Information Systems | Mini-Monograph Use of GIS and Exposure Modeling as Tools in a Study of Cancer Incidence in a Population Exposed to Airborne Dioxin A. Poulstrup and H.L. Hansen Regional Public Health Ofﬁce, Vejle, Denmark In environmental health research there is a recognized need to develop improved epidemiologic and statistical methods for rapid assessment of relationships between environment and health. Exposure assessment is identiﬁed as a major challenge needing attention. In this study an exposure simulation model was used to delimit almost exactly in space and time an urban population exposed to air- borne dioxin. A geographic information system (GIS) was used as the electronic environment in which to link the exposure model with the demographic, migration, and cancer data of the exposed population. This information is available in Denmark on an individual basis. Standardized inci- dence ratios (SIRs) for both men and women in 10-year age bands were calculated for three differ- ent exposure areas. Migration patterns were outlined. SIRs showed no excess of cancer incidences during the time span chosen (13 years; 1986–1998) in the whole exposed area or in the medium or higher polluted areas. The exposure model appeared very useful in selection of the appropriate exposure areas. The integration of the model in a GIS together with individual data on addresses, sex, age, migration, and information from routine health statistics (Danish Cancer Registry) proved its usefulness in demarking the exposed population and identifying the cancers related to that pop- ulation. Less than one-third of the study population lived at the same address after 13 years of observation, and only half were still residing in the area, indicating migration of people as a major misclassiﬁcation. Key words: air pollution, cancer, dioxin, environmental epidemiology, exposure model, GIS, health registers, migration. Environ Health Perspect 112:1032–1036 (2004). doi:10.1289/ehp.6739 available via http://dx.doi.org/ [Online 15 April 2004] A major challenge for investigators in environmental epidemiology is to correctly identify populations at risk from exposure to environmental contaminants. To date, three methods have been used to identify the popu- lations at risk from point sources of air pollu- tion: physical monitoring, environmental monitoring, or mathematical modeling (Williams and Ogston 2002). This article is a discussion of the utilization of a computer- ized air pollution model, normally used by the environmental protection authorities for assessing pollution values (immissions), and the putative offense of legally set thresholds of emission. To test the model for its appropri- ateness as an improved tool for assessment of exposure, an actual case was used of known dioxin air pollution in an urban area. In the town of Kolding in the southern part of the Jutland peninsula, Denmark, three outlets of dioxin were identified. All three emitted dioxin into the air through their chimneys. The dioxin consisted mainly of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, or dioxin). One outlet in particular, an aluminum recycling plant, was found on two occasions—early November and early December 2000—to have emitted large quantities of dioxins, up to 180 ng/m3/hr. All three plants had been operating for years. The main culprit was the aluminum recy- cling plant, which had been in continuous operation since 1970 with an almost unchanged method of production and output. 1032 Our plan was to layer the computer- simulated exposure model in a geographic information system (GIS) and use the simu- lated immission concentrations to more accu- rately demarcate the exposed population. The information on addresses, vital statistics, migration, and cancer of the population of Denmark or any subset was available on indi- viduals and on the delineated population in this study. This information was layered into the same GIS environment, enabling a more exact identiﬁcation of the exposed population in both space and time. All malignant cancers were used as the health indicators of the exposed population to assess eventual negative health outcomes caused by the dioxin pollution. TCDD is a major environmental carcinogen causing various types of cancers (IARC 1997). Materials and Methods The air pollution simulation model used in Denmark to assess hourly immissions of air- borne pollutants is a Gaussian air dispersion model based on emission data of the actual pollutant(s) and time series of meteorological data such as wind speed, wind direction, wind temperature, rain, snow, number of stacks, their heights, surrounding buildings, and surrounding terrain. The model [OML, Operationel Meteorologiske Luftkvalitets- modeller (Danish)] has been widely validated both in Europe and North America and is reliable in predicting hourly immissions of one or more airborne pollutants (DMU 2001). Only two measurements of dioxin were available as input source, and both were obtained in November and December 2000. The GIS used was the software pack- age ArcGis version 8.12 (ESRI, Atlanta, GA, USA). All current and past addresses in Denmark since 1999 were geocoded with Universal Transverse Mercator coordinates with a preci- sion of a few meters and subsequently layered into the GIS. The Address Project is described elsewhere (Briggs et al. 2002). By linkage of all individuals to these addresses using the unique Central Population Register (CPR) number (10-digit number in the Civil Registration System), the GIS eventually contained all the following information in addition to the addresses of each individual: date of birth, sex, migration (into, out of, and around the study area), and date of death (Figure 1). Each green spot represents an address and a table of the mentioned attributes. The CPR contains data on more than 7 million people who are or have been resi- dents in Denmark since 1968. The key to the register is the personal identiﬁcation number, the CPR number, which is a unique 10-digit number that all residents in Denmark are assigned at birth or when immigrating. In addition to the present address of all residents, the CPR also contains historical addresses and the dates on which the individual moved to and from that address. If a person dies, disap- pears, or takes up residence abroad, this is also recorded as having moved away from the address. The CPR, its structure, updating, and other details are described elsewhere (Briggs et al. 2002). This article is part of the mini-monograph “Health and Environment Information Systems for Exposure and Disease Mapping, and Risk Assessment.” Address correspondence to A. Poulstrup, Vedelsgade 17A, DK 7100 Vejle, Denmark. Telephone: 45 75 82 37 99. Fax: 45 75 72 35 64. E-mail: arne@eli.dk This study was supported by grants from the Danish Ministry of Internal Affairs and Health, Environmental Cancer Research Programme (383-38-2001); the European Commission, Health and Consumer Protection Directorate-General [SI2.329122 (2001CVG2-604)]; and the National Survey and Cadastre, Denmark. The study obtained approval in all aspects of the research from the Danish Data Protection Agency. The authors declare they have no competing ﬁnancial interests. Received 15 September 2003; accepted 2 February 2004. VOLUME 112 | NUMBER 9 | June 2004 • Environmental Health Perspectives