A Health Canada study has found that the overall cancer rates in the town of Port Hope, Ontario are comparable to rates throughout the Province of Ontario. The study, designed to investigate cancer patterns in Port Hope, was commissioned by the Canadian Nuclear Safety Commission (CNSC) as part of its responsibility to the community for matters of health, safety, security and the environment.
The study was conducted by scientists at Health Canada as part of its mandate to provide leadership in cancer surveillance. Using data from the Ontario Cancer Registry, the study compared cancer incidence in Port Hope with provincial rates. It also examined cancer incidence in different areas within Port Hope.
The study was done in response to concerns raised by some Port Hope residents over increased environmental exposure to radioactive and other materials in Port Hope since the 1930s. The study found that overall cancer incidence in Port Hope was what would be expected based on province-wide cancer rates. The study also compared cancer patterns in Port Hope with those in four other Ontario communities. There was no evidence of large systematic variations among any of the municipalities studied.
Some statistically significant differences in certain cancer types were observed in each community. Given that 45 different cancers were examined among both males and females, some variation would be expected on the basis of chance alone due to natural variations in each community.
On the whole, the study findings demonstrate that patterns of cancer incidence in Port Hope are no different from those in other communities studied and throughout Ontario. Nevertheless, increased environmental levels of known carcinogens do exist in Port Hope, and although levels are such that no adverse effects are predicted, the CNSC believes it is prudent to periodically monitor the incidence of cancer in the Port Hope community.
The CNSC has proposed that a Health Studies Advisory Panel be set up in Port Hope to formally consult with the community, evaluate information from current studies and make recommendations on the need for and direction of future studies. Health Canada has agreed to participate in this panel.
Copies of the Health Study are available at the Port Hope Town Council Office, 56 Queen Street, Port Hope and at the Port Hope Public Library, 31 Queen Street, Port Hope. Copies may also be requested from the CNSC by calling 1-800-668-5284 (in Canada) or e-mail to firstname.lastname@example.org.
Contact: Sunni Locatelli
Media and Community Relations
Tel: (613) 996-6860 or 1-800-668-5284 (in Canada)
The Port Hope Cancer Incidence Study
Public concern had been raised over increased environmental exposure to radioactive and other materials in Port Hope that were byproducts of radium and uranium processing activities since the 1930s. In response to this concern, an ecological study of cancer incidence in Port Hope was conducted. The results showed that compared to cancer incidence in the general population of Ontario, there was no overall evidence for an increased elevation of cancer in Port Hope. For the period 1986 to 1996, there were 589 cancers observed which was exactly the number expected (589) based on population rates. Comparisons with four municipalities in the same region within Ontario also indicated no unusual patterns that would suggest the influence of significant radiation or other exposures within the Port Hope community. Significant exposures to external radiation would, a priori, have been anticipated to increase the risk of leukemia and perhaps thyroid and breast cancer, but these cancer rates were not elevated. Further, there was no evidence that childhood leukemia in particular, a cancer very sensitive to radiation exposure was increased above expectation. Increased exposure to radon progeny at indoor levels is believed to be an important risk factor for lung cancer and slight elevations were noted for women, but not men. The radon levels reported in Port Hope, however, do not seem sufficiently high to result in a detectable increase in lung cancer and a previous analytic epidemiologic study conducted in this area was not able to link convincingly radon to lung cancer, although cigarette smoking was confirmed as a potent carcinogen.
While there were some increases and some decreases in cancer occurrence when data were subdivided into finer units by gender and calendar time, the observed patterns were similar to those of other communities in Ontario. These findings are, on the whole, reassuring that the patterns of cancer incidence are comparable to the Province of Ontario and of other similar communities. The limitations of ecologic surveys must be kept in mind, however, as they can only paint with a broad brush the possibility that environmental exposures have affected disease occurrence in a community: exposure to individuals is not known, assigning cumulative radon or radiation exposures even to groups is based on few measurements and many assumptions about residential occupancy and constancy of exposure over decades, population mobility impacts on assignment of environmental exposures, and errors are known to occur in assigning place of residence. Nonetheless, as there was industrial activity in Port Hope that has increased environmental levels to known carcinogens, albeit at low levels, it would be useful to periodically monitor cancer incidence in the Port Hope community to learn whether any changes might occur. Conducting more analytic studies, such as case-control investigations of certain cancer types of cancer, would not seem a useful exercise based on the data presented in this survey. However, periodically evaluating the cancer statistics that are routinely collected, similar to what was done in the current study or with enhanced residence information, would be prudent.
1. What was the purpose of this study?
Some residents of Port Hope, in particular members of the Port Hope Community Health Concerns Committee, have long been concerned about the potential health effects of the town’s refining industries. Historic operations of plants processing radium and uranium ores resulted in disposal of low-level radioactive waste in the community and the use of contaminated fill at various construction sites. Additionally, historic operations of a foundry manufacturing ceramics caused heavy metal soil contamination in several areas of the community. Concerns have been expressed about the potential health impact of these, as well as about current emissions from the Cameco uranium processing facility.
A government-sponsored clean-up of radioactive materials in the community, which included remediation of about 400 properties and removal of contaminated soil and contaminated demolition debris from the community, was carried out in the 1980s. Concerns exist, however, over the possible health impact of any remaining radioactive and heavy metal contaminants and the impact of pre-remediation wastes. Evidence is sought by concerned citizens to demonstrate that no adverse health effects are occurring.
Canada’s nuclear regulatory agency, the Canadian Nuclear Safety Commission (CNSC), has therefore initiated two reviews of available health statistics, including statistics on cancer incidence and on causes of death (mortality). These investigations characterizing the population’s health status are particularly relevant to health concerns related to heavy metal and radiological contamination, both known to cause human cancer at sufficiently high levels of exposure.
The main purpose of the first study, Cancer Incidence in Port Hope, 1971-1996, was to compare cancer incidence in the town with that of the province, using data available from the Ontario Cancer Registry. Secondary objectives were to determine if patterns of other communities were comparable to Port Hope and to investigate if cancer incidence varied by regions within the town grouped by contamination levels.
The second study, Mortality in Port Hope, 1950-1997, will examine patterns of causes of death in the community. It is expected to be completed later in 2000.
2. Who is conducting these studies?
The CNSC has commissioned Health Canada’s Cancer Bureau (Environmental Risk Assessment and Case Surveillance Division) of the Laboratory Center for Disease Control to carry out the health statistics reviews.
3. What were the sources of information about cancer incidence in Port Hope?
Anonymous cancer patient data was obtained from Cancer Care Ontario, a provincial agency that maintains a registry of all cancer cases in the province. Apart from the age and gender of the patients, the data included general information on the mailing address of persons at time of cancer diagnosis. However, in order to maintain confidentiality of private information, exact addresses are not provided. The location of a patient’s residence is identified by a municipal residence code for the full period of the study (1971 to 1996), and from 1986 to 1996, also by postal code. Postal code information permits investigation of cancer rates at a sub-municipal level, allowing for investigation of patterns in select areas of town.
Unfortunately, there are some inaccuracies in the municipal residential code and also in the postal codes so that results need to be interpreted with some caution. Specifically, municipal location codes tend to overstate the number of cases in any given municipality because cases of cancer diagnosed in the rural areas surrounding municipalities are often added to those occurring in the municipality. This tends to overestimate the number of cases occurring in a town (and inappropriately inflates the municipal cancer rates, and hence, cancer risk). By contrast, because it is easy to make mistakes in recording postal codes, cases may be wrongly classified, either into or out of the community.
Since it is known that each location’s data sources have certain shortcomings, cancer rates according to both sources of location are presented in this study for the period 1986-1996.
4. What kind of investigations on cancer patterns were conducted?
The main focus of the study was to compare rates of cancer diagnoses in Port Hope to provincial rates, adjusting for any differences in age structure between the town and the province as a whole. The study looked at rates of 45 different types of cancer in males and females of all ages, among men and women 20-75, and 75 + years, as well as for select cancers among children. Period-specific rates (1971-85, 1986-96, 1971-96) were investigated, partly due to the availability of two location codes for different time periods, and partly, to help evaluate the consistency of findings.
The study also determined cancer rates for areas of town that were roughly grouped according to estimated levels of heavy metal and radioactive contamination and looked for evidence of trends to see if increasing cancer rates corresponded with increasingly contaminated areas. Researchers
also examined cancer incidence patterns in several other Ontario communities. The intent of this was to evaluate whether overall patterns of cancer in Port Hope were substantially different from those seen in other communities (Cobourg, Lindsay, Belleville, and Orillia).
5. How did cancer rates in Port Hope compare to provincial rates?
The study found that 1,208 residents of Port Hope were diagnosed with cancer between 1971 and 1996. When compared with province-wide information on cancer rates, this number of cases is in the range which would be expected. For the most recent period, 1986-1996, 589 cases were reported in Port Hope, as would be expected on the basis of provincial rates.
Similarly, when all cancers combined among males were considered, there were no statistically significant variations from provincial rates. The same observation held true for all cancers combined for females as well.
In terms of overall cancer rates, therefore, the study provides reassuring information. As the number of cancer cases was large enough among even males and females investigated separately, there was sufficient power to rule out even a small excess in rates of all cancers combined.
6. What about specific cancer types?
Some increases and some decreases in cancer occurrence were noted when rates of specific cancer types were investigated. As researchers examined 45 different types of cancers across several categories of gender, age-group, time period, geographic code and town regions, a small number of these were expected to appear at an unusual rate by chance alone. Such chance findings are expected due to random fluctuations in rare disease rates.
It is very difficult to disentangle any true differences in rates from chance differences. For this reason, it is important to evaluate consistency in the available information. If true differences in rates exist they should appear consistently. For instance, consistent elevations in rates among both males and females, and over different time periods, are more suggestive of a true excess or a deficit in cancer rates than when one isolated excess or deficit rate is observed in one of the periods, in only one gender. Consistent patterns were not seen across periods and gender for any cancer. A possible exception was brain cancer, however, the rarity of the cancer makes interpretation difficult. The brain and nervous system are known to be relatively insensitive to the carcinogenic effects of radiation.
Increased radon progeny indoors is known to be a risk factor for lung cancer. Excess lung cancer in the community could therefore indicate impact of residential radon exposures. While lung cancer rates were increased among women in the most recent period, they were not increased in males, or for either gender in an earlier period. Although the increases as described for the recent period were in the areas with small increases above background radon levels before remedial work done in the area by the federal government, the radon levels in Port Hope are not of a magnitude at which a detectable increase in lung cancer would be expected. A previous analytic epidemiological study of lung cancer in Port Hope was not able to convincingly link radon to lung cancer, although it did confirm cigarette smoking as a potent carcinogen and smoking was associated with residence in homes with higher radon levels. The increased lung cancer among women in the recent period was accompanied by a concurrent excess pharyngeal cancer among women. As both have smoking as a strong risk factor, their coincident excess may be suggestive of a smoking related excess.
Significant radiation exposure is known to induce the development of some cancers more than others. These cancers are known as “marker” or “sentinel” cancers and would be expected to be increased in the presence of significant radiation exposure. Leukemia is just such a “marker” cancer and one with a short latency period. It is therefore reassuring that there were no noted excesses of leukemia in Port Hope in any period specific analyses, whether these were grouped by gender or were separate analyses. Particularly reassuring is the absence of excess leukemia cancer rates among children, as the minimum latency for childhood leukemia is short, and the radiation risk coefficients relatively high. Other potential “sentinel” cancers include breast and thyroid cancer, but there was no indication to suggest excess rates of either of these cancers.
Other cancers that can be considered “sentinel” cancers are those among males. Because of the potential for occupational exposures, in addition to exposures that might exist in the community, males would be expected to be the most exposed population. Males in Port Hope, however, did not have increased rates of all cancers combined in any period and no cancer type was consistently elevated over the span of the study period.
7. Are there limitations to this kind of study?
The study is what is called an ecological (geographical correlation) study. This means that the unit of analysis is the population or groups of people, rather than individuals. It is has some limitations, including the inability to accurately estimate exposures to individuals. Further, information on important confounding factors, such as diet and smoking, are not known. The study is also limited because of the mobility of persons, as census information shows that about 25% of people move from one community to another between census periods and almost 50% have a different address after a five-year census. Thus, it was not possible to assign cumulative exposure levels over time and the assessment of contamination levels was therefore fairly rough. Exposures were assigned to populations in areas of town but not to individuals, and people moved frequently. Other limitations relate to the inaccuracies associated with the addresses. While the municipality residential code may have resulted in biased (incorrect) overestimates of risk, the postal code may have under or over-estimated rates.
Thus, while these general population statistics are informative and can rule out an appreciable increase in cancer risk in this community (in comparison with Ontario or other communities studied), the limitations of this study should be kept in mind. Ecological studies are such that they can only paint with a broad brush the possibility that environmental exposures have affected disease occurrence in a community.
8. Is further study to evaluate the health of Port Hope residents called for?
The findings of this study are, on the whole, reassuring in that the patterns of cancer incidence are comparable to those throughout the Province of Ontario and in other Ontario communities. Nevertheless, it is recognized that there are increased environmental levels of known carcinogens in Port Hope. While these levels are such that no adverse effects are predicted, it would be prudent to periodically monitor the incidence of cancer in the Port Hope community.
Further, it is recognized that people will be concerned about reports of select excess cancer rates even though some such excess rates would normally be expected by chance alone. It is difficult with this kind of a study to determine if higher than expected rates are attributable to chance, differences in population behaviours, or presence of environmental contaminants. Thus, additional follow up may be appropriate.
9. What next?
The CNSC has proposed that a Health Studies Advisory Panel be formed in Port Hope. This Panel is proposed as a means of formal consultation with the community about health concerns and the mechanisms to address them. The proposed Panel, to be set up in consultation with the Port Hope Town Council, may include local residents, health care professionals, current or former industry workers, environmentalists, and others as may be selected to represent the community interests. It has been proposed that, in conjunction with scientific advisors, this Panel would evaluate information from current studies underway and make recommendations on the need for and direction of any subsequent follow up work or any new studies that might be undertaken.
Copies of the Health Study are available at the Port Hope Town Council, 56 Queen Street, Port Hope and at the Port Hope Public Library, 31 Queen Street, Port Hope. Copies may also be requested from the CNSC by calling 1-800-668-5284 (in Canada) or e-mail to email@example.com.
Contact: Sunni Locatelli
Media and Community Relations
Tel: (613) 996-6860 or 1-800-668-5284 (in Canada)