Transcript Assessing the Human Health and Ecological Risk of Tritium Associated with Vermont Yankee Brooke Churas, Allison Rapp, Kacy Roeder, Natasha Yandow.

Assessing the Human Health and Ecological Risk
of Tritium Associated with Vermont Yankee
Brooke Churas, Allison Rapp, Kacy
Roeder, Natasha Yandow
Background Information
• What is tritium?
- Radioactive isotope of hydrogen
- Low energy beta emitter
- Same physical, chemical, pharmalogical properties as hydrogen
• Where does tritium come from?
- Naturally present in the environment in small amounts as:
Tritiated water (HTO)
Gaseous tritium (HT)
Organically bound tritium (OBT)
- Byproduct of nuclear fission
• What are the regulatory limits on tritium?
http://i133.photobucket.com/albums/q80/Orego
n_Sunset/Ball%20HydroCarbon%20Chrono/IM
G_7753.jpg
- The EPA sets limits on tritium in drinking water at 20,000 picocuries per liter
Understanding Units
• 1 curie = amount of material
that will produce 3.7 x 1010
nuclear decays per second.
• 1 becquerel = amount of
material which will produce 1
nuclear decay per second.
•1 curie = 3.7 x 1010 becquerels.
•1 picocurie = 1x10-12 curies
• 1 Sievert = 100 Rem
http://hyperphysics.phy-astr.gsu.edu/HBASE/nuclear/radrisk.html
Tritium and Vermont Yankee:
Department of Health Timeline
• January 7, 2010 – tritium contamination reported
• February 14, 2010- major source of tritium leak was identified
• Soil and water testing confirm pathway of contamination through the discovery of
cobalt-60, manganese-54, zinc-65 and cesium-137
• Tritium concentrations have been decreasing in samples from groundwater
monitoring wells, confirming that the leak has been stopped.
• Increase in frequency and number of water and environmental samples
• Contaminated groundwater found to move west to east into the Connecticut River.
• March- Rigorous monitoring continues
• April- new groundwater well in service
• Continued testing shows no tritium in excess of the lower limit for detection
(Vermont Department Health 2010)
Most recent well results in (pCi/l) or
below the lower level of detection
(<LLD).
GZ-1: <LLD
GZ-2: <LLD
GZ-3: 52,000
GZ-4: 2,400
GZ-5: <LLD
GZ-6: <LLD
GZ-7: 757,000
GZ-8: No sample; dry well
GZ-9: <LLD
GZ-10: <LLD
GZ-11: 750
GZ-12: 267,000
GZ-13S: <LLD
GZ-13D: 1,200
GZ-14S: 258,000
GZ-14D: <LLD
GZ-15: 710,000
GZ-16: <LLD
GZ-17: <LLD
GZ-18: no well yet
GZ-19S: <LLD
GZ-19D: <LLD
GZ-20: 130,000
GZ-21: 2.028 million
(Vermont Department Health 2010)
Goal
To combine evidence of the health impacts of tritium
with case studies and current knowledge pertaining
to the Vermont Yankee controversy in order to
provide a risk assessment of the Vermont Yankee
tritium leak to human and environmental health.
Objectives
• Compare case studies with the situation at Vermont Yankee
• Use lab studies to assess health effects of tritium on human
and non-human organisms
• Study biological pathways of tritium in plants and in the
human body
• Utilize information given during interviews with State
Toxicologist Bill Bress, Radiological Health Chief Bill Irwin
• Present key recommendations regarding Vermont Yankee
while accounting for uncertainties
Tritium Sources
•
Natural tritium is created at a rate of 0.150.2 kg/yr
•
Nuclear sources contribute 0.06 kg/yr
•
Atmospheric weapon tests totaled 560 kg
by 1963 but by 2008 were reduced to
about 40 kg
(Boyer 2009)
The Tritium Cycle
•
•
Tritium is most commonly
found as tritiated water,
tritiated methane and tritiated
molecular hydrogen.
Tritiated water moves
through the water cycle as
normal water does, moving
through water bodies,
atmosphere, soils,
groundwater, largely ending
up in oceans.
http://dnr.wi.gov/org/caer/ce/eek/earth/groundwater/ima
ges/groundwater.gif
Findings: Tritium in Plants
Plant Absorption of Tritium
• Plants take in tritium through their foliage and through soil
• Most tritium is quickly released back into the atmosphere through
transpiration
• Tritium absorbed by a plant will quickly reach equilibrium with the
tritium in the soil
• Tritium absorption depends on several factors
• Plant type, stage of development, water mass of organism, leaf
area index
• Stomatal resistance, stomatal gating, stomatal gating
• Soil type, soil bacteria
• Meteorological conditions, temperature, relative humidity
(Boyer 2009)
Findings: Tritium in Plants
• Differences in plant
absorption of Tritium
• C3 plants absorb more
atmospheric tritium during the
day than at night
• C4 plants typically contain
less tritium than C3 plants
• Lichen, mosses and fungi
absorb tritiated water rapidly
because they lack a cuticle
and stomatal apparatus
http://img.sparknotes.com/figures/B/b1a
b5bb87aee74a86fdae78ed564e663/stom
a.gif
(Boyer 2009)
Findings: Tritium in Plants
• Boyer’s Conclusions
• It is assumed that high levels of tritium
exposure will cause DNA mutations but the
environmental impacts are minimized by
extremely limited exposure.
• Based on Boyer’s findings the environmental
health impacts of the Vermont Yankee tritium
leaks will not be significant.
(Boyer 2009)
Findings: Studies on Rats and Mice
• Yamamoto (1998) orally exposed mice continuously throughout their lives:
- High (5.0 x 1011 pCi/L – 1.6 x 1013 pCi/L) dose rates mice died of haematopoietic
injury.
- Moderate (1.0 x 1010 pCi/L – 2.5 x 1011 pCi/L) dose rates the mice died from
tumor development.
• A threshold dose rate was determined to be
12mGy/day.
• The lowest dose rate of radiation that the mice
were exposed to was 2.35 x 108 pCi/L.
• Vermont Yankee Maximum:
2.5 x 106 pCi/L (Bress 2010).
• Cancer-causing thresholds in mice are not
being crossed.
http://www.reptilecity.co.za/catalog/images/MiceWA.jpg
Most recent well results in (pCi/l) or
below the lower level of detection
(<LLD).
GZ-1: <LLD
GZ-2: <LLD
GZ-3: 52,000
GZ-4: 2,400
GZ-5: <LLD
GZ-6: <LLD
GZ-7: 757,000
GZ-8: No sample; dry well
GZ-9: <LLD
GZ-10: <LLD
GZ-11: 750
GZ-12: 267,000
GZ-13S: <LLD
GZ-13D: 1,200
GZ-14S: 258,000
GZ-14D: <LLD
GZ-15: 710,000
GZ-16: <LLD
GZ-17: <LLD
GZ-18: no well yet
GZ-19S: <LLD
GZ-19D: <LLD
GZ-20: 130,000
GZ-21: 2.028 million
(Vermont Department Health, 2010)
Findings: Studies on Rats and Mice
Study by Takeda (2001):
• Effects of chronic ingestion of tritiated food is perhaps worse than the effects of
chronic ingestion of tritiated water.
• Tritium was retained longer in body tissues when ingested with food.
• Greatest risk might come from the ingestion of organically bound tritium
being consumed as food.
• Bress (2010) assured that ingestion of tritiated water is the main concern.
Findings:
Tritium in the Human Body
• Chemical half life = 12.35 years
• Biological half life:
• 10 days for HTO (90% of uptake)
• 30 days for OBT (10% of uptake)
• 450 days for trace amounts
• Pathways: inhalation, ingestion, absorption
through dermis
• Rate of absorption depends on chemical form
• HTO transferred fastest
• Radiation penetrates 6 m, but human
epidermis is 20-100 m thick
Tritium in the Human Body
• Travels through same biokinetic pathways as
water/organic compounds
• Uniform distribution as HTO
• Uneven distribution as OBT: stored in adipose tissue
and tissue with high multiplication rate
• Replaces hydrogen in all compounds
• Same physical, chemical, pharmacological properties
• 99% excreted as HTO and OBT
Tritium in the Human Body
• Effective dose of OBT is 2.3 times higher than
that of HTO
• Accounts for risk of incorporation into DNA (impacts
unknown)
•
•
•
•
Difficulty of dose measurement
Low number of contamination cases
Not highly radioactive
To have potential impacts, exposure must be
1000 times the levels found in nature
Tritium in the Human Body
• Effects on human body similar to those observed
in plants
• Once absorbed, it quickly passes through
• Assumptions:
• DNA mutations
• Cell damage
}
Exposure to high doses
• Damage caused from radiation, not from
molecule itself!
• Unlikely that humans will be exposed to high
enough concentrations at Vermont Yankee
Studies
• Long term effects unknown
• Exposed lymphocytes and marrow cells to HTO
showed:
• Does not increase RBE
• Chromosomal aberrations increased but
sister- chromatid exchanges did not
• No conclusions about uptake via fruits and
vegetables should be made
(Tanaka 1994), (Boyer 2009)
Impacts of Controlled Releases
Flamanville, Manche, France
• Dose levels account for
people living close to site
• Adults eating fish within a
500 m radius
• Sunbathing (100 h/yr)
• Swimming (20 h/yr)
• Increased risk for certain
groups (ex. fisherman)
• Risk of exposure
extremely low
http://www.world-nuclearnews.org/uploadedImages/wnn/Images/F
lamanville%203.jpg
(Le Guen 2009)
Findings: Case Studies at
Savannah River Site (SRS)
• Savannah River
Site
• South Carolina
• Not in operation today
• Clean up of past
nuclear weapons
manufacturing
http://en.wikipedia.org/wiki/File:SavannahRiverSi
te_ISS012-E-16633.jpg
(Little 2007)
Findings: Case Studies at SRS
Cragle et al (1998)
• Study
– Mortality of 9,860 white male workers at the SRS, 1952 to 1980
– Little data on actual tritium doses
– Estimated doses:
• 800 employees received > 0.5 mSv per year
• 1 employee > 30 mSv per year
•
Findings
– Few indications of excess mortality
– 18 prostate cancer deaths versus 21.15 expected deaths
– Marginally increasing trend for leukemia at 25 deaths versus
19.63 expected deaths
– Further analysis
(Little 2007)
Findings: Case Studies at SRS
Richardson and Wing (2007)
• Study
• Association between radiation exposure and leukemia, 1950-2002
• Doses of tritium, photons, and neutrons were estimated
• Findings
– Results into 3 different groups:
• Leukemia
• Leukemia excluding chronic lymphocytic leukemia (most common
type)
• CLL: slow progression, affects lymphoid cells (white blood cells)
• Myeloid leukemia
• Myeloid: rapid progression, affects the myeloid cells (red blood
cells, granulocytes, and platelets)
• 84 from leukemia, 62 from leukemia excluding CLL, 40 from myeloid
leukemia
– Excess Relative Risk, respectively: 4.1 Sv-1, 7.7Sv-1, and 12.3 Sv-1
(Little 2007)
Findings: Case Studies at SRS
•
General Issue
– No analysis accounting tritium separately
– Difficult to infer much about tritium risks from
studies
(Little 2007)
Findings: Case Study at Chapelcross
•
Chapelcross
– Town of Annan,
southwest Scotland
– Purpose was to
produce plutonium
and tritium for UK
nuclear weapons
program and
electricity for grid
http://en.wikipedia.org/wiki/File:Chapelcross_Nuclear_Powe
r_Station_2.jpg
(Little 2007)
Findings: Case Study at Chapelcross
McGeoghegan and Binks (2001)
• Study
• 2,628 workers assessed, 1955-1995
• Tritium doses not available
• Findings
• Mortality below that expected for non-tritium exposed for Scotland,
England, and Wales
• Standardized Mortality Ratio (SMR) <1
• Prostate cancer the only statistically significant positive trend of cancer
mortality, 8 deaths
• When lag increased, statistical significance eliminated
• Statistical significance for bronchitis deaths, 6 deaths
• Suggestive increasing trend for prostate cancer, based on 12 cases
• Cases not monitored for tritium
• All but 2 workers left prior to tritium production
(Little 2007)
Findings: Case Study of
Canadian Nuclear Workers
Zablotska et al (2004)
• Study
• Mortality follow up of 45,468 Canadian nuclear workers, 19571994
• Mean dose exposure of 13.5 mSv/ year, up to 19.7 mSv / year
• Findings
• Mortality due to all cancers and leukemia excluding CLL less
than national rates
• All cancers: 531 observed deaths versus 721 expected
• Leukemia excluding CLL: 18 observed versus 22.6 expected
(Little 2007)
Findings: Case Study of Offspring of
Canadian Electric Power Workers
Green et al (1997)
• Study
• Instances of congenital abnormalities for offspring of Canadian
electric power workers
• Doses included, further analysis for parents with a recorded
tritium dose 60 days before conception
• 763 case-control pairs of fathers, 165 case-control pairs of
mothers
• Abnormalities determined using Canada’s congenital anomalies
surveillance system
• Abnormalities detected within year 1
• Each child with an abnormality paired with a random child
• Ontario system (same year of birth, maternal age, marital
status, and birthplace of each parent)
(Little 2007)
Findings: Case Study of Offspring of
Canadian Electric Power Workers
• Findings
• Little risk for offspring abnormality when parents exposed to
tritium
http://iopscience.iop.org/0952-4746/28/1/R01/pdf0952-4746_28_1_R01.pdf
(Little 2007)
Expert Opinions:
State Toxicologist, Dr. Bill Bress
• Tritium is a weak beta emitter
- Can not penetrate the skin
- Ingestion of tritiated water as main route of exposure
- Most human cancers are linked to gamma emitters
• “could not project a dose large enough at this site to be an acute human health risk”.
- Consumption of two liters of tritiated water per day, at a concentration of
20,000 pCi/L in order to cause cancer
- 2.5 million pCi/L is the absolute maximum concentration of tritium
- Tritium is water soluble
• Low potential for human ingestion of tritiated water
- Contamination limited to surface and subsurface levels
- No drinking water comes from the Connecticut River
• Minimal environmental health effects
• Levels of tritium in the monitoring wells are dropping and the leak has been stopped.
Expert Opinions:
Radiological Health Chief, Dr. Bill Irwin
• Possibility of greater risks
• Environmental effects not likely because of the dilution.
• Assumed that someone will drink from the Connecticut River
• Examples of tritium leaks from nuclear power plants taking place in New Jersey and
Georgia.
• More preventative action
- Aboveground pipes
- Multiple barriers
• Routine monitoring and sampling
http://www.burlingtonfreepress.com/blog/secondopinion/uploaded_images/vermontyank-733499.jpg
Conclusions
• Case studies show that the number of cases of cancer linked with tritium were
equal or less than those expected
• Offspring of those exposed to tritium showed no increased abnormalities over
those offspring with parents not exposed to tritium
• The metabolism of tritium within the human body provides evidence for a
minimal risk of cancer
• The location of Vermont Yankee on the Connecticut River has allowed for the
dilution of tritiated water
• The radionuclide tritium does not exist in high enough concentrations at this
site to cause negative human or environmental health effects.
Recommendations
• Continued monitoring of the soil and water surrounding Vermont Yankee
to ensure levels of tritium continue to drop
• Consider the tritium leak as a potential indicator for the possibility of
greater risks associated with Vermont Yankee.
• Increase the number of sampling sites in order to ensure high quality
monitoring for not only tritium, but other harmful substances that might be
leaking from the plant.
Updates on Yankee
•
Vermont Yankee will be shut down as of
2012 unless it is relicensed in 2011
•
The Vermont House of Representatives
has passed a bill requiring Vermont
Yankee to set aside 20 million dollars for
the decommissioning
Summary
Goal: To combine evidence of the health impacts of tritium with case studies and current
knowledge pertaining to the Vermont Yankee controversy in order to provide a risk assessment
of the Vermont Yankee tritium leak to human and environmental health.
Objectives
Use information from
- Case studies with the situation at Vermont Yankee
- Lab studies on the health effects of tritium on human analogs
- Biological pathways of tritium in the human body
- Mechanisms of tritium in plants.
- Interviews with State Toxicologist Bill Bress, Radiological Health Chief Bill Irwin
Conclusions:
- The location of Vermont Yankee on the Connecticut River has allowed for the dilution of tritiated
water
- The radionuclide tritium does not exist in high enough concentrations at this site to cause
negative human or environmental health effects.
Recommendations
- Continued monitoring
- Consider the tritium leak as a potential indicator
- Increase the number of sampling sites
Works Cited
Boyer, C.; Vinchot, L.; Fromm, M.; Losset, Y.; Tatin-Froux, F.; Guetat, P.; Badot, P. M. Nov 2009. Tritium in Plants:
A Review of Current Knowledge. Environmental and Experimental Botany, 67, (1), 34-51.
Bress, Dr. Bill (19 March 2010). State Toxicologist, Vermont Department of Health. Interview
Irwin, William (19 March 2010). Radiological Health Chief, Vermont Department of Health. Interview
Le Guen, Bernard. 2009. "Impact of tritium around EDF nuclear power plants." Journal of Radiological Protection.
29: 163-173.
Little, M. P. Sep 2007. Systematic review of epidemiological studies of exposure to tritium. Journal of Radiological
Projection, 28, 9-32.
Takeda, et al. 2001. "Comparative biokinetics of tritium in rats during continuous ingestion of
tritiated water and tritium-labeled food." International Journal of Radiation Biology 77.3: 375-381.
Vermont Department of Health. (2010). Investigation into tritium contamination at vermont yankee nuclear power
station. Retrieved from healthvermont.gov/enviro/rad/yankee/tritium.aspx
Yamamoto, O., Seyama, T., Iton, H., & Fujimoto, N. 1998. Oral administration of tritiated water (hto) in mouse. iii:
low dose-rate irradiation and threshold dose-rate for radiation risk. International Journal of Radiation Biology,
73(5), 535-541.