human health and the biological effects of tritium in drinking water boreham
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Human Health and the Biological Effects of Tritium in
Drinking WaterDouglas Boreham, Professor
McMaster UniversityMedical Physics and Applied Radiation Sciences, Hamilton,
Ontario, Canada.
Principal Scientist, Bruce Power.
McMaster and Bruce Power
McMaster
AECL - CRL
Bruce B
Nuclear 101
Antoniazzi August 26, 2010
Basic CANDU OperationBasic CANDU Operation• CANDU’s (CANadian Deuterium Uranium)
reactors use heavy water in the primary heat transport system (the coolant) and as a moderator of the nuclear reaction
http://en.wikipedia.org/wiki/CANDU_reactor
Bruce Power 2009 Tritium in Drinking Water
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Bruce A
Bruce B
proposed 20 Bq/L
Approx. Minimum Detection
Environmental Monitoring
Radiological Environmental MonitoringTritium in Drinking Water 2001-2009
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Bq/
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Background + Past Emissions Kincardine Port Elgin Southampton Background
Recommendations1. The Ontario Drinking Water Quality Standard for
Tritium should be revised to 20 Bq/L, recognizing that:
• 20 Bq/L relates to health effects from long term, chronic exposure over a life time of exposure of 70 years;
• 20 Bq/L is within the range of variations considered by the council (7 Bq/L to 109 Bq/L), for a 10-6 risk level; and
• 20 Bq/L, based on a running annual average, is achievable in drinking water, without significant cost to the nuclear power industry, according to the Canadian Nuclear Association.
Antoniazzi August 26, 2010
Tritium, Heavy Water & CANDU•Heavy water is used in the CANDU reactor to control the nuclear reaction using natural uranium
•Heavy water in the presence of the neutrons (capture by deuterium atom) continuously generates tritium (DTO).
•Production rate ~2 x 1012 Bq/MW(e).a in the heat transport (PHT) system and ~7.2 x 1013
Bq/MW(e) in the Moderator (~97% generated in the moderator)
Biological Half-Life Heavy Water (D2O)
First Human Isotope Tracer Experiment
(Tea Cup)
• 55 samples of urine and other excreta
• 1000 distillation operations
Conclusion :body’s water turned over every 9 days
Hevesy, G. and Hofer, E. Elimination of water from the human body. Nature 134: 879; 1934
What is Bq/L (beta Emitters)
Tritium – Naturally 1-7 Bq/L
Potassium – 40 100-150 Bq/L
Water
Banana Smoothie
Carbon – 14 200-300 Bq/L
Veggie Shake
Nuclide Total Mass of Nuclide Total Activity of Nuclide Found in the Body Found in Body
Uranium 90 µg 1.1 BqThorium 30 µg 0.11 BqPotassium-40 17 mg 44,000 BqRadium 31 pg 1.1 BqCarbon-14 95 µg 20,000 BqTritium 0.06 pg 23 Bq
Polonium 0.2 pg 37 Bq
Natural Radioactivity in Your Body
Bq is a decay per second
Uranium alpha particles 90,000 per dayTritium beta particles 2,000,000 per dayPotassium beta particles 3 billion/day
Radiation Dose (2L per day x 365 days)
70,000 Bq/L = 1.0 mSv/a (Australia)7,000 Bq/L = 0.1 mSv (Canada)20 Bq/L = 0.0003 mSv/a (Ontario)
What is Bq/L and Dose70,000 Bq/L = 1.0 mSv per year = 1 mammogram
(2.0 mSv/yr – 200+ mSv is natural)
7000 Bq/L = 0.1 mSv per year = Standard X-ray
70 Bq/L = 0.001 mSv = Human (7000 Bq)
20 Bq/L = 0.0003 mSv = 3 minutes flying/change in 6 feet of elevation.
Radiation Tracks and Biological Cells
At low dose the density of radiation ‘tracks’ is low; some cells are ‘hit’ and others are not.
The radiation energy deposited in any individual cell is a random variable and covers a range that depends on the radiation type.
The average dose per hit for a spherical volume 5µm in diameter (approximate diameter of a mammalian cell nucleus) from the experiments of Ellet and Braby
δ
= 11.2 mGy
For a tritium concentration of 20Bq/L the committed dose is 0.286 µGy
and therefore the fraction of exposed cells
with hit nuclei is:-2.5 per 100,000 cells
What are the Event Frequencies for Tritium
F1
= [1-e-D/δ
]
Sleeping next to someone most nights of a year results in a radiation dose about the same as that from an X-ray of your hand.
0.02 mSv/a
=
Potassium-40 X-ray
Same Dose Rate per Hour (0.004 mSv/h)
=
1 metre 30,000 ft
60 hours = 0.24 mSv
Public radiation dose
Frank Saunders
French Academy Vs BEIR
Pacific Basin Nuclear Conference Position Statement
Pacific Basin Nuclear Conference Position Statement
•The risk of cancer generation is trivial or zero up to more than a hundred times the average of natural background radiation.
•There are adaptive responses to low levels of radiation exposure which reduce the effects of damage from all causes, including those from radiation, thus reducing risk to levels lower than those observed in the absences of the radiation exposure.
In Press: Radiation Protection Dosimetry 2010.
“Recent radiological studies in the low dose region demonstrate that the mechanisms of action for many biological impacts are different than those seen in the high-dose region. When radiation is delivered at a low dose rate (i.e. over a longer period), it is much less effective in producing biological changes than when the same dose is delivered in a short period. Therefore, the risks due to low dose-rates effects may be over-estimated.”
Implications for Radiation Protection
At low dose• Dose is NOT a surrogate for risk
• Dose (risk) is NOT additive and risk can increase OR DECREASE
• Risk per unit dose is NOT constant, dose thresholds exist, for overall risk and for each tissue (WT )
• The assumptions of the LNT hypothesis and radiation protection practices are
not compatible with the observations in vitro or in vivo
•• Human and environmental risk Human and environmental risk assessments must consider real effectsassessments must consider real effects
• A new approach to radiation protection at low doses is needed
CONCLUSIONSAt low doses
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