENTS ON THE DUMPING OF
What happened to the NPD reactor on July 19, 1981?
A 200,000 gallon reservoir of emergency cooling water (consisting of ordinary water) was accidentally drained when a rubber sleeve connecting two pipes came loose, flooding the boiler room of the NPD reactor (a prototype CANDU reactor at Rolphton Ontario with a capacity of 22 megawatts) to a depth of 25 feet.
Was it a dangerous reactor accident?
No. Since the regular cooling was uninterrupted during this incident, there was no danger of the reactor core overheating. The emergency cooling water is only needed when the regular cooling is lost, which has never happened in a CANDU reactor as yet. However, the incident does raise some important questions as to how reliable the emergency cooling system would be in the event of a genuinely serious reactor accident.
How did the NPD cooling water become radioactive?
The flooding incident shorted out two heavy water recirculating pumps. As a result, radioactive heavy water ["tritiated" water] leaked out from the core area of the reactor through the pump seals and mingled with the emergency cooling water, contaminating it with 3,500 curies of radioactive tritium.
What is a curie?
A curie is a unit of radioactivity, corresponding to 37 billion disintegrations per second. Thus 3,500 curies corresponds to 129.5 trillion disintegrations per second (1.295 x 1014 dps, or 129,500,000,000,000 dps). That is a great deal of radioactivity.
One disintegration per second (dps) is called a "becquerel".
Thus one curie is 37 billion (37,000,000,000) becquerels.
A microcurie is one millionth of a curie, or 37,000 becquerels.
A picocurie is a trillionth of a curie; that is, 0.037 becquerels.
What is tritium?
Tritium is a weakly radioactive form of hydrogen, with a half-life of 12.3 years. The radiation emitted by tritium is not penetrating; it is a very low-energy form of radiation. About 99 percent of all tritium occurs in the form of "tritiated water" (HTO or DTO); see the explanation given below.
The letters in parentheses are based on a kind of chemical shorthand:
H = an atom of normal hydrogen (hydrogen-1), known as "protium".
Hydrogen is the lightest and most abundant element in the universe.
It is essential to life, forming an integral part of every organic molecule.
D = an atom of heavy hydrogen (hydrogen-2), known as "deuterium".
D behaves exactly like H, except that it's twice as heavy as H.
For technical reasons, it is used in the CANDU reactor.
("CANDU" means "CANadian Deuterium Uranium".)
T = an atom of radioactive hydrogen (hydrogen-3), known as "tritium".
It behaves like H, but it's three times as heavy, and it is also radioactive.
When a deuterium atom (D) absorbs a neutron it becomes a tritium atom (T); this happens often inside every CANDU nuclear reactor.
H2O = a molecule of ordinary water (or "light water").
An ordinary water molecule is formed when two ordinary hydrogen atoms (H + H = H2) combine with one oxygen atom (O).
D2O = a molecule of heavy water.
In every molecule of "heavy water", both of the ordinary hydrogen atoms in ordinary water have been replaced by heavy hydrogen atoms.
Heavy water is used in the core of a CANDU reactor as a "moderator" (to slow down the neutrons) and as a "coolant" (to remove the heat produced by the nuclear fuel).
HTO or DTO = a molecule of tritiated water.
If one of the ordinary hydrogen atoms (H) in ordinary water (H2O)
-- or one of the heavy hydrogen atoms (D) in heavy water (D2O) --
is replaced by a tritium atom (T), "tritiated water" is created.
This happens when one or two neutrons are captured.
Where did the contaminated NPD cooling water get dumped?
The tritium-contaminated water was eventually pumped from the boiler room back into the reservoir from which it came, but it was contaminated with grit and oil as well as with radioactivity. In order to clean out the reservoir, Ontario Hydro officials decided to dump the dirty water into the Ottawa River. Many communities downstream from the reactor site draw their drinking water from the Ottawa River. Tritium cannot be filtered or otherwise removed from drinking water by any standard water-treatment processes.
Is this kind of radioactive dumping allowed?
According to the United Nations Scientific Committee on the Effects of Atomic Radiation, radiation protection policies are supposed to be based on "the principle of eliminating any exposures which are not necessary and of keeping all doses as low as is reasonably achievable" (UNSCEAR 1977 p.14). Evidently, the Atomic Energy Control Board (AECB) does not enforce this principle rigorously; instead, it sets limits and establishes guidelines on how much radioactivity can be released by the nuclear industry into the environment, wehether it is necessary or not. In this particular case, the resulting radiation exposure of people downstream was clearly unnecessary, but was nevertheless allowed.
Do the radiation guidelines prevent biological damage?
No. In the case of cancer, leukemia, and genetic damage, the scientific consensus is that every additional exposure to radiation adds to the total risk and therefore to the incidence of these diseases in exposed populations. In the case of developmental damage to unborn babies exposed in the womb, scientists have so far found it impossible to determine what level of exposure to tritium constitutes a "damaging dose".
According to a 470-page report published by the British Columbia Medical Association (BCMA) in 1980, existing AECB standards for public exposure to another radioactive substance -- radon -- "may well be viewed as tantamount to allowing an industrially-induced epidemic of cancer". Chapter XXII of the BCMA Report is entitled "Atomic Energy Control. Board -- Unfit to Regulate", based on the AECB's poor record of protecting the public health and safety (BCMA p.283).
What is the AECB limit for tritium emissions from NPD?
According to the AECB, the maximum permissible release limit from the NPD reactor into the Ottawa River is 220,000 curies of tritium per month, or 2.64 million curies per year. As an operating target, the AECB tries to keep releases to within 1 percent of this limit; that is, 2,200 curies of tritium per month or 26,400 curies per year (equivalent to an average of 7.3 curies per day).
Did the NPD dumping meet the AECB operating target?
Obviously not. Since 3,500 curies is larger than 2,200 curies, the dumping exceeded the AECB operating target by about 60 percent (if calculated on a monthly basis). However, since the 3,500 curies were dumped in less about five days, at an average rate of more than 700 curies per day, the AECB operating target was exceeded by about 1000 percent if calculated on a daily basis.
Does it matter if tritium is released slowly or quickly?
According to Dr. Edward Radford, Chairman of the U.S. National Academy of Sciences' Third Committee on the Biological Effects of Ionizing Radiation (BEIR-III), a sudden burst of tritium in the drinking water may be much more dangerous to a female embryo in the early stages of pregnancy than the same amount of tritium spread out over a longer period of time (testimony to the Select Committee on Ontario Hydro Affairs, July 10 1979).
Where does tritium come from?
Tritium is produced in nature by the action of cosmic rays from outer space. It is also produced by atomic explosions and by nuclear power plants. Each CANDU reactor produces from 30 to 100 times as much tritium as a comparable American light water reactor, because the heavy water in a CANDU "breeds" tritium while the reactor is operating.
How much tritium is produced globally?
Before the advent of nuclear energy, it is estimated that the global inventory of naturally-occurring tritium was about 34 million curies, of which 22.2 million curies were contained in the oceans and 9.2 million curies were present in inland areas (UNSCEAR p.55).Nuclear weapons testing has added about 3,600 million curies of tritium in the northern hemisphere. By 1970, only about 2,900 million curies was left, mostly in the oceans; the rest had undergone radioactive disintegration to become helium-3 (UNSCEAR p.117).
American light-water reactors generate about 15 to 23 curies of tritium per megawatt-year, of which no more than 1 curie is normally released into the environment. CANDU reactors generate about 620 curies per megawatt-year, of which about 20 curies are normally released into the environment (16 curies to the air, 4 curies to the water -- UNSCEAR p.180).
At that rate, one would expect the Pickering nuclear complex (2,000 MW) to release about 32,000 curies of tritium into the air each year, yet in 1978 only 26,000 curies were released. One would expect the NPD reactor (20 MW) to release about 80 curies of tritium into the Ottawa River each year.
Is tritium a biological hazard?
The radiological significance of tritium is not related to its inherent toxicity, as it is a very low energy form of radiation, but to its easy incorporation into all parts of the body that contain water (Select Committee Report p.15).
Tritiated water can be ingested in the liquid form. It can also be inhaled or absorbed through the skin in the form of water vapour or steam, which makes tritium an occupational hazard in CANDU nuclear power plants. In pregnant females, tritium ingested by the mother can cross the placenta and be incorporated directly into the foetus.
Like all radioactive substances, tritium can cause cancer, genetic mutations, or developmental defects in unborn children (the latter following pre-natal exposure of the foetus). No threshold or "safe dose" of tritium has been scientifically established for any of these effects.
What scientific evidence is available?
"There is now experimental evidence, both in terms of changes in the developmental effects on foetuses in utero in animals and also in studies of cancer induction, that tritium [is] four or five times more effective than would be predicted just on the basis of its energy alone" (Dr. Edward Radford, testimony to the Select Committee on Ontario Hydro Affairs, July 10 1979).
"Concerning the passage of tritium administered under the form of tritiated water from the mother through the placenta and into the foetus... several statistically significant effects were found at various HTO levels, in no apparent relationship with dose. These included microcephaly [shrunken heads, also observed at Hiroshima], sterility, stunting, reduction of the litter size,..." (UNSCEAR p.695 -- these are, of course, animal studies).
"During the past few years, there has been a growing interest in the study of the biological effects of radio-isotopes, particularly of plutonium-239 and tritium. A number of genetic and cytogenic [i.e. cellular] studies that have so far been carried out in mice demonstrate that these isotopes are capable of inducing dominant lethal mutations, chromosome aberrations and point mutations (for the last category, only the effects of tritium have been studied)" (UNSCEAR p.477).
- BEIR III (National Academy of Sciences: Third Committee on the Biological Effects of Ionizing Radiation). The Effects on Populations of Exposure to Low Levels of Ionizing Radiation. Academy Press. Washington: 1982.
- UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation). Sources and Effects of Ionizing Radiation. Report to the UN General Assembly. United Nations, New York: 1977.
- Annex H: Genetic Effects of Radiation. Part 2: Tritium.
- Annex J: Developmental Effects of Radiation. Part V-B: Tritium
- Select Committee on Ontario Hydro Affairs. The Safety of Ontario's Nuclear Reactors. Ontario Legislature, Toronto: 1980.
- BCMA (British Columbia Medical Association). Health Hazards of Uranium Mining. BCMA, Vancouver: 1980.
- Chapter XXII: AECB -- Unfit to Regulate.
back to [ Table of Contents ]
The Effects on Populations
of Exposure to
Low Levels of Ionizing Radiation
published in 1980 by
The U.S. National Academy of Sciences'
(BEIR = Biological Effects of Ionizing Radiation)
Excerpt from pp. 485-486:
"Somatic Effects Other Than Cancer"
Because tritium (hydrogen-3) is a potential pollutant from nuclear-energy production, it's effect on development [of unborn babies] has been the subject of a number of studies.
Tritiated water (HTO) is a common chemical state of tritium, and it has easy and rapid access to living cells, including those of the embryo or foetus.
HTO administered in the drinking water to rats throughout pregnancy produced significant decreases in relative weights of brain, testes, and probably ovaries, and increases in norepinephrine concentration, at doses of 10 microcuries per millilitre (estimated at 3 rads per day), and produced weight decreases in a number of [other] organs at higher doses.
Because the length of the critical period [of vulnerability to damage] for various organs is not known, the total damaging dose cannot yet be estimated. Relative brain weight was found to be reduced at only 0.3 rads per day (one microcurie per millilitre of drinking water) when exposure began at the time of the mother's conception.
Even lower exposures (0.003 rads per day and 0.03 rads per day) have been implicated in the induction of behavioral damage, such as delayed development of the righting reflex and depressed spontaneous activity. However, because the data fail to show a clear dose dependence, there is some doubt about the validity of this suggestion.
Tritiated drinking water has been used to study the effects of radiation on development of a sensitive cell type, the oocyte. Oocyte counts were made in serial sections of exposed and control animals. In squirrel monkeys continuously exposed from conception to birth, the LD-50 was 0.5 microcuries per millilitre of body water, giving a foetal dose rate estimated at 0.11 rads per day. Because the sensitive period for oocyte development is probably the last trimester, the LD-50 was calculated to be 5 rads. In the mouse, the sensitive period occurs during the first two weeks after birth, and, by a similar calculation, the LD-50 from tritiated drinking water at that time is slightly below 5 rads.
... from the Summary section, page 493
Until an exposure has been clearly established below which even subtle damage does not occur, it seems prudent not to subject the abdominal area of women of child-bearing age to quantities of radiation appreciably above background, unless a clear health benefit to the mother or child from such an exposure can be demonstrated.
Ed. note: This does not refer to tritium only, but to any form of radiation exposure.
back to [ Table of Contents ]
Sources and Effects of Ionizing Radiation
1977 UNSCEAR Report
to the U.N. General Assembly
[ UNSCEAR = U.N. Scientific Committee on the Effects of Atomic Radiation ]
Genetic effects of radiation
(a) Induction of dominant lethal [mutations] in mice
Carsten and Commerford and Carsten and Cronkite have published the results of their studies on the induction of dominant lethals [dominant lethal mutations] in mice (random-bred, Hale-Stoner-Brookhaven strain) fed with tritiated water (HTO).
The HTO test animals were first-litter mice resulting from breeding of eight-week-old animals that had been maintained on HTO (3 microcuries per millilitre) since weaning at four weeks of age. The control animals were first litter mice taken from the colony and maintained on tap water.
From the second generation animals, four experimental groups were established for dominant lethal tests.
- Group 1 consisted of animals
where both the male and female were on HTO.
- Group 2 females received HTO,
males, tap water.
- In Group 3, the situation
was the reverse of that in Group 2, and
- Group 4 received only tap water
(both males and females).
At eight weeks of age, in each group, each male was mated to five females for a 5-day period, the females were killed and their uterine contents examined for assessing dominant lethality.
The results, based on 366 pregnant females in the controls, 764 in Group 1, 315 in Group 2, and 316 in Group 3, clearly demonstrated that dominant lethals are induced by HTO in both sexes.
Significantly fewer viable embryos were found when either both mating partners or only the female was maintained on the tritium regimen. Similarly, when both the partners were on tritium, the incidence of early death (dark mole) is significantly higher than in the control group. Treatment of the males only gave similar effects, but these were not [statistically] significant.
When post-implantation mortality (early plus late deaths in the authors' terminology) is used as the basis for comparison, the increased mortality due to HTO in Groups 2 and 3 is of the same magnitude in both sexes, and in Group 1 (both sexes on HTO) the effect is nearly twice that in Groups 2 or 3.
Current experiments are directed at repeating these studies with a lower concentration of 1.0 microcuries per millilitre.
(b) Induction of specific-locus mutations in male mice
Cumming et al. (128) have completed the first series of experiments on tritium-induced specific locus mutations in mice, providing the only data available on such gene mutations in any mammal.
In view of possible levels of tritium release, not only from existing nuclear installations but also from contemplated controlled thermonuclear reactors, these data are of great relevance.
A total of 14 groups of males was used. Two groups were injected with 0.75 millicuries, and the 12 others with 0.50 millicuries, of tritiated water per gram of body weight.
The results demonstrate that beta radiation from the decay of tritium can induce specific-locus mutations in spermatogonia as well as in post-meiotic stages: 16 mutations have been recovered among a total of 20,626 offspring derived from germ cells irradiated as spermatogonia and 11 in 7,943 offspring from irradiated post-meiotic stages.
The mean absorbed dose to the spermatogonial cells has been estimated to be 700 rad and that to post-meiotic cells, 430 rad. These data thus permit mutation-rate estimates of 1.58 x 10-7 per rad per locus for spermatogonia and 4.60 x 10-7 per rad per locus for the other stages. These rates are within the statistical limits of what would have been expected from a comparable external dose of x [-irradiation] or gamma irradiation.
The point estimate of the RBE [Relative Biological Effectiveness] for post-spermatogonial stages is close to 1, with fairly wide confidence intervals; that for spermatogonia is slightly above 2, with confidence intervals that include 1.
There are some indications that the distribution of mutants among the seven loci may differ from that produced by gamma rays; noteworthy is the observation that only one of the mutations was at the s locus (the expectation would be about 5 or 6).
In more recent studies, currently in progress at Oak Ridge, Cumming and W.L. Russell (129) are engaged in collecting more extensive data on tritium irradiation, focusing attention on the induction of mutations in spermatogonia.
(c) Induction of chromosome aberrations
in human lymphocytes by tritiated water (HTO)
Hori and Nakai (233) and Bocian et al. (39) have reported on the induction of chromosome aberrations in human lymphocytes exposed to tritiated water in vitro. Exposures were carried out by the addition of whole blood to the culture medium containing tritiated water.
In the work of Hori and Nakai, the concentration of tritium ranged from one millionth of a microcurie per millilitre to one hundredth of a microcurie per millilitre, and the cells were exposed during their entire period in culture (48 hours).
Bocian et al., used two regimens: in one ("acute exposures" in the authors' terminology), the lymphocytes were exposed for a 2-hour period prior to PHA stimulation (range of concentrations, 1.71 to 14.36 millicuries per millilitre), after which they were washed and cultured (53-hour cultures); in the other ("protracted series") the cells were exposed during 53 hours (concentration range, 0.063 to 0.51 millicuries per millilitre).
The results indicate that with protracted exposures (48 or 53 hours) the [chromosome] aberrations produced were mostly of the chromatid type, such as gaps, deletions and fragments, and there were relatively few chromatid exchanges.
In the concentration range used by Hori and Nakai, the dose-effect curve for the number of [chromosome] breaks induced was quite complex at low concentrations. In the work of Bocian et al. and with the range of concentrations they used, the frequency of chromatid aberrations increased linearly with dose.
A quantitative comparison of the frequencies between the two groups of authors is, however, not possible because each group used only one (but different) fixation time, and in addition, the ranges of concentration were different.
In the 2-hour exposure experiments of Bocian et al., chromosome-type aberrations were found to be induced (dicentrics, centric rings, terminal and interstitial deletions). The data for dicentrics plus rings, as well as those on deletions, gave a good fit to a linear plus quadratic model.
Using the data obtained in x-irradiation experiments (acute doses of 50 to 300 rad), Bocian et al. have estimated that the RBE [Relative Biological Effectiveness] for the induction of dicentrics plus centric rings is about 1.2.
3. Summary and conclusions
[Annex H: Genetic Effects]
During the past few years, there has been a growing interest in the study of the biological effects of radioisotopes, particularly of plutonium-239 and tritium.
A number of genetic and cytogenetic studies that have so far been carried out in mice demonstrate that these isotopes are capable of inducing dominant lethals [i.e. lethal mutations], chromosome aberrations and point mutations (for the last category, only the effects of tritium have been studied).
Autoradiographic studies have shown that in mice, intravenously injected plutonium-239 (as citrate solution) is inhomogeneously distributed in the testis and is largely localized in the interstitial tissue outside and between the seminiferous tubules. A consequence of this is that the alpha-irradiation dose rate to the spermatogonial stem cells is from 2 to 2.5 times greater than the average for the testis as a whole.
When plutonium-239-injected males are mated to females, there is a significant excess of intra-uterine mortality relative to controls and the effect persists in matings up to five weeks after injection (post- and peri-meiotic stages sampled). In addition, the effect appears to be unrelated to the amount of plutonium-239 injected (in the range of 0.05-0.5 microcuries per mouse).
Dominant lethal [mutation] tests performed on F1 males sired by fathers which received plutonium injection (and derived from matings during the ninth, fourteenth and sixteenth weeks) showed that here again there was an increase in intra-uterine mortality relative to controls.
Relative to chronic gamma irradiation, alpha particles from plutonium-239 seem to be more than 20 times as effective in inducing dominant lethality (post-implantation) in meiotic and post-meiotic stages.
In male mice exposed to alpha particles from plutonium-239 (intravenously injected citrate solution) for a duration of 6 to 34 weeks, reciprocal translocations (in spermatogonia) and chromosome fragments (in spermatocytes) are induced.
Relative to chronic gamma irradiation, alpha-particle irradiation from plutonium-239 is more than 20 times as efficient for the induction of these effects. This finding is similar to that recorded for the induction of dominant lethals in meiotic stages.
These calculations do not take into account the inhomogeneous distribution of plutonium-239 in the testis.
Male and female mice fed on tritiated water, show, in dominant lethal tests, an increased amount of intra-uterine death.
In specific-locus tests, mutations have been found to be induced in male mice fed with tritiated water. The data currently available suggest that the rate of induction [of mutations] per unit dose of irradiation with beta particles from tritium is about the same as that of x-irradiation. The estimates are 1.58 x 10-7 per rad per locus for spermatogonial mutations and 4.60 x 10-7 per locus for post-spermatogonial stages. These estimates have wide confidence limits. There is some evidence that the distribution of mutants among the seven loci may be different from that after x-irradiation.
In human lymphocytes exposed to tritiated water in vitro, both chromosome- and chromatid-type aberrations are induced, depending on the concentration of tritium and the duration of exposure.
back to [ Table of Contents ]
Sources and Effects of Ionizing Radiation
1977 UNSCEAR Report
to the U.N. General Assembly
[ UNSCEAR = U.N. Scientific Committee on the Effects of Atomic Radiation ]
Developmental effects of radiation
[that is : Harmful Effects on Infants Exposed in the Womb]
V. INTERNAL IRRADIATION
[this includes tritium]
The first reported observations on the effect of injected radioisotopes in the foetal mammal are those of Bagg. He injected radon solutions in amounts of tens of millicuries into pregnant rats at different gestation times and described post-implantation death and various types of malformations in the offspring.
More recently, some data on teratogenic effects of internal irradiation have been published, but information on any one nuclide is still very scanty. It does not seem possible to draw general conclusions, and the main value of the existing data is the indication of possible levels of toxicity for the various radioisotopes.
The available data will be reviewed according to the nuclide tested, but only for those nuclides for which there seems to be significant information. It was felt that the present state of knowledge in this field would not justify any attempt to express the data in terms of the radiation dose actually received by the conceptus or its organs and tissues. Exposures or dose data are therefore given according to the way they were reported in the original publication.
Two documents have been submitted to the Committee summarizing the effects on foetus and progeny of mothers exposed to radionuclides before conception and reviewing the various effects in animals treated with radioactive substances in the course of intra-uterine development; both of them dealt with work carried out in the USSR.
An indexed bibliography dealing specifically with the transfer through the placenta and into the foetus of radioactive substances injected to mothers is also of interest for reference to published data on this subject.
The emphasis of the presentation to follow, in accordance with the objects specified in the introduction, will however be centred on the teratological effects [malformations] themselves induced by different doses of the administered nuclides, rather than on the mechanisms and rate of transfer of such nuclides from the mother to the foetus. For these the reader is referred to the specialized literature included in the previously mentioned publications.
Concerning the passage of tritium administered under the form of tritiated water from the mother through the placenta and into the foetus,
Lyaginskaya investigated the relationships between the pregnancy stage at the time of treatment with HTO [tritiated water] in the rat and the ensuing effects in post-natal development. For a dose of 0.3 microcuries per gram, little relationship was found among these variables, although
However, at this dose no teratological effects [malformations] were manifest.
LD-50 values ["lethal-dose 50 percent values"] for foetal mortality in rats after single HTO [tritiated water] treatments at various doses were
Cahill and Yuile evaluated the resulting foetal tissue doses [radiation doses to unborn babies] in rats, the body water of which was maintained throughout pregnancy at a constant tritium level in the range 1 to 100 microcuries per millilitre. This was achieved by adjusting the ingestion of tritiated water. Dose rates in embryos and foetuses were calculated to range from 0.3 to 30 rads per day. Most mothers were sacrificed before birth for observation of the conceptuses, but in some cases the observations were carried out on born offspring and followed to their adulthood.
Several statistically significant effects were found at various HTO [tritium] levels, in no apparent relationship with dose. These included
Stunting appeared at 20 microcuries per millilitre and its degree increased at higher concentrations in direct relation to dose. Organ weight decreased in proportion to dose.
The incorporation of tritium into foetal organs was directly proportional to the maternal HTO [radio-]activity during gestation and amounted to 20 to 30 percent of this [radio-]activity. After 180 days of life, stunting only persisted in males with concentrations in the range 50 to 100 microcuries per millilitre.
A paper by Dobson dealt specifically with the RBE [relative biological effectiveness] of tritium relative to cobalt-60 gamma radiation in long-term exposures. To this end, tritiated water in various doses was administered in drinking water to pregnant mice throughout gestation and lactation for a total of 33 days, the specific [radio-]activity of the body water being checked by the radio-assay of urine samples. Other groups of mice were exposed to cobalt-60 gamma radiation at various dose rates for the same time lapse.
The number of oocytes in the progeny of these animals was counted at the end of treatment, and it was found that oocyte survival decreased exponentially with tritium concentration in body water with an LD-50 level ["lethal-dose 50 percent level"] of about 2 microcuries per millilitre body water, corresponding to an effective dose to the foetus and the new-born offspring of about 6.5 rads. The survival curve of oocytes with respect to cobalt-60 gamma rays was convex upward, indicating a decreased killing effectiveness of the gamma-ray treatment at low doses [but not for the tritium treatment -- see next paragraph].
By comparing individual gamma-ray and tritium experiments it was shown that tritium was more effective [than gamma rays from cobalt-60], and limiting RBE [Relative Biological Effectiveness] values were found to vary between 2.5 and 4.2 with a likely maximum value of about 3 at doses approaching zero. Short-term and protracted exposures were also compared by the same end-point, and higher RBEs for protracted irradiations were obtained.
Recent attempts were made by Cahill et al. to assess by a number of different end-points (morphological, biochemical and functional) the effects on rats of a simultaneous long-term administration of lead and tritiated water.
The experiments allowed the important general conclusions that combination of the treatments resulted in less-than-additive effects and that a significant reduction of brain weight by tritium exposure was apparent at dose rates of the order of 300 millirads per day continuously from conception to 180 days of age.
Haemopoietic [blood] disturbances (anisocytosis, leukopenia, thrombopenia) in the progeny of rats given tritiated water at doses of 0.008 to 0.3 microcuries per gram were described by Zhukova. Animals from mothers treated at 0.3 microcuries per gram on day 4 p.c. [after conception] were the most severely affected.
Finally, Lyaginskaya reported a decrease in the life-span of three subsequent generations of rats irradiated in utero with tritiated water on day 4, 11 and 17 p.c. [after conception], particularly upon treatment on day 4 p.c. [after conception].
Concerning administration of tritium in the form of tritiated thymidine (3HTdR), it has been possible to study a number of effects on both the mother and the foetus -- induced by a continuous perfusion of tritiated thymidine to pregnant rats from day 9-22 p.c. [after conception].
Activities of 1.6 microcuries per gram per day were in general well tolerated; but higher levels, from 3.2 to 6.4 microcuries per gram per day, produced a marked bone-marrow syndrome in the mother.
Although the litter size at birth did not appreciably change at these levels, the percentage of still-born offspring increased with the [radio-]activity injected, while the number of offspring surviving more than 12 hours after birth decreased in proportion to that [radio-]activity.
With 8 microcuries per gram per day, no rat was born alive. Retardation of growth and macroscopic and microscopic malformations of the head, brain, eyes, ears, mouth and extremities were observed at these high levels.
With 6.4 microcuries per gram per day, no gross external abnormalities were seen, but the general development and the haemopoietic system of the animals were severely impaired in proportion to the administered [radio-]activity. The post-natal growth and weight of surviving animals also showed [radio-]activity-related pathological changes.
In another paper, the incorporation of tritium from tritiated thymidine in developing rats was studied by biochemical techniques. The total incorporated [radio-]activity and the DNA [molecule] specific [radio-]activity showed a direct relation to the [radio-]activity of the tritium injected in the mother.
The distribution of radioactivity between the DNA [molecules] and the low-molecular-weight fraction was independent of the administered [radio-]activity, and the time variation of the DNA [molecule] specific [radio-]activities was characteristic for each organ.
Because of all these facts, the system of continuous perfusion was recognized as a suitable procedure for studying tritiated thymidine toxicity in the embryo.
Mouse embryos were also grown in vitro from the 2-cell stage to the blastocyst stage in the presence of tritiated thymidine. Concentrations of tritium above 0.1 microcuries per millilitre were definitely lethal, and concentrations between 0.01 and 0.1 microcuries per millilitre caused a highly significant reduction of the number of cells in the blastocyst.
The latter effect could be largely accounted for by selective cell death occurring at the 16-cell stage. As the cells in the inner mass were most susceptible to killing, it was possible to obtain blastocysts composed entirely of trophoblast.
The routine emissions from nuclear reactors include a number of different elements. Two were of special interest to the Committee, carbon-14 and tritium (or hydrogen-3).
In 1978, the principal airborne releases of radioactivity from Pickering A were measured at 26 000 curies of tritium; 4 100 curies of noble gases and assumed to be 1 100 curies of carbon-14. (A curie is a common unit for measuring the radioactivity from different elements.)
Although all releases are of concern and require emission standards, the noble gases are of somewhat less concern because their short half-life (a few hours to a few days) ensures that they cannot accumulate in the environment.
Carbon-14 and tritium are of comparable and special concern for similar reasons.
: 5 730 years for carbon-14 and 12.3 years for tritium. Long half-lives allow them to accumulate in the environment around a reactor and in the global biosphere.
Thus the radiological significance of both elements is not related to their inherent toxicity, as each is a very low energy form of radiation, but to their easy incorporation in the body.
The basis for regulatory emission standards is the 'safe limits' established by the International Council for Radiological Protection (ICRP). The ICRP is an international body drawn from experts in radiology from all over the world, and including many of the leading authorities in radiological protection. Some critics claim it is a self perpetuating body drawn from the nuclear establishment with no inclination to 'rock the boat' by imposing overly tight standards. Its supporters claim that it is made up of leading scientists and medical doctors whose reputation is beyond dispute and who safeguard the independence of the Commission by not allowing membership selection by political bodies.
The ICRP has a Chairman and permanent Secretariat who call the Commission together when, in their opinion, there is a need to review overall or specific standards. The ICRP have established a 'safe limit' of 500 millirem per year for the most exposed individual from a nuclear facility and 5 rem or 5 000 millirem per year for workers. (A "rem" is the unit used to measure the exposure of man to radiation; a "millirem' is 1/1 000 of a rem). The ICRP also emphasize the "ALARA" principle which means that despite the 'safe limit', radiation doses should be kept As Low As Reasonably Achievable, economic and social factors being taken into account.
The AECB, as a matter of explicit policy, accepts the ICRP approach and specific standards. In their view it provides the most authoritative basis for setting emissions standards for radioactive products. The AECB take responsibility for the next phase of regulatory control, reviewing and approving the specific allowable levels for the various categories of radioactive releases, including air and water borne tritium, iodine, noble gases, and particulates and establishing limits for normal operations and accident conditions. The AECB require the licensee to conduct a "pathways analysis", analyzing the various pathways by which the radioactivity can reach man and determining the resultant radiation dose to the most exposed individual. On the basis of this analysis, the AECB then sets the release limits that equate curies of radioactive releases to the ICRP limit of 500 millirem to the most exposed individual.
In the routine operation of nuclear reactors, emissions can be kept considerably lower than the derived limit. Designers and operators of Hydro stations set a release target of one percent from each category of radioactive release. In most cases the targets can be met. For example, Hydro's pathways analysis shows that they could release 10 400 000 curies of airborne tritium before the most exposed individual in the public would receive a dose of 500 millirem. The release target is set at one percent of that derived limit or 104 000 curies. In 1978 the Pickering release was 26 000 curies or 1/4 of one percent of the derived limit resulting in a dose to the theoretically calculated "most exposed individual" of about 1 1/4 millirem.
Dr. E.P. Radford, a Professor of Environmental Epidemiology at the University of Pittsburgh was critical of this approach when he appeared as a witness before the Committee. Dr. Radford is familiar with radiation protection as the Chairman of the National Academy of Science's Committee on the Biological Effects of Ionizing Radiation. Dr. Radford believes that regulatory authorities should set the regulatory limits at the low levels that can be achieved by careful design and operation -- the one percent level -- rather than accepting the potential risks implicit in the ICRP's 'safe limit'.
At this time there is no derived release limit for carbon-14 for two reasons.
Ontario Hydro's Health Physics Branch recently concluded some work on measuring releases and on tracing pathways to man that could result in a dose to the most exposed individual that is somewhere between a small fraction of a millirem and 2 1/2 millirem. At that potential dose level the AECB has become more interested in carbon-14 and is now awaiting a submission from Ontario Hydro on derived release limits and operating targets.
By focusing on carbon-14 at this preliminary stage of developing a derived release limit, the Committee was able to see clearly the range of assumptions that make up a pathways analysis and the consequent uncertainty in the very specific calculations that are made.
At this time the uncertainties are in:
In addition to these admitted uncertainties, the Committee itself was concerned that neither Ontario Hydro nor AECB know enough about the propensity of carbon-14 to accumulate in the food chain and biosphere around a plant, and the rate at which it is dispersed as it moves further from the source.
Carbon-14 is not just a problem of the 'most exposed individual'. Its long half-life makes it a problem for the global environment. In 1977 a group of experts of the OECD's Nuclear Energy Agency identified four nuclides that may be of greater global than of local concern. The four are krypton-85, iodine-129, tritium and carbon-14. The half-lives of these nuclides vary from 10.8 years for krypton-85, to 12.3 years for tritium, to 5 730 years for carbon-14 and 17 million years for iodine-129. Each of these elements occurs naturally in the environment as a result of the interaction of cosmic rays from the sun with the atmosphere. They are of concern in nuclear power programs because their artificial production is a significant proportion of the natural production which will result in an increase in the global inventory of each nuclide. The large-scale atmospheric testing of nuclear weapons in the '50s did, in fact, result in large increases in the global inventory. Since atmospheric testing ended, global inventories in man's immediate environment have been declining as these elements sink into the deep oceans.
As long as Canada does not reprocess its used fuel, krypton-85 and iodine-129 are of lesser importance to Canadian regulators. These nuclides remain bound up in the used fuel and will only be released in reprocessing or in a severe accident involving fuel melting.
Tritium and carbon-14 are of special concern to Canada.
The Committee is concerned that Canada -- and Ontario in particular -- may have a special global responsibility for controlling carbon-14 and tritium that goes beyond consideration of local effects. Although Ontario Hydro and AECL have programs ongoing to consider ways of further reducing tritium and carbon-14 releases, there is no national or regulatory framework for guiding their implementation.
The Committee also noted that radiation protection and the appropriateness of radiation standards is a health topic of great concern to people in Ontario -- the workers in the industry and populations located near industry facilities. Legislative responsibility for nuclear safety rests with the Federal government and Ontario has deferred responsibility to the AECB.
The AECB, with its limited staff, accepts the recommendations of the ICRP. The major Canadian role in standard-setting has been to provide representatives -- and in one case the chairman -- to the ICRP from AECL. Thus, the basic Canadian regulatory standards come from a body reputed to be dominated by those the critics call the nuclear establishment -- manufacturers, utilities, regulators.
The AECB has recently established an advisory committee of experts in radiation including some people from outside the "nuclear establishment."
The Committee believes that there is an additional need to provide a body that can focus on Ontario problems, that can do so openly and with participation from the public, and that can relate directly to the federal body.
A COUNCIL SHOULD BE FORMED
BY THE GOVERNMENT OF ONTARIO
WITH GIVEN TERMS OF REFERENCE
AND REPRESENTATION FROM WITHIN AND OUTSIDE
THE NUCLEAR ESTABLISHMENT
TO PROVIDE AN INSTITUTIONAL FORUM
FOR PUBLIC PARTICIPATION
AND A FOCUS FOR CONCERNS
ABOUT RADIATION PROBLEMS IN ONTARIO,
TO BUILD UP ONTARIO-BASED TECHNICAL KNOWLEDGE
AND TO OVERSEE
AS MUCH EPIDEMIOLOGICAL WORK AS IS NECESSARY
TO DECIDE WHAT THE STANDARDS SHOULD BE
FOR THE HEALTH AND SAFETY
OF PEOPLE IN ONTARIO.
THE COUNCIL SHOULD REVIEW
PARTICULAR PROBLEMS OF RADIATION
ASSOCIATED WITH OPERATING OR PLANNED REACTORS,
INDEPENDENT OF ONTARIO HYDRO AND THE GOVERNMENT.
THE COUNCIL SHOULD WORK TOWARD
THE ESTABLISHMENT OF A FEDERAL-PROVINCIAL WORKING GROUP
TO CO-ORDINATE THE NATIONAL STANDARDS
WITH THE WORK AND FINDINGS OF THE PROVINCIAL GROUP.
THE POWERS OF THE COUNCIL SHOULD BE THAT OF
MAKING INDEPENDENT AND PUBLIC RECOMMENDATIONS
TO AN APPROPRIATE MINISTER.
ONE OF THE FIRST TASKS THE COUNCIL SHOULD TAKE ON
AND GIVE HIGH PRIORITY TO
IS AN INDEPENDENT REVIEW
OF THE ADEQUACY OF CURRENT PROPOSED RELEASE LIMITS
FOR CARBON-14 AND TRITIUM,
TAKING INTO ACCOUNT BOTH LOCAL AND GLOBAL CONCERNS.
[ THESE RECOMMENDATIONS WERE NEVER ACTED ON... ]
TESTIMONY OF DR. EDWARD RADFORD
ON ONTARIO HYDRO AFFAIRS
The Safety of Ontario's Nuclear Reactors
Tuesday, July 10, 1979
MEMBERS OF THE SELECT COMMITTEE ON ONTARIO HYDRO AFFAIRS:
Counsel: Schwartz, Alan M. Consultant: Fisher, J.D., Canada Consulting Group, Toronto
Clerk: Richardson A. Assistant Clerk: Stenky, J.
Broem, Dr. I.D.J., Director of Biostatistics, Roswell Park Memorial Institute for Cancer Research, Buffalo, New York.
Radford, Dr. E.P., Professor of Environmental Epidemiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pennsylvania.
Dr. Radford: The low energy of the tritium beta means that when tritium is taken into the body the radiation dose to the tissues per unit of radioactive decay expressed in millicuries or microcuries is low, compared to other radionuclides that are present in reactor waste. In addition, the fact that it will usually be ingested or inhaled in water molecules means that it will be excreted from the body mostly as water and with a turnover rate characteristic of body water. We excrete about half of our body water every 10 days, of course making up the loss with fresh intake, so this means that tritium stays in the body only a relatively short time compared, say, with radioactive radium atoms, which may remain in the body for years or even decades.
I would like to add to that that we have to consider two situations with regard to tritium uptake and release-state situation. One is what I will call a steady-state situation.
The kinds of arguments I just expressed here and which were expressed yesterday by Dr. Myers I believe means that we come into a new equilibrium with the intake. For example, take the water outside the Pickering reactors. It means the population that has been drinking that water has now come into equilibrium with it. The ratio of tritium atoms to hydrogen atoms in their bodies is the same as the ratio in the water supply. That is what that means. It doesn't mean there is any really serious problem associated with it, but that is the way that tritium operates.
In this regard tritium is somewhat different from other radionuclides in that there is no so-called concentration factor. That is, there exists no biochemical mechanism that means the body knows the difference between a tritium atom and anything else or a hydrogen atom. Therefore it is always diluted in proportion to the hydrogen.
This is not exactly true, but it is close enough to being true. Somehow the body does know the difference between tritium and hydrogen but it doesn't know that much that it makes any difference.
This is in contrast, for example, to zinc which is a common contaminant of coolant water. Where the body knows about zinc it grabs it up avidly. It takes it out of the intestinal tract contents and has enzyme mechanisms to do just that because zinc is an essential element and we have to have it in our bodies all the time. In that situation the concentration of zinc in the body of a person drinking the water or eating a food or whatever that contains the radionuclide may be much higher than would be present in the food or the water that they drink. So that is the difference with tritium which in effect works to reduce the hazard from it.
For all these reasons tritium is sometimes said to be one of the least harmful radionuclides among all those potentially reaching the worker or the public from the nuclear cycle. I believe, however, that current evidence indicates that the harmful effects of tritium ingestion are somewhat greater than the standard view indicates, especially for effects on the foetus in pregnant women who are exposed.
Mr. Schwartz: Could you tell us what evidence you are referring to and help define the phrase, "somewhat greater," for us?
Dr. Radford: First, with regard to the relative effectiveness of this very weak beta, there is now experimental evidence, both in terms of changes in the developmental effects on foetuses in utero in animals and also in studies of cancer induction, that suggest that tritium has somewhat more effect. How much more? Four or five times more effective than would be predicted just on the basis of its energy alone. It has what we call an RBE [a "relative biological effectiveness" factor] of about four or five. So that factor has to be borne in mind.
There is another more subtle factor which may or may not be very practically important -- and I want to emphasize that. It goes to the question of what I will call "pulse labelling" with tritium.
We have the case of a water supply. The people drink it and pretty soon their tritium level is the same as in the water. I have already explained that. It may be very low and unimportant. But let's take the case of sending a burst -- a high concentration -- of tritium out into a lake or river somewhere. That burst now goes into the water supply and is drunk by people.
On the classical model it wouldn't make any difference: it would just be averaged out over the time. But there is one special case that I think is important.
What if a woman is in the early stages of pregnancy and the child is a girl -- 50 per cent chance? That woman is going to be laying down her ova in the uterus at the time that slug of tritium comes in. Now the DNA of the ova will be labelled with the level of concentration of tritium that is appropriate at that time, within a day or two or three, rather than averaged over a longer time. As far as we know that tritium that is laid down in the DNA of the ova of that developing girl will remain for her whole reproductive lifespan. There is no exchange of that type of hydrogen. It is a very different kind of hydrogen as far as the body is concerned. Most of the hydrogen in our body exchanges readily with tritium.
Mr. Nixon: So those nuclei could (inaudible) with tritium and not with hydrogen?
Dr. Radford: They will have tritium in them as long as that girl is alive. After she is born the tritium is still there, it is hung on to. That hydrogen is held very tightly, in contrast to most hydrogen. Therefore, the probability is that that tritium will decay at some time during the reproductive period of that girl. Under those circumstances the concentration of tritium in that particular, very small compartment of the body of that woman is much higher than one would predict on the basis of the classical models.
Again I come back to the point that this is perhaps more a theoretical concern than a practical one because pulsing out of large volumes of highly tritiated water is not a common practice, I would guess.
Ms. Gigantes: It just happened in Pickering.
Dr. Radford: How about that? It is not common, but it can happen. At least on theoretical grounds, that might be a cause for concern; namely, you now have, you might say, a time bomb sitting in the DNA of that ovum.
Mr. Nixon: The pulse that produced the pollution level that Ms. Gigantes mentioned to you when she was talking about the specific level.
Dr. Radford: I'm sorry, what is the question?
Mr. Nixon: Referring to a pulse that we just had, it produced a level of tritium pollution, if I can call it that, that was referred to by Ms. Gigantes in her specific question.
Ms. Gigantes: Eighteen thousand curies.
Dr. Radford: What was the concentration in the water? That is the item that's important.
Ms. Gigantes: It certainly raised the drinking water readings. I don't have a drinking water reading associated with that specific pulse. There is an average for the first four months of the year and this happened in February.
Dr. Radford: This is one theoretically possible circumstance in which averaging over a year, or two, or ten, is not necessarily giving the full health impact of pulsing out a lot of tritium all at once. Whether this happens as a practical matter I leave to others to discuss.
Mr. Nixon: You may be sure that it will be discussed.
Dr. Radford: Have I answered your question, Mr. Schwartz?
Mr. Nixon: I will wait until the next sentence to ask the next questions.
Dr. Radford: I discussed the foetus. Moreover, because tritium is more difficult to contain at the source than other radionuclides, especially during nuclear fuel reprocessing, vigilance is warranted in keeping exposures adequately low to the general public.
Mr. Nixon: My question there is for you to define for us what "adequately low" means.
Dr. Radford: As I say, for now I am perfectly satisfied with 10 picocuries per millilitre [370 becquerels per liter]. In other words, if the body of water is big enough to dilute it and it is kept at that level, I see no real public health problem. If it goes above that by a substantial amount, then there may be a problem.
Mr. Nixon: I am sorry to keep coming back to numbers, but what is "a substantial amount" above that in your mind? When would we be concerned that we are getting into a public health problem?
Dr. Radford: Ten times that [3700 becquerels per liter].
The Health Dangers of Uranium Mining
and Jurisdictional Questions
published in August 1980 by
The British Columbia Medical Association
LD-50 = "lethal dose 50 percent" = dose required to kill half of the individuals exposed within 48 hours.
In the case of LD-50 for oocyte exposure, it is the death of oocytes that is in question, not the death of animals.