Tritium Hazard Report:
Pollution and Radiation Risk from
Canadian Nuclear Facilities
By Dr. Ian Fairlie

June 2007

1

2

PREFACE
This report on tritium releases in Canada is in two parts. Part 1 discusses tritium discharges
from nuclear facilities in Canada and compares them with those from reactors in othercountries. It examines the resulting tritium concentrations in drinking water, air and in foodnear Canadian nuclear stations. Although tritium releases from Candu facilities are very large,
radiation protection regulators continue to maintain that these releases are of little concern
because tritium’s radiation doses and its resulting hazards are small.
Part 2 examines these contentions in considerable detail. It shows that tritium’s radiation“doses” are, questionably, estimated to be several hundreds of times lower than most otherradioactive elements.
Radiation and radioactivity (including risks, doses, biology and epidemiology) are complex
matters which are often difficult to grasp. Therefore Part 2 is designed to be read primarily byhealth physicists and radiation protection scientists. However, efforts have been made to
make this report more accessible to the wider public. In particular, technical terms have been
explained and scientific jargon has been avoided.
The report concludes that official attitudes on tritium are unscientific and incorrect, that
tritium’s hazardous nature should be fully acknowledged by radiation protection agencies in
Canada, and that tritium’s dose coefficient should be increased substantially.

3

ACKNOWLEDGEMENTS
The author wishes to thank the Canadian Nuclear Safety Commission (CNSC) for its kindpermission to reproduce two figures from their report, Tritium in the Canadian Environment:
Levels and Health Effects. Report RSP-0153-1. Prepared for the Canadian Nuclear Safety
Commission under CNSC contract no. 87055-01-0184 by Ranasara Consultants and Richard
Osborne. The author wishes to acknowledge that the approach used in chapters 5 to 8 below
is adapted from that used in the CNSC report. However the dosimetric conclusions in thepresent report differ considerably from those in the CNSC report.
The author thanks Norm Rubin, Shawn-Patrick Stensil, David Martin, Jake Torrie and thelibrarians at the Scitech department of the British Library for helping to obtain references. The
author also thanks a number of scientists who have provided insights and help in theirreviews of drafts of this report, but who wish to remain anonymous.
Any mistakes, of course, remain the sole responsibility of the author.
Dr Ian Fairlie
LondonUnited Kingdom
May 2007

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EXECUTIVE SUMMARYPart 1 examines the high tritium discharges from Canadian nuclear power stations, which areconsiderably larger than those in other countries. Canadian tritium discharge limits are muchless stringent than those in other countries. Canadian tritium limits in drinking water are
considerably more lax than those in force in Europe and the US.
Those Great Lakes with nuclear reactors on their shores have tritium levels 2 to 5 times greaterthan those of Lake Superior, which has no reactors. The tritium level in Lake Ontario isincreasing each year, due to discharges and to major tritium leaks in past years from Candu
stations.
Tritium concentrations in drinking water, in air, and in vegetation and food near Candu stations
are all significantly increased. These result in high tritium intakes in residents living within 5 to 10
km of Candu reactors and very high tritium intakes in residents who live within 1 to 2 km.
However, because of tritium’s very low dose factors, the radiation “doses” to those exposed areconsidered insignificant and are declared “within safety limits” by nuclear regulators.
Part 2 examines the science on tritium’s doses. It finds that significant objections have been
made in the past to tritium’s official dosimetry and the official models used to estimate tritium
doses, especially from organically bound tritium. A number of recent UK and US reports
continue to raise questions about tritium’s official doses.
The report concludes that scientific concerns about tritium's hazards are inadequately
recognised by Canada's nuclear regulators. It therefore recommends that a precautionary
approach to tritium discharges should be adopted in Canada. In particular, it recommends
that:1) the Ontario and Federal governments should establish a committee (whose members
should include scientist representatives from environmental groups) to examine
tritium's dosimetry and risks. In particular, the committee should examine recent
authoritative reports which raise questions about currently-accepted views on tritium's
dosimetry and risks;
2) case-control and cohort epidemiology studies should be commissioned to examine
possible adverse health effects in tritium-contaminated areas;3) pregnant women and young (less than 4 years old) children and their mothers should
be advised not to live near tritium-emitting facilities (i.e., within 10 km);4) people who live very near (i.e., within 5 km) tritium-emitting facilities should be
advised not to consume food from their own gardens, bee hives and orchards, andnot to consume wild foods, e.g., blackberries and mushrooms, growing very near thefacilities;5) because tritium reduction facilities themselves release large quantities of tritium,
nuclear reactor operators should be requested to examine the option of long-term
storage of tritiated water from moderator circuits in decay tanks as a way of reducing
tritium discharges; and6) operators of tritium-emitting facilities should give further consideration to other ways
and means of reducing tritium releases.

5PART 1: TRITIUM RELEASES IN CANADA
Chapter 1 INTRODUCTION ..................................................................................................6
What is tritium? ..................................................................................................................7
Organically bound tritium (OBT) ........................................................................................8
Chapter 2 TRITIUM RELEASES IN CANADA.......................................................................9Tritium Releases Compared ............................................................................................10
Why do heavy water reactors discharge large amounts of tritium? .................................10
Tritiated Water Vapour Emissions to Air ..........................................................................11
Tritium - Liquid Water Discharges....................................................................................11
History of Tritium Inventories of Candu Reactor Circuits .................................................12
Problems with High Tritium Concentrations.....................................................................13
Can Tritium Releases be Reduced? ................................................................................15
Chapter 3 TRITIUM DISCHARGE LIMITS ..........................................................................16
Chapter 4 TRITIUM LIMIT IN DRINKING WATER ..............................................................18
Only one year’s exposure assumed.................................................................................18
Ontario Government’s ACES Report (1994): A Sorry Episode ........................................19
Chapter 5 TRITIUM CONCENTRATIONS IN THE GREAT LAKES ....................................20
History of Tritium Leaks into the Great Lakes..................................................................21
Chapter 6 TRITIUM-IN-AIR CONCENTRATIONS NEAR NUCLEAR STATIONS...............22
The real background level of airborne tritiated water vapour ...........................................24
Historical trends ...............................................................................................................24
Chapter 8 HOW MUCH TRITIUM DO PEOPLE TAKE IN? .................................................28
Are these levels hazardous? ...........................................................................................32
Chapter 9. ARE HIGH TRITIUM LEVELS HAZARDOUS TO HEALTH? ...............................33
Recent Reports................................................................................................................34
Would increasing tritium’s dose factors make a difference? ............................................34
Occupational doses .........................................................................................................35
Epidemiology ...................................................................................................................35
Chapter 10 CONCLUSION and RECOMMENDATIONS.....................................................36
REFERENCES in Part 1 .....................................................................................................37
Annex 1. Carbon-14................................................................................................................42
Annex 2. Wind Frequencies for Darlington and Pickering.......................................................43
Annex 3. Tritium Releases from SRB Technologies, Pembroke Ontario.

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Chapter 1

Introduction

What is tritium?
Tritium is the radioactive isotope of hydrogen, the smallest and lightest element. It has aradiological half-life of 12.3 years and decays to the stable isotope helium (3He), emitting a beta
particle (and a neutrino). The beta particle has a maximum energy of 18.6 kilo electron volts(keV) (average energy of 5.7 keV) with a short range—a few centimetres in air, 0.9
micrometers (µm) in water, and about 0.6µm in tissue. This means that tritium is notdangerous externally, but it is an internal radiation hazard when inhaled, or ingested via foodor water, or absorbed through the skin. Tritium is the most commonly encountered andimportant beta-emitting radionuclide.
Tritium has always kindled much interest among scientists and has been widely studied in the
past: see Appendix 1 to Part 2 of this report, NCRP (1979), NEA (1980), ACRP (1991), and
CCNR, http://www.ccnr.org/tritium_1.html. More recent studies on tritium can be found invarious reports and websites. For example, see the following:• US Environmental Protection Agency website on tritium,
http://www.epa.gov/radiation/radionuclides/tritium.htm (accessed February 26, 2007)• The report by Richard Osborne (2002), Tritium in the Canadian Environment: Levels and
Health Effects. Report RSP-0153-1. Prepared for the Canadian Nuclear Safety
Commission under CNSC contract no. 87055-01-0184 by Ranasara Consultants andRichard Osborne• A tritium report by the US Agency for Toxic Substances and Disease Registry
http://www.atsdr.cdc.gov/hac/PHA/livermore4/lms_toc.html• A forthcoming report on tritium by the UK Government’s Advisory Group on Ionising
Radiation http://www.hpa.org.uk/radiation/advisory_groups/agir/index.htm
Tritium is discharged in two main forms. In its elemental form (HT), it is an invisible, odourlessgas chemically identical to hydrogen gas. In its water form (i.e., tritiated water, or HTO), it ispractically indistinguishable from ordinary water. In fact, it is useful to think of tritium asradioactive water because this is by far its most common form. Tritium releases from Canadian
nuclear plants are mostly tritiated water; the tritium recovery facility at Darlington emits tritiumgas (HT).
Both forms of tritium are very radioactive (in technical terms, they have high specific activities).
One gram of HT contains about 360 terabecquerels1 (TBq) of radioactivity, and one gram of
HTO contains about 55 TBq2 of radioactivity. Both forms of tritium are very pervasive; HTpermeates most materials, rubber and many grades of steel with relative ease, and HTO—being
chemically identical and physically similar to ordinary water—very rapidly mixes throughout theatmosphere, hydrosphere, lithosphere and biosphere, in short, everywhere. HT is converted to
HTO in dry indoor conditions at the rate of about 1% per hour—faster in humid conditions. It isreadily converted to HTO by bacteria in soil.
Tritium has a number of unusual properties apart from its rapid distribution throughout theenvironment. One is its property of exchanging rapidly with other H atoms in the environment—
129,800 curies (Ci) in old units
1,500 Ci in old units

7

including in humans. Another is its propensity to form strong bonds with carbon to form
organically bound tritium (OBT) during metabolic reactions and in cell reproduction (see box
below).
Organically bound tritium (OBT)OBT is tritium which has become chemically attached to carbon atoms3 in organic molecules.
Organic binding is tritium’s most significant property, but, unfortunately, official dose models
for OBT underestimate its hazards.
Humans can accumulate OBT in two ways. The first is by consuming OBT in food, e.g.,vegetables, wheat, honey, milk, that has been grown and harvested in areas near Candu
reactors contaminated by tritiated water vapour. The second is by drinking/eating, breathing,
and absorbing tritiated water that then is then both metabolised into organic moleculesneeded by the body, and incorporated into new cells.
OBT is more problematic than HTO for two reasons. First because OBT’s residence time (i.e.,
half-life) in humans is much longer (20 to 50 times) than HTO’s residence time (see Part 2 ofthis report). And second because OBT must by definition be located near organic molecules(such as DNA) more often than HTO. As stated by Taylor et al (1990) ”... the concentration of
OBT in tissues of interest, are greater by up to an order of magnitude after ingestion of OBT
than after HTO ingestion...”. This means that radiation exposures from OBT are much larger
than that from HTO.
Like most radionuclides, tritium is a carcinogen, mutagen and teratogen. Many scientists haveexpressed concerns about tritium’s radiotoxicity (see Appendix 1 of Part 2). However, someradiation authorities continue to assert, rather misleadingly, that tritium is a “weak” radionuclide
because the energy of its decay particle is very low. However, paradoxically, in radiation biology
the weaker a particle the more effective it becomes. Unfortunately this remains unrecognised in
official circles and tritium’s official dose factor (i.e., the dose given by the disintegration of one
atom of tritium) is currently very small. Indeed, it is the lowest among common radionuclides bysome margin. There are many questions about tritium’s official radiation doses: these areconsidered in detail in Part 2.
Tritium is naturally formed in the upper atmosphere by cosmic rays. The quantity of tritium thus
produced each year is ~ 7.4 x 104 TBq (Luykx and Fraser, 1986). In Western developed
countries in the early 1980s, the annual amounts released by civil nuclear power andreprocessing facilities (Masschelein and Genot, 1983; NEA/OECD, 1980) were about the sameor higher. These will have increased since then to exceed tritium’s natural production rate.
In addition, much larger amounts of tritium are released from military activities. Between
1954 and 1962, atmospheric weapons testing released extremely large amounts of tritium—
1.6 x 108 TBq, almost all in the northern hemisphere (UNSCEAR, 1988). By 2007, this will
have decayed about 16-fold. In addition, at the height of the cold war in the 1970s and 1980s,
annual tritium discharges from nuclear weapons manufacturing amounted to 2.8 x 106 TBq(Jaworowski, 1982). This included the US nuclear weapons plants at Savannah River and3

Another form of OBT is tritium that attaches to O, P, N and S atoms. These bonds are weaker than C-H bonds
and their average half-life is shorter (about 30 days) than that of tritium bound to C atoms (1 to 2 years). This isexchangeable OBT and is discussed in Part 2.

8

Hanford, which annually emitted on average 1.1 x 105 TBq (NCRP, 1979) in the 1950s to the
1980s.
Chapter 2

Tritium Releases In Canada

Most tritium releases in Canada are from Candu nuclear power generating stations, as shownin the following tables. In addition, substantial tritium releases occur from the SRB
Technologies facility in Pembroke, Ontario, which are reported in Annex 3 below. This facility
manufactures tritium-containing emergency lighting equipment.
Tables 2.1 to 2.4 reproduce recent releases of tritium from Candu nuclear stations.
Table 2.1 Recent emissions of tritium oxide (HTO) to air (TBq/a)
2001
2002
2003
2004
Bruce A + B
650
580
560
864
Pickering A + B
580
510
480
620
Darlington
240
190
170
280
Gentilly-2
190
180
150
260*
Point Lepreau
140
130
100
100*
TOTALS
1800
1590
1460
2120

2005
731
500
130
180*
180*
1720

*estimated reading from graphs

Table 2.2 Recent discharges of tritium oxide (HTO) to water (TBq/a)
2001
2002
2003
2004
2005
Bruce A + B
163
414
860
585
426
Pickering A + B
280
427
258
290
260
Darlington
94
69
100
160
220
Gentilly-2
450
500
350
120*
360*
Point Lepreau
150
140
81
100*
220*
TOTALS
1187
1410
1649
1250
1490
*estimated reading from graphs

Table 2.3 Air releases of elemental tritium (HT) (TBq/a)
2001
2002
2003
Darlington
108
56
66

2004
750

2005
790

Table 2.4 Canada—Total tritium released (TBq/a, rounded to 3 figs)
2001
2002
2003
2004
2005
HT
110
56
66
750
790
HTO to water
1190
1410
1650
1250
1490
HTO to air
1800
1590
1460
2120
1720
TOTALS
3100
3100
3200
4120
4000
Sources: NPRI, 2004, 2003, 2002.
OPG and Bruce Power annual environmental reports—OPG (2006) and Bruce Power (2006).

9

In Table 2.4, the figures for HT and HTO have been added together to arrive at total tritium
releases, although their dosimetric impacts are different. This matter is discussed further
below.
From the above tables, it can be seen that the total amount of tritium released by major
nuclear facilities each year in Canada is of the order of ~3,000 TBq. This is about 10% of thenatural production of tritium in the northern hemisphere of ~30,000 TBq per year. (Relatively
little mixing occurs between the atmospheres of the northern and southern hemispheres).
Tritium releases from reactor types compared
Tables 2.5 and 2.6 below compare tritium releases from various reactor types. It can be seenthat heavy water reactors emit considerably more tritium than other reactors, whether total
discharges or normalised discharges (i.e., per GW year of electricity produced) are compared.
Table 2.5 Tritium (HTO) releases (gaseous + liquid) from various reactor types (TBq/a)
Reactor TypeUNSCEAR 1993 Reactor TypeUNSCEAR 2000
(for year 1985)(for year 1997)
HWR
600
HWR
660
(Bruce 1-4, Canada)(Bruce 1-4, Canada)
PWR
17
PWR
55
(Diablo Canyon 2, US)(Diablo Canyon 1+2 US)
AGR
12
AGR
18.7
(Hinkley Point B, UK)(Hinkley Point B, UK)
BWR
2
BWR
1.6
(Wurgassen, Germany)(Philippsburg, Germany)
Table 2.6 Normalised tritium (HTO) releases (gaseous + liquid) from various reactor types(TBq per GW year)
OECD/NEA UNSCEAR 2000
European
Sood et al,
1980
Table 37
Commission
19904
for years 1995–1997 for year 1999
HWR
750
670
650
PWR
37
21.4
20
BWR
7
1.7
1.3
Sources: OECD/NEA (1980); UNSCEAR (2000); EC (2000).

Why do heavy water reactors discharge large amounts of tritium?
Heavy water reactors discharge far more tritium than other reactor types because—as theirname suggests—they use heavy water (deuterium) as coolant and moderator. During reactor
operation, deuterium is activated by fission neutrons to form tritium via the following reaction:2

H + neutron -> 3H

4

Sood et al (1990) stated that 1.35 GWe in Ontario nuclear power stations produce 0.88x104 TBq of tritium on
average per year.

10Other reactor types use different materials as coolant and moderator; for example, PWRs and
BWRs use ordinary water and AGRs use CO2 and graphite as coolant and moderator
respectively. In these other reactor types, tritium is formed mostly as a tertiary fission product;i.e., it is split off from U-235 and Pu-239 when they undergo fission. This occurs within Candu
reactors as well: the H-3 activation rate in Candu reactors is about 1,000 times greater thanthe H-3 fission product rate.
Tritiated water vapour emissions to air
When a reactor is in operation, tritium is continuously formed and continuously released to theatmosphere in the form of radioactive water vapour. Contrary to what many people assume,
few tritium air emissions are via a stack or chimney; most are via the continuous leakage oftritiated water vapour from machines, pumps, seals, pipes, reactor walls, etc. That is, tritiatedwater vapour literally oozes out of practically every surface, nook and cranny of the reactor
building.
The volumes of heavy water in Candu nuclear reactors are very large, more than 3 million
litres (3,000 tonnes) each at Pickering, Darlington and Bruce stations. In addition,
considerable efforts have to be expended to keep water (whether tritiated or not) at hightemperatures and pressures from escaping from the pipe work, especially of the cooling
circuits. The result is that heavy water losses from the cooling water circuits in Candu reactors
are very large—about 3% of their inventory per year. Heavy water losses from the moderator
circuits inside the reactor are lower, at about 0.1% of their inventory per year, mainly because
the circuits are smaller and are mostly inside the reactor, i.e., leaks are potentially
recoverable (data from Song et al, 1995).
Although most heavy water releases come from the coolant, most (~2/3rds) of the tritium
releases are from the moderator because its tritium concentrations are considerably higher(~20–30 times) than those in the moderator.
Tritium—liquid water discharges
Liquid water discharges to the Great Lakes from Candu stations largely result frommaintenance operations, that is, from opening pipes, valves, seals, etc., which inevitably
result in spillages and discharges. With both vapour emissions and liquid water discharges,
efforts are made to trap and retrieve the lost amounts and re-use them in their respective
circuits, but large amounts are still lost and released as emissions and discharges.
The amount of heavy water which escapes from a single Candu 6 reactor is surprisingly large—about 4,000 litres per year (Song et al, 1995). About 90% leaks from the coolant and ~10%from the moderator. Therefore, about 32,000 litres of heavy water escape (via vapour
emissions) each year from Pickering when its eight 500 MW reactors are all operating. Thismeans that every day about 100 kg of heavy water in vapour form is released from the
Pickering station on average, though there are fluctuations. By extrapolation, it is estimatedthat the Bruce station, with eight 750 MW reactors, will emit about 150 kg each day, and thatthe Darlington station, with four 850 MW reactors, will also release about 100 kg of heavy
water each day when all its reactors are operating.

11Tritium—HT gaseous emissions
The Darlington Tritium Recovery Facility and the SRB Technologies plant at Pembroke
Ontario (see Annex 3) emit very large quantities of tritium in the form of hydrogen gas or HT.
HT has very different dosimetric properties from tritiated water. The International Commission
on Radiation Protection (ICRP) considers that HTO’s doses from inhalation and ingestion are
25,000 times greater than those for HT (ICRP, 1989)5. This is because the body is notthought to absorb or metabolise hydrogen gas, whereas water is a vital component of all bodytissues and metabolic processes. Therefore the important factor is how fast HT is converted(oxidized) to HTO. This had been the subject of differing views in the past (Sweet and Murphy
1984, and Spencer and Dunstall 1986). However, nowadays it is understood that HT
dispersed into the atmosphere diffuses readily into the soil and is converted to HTO by
enzymatic reactions, the rate of which depends on the porosity, water content and microbialactivity of the soil. The converted HT is subsequently transported as HTO (Ichimasa, 1995).
Generally, for conservatism in assessments, released tritium is often assumed to be in theform of HTO, as eventually almost all HT will be converted to HTO over longer time periods.
(Davis et al, 1997).
History of tritium inventories of Candu reactor circuits6
Because of continuous neutron activation, tritium concentrations in both moderator andcoolant steadily increase during each year of operation. This results in tritium releases
increasing each year after start-up, as shown in Figure 2.1 below, reproduced from Song et al(1995).
Figure 2.1
Tritium Release Rates at Candu 6 Reactors

Curies per year

20000
15000
Pt Lepreau
10000

Gentilly-2
Wolsong-1

5000
0
1

2

3

4

5

6

7

8

8 10 11 12

Operating Year

Tritium concentrations continue to rise in each year of operation in both moderator andcoolant circuits until equilibrium levels are reached (where possible). Equilibrium means the5More precisely, the maximum derived air concentration for HTO is 25,000 times greater than that for HT.
This section on tritium reactor inventories is partly based on information contained in an article discussing the
Candu 6 reactor in Wolsong, South Korea (Song et al, 1995). The article states that, as all Candu 6 reactors are
generically similar, their tritium characteristics during operating periods are also very similar.

612

rate of creation is equal to the rate of elimination. However, until 1990 there were only two
mechanisms which decreased tritium concentrations: one was tritium’s radioactive decay,
which reduces its concentration by about 5% per year, and the other was by leakage (in otherwords, discharges and emissions) and by the replacement of leaked amounts with nonradioactive heavy water. The latter mechanism was more important. However these two
mechanisms were slow in comparison with tritium activation rates in moderator and coolant
circuits. The result was that, in the case of the coolant, equilibrium was only approached after
about 30 years’ operation (90% of equilibrium level reached after ~27 years (Song et al,1995)). In the case of the moderator, the tritium activation rate was so high that equilibrium
was never reached.
This meant that the tritium production rates in Candu reactors were extremely large. Indeed,
Ontario Hydro engineers (Sood et al, 1990) stated that Ontario Hydro’s (as it was then called)
20 reactors would produce 8,800 TBq of tritium per year on average over the next 30 years.
The continuous increase in tritium inventories results in continuous increases in tritium
discharges and emissions and this can be seen from the following table of tritium releases
from Ontario Power Generation (formerly Ontario Hydro) nuclear plants.
Table 2. 7 Tritium releases from Candu reactors after start-ups (TBq/a)YEAR
HTO (to air)HTO (to lakes)
TOTAL
1972 {1}
530
40
570
1973
1,400
190
1,590
1974
920
540
1,460
1975
760
390
1,150
1976 {2}
940
221
1,161
1977
1,944
736
2,680
1978
1,460
1,353
2,813
1979
2,550
1,950
4,500
1980
2,280
1,370
4,650
1981
3,980
1,020
5,000
1982
2,180
1,340
3,520
1983 {3}
4,504
1,966
6,470
1984 {4}
2,979
1,018
3,997
1985
2,108
2,815
4,923
1986
2,506
2,397
4,903
1987
3,428
3,343
6,771
1988
3,758
3,425
7,183
1989
4,436
2,638
7,074
1990
3,311
1,980
5,291
Sources: AECB (1990), Ontario Hydro (1990), Ontario Hydro (1991).
{1} Pickering A started.
{2} Bruce A started.
{3} Pickering B started.
{4} Bruce B started.

Problems with high tritium concentrations
These increasing tritium concentrations caused considerable problems in the past. An
important problem was the increasing exposures to radiation to operators, from ingestion and13inhalation of tritiated water vapour. There also were problems with radiation degeneration ofseals, resins and filters, resulting in increased shutdowns and lower capacity factors. In
addition, in the late 1980s, the emissions caused high levels of tritium contamination at the(then) Ontario Hydro laboratories adjacent to the Pickering plant. This resulted in incorrect
tritium measurements at the laboratory. In the end, the labs had to be closed and moved
further away from the reactors.
There were environmental concerns too: in the early 1980s, Environment Canada grewalarmed at the large and growing discharges of tritium (see Finlay et al, 1982). Their studies
showed that, without a facility for reducing tritium concentrations (then in design stage), tritium
release rates would increase each year of operation (Environment Canada, 1986: see pages
195–197). The resulting code of practice (Environment Canada, 1986) pointed to several
technologies for reducing tritium emissions in addition to a tritium reduction facility. This
included proposals for the withdrawal and storage in tanks of moderator heavy water to permit
the decay of tritium. However, the draft code’s proposals were opposed by the nuclear
industry and the AECB, and were not implemented (Ottawa Citizen, 1984; Toronto Star,
1984).
The nub of the problem was the very high tritium concentrations in the coolant and particularly
the moderator. Before 1990, the only active way to reduce these was to release contaminatedheavy water and replace it with tritium-free heavy water, but this meant higher tritium
discharges. To allow the continued operation of the reactors, in early 1990 a tritium reduction
facility (TRF) at Darlington was started up which extracts tritium from tritiated heavy water.
This was licensed from the French Atomic Energy Commission and stems from a Swiss design.
In this facility, tritium atoms on water molecules are transferred to deuterium gas molecules bymeans of catalytic exchange at 200°C. Then the tritiated deuterium (i.e., tritium gas) is separated
from deuterium gas by cryogenic distillation at -250°C and then stored.
Ontario’s reactors contain ~10,000 tonnes of moderator and coolant heavy water. It takes anumber of years for this large inventory to be treated once through at the TRF. The theoreticalmaximum design flow rate of the TRF is 360 kg per hour (Sood et al, 1990 page 366). Assuming
this maximum rate, 24 hours per day for 365 days, it would take over 3 years to put the 10,000
tonnes at Bruce, Pickering and Darlington through the TRF once. Each treatment reduces thetritium concentration by about 2/3rds. Under realistic batch-operating conditions, with shutdowns
for maintenance and repairs, it is estimated to take about 4 to 5 years to put the 10,000 tonnesof heavy water at Bruce, Pickering and Darlington once through the TRF. During this time, more
tritium would be created, therefore reducing the tritium concentrations in Ontario reactors is aslow process, and the TRF has to be run continuously to keep tritium concentrations at Bruce,
Pickering and Darlington from increasing.
Other problems are the estimated 4,000 truckloads per year to transport heavy water to andfrom Darlington, and the TRF’s own substantial high tritium emissions (790 TBq in 2005). In fact,
the TRF’s net contribution to reducing tritium discharges to the Ontario public is relatively small.
Its main function is to keep tritium concentrations in Ontario reactors low enough to permit theircontinued operation.

14

Can tritium releases be reduced?
In the 1980s, Environment Canada tried to persuade the then-OH and AECB to undertake anumber of technical steps to reduce tritium emissions. It is recommended that Environment
Canada’s suggestions in 1986 should now be reconsidered.

15

Chapter 3

Tritium Discharge Limits

Derived release limits (DRLs) are the amounts of a nuclide whose discharges are estimatedto result in the public dose limit of 1 millisievert (mSv) per year not being exceeded, tomembers of the most exposed group (critical group) living near nuclear stations. This is a
representative group of people thought to receive the highest doses: in some cases it will be atheoretical group. The dose is estimated by using computer models for environmental
transport and nuclide intakes in humans. However, there can be considerable uncertainty
about these dose estimates, as shown by the CERRIE (2004) report.
The limit applies to the sum of all man-made radiation exposures to the critical group, but the
DRL calculation is done on each nuclide individually, as if it were the only one released.
The Canadian Nuclear Safety Commission (CNSC, 2005) has stated “… to ensure that the
public dose limit is not exceeded, CNSC licences restrict the amount of radioactive materials
that may be released in effluents from nuclear generating stations (emphasis added). These
effluent limits are derived from the public dose limit and are referred to as derived release
limits (DRLs). In addition, the nuclear generating stations set operating targets that are asmall percentage of the derived release limits”.
However, as can be seen in the tables below, the DRLs for tritium are extremely lax. They arein the range of hundreds of thousands of TBq of tritium per annum, that is, hundreds of times
higher than actual discharges. Contrary to what the CNSC has stated above, its DRLs do not“restrict” the amounts actually discharged. In practice, nuclear stations are operated so thatthey actually discharge only a few percent of the DRLs.
Table 3.1 Derived release limits (DRLs) for tritium air and water emissions
Nuclear station Tritium (HTO) emissions Tritium (HTO) discharges
to air (TBq/a)to lakes (TBq/a)
Bruce-A*
88,00045,000Bruce-B
93,000600,000
Darlington
460,000 (HTO)
880,000
Darlington TRF
4,600,000 (HT)NA
Pickering-A
70,000170,000
Pickering-B
70,000170,000
Gentilly-2
440,000
1,200,000
Point Lepreau**
430,000
16,000,000
Data source: CNSC (2005).
*Liquid DRLs for Bruce A are based on one condenser cooling water pump operating.
Higher liquid DRLs apply for 2, 3, or 12 pumps operating.
** DRL for tritium in liquid releases at Point Lepreau is higher than for the other nuclear generating
stations, as the effluent is discharged to sea, i.e., there is no drinking water pathway.

16

TABLE 3.2 Combined limits for HTO (liquid and vapour) (TBq /year)
CountrySite
TBq /Year
CanadaPoint Lepreau
16,400,000
CanadaGentilly
1,640,000
CanadaDarlington
846,000
CanadaBruce
826,000
CanadaPickering
480,000
FranceBelgium
Germany
Netherlands
UKUK

per siteDoelper site
Borssele
Torness AGR
Sizewell PWR

1,800
100
70
30
20
8

Sources: Belot et al, 1996; Commission of the European Communities, 1988; FSA, 2006.

The central point revealed by this table is that the CNSC’s limits permit much greater
discharges of tritium in Canada than is permitted in Europe. For example, Canadian limits are
two to four orders of magnitude more lax than limits for nuclear reactors in European
countries. It may be argued that the above table does not permit proper comparisons because
electricity throughputs are not equalised, but we are looking at regulatory limits here andthese are based on health considerations, i.e., the total amounts released.
Given the disparity between European and Canadian limits, it is difficult to see how healthconsiderations have been applied in the two cases. These figures raise questions about
Canadian DRL limits.

17

Chapter 4

Tritium Limit in Drinking Water

Canada Health has had a long history of adopting soft standards on radioactive pollutants
compared to other pollutants, especially for tritium. For example, its former 1978 guidelines(Health and Welfare Canada, 1979) formerly recommended a very lax tritium limit of 40,000
becquerels per litre (Bq/L) for drinking water. Even then, it acknowledged that its limits forradionuclides were based on contested health risk estimates instead of the tighter concept ofminimum detection levels used for most other pollutants.
In 1980, the Porter Commission (1980) on electric power in Ontario requested a FederalProvincial Working Party to examine the question of radiological limits for drinking water. The
Working Party recommended a chronic (lifetime) maximum concentration of 4,000 Bq/L.
However, Canada Health and Welfare waited for another 14 years before it tightened the limit to
4,000 Bq/L in 1994.
The current Canadian Federal limit for tritium in drinking water is 7,000 Bq//L, which is verylax compared with the limits set by the European Commission and the US EPA. The current
US limit7 is 740 Bq/L, based on a maximum dose to the public of 40 µSv per year fromdrinking water.
In the US, the state of Colorado has set a stricter standard8 for tritium in surface water, of
18.5 Bq/L9. The US state of California uses a limit10 of 15 Bq/L. Both are based on a one-in-amillion lifetime risk of a fatal cancer, which is the goal of cleanup under the US
Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), morecommonly known as the Superfund.
Table 4.1 Tritium limit in drinking water (Bq/L)
AgencyCanada Health and Welfare
US EPA*
European Union**
Recommended by Ontario Government’s
ACES*** in 1994 but not implemented
US State of Colorado
US State of California

Tritium limit (Bq/L)
7,000
740
100
100 (initially)
20 (after 5 years)
18
15*EPA (1999).
**European Commission (1998).
*** Advisory Committee on Environmental Standards.

Only one year’s exposure assumed
The current Canadian Federal limit for tritium corresponds to a risk of 350 excess fatal cancers
per million people. On the other hand, the Canadian Federal drinking water objectives forchemicals are set at levels that provide a lifetime risk of 1–10 excess fatal cancers per million
7

20,000 picocuries per litre.
500 picocuries per litre.
9
For example, the US Department of Energy has specified the Colorado state action level for tritium in surface
water in its clean-up program at the Rocky Flats plutonium plant in Colorado.
10
400 picocuries per liter.
818

people. The primary reason for the difference is that the excess cancers predicted from radiation
exposure are calculated by assuming one year’s consumption of drinking water: the lifetime risk
is calculated as if that year of consumption were the only consumption. With chemicals, theassumption is that people consume the affected drinking water for their whole lifetime—commonly set at a 70-year exposure. Why such a difference should exist is strange—it’s anotherexample of the apparently favoured status of radiation in Canada.
Ontario Government’s ACES report (1994): A sorry episodeIn 1992, the Ontario Government requested its Advisory Committee on Environmental
Standards (ACES) to enquire into this issue for setting an Ontario drinking water standard fortritium. It reviewed the above differences in approach to standard setting, and its report(ACES, 1994) concluded that it was inappropriate to assume only one year’s consumption in
calculating the fatal cancer risk.
At the time, 7000 becquerels per litre (Bq/L) for tritium had been proposed as a Federal
drinking water guideline. ACES advised that in order to estimate the risk rationally and make itcomparable with the approach used for chemicals, the 7000 figure should be divided by 70
years.
In addition, ACES recommended that the 7000 Bq/L limit should be further divided by 5
because the limit had relied on a risk of 5 fatal cancers per million persons being acceptable,
when the more acceptable risk was 1 in a million. ACES thus arrived at its recommended
figure of 20 Bq/L (i.e., 7000/350). However, ACES acknowledged that Ontario Hydro wouldfind that meeting this limit immediately was not possible without shutting down the reactors,
and it therefore suggested a less strict limit of 100 Bq/L for a 5-year period for Ontario Hydro
to prepare for the new limit.
ACES also reviewed the history of creation of tritium exposure from human activities. It notedthat routine releases of tritium from CANDU nuclear generating stations are among theworld’s largest sources of tritium. ACES agreed that tritium exposures should be reduced tobackground levels and therefore advised that the drinking water standard should be set at
100 Bq/L immediately, with a five-year phase-in period to 20 Bq/L. This was to give Ontario
Hydro time to put into place any additional measures needed to reach a 20 Bq/L standard.
ACES noted that neither standard should be a problem in any event, given that the averagelevels at drinking water intakes nearest the nuclear generating stations were generally belowthat level. ACES also acknowledged that one water intake—Port Elgin—was a problem.
The ACES report in May 1994 was welcomed with over 2,000 letters of support, but Ontario
Hydro alleged that the ACES-recommended standard would cost billions to implement. In
December 1994, the Provincial Government deferred to Hydro’s views and announced astandard of 7,000 Bq/L, to widespread criticisms by environmental groups. This sorry episodefor Ontario’s environment is described in more detail by McMullan and Eyles (1999).

19

Chapter 5

Tritium Concentrations In The Great Lakes

As explained in Chapter 1, tritium is formed naturally in the upper atmosphere from thebombardment of cosmic rays. In addition, residual concentrations of tritium remain fromatmospheric bomb testing in the 1950s and 1960s. The resulting background tritium level11 in
Lake Superior (which has no nuclear facilities) was 2 Bq/L in 1997/1998 (King et al, 1998).
This is commensurate with background levels throughout Canada (i.e., very remote from
nuclear facilities). Therefore this can be taken as a background level12 for all the Great Lakes.
However, the four Great Lakes other than Lake Superior have higher tritium levels resulting
from nuclear discharges, as shown in Table 5.1. It can be deduced from this table that, on
average, a third of present tritium levels in Lakes Huron, Erie and Ontario result frombackground and two-thirds from nuclear discharges.
Table 5.1 Average tritium concentrations in the Great Lakes in 1997/98
Average tritium
concentration (Bq/L)
Lake Superior
2
Lake Michigan
3
Lake Huron
7
Lake Erie
5.5
Lake Ontario
7.1
Sources: King et al (1998, 1999).

As the Canadian background tritium water concentration is 2 Bq/L, tritium levels in Lakes
Huron, Erie and Ontario have been elevated 2 to 5–fold by tritium discharges, mostly from
Canadian reactors.
The same is true of tritium levels in Ontario drinking water; these have also been increased 2
to 5 times by tritium discharges. From Ontario Ministry of Labour and Ministry of theEnvironment data (reported in Health Canada, 2006), the average tritium concentration inover 3,000 drinking water samples across Ontario was between 5 and 10 Bq/L during 2000–
2006. Many of these samples will have been from lake supplies but some samples will havecome from wells13.
Near the Candu stations on Lake Ontario and Lake Huron, lake tritium concentrations arehigher than the above averages. For example, the Ontario Ministry of Labour and Ministry of
the Environment has observed tritium values of 120 Bq/L in drinking water at Southamptonand 24 Bq/L at Port Elgin, both near the outflow of the Bruce nuclear station. A high value of18 Bq/L was observed at the R.C. Harris water treatment plant near the outflow of the
Pickering nuclear station in Toronto. (data from Health Canada, 2006) (No dates, tables orfurther explanations given).
11

Tritium levels in the Great Lakes increased to about 20–30 Bq/L in the late 1950s and early 1960s as a resultof atmospheric atomic bomb testing. This has now mostly decayed to about 1 Bq/L and constitutes a part—
perhaps as much as a half—of background tritium levels.
12
It appears that there are no published average levels more recent than 1998.
13
It should be recalled that tritium in most wells will originate from tritium emissions to air and not tritium
discharges to lake water.

20

As a result of discharges from nuclear facilities, tritium concentrations in the Great Lakes aregradually increasing. Tritium is removed from the Great Lakes by radioactive decay,
sedimentation, and flushing (i.e., down the St Lawrence Seaway), but the annual amounts
added are greater than the annual amounts removed. Chant et al (1993) estimated that the
average tritium concentration in Lake Ontario was increasing by 0.12 Bq/L each year from
Candu operations. Since Lake Ontario contains 1,640 km³ (1.64 x 1015 litres) of water, thismeans a net increase of ~200 TBq each year, which is a large amount.
History of tritium leaks into the Great Lakes
In addition to routine releases to surface waters, significant groundwater and lake
contamination has occurred at Canadian nuclear facilities in the past.
• In 1979, tritium groundwater concentration reached 2.15 MBq/L following a release of
666 TBq at Pickering.
• In August 1983, a pressure tube at Pickering-2 ruptured due to embrittlement, dumping
an unspecified amount of coolant into the reactor building.
• In September 1983, a leak of 222 TBq of tritium occurred from the Douglas Point
reactor on Lake Huron. The prevailing counter-clockwise circulation pattern in the lake
carried the tritium plume northeast to Port Elgin, where drinking water levels reached1,600 Bq/L during a 2-day period.
• In January 1990, a loss-of-coolant accident at Bruce-4 resulted in a 12,000 kg leak ofheavy water into Lake Huron.
• In June 1991, following a leak from Chalk River Nuclear Laboratories into the Ottawa
River, the tritium concentration in drinking water at Petawawa was about 400 Bq/L. At
Ottawa (200 km downstream), the tritium level was ~150 Bq/L.
• In August 1992, a tube break at Pickering-1 caused the release of 2,300 TBq of tritium
into Lake Ontario. A nearby drinking water plant was shut down and elevated levels oftritium (up to 195 Bq/L) were found in Toronto drinking water.
• In May 1994, Ontario Hydro found a tritium groundwater concentration of 0.7 MBq/L
following a leak at Pickering.
• In December 1994, a valve failure at Pickering-2 led to 140 tonnes of heavy water
being discharged into Lake Ontario.
• In May 1995, a valve failure at Bruce-5 caused a 25-tonne leak of radioactive heavy
water.
• In April 1996, a heavy water leak at Pickering-4 released 50 GBq of tritium into Lake
Ontario: tritium levels in local drinking water reached 100 times background levels.
• In July 1997, it was revealed that Ontario Hydro (the predecessor to OPG) had failed toreport tritium contamination of groundwater on the Pickering site for a period of 20
years.
The raised tritium concentrations in drinking water, the continued rise in tritium levels in mostGreat Lakes, and the many spills of large quantities of tritium are all matters of concern. Thisis particularly the case for the health of women (see Bertell, 2005). As a matter of publichealth policy, it is unfortunate that discharges of tritium are made near drinking water intake
pipes for large populations in Ontario. At the least a more precautionary approach should be
adopted. Operators of tritium-emitting facilities should give further consideration to other ways
and means of reducing tritium emissions.
21

Chapter 6

Tritium-In-Air Concentrations Near Nuclear Stations

Raised tritium levels in drinking water are a serious matter, but raised tritium levels in air areeven more serious. This is because, near Candu stations, tritium exposures from skinabsorption, inhalation, swimming, and food ingestion (all contaminated by tritium water
vapour) are larger than tritium exposures from drinking water. The same is likely to be true forcollective doses from tritium in air and in water. For this reason, it is important to pay
particular attention to tritium-in-air concentrations near nuclear reactors.
The process of tritium intake
Tritium air emissions from Candu reactors are in the form of tritiated water vapour. This water
vapour travels downwind of the reactor and, via the (not widely known) process of atomic
exchange, tritium rapidly enters all material containing hydrogen. This includes all biota,
including all plants, animals and of course, people. For example, it enters fruit and vegetables
in market stalls and shops, including supermarkets (Inoue et al, 1993). Put succinctly, all biota
including humans become tritiated to the ambient levels in the environment (as shown in
Figure 6.1). The level of tritium contamination depends on tritium concentrations in water
vapour emissions from the reactors.
More worryingly, some of this absorbed tritium is fixed into carbon molecules during thegrowing season in plants, and in animals during cell reproduction and cell metabolism. This iscalled organically bound tritium (OBT) and is an important component of tritium exposures.
When there are repeated (i.e., chronic) exposures to tritium, as occur near nuclear reactors,
OBT concentrations gradually increase in all biota. After a few years, average OBT levels area significant fraction of tritiated water levels in Ontario sites near Candu reactors (Osborne,2002). Unfortunately, the ICRP and CNSC refuse to fully recognise these increases in OBT
concentrations from repeated exposures, in their dose models for tritium (see Part 2).
Tritium levels in water vapour in air
Tritium air concentrations are often expressed in Bq in air. However, we need to know theamount of tritium in the air’s water vapour. For example, if the air concentration is given as 1
Bq/m3 of air and the water vapour content in local air is ~10 grams per m3 (a representativevalue, see Davis et al, 1996) then people in the locality are breathing in and absorbing water
vapour with a tritium concentration of 100 B/L. This latter figure (i.e., the tritium
concentration in air’s water vapour) is the crucial parameter in estimating doses topeople living near Candu reactors.
Tritium concentrations in water vapour near nuclear stations depend on the distance from thestation. This is shown in Figure 6.1, reproduced with the permission of the CNSC from
Osborne (2002), using data from Health Canada (2001).

22

Figure 6.1 Annual averages of tritium concentrations in air measured at distances from
nuclear power stations in Canada, 1985–1999.

Sources: Tritium in the Canadian Environment: Levels and Health Effects. Report RSP-0153-1. Prepared for the
Canadian Nuclear Safety Commission under CNSC contract no. 87055-01-0184 by Ranasara Consultants andRichard Osborne. Data from Health Canada (2001).

A number of points need to be made here. The first is that the logarithmic scale of the Y- axis:
compresses the data range. Although this is needed for a table of manageable size, it isslightly misleading in that the range of concentrations appears not to be large. This is not thecase; for example, the highest air concentration here (30 Bq per cubic metre) is 3000 times
greater than the lowest (0.01 Bq per cubic metre).
A second point is that, as explained above, we need to know the tritium concentration in water
vapour and not in air. If we assume a reasonable value of 10 grams of water per cubic metreof air, then the tritium water vapour concentration 1 to 2 km from Pickering is 100 to 3,000
Bq/L. The latter is a high value.
Third is that the suggested background range (0.04 to 0.13 Bq/m3) at Ottawa is not free of
man-made tritium. Although Ottawa is 190 km from AECL Chalk River, the nearest reactor, it
still is subject to raised tritium levels because it is downstream from it. For example, AECL
(Neimi et al, 2002) has reported that discharges from Chalk River Laboratories to the Ottawa
River increased the tritium concentration from about 3 Bq/L to 10 Bq/L, 10–30 km downriver:there would have been slightly raised levels all the way to Ottawa. Also in June 1991, Health
Canada monitored the levels of tritium in the Ottawa River following a spill from Chalk River
Nuclear Laboratories. The concentration in drinking water at Ottawa (downstream) was about
150 Bq/L.
Fourth, Figure 6.1 indicates tritium concentrations in selected materials, and of course, ALLenvironmental materials are tritiated near Candu reactors. This includes water in rivers,
streams and drinking water in wells. Osborne (2002) has reported tritium concentrations
ranging up to 30 Bq/L in one well close to the Pickering station and about 60 Bq/L in seasonalwells close to the Bruce station. Concentrations of tritium in drinking water wells close to an
23unnamed “small tritium-handling facility” ranged up to 230 Bq/L, with most measurements
being less than 50 Bq/L.
Fifth it is useful to multiply the Y axis values by 100 and label it as tritium in water vapour inair. This shows that these values can rise to 3,000 Bq/L close to the Pickering station.
Finally, yet importantly, the data points are annual averages. Actual air concentrations willvary considerably, which is worrying as large pulses of tritium emissions may occur but theseare obscured by the publication only of average concentrations (and annual ones, as well).
Pulsed tritium concentrations could in theory result in heavy labeling of cells being formed in
the embryos and fetuses of pregnant women at that particular moment. This fear was
expressed by Professor E. Radford in his 1979 testimony to the Ontario Government’s SelectCommittee on Ontario Hydro Affairs (Hearings on The Safety of Ontario's Nuclear Reactors,
Tuesday, July 10, 1979, http://www.ccnr.org/tritium_2.html#scoha).
The real background level of airborne tritiated water vapour
It is important to know the true background concentration of airborne tritiated water vapour in
Canada, so that we can deduct this value from observed values near nuclear stations toestablish what concentrations are due to the discharges. The difficulty is that most tritium
measurements are made near nuclear stations and one has to be very remote, at least >300
km away, in order to escape from low levels of tritium contamination from nuclear stations.
Only a few tritium-in-air measurements are made very remote from nuclear facilities. One is in
Table 3.3 of the Bruce Power Group’s Annual Summary and Assessment of Environmental
Radiological Data for 2005 (Bruce Power, 2006). This shows that the average tritium
concentrations in precipitation at Calgary AB, Saskatoon SA, and Fredericton NB are all
below the limit of detection of the instruments used. This limit was 3.7 Bq/L, which points tothe air concentration14 being lower than 0.037 Bq/m3.
However, remote measurements in water (see Table 4.2) and in vegetation (see Table 7.1),
both of 2 Bq/L of water, give support to the view that the background level for tritium inatmospheric moisture in Canada is about 2 Bq/L of water, which translates to ~0.02 Bq/m3 ofair.
The value of 0.02 Bq/m3 is very near the bottom line of Figure 6.1. Therefore it can be seenthat most of the data points in Figure 6.1 are 10 to 100 times higher than background levels.
In particular, the tritium-in-air moisture levels 1 to 2 km from Pickering as reported by Health
Canada (2002) are 50 to 1,500 times higher than the Canadian background level.
Historical trends
Given the importance of tritium-in-air concentrations, it is relevant to examine their historical
trends and it is reassuring to note that at Ontario reactors these have declined since ~1989.
See figures below from OPG (2006) and Bruce Power (2006). These declines are probably
due to the commencement of the TRF at Darlington in 1990. Before 1990, stocks of heavy
water were withdrawn from OH reactors to supply the initial feed tanks at the TRF.
14

The real figure will depend on the amount of water in each cubic meter of air at the place of measurement.
This varies but an average figure of 10 grams per cubic meter is often used (Davis et al, 1996)

24

Figure 6.2 Pickering nuclear site tritium-in-air trend

Figure 6.3 Darlington nuclear site tritium-in-air trend25Figure 6.4 Tritium-in-air at Bruce Power indicator sites—annual average

26

Chapter 7

Tritium Concentrations in Food

The tritium-in-air described in the previous chapter is discharged continuously from Candu
stations. As a result, the moisture in vegetation and foods in areas near them become tritiatedto levels similar to the tritium concentrations in the moisture of downwind air. Figure 7.1
shows that as we go further way from the station, the concentrations in air and therefore in
vegetation decline.
Figure 7.1 Tritium concentrations in the moisture of vegetation and foods

Sources: Reproduced with permission of the CNSC from Tritium in the Canadian Environment: Levels and
Health Effects. Report RSP-0153-1. Prepared for the Canadian Nuclear Safety Commission under CNSC
contract no. 87055-01-0184 by Ranasara Consultants and Richard Osborne. Data from Health Canada (2001).

This figure shows tritium concentrations in the moisture of vegetation, soil and locally
produced foods at different distances from a nuclear generating station. The vegetation andsoil data are for samples collected in 1997 and 1998 near the Pickering reactors (Kotzer et al,1999). The food data are for locally produced samples collected at the Pickering station,
Ajax, and Perth, in 1990 (Brown, 1995).
It is interesting to compare these data with the annual averages of tritium-in-air concentrations
shown in Figure 6.1. There is a good fit between the data in the two figures, showing that
tritium concentrations in food and vegetation moisture are directly the result of tritium-in-air
concentrations.
All of these data show that tritium concentrations in food and vegetation in Canada, even
hundreds of kilometres from nuclear power stations, are elevated above the background ofreadings even further distant from nuclear stations. The benchmark level is that set by thedata point to the extreme lower left in figure 7.1, i.e., 2 Bq/L found about 3,000 km from thenearest nuclear station. This is the background level from which all other concentrations need
to be measured.
27

Chapter 8

How Much Tritium Do People Take In?

In previous chapters, we have examined the high levels of tritium discharges to the Great Lakes
and to the atmosphere from Candu reactors. Next, we examined the resulting high tritium
concentrations in areas near Candu reactors. Now we turn to the question: do these high tritium
concentrations in air and water result in high tritium concentrations in people living near Candu
reactors?
To answer this requires us to add up the tritium that people take into their bodies from eachsource every year. There are four main sources:••••from breathing tritium-contaminated air,from eating tritium-contaminated food,from drinking tritium-contaminated water, andfrom skin absorption of tritium-contaminated water vapour.

In order to calculate these amounts we need to know dietary habits and breathing and eating
rates etc. These have been compiled by Health Canada (1994) from a national habit and dietsurvey15. These values, together values for air and drinking water intakes from Health Canada(2001), allow one to estimate intakes. The values for adults are shown in Table 8.1.
Table 8.1 Annual food, water and air intakes by adult Canadians
Source of tritium
Annual intake
Vegetables
Fruit
Meat, poultry, fish and eggs
Dairy products
Cereals
Miscellaneous
Total foods

90 kg/yr
70 kg/yr
70 kg/yr
100 kg/yr
90 kg/yr
70 kg/yr
490 kg/yr

Drinking water and made-up drinks
Air

550 litres per year
8,400 cubic metres per year

Source: Health Canada (1994)

If we multiply together the above average rates by the measured tritium concentrations shownin Figure 6.1, we arrive at annual tritium intakes. We do this (similar to the examples used by
Osborne, 2002) for three types of tritium exposures:(a) areas very remote (i.e., >300km) from any nuclear facility,(b) areas near (5–10 km) to Candu facilities, and(c) areas very close (1–2 km) to Candu facilities.
Table 8.1 below shows the intake of tritium for a Canadian adult living very remote (>300 km)
from nuclear facilities. It shows average annual intakes are 2,200 Bq of HTO and 200 of OBT.
15

Daily rates in Health Canada (2001) are here multiplied by 365 days per year.

28

Most comes from drinking water (50%) and food (39%). These estimates are similar to those by
Osborne (2002) who, using different assumptions, estimated that adults living in areas “close to
the general Canadian background” would have annual intakes of 5,900 Bq of HTO and 350 Bq
of OBT.
In the tables below, all totals are rounded to two significant figures.
Table 8.1 Annual Intake of tritium for Canadians living far away from nuclear facilities(i.e., background tritium intakes)
Source of water tritium Intake per annum
HTO concentration HTO(HTO)
Bq/year
Water in drinks
550 l
2 Bq/L
1,100
Water in food
500 kg x 0.85
2 Bq/L
850= 425 litres
Air inhalation
8,400 m3
0.02 Bq/m3
170
3
Skin absorption
60% of inhalation
0.02 Bq/m
100
TOTAL
2,200
SourceofTritium (OBT)OBT in foodorganic Intake per annum
500 kg x 0.15
= 75 kg

OBT
Concentration~2.6 Bq/kg

OBT
Bq/year
~200

TOTAL

~200

Sources: Data from Osborne (2002), Trivedi et al (1997).
Assumptions:• background tritium level is 2 Bq per litre• 1 kg water = 1 litre• average specific activity of OBT = 1.3 x average specific activity of HTO (Osborne, 2002)• 2 litres of water consumed per day in drinks• on average, 85% of food is water, 15% is organic matter• annual skin absorption is 60% of inhalation intake (Osborne, 1966)

If we compare these estimates with the annual tritium intake of an adult living in the area
further away but still relatively near (i.e., within 5 to 10 km) to a Candu facility, the tritium
uptakes are appreciably higher, as seen in Table 8.3.

29

Table 8.3 Annual Intake of tritium for Canadians living near a nuclear facility (withinapproximately 5 to 10 km).
Source of tritium (HTO) Intake per annum
HTO
HTO
concentration
Bq/year
Water in drinks
550 litres
30 Bq/L, from
16,500Osborne (2002)
Water in food
500 kg x 0.85 = 425 l
100 Bq/L, from42,500Osborne (2002)
Air inhalation
8,400 m3
1 Bq/m3, from
8,400
Osborne (2002)
Skin absorption
60% of inhalation intake
1 Bq/m3
5,040
Swimming
0.024 l per hour x 100
30 Bq/L
70
hours = 2.4 l
TOTAL
73,000Source of tritium (OBT) Intake per annum
OBT in food

500 kg x 0.15
= 75 kg

OBT
concentration
80 Bq/g
estimated fromfigs 2 and 3 ofOsborne, 2002

TOTAL

OBT
Bq/year
6,000

6,000

Sources: Data from Osborne (2002) and checked with data in Trivedi et al (1997).
Assumptions: See Table 8.2.

The main point from this table is that tritium intakes for those living near (5 to 10 km) to Candu
reactors are 30 to 40 times greater than background intakes. Here water in food (58%) is amore important source than drinking water (23%). Note that in this exercise, drinking water isfrom a well, i.e., contaminated by tritium emissions to air and not tritium discharges to lakes.
These estimates are not too different from estimates by Osborne (2002) of 67,000 Bq for HTO
and 7,000 for OBT per year. Trivedi et al (1997) calculated that the annual uptakes in adults
living in Deep River, Ontario (10 km from the AECL Chalk River reactor) were about 20,000 Bqof tritium as HTO and 800 Bq of tritium as OBT. The above estimates are not inconsistent withthose from Trivedi et al, taking into account that tritium discharges from Chalk Riverlaboratory are considerably lower than those from the larger Pickering, Darlington and Bruce
nuclear power stations.
Finally, if we compare these estimates with the annual tritium intake of an adult who lives very
near a Candu reactor, i.e., within 1 to 2 km, and who eats produce from his/her own garden,
the tritium intakes are much higher, as shown in Table 8.4.

30

Table 8.4 Annual Intake of tritium for those living very close to a nuclear facility (1 to 2km) who eat produce from a highly contaminated garden
Source of tritium Intake per annum
HTO concentration HTO(HTO)(Bq/year)
Water in food
500 kg x 0.85 = 425 l~2,000 Bq/L
850,000
read from Fig 7.1
3
Air inhalation
8,400 m10 Bq/m3
84,000
Water in drinks
550 litres
100 Bq/L
55,000from Osborne, 2002
Skin absorption
60% of inhalation intake 10 Bq/m3
33,000Swimming
0.024 l per hour x 100
100 Bq/L
2,400
hours/year = 2.4 litres
TOTAL~1,000,000
Source of tritium Intake per annum
OBT concentration OBT(OBT)(Bq/year)
OBT in food
500 kg x 0.15~700 Bq/kg~53,000= 75 kg
estimated from figs.
2 and 3 in Osborne,
2002
TOTAL
~53,000
Sources: Data from Osborne (2002), Trivedi et al (1997).
Assumptions: See Table 8.2.

This table indicates that people living very near Candu reactors can receive large amounts oftritium, with annual intakes of 1 million Bq per year of HTO and a third of a million Bq per yearof OBT. These values are 500 to 1,400 times greater than Canadian background levels. They
indicate that people living very near Candu reactor sites who eat produce from their gardens
are likely to be highly contaminated with tritium. In comparison, Osborne (2002) estimatedthat the intakes of those living very close to Candu reactors were two thirds of a million Bq per
year of HTO and 42,000 Bq of OBT. These are not too different from the above estimates.
Notice that about 90% of their tritium (water) intake is from food and if the OBT from food is
added, it can be seen that almost all their tritium intake is from food. These results are
summarised in tables 8.5 and 8.6.
Table 8.5 Annual HTO tritium intakes at different distances from a Candu facility (Bq per year)
Location
This study
Osborne, 2002
km away from Candu
Bq HTO per year
Bq HTO per year
>300 km
2,200
5,900
5–10 km73,00067,000
1–2 km
1,400,000
640,000
Table 8.6 Annual OBT tritium intakes at different distances from a Candu facility (Bq per year)
Location
This study
Osborne, 2002
km away from Candu
Bq OBT per year
Bq OBT per year
>300 km200
350
5–10 km
6,000
7,000
1-2 km53,00042,00031

From tables 8.5 and 8.6, it can be seen that the closer people live to Candu facilities, thegreater their tritium contamination and tritium intakes. It can also be seen that the relationshipbetween distance from reactor and intake is not linear but exponential, so that people living
close to the reactors who eat produce from their own gardens are very highly contaminatedindeed.
Are these levels hazardous?
To answer this we have to define a level of risk we are prepared to accept. Then we have tocalculate how much tritium a member of the public could ingest/inhale/absorb without
exceeding this risk.
It is usually agreed that an annual16 risk of about one in a million of dying from cancer from aradiation exposure is acceptable. Using this risk and assuming an average adult consumes
730 litres of drinking water per year, the European Union (1998) has estimated that the
maximum concentration of tritium in drinking water is 100 Bq per litre - see table 4.1. Thismeans 730 litres per year x 100 Bq per litre = 73,000 Bq per year. Notice that this limit is forthe total for tritium intake in a year, and no more (man-made) radiation would be allowed,
otherwise the maximum risk would be exceeded.
Applying this suggested maximum to table 8.5, reveals that most people living within 5 to 10
km of Candu stations would have this level of intake. Those living very near (1 to 2 km) would
have ten to twenty times that amount. And this does not take into account OBT intakes which
will occur simultaneously. Therefore the answer to the question “Are these levels hazardous?”is yes, by European standards.
Another, simpler, way of looking at the matter is as follows. Scientists working repeatedly withradionuclides tend to develop “rules of thumb” for dealing quickly with radioactivity quantities.
Although rough and ready, they are not unscientific. One of these is that intakes (of betagamma emitters) greater than 100,000 Bq would trigger the need for some kind of action or
investigation. And this is what would strike most radiation protection scientists about the
intake estimates for those living close to Candu stations discussed in this chapter. However
official agencies state that because these intakes are of tritium (and not any other nuclide),the “doses” are low and their intakes are therefore below public health limits. We shall discuss
how “safe” these tritium levels are in the next chapter.

16

lifetime risks were discussed in chapter 4.

32

Chapter 9

Are High Tritium Levels Hazardous to Health?

In previous chapters, we examined the high tritium discharges to the Great Lakes and to theatmosphere from Candu reactors. Next, we examined the resulting high tritium concentrations invegetation and water near Candu reactors. In the previous chapter, we examined the resulting
high tritium intakes in people living near Candu reactors. Now we examine how hazardous theselevels of tritium intake are.
To do this is a seemingly simple step—one multiplies the totals in tables 8.3 and 8.4 by theofficial ICRP “dose factors” for HTO and OBT. A dose factor converts each Bq of a nuclide to aradiation “dose” expressed in sieverts (Sv). One then compares this calculated dose to thepresent Canadian public dose limit of 1,000 microsieverts (µSv) per year.
The problem, and here we get to the nub of the matter, is that the official dose factors for HTO
and OBT are the smallest (by considerable margins) of all common radionuclides. For
example, the ingestion dose coefficient for tritiated water (1.8 x 10-11 Sv per Bq) is ~700 times
lower than that for Cs-137, a common man-made radionuclide. When tritium’s tiny dose
factors are used to calculate doses, the resulting doses are miniscule. For example,
according to official dose factors, the highest exposed persons in Table 8.4 above only
receives about 20 µSv per year from tritium (i.e., 50 times lower than the annual 1000 µSv
safety limit). Therefore Canadian health agencies and radiation regulators consider tritium
discharges not to be dangerous.
But these official considerations depend crucially on tritium’s dose factors’ being
correct. Are they correct? The answer is so important that we have devoted Part 2 of thisreport to it. The box below contains a brief précis of Part 2.
Summary of Part 2: The Radiation Hazards of Tritium
Many scientists have expressed concerns about tritium’s low dose factors and its radiotoxicity:
indeed, demurring views about tritium’s official doses have existed for decades (for more recent,see Fairlie, 2007; Harrison et al, 2003, and CERRIE, 2004).
Part 2 reveals that a number of radiation protection precepts and procedures are deficient or
inappropriate when determining tritium’s hazards. The report’s main arguments about tritium
are summarised below.
1. Tritium’s unusual properties of extremely high mobility, exchangeability, and binding
with organic materials are not properly recognised by official dose models.
2. Because of the short range of tritium’s beta particle, tritium’s damage depends on its
exact location in the cell. For example, tritium next to a DNA molecule exerts moredamage than tritium in, say, extracellular water. At present, it is not possible to model
where tritium goes in the body with any accuracy. Official models assume that tritium(HTO) is distributed equally throughout the body, but we don’t know that. Some
scientists think we should use safer models, in case equal distribution turns out to be
wrong.
3. Tritium is often described as a “weak” beta-emitter, but in radiation biology, so-called“weak” beta particles are more effective (i.e., dangerous) than energetic ones. This isespecially the case with tritium, but this is not acknowledged in setting its dose factor.
4. Much evidence indicates that tritium’s effectiveness (in radiation biology experiments
33

comparing tritium with gamma rays) is two or three times that recognised by the ICRP.
5. Little official recognition is given to tritium’s ability to incorporate in organic molecules
to high levels as a result of chronic exposures that occur near Candu reactors.
6. Official dose models for organically bound tritium therefore significantly underestimate
its doses.
From these points, examining tritium’s doses tends to turn into a critique of current official
radiation protection precepts and practices. This is unfortunate, because few people outsideof the nuclear industry and its regulators understand these. However, it is important that aneffort is made, in order to appreciate the true degree of tritium’s hazards.
In a nutshell, the second part of this report concludes official attitudes on tritium are
unscientific and incorrect. It concludes that the recent evidence of tritium’s hazards should be
acknowledged by radiation protection agencies in Canada, that a precautionary approachshould be adopted with dose factors for HTO and OBT being significantly increased.
Recent reports
Very recently, a number of reports have been published which also raise questions about
tritium’s dosimetry. These include the US IEER report (Makhijani et al, 2006—see Chapter 7),
which recommends a much stricter US EPA standard for tritium in drinking water. In addition, thereports of the UK Government’s CERRIE Committee (2004) and AGIR (2007) Committee both
examine questions surrounding current methods of determining tritium doses. Also, in a very
recent article, the author (Fairlie, 2007) examines objections to ICRP’s current approach to theeffectiveness of tritium’s beta decay particle. These recent articles and reports should be studied
by the Federal Canada and Ontario Governments and by the CNSC.
The recent history of the CERRIE Committee in the UK is instructive on the debate about tritium.
This Committee was set up by the UK Government in 2001 because of concerns about the risks
of internal radiation. Tritium is an example, par excellence, of internal radiation. Because its
external radiation is considered harmless, it is only an internal hazard. The Committee spent agreat deal of time considering tritium’s risks and examining proposals for increasing tenfold
HTO’s dose factor, and for increasing OBT’s dose factor to five times greater than that for HTO.
In the end, the Committee could not reach a consensus on tritium’s risks, despite much
constructive discussion. (See the documents on tritium in www.cerrie.org.) Most official
representatives voted for current values, while representatives of environment groups voted forincreased values. Nevertheless, the UK Government’s permanent COMARE Committee in its
response to the CERRIE Report recommended yet more investigation into tritium’s dosimetry.
The outcome has been the recent report of the UK’s AGIR Committee (2007) which
recommended (at least) doubling HTO’s dose factor.
Would increasing tritium’s dose factors make a difference?
If we increased tritium’s dose factors significantly (e.g., for HTO’s dose factor to be increased
10-fold and for OBT’s dose factor to be 5 times greater than HTO’s dose factor), would thisresult in different conclusions? The answer is yes. For example, the revised radiation dose to
the most exposed persons in Table 8.4 would be well over the public dose limit of 1,000 µSv
per year.
34

Occupational doses
We have not considered the matter of occupational doses mainly because of the lack ofavailable data, but there may be a problem with members of the public who live with a worker
who is occupationally exposed to tritium. Workman et al (1998) showed that the indoor air ofsuch homes had 70-fold elevated tritium levels (compared with outdoor concentrations), andthat their daily tritium intake was 18 times higher than adults living in a non-occupationally
exposed home. (See also Part 2, Appendix VII.)
Epidemiology
An obvious question is, can we see any adverse health effects at locations with high tritium
concentrations? Health effects can sometimes be spotted by means of epidemiology studies,particularly among those who are most exposed. But radiation health effects are notoriously
difficult to pick up because cancers caused by radiation are not different from naturallyoccurring cancers, and there are many such cancer cases; indeed in the UK about 25% of alldeaths are from cancer17. This requires us to look for small increases in cancer rates among
exposed populations which already suffer many cancers. It is difficult to pick up small
increases in radiation-induced cancers (the signal) among the many natural cancers (thenoise). Very large expensive epidemiology studies are required to get a big enough signal tosatisfy scientists that that there really is an effect and that any increase has not occurred bychance or from statistical blips.
In any event, relatively few such studies have been carried out. (See Appendix VII to Part 2.)
These have shown increases in childhood leukemia but these studies are first-stage studies(often termed “ecologic”) which may be subject to bias such as social class, or to confounding
factors such as smoking. The result is that their findings are indicative, not conclusive. What
are needed now are second-stage (i.e., case-control or cohort studies) to match cases ofcancer with people who do not have cancer, to obtain more conclusive results. These shouldhave been carried out after the first-stage studies in the 1980s and early 1990s showed signsof increased incidences of leukemia in affected areas.

17

The figure for Canada is thought to be similar.

35

Chapter 10 Conclusion and Recommendations
This report has examined tritium discharges from Canadian nuclear power stations, which aremuch greater than from nuclear power stations in other countries. Canadian tritium discharge
limits are considerably less stringent than those in other countries. Canadian tritium limits indrinking water are also considerably more lax than those in Europe and the US.
The report also shows that tritium levels in those Great Lakes with nuclear reactors on theirshores are 2 to 5 times greater than in Lake Superior, which has no reactors. The tritium level in
Lake Ontario is also increasing each year, mainly due to Candu discharges and to major tritium
leaks in past years. Tritium concentrations in drinking water, in air, and in vegetation and foodnear Candu stations are all significantly increased. These result in turn in high tritium intakes inresidents living within 5 to 10 km of Candu stations and very high tritium annual intakes inresidents who live within 1 to 2 km of the Candu stations.
However, because of tritium’s very low dose factors, the radiation “doses” which result fromtritium exposures are very small and are considered safe or within health limits by Canada’s
nuclear regulators. But the report points to significant objections to tritium’s dosimetry and tothe models used to estimate tritium doses, especially from organically bound tritium. It notes anumber of recent reports in the UK (AGIR, 2007; Fairlie, 2007; CERRIE, 2004) and the US(Makhijani et al, 2006) which raise questions about tritium’s official dosimetry.
The report concludes that scientific concerns about tritium's hazards are inadequately
recognised by the Canada's nuclear regulators. It therefore recommends that a precautionary
approach to tritium discharges should be adopted in Canada. In particular, it recommends
that:1) the Ontario and Federal governments should establish a committee (whose members
should include scientist representatives from environmental groups) to examine
tritium's dosimetry and risks. In particular, the committee should examine recent
authoritative reports which raise questions about currently-accepted views on tritium's
dosimetry and risks;
2) case-control and cohort epidemiology studies should be commissioned to examine
possible adverse health effects in tritium-contaminated areas;3) pregnant women and young (less than 4 years old) children and their mothers should
be advised not to live near tritium-emitting facilities (i.e., within 10 km);4) people who live very near (i.e., within 5 km) tritium-emitting facilities should be
advised not to consume food from their own gardens, bee hives and orchards, andnot to consume wild foods, e.g., blackberries and mushrooms, growing very near thefacilities;5) because tritium reduction facilities themselves release large quantities of tritium,
nuclear reactor operators should be requested to examine the option of long-term
storage of tritiated water from moderator circuits in decay tanks as a way of reducing
tritium discharges; and6) operators of tritium-emitting facilities should give further consideration to other ways
and means of reducing tritium releases.

36

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41

Annex 1

Carbon-14

Canada’s reactors also discharge relatively high amounts of carbon-14. Carbon-14 and tritium
have similar properties; for example, both bind with organic molecules in plants and animals.
A major difference between them is that carbon-14’s half-life is 5,730 years, which is ~460
times greater than tritium’s half-life of 12.3 years. This means that C-14 is a potent contributorof radiation doses to future populations—not just in Canada but in the rest of the world, as C14 is distributed globally. The estimation of collective doses to Ontario and to Canadian
populations from Candu releases is a task for the future.
The important point is that tritium’s discharges are 100 to 1,000 times greater than C-14
discharges. For this reason, the report has examined tritium discharges. However, any future
epidemiological studies will need to take into account exposures to C-14 as well as to tritium.
The following tables report C-14 releases and DRLs at Canadian nuclear plants.
Table A Air releases of carbon-14 from nuclear power plant facilities (TBq/a)Facility
2001
2002
2003
2004
2005
Bruce A + B
3.09
2.49
4.81
3.81
10.44
Pickering A + B
6.46
1.99
3.7
2.7
4.8
Darlington
3.5
2.8
3.5
1.9
1.6
Gentilly-2
0.40
0.37
0.39
Point Lepreau
0.22
0.29
0.21
TOTALS
13.67
7.94
12.61
Sources: NPRI, 2004, 2003, 2002.

Table B Water releases of carbon-14 from nuclear power plant facilities (GBq/a)Facility
2001
2002
2003
2004
2005
Bruce A + B
9.5
8.5
8.2
14
14
Pickering B
3.3
1.5
0.1
4
5.5
Darlington
3
1.7
1.2
0.4
0.28
Gentilly-2
0.3
0.3
0.3
Point Lepreau
2.8
3.4
1.8
TOTALS
18.9
15.4
11.6
Sources: NPRI, 2004, 2003, 2002.

42

Annex 2

Wind Frequencies for Darlington and Pickering

The table below indicates that wind frequencies are fairly well spread around the compass at
both locations, with a slight preponderance of winds from the West.
Table A Wind Frequency by Direction (at 10 m height)
Direction
Darlington nuclear
Pickering nuclear
fromwind frequency (%)
wind frequency (%)
N
NNE
NE
ENE
E
ESE
SE
SSE
S
SSW
SW
WSW
W
WNW
NW
NNW
Total

3.64
4.03
8.22
8.67
4.65
3.22
2.15
1.94
2.36
6.97
9.22
7.13
9.09
9.69
12.42
6.59
100

7.8
4.56
4.6
6.17
5.94
3.32
1.77
2.56
8.9
9.17
4.91
4.9
7.29
9.27
9.39
9.43
100

43

Annex 3

Tritium Emissions from SRB Technologies, Pembroke, Ontario

In the past, the SRB Technologies facility at Pembroke, Ontario emitted very large quantities
of HT gas and HTO water vapour (see table below.) In recent years these discharges havedeclined, due to licence restrictions, but these restrictions have recently been relaxed.
HT has very different dosimetric properties from tritiated water. The ICRP considers that
HTO’s doses from inhalation and ingestion are 25,000 times greater than those for HT (ICRP,
1989)18. This is because the body is not thought to absorb or metabolise hydrogen gas,
whereas water is a vital component of all body tissues and metabolic processes. Therefore
the important factor is how fast HT is converted (oxidized) to HTO. This had been the subjectof differing views in the past (Sweet and Murphy, 1984, and Spencer and Dunstall, 1986).
However nowadays it is understood that HT dispersed into the atmosphere diffuses readily
into the soil and is converted to HTO by enzymatic reactions, the rate of which depends on
the porosity, water content and microbial activity of the soil. The converted HT is
subsequently transported as HTO. (Ichimasa, 1995). Generally, for conservatism inassessments, released tritium is often assumed to be in the form of HTO, as eventuallyalmost all HT will be converted to HTO over longer time periods. (Davis et al, 1997).
For these reasons, HT and HTO discharges are summed in the table below to indicate total
tritium releases.
Table A Annual tritium emissions from SRB Technologies (TBq per year)Year
HTO (vapour and liquid)
HT (gas)
Total
1996
572
2,319
2,891
1997
1,024
8,679
9,703
1998
1,362
12,89014,252
1999
671
6,624
7,295
2000
1,388
16,59817,986
2001
993
12,875
13,868
2002
868
8,398
9,266
2003
420
6,338
6,758
2004
342
3,973
4,315
2005*
247
935
1,224
2006**
72
213
285
Sources: Pre-2000 data: Dr. Patsy Thompson, from presentation to the Pembroke Municipal Council, November
19, 2002, Canadian Nuclear Safety Commission. 2000–2006: SRBT Annual Compliance Reports(http://www.betalight.com/pip/relations.htm).
NB: SRBT subsequently reported in a letter to CNSC staff dated August 24, 2005 that it had found an error in
the calculation of the quantity of gaseous emissions per week, which resulted in a 10-fold underestimation in thereported values of the gaseous emissions from all previous years (Canadian Nuclear Safety Commission, Report
CMD 05-H26.B (http://www.nuclearsafety.gc.ca/eng/commission/pdf/05-H22A-UpdatedAgenda.pdf). Data foryears prior to 2005 have been corrected for this error.
*In a letter dated November 17, 2005, and orally on November 18, 2005, SRBT informed the CNSC staff that“the tritium emission monitoring system may not be providing reliable measurements of the concentration andquantity of tritium released to the environment” (Canadian Nuclear Safety Commission, document CMD 05H26.C, http://www.nuclearsafety.gc.ca/eng/commission/pdf/2005-11-30-H34C-UpdatedAgenda.pdf).
18

More precisely, the maximum derived air concentration for HTO is 25,000 times greater than that for HT.

44

This may have affected measurements during the 5-year licensing period, 2001–2005.
** During 2006, SRBT’s Nuclear Substance Processing Facility Operating Licence NSPFOL-13.00/2006
restricted the company to use only one unit—the reclamation unit or a single betalight production filling rig toprocess tritium—at any given time. Prior to 2006, SRBT operated many units simultaneously.

In a comment, SRB tritium discharges, particularly in the years 1997 to 2003, were extremely
high and they merit considerable CNSC attention and concern. In the author’s view, it may be
worthwhile to carry out OBT measurements in flora and fauna downwind and downstream of
the SRB plant. Consideration should also be given to tritium measurements among thoseliving near the SRB facility and SRB employees.

45

PART 2:The Radiation Hazards Of Tritium

Chapter 11 INTRODUCTION
Chapter 12 TRITIUM’S DOSE COEFFICIENTS
Chapter 13 ORGANICALLY BOUND TRITIUM (OBT)
Exchangeable and non-exchangeable tritium
Biokinetic Models for HTO
Biokinetic Models for OBT
Chapter 14 INTERNAL DOSIMETRY OF TRITIUM
RBE values for tritiumwR value of tritium(Ionisation-density (LET) effects
Tritium’s incorporation in DNA(i) Doses from HTO(ii) Doses from OBT
Chapter 15 CONCLUSIONS(a) Tritium’s hazardous properties(b) Dose coefficients(c) Possible risks from tritium exposures
Appendix I:
Appendix II:
Appendix III:
Appendix IV:
Appendix V:
Appendix VI:
Appendix VII:

Previously expressed concerns about tritium
Equilibria in OBT/HTO Levels after chronic HTO exposures
Isotope effects In DNA’s hydration shell
Controversy over tritium’s wR value
Transmutation effects
ICRP 92 arguments for retaining a wR of 1 for tritium
Epidemiological evidence

References in Part 2
Annex A.
Annex B.
Annex C.
Annex D.
Annex E.

Acronyms and Abbreviations
Radiation and Radioactivity Units of Measurement
Conversions between European and US units of Radiation and Radioactivity
Glossary
Recommended Reading46

Chapter 11 Introduction
1. Tritium (H-3) is the radioactive isotope of hydrogen. It is a beta-emitter with a maximum
decay energy of 18 keV (average 5.7 keV), and a half-life of 12.33 years. Tritium is formed
naturally through cosmic ray interaction with H in the upper atmosphere and is transferred tothe troposphere. Tritium emission rates from civil and military nuclear facilities considerably
exceed natural production rates—indeed by over two orders of magnitude. Tritium is createdin nuclear fuel through activation of 1H and 2H and as a tertiary fission product. In comparison
with other nuclides, large amounts of tritium are released from heavy water reactors, nuclear
fuel reprocessing plants and pharmaceutical plants. Tritium most commonly occurs as tritiatedwater (HTO), organically bound tritium (OBT) and elemental tritium gas. This report willconcentrate on the former two forms19.
2. Tritium is ubiquitous in all biological systems through mixing, cycle, transfer, and dilution of
the hydrosphere. It is exceedingly mobile, due to its existence as water and to its ease of
exchange among all chemical species containing hydrogen, including biota. Consequently,
tritium can be viewed as a very efficient distributor of radioactivity in the environment andhumans. Ingested tritiated water has a biological half-life of about 10 days in humans: this is
assumed to be homogeneously distributed in tissue. Tritiated foodstuffs contain organicallybound forms of tritium with longer biological half-lives, which are variable and may extend toseveral years. OBT dose coefficients are therefore larger than those for HTO.
3. As the radioactive isotope of hydrogen, tritium has a number of unusual properties,
including high mobility; ubiquity in the environment; cycling in the biosphere; multiple
pathways to man; ease of exchange with stable H atoms in biomolecules; binding withbiomolecules to form OBT with higher dose coefficients; and the heterogeneous distribution
OBT in cells/tissues. The short range of tritium’s beta particle in tissue means that tritium’s
microdosimetric effects and distribution in tissues and cells must be considered. For thesereasons, many scientific concerns have been expressed about tritium (see Appendix I; Fairlie,
1992; Taylor et al, 1990).

19

ICRP’s derived air concentration for HT gas is 25,000 times lower than that for HTO.

47

Chapter 12 Tritium’s Dose Coefficients
4. Paradoxically, tritium’s dose coefficients are, by some margin, the lowest among common
nuclides. (The dose coefficient of a nuclide is the estimated radiation dose imparted to a cell,tissue or organism by the radioactive decay of one atom of that nuclide.) The ingestion dosecoefficient for tritiated water (1.8 x 10-11 Sv per Bq) is ~700 times lower than that for Cs-137,
for example. As a result, tritium is widely regarded as a “weak” radionuclide and official
radiotoxicity schemes continue to list tritium in the lowest radiotoxicity category. For example,
Table 11.1.1.1 of the IAEA’s "Health Physics and Radiological Health Handbook" (1990)
provides a Toxicity Classification of Radionuclides. The table is similar to the ILO "Guidelines
for the Radiation Protection of Workers in Industry—Ionizing Radiations" (1989). This lists
nuclides in descending order of radiotoxicity, as shown in Table 12-1. (See also the USEPA
website, http://www.epa.gov/radiation/radionuclides/tritium.htm#inthebody.)
Table 1 IAEA Radiotoxicity Scheme
Group
Radiotoxicity
Group 1
Very HighGroup 2HighGroup 3Moderate
Group 4Low

ExamplesRa-226, Pu-239, Am-241, Cf-252
Co-60, Th-232, Sr-90
low beta yield radionuclides, eg Be-7, Co-57
H-3, Tc-99m, U-238

5. But there is a major misconception here. In radiobiology, so-called “weak” particles in fact
have higher radiobiological effectiveness, and the lower their energy, the more effective they
become. Tritium beta particles, as we shall see later, are actually 2 to 3 times moredamaging20 than gamma rays, for example. Therefore to call such particles “weak” is very
misleading: it is better to call them “low-range”.
6. Concern arises at the conjunction of two facts about tritium: its low dose coefficient andthe large emissions from various facilities. If tritium’s dose coefficient were found to containsignificant errors or uncertainties, the health consequences could be large. Studies whichhave examined tritium’s contribution to doses in specific circumstances have usuallydismissed a major contribution from tritium (see, for example, in the UK: COMARE21, 1996).
However, these studies depend on tritium’s existing dose coefficient’s being substantiallycorrect. Many researchers have expressed concern about tritium’s dosimetry and havepressed for increases in tritium’s dose coefficient. Tritium’s dose coefficients were recently
reviewed (Harrison et al, 2002) in a report which stated that an ICRP Task Force would beconsidering recommendations to double tritium’s dose coefficients for tritiated water andorganically bound tritium, mostly due to uncertainties in tritium’s RBE. However, the ICRP has
decided not to increase tritium’s dose coefficient.
7. For these reasons, it is necessary to review how the ingestion dose coefficient for tritium
20

The reason has to do with the track structure on ionising radiations. So-called “strong” radiations such as Co60 gamma rays have very long tracks in tissue, but most of their energy is frittered away over the long track.
Damaging amounts of energy are deposited only at the ends of their tracks. Low-range beta emitters such as H3 consist ONLY of such track ends, and therefore can be more damaging per disintegration than higher energy
emitters.
21
For its 4th Report, the UK Government’s COMARE Committee carried out a sensitivity analysis, multiplying
tritium doses by 16 (see para 3.105) to account for the possibility of all tritium being bound to DNA. The resulting
tritium doses were small.

48

(HTO) is calculated. Essentially, the dose coefficient is derived from the first principles ofradiation physics and from the biokinetic assumptions of (a) homogenous distribution in soft
tissue, (b) 100% instantaneous distribution among soft tissues, (c) 63 kg of soft tissues inman, (d) retention described by a single exponential with a half-life of 10 days, and (e) OBT
doses neglected. These assumptions are considered next.

49

Chapter 13 Organically Bound Tritium (OBT)
8. Tritium is attached to organic compounds either by exchange reactions or by
enzymatically-catalysed reactions. In exchange reactions, tritium swaps with H atoms bonded
to oxygen, sulphur, phosphorus or nitrogen atoms in hydroxides, thiols, phosphides andamines, respectively. Conventionally this is termed “exchangeable” OBT. In enzymaticallycatalysed reactions, tritium is bonded to a carbon atom of an organic molecule: this is usuallytermed “non-exchangeable” OBT. Tritium thus bound is more strongly attached and has
longer retention times than exchangeable tritium: such bonds are only dissolved by catabolic
reactions. Other nuclides (including S-35, P-32 and C-14) also have the property of organic
binding, but H is much more common. Sixty percent of the body’s atoms are H atoms, ofwhich about 5% are involved in metabolism reactions each day. In exchange reactions, H
atoms are also much more active than S, P or N atoms.
Exchangeable and non-exchangeable tritium
9. In all elements, atoms engage in exchange reactions with other atoms of the sameelement to varying degrees. Thus, stable H atoms in organic molecules (i.e., bound to O, N, P
or S atoms) can swap positions with tritium atoms in HTO. H, the smallest atom, is by far themost prominent as regards exchange reactions. The practical consequence is that all organic
molecules downwind of a tritium (HTO) discharge plume which encounter HTO will quickly
become tritiated, albeit at low concentrations. This includes all plant and animal species, allwater-bearing material, and soil. It would include vegetables and fruit in exposed market stalls
and shops, for example. (See Inoue Y et al, 1993. Uptake of atmospheric tritium by market
foods. Fusion Technology 21, pp 494–499.)
10. Differing views exist on whether the definition of OBT should be restricted to nonexchangeable tritium or should include exchangeable tritium. The nub of the problem is that
tritiated water, i.e., HTO, by definition, is a form of exchangeable OBT. This review adopts themore common latter view, but continues to make a distinction between the N, P and S forms
and the HTO form of exchangeable OBT, because of their different biological half-lives andbecause of the ubiquity and high concentrations of water in biota.
Biokinetic models for HTO
11. Following HTO intake, the current ICRP model (1989) assumes 100% is absorbed andenters the blood. It assumes a turnover half-life of 10 days for HTO. It also assumes that 3%of HTO administered is bound as OBT, and that OBT doses from HTO administration may besafely neglected. Animal studies are informative and reveal that doses from OBT must be
considered. Commerford et al (1982) found that, after a transient HTO exposure to mice, all
the remaining tritium was bound to DNA and histone 8 weeks after exposure. Although theamounts were small compared to HTO, cell nucleoproteins were much longer-lived: theauthors concluded that doses from them would exceed HTO doses. In addition, Trivedi et al(1997) estimated that an acute HTO administration in humans results in the range 3%–9%being bound as OBT, not the 3% currently assumed by the ICRP.
12. The problem is that the ICRP biokinetic model ignores chronic exposures to tritium. These
are important in the case of those living downwind from facilities which discharge tritium 24hours a day. The ICRP considers chronic exposures to be merely repeats of one acuteexposure. That is, in each case, the main dose from HTO and none from OBT, and the HTO
50

and OBT being excreted before the next acute exposure. However, this is incorrect: animalstudies reveal that after chronic exposures to HTO most of the dose comes from OBT. For
example, Commerford, Carsten and Cronkite (1977) found most tritium doses came from theOBT component, 2 to 3 days after the cessation of a lengthy chronic HTO administration to
mice. Rogers (1992) concluded that because OBT was cleared much more slowly than tissue
water tritium, OBT was the principal determinant in estimated radiation doses to mice,following chronic HTO exposure.
13. In fact, chronic HTO administrations result in OBT concentrations increasing to higher
levels, depending on how long the administration lasts. In situations of chronic exposuresover a few months or so, Osborne (1972) stated there was a theoretical maximum to Tlabelling of organic molecules by HTO, due to the fixed percentage (~30%) of exchangeable
H bonds in the body. There is some evidence to support this: Rodgers (1992) fed micetritiated water to establish a steady state of T turnover: OBT levels rose to 22% of body HTO
levels after 56 days. However, it is unclear what would have happened had the experimentcontinued. Much evidence suggests that OBT levels would slowly continue to increase astritium continues to be taken up by metabolic reactions. Eventually OBT levels, because of
their very long half-lives, would equilibrate with body HTO levels. The evidence for this isdiscussed in Appendix III. Most important are the studies of exposures from naturallyoccurring tritium, which indicate OBT/HTO ratios of 1. Essentially, there is a disjunction
between the evidence from animal experiments and the evidence from background tritium
levels/environmental studies. This may be due to the limited time lengths of existing biokinetic
experiments. These experiments may need to continue for years, i.e., for the half-life of OBT
in humans, which could be many years.
Biokinetic models for OBT
14. OBT has longer retention times than tritiated water, as it is incorporated in a variety ofbiochemical compounds, including amino acids, sugars, starches, lipids and cell structural
materials. Some biomolecules are well-preserved and long-lived, e.g., phospholipids in nerve
cells, and DNA and RNA macromolecules. These longer retention times result in a greater
radiotoxicity than that of tritiated water. The ICRP (1989) has stated that "the major part oftritium uptake of the public will occur by ingestion of food into which tritium has been
incorporated into both plant and animal components", and has recommended an OBT
ingestion dose coefficient 2.3 times greater than that for HTO22.
15. Following OBT intake, the current ICRP (1989) model assumes 50% reaches the blood as
OBT and the rest is catabolised to HTO, which also reaches the blood. OBT is assumed to be
excreted with a turnover half-life of 40 days. This figure comes from the assumption that all
OBT is bound to C and the assumption of a 40 day half-life of C in the body (ICRP, 1975).
16. Serious problems exist with this model. The evidence for a carbon half-life of 40 days isderivative: it does not take into account experimental evidence in humans of considerably
longer half-lives for the long-lived component of OBT. Table 13.2 below shows the 1st OBT
component has a half-life of about 30 to 40 days, and the 2nd OBT component has a half-lifeof over 500 days in humans. The 1st component is conventionally assumed to beexchangeable OBT (i.e., bound to S, P and N atoms) and the 2nd component to be non22

ICRP dose coefficients for adults are 1.8 x 10-11 Sv/Bq for tritiated water and 4.2 x 10-11 Sv/Bq for OBT.

51

exchangeable OBT.
Table 2 Tritium retention half-lives in humans after ingestion of HTO
Reference
No. of cases
Biological half-life (days)
Pinson and Langham 1957
Butler and Leroy 1965
Osborne 1966
Snyders et al 1968
Sanders and Reinig 1968
Minder 1969
Lambert et al 1971
Moghissi et al 1971
Moghissi et al 1972
Balonov et al 1974
Rudran et al 1988

HTO
11.3
9.5
10.5
8.7
6.1
9.1
9.0
12.0
6.0

9
310
30
1
1
1
1
1
8

OBT1
34
23
1-30
36
21-26
30
39-76
30

OBT2
344
139-230
280-550450
226

17. Although little human data is available on the percentages of HTO retained as OBT1 andOBT2 after chronic intake, a reasonable (but not necessarily conservative) assumption would
be about 30% and 6% respectively, assuming a continuous exposure limited to a few months’
duration. Using half-lives of 30 days for OBT1 and 550 days for OBT2 would result in a ~ 3fold increase in the HTO dose coefficient. If a more precautionary approach were adopted,
i.e., if OBT/HTO equilibria were created, then OBT dose coefficients would be greater.
However, it is unclear whether such equilibria occur in the timespans of most occupational
and public exposures from current HTO releases. Clearly, long-term exposures from even low
levels of HTO are contra-indicated, due to the build-up of OBT levels.
18. The current ICRP metabolic model for OBT results in ICRP’s OBT dose coefficient being
2.3 times greater than the HTO dose coefficient. More accurate models of tritium metabolism(Etnier et al, 1984) and (Saito et al, 1989) indicate OBT doses are 1.7 to 6.4 times higher thancalculated HTO doses, depending on OBT/HTO ratios in consumed food. Rudran (1988)
estimated the OBT/HTO dose ratio was 3.4 for workers. If the longer-lived OBT components
were included, the OBT dose coefficient would be 4 to 5 times higher than the HTO dosecoefficient. This estimate is suggested by the findings of Komatsu et al (1990), who fed rats
tritiated OBT. After 22 days' ingestion, 37% of the total tritium dose came from DNA and wasdue to the long half-lives of DNA. The authors calculated that OBT doses were 4.6 times higher
than after HTO ingestion.
19. It is concluded here that the ICRP’s biokinetic models for both HTO and OBT aresignificantly in error in a number of respects: their use may result in unconservative dose
estimates. From this analysis, the dose coefficient for HTO should be increased by a factor of3, and that OBT’s dose coefficient should be increased to be 4 to 5 times greater than that for
HTO.

52

Chapter 14 Internal Dosimetry of Tritium
20. This review focuses on tritium’s internal dosimetry: external tritium is not normallyregarded as hazardous. Five aspects are examined:(a) tritium’s RBE(b) tritium’s wR value(c) ionisation-density (LET) effects(d) distribution effects(e) incorporation in DNA(a) RBE values for tritium
21. Tritium’s RBE values have been the subject of much controversy in the past. (SeeAppendix IV for a short history of the matter.) Some may reflect that this controversy
continues to this day. Straume (1991) and Straume and Carsten (1993) comprehensively
reviewed tritium RBE experimental data for a range of species and endpoints. They
concluded that a radiation-weighting factor of 3 was appropriate for tritiated water (HTO).
Higher RBEs were found when the comparison radiation was gamma rays. Table 3 sets out
the RBE values from the radiobiological experiments cited in Straume’s tables. Since
Straume’s review, an RBE for HTO of 1.2 ± 0.3 for the induction of myeloid leukaemia in mice(Johnson et al, 1995) has been reported and is included in Table 3.
Table 3 Tritium RBE values
Mammary tumours in SD rats
AML CBA/H mice
Various tumours in
C57BI/6NxC3H/He mice

Cancer induction
HTO/chronic x-rays
1.2 ± 0.3

Gragtmans et al 1984

1.2 ±0.3~1

Johnson et al 1995
Yokoro 1989

HTO/x-rays
HTO/acute x-rays

Human lymphocytes
Human lymphocytes
Human lymphocytes
Human lymphocytes

Chromosome aberrations
HTO/acute x-rays
1.9 ±0.7
HTO/sub-acute γ
1.49 ±0.21
HTO/acute x-rays
1.13 ±0.18
HTO/acute γ
3.4 ±0.64

Human lymphocytes
Human lymphocytes

HTO/250 kVp x-rays
HTO/250 kVp x-rays

Mouse spermatogonia
Mouse spermatogonia
Mouse oocytes
Fish germ cells
Fish fertility
Mouse testis weight loss
Mouse testis weight loss
Mouse zygotes
Micronuclei inmammalian cells
Micronuclei inmammalian cells

2.6
2.0

Reproductive effects
HTO/chronic x-rays
2.4
3
HTdR/chronic x-rays
1.6
HTO/chronic x-rays
2.9
2.2
HTO/chronic γ~2
HTO/chronic γ
1.4
HTO/chronic γ
3
2.1
HTdR/chronic γ
1.8
HTO/chronic γ
2.0
HTO/chronic γ
HTO/chronic γ

2.7

53

Prosser et al 1983
Morimoto et al 1989
Prosser et al 1983
Prosser et al 1983, Lloyd etal 1988
Vulpis 1984
Prosser et al 1983, Lloyd etal 1988
Lambert 1969
Lambert 1969
Dobson and Kwan 1976
Etoh, Hyodo-Taguchi 1982
Hyodo-Taguchi, Hyodo 1985
Carr and Nolan 1979
Carr and Nolan 1979
Matsuda et al 1985
Ueno et al 1982
Kashima et al 1985

Drosophila mutations
Mouse mutations
Mouse dominant lethals
Mouse dominant lethals
Mouse dominant lethals
Mouse specific locus
mutations6-Thioguanine resist. inmouse cells in vitro
6-Thioguanine resist. inmouse cells in vitro
6-Thioguanine resist. inmouse cells in vitro
6-Thioguanine resist. inmouse cells in vitro
6-Thioguanine resist. inmouse cells in vitro
Chromosome
aberrations in humansperm in vitro
Chromosome
aberrations in fish
lymphocytes in vitro
Chromosome
aberrations in mousezygotes
Chromosome
aberrations in CBA/H
mice lymphocytes
Chromosome
aberrations in CBA/H
mice spermatogonia
Mouse embryo
Rat embryo
Cell killing in vitro
Cell killing in vitro
Cell killing in vitro
Source: Straume (1991).

Genetic endpoints
2.7
HTO/γ
2.7
HTO/chronic γ
HTO/chronic γ
HTO/chronic γ
HTO/chronic γ
HTO/chronic γ

2.5
1.5
2.5
2

Byrne and Lee 1989
Nomura and Yamamoto
1989
Searle 1974
Carsten, Commerford 1976
Xiang-yan et al 1986
UNSCEAR 1982

HTO/chronic γ

2.9

Ueno et al. (1989)

3H-amino acid/chronic γ

2.6

Ueno et al. (1989)

tritiated thymidine (3HTdr) and chronic γ
HTO/ γ at 10-5 mutant
frequency acute
HTO/γ at 10-5 mutant
frequency
HTO/chronic X rays

5.9

Ueno et aI. (1989)

1.5

Nakamura et al. (1985)

2.4

Nakamura et al. (1985)

3

Kamiguchi et al. (1990)

HTO/chronic γ

1.9

Suyama and Etoh (1985)

HTO/chronic γ

1.8

Matsuda et aI. (1985)

HTO/X rays

1.1

Chopra and Heddle (1988)

HTO/X rays

1.2

Chopra and Heddle (1988)

Developmental effects
1.7
HTO/chronic γ
2.6
HTO/chronic γ
1.3
HTO/chronic γ
31.7
H-amino acids/chronic γ
3
3.5
H thymidine/chronic γ

Yamada et al 1982
Satow et al 1989
Ueno et al 1989
Ueno et al 1989
Ueno et al 1989

22. From this table it can be seen that two reference radiations are commonly used in RBE
studies: hard gamma rays (usually from Co-60) and x-rays (usually 200-250 kVp). Paragraph
53 of ICRP 92 (2004) noted RBE differences of 2 to 3 between these two radiations with thelatter being more effective. As a result, these two reference radiations have been the sourceof much confusion in determining the RBEs of tritium because a factor of 2 to 3 embraces
tritium’s own RBE values when compared with these radiations.
23. Hard gamma radiation (rather than 250 kVp x-rays) is the more appropriate reference
radiation to use with tritium for three reasons:(a) The Compton/photoelectron ratio produced by gamma rays is more similar tothat produced by beta particles.
54

(b) The ICRP in Publication 92 (2004) has recommended that hard gammas
should be used as the reference radiation for a number of other technicalreasons.
(c) ICRP 92 also stated that x-rays are approximately twice as effective as hard
gamma rays, indicating that the RBE values in the X ray experiments in table
3 above are about half the true RBE value.
24. For these reasons, Figure 1 presents a histogram of RBE results for tritiated water (HTO)/
gamma comparisons from Table 3. These range from 1.3 to 3.4, with a median of 2.2.
Figure 1 Distribution of RBE values for HTO/gamma comparisonsDistribution of RBEs for HTO/gamma
4
3.5

RBE

3
2.5
2
1.5
1
0.5
0
1

3

5

7

9

11

13

15

17

19

21

23

Experiment

25. Harrison et al (2002) reviewed the data on which current ICRP dose coefficients for HTO
were based and estimated that the RBE for tritium (HTO) was uniformly distributed between 1
and 2.5, with a median of 1.75. The authors also stated that an ICRP Task Force would beconsidering recommendations to double tritium’s dose coefficients for tritiated water andorganically bound tritium mostly due to uncertainties in tritium’s RBE. These
recommendations were not implemented, as the wR for tritium (HTO) remains at unity as ofJune 2005 and tritium’s dose coefficients have not been increased. Nevertheless, someauthors (see Lambert, 2001) have used increased dose coefficients for tritium in specific dosestudies.
(b) wR value for tritium
26. The latest ICRP Publication to discuss this matter was ICRP 92 (2004). This report statedthat it considered all the new RBE evidence, but it did not discuss the above evidence on
tritium. The ICRP decided to continue with a wR of 1 for all photons and electrons including
tritium. The report contained a number of arguments for this position which are considered indetail in Appendix VI. The conclusion is that the ICRP’s arguments are unconvincing and thatthe scientific evidence for an increase in tritium’s wR is very strong.

55

(c) Ionisation-density (LET) effects
The range of the beta-particle (i.e. electron) from the decay of a tritium nucleus is small becauseof its low energy of emission. A tritium beta particle of average (5.7 keV) or maximum (18.6 keV)
energy, has a range in tissue of approx 1 µm or 7 µm, respectively (ICRU 1970). Hence,
energies deposited per unit length of track are relatively large. Vennart (1969) stated they are"far greater for tritium than for carbon-14 and other ß-emitting particles."
27. When beta-particles move through tissue, they lose energy by ionising and exciting
molecules along their track, until they (and their secondary electrons) slow down to thermalenergies. Towards the end of the electron tracks, the average distance between ionisations issmall, so they deposit relatively large amounts of energy in very short distances. Fromexperiments with ultrasoft (photon energies 0.28–8.0 keV) x-rays, Goodhead and Nikjoo (1990)
concluded that:• ultrasoft x-rays, which interact in tissue to produce low-energy electrons, were morebiologically effective than equal doses of hard x-rays or gamma rays;• their RBEs increase with decreasing x-ray energy down to very low energies, for which theelectron track lengths are very short (~7 nm);• low-energy electron track ends were a predominant cause of cell inactivation in all low LET
radiations, by virtue of the contribution from the low-energy secondary electrons that arealways produced within the tissue; and• the isolated sparse ionisations and excitations along the remainder of the track were "ofrelatively little biological significance."
28. These conclusions have been widely supported, for example, by Frankenberg et al23 (1990)
and other studies summarized by Hill et al (2001). The particular microdosimetric approachtaken by the ICRU (1986), based on lineal energy over micrometre dimensions, also predicted
increased effectiveness for tritium beta particles and other low-energy electrons. Nikjoo andGoodhead (1991) further reported that low energy electrons were particularly efficient at
producing highly localised clusters of atomic damage over DNA-size (nanometre) dimensions,which could be responsible for a major part of the biological effectiveness of low-LET radiations.
29. These findings indicate that so-called "weak" radiations, which pack almost all of their punchat track ends, are equally as effective as "strong" radiations which dissipate as much as 70% of
their energies as sparse ionisations during the higher energy parts of their tracks. ICRP 30(1979) implicitly recognised this when it stated that the Q factor for internal emitters varied along
their disintegration tracks. However, the ICRP assumed that the Q factor was constant for agiven radiation. This may be a reasonable assumption for external radiations but it is inadequate
to describe microscopic features of the short track of tritium's beta particle.
30. Because of its short track, tritium’s energy deposition closely follows its cellular
distribution. Tritium’s RBE is therefore considered highly dependent on its congruence withradiosensitive sites. Current dosimetric models assume tritiated water intakes arehomogenously distributed as water. This is an assumption, as in most cases this is notknown. In addition, it is difficult to distinguish experimentally whether a biological effect fromtritium, relative to that from another radiation, is the result of(i) the heterogeneity of its concentration, or
23

Who observed, inter alia, that electron track ends induced double strand breaks in DNA.

56

(ii) an inherently greater effectiveness of tritium decaying from one particularorganic molecule rather than another.
(d) Tritium’s incorporation in DNA
31. Perhaps the most important target is DNA. Chromosome diameters for most cells are
between 0.3 and 1.0 µm. The average track length of the tritium beta particle in tissue is 0.5
to 0.7 µm (NCRP, 1979a). In this distance, the beta particle from tritium decay creates many
ionisations. Because this track length is of the same magnitude as the diameter of a humanchromosome, concern has been expressed (Ikushima et al, 1984), (Mathur-De Vre and Binet,1984) and (Commerford, Carsten and Cronkite, 1977) about tritium doses when incorporated
in DNA.
32. Although tritium is not the only nuclide which may be incorporated in DNA, hydrogen is by
far the most common element in the DNA molecule. Saito and Ishida (1986) indicated thatOBT from tritiated food was clearly incorporated within DNA. Commerford et al (1977)
indicated the same from chronic HTO ingestion. Commerford et al (1982) also found, after atransient HTO exposure to mice, all the tritium remaining 8 weeks post-exposure was boundto DNA and histone24. Although the amounts were small compared to the HTO in the cell, cell
nucleoproteins were much longer-lived. The authors concluded that doses from them would
exceed doses from HTO. DNA half-lives were extremely long: 318 days for mice liver DNA
and 593 days for mice brain DNA, i.e., about the lifespan of mice. In humans, DNA half-lives
would be longer. The authors concluded that the cells at most risk would be those dividing at
the time of exposure which afterwards were long-lived, i.e., key cells in embryos, nerve cells
and oocytes.
33. Tritium doses to DNA occur because of its incorporation within the nucleus. The
constituents of the nucleus are, on average, 70% (by weight) water, about 20% proteins, 3%
lipids, and the rest nucleoproteins: DNA constitutes about 3% of nucleus weight25(Commerford, 1982). Saito and Ishida (1986) calculated the percentage contribution ofvarious cell components, including DNA, to total cell dose, following the chronic ingestion oftritiated milk by suckling mice. They observed that initially between 1%–3% of the total dosein liver cells came from DNA-incorporated tritium. After 14 weeks’ ingestion of tritiated food,this rose to 10% and after 41 weeks’ ingestion to 52% of total tritium dose.
(i) Doses from HTO
34. Commerford, Carsten and Cronkite (1977), after chronic administration of HTO to mice,found nearly all the tritium in cell nuclei was tritiated water. Immediately at the end ofingestion, tritiated water gave the largest dose. Two to three days after the cessation of HTO
administration, most doses came from OBT. After 15 months, the DNA of the cells of various
mice organs was still tritiated at about the same concentration as the originally administered
HTO. Ovary DNA had the highest concentration ratio (1.07) of the HTO activity ingested, andspleen DNA the least (0.72). The same authors (1982) later found, after a transient HTO
exposure, all the tritium remaining after 8 weeks was bound to DNA and histone.
(ii) Doses from OBT
35. Etnier, Travis and Hetrick (1984) estimated that most protein in food crosses the human gut
24
25

Protein bead on which the DNA is helically wound inside the chromosome.
These proportions are illustrative, as ratios vary considerably among cell types.

57

wall and is available for incorporation, particularly essential amino acids. Commerford, Carsten
and Cronkite (1983) estimated that, on average, 55% of dietary protein was transferred to tissue
protein. They further estimated that, following an intake of the US recommended minimum daily
amount of daily tritiated protein, a standard nucleus would contain 4 times more tritium in theform of nuclear proteins than in the form of water. Komatsu et al (1990) fed rats with shrimps
containing tritiated protein. After 22 days' ingestion, 37% of the total tritium dose came from DNA
and was due to the long half-lives of DNA. They calculated that OBT doses to DNA in liver cells
were 4.6 times higher than after HTO ingestion.
36. Feinendegen et al (1980) found that chronically-administered amino acids were 2 to 4 times
more efficiently incorporated than thymidine into "the long-lived components of proliferating
tissues", i.e., DNA. They also found the distribution of amino acids among these components
was similar to that of nucleic acid precursors (see next paragraph) in some organs, and thesame was true for their turnover rates. They concluded that doses from tritiated amino acids inbone marrow stem cells were similar to tritiated thymidine and that tritiated amino acids were
therefore radiologically 25–50 times more effective than HTO.
37. Nucleic acid precursors have been studied extensively, particularly thymidine anddeoxycytidine, which is incorporated only in DNA. About 20 grams of DNA are synthesized each
day in humans: 4 grams of thymidine are required for this production. Other precursors, e.g.,
uridine and cytidine, are incorporated into RNA as well as DNA. Very small amounts of tritiatedthymidine and other precursors can be obtained directly from eating tritiated plants and animals(NCRP, 1979b). Lambert and Clifton (1968) estimated that, after an acute ingestion of tritiatedthymidine, more than 90% was broken down in the GI tract, and only 2% was incorporated into
DNA. NCRP Report 63 (1979b) estimated that 5% to 10% of tritiated thymidine would beincorporated in humans after eating tritiated foodstuffs. Takeda (1991) observed uptake levels of
7%–20% into OBT (i.e., some into DNA), depending on the organ, after 22 days' chronic
ingestion of tritiated thymidine in rats.
38. In the past, differences of view have existed about the dangers of tritiated thymidine, which isa laboratory tracer, not a food. In practice, the greater danger is likely to emanate from tritiatedprotein in foodstuffs, as tritiated protein is more likely to be ingested (e.g., from foods grown,
reared or cultured near tritium-releasing facilities) than tritiated thymidine. However, great carehas to be taken with facilities which manufacture (and discharge to the environment) tritiatedproteins and nucleic acid precursors.
39. It is concluded that tritium clearly can be incorporated in DNA. The studies by Commerford
et al, Komatsu, and Saito and Ishida indicate that tritiated foods (OBT) are quicker and more
effective than HTO in delivering radiation doses to the cell nucleus and DNA. Proteins (aminoacids) are more efficiently incorporated into nucleoproteins than thymidine, and doses fromtritiated proteins to DNA are four times greater than from HTO.

58

Chapter 15 Conclusions
40. Conclusions and recommendations are made on the following matters:• tritium’s hazardous properties,• tritium’s dose coefficients, and• possible risks from tritium exposures.
(a) Tritium’s hazardous properties
It is concluded that tritium’s properties, including its ubiquity, rapid transport, and propensities
to exchange, bind with organic molecules, concentrate in DNA’s hydration shell, and haveionisation density in small volumes should be more widely recognised and discussed. It is
recommended that up-to-date information on tritium’s properties should be published andmade available to regulatory agencies. In particular, a hazard guide for common radionuclides
should be published, taking into account the properties of nuclides as well as theirradiotoxicities. Such properties should include (see Kirchner, 1990):
(i)
(ii)
(iii)
(iv)
(v)
(vi)
(vii)
(viii)

radiotoxicity (i.e., ICRP dose coefficient),
rapid nuclide transport and cycling in the biosphere,
global distribution,
rapid pathways to man,large nuclide fractions ingested or inhaled,organic binding,long half-lives, andnuclide decay chains and their products.

(b) Dose coefficients
It is recommended that tritium’s dose coefficients should be increased as follows. First,
tritium’s wR should be increased to 2. Second, its biokinetic model should be improved torecognise tritium’s long-lived OBT components and chronic exposures. This would increase
HTO’s doses by a factor of ~3. Third, tritium’s other properties of rapid transport and uptake
merit a factor of 2. Multiplying these factors means that HTO’s dose coefficients should be
increased by 2 x 3 x 2 = 12—or more simply, an order of magnitude. This would still leavetritium’s dose coefficient ~70 times lower than that for Cs-137.
41. It is also recommended that OBT’s dose coefficient should be ~5 times greater than that
estimated for HTO; currently it is 2.3 times greater. The rationale for the factor 5 is as follows.
The most hazardous form of OBT in diet appears to be tritiated protein. It is recalled thatabout 22 of the 40 or so amino acids which constitute proteins are essential amino acids (e.g.,leucine and lysine), in that they are not manufactured in the body but taken up directly fromdiet. From the study by Komatsu et al (1990), OBT doses following tritiated protein intake were
4.6 times greater than from HTO. Feinendegen et al (1980) estimated even greater doses fromtritiated proteins. A conservative approach would be to provide a level of protection for tritiatedprotein which would cover the other constituents of food, i.e., tritiated lipids and tritiatedcarbohydrates. Therefore a factor of 4 or 5 should be applied to all OBT in diet.

59

(c) Possible risks from tritium exposures
42. In pregnant women, cell proliferation occurs in the zygote, embryo, and foetus stages.
Transient high concentrations of HTO could result in the ingestion/inhalation of HTO by
pregnant women and tritium labelling at crucial points of embryo development. This could
result in increased rates of untoward pregnancy outcomes, including stillbirths, congenital
malformations and neonatal deaths. This concern was first raised by Professor Edward
Radford (Provincial Government of Ontario, 1978) in testimony to the Ontario SelectCommittee on Hydro Matters, which examined possible health effects of large tritium
discharges from nuclear facilities near Toronto, Canada. It was also raised by Commerford etal (1982), who stated that cells at most risk would be those dividing at the time of exposure
which afterwards were long-lived, i.e., key cells in embryos (including nerve cells andoocytes). Straume (1991, 1993) estimated that tritium’s teratogenic risks were 6-fold greaterthan tritium’s carcinogenic risks, although strictly speaking it is difficult to compare thesedifferent risks. It is recommended that further epidemiological research should be carried out
on possible teratogenic risks of exposure to tritium, which takes due account of the findings of
the AECB reports.

60

Appendix I to Part 2

Previously Expressed Concerns about Tritium"The present study clearly demonstrated that HTO [tritium] severely injures human stem cells
to the same extent as 252 Cf neutrons, especially in the low dose range." Shigeta et al(1989).
"Although classified among the least toxic of the important radioactive atoms, there isconsiderable hazard with the ingestion of even low doses of tritium." Killen and Carroll (1989).
"The extreme sensitivity of the pre-implanted mammalian embryo to the ß radiation of tritiatedcompounds of metabolic importance points to the necessity for a re-evaluation of tritium risks
for human beings, not only for workers exposed to occupational hazards, but also for thosesubject to chronic low doses." Clerici et al (1984).
"The question of main practical concern is ... the possibility that significant biological effects
may result from protracted exposure to low tritium concentrations in water.” Vulpis N (1984).
"For mouse immature oocyte killing, tritium administered chronically as 3HOH is of near
maximum possible radiobiological effectiveness. The implication: tritium in the form mostcommonly encountered as an environmental pollutant may actually be as effective as themost damaging high-LET radiations in reducing the fertility of certain other species as well... ahighly sensitive germ-cell stage exists prenatally in at least some primate species... By
implication, such a highly vulnerable stage may also exist in the prenatal human female."
Straume T, Kwan TC, Goldstein LS, and Dobson RL (1989) (emphasis in original)"...through various metabolic pathways [tritiated water] may enter any hydrogen position inorganic matter including DNA, the most sensitive target for various radiation effects. The low
energy of the ß emission from tritium produces relatively dense radiation tracks and causes
localised deposition of dose in tissue. Considering these facts, there is concern about theability of HTO to produce cytogenetic damage." Ikushima et al (1984)“...the absorption of tritium energy occurs in the immediate vicinity of the tritiated nucleotide(DNA). Thus, tritiated water represents a very complex internal source of radiation causing
concern about the health risks arising from exposure of human beings to it." Mathur-De Vre R
and Binet J (1984)"The tritium content of the chromosome, especially DNA, is particularly significant since suchtritium is likely to cause genetic and somatic damage and to persist for very long periods oftime." Commerford SL, Carsten AL, Cronkite EP (1977).
"When tritium is incorporated into biologically important molecular sites such as the DNA, its
production of genetic damage per unit of energy deposited has been measured to be higher
than a similar dose from protracted exposure from most (low-LET) external radiation. Thismay be related to the increase in LET at the end of the ß-particle range and the short range ofthe ß-particle from 3H. This would result in much of the energy being deposited in the nucleus
with a higher LET and effectiveness." NCRP Report No. 89 (1987).
"...it is...becoming increasingly important to study the genetic damage that this isotope canproduce in man after incorporation, resulting both from irradiation by the tritium ß
particles...and from the local effects of transmutation." Pelliccia et al (1988).
61

“.. there has been considerable apprehension about the incorporation of tritium into genetic
material as the result of the very short range of the tritium ß particle and the possible effectsof transmutation." Cronkite EP, Robertson JS and Feinendegen LE (1973).
"the radiation dose [of tritium] delivered to specific tissues, for example bone marrow, may begreater following the ingestion of organically bound tritium by almost an order of magnitude ascompared to HTO [tritiated water]." Taylor DM, Moroni JP, Snihs O, Richmond CR (1990).
"The major part of the tritium uptake by members of the public will occur by ingestion of foodinto which tritium has been incorporated into both plant and animal components. Suchorganically bound tritium (OBT) will be present in many different chemical compounds
including proteins, carbohydrates, fats and nucleic acids." ICRP Publication 56, 1989.
"All tritium models currently in use ignore the fact that organically-bound tritium in foodstuffs
may be directly assimilated in the bound compartments of body tissue without previous
oxidation ... properly accounting for metabolism of organically bound tritium in foodstuffs canincrease cumulative dose estimates by as much as a factor of 4 or 5 over doses estimated forfree body water [tritium] alone.” Travis CC et al (1984).
"... in view of the relatively large amounts of 3H and 14C which may be produced fromexpanded fission energy or from future fusion energy programmes, it is desirable to reevaluate their potential to cause serious damage to human health." Taylor DM, Moroni JP,
Snihs O, Richmond CR (1990).
"The hazards of tritium in the environment are becoming of increasing concern as by-productsof nuclear power generation and fusion research." Little JB (1988).

62

Appendix II to Part 2

Equilibria between OBT and HTO Levels after Chronic HTO
Exposures

In animals, Commerford et al (1977) showed OBT/HTO ratios between 0.73 and 1.07 in the
DNA of cell nuclei of various mice organs after 15 months' HTO ingestion. Other studies(Koranda and Martin 1973) (Hatch et al, 1970) and (Evans, 1969) of animals living in tritiumcontaminated sites indicated OBT/HTO ratios between 0.85 and 1.5. However it is possible
these animals could have consumed OBT as well as HTO in their natural habitats.
In humans, Pinson and Langham (1957) found tritium concentrations in the organic
constituents of fat and hair (i.e., OBT) removed from a man who died after eight months'
chronic exposure to tritiated water were higher than that in body water at the time of autopsy.
Rudran (1988b) studied the retention of tritium in eight workers chronically exposed to HTO ata heavy water nuclear station. She concluded that the fraction of HTO organically bound waslarger than that assumed by the ICRP, and that the committed OBT dose equivalent was 3.4
times higher than that based on HTO alone.
Everyone is chronically exposed to background tritiated water levels (approximately 5–10
Bq/L). A number of older studies have examined naturally-occurring OBT/HTO ratios inhumans. Bogen et al (1973), Bogen et al, (1979), Ujeno et al (1989), and Hisamatsu et al(1989) in the US and Japan found these ratios were usually unity or slightly higher than unity.
The same is found in older studies of background OBT/HTO ratios in plants (Belot, 1986).

63

Appendix III to Part 2

Isotope Effects In DNA’s Hydration Shell

Mathur-De Vre and Binet (1984) and Mathur-De Vre (1979), using magnetic resonance (MR)techniques, showed that water molecules were bound to DNA and RNA by electrostaticinteractions and extensive hydrogen bonding. This water of hydration accounts for 60% (Cooke
and Kuntz, 1974) of the weight of the DNA macromolecule. Mathur-De Vre et al (1983)
estimated that the biological half-life of the hydration water of human DNA was 30 days. Gregolis
et al (1982) found using MR techniques that hydrated DNA was more sensitive to gamma
radiation than DNA without its bound water.
Mathur-De Vre and Binet (1982) observed that tritiated water was concentrated in the hydrationwater of DNA. This was due to the fact that hydrogen bonds between macromolecules and HTO
are stronger than those with ordinary water, because intermolecular bonds between H-1 and H-3
are energetically more stable than those between H-1 and H-1. This is an example of an isotopic
effect. The isotopic difference between H-1 and H-3 is a factor of three—the largest difference
between any isotopes.
Mathur-De Vre and Binet stated that the role of hydration water in mediating initial radiation
damage was "of great significance but has received little attention so far." They added that "thehydration water of DNA represents the fraction of cell water that is most effective for inducing
radiobiological effects." Mathur-De Vre and Binet concluded "the hydration fraction of HTO
constitutes an effective source for inducing initial molecular damage. At least some of these
tritiated water molecules are located in very close contact with the macromolecular chains at a
distance that is shorter than the maximum range of tritium ß-particles. This points out theimportance of micro-localisation of initial energy deposition from hydration tritiated water in
defining the RBE of HTO." However, few other scientists have discussed these findings (seeCommerford,1982; and Baumgartner, 2002).

64Appendix IV to Part 2

Controversy over Tritium’s RBE

In the past, considerable controversy existed over tritium’s RBE and its Q or wR value. ICRP
Report 2 (1959) established the RBE for tritium's beta-radiation to be 1.7 and the ICRP (1963)
assigned a Q factor for tritium of 1.7. However in 1969 the ICRP reduced it to 1.0 (Dunster,1969) with little explanation, despite the preponderance of evidence to the contrary at the time
(Brues et al, 1952; Oliver and Lajtha, 1960; Dewey et al, 1965; Hall et al, 1967; andLambert,1969).
Unfortunately, in the past, non-scientific considerations may have played a part in thesetting of tritium’s quality factor, at least in the US. Professor Karl Morgan, former member of
the ICRP and former chairman of a main ICRP committee, stated (1990) that during the Cold
War in the 1950s and 1960s"…there was constant pressure to set the RBE at 1.0 instead of 1.7. One ICRP member
even went so far as to lament the difficulties they were having in keeping down to thetritium Maximum Permissible Concentrations (MPCs) in their weapons production plant,
and our lowering the RBE to one would be a great help... Thus the way of reducing risk ina weapons production plant has been to get the ICRP and the US National Council on
Radiation Protection (NCRP) to relax radiation protection standards, raise the MPC
values, and have them adopted by the US Department of Energy and the US Nuclear
Regulatory Commission."
After 1969, many observers (Johnson 1973; Cronkite, Robertson and Feinendegen, 1973;
Moskalev et al, 1973; Berry et al, 1973; and Carsten, 1979) continued to query the choice of 1
for tritium’s RBE. The NCRP (1979a, 1979b) reviewed the matter at length and concluded
that an RBE of 1 could be ascribed to tritium, but only where the reference radiation was 60–
80 kVp x-rays. In the body (but not the conclusion) of the report, it stated that, using thenormal reference radiation of 200 kVp x-rays, its RBE was closer to 2. In 1980, Till et al(1980a, 1980b) from the US Oak Ridge National Laboratory mounted rigorous andcomprehensive examinations of tritium’s RBE. Their reports criticised the choice of unity andconcluded that copious evidence indicated tritium's Q factor should be at least 2.
In 1986, a joint Committee from the ICRP and the ICRU26 recommended an increase in thequality factor for tritium from 1 to 2, for microdosimetric reasons (ICRU, 1986). This
recommendation was not implemented by the ICRP. Instead, ICRP 60 continued torecommend a radiation weighting factor (wR) of 1 (ICRP 1990) for all (except Auger)
electrons. For Auger emitters, it recommended microdosimetric techniques be used, although
the likely doses from doing so were not discussed.

26

International Commission on Radiation Units and Measurements, sister organisation to the ICRP.

65

Appendix V to Part 2

Transmutation Effects

When a tritium atom disintegrates, it emits radiation in the form of a ß-particle and transmutes toa helium ion, chemically and physically different from a hydrogen atom. This helium ion recoilsfrom its ß-particle emission and has associated excitation energy. These processes rupture thebond to the compound to which the former tritium atom had been attached; this results in thecompound acquiring a positive charge and becoming chemically active. The above effects, apartfrom radiation, are collectively known as transmutation effects. Since the recoiling nucleus is thesecond smallest of all radionuclides, the associated recoil velocity might be expected to beconsiderable.
NCRP Reports 62, 63 and 87 (1979a, 1979b and 1987) reviewed earlier studies on tritium's
transmutation effects: no recent studies exist. Feinendegen and Bond (1973) concluded tritium's
transmutation effects were small in comparison to the effects of its ß-radiation. It is difficult todistinguish these effects experimentally because of the short track length of the ß-particle.
Concern about transmutation has focussed primarily on the mutagenic effects of tritiumincorporated into protein, including DNA, precursors. For reasons that are not understood,
strong transmutational effects occur when tritium is situated at certain carbon positions in theirpurine and pyrimidine rings. Tritium at the number 5 carbon position in cytosine (incorporated in
DNA as uridine or uracil) was found (Person et al, 1964) to be 7 times more mutagenic thantritium at other positions on the ring. This increase was estimated to be due to transmutation
alone and not to radiation. Smaller transmutation effects for tritium at 6-thymidine and 2-adenine
positions have also been found (Person et al, 1976). Krasin et al (1976) observed that half oftritium decays in 2-adenine in DNA resulted in strand-strand DNA cross-links, due totransmutation alone, over and above radiation effects. Tisljar-Lentulis et al (1983) found about athird of single-strand DNA breaks caused by tritium decay in 6-thymidine were due totransmutation. Ueno et al (1989) found that tritium in 6-thymidine position was 2.7 times morelethal to cells and 2 times more mutagenic than HTO. They postulated this could be due to"mechanisms other than radiation." Ueno et al (1982) and Tano (1986) found similar effects forthymidine tritiated at the methyl position, not previously reported as having transmutational
effects.
The percentage of hydrogen atoms at the positions mentioned above in a DNA molecule issmall. For example, only about 2% of the hydrogen atoms in a DNA molecule are at the 5position of cytosine. More research needs to be carried out to elucidate the mechanisms andeffects of transmutation. However, for the time being, these do not appear to have as muchsignificance as OBT doses, RBE evidence and distributional effects.

66Appendix VI to Part 2

ICRP 92 Arguments for Retaining a wR of 1 for Tritium

ICRP 92 defended its recommendation of a wR of 1 for all photons and electrons by statingthat there was little epidemiological evidence on which to base any differences (preface
Editorial). It also stated that uncertainties in risks were large“… given the UNSCEAR 2000 judgement of several-fold uncertainty on the judgement of
the nominal risk coefficient for cancer, including that for the dose and dose-rate
effectiveness factor (DDREF), we do not see the need to ascribe different values of wR todifferent low-linear-energy-transfer (LET) radiations. A wR of 1 may therefore be retained
for all low-LET radiations” (preface Editorial).
However the same points (scarcity of epidemiological evidence, uncertainty in risks) also
apply with greater force to neutrons and protons, but this did not stop recommendations being
made for different wR values in their cases. In fact, the report recommended differences in wRvalues for neutrons (which vary by about a factor of 4, depending on energy), and for protons(whose wR is reduced from 5 to 2, i.e., a factor of 2.5). However the ICRP 92’s findings (seeparagraph 53) of RBE differences of 2 to 3 between conventional x-rays and hard gamma
rays were not accommodated. Similarly, RBE differences between beta particles and gamma
rays were also not discussed.
In the extract above, the ICRP states that a wR of 1 may be applied to “all low-LET radiations,”
but this leaves unexamined the higher LET radiations from low-energy beta and Auger
emitters. This matter was examined in the mid-1980s by a joint ICRU and ICRP Task Group.
Its report—ICRU Report 40—stated that RBE values of photons/electrons were inversely
energy dependent: as photon/electron energies decreased, their RBEs increased. For
photons/electrons with energies below about 10 keV, ICRU Report 40 stated that differencesin RBE could amount to 2 at doses below 100 mGy and it therefore recommended a Q valueof 2 for low-energy beta particles, including those from tritium (ICRU, 1986). These
recommendations were never implemented by the ICRP.
Second, the ICRP is understood to have defended its decision to continue with a wR of 1 fortritium by referring to RBE values of 1.2 in two RBE studies (by Gragtmans et al, 1984; andJohnson et al, 1995) on cancer induction in mice and rats. Although animal data on
carcinogenicity need to be taken into account, the ICRP reply nevertheless indicates a
selective view of the large body of RBE evidence available on tritium, as set out in Table 3.
More important, these two animal studies used x-rays as their reference radiation. However,
hard gamma would have been the more relevant reference radiation to have used, for two
reasons. First, the Compton/photoelectron ratio produced by gamma rays is more similar tothat produced by beta particles. Second, the ICRP itself has recommended that hard gammas
should be used as the reference radiation for a number of other technical reasons. As statedby ICRP 92, x-rays are approximately twice as effective as hard gamma rays, which meansthat the correct RBE would be about double the observed value of 1.2, thus fitting in with mostother values observed with gamma as the reference radiation.
Third, ICRP 92 stated that wR and RBE values may be different as they are used for different
purposes:67

“…there is no conflict between the fact that all photon radiations are …given the same
weight, while risks… of soft x-rays, conventional x-rays, and hard gamma rays areassessed differently. wR is designed for the practice of radiological protection, not for
specific risk assessment. … it is not meant to be applied in the derivation of quantitativerisk estimates under specific conditions” (paragraphs 82 and 83).
It further explained that“…wR is a quantity intended for use in radiological protection and was not developed foruse in epidemiological studies or other specific investigations of human exposure. For
these other studies, absorbed dose in the organs of interest and specific data relating to
the RBE of the radiation type in question are the most relevant quantities to use” (preface
Editorial).
These statements are disingenuous as the distinction between RBE and wR is simply notmade in practice: when quantitative risk estimates under specific conditions are being
estimated, ICRP wR values are almost invariably used by practitioners and regulators. The
reason is that ICRP guidance on recommended RBE values does not exist at present (except
for Auger emitters). Given this absence, wR values and effective doses will continue to be
used routinely in retrospective dose assessments, epidemiological studies or medical
exposures, regardless of the ICRP’s admonitions to the contrary. If the ICRP really wishes wRvalues not to be used in the above circumstances, then it will need to recommend RBE values
for use in such situations, i.e., for specific nuclides, ideally in their various chemical forms andfor specific organs or tissues. Without such guidance, a danger exists of different regulatory
bodies using differing RBE values for the same nuclides in specific dose assessments, etc.,
which would be a recipe for confusion.
The ICRP policy not to recommend more realistic higher wR values for low-range photons andelectrons is unsatisfactory for a number of reasons. It is not precautionary: that is, it does not
err on the safe side for radiation protection purposes. The ICRP’s disinclination to allocate
higher wR factors to low-range photons and electrons has direct implications, as regards
radiation protection, for low-energy beta emitters are commonly discharged from nuclear andother industrial facilities. It may also have consequences for radiation protection in nuclear
medicine, as regards widely-used Auger emitters, and for mammography x-rays.

68Appendix VII to Part 2

Epidemiological Evidence

For a number of reasons, epidemiology studies are a blunt tool for discovering whether
adverse effects result from radiation exposures. This is because epidemiology studies,
generally speaking, have many methodological limitations. These include the following:• Strict data requirements: Ideally, epidemiology data is required with good case identification,
uniform registration, clear diagnostic criteria and uniformity of data collation. These datarequirements are often difficult to fulfil and make large demands on time and resources.
• Confounding factors: The true causes of morbidity or mortality can be uncertain, due to
confounding factors such as socio-economic status and competing causes of death.
• Bias: Smoking and alcohol cause major increases in overall mortality and morbidity, and incancer and cardiovascular disease. These require careful handling of the raw data to avoid
bias.
• Poor signal to noise: Only large, expensive and lengthy epidemiology studies are able toreveal effects where the signal (added cancers) is weak, and the noise (large numbers of
spontaneous cancers) is strong.
• Uncertain doses: Establishing causality often requires estimating doses in order to show adose-effect relationship. However, large uncertainties often exist in estimating doses—
especially from internal radiation, e.g., from tritium.
• Wide confidence intervals: Usually findings (e.g., risks or odds ratios) are expressed with
95% confidence intervals. That is, the range of values within which the true value lies 95% of
the time. But often this range can be very wide—simply because of low numbers of cases—
which severely limits what we can conclude from the findings.
Many epidemiology studies are first stage “ecologic” studies, that is, they are quick studies
which look at health or population data and not at individual data. Their findings should be
regarded as perhaps indicative and not conclusive. If their findings are suggestive of an
adverse effect, then these should be investigated further by more detailed second-stage
epidemiology studies, that is, cohort or case-control studies. These studies match “cases”(i.e., those who have an adverse effect) with randomly-selected similar individuals, in order tominimise bias and confounding influences. However, fewer of these are carried out becauseof their greater expense and longer timespans. The conclusions are that we need to be moreaware of the factors to be taken into account when considering epidemiology studies, and that
we need to interpret their findings with great care. Therefore readers are advised to lower
their expectations when considering individual epidemiology studies.
Another problem is that the results of epidemiology studies are unfortunately often the subjectof controversy. On the one hand, official agencies are often accused of “playing down” thefindings of increased incidences of ill health, much to the concern of local groups who may
have a different viewpoint. It is often difficult to keep to the scientific findings of epidemiology
studies and to accurately assess their worth, especially when they are contested in the media.
But that is what is necessary, and is what this report will attempt to do.
Despite these caveats, epidemiology studies are still useful as they are one of only twosources of information (the other being cell or animal studies) about the effects of radiation.
They are also the main source of information about their effects in humans.

69

1. Leukemia in children near Candu nuclear facilities (ecologic study)
Clarke et al. (1989, 1991) studied mortality and incidence of childhood leukemia near
nuclear facilities in Ontario. The first report (Clarke et al. 1989) considered leukemia deaths
and cases at ages 0–4, and the second (Clarke et al. 1991) considered cases and deaths atages 0–14. Data for areas “nearby” (<25 km), the 16 reactors at Bruce and Pickering overthe period 1971–1987, were pooled together to increase statistical significance. The findings
were 36 leukemia deaths at ages 0–14 vs 25.7 expected (SMR = 1.40, 95% CI 0.98–1.9)
indicating an excess leukemia mortality with borderline statistical significance, However theconfidence intervals were wide: the data were consistent with there being no increase andwith there being a 90% increase in leukemia.
However there were indications which warranted further investigation: higher leukemia death
rates after the reactors had started than before; more deaths when counted at place of birththan at place of death; and the magnitude of the higher confidence interval. It is notable thatdifferent levels of statistical significance were adopted by the two reports. The first was 10%,and the second 5%. If the 10% level had been chosen in the second study as it had been in
the first, the leukemia increase would have been considered "statistically significant".
Unfortunately there were no estimates of tritium doses in this study. The authors
recommended further case-control research.
2. Birth defects and infant mortality in the vicinity of the Pickering nuclear facility,
Ontario (ecologic study)
Johnson and Rouleau (1991) studied birth defects, stillbirths, perinatal, neonatal and infantmortality within 25 km of the Pickering nuclear station. They also studied these endpoints inrelation to airborne and waterborne discharges of tritium from Pickering, concentrating on the
Pickering and Ajax townships closest to the Pickering plant. Again there were no estimates oftritium doses.
The incidence of central nervous system defects was significantly elevated in Pickering
township for the highest level of airborne emissions (odds ratio in highest group = 4.01 (95%
CI 1.25, 14.04), based on 6 cases), but no statistically significant trends with tritium
emissions (p=0.197) or ground-monitoring data (p=0.24) were observed.
There was a statistically significantly raised prevalence of births with Down syndrome in
Pickering township (24 observed vs 12.9 expected [relative risk = 1.85, 95% CI 1.19, 2.76]),
But 23 other birth defect endpoints did not show such an excess. There was a correlation,although not statistically significant (p=0.468), between Down syndrome prevalence andairborne tritium release, but no correlation with ground tritium concentrations. There were nosuch excess birth defect risks in Ajax township (slightly further away), although there was apositive correlation, but again not statistically significant (p=0.282) with ground tritium
concentrations.
The very mixed results from this study are difficult to interpret, but the raised incidence of
Down Syndrome (formerly called mongolism) cases is notable, as many Chernobyl studies(see box below) also indicated excess cases in areas exposed to radioactive fallout,
including tritium. However, the authors of the study stated that it was difficult to see why theincidence of Down Syndrome alone should be increased and not the many other forms ofcongenital malformation, e.g., spina bifida and cleft lip/palate. This is a good question andthere is no answer at present. However, just because we do not know the answer does not70

provide a reason to discount the observed association and a possible connection between
tritium exposures and Down Syndrome.
Studies of increased incidences of Down Syndrome after Chernobyl exposures
Boice J, Linet M (1994) Chernobyl, childhood cancer, and chromosome 21. BMJ. 1994 Jul
16;309(6948):139-40.
Burkart W, Grosche B, Schoetzau A (1997) Down syndrome clusters in Germany after the Chernobyl
accident. Radiat Res 1997 Mar;147(3):321-8.
Ericson A, Kallen B (1994) Pregnancy outcome in Sweden after the Chernobyl accident. Environ Res
67:149-59.
Harjulehto-Mervaala T, Salonen R, Aro T, Saxen L (1992) The accident at Chernobyl and trisomy 21
in Finland. Mutat Res. 1992 Mar;275(2): 81-6.
Hoffmann W (2001) Fallout from the Chernobyl nuclear disaster and congenital malformations in
Europe. Archives of Environmental Health 56 478-484.
Little J (1993) The Chernobyl accident, congenital anomalies and other reproductive outcomes: areview. Paediatr Perinat Epidemiol. 1993 Apr;7(2):121-51.
Ramsay CN et al (1991) Down’s syndrome in the Lothian region in Scotland – 1978-1989. Biomed.
Pharmacother. 45:267-272.
Scherb H, Weigelt E (2003) Congenital Malformation and Stillbirth in Germany and Europe Before andAfter the Chernobyl Nuclear Power Plant Accident. Environmental Science Pollution Research ESPR
Special (1) 117-125.
Sperling K et al (1994) Significant increase in trisomy 21 in Berlin nine months after the Chernobyl
reactor accident: temporal correlation or causal relation? BMJ. 1994 Nov 12;309(6964):1299.
Sperling K, Pelz J, Wegner RD, Dorries A, Gruters A, Mikkelsen M (1994) Fallout from Chernobyl.
Authors stand by study that Chernobyl increased trisomy 21 in Berlin. BMJ. 1994 Jul
16;309(6948):139-40.
Sperling K et al (1991) Frequency of Trisomy 21 in Germany before and after the Chernobyl Accident.
Biomed and Pharmacother 45, 255-262.
von Muhlendahl KE, Muck K (1996) Chernobyl, low-dose radiation, and trisomy 21: possibly
something to worry about. Eur J Pediatr. 1996 Jul;155(7):612-4.

3. Offspring of Canadian nuclear workers (case control study)
Green et al (1997) assessed cases of congenital abnormalities and matched controls in theoffspring of Canadian nuclear workers. (763 case-control pairs of fathers, and 165 casecontrol pairs of mothers.) Tritium doses were assessed for those cases/controls having arecorded tritium dose 60 days before conception versus those with no dose. The study
revealed possible evidence of increased chromosomal disorders with tritium exposure, but
the number of cases (two) is very small and confidence intervals very wide. Why there should
be a tritium-associated increase only in chromosomal disorders but not other disorders is notknown. However, as stated above, just because we do not know the answer does not provide
a reason to discount the observed association and a possible connection between tritium
exposures and chromosomal disorders.

71Table A Adjusted odds ratios (and 95% CI) for congenital abnormalities according to tritium
exposure (recorded dose 60 days before conception vs none)
DisorderOdds Ratio (95% CI)
Single gene disorders
Chromosomal disorders
1.46 (0.24, 8.80)
Multifactorial disorders
1.13 (0.66, 1.94)
Genetic, unspecified
0.80 (0.27, 2.32)
Unknown disorders
0.84 (0.40, 1.76)
Total
0.99 (0.67, 1.47)
Source: From Table 2 in Green et al (1997).

4. Offspring of Ontario radiation workers
McLaughlin et al (1992, 1993) considered cases of childhood (ages 0–14) leukemia in theoffspring of Ontario radiation workers and matched cases. Tritium workers were those
employed at the AECL laboratories at Chalk River, and 5 power stations (Rolphton,
Pickering (A, B), Bruce (A, B) (112 cases and 896 controls). Preconceptional tritium doses
were assessed for this group. There was some evidence of raised risks with internal tritium
plus external radiation exposures but with wide confidence intervals (see Table B). It isdifficult to be more precise, as apparently there were no leukemia cases in the offspring ofparents estimated to be only receiving tritium doses (see Table C).
Table B and Table C
Odds ratios (and 95% CIs) for leukaemia cases among offspring of workers monitored fortritium in Ontario
Table B

Cases (number)Controls (number)Odds ratio (95% CIs)

Estimated whole dose (external + tritium) before
diagnosis (mSv)
0 mSv≥0.1 mSv
103
9
826
64
1.00
1.19 (0.51, 2.73)

Table C

Cases (number)Controls (number)Odds ratio (95% CIs)

Estimated tritium dose before conception (mSv)
0 mSv≥0.1 mSv
112
0
876
14
1.00
0.00 (0, 2.39)*

Source: From table III in McLaughlin et al (1993).
*
1-sided p=0.25 (Fisher’s exact test).

The odds ratio is defined as the ratio of the odds of an event occurring in a group under study
to the odds of it occurring in another (control) group. An odds ratio of 1 indicates that theincidence under study is equally likely in both groups. An odds ratio greater than 1 indicatesthat the condition is more likely in the study group. And an odds ratio less than 1 indicatesthat the condition is less likely in the study group.

72

5. Canadian nuclear workers
Zablotska et al. (2004) studied mortality in more than 45,000 Canadian nuclear workers
between 1957 and 1994. Tritium doses were calculated from urinalysis data, and added toexternal (film-badge) doses. The study did not indicate tritium doses, but states that for someworkers these could have been large. Overall, the mean dose was 13.5 mSv, and among
those recorded as having “some dose” it was 19.7 mSv. The resulting excess relative risks(ERRs) per Sv were high and were mostly statistically significant, though with wide CIs (seeTable D).
Table DAll leukemia, excluding CLL
Rectal cancer
All solid cancers

ERRs per Sv
52.5
34.1
2.80

95% CI
0.205, 291
1.41, 165
-0.038, 7.13,

2-sided p test
0.048*
0.029*
0.054+*Statistically significant at 5% level.
+Borderline significance.

Of interest, is the fact that, with an ERR per Sv of 52.5 for leukemia, the ERR for nuclear
workers with the average dose of ~20 mSv would be 1.05, i.e., their leukemia risk was about
double the spontaneous risk of leukemia in the population. Similarly the ERR for all solidcancers of 2.8 means that the ERR for nuclear workers with the average dose of ~20 mSv
would be 0.056, that is, about a 5% or 6% increase in the spontaneous risk—or a rise from
30% to 35% in their risk of dying from a solid cancer.
Interestingly, the study examined the risks of those exposed only to external radiation (i.e.,
gamma rays) and compared them with the risks of those exposed to both external gamma
and internal tritium doses. If the average risks per Sv for two groups were found to be thesame this would indicate that the risk from (say) one Sv of tritium’s beta radiation wasapproximately the same as the risk from one Sv of gamma rays. However, this was notfound. Instead, those exposed to tritium were subject to higher risks, per sievert of tritium
exposed, as indicated in Table E below. Unfortunately it is not possible from the study data toascertain by how much tritium doses are more effective (risk-wise) than gamma doses.
These data suggest that tritium doses were underestimated, or that tritium’s dose coefficientsare too low, or both of these.
Table EAll leukaemia
All
solid
cancers

ERR Sv-1
without tritium doses
16.3
2.67

ERR Sv-1
with tritium doses
18.9
2.80

% Increase
16%
5%Studies of radiation-associated risks among workers chronically exposed to low doses ofradiation are important, both to estimate risks directly and to assess the adequacy of
extrapolations of risk estimates from high-dose studies. Zablotska et al examined 45,468
nuclear power industry workers from the Canadian National Dose Registry, monitored (formore than one year) for chronic low-dose whole- body ionising radiation exposures between
1957 and 1994 (mean duration of monitoring = 7.4 years, mean cumulative equivalent dose =13.5 mSv). The excess relative risk for leukemia (excluding chronic lymphocytic leukemia)
73was 52.5 per sievert (95% confidence interval [CIs]: 0.205, 291) with the association having ap-value close to 0.05 (i.e., the association was statistically significant at the 5% level).
Relative risks for leukemia increased as the dose increased.
The excess relative risk for all solid cancers was 2.80 per sievert (95% CIs: -0.038, 7.13)
with the association having a p-value also close to 0.05. The relationship between solidcancer risk and dose was less consistent than with leukemia risk. Although these point
estimates are considerably higher than those found in other studies of whole-body irradiation,
the difference could still be due to chance because of the wide confidence intervals. (Recall
that readers were warned earlier not to have high expectations of epidemiology studies).
6. Congenital malformations in India
In April 1991, the UK Channel 4 TV programme "The Price of Power" revealed apparently
high incidences of congenital malformations in babies born downwind of the two Candu
reactors at Kota in Rajasthan in India, which discharge large amounts of tritiated water.
Gadekar et al (1994) also found significantly increased incidences in congenital
malformations in children, compared with those in an area remote from the reactors. The
relative risk (RR) of congenital malformations in children (<18 years) for the area near thereactors was 3.45 (CI 1.67 and 7.59). In younger children (<11 years) the RR was 5.08 (CI2.14 and 12.06). The authors stated that tritium discharges from the reactors were larger thanthe published emissions from Canadian reactors and they recommended further studies.
These have not been carried out.
7. Unpublished studies
In 1988, Durham Nuclear Awareness, an environment NGO in Canada, published a report by anindependent researcher (David McArthur), which found a correlation between fatal birth defects
and neonatal deaths with lagged tritium water emissions from the Pickering nuclear plant
between 1978 and 1985. This report is similar in its findings to that of another independent
researcher (Hugh Richards) who also found a correlation between lagged tritium emissions froma plant near Cardiff with neonatal deaths. It is understood that the 2 authors are unaware ofeach other’s findings. The similarity of the findings is interesting. However neither of thesereports has been published in the scientific literature and they are understood to have been
criticised by others for statistical inadequacies.

Conclusion
As stated in the introduction, epidemiology studies are a blunt tool for finding out about therisks of hazardous substances. The reality is that there is a very large gap between thecancer risks that most individuals will tolerate from industrial activities (e.g., 1 in a million)
and the risks that can be detected by epidemiological study of reasonable-sized populations.
The above studies, except for Zablotska et al, show either no increases or possible
increased incidences with borderline statistical significance in most cases. However it must
be remembered that just because these studies were unable to detect increased effects, thisdoes not mean that there are no effects. As Altman and Bland (1995) stated “absence ofevidence is not evidence of absence”. The methodological limitations of many epidemiology
studies mean that they are simply not able to detect any effect with statistical certainty.

74

Another matter is that if the detected excesses of childhood leukemias around Pickering andBruce turn out to be both real and caused by radiation exposures from the nearby Candu
stations, then either the estimated radiation doses to people are too small, or the risk
coefficients for radiation are too small, or a combination of both. Indeed the real doses andreal risks could be higher than our regulators assume, and could even be higher than thisreport suggests.
With this in mind, our conclusion is that the above studies taken together provide suggestive,
albeit limited, evidence for increased health effects from exposure to tritium. However thisevidence remains indicative and not conclusive. We conclude that more epidemiology studies
should be carried out in areas downwind of the Canadian nuclear reactors.

75

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85

Annex A to Part 2
AECB
ACRP
Bq
CERRIECi
COMARE
CNSC
ddref
DNA
DoE
EC
EPA
err
Gy
HPA-RP
IAEA
IEER
ICRP
LET
LNT
NEA
NCI
NRC
NRPB
OECD
rad
rem
RERF
Sv
TRF
UNSCEAR
WHO

Acronyms and Abbreviations

former Atomic Energy Control Board (now CNSC qv)
former Canadian Advisory Committee on Radiation Protection
becquerel (unit of radioactivity)
UK Committee Examining the Radiation Risks of Internal Emitterscurie (unit of radioactivity)
UK Committee on the Medical Aspects of Radiation in the Environment
Canadian Nuclear Safety Commission
dose and dose-rate effectiveness factor
deoxyribose nucleic acid
US Department of Energy
European Commission
US Environmental Protection Agency
excess relative riskgray (unit of absorbed radiation dose)
Radiation Protection Unit of the UK Health Protection Agency (formerly
NRPB qv)
International Atomic Energy Agency
Institute of Environment and Energy ResearchInternational Commission on Radiation Protection
linear energy transfer
linear no-threshold (radiation’s dose-effect relationship)
Nuclear Energy Agency of the OECDUS National Cancer Institute
US Nuclear Regulatory Commission
former UK National Radiological Protection Board
Organisation for Economic Cooperation and Developmentrad (unit of absorbed radiation dose used in the US)
rem (unit of radiation dose used in the US)
Radiation Effects Research Foundation
sievert (unit of equivalent or effective radiation dose)
tritium reduction facility
United Nations Scientific Committee on the Effects of Atomic Radiation
World Health Organisation

86Annex B to Part 2
Radiation Dose Units
A measure of the effect of radiation is the amount of energy it deposits in unit mass of bodytissue. This quantity is called the absorbed dose. The unit of absorbed dose is the gray (Gy).
One gray is equal to the energy deposition of 1 joule in 1 kilogram of tissue.
The biological effects of alpha particles and neutrons (high-LET27 radiation) are, in general,
greater than the effects of beta particles and gamma rays (low-LET radiation) of the sameenergy. The radiation weighting factor (wR ) was introduced to take account of the different
biological effectiveness of alpha and beta particles, neutrons, and x- and gamma rays.
The quantity equivalent dose is then defined as: equivalent dose = absorbed dose multipliedby the wR. The unit of equivalent dose is the sievert (Sv).
In studies of low-dose radiation, the sievert is too large a unit and doses are usually given in
millisieverts (mSv), where 1 Sv = 1,000 mSv (see below).
For low-LET radiation, wR = 1, so grays and sieverts will be numerically equivalent. However,for alpha particles wR = 20, so an absorbed dose of 1 mGy produced by alpha particles will
have an equivalent dose of 20 mSv.

International System of Nomenclature (commonly used units)
E = exa
P = peta
T = tera (one trillion)
G = giga (one billion)
M = mega (one million)k = kilo (one thousand)= 1018= 1015= 1012
= 109
= 106
= 103

d = deci (one tenth)= 10-1c = centi (one hundredth) = 10-2m = milli (one thousandth) = 10-3
µ = micro (one millionth) = 10-6n = nano (one billionth)= 10-9p = pico (one trillionth)= 10-12

Common examples are:
PBq = petabecquerel (one million billion becquerels)
TBq = terabecquerel (one trillion becquerels)
GBq = gigabecquerel (one billion becquerels)= 1015 Bq= 1012 Bq= 109 BqmSv = millisievert (one thousandth of a sievert)µSv = microsievert (one millionth of a sievert)
nSv = nanosievert (one billionth of a sievert)= 10-3 Sv= 10-6 Sv= 10-9 Sv

27

LET= linear energy transfer, i.e., the energy transferred per unit length of the radiation track.

87Annex C to Part 2

Conversion between European and US unitsa. Radioactivity units
CURIES TO BECQUERELS
1 curie= 1 Ci1 millicurie= 1 mCi (10-3 Ci)
1 microcurie= 1 µCi (10-6 Ci)
1 nanocurie= 1 nCi (10-9 Ci)
1 picocurie= 1 pCi (10-12Ci)= 37 x 109 becquerels= 37 x 106 becquerels= 37 x 103 becquerels= 37 x 1 becquerels= 37 x 10-3 becquerels

BECQUERELS TO CURIES
1 petabecquerel= 1 PBq (1015 Bq)
1 terabecquerel= 1 TBq (1012 Bq)
1 gigabecquerel= 1 GBq (109 Bq)
1 megabecquerel = 1 MBq (106 Bq)
1 kilobecquerel= 1 kBq (103 Bq)
1 becquerel= 1 Bq= 27 x 103= 27= 27 x 10-3
= 27 x 10-6
= 27 x 10-12= 27 x 10-15

curiescuriescuriescuriescuriescuriesb. Radiation units
REMS TO SIEVERTS
1 rem= 1 rem
1 millirem= 1 mrem
1 microrem= 1 µrem= 100 rem
= 10-3 rem= 10-6 rem= 10 millisieverts= 10 microsieverts= 10 nanosieverts

SIEVERTS TO REMS
1 sievert= 1 Sv
1 millisievert= 1 mSv
1 microsievert= 1 µSv= 100 Sv
= 10-3 Sv= 10-6 Sv= 100 rem
= 100 millirem= 100 microrem88Annex D to Part 2 Glossary of Scientific Terms
Absorbed dose — Quantity of energy imparted by ionising radiation to unit mass of mattersuch as tissue. 1 Gy = 1 joule per kilogram.
Activity — The rate at which radioactive substances decay. Unit: the becquerel; symbol: Bq.
One Bq = 1 disintegration per second.
Annual limit of intake (ALI) — The amount of material inhaled or ingested in 1 year that would
result in a committed effective dose of 20 mSv.
Becquerel — See activity.
Beta particle — An electron emitted by the nucleus of a radionuclide.
Decay — The process of spontaneous transformation of a radionuclide. The decrease in theactivity of a radioactive substance.
Decay product — A nuclide or radionuclide produced by decay. It may be formed directly froma radionuclide or as a result of a series of successive decays through several radionuclides.
Dose — General term for quantity of radiation. See absorbed dose, effective dose, equivalent
dose.
Dose factor — The committed effective dose resulting from the inhalation or ingestion of 1 Bq
of a given radionuclide. Unit: sievert per Becquerel; symbol: Sv/Bq.
Effective dose — The quantity obtained by multiplying the equivalent doses to various tissues
and organs by the tissue weighting factor appropriate to each and summing the products.
Unit:sievert; symbol: Sv.
Equivalent dose — The quantity obtained by multiplying the absorbed dose by the appropriate
radiation weighting factor to allow for the different effectiveness of the various ionizing
radiations in causing harm to tissue. Unit: sievert; symbol: Sv.
Gamma ray — A discrete quantity of electromagnetic energy, without mass or charge.
Gray — See absorbed dose.
Half-life — The time taken for the activity of a radionuclide to lose half its value by decay.
Ionisation — The process by which a neutral atom or molecule acquires or loses an electriccharge. The production of ions.
Ionising radiation — Radiation that produces ionisation in matter.
Nuclear fission — The process in which a nucleus splits into two or more nuclei and energy isreleased.
89

Radionuclide — An unstable nuclide that emits ionizing radiation.
Risk factor — The probability of fatal cancer or leukaemia per unit effective dose.
Sievert — See effective dose.

90Annex E to Part 2

Recommended Reading

A. On radiation and radioactivity
Caufield C (1990) Multiple Exposures: Chronicles of the Radiation Age. Penguin Books.
London UK.
CERRIE (2004) Committee Examining the Radiation Risks of Internal Emitters.
www.cerrie.org.
Gofman JW (1981) Radiation and Human Health. A Comprehensive Investigation of the
Evidence Relating Low-level Radiation to Cancer and Other Diseases. Sierra Club Books.
San Francisco.
Greenberg M (1991) The Evolution of Attitudes to the Human Hazards of Ionising Radiationand to its Investigators. Am J of Industrial Medicine Vol 20 pp 717-721.
Greene G (1999) The Woman Who Knew Too Much. University of Michigan Press. Ann
Arbor, MI, US.
Lambert B (1990) How Safe is Safe? Radiation Controversies Explained. Unwin. London UK.
(Out of print but copies may be available in libraries. A good introduction but now out of date.)
Proctor RN (1995) Cancer Wars: How Politics Shapes What We Know and Don’t Know about
Radiation. Basic Books. New York, NY, US.
Rose G (1991) Environmental Health: Problems and Prospects. J of Royal College ofPhysicians of London Vol 25 No 1, pp 48-52.
Stewart AM (1991) Evaluation of Delayed Effects of Ionising Radiation: An Historical
Perspective. Am J of Industrial Medicine Vol 20 pp 805-810.
Sumner DS, Watson D and Wheldon T (1994) Radiation Risks. Tarragon Press. (Out of print
but copies may be available in libraries. A good introduction but now out of date.)
US EPA website, http://www.epa.gov/radiation/understand/index.html, contains a basic
description of radiation and its effects.

B. On tritium
Advisory Committee on Environmental Standards, A Standard for Tritium, A Recommendation
to the Minister of the Environment and Energy, ACES Report 94-01, May, 1994, ISBN: 07778-2979-7. Difficult to obtain, but still the best official report on tritium ever published in
Canada. Worth seeking out.
Advisory Committee on Radiological Protection. (1991) Toxicity and Dosimetry of Tritium: A
Review. A report prepared for the Advisory Committee on Radiological Protection (ACRP- 10)91

DK Myers and JR Johnson. Dense scientific report which contains the official view on tritium’s(minimal) hazards.
Federal-Provincial Subcommittee on Drinking Water of the Federal-Provincial Committee on
Environmental and Occupational Health, "Summary of Guidelines for Canadian Drinking
Water Quality", April 1998. Official review on tritium’s (minimal) hazards.
Health Canada; Atomic Energy Control Board, Assessment and Management of Cancer
Risks from Radiological and Chemical Hazards, Canada, Joint Working Group, 1998, ISBN:
0-662- 26624-2. Official review on tritium’s (minimal) hazards.
Ministry of Environment and Energy, Ontario, Rationale Document for the Development of anInterim Ontario Drinking Water Objective for Tritium, December, 1994, Queen's Printer for
Ontario, ISBN: 0-7778-3826-5. Official report capitulating to nuclear industry demands not totighten standards.
Ministry of Environment and Energy, Ontario, "Backgrounder on a recommended Interim
Ontario Drinking Water Objective for Tritium", Fall, 1993. Official report capitulating to nuclear
industry demands not to tighten standards.
Energy Probe, FactSheet: "Estimated Risk of Cancer from Regulated Levels of Carcinogens
in Drinking Water". (undated) Energy Probe. Toronto, Ontario.
Fairlie I (1992) "Tritium: The Overlooked Nuclear Hazard". The Ecologist. Vol 22:5 pp 228232.

92