Solid-Tumor Mortality in the Vicinity of Uranium Cycle Facilities and Nuclear Power Plants in Spain
Lopez-Abente, Gonzalo, Aragones, Nuria, Pollan, Marina, Environmental Health Perspectives
To ascertain solid tumor mortality in towns near Spain's four nuclear power plants and four nuclear fuel facilities from 1975 to 1993, we conducted a mortality study based on 12,245 cancer deaths in 283 towns situated within a 30-km radius of the above installations. As nonexposed areas, we used 275 towns lying within a 50- to 100-km radius of each installation, matched by population size and sociodemographic characteristics (income level, proportion of active population engaged in farming, proportion of unemployed, percentage of illiteracy, and province). Using log-linear models, we examined relative risk for each area and trends in risk with increasing proximity to an installation. The results reveal a pattern of solid-tumor mortality in the vicinity of uranium cycle facilities, basically characterized by excess lung [relative risk (RR) 1.12, 95% confidence interval (CI), 1.02-1.25] and renal cancer mortality (RR 1.37, 95% CI, 1.07-1.76). Besides the effects of natural radiation, these results could well be evincing the influence on public health exerted by the environmental impact of mining. No such well-defined pattern appeared in the vicinity of nuclear power plants. Monitoring of cancer incidence and mortality is recommended in areas surrounding nuclear fuel facilities and nuclear power plants, and more specific studies are called for in areas adjacent to installations that have been fully operational for longer periods. In this regard, it is important to use dosimetric information in all future studies. Key words: environment, epidemiology, ionizing, mortality, neoplasms, nuclear facilities, radiation, uranium mines. Environ Health Perspect 109:721-729 (2001). [Online 11 July 2001] http://ehpnet1.niehs.nih.gov/docs/2001/109p721-729lopez-abente/abstract .html
The report that appeared in late 1983 of a cluster of leukemias in young residents living near a nuclear fuel reprocessing plant in Sellafield, England, triggered a considerable amount of investigation into cancer incidence and mortality in areas near nuclear installations. The nuclear industry generates a great deal of social concern, exacerbated recently by the serious accidents that have affected nuclear power plants, such as that of Chernobyl in 1986, and uranium processing facilities, such as the one at Tokaimura in 1999.
Cancer incidence and mortality studies in areas near nuclear facilities have failed to eliminate doubts about possible adverse population effects attributable to routine operations, despite the fact that numerous studies performed in different countries have reported an absence of cancer risk in areas around nuclear fuel facilities and power plants (1-4). In the main, epidemiologic studies have targeted hematologic tumors and young age groups, and very few have sought to assess in depth the remaining malignant tumors. The concern voiced by society regarding the consequences of industry in its immediate vicinity has essentially focused on nuclear power plants. With respect to industries linked to uranium production, considerable effort has been made to ascertain the risk in cohorts of miners (5-7), and although the environmental impact of nearby uranium mines, particularly of uranium mill tailings (8-10), has been studied, the related public health consequences have received scant attention.
Spain currently has seven nuclear power plants, with a total of 10 reactors (nine fully operational and one being dismantled) and nine nuclear fuel facilities (three fully operational, one shut down, and five being dismantled). We therefore performed a cancer mortality study covering towns near nuclear power plants and fuel facilities. Death certificates were the only nationwide source of information on mortality in Spain on which a first analysis of this nature could be based.
In a previous study we reported the results for hematologic tumors (11). In this article we report the results of that study for solid tumors. The analysis presented here sought to quantify the relative risk of death in the vicinity of such installations; to ascertain said risk before and after the date on which these installations first came into operation; to study changes in risk according to subjects' relative proximity to the respective installations; and, given the descriptive and exploratory nature of this study, to provide further pointers for new research.
Materials and Methods
A more detailed description of the methodology may be found in a previous study (11). Here we present results on mortality caused by stomach cancer [International Classification of Diseases-9 (ICD) 151] and colorectal (ICD 153-154), lung (ICD 162), bone (ICD 170), connective tissue (ICD 171), breast (in women, ICD 174), brain (ICD 191), thyroid (ICD 193), bladder (ICD 188), kidney (ICD 189), ovary (ICD 183), and all malignant tumors (ICD 140-208), in towns situated near nuclear facilities. We included towns near four nuclear power plants (NPP) with six reactors that had been operational from 1975 to 1993, and four nuclear fuel facilities (NFF) that had likewise been operational in the same period. With the exception of El Cabril, a nuclear waste storage facility (NWSF) built on the site of an abandoned uranium mine, the NFF are uranium-concentrate-processing facilities located in mining areas where the ore is extracted. The latency periods used were 10 years. This lag rules out the possibility of study for the areas surrounding the Asco, Cofrentes, Trillo, and Juzbado facilities, since all these plants were inaugurated relatively recently.
Figure 1 shows the site and year of startup of these installations. This was a spatial mortality study whose population base comprised inhabitants of towns neighboring the nuclear installations under review. For description and analysis, the area within a 30-km radius of any such installation was called the "exposed zone"; and towns (selected as outlined below) lying within a 50- to 100-km radius of the installation were called the "reference zone." With a Geographic Information System, we used the UTM (Universal Transversa Mercator projection) centroid coordinates for towns to measure the distance from the population centroids to the nuclear installations.
Follow-up took place from 1 January 1975 through 31 December 1993. For all four nuclear power plants, 184 towns within a 30-km radius and 178 within a 50- to 100-km radius were included in the study, matched by income level, number of inhabitants, proportion of the active population engaged in farming, proportion of unemployed, percentage of illiteracy, and province. We selected reference towns at random from among all those that met the matching conditions. For all four nuclear fuel facilities, 99 and 97 towns in the exposed and reference zones respectively were included in the study, matched as above. The study covered 513,248 persons in the exposed zone for all types of installations. We took sociodemographic data from the 1991 census (12) and information on income levels from the Spanish Market Yearbook (Anuario del Mercado Espanol) (13).
Data specific to this study were supplied on computer files by the National Statistics Institute (Instituto Nacional de Estadistica, Madrid, Spain). Individual records were broken down by cause of death, sex, age group, year of death, and town of residence. Town-of-residence data for deceased persons are treated as confidential in Spain for towns having fewer than 10,000 inhabitants, so we obtained special permission from the National Statistics Institute for this study.
To obtain a population breakdown by sex, age, and year for towns included in the study, we referred to the 1981 population census, 1986 municipal roll, and 1991 census, as furnished by the National Statistics Institute. Relying on a log-linear polynomial regression model, we used interpolation to estimate annual municipal population figures for 1981-1991 (14). We extrapolated pre-1981 and post-1991 populations by adopting a linear procedure, allocating more weight to the nearest census year. With the annual population estimates for each town, we calculated person-years for each age band (0-4, 5-14, 15-24, 25-34, 35-44, 45-54, 55-64, 65-74, 75+), sex, and period (1975-1978, 1979-1983, 1984-1988, 1989-1993), taking into account variables that had changed over time, such as operational start-up of reactors and installations.
We fitted log-linear models on the assumption that the number of deaths per stratum followed a Poisson distribution. In these models, observed cases were the dependent variable. As an external standard (15), we used concurrent Spanish cause-specific mortality rates, with expected cases computed by age, sex, and period for each town in the exposed and reference (control) zones. Expected cases were included as offset in the models. A term we called "exposure" (a radius of 30 km or less from the facility), was included as the independent variable. The regression coefficient of this exposure term gave us the logarithm of the ratio between the respective standard mortality ratios (SMRs) for the exposed and reference zones, which we called "relative risk" (RR). This estimator was adjusted for age, sex, period, and matching variables.
We fitted similar models to study the effect of distance on mortality. We constructed this variable by categorizing distances in the 0- to 30-km belt into five levels (consisting of circular sectors having equal surface areas), and using towns situated at a distance of 50-100 km as the reference level. Expressed in kilometers, the cut-off points for the intervals were 0-, 13.4-, 19.6-, 23.2-, 26.8-30, and 50-100. This was included in all models both as a categoric and as a continuous variable (in kilometers). Thus, it was possible, for the former, to estimate the effect for the respective distances and, for the latter, to ascertain the existence of radial effects (rise in RR with increasing proximity to an installation) and, by applying the likelihood ratio test, the statistical significance of such distance-induced effects. The test was also applied to the 0-30-km area with the reference area excluded. We included matching variables in this analysis to ensure control of possible gradients in these variables with proximity to the installation. Given the heterogeneity of the installations, we ran specific analyses on individual and a joint analysis on all installations.
We studied changes in risk by comparing the positions before and after the date on which nuclear power plants and fuel facilities first came into operation (start-up), taking latency periods into account. These periods were included in the assessment of risk before start-up. The statistical significance of this change was obtained following two criteria: fitting a model that compares the SMRs before versus after start-up only for the 0-30 km areas; and a likelihood ratio test, which evaluates the interaction term--exposure x plant operation--in regression models, also including reference areas. The former evaluates time trends in exposed areas in contrast with trends at the national level, and the latter evaluates time trend differences between exposed and unexposed areas (reference areas).
We calculated relative risk confidence intervals (CIs) using the standard errors of the parameters …
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Publication information: Article title: Solid-Tumor Mortality in the Vicinity of Uranium Cycle Facilities and Nuclear Power Plants in Spain. Contributors: Lopez-Abente, Gonzalo - Author, Aragones, Nuria - Author, Pollan, Marina - Author. Journal title: Environmental Health Perspectives. Volume: 109. Issue: 7 Publication date: July 2001. Page number: 721. © 2006 National Institute of Environmental Health Sciences. COPYRIGHT 2001 Gale Group.
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