Childhood leukemia in the vicinity of Canadian nuclear facilities

A Short Latency between Radiation Exposure from Nuclear Plants and Cancer in Young Children

Previous reports document a short latency of cancer onset in young children exposed to low doses of radioactivity. The standard mortality ratio (SMR) for cancer in children dying before age ten rose in the period 6–10 years after the Three Mile Island and Chernobyl accidents in populations most exposed to fallout. SMRs near most nuclear power plants were elevated 6–10 years after startup, particularly for leukemia. Cancer incidence in children under age ten living near New York and New Jersey nuclear plants increased 4–5 years after increases in average strontium-90 in baby teeth, and declined 4–5 years after Sr-90 averages dropped. The assumption that Sr-90 and childhood cancer are correlated is best supported for a supralinear dose-response, meaning the greatest per-dose risks are at the lowest doses. Findings document that the very young are especially susceptible to adverse effects of radiation exposure, even at relatively low doses.

Childhood leukaemia, nuclear sites, and population mixing

The excess of childhood leukaemia (CL) in Seascale, near the Sellafield nuclear reprocessing site in rural NW England, suggested that an epidemic of an underlying infection, to which CL is a rare response, is promoted by marked population mixing (PM) in rural areas, in which the prevalence of susceptibles is higher than average. This hypothesis has been confirmed by 12 studies in non-radiation situations. Of the five established CL excesses near nuclear sites, four are associated with significant PM; in the fifth, the Krummel power station in Germany, the subject has not been thoroughly investigated.

Cancer incidence in the vicinity of Finnish nuclear power plants: an emphasis on childhood leukemia

The objective of this paper was to study cancer incidence, especially leukemia in children (<15 years), in the vicinity of Finnish nuclear power plants (NPPs). We used three different approaches: ecological analysis at municipality level, residential cohorts defined from census data, and case–control analysis with individual residential histories. The standardized incidence ratio of childhood leukemia for the seven municipalities in the vicinity of NPPs was 1.0 (95% CI 0.6, 1.6) compared to the rest of Finland. The two cohorts defined by censuses of 1980 and 1990 gave rate ratios of 1.0 (95% CI 0.3, 2.6) and 0.9 (95% CI 0.2, 2.7), respectively, for childhood leukemia in the population residing within 15 km from the NPPs compared to the 15–50 km zone. The case–control analysis with 16 cases of childhood leukemia and 64 matched population-based controls gave an odds ratio for average distance between residence and NPP in the closest 5–9.9 km zone of 0.7 (95% CI 0.1, 10.4) compared to ≥30 km zone. Our results do not indicate an increase in childhood leukemia and other cancers in the vicinity of Finnish NPPs though the small sample size limits the strength of conclusions. The conclusion was the same for adults.

Systematic review of epidemiological studies of exposure to tritium

Tritium (3H) is a radioactive isotope of hydrogen. A number of factors combine to create a good deal of interest in the risks arising from exposure to tritium of both workers and members of the public. Tritium is ubiquitous in environmental and biological systems and is very mobile due to its occurrence as tritiated water. In this paper we systematically review epidemiological data relating to tritium exposure with a view to assessing the risk of such exposure using those studies that are potentially informative. The usefulness of the available studies of cancer and other adverse health effects in workforces and members of the general public is often impaired by a lack of tritium-specific dose data, low doses and small numbers of cases. A number of workforce studies have been identified in which tritium-specific individual doses have been estimated, although none of them, as presently reported, enable reliable inferences to be made on risks associated with exposure to tritium. In general, the available epidemiological studies on the offspring of radiation workers or on pregnancy outcome in areas subject to releases of tritium do not contain enough detail to estimate risks from tritium exposure. Although the studies presently reported are uninformative on risks from tritium, a number of the occupationally exposed cohorts would be potentially informative, particularly if data were suitably combined.

Epidemiological studies of leukaemia in children and young adults around nuclear facilities: a critical review

The existence of an increased risk of childhood leukaemia near nuclear installations is a recurrent issue. A review of the related epidemiological literature is presented here. Results for 198 nuclear sites throughout 10 countries were included in the review. In addition to local studies, 25 multi-site studies have been published for eight countries. A large variability was noticed in the quality of the data as well as in the definition of the study population and in the methods of analysis. Many studies present important limits that make the results difficult to interpret. The review confirms that some clusters of childhood leukaemia cases exist locally. However, results based on multi-site studies around nuclear installations do not indicate an increased risk globally. Many studies were launched to investigate possible origins of the observed clusters around specific sites, but up to now, none of the proposed hypotheses have explained them.

Meta-analysis of standardized incidence and mortality rates of childhood leukaemia in proximity to nuclear facilities

The meta-analysis combined and statistically analysed studies of childhood leukaemia and nuclear facilities. Focus was on studies that calculated standardized rates for individual facilities. Due to variability between study designs, eight separate analyses were performed stratified by age and zone. One hundred and thirty-six sites were used in at least one analysis. Unadjusted, fixed effects and random effects models were used. Meta-rates greater than one were found in all models at all stratification levels often achieving statistical significance. Caution must be used when interpreting these results. The meta-analysis was able to show an increase in childhood leukaemia near nuclear facilities, but does not support a hypothesis to explain the excess. Each type of model utilized has limitations. Fixed effects models give greater weight to larger studies; however, population density may be a risk factor. Random effects models give greater weight to smaller studies that may be more likely to be affected by publication bias. A limitation of the overall study design is that standardized rates must be available for individual sites which led to exclusion of studies that only calculated rates for multiple sites and those that presented other statistical methods. Further, dose-response studies do not support excess rates found near nuclear facilities. However, it cannot be ignored that the majority of studies have found elevated rates, although not usually statistically significant.

Geocoding in cancer research: a review

There is now widespread agreement that geographic identifiers (geocodes) should be assigned to cancer records, but little agreement on their form and how they should be assigned, reported, and used. This paper reviews geocoding practice in relation to major purposes and discusses methods to improve the accuracy of geocoded cancer data. Differences in geocoding methods and materials introduce errors of commission and omission into geocoded data. A common source of error comes from the practice of using digital boundary files of dubious quality to place addresses into areas of interest. Geocoded data are linked to demographic, environmental, and health services data, and each data type has unique accuracy considerations. In health services applications, the accuracy of distances computed from geocodes can differ markedly. Privacy and confidentiality issues are important in the use and release of geocoded cancer data. When masking methods are used for disclosure limitation purposes, statistical methods must be adjusted for the locational uncertainty of geocoded data. We conclude that selection of one particular type of geographic area as the geocode may unnecessarily constrain future work. Therefore, the longitude and latitude of each case is the superior basic geocode; all other geocodes of interest can be constructed from this basic identifier.

Incidence of childhood leukaemia in the vicinity of nuclear sites in France, 1990-1998

Overall, 670 cases (O) of childhood leukaemia were diagnosed within 20 km of the 29 French nuclear installations between 1990 and 1998 compared to an expected number (E) of 729.09 cases (O/E=0.92, 95% confidence interval (CI)=[0.85–0.99]). Each of the four areas defined around the sites showed non significant deficits of cases (0–5 km: O=65, O/E=0.87, CI=[0.67–1.10]; 5–10 km: O=165, O/E=0.95, CI=[0.81–1.10]; 10–15 km: O=220, O/E=0.88, CI=[0.77–1.00]; 15–20 km: O=220, O/E=0.96, CI=[0.84–1.10]). There was no evidence of a trend in standardised incidence ratio with distance from the sites for all children or for any of the three age groups studied. Similar results were obtained when the start-up year of the electricity-generating nuclear sites and their electric nuclear power were taken into account. No evidence was found of a generally increased risk of childhood leukaemia around the 29 French nuclear sites under study during 1990–1998.

Cancer mortality in counties near two former nuclear materials processing facilities in Pennsylvania, 1950-1995

There has been concern that living near nuclear installations might increase the risk of cancer, including childhood leukemia, in surrounding communities. Such concern has been voiced by residents in Armstrong and Westmoreland Counties in Western Pennsylvania in conjunction with the operation of two former nuclear materials processing facilities located in the Apollo borough and the Parks township, just three miles apart. These facilities began operating in 1957 and 1960 and processed uranium and plutonium for commercial and naval applications. To evaluate the possibility of increased cancer rates in communities around the Apollo-Parks nuclear facilities, a cancer incidence and a cancer mortality survey were conducted. The county mortality findings are reported here. Nearly 40,000 cancer deaths occurred in the population residing in Armstrong and Westmoreland Counties from 1950 through 1995. Each of these two study counties was matched for comparison to three control counties in the same region on the basis of age, race, urbanization, and socioeconomic factors available from the 1990 U.S. Census. There were over 77,000 cancer deaths in the 6 control counties during the 45 y studied. Following similar methods used by the National Cancer Institute, Standardized Mortality Ratios (SMRs) were computed as the ratio of observed numbers of cancers in the study and control counties compared to the expected number derived from general population rates of the United States. Relative risks (RR) were computed as the ratios of the SMRs for the study and the control counties. There were no significant increases in the study counties for any cancer when comparisons were made with either the U.S. population or the control counties. In particular, deaths due to cancers of the lung, bone, liver, and kidney were not more frequent in the study counties than in the control counties. These are the cancers of a priori interest given that uranium and/or plutonium might be expected to concentrate in these tissues. Deaths from all cancers combined also were not increased in the study counties, and the RRs of cancer mortality before the facilities operated (1950-1964), during plant operations (1965-1980) and after plant closure (1980-1995) were similar: 0.96, 0.95 and 0.98, respectively. For childhood leukemia mortality, the relative risk comparing the study counties with their controls before plant start-up was 1.02, while during operations (RR 0.81) and after closure (RR 0.57) the relative risks were lower. The study is limited by the correlational approach and the relatively large size of the geographic areas of the counties studied.

Positional accuracy of geocoded addresses in epidemiologic research

BACKGROUND

Geographic information systems (GIS) offer powerful techniques for epidemiologists. Geocoding is an important step in the use of GIS in epidemiologic research, and the validity of epidemiologic studies using this methodology depends, in part, on the positional accuracy of the geocoding process.

METHODS

We conducted a study comparing the validity of positions geocoded with a commercially available program to positions determined by Global Positioning System (GPS) satellite receivers. Addresses (N = 200) were randomly selected from a recently completed case-control study in Western New York State. We geocoded addresses using ArcView 3.2 on the GDT Dynamap/2000 U.S. Street database. In addition, we measured the longitude and latitude of these addresses with a GPS receiver. The distance between the locations obtained by these two methods was calculated for all addresses.

RESULTS

The distance between the geocoded point and the GPS point was within 100 m for the majority of subject addresses (79%), with only a small proportion (3%) having a distance greater than 800 m. The overall median distance between GPS points and geocoded points was 38 m (90% confidence interval [CI] = 34-46). Distances were not different for cases and controls. Urban addresses (median = 32 m; CI = 28-37) were slightly more accurate than nonurban addresses (median = 52 m; CI = 44-61).

CONCLUSIONS

This study indicates that the suitability of geocoding for epidemiologic research depends on the level of spatial resolution required to assess exposure. Although sources of error in positional accuracy for geocoded addresses exist, geocoding of addresses is, for the most part, very accurate.

Elevated childhood cancer incidence proximate to U.S. nuclear power plants

Numerous reports document elevated cancer rates among children living near nuclear facilities in various nations. Little research has examined U.S. rates near the nation's 103 operating reactors. This study determined that cancer incidence for children < 10 yr of age who live within 30 mi (48 km) of each of 14 nuclear plants in the eastern United States (49 counties with a population > 16.8 million) exceeds the national average. The excess 12.4% risk suggests that 1 in 9 cancers among children who reside near nuclear reactors is linked to radioactive emissions. If cancer incidence in 5 western states is used as a baseline, the ratio is closer to 1 in 5. Incidence is particularly elevated for leukemia. Childhood cancer mortality exceeds the national average in 7 of the 14 study areas.

A cluster of childhood leukemia near a nuclear reactor in northern Germany

Between February 1990 and December 1995, professionals diagnosed six cases of childhood leukemia among residents of the small rural community of Elbmarsch in northern Germany. Five of these cases were diagnosed in only a 16-mo period between February 1990 and May 1991. All cases lived in close proximity (i.e., 500-4,500 m) to Germany's largest capacity nuclear boiling-water reactor. We calculated standardized incidence ratios and exact 95% confidence intervals for a 5-km-radius circular area around the plant. The standardized incidence ratio for the time period 1990-1995 was 460 (95% confidence interval: 210, 1,030). The analysis was restricted further to the years 1990 and 1991, and the standardized incidence ratio increased to 1,180 (95% confidence interval: 490, 2,830). Presently, this cluster of childhood leukemia cases cannot be explained in terms of established and putative risk factors--including radiation from medical sources--for childhood leukemia.

What are the risks of diagnostic medical radiation?

It is both ethically and economically desirable to restrict the use of diagnostic medical radiation to only those who will benefit from it. However, patients should not refuse diagnostic tests based on an exaggerated estimation of the risks because most of these tests involve low doses of radiation. It is probable that the risks derived from studies of the atomic bomb survivors, who were exposed to high doses of radiation, overestimate the risks at low doses. No evidence of thyroid cancer, leukaemia or non-Hodgkin's lymphoma has been found in patients exposed to diagnostic levels of ionising radiation. For most diagnostic tests, the risks arising from the radiation exposure are too small to be observed and the benefits will almost always outweigh the risk.

Incidence of childhood leukaemia and non-Hodgkin's lymphoma in the vicinity of nuclear sites in Scotland, 1968-93

OBJECTIVES

The primary aims were to investigate the incidence of leukaemia and non-Hodgkin's lymphoma in children resident near seven nuclear sites in Scotland and to determine whether there was any evidence of a gradient in risk with distance of residence from a nuclear site. A secondary aim was to assess the power of statistical tests for increased risk of disease near a point source when applied in the context of census data for Scotland.

METHODS

The study data set comprised 1287 cases of leukaemia and non-Hodgkin's lymphoma diagnosed in children aged under 15 years in the period 1968-93, validated for accuracy and completeness. A study zone around each nuclear site was constructed from enumeration districts within 25 km. Expected numbers were calculated, adjusting for sex, age, and indices of deprivation and urban-rural residence. Six statistical tests were evaluated. Stone's maximum likelihood ratio (unconditional application) was applied as the main test for general increased incidence across a study zone. The linear risk score based on enumeration districts (conditional application) was used as a secondary test for declining risk with distance from each site.

RESULTS

More cases were observed (O) than expected (E) in the study zones around Rosyth naval base (O/E 1.02), Chapelcross electricity generating station (O/E 1.08), and Dounreay reprocessing plant (O/E 1.99). The maximum likelihood ratio test reached significance only for Dounreay (P = 0.030). The linear risk score test did not indicate a trend in risk with distance from any of the seven sites, including Dounreay.

CONCLUSIONS

There was no evidence of a generally increased risk of childhood leukaemia and non-Hodgkin's lymphoma around nuclear sites in Scotland, nor any evidence of a trend of decreasing risk with distance from any of the sites. There was a significant excess risk in the zone around Dounreay, which was only partially accounted for by the sociodemographic characteristics of the area. The statistical power of tests for localised increased risk of disease around a point source should be assessed in each new setting in which they are applied.

Cancer mortality around French nuclear sites

This study was designed to investigate cancer mortality in the population aged 0 to 64 years residing around the 13 main French nuclear sites in operation before 1985. Five hundred and three communes located within 16 km of the installation were identified and their populations were followed from 1968 to 1989. A total of 8,970,000 person-years of observation was accumulated. The number of cancer deaths and the number of deaths for cancers possibly related to radiation observed in these communes were compared to national mortality rates. There was no difference in overall cancer mortality or in the risk of mortality by cancer site except for breast cancer, for which a deficit was observed in the vicinity of nuclear sites. After correction for the multiplicity of tests, this difference was not significant. Our study showed no excess cancer mortality in the population aged 0 to 64 years residing around French nuclear sites.

Blood and Air Pollution; State of Knowledge and Research Needs

The ready access to blood (plasma and formed cellular elements) makes it unusually susceptible to the deleterious effects of pollutants whose origins may be in the air. The red blood cells' hemoglobin may be rendered useless for oxygen transport by combination with carbon monoxide or conversion to methemoglobin or sulfhemoglobin. Lead and arsine can damage the erythrocytes' membranes, resulting in anemia. Metabolites of benzene and other volatile polycyclic hydrocarbons are implicated in the causation of leukemias. The extensive use of pesticides and herbicides may be associated with the development of Hodgkin's disease, non-Hodgkin's lymphoma, and aplastic anemia. The carcinogenic risks from ionizing radiation, especially for leukemia, are well known. More information is needed concerning the epidemiology of environmental factors responsible for damage to blood. Enhanced knowledge about the molecular biology of toxins' effects on the hematopoietic system and improved detection and prevention technologies are needed to answer environmentally related health questions.

Paternal radiation exposure and leukaemia in offspring: the Ontario case-control study

OBJECTIVES

To test the hypothesis that there is an association between childhood leukaemia and the occupational exposure of fathers to ionising radiation before a child's conception.

DESIGN

Case-control study with eight matched controls per case.

SETTING

Regions of Ontario, Canada, with an operating nuclear facility.

SUBJECTS

Cases were children (age 0-14) who died from or were diagnosed as having leukaemia from 1950 to 1988 and were born to mothers living in the vicinity of an operating nuclear facility. Controls were identified from birth certificates, matched by date of birth and residence at birth. There were 112 cases and 890 controls.

MAIN OUTCOME MEASURES

Paternal radiation exposure was determined by a record linkage to the Canadian National Dose Registry.

RESULTS

Six fathers of cases and 53 fathers of controls had had a total whole body dose > 0.0 mSv before the child's conception, resulting in an odds ratio of 0.87 (95% confidence interval 0.32 to 2.34). There was no evidence of an increased leukaemia risk in relation to any exposure period (lifetime or six months or three months before conception) or exposure type (total whole body dose, external whole body dose, or tritium dose), except for radon exposure to uranium miners, which had a large odds ratio that was not significantly different from the null value.

CONCLUSIONS

The findings of this study in Ontario did not support the hypothesis that childhood leukaemia is associated with the occupational exposure of fathers to ionising radiation before the child's conception.