Journal of Environmental Protection, 2011, 2, 1149-1161
doi:10.4236/jep.2011.29134 Published Online November 2011 (http://www.scirp.org/journal/jep)
Use of a Weight of Evidence Approach to
Determine the Likelihood of Adverse Effects on
Human Health from the Presence of Uranium
Facilities in Port Hope, Ontario
Rachel Lane1, Patsy Thompson1*, Michael Ilin1, Marcelle Phaneuf2, Julie Burtt1, Pascale Reinhardt1
1Directorate of Environmental and Radiation Protection and Assessment, Canadian Nuclear Safety Commission, Ottawa, Canada;
2International Atomic Energy Agency, Vienna, Austria.
Received August 30th, 2011; revised October 1st, 2011; accepted November 3rd, 2011.
ABSTRACT
The radium and uranium processing industry exists in Port Hope, Ontario, since 1932. Between 1932 and 1966, most of
the waste material from these industries was deposited throughout the town. During these years, waste management
practices did not prevent the spread of contamination. Several environmental and health studies have been conducted to
assess the potentia l contamination effects in th e Port Hope Community over the last 70 years. The current study used a
weight of evidence approach to assess the types and levels of contaminants of concern in the environment, and the po-
tential human exposure to these contaminants. Their toxicological and radio-toxicological properties were also as-
sessed to determine their potential health effects. The results of these assessments were further compared to findings of
earlier epidemiological studies of Port Hope residents and nuclear industry workers. The conclusions of this study in-
dicated that: 1) Levels of exposure to radioactive and non-radioactive contaminants in Port Hope are below levels
known to cause adverse health effects. 2) Epidemiological studies provide no evidence of health effects as a result of
past and present activities of the Po rt Hope nuclear industries. 3) The environmental risk assessments and the epidemi-
ological studies are consistent and support each other. 4) Port Hope’s findings are co nsistent with the results of over 40
epidemiolog ical studies conducted elsewhere on popu lations living around similar fa cilities or exposed to similar envi-
ronmental conta minants.
Keywords: Uranium, Radiation, Cancer, Environment
1. Introduction
Radium and uranium processing industries have been
operated in Port Hope, Ontario, since 1932. Low level
radioactive wastes that contained large amounts of ura-
nium, the radioactive decay products of uranium, and
other minerals in the ore feed, such as arsenic, cobalt, co-
pper, and nickel and trace amounts of antimony and lead,
were produced during early years of operation when the
waste management practices did not fully limit the
spread of contamination. During these years, the levels
of plant emissions were elevated and wastes were placed
in a landfill or in various locations within the community.
Scrap material used for construction of homes and build-
ings was also found to be contaminated.
From 1976 to 1981, the most serious contamination in
Port Hope homes and businesses was remediated. As a
result, over 100,000 tons of waste were removed and sent
to a licensed waste management facility, while 600,000
tons were left in Port Hope in 11 large storage sites. A
federally funded clean up project was further put in place
to deal with the remaining volume of waste. Since 1984
uranium processing methods have improved and are now
using uranium trioxide (UO3) as feed material. In addi-
tion, better waste management practices have been put in
place to reduce the waste and plant emissions that, nowa-
days, contain only uranium, ammonia and fluoride.
Despite better environmental performance of the cu-
rrent uranium processing operations, some health and en-
vironmental advocacy groups in the Port Hope com-
munity remain concerned about the health impacts that
may have been caused by the presence of low-level ra-

Use of a Weight of Evidence Approach to Determine the Likelihood of Adverse Effects on Human Health 1150
from the Presence of Uranium Facilities in Port Hope, Ontario
dioactive waste in Port Hope residential and public areas.
During the last thirty years, various epidemiological stu-
dies of residents and workers have been undertaken to
determine if some of the health effects observed in Port
Hope residents could be related to the presence of these
contaminants. Environmental risk assessments included
measurements of the radiological and non-radiological
contaminants in soil, air, water, and vegetables. They
also estimated the multi-pathway of exposure and the
health risks to the population using environmental moni-
toring data or dose re-construction methods based on a
variety of guidelines or standards.
The current study is a comprehensive assessment of all
existing data. This assessment used the weight of evi-
dence approach to achieve its goal. This approach is re-
cognized in the Canadian Environmental Protection Act
(CEPA) [1], and by the U.S. Environmental Protection
Agency [2] as a method whereby judgment involves
consideration of the quality and adequacy of the avai-
lable data and its consistency across the lines of evidence.
The strength of the weight of evidence approach is that it
requires a full interdisciplinary analysis of all the rele-
vant information to develop an overall assessment and
that it does not rely on any single study, whether positive
or negative [3].
The weight of evidence assessment method includes
reviewing site-specific doses, epidemiological studies
and chemical specific toxicity data to evaluate exposure
and potential health effects in a community [4].
This paper presents the results of the assessment con-
ducted to determine the potential existence of health
effects due to uranium and radium facilities operation in
Port Hope.
2. Material and Methods
The qualitative weight of evidence standards, such as,
the number of studies, the strength of association, the
breadth and consistency of evidence, the correlation po-
wer and the biological plausibility, were used in this as-
sessment. Data on the levels of contaminants in air, water,
soil and garden produce were used in combination with
health standards and guidelines to assess risks to the lo-
cal population. The risk estimates were then compared to
the results of epidemiological studies conducted on Port
Hope residents and nuclear industry workers. The criteria
used to weigh the various lines of evidence were the
same as the US EPA criteria [2] and were as follow:
 shortness of the period of time between exposure and
outcome (taking into consideration latency period);
 consistency between results from independent stu-
dies;
 strength of association between the substance and the
effect;
 reliability of exposure data;
 absence of biases or confounding factors; and
 strength of the statistical significance for a given ef-
fect.
Exposure estimates were derived from more than 30
environmental epidemiological studies that covered the
period from the early 1930’s to present. Thirteen epide-
miological studies considered all health outcomes and all
causes of mortality. To aid in the interpretation of these
studies, plausible health effects in Port Hope residents
were identified through a review of the available radio-
logical and toxicological peer reviewed literature for the
following contaminants of concern: radon, radium-226,
uranium, arsenic, ammonia, and fluorides.
In order to test consistency, the weight of evidence
approach was used to compare the findings of the Port
Hope epidemiological studies with the environmental
risk and with more than 40 additional similar epidemio-
logical studies conducted elsewhere in the world.
In accordance with US EPA’s guidance [5] on scien-
tific information intended to support regulatory decisions,
the assessment was also peer-reviewed by internal ex-
perts and external independent experts [6].
3. Results
3.1. Port Hope Residents’ Exposure to
Environmental Contaminants
The levels of exposure to radioactive and non-radioactive
contaminants of potential concern were estimated based
on a large amount of environmental monitoring data col-
lected since the mid-1970s [7-13], and from dose recon-
struction [14].
Exposure estimates were obtained from multi-pathway
calculations of intake using the International Commis-
sion on Radiation Protection (ICRP) “critical group”
concept [15]. This entails conservative assumptions, such
as occupancy factors, origin of food and water, and con-
sumption of contaminated soil by infants.
3.2. Radioactive Contaminant
Table 1 provides dose estimates of radioactive contami-
nants to members of the public in Port Hope, for the pe-
riods before and after the remediation activities (con-
ducted from 1976 to 1981) combined, and for the current
period of operation of the uranium processing industry.
The average dose resulting from natural background in
Canada is about 2.4 mSv/year; this is in the same range
as elsewhere in the world. Port Hope’s industrial sources
of radiation represent an incremental exposure that is
within the geographical variability of natural background.
At this low level of exposure no adverse health effects
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Use of a Weight of Evidence Approach to Determine the Likelihood of Adverse Effects on Human Health 1151
from the Presence of Uranium Facilities in Port Hope, Ontario
Table 1. Radiation Levels in Port Hope.
Annual radiation doses mSv/year
Radon (indoor) in Port Hope (1955-1993) 0.69 - 1.46
Gamma (indoor) in Port Hope (1955-1993) 0.25 - 0.27
Cameco Port Hope Conversion Facility (2007) 0.064
Cameco Fuel Production Facility (2007) 0.004
are expected. Studies have indicated that incidence of
cancer in populations chronically exposed to radiation
doses lower than 100 mSv is not statistically different
from incidence of cancer due to background exposure in
the general population [16].
3.3. Non-Radioactive Contaminants
The levels of contaminants (uranium, arsenic, fluoride,
ammonia and other non-radiological contaminants) mea-
sured in Port Hope’s air, water, and vegetation, have
been compared to the current health protection limits or
guidelines (Table 2).
Concentrations of uranium and arsenic in some of Port
Hope soil samples are above soil quality guidelines due
to historic contamination. Nonetheless, recent studies
have indicated that the implementation of emission aba-
tement technology at the Port Hope refinery in 1984 has
resulted in lower uranium concentrations in soils4. Stack
testing has also shown that arsenic is no longer being
discharged from this facility. Exposure assessments have
shown low intakes of uranium and arsenic mainly due to
their low bioavailability in soils5 and their relatively
Table 2. Comparison of the current levels of some contami-
nants present in Port Hope to guidelines/standards.
Guidelines/Standards Current Levels in Port Hope
Air1 Water2 Soil3 Air Water Soil
Uranium 0.03
µg/m3
0.02
mg/L
23
mg/kg
0.00028 -
0.005
µg/m3
0.00055
mg/L
0.24 - 93.6
mg/kg
Arsenic N/A
0.025
mg/L
12
mg/kg N/A 0.0005 - 0.002 mg/L
1 - 94
mg/kg
Fluoride N/A 1.5
mg/L N/A N/A ≤0.25 mg/LN/A
Ammonia 100
µg/m3 1 mg/L N/A 1.5 - 15.2 µg/m3
0.12 - 0.21
mg/L N/A
short biological half-life. Exposure to arsenic in Port
Hope is estimated to result in a skin cancer risk similar to
the average estimated cancer risk for arsenic for the av-
erage Ontario residents6.
The contaminants that have mostly accumulated over
time in Port Hope soils are uranium, antimony, chro-
mium, copper, nickel, cadmium, cobalt, selenium and
zinc. Levels of exposure are low and risk quotients re-
main below 1. Consequently, no adverse health effects to
Port Hope residents are expected to be linked to these
environmental contaminants [8].
3.4. Identification of the Plausible Health Effects
from the Contaminants Present in Port
Hope
The contaminants of potential concern in Port Hope oc-
cur both naturally and as a result of the activities of the
radium and uranium refining and processing industry in
the community. The effects of ionizing radiation, ura-
nium, arsenic, fluoride and ammonia are well understood.
They have been extensively studied in laboratory animals
and cell cultures and through epidemiological studies
conducted in human populations.
Many comprehensive toxicological data reviews have
been conducted nationally and internationally to estab-
lish standards and guidelines to protect human health
from exposures in occupational settings [17-20] and from
environmental exposures. These criteria are, for example,
drinking water standards and air and soil quality stan-
dards [5,21,22] and [23]. Plausible health effects of con-
taminants of concern in Port Hope were identified and
weighted for their strength of evidence taking into ac-
count their toxicological and radio-toxicological evalua-
tion and exposures estimation (Table 3). The result of
this assessment was further compared with the findings
of epidemiological studies.
3.5. Epidemiological Studies Conducted in Port
Hope
Thirteen epidemiological studies were conducted in Port
Hope in the past 30 years. They included the period of
remediation of the low level radioactive waste (1976 to
1981), the period of the solvent extraction plant (1967 to
1984) when uranium emissions were elevated and cur-
rent times (from 1984 to the present) when the imple-
mentation of mitigation measures significantly reduced
uranium emissions. The studies assessed all causes of
death, all cancers and all birth defects.
1Ontario Ambient Air Quality Criteria.
2Ontario Drinking Water Standards.
3Canadian Council of Ministers of the Environment Soil Quality Gui-
deline for the Protection of Environmental Health (residential/parkland
use).
4EcoMatters, 2004. Uranium Concentrations in Port Hope Soils and
Vegetation and Toxicological Effect on Soil Organisms. Final Report
to the Canadian Nuclear Safety Commission.
5SENES Consultants Limited, 2008. Soil Characterization and Evalu-
ation Study at Port Hope. Final Report. Prepared for Cameco Corpora-
tion.
Among these thirteen studies:
6CANTOX, 1999. Deloro Village Exposure Assessment and Health
Risk Characterization for Arsenic and Other Metals. Final Report. Can-
tox Environmental Inc.

Use of a Weight of Evidence Approach to Determine the Likelihood of Adverse Effects on Human Health
from the Presence of Uranium Facilities in Port Hope, Ontario
1152
Table 3. Plausible Health Effects Associated with Exposure to Contaminants due to the Presence of the Radium and Uranium
Processing Industry in Port Hope.
Contaminants Most plausible health effects Probability of occurrence Strength of the supporting
evidence
Uranium
(UO3, UF6)
Kidney disease
Uranium at very high levels can cause kidney
disease in animal experiments. In humans, very
high levels of uranium can cause changes to
kidney cells, which are largely reversible
Unlikely
Evidence: Risk quotients are generally below 1.
Levels of uranium in soil in some locations are
above the soil quality guidelines for protection
of human life but bioavailability is low
Moderate to
high
Radon
Radon decay products
UO2
Lung Cancer
Radon and its decay products, and long-lived
radioactive dust (UO2) are known to cause lung
cancer.
Low probability of occurrence
Residential radon exposure ranged from 0.69
-1.46 mSv/year. Doses are either below the
regulatory limit of 1 mSv/year or within the
range of natural background in the area
Moderate
Radium
(Ra-226)
Bone Cancer
Radium, if ingested, can deposit in the bone
and cause bone cancer at very high levels, with
a threshold of about 10 Sv.
Unlikely
Total radiation doses from uranium, Ra-226
and other uranium decay products are estimated
to have been below 1 mSv/year even during the
early period
High
Arsenic
Skin cancer, tumors of the bladder and the
lung, potential for liver, kidney and prostate
tumours (high exposures)
Low probability of occurrence
Arsenic exposure from historical releases in
Port Hope represents an incremental life time
risk of 1 excess skin cancer risk every 139
years
Moderate to
high
Ammonia
Lung edema (high acute exposures)
Eye, nose and throat irritation
(lower exposures)
Unlikely
Ammonia air concentrations are well below the
air quality standard
High
Fluoride
Yellowing of the teeth, hypothyroidism,
brittle bones and teeth
(chronic low level oral exposure)
Unlikely
Fluoride concentrations are well below
drinking water standard High
Lead-214,
Bismuth-214
(gamma-ray radiation
emitting uranium
decay products)
Leukemia, breast cancer, lung cancer and other
cancers (associated with high whole body
gamma ray doses)
Low probability of occurrence
Indoor gamma radiation doses in Port Hope
(1955-1993) range from 0.25 to 0.27 mSv per
year and are below the regulatory limit of 1
mSv/year.
Moderate to
high
 nine were descriptive ecological studies that com-
pared the rates of all causes of death, of cancer inci-
dence, and of birth defects among Port Hope resi-
dents with the general population of Ontario, similar
communities, and the rest of the population of Can-
ada [24-35];
 two were case-control studies, one investigated the
relationship between lung cancer and residential ra-
don exposure in homes [36,37], the second one stu-
died if there was an association between childhood
leukaemia and father’s occupational exposure to ion-
izing radiation before the child’s conception [38]; and
two were cohort studies on Eldorado workers [39,40]
and provided data on approximately 50 years of mor-
tality and 30 years of cancer incidence for Port
Hope’s radium and uranium refining and processing
facility workers.
The epidemiological studies provided no evidence of
excess kidney disease or bone cancer. During the entire
period of the radium and uranium refining and process-
ing industry operation in Port Hope, there has been no
statistically significant excess of kidney disease mortality
in residents or in radium and uranium workers. Similarly
no statistically significant excess of bone cancer inci-
dence or mortality in residents or in radium or uranium
workers (Figures 1(a), 1(b), 2(a) and 2(b)) was found.
No relationship could be established between workers’
occupational radiation exposures and kidney disease
mortality or bone cancer incidence or mortality [6].
A small evidence of excess in lung cancer was found
in Port Hope women in the period from 1986 to1996, but
no excess could be demonstrated in the period from 1971
to 1985 in women, or in men between 1971 and 1996.
The same observation was made in Northumberland
County and in the HKPR District indicating that elevated
rates of lung cancer in women (1986-1996) was not spe-
cific to Port Hope [38].
Similarly, no statistically significant excess lung can-

Use of a Weight of Evidence Approach to Determine the Likelihood of Adverse Effects on Human Health 1153
from the Presence of Uranium Facilities in Port Hope, Ontario
0.00.2 0.40.60.8 1.0 1.21.4 1.61.8 2.02.2 2.42.62.8 3.0 3.23.4
ALL CANCERS
Trachea, bronchus and
lung
Colon and rectum
Breast
Prostate
Uterus excluding cervix
Leukemia
Pancreas
Stomach
Kidney
Non-Hodgkin's lymphoma
Malignant melanoma of
skin
Ovary
Tongue, gum and mouth
Lip
Cervix uteri
Hodgkin's disease
Other female genital
organs
Thyroid
Bone
Ill-defined and unknown
sites
SIR
(a)

Use of a Weight of Evidence Approach to Determine the Likelihood of Adverse Effects on Human Health 1154
from the Presence of Uranium Facilities in Port Hope, Ontario
0.00.30.50.81.01.31.51.82.02.32.52.83.0
ALL CAUSES
CIRCUL ATO RY DISEASE
Ischemic heart disease
ALL CANCERS
Cerebr ov ascular di sea se
RESPIR ATO RY DISEASE
ACCIDENTS/ POISONING,
VIOLENCE
Pneumonia
Diseases of arteries, arterioles
and capillaries
Chronic obstructive pulmonary
disease
Motor vehicle traffic acci dents
Accidental falls
Cirrhosis of liver
PERINATAL MORTALITY
Diabetes
Kidney disease
Hypertensive disease (1969–1997)
Suicide
CONGENITAL ANOMALIES
Alzheimer's disease (senile
and pre- senile)
INFECTIOUS AND
PARASITIC DISEASES
Influenza
Ulcers
Fire
Homicide
SMR
(b)
Figure 1. (a) Standardized Incidence Ratios (95% Confidence Intervals) For Selected Cancers for Port Hope, Ontario Com-
pared With Ontario Cancer Incidence Rates, from 1971 to 1996, Both Sexes Combined, All Ages (0-85+ years); (b) Standard-
ized Mortality Ratios (95% Confidence Intervals) For Selected Causes of Death for Port Hope, Ontario Compared with On-
tario Mortality Rates, from 1956 to 1997, Both Sexes Combined, All Ages (0–85+ years).
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Use of a Weight of Evidence Approach to Determine the Likelihood of Adverse Effects on Human Health 1155
from the Presence of Uranium Facilities in Port Hope, Ontario
0
.
0
0
.
5
1.
0
1.
5
2.
0
2.
5
3
.
0
3
.
5
4.
0
4.
5
5
.
0
ALL CANCERS
Lung cancer
Prostate cancer
Colon cancer
Bladder and other urinary
cancer
Rectal cancer
Non-Hodgkin’s lymphoma
Stomach cancer
Laryngeal cancer
Malignant melanoma
Pancreatic cancer
Leukemia
SIR
(a)

Use of a Weight of Evidence Approach to Determine the Likelihood of Adverse Effects on Human Health 1156
from the Presence of Uranium Facilities in Port Hope, Ontario
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
ALL CAUSE S
Ischemi c he art di sea se
ALL CANCERS
Lung cance r
All other ca rdi ovascul ar di seases
Stroke
ALL DIGESTIVE DISEASES
Pneumonia
Other external causes
Chronic obstructive lung disease
Motor vehicle accident s
Colon ca nc er
Prostate canc er
Genitouri nary diseases
Suicide
Rectal ca nc er
Stomach cancer
Diabetes mellitus
Hypertensive disease
ALL NERVOUS SYSTEM
DISEASES
Pancreatic canc er
Bladder and ot he r urin ary cancer
SMR
(b)
Figure 2. (a) Standardized Incidence Ratios (95% Confidence Intervals- adjusted for age (five year intervals) and calendar
year at risk (five year intervals)) For Selected Cancers for Port Hope Eldorado Male Employees Compared With Canadian
Male Cancer Incidence Rates, from 1969 to 1999; (b). Standardized Mortality Ratios (95% Confidence Intervals - adjusted
for age (five year intervals) and calendar year at risk (five year intervals)) For Selected Cancer Deaths for Port Hope Eldo-
rado Male Employees Compared With Canadian Male Mortality Rates from 1950 to 1999.
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Use of a Weight of Evidence Approach to Determine the Likelihood of Adverse Effects on Human Health
from the Presence of Uranium Facilities in Port Hope, Ontario
1157
cer incidence or mortality could be observed in Port
Hope nuclear workers, and more importantly, there was
no statistically significant relationship between workers’
occupational radiation exposures and lung cancer (Table
4).
Workers’ average cumulative exposures were 52 mSv
for radon and 101.5 mSv for gamma radiation [39] and
[40]. Many of these workers were living in the commu-
nity which implied they were also exposed to some ra-
diation at home. The case-control study conducted in
Port Hope [37] on residential radon exposure and lung
cancer showed no conclusive evidence of an increased
risk of lung cancer in “problem homes” (where annual
exposure was above 0.229 Working Level Months or
1.15 mSv per year). In addition, no statistically signifi-
cant excess of lung cancer mortality in Port Hope resi-
dents for the period from1954 to 1997 [24,25,33] and [6]
was demonstrated.
Table 5 summarizes the weight of evidence obtained
from the various epidemiological studies conducted in
Port Hope taking into consideration the robustness of
each study; cohort studies being weighted more strongly
than case-control and ecological studies.
4. Discussions
Taken together, the findings of the 13 epidemiological
studies conducted on the general population and the ra-
dium and uranium workers support and strengthen the
evidence obtained from the risk assessments that adverse
health effects are unlikely to be the result of exposure of
Port hope residents to environmental contaminants from
the radium and uranium processing.
4.1. Circulatory Diseases
In the 1956-1997 period, the overall excess of mortality
in Port Hope was dominated by an excess of circulatory
disease, which represented over 50% of all deaths [33].
Circulatory disease is recognized to be the leading cause
of death in Canada [41]. The scientific data available to
date are not sufficient to conclude that there is a causal
relationship between ionizing radiation exposure and car-
diovascular disease for doses lower than 1 to 2 Sv [42].
Given the level of radiation in Port Hope, 0.69 - 1.46
mSv/year from 1967 to 1976 and 0.004 - 0.064 mSv/year
in 2007, it is highly unlikely that circulatory diseases
could be associated with radiation in the municipality.
The excess observed in circulatory diseases is likely
mostly due to other risk factors, such as smoking, obesity,
physical inactivity, high blood pressure, diabetes, stress
and alcohol consumption [43].
The same excess in circulatory disease was found in
the whole Northumberland County which confirmed it
was not specific to Port Hope. The Rapid Risk Factor
Surveillance System (RRFSS) also reported that the
overall community (HKPR District) had a high preva-
lence of risk factors for circulatory disease, including
poor diet, physical inactivity and high rates of cigarette
smoking [35]. Meanwhile, Eldorado radium and uranium
workers’ overall mortality for all causes of death was ge-
nerally comparable with the mortality of the general
male population of Canada.
4.2. All Cancers except Lung Cancer
Even if increases in some cancers (e.g. colorectal, brain
and other nervous system, esophagus, lip, pharynx, nose/
sinuses) could be observed after stratification of the re-
sults by age group, sex, time period, and residence cod-
ing, it was unlikely that these cancers could be related to
activities of the nuclear industry in Port Hope. The lack
of biological plausibility and of experimental evidence
made it impossible to link them to the presence of con-
taminants of concern in Port Hope.
The available evidence indicates that colorectal cancer
is inducible by high whole-body gamma ray doses, but
the risk appears very low at doses lower than 1 Gy [15]
[42] and [44]. Ionizing radiation can induce brain and
central nervous system tumors, but most of these radia-
tion-associated tumors are benign [42]. Cancers of the
esophagus, lip, pharynx, nose/sinuses, and lung are most
likely linked to tobacco smoking [35,45] and [46]. Other
than lung cancer, these cancers are not known to be as-
sociated with exposures to environmental contaminants
such as those present in Port Hope. Hence, it was not
surprising that no relationship was found between these
cancers and occupational radiation exposures in the El-
dorado workers [39] and [40].
4.3. Lung Cancer
The excess in lung cancer incidence in women observed
in one time period (1986 to 1996) in Port Hope is un-
likely to be related to environmental contaminants expo-
sure since this was not observed during the earlier period
[24] and [25] when the level of contaminants was higher;
the latency period having been sufficient to have given
the disease the opportunity to appear during the earlier
period. A temporal relationship is therefore absent.
In addition, a case control study conducted in Port
Hope [36] and [37] has not been able to establish a con-
clusive relationship between residential radon and lung
cancer. The levels of residential radon in Port Hope re-
mained much lower than those to which radium and ura-
nium industry workers were exposed [39] and [40] and
the workers did not show any excess in lung cancer inci-
dence or mortality. The lack of relationship between lung

Use of a Weight of Evidence Approach to Determine the Likelihood of Adverse Effects on Human Health 1158
from the Presence of Uranium Facilities in Port Hope, Ontario
Table 4. Excess Relative Risk Estimates for Lung Cancer Mortality and Incidence due to Radon Decay Products/100 Work
Level Months exposure in Port Hope Eldorado Male Employees, 1950-1999 [40].
Lung Cancer Observed ERR Estimate 95% Confidence Interval p-value
Mortality (1950-1999) 101 0.18 –0.10, 1.49 0.59
Incidence (1969-1999) 110 0.68 –0.23, 3.07 0.17
Table 5. Strength of evidence of the potential adverse impacts on human health based on the epidemiological studies
conducted in Port Hope’s reside nts and in uranium and radium workers.
Disease Evidence Description Strength of evidence References
Kidney disease
No evidence of excess kidney disease - No statistically
significant excess kidney disease mortality in Port Hope
residents or in radium and uranium workers for the entire
period of study.
High
[24][25] [31] [33] [39] and
[40]
Little evidence of excess lung cancer
No statistically significant excess lung cancer incidence or
mortality in Port Hope radium and uranium workers. High [40] and [41]
No conclusive evidence of increased lung cancer risk from
residential radon exposure in “problem homes” in the
case-control study.
Moderate [37]
No statistically significant excess lung cancer mortality in Port
Hope residents from 1956 to 1997. Moderate [32] [33] and [37]
Lung cancer
Statistically significant excess lung cancer incidence in women
in Port Hope from 1986 to1996. No excess was noted during
other time periods or in men.
Moderate [32]
No evidence of excess bone cancer
Bone cancer No statistically significant excess bone cancer incidence or
mortality in Port Hope residents or radium and uranium
workers for the entire period of study.
High [32] [33] [39] and [40]
No evidence of health effects from occupational exposures
Skin cancer and
other diseases No statistically significant relationship between workers’
occupational exposures and any cause of death or cancer
incidence.
High [40]
cancer and occupational exposures in these workers pro-
vides another line of evidence that environmental radon
levels in Port Hope are unlikely to cause lung cancer.
5. Conclusions
The findings of the environmental risk assessments and
the epidemiological studies conducted in Port Hope are
consistent with each other (Tables 3 and 5) and with
other epidemiological studies conducted on similar popu-
lations elsewhere, [47-57]. Other studies on populations
exposed to high concentrations of uranium and radionu-
clides in drinking water [58-60] also support this conclu-
sion.
The weight of evidence approach was used in the cur-
rent study to provide a structured framework in order to
conduct a transparent interdisciplinary analysis of the
numerous health and environmental studies conducted in
Port Hope over the last 30 years. By considering all the
available lines of evidence and their relative strengths it
can be concluded that there is no evidence that adverse
health effects have occurred or are likely to occur as a
result of the operations of the nuclear industry in the mu-
nicipality of Port Hope.
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