radiation and health

RADIATION
AND HEALTH
NOVEMBER 1996
Radiation and Health in Durham Region
Durham Region Health Department
November, 1996
Executive Summary
All humans are exposed to ionizing radiation from the atmosphere, earth and even other
humans. People living near nuclear generating stations (NGSs) are also exposed to low levels
of ionizing radiation from the NGS. Surveillance of health effects in populations living close to
NGSs is not uniform around the world. There are no international standards to guide which
indicators should be used to measure potential health effects from low levels of ionizing
radiation.
Durham Region has 185,000 people living within 10 km of two NGSs: the Pickering NGS in the
municipality of Pickering and the Darlington NGS in the municipality of Clarington. Radiation and
Health in Durham Region examines health indicators associated with radiation to explore
whether populations close to the NGSs have higher than expected rates of certain diseases and
conditions.
All of the health indicators examined can be caused by a multitude of factors. Radiation would
be a small attributable risk compared to other risk factors prevalent in the population, many of
which are modifiable, including smoking, and alcohol use.1 As well, radiation from an NGS
contributes less than 1% to a person’s total radiation dose, even if a person theoretically lives at
the boundary of the NGS 24 hours a day and consumes local produce and water.2,3 Thus,
isolating radiation as the cause of an increase in a given health outcome is beyond the scope of
this descriptive study. However, the results are useful in providing an indication of which areas
need to be pursued more closely in the future.
The objectives of Radiation and Health in Durham Region are:
• To develop a framework to categorize health indicators according to their level of association
with radiation.
• To compare health indicators that are associated with radiation for Durham Region and
Ontario.
• To include Halton and Northumberland in this comparison to provide an appreciation of how
indicators vary geographically among small populations.
• To compare municipalities within Durham Region, grouped into Ajax-Pickering, OshawaWhitby, Clarington and North Durham (Uxbridge, Scugog, and Brock), to assess whether any
of the indicators are significantly higher than Ontario.
• To suggest further areas of investigation to better understand the patterns of health
outcomes described.
• To have our work reviewed by experts in radiology, epidemiology and public health.
A framework of health indicators was devised by the Health Department since no pre-existing
surveillance tool was readily available to examine health effects around NGSs. The framework
is based on the most current information available from scientific studies and may change in the
future depending upon new research. The people in these studies were usually exposed to high
doses of radiation. Consequently, it is difficult to extrapolate these findings to populations
exposed to chronic low doses of radiation, such as those living near NGSs.
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The framework categorizes health indicators according to their level of association with radiation
and describes the pattern that would be expected if radiation was causing an effect in Durham
Region, taking into account the latency period between exposure and health outcome. Health
indicators were divided into four categories based on 1) the consistency of research findings in
the scientific literature, 2) the strength of the association, and 3) whether there was an
increased effect with increasing dose.
A. Significant Radiological Health Indicators
The following health indicators show consistent evidence across different studies for a
statistically significant association with radiation exposure and an increasing association with
radiation dose: all cancer sites combined, bone cancer, breast cancer, colorectal cancer,
leukemia (excluding chronic lymphatic leukemia), lung cancer, microcephaly and brain
reduction congenital anomalies, ovarian/uterine cancers, stomach cancer, and thyroid
cancer.
B. Possible Radiological Health Indicator
Evidence for this indicator is generally consistent across different types of studies, and
increases with increasing dose. However, the effect is not large. Only one indicator is in this
category: kidney/urinary cancers (excluding bladder cancer).
C. Inconsistent Radiological Health Indicators
Evidence for these indicators is not consistent across different types of studies, may or may not
show a statistically significant effect, and may or may not increase with increasing dose. The
indicators are: esophageal cancer, multiple myeloma, non-Hodgkin’s lymphoma, and
prostate cancer.
D. Theoretical Radiological Health Indicators
Although studies have found genetic effects in animals exposed to ionizing radiation, no genetic
defects due to radiation have been found in humans.4 As a result, indicators reflecting a genetic
effect in humans are a theoretical risk. Indicators that are theoretically associated with radiation
are: all congenital anomalies combined, Down syndrome, and other chromosomal
congenital anomalies.
Data for the above health indicators come from the Ontario Cancer Registry, to assess new
cases and death from cancer, and the Canadian Congenital Anomalies Surveillance System, to
examine birth defects.
Radiation and Health in Durham Region makes the following assumptions:
• Radiological health indicators categorized as significant carry more weight in suggesting
whether health effects from ionizing radiation are occurring than do possible, inconsistent,
or theoretical health indicators.
• Health effects from low-level radiation, if they exist and are discernible, would be seen
primarily in Ajax-Pickering and Clarington, but less so in Oshawa-Whitby and North Durham
because the latter are further away from the NGSs. Radiation levels in air and water fall
significantly with distance from the source3, thus decreasing Oshawa-Whitby and North
Durham residents’ exposure.
2
• Health effects from low-level ionizing radiation, if they exist and are discernible, would be
expected to occur after an appropriate time that is consistent with known latent periods. Most
cancers generally do not appear until 10 or more years after exposure to a cancer-causing
agent, with the exception of leukemia which has a peak latency of 7-8 years.1 Since the
Pickering NGS began operation in 1971, most cancers would not be expected to be high in
Ajax-Pickering until after 1981. Since Darlington NGS did not begin operating until 1989, an
increase in cancers other than leukemia would not be expected in the data presented here
because the most recent time period is 1989-1993. Other health indicators, such as
microcephaly and brain reduction congenital anomalies, would appear immediately from
exposure in utero.
• Since all of the health indicators can be caused by factors other than ionizing radiation, any
excess is not automatically attributed to the NGSs. Risk factors, such as smoking and
occupational exposures, are not examined in this document.
Limitations that prevent this descriptive study from determining cause and effect relationships
are:
• The study uses data at the level of the community, not the individual and assumes that
exposure is constant for all people in an area, even though this is not true. How long a
person has lived in a particular area, for example, is not taken into consideration.
• Factors other than ionizing radiation may be associated with living in an area and a particular
health indicator.
• The study has a limited scope and does not consider risk factors or other determinants of
health, such as smoking, occupational exposures, diet, etc.
• The comparison communities of Halton and Northumberland are different from Durham
Region in many ways. No community exists that is identical to Durham Region but that does
not have an NGS.
• Cancer and congenital anomalies are complex and caused by other factors which are
generally more likely to cause disease in the population than low-level radiation exposure.
• Other indicators potentially associated with radiation such as spontaneous abortion, thyroid
nodules, liver cancer and skin cancer are not included because of the lack of accurate data in
Ontario.
• Data from small geographical areas are often less accurate because residence is sometimes
misclassified.
• Since most of the health indicators examined are rare, small numbers fluctuate greatly over
time. This fluctuation makes it difficult to determine trends or to know whether health effects
are due to chance or other exposures.
• Making many comparisons means that 5% of rates that are statistically high or low are so
due to chance. Because comparisons of Durham Region, Ajax-Pickering, Oshawa-Whitby,
Clarington and North Durham with Ontario for all health indicators results in 300
comparisons, fifteen of these would theoretically be statistically different just by chance.
Without further study, no one knows which rates are high because of chance fluctuation or
which reflect real problems. Rather than looking at as many rates as possible, it is thus more
meaningful to look for patterns within known radiation-related disease and death.
• No baseline data are available for Ajax-Pickering before the Pickering NGS began operating
in 1971.
• Few data are available for Clarington after Darlington NGS started up in 1989.
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Results
There is no consistent pattern among significant radiological health indicators to suggest
that ionizing radiation is affecting the health of Durham Region residents. Rates in AjaxPickering for all cancer sites combined, bone cancer, breast cancer, colorectal cancer, lung
cancer, microcephaly and brain reduction congenital anomalies, ovarian/uterine cancers, and
stomach cancer were generally similar to Ontario as a whole.
However, mortality from leukemia (excluding chronic lymphatic leukemia) was higher in AjaxPickering females in 1984-86 than in Ontario females, as was the incidence rate for thyroid
cancer in 1989-93. These diseases are uncommon so numbers fluctuate greatly. Halton
similarly experienced high leukemia incidence among females in 1989-93. Leukemia and thyroid
cancer rates in Ajax-Pickering males in all time periods and for females in other years were not
different from Ontario.
Data for kidney/urinary cancers, the possible radiological health indicator, found no
significant differences between any of the study areas and Ontario. Neither incidence nor
mortality rates for kidney/urinary cancers within Durham Region showed a pattern consistent
with a radiological effect.
Inconsistent radiological health indicators show areas of concern with multiple myeloma and
prostate cancer but these do not suggest a radiological effect because the patterns are not
consistent with known latency periods. Females in Durham Region and Ajax-Pickering had
significantly higher death rates from multiple myeloma in 1979-83 than Ontario females. This
effect is too early to be linked with radiation because myeloma has a latency of about 20 years4
and Pickering NGS began operating in 1971. Many of the other rates in Ajax-Pickering were too
low to report (less than five people), while others appeared high but were not statistically
different from Ontario. Incidence of myeloma was significantly higher than Ontario in Durham
and Oshawa-Whitby females in 1989-93 as was mortality in Durham males in that same time
period.
Prostate cancer incidence and mortality have been higher in Durham Region than Ontario for as
far back as we have data. This is unlikely to be linked with ionizing radiation because rates were
high too early to be a radiation-induced effect and the elevation was observed throughout
Durham Region, although most pronounced in Ajax-Pickering. Incidence rates were significantly
higher in Clarington before Darlington NGS began operating, and subsequently declined.
Prostate cancer is generally thought to be not linked with ionizing radiation4 although a few
studies have found an association5. More investigation is needed to probe why prostate cancer
rates might be elevated in Durham Region.
The other health indicators with an inconsistent association to radiation, namely cancer of the
esophagus and non-Hodgkin’s lymphoma, were not different from Ontario and thus not
indicative of a radiological effect. Ajax-Pickering males had significantly lower rates of nonHodgkin’s lymphoma in 1989-93 than Ontario males.
Theoretical radiological health indicators are difficult to interpret because studies of humans
have failed to find elevated rates of these health outcomes in those exposed to ionizing
radiation. Rates for all congenital anomalies combined and for Down syndrome were at
provincial levels in both Ajax-Pickering and Clarington for each of the five time periods
examined, except for a significantly low rate of all congenital anomalies combined in AjaxPickering in 1990-91. However, the rate of Down syndrome for the entire 1978-91 time period
was significantly higher in Ajax-Pickering than Ontario. Rates for other chromosomal congenital
4
anomalies were similar to Ontario rates, except for a higher than expected rate in Ajax-Pickering
in 1984-86.
Other studies of birth defects, including The Birth Defects Atlas of Ontario: 1978-1988 and a
1991 AECB report, Tritium Releases, Birth Defects and Infant Deaths, have found elevated
rates of Down syndrome in Pickering. Scientific committees reviewing data from various studies
have concluded that while radiation can induce changes in the structure of DNA within a
chromosome, it is unlikely to change the number of chromosomes in a cell, as happens with
Down syndrome and other chromosomal congenital anomalies4,6. Nevertheless, rates for Down
syndrome in Ajax-Pickering appear to be decreasing after peaking in 1984-86.
Results from Radiation and Health in Durham Region suggest further work:
•
Surveillance of the communities living around the Pickering NGS and Darlington NGS
should continue. Future considerations include: more in-depth mapping of health indicators
to investigate spatial clustering, and adding other data sources. The prenatal diagnostic
program that has been operating in Durham Region since 1986 is a potential source of new
data, as is hospitalization data from the Ministry of Health.
•
The Health Department must continue monitoring the literature on health effects from lowlevel ionizing radiation to update the surveillance framework used in this document.
•
Higher than expected rates of leukemia, thyroid cancer, multiple myeloma, prostate cancer,
and Down syndrome in Ajax-Pickering warrant further investigation. The elevated rates for
leukemia and thyroid cancer are isolated and show no pattern. However, the higher rates
for multiple myeloma, prostate cancer, and Down syndrome are more consistently elevated.
•
A special study may be needed to investigate the accuracy of residence coding in Durham
Region. Because this study used data for small geographical areas, accuracy of residence
codes in cancer and congenital anomaly data is crucial. A validation study at the Ontario
Cancer Registry suggested that 16% of cancer cases in Ontario have a wrong residence
code7. Most of this miscoding is at the level of town, city or township and is not a problem
for studies analysing at the county level. Special studies such as this pose unique
difficulties. It is not known whether residence coding is more or less accurate in Durham
Region or whether there are biases in the coding. The data suggest that cancer rates are
generally lower in the rural areas of North Durham and Clarington than in Oshawa-Whitby
and Ajax-Pickering. This trend may be due to cases being attributed to a town or city rather
than to the rural area where the person actually lives, thus inflating rates for urban areas.
This is known to occur in some areas of the province8, and may also be a problem in
Durham Region.
•
More investigation is needed to find out how health indicators are affected by changes in the
population. Inaccurate population estimates for high growth areas such as Ajax-Pickering
may be affecting results. For example, cancer rates for 1984-88 likely overestimated the
true rate because 1986 Census figures underestimated the number of people living in the
area during that whole time period.
•
The next edition of Radiation and Health in Durham Region is not anticipated until after
2001, to allow for sufficient accumulation of data. However, work on the above projects will
continue in the interim.
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Conclusion
The surveillance framework developed by the Health Department to categorize health indicators
according to their level of association with radiation is a useful tool for assessing whether
populations close to the Pickering and Darlington NGSs have higher than expected rates of certain
diseases and conditions. Results show no consistent pattern among significant and possible
radiological health indicators to suggest that ionizing radiation is affecting the health of Durham
Region residents. Inconsistent radiological health indicators show areas of concern with
multiple myeloma and prostate cancer but these do not suggest a radiological effect because the
patterns are not consistent with known latency periods. Other indicators in this category were at or
lower than provincial levels. Theoretical radiological health indicators are difficult to interpret
because studies of humans have failed to find elevated rates of these health outcomes in those
exposed to ionizing radiation. Only one area of concern was identified – higher than expected
rates of Down syndrome in Ajax-Pickering over the entire 1978-91 time period. The rate of Down
syndrome has declined since peaking in 1984-86. Overall, the pattern of results do not suggest
adverse health effects in Ajax-Pickering or Clarington from the nuclear generating stations.
References
1. International Agency for Research on Cancer (1990) Cancer: Causes, Occurrence and Control.
Tomatis, L., Aitio, A., Day, N.E., Heseltine, E., Kaldor, J., Miller, A.B., Parkin, D.M., & Riboli, E.
(eds), IARC Scientific Publications No. 100. New York: Oxford University Press.
2. Atomic Energy Control Board (1995) Radiation Monitor for Second Quarter and Third Quarter
1995.
3. Ontario Hydro Nuclear (1996) Annual Summary and Assessment of Environmental
Radiological Data for 1995, Nuclear Waste and Environment Services Division, Environment
Department.
4. National Research Council, Committee on the Biological Effects of Ionizing Radiation (BEIR V)
(1990) Health Effects of Exposure to Low Levels of Ionizing Radiation. Washington, DC:
National Academy Press.
5. Beral, V., Fraser, P., Carpenter, L., Booth, M., Brown, A., & Rose, G. (1988) Mortality of
Employees of the Atomic Weapons Establishment, 1951-82, British Medical Journal, 297:757770.
6. Advisory Committee on Radiological Protection (1996) Biological Effects of Low doses of
Radiation at Low Dose Rate, ACRP-18.
7. Ontario Cancer Registry Validation Study, personal communication with Dr. Eric Holowaty,
Director, Ontario Cancer Registry, 1996.
8. Marrett, L.D. & Weir, E. (1993) Accuracy of Municipality-Level Residence Information in the
Ontario Cancer Registry: Results of a Pilot Study. Health Reports, 5 (1):11-16.
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