EPER provides data on emissions of key pollutants to air and water from major European industrial facilities. The first set of emissions data, published in February 2004, should be used with caution because of several limitations. One of them is the non-registered industrial plants and/or unquantified emissions, due to the fact that industries are still in the phase of adaptation to EPER regulations and the emission reporting will not become compulsory until 2007. Therefore, data were gathered in 2001 from industries participating in EPER in a voluntary way. In view of the EPER's novelty, the completeness or data quality of this register is not well-known, though given the IPPC's regulatory stance with respect to industrial activity, sufficient quality for the proposed description can be reasonably assumed. However, the 'picture' derived from our study could change in part if completeness and accuracy data were improved.
On the other hand, it should be noted that reported emission data can be obtained by monitoring or modelling. There are three possible codes to indicate the emission determination method for the reported emission data:
Code M: is used when the emissions of a facility are derived from direct monitoring results for specific processes at the facility, based on actual measurements of pollutant concentrations for a given discharge route.
Code C: emission data are based on calculations using nationally or internationally agreed estimation methods (like as fuel used, production rate) and emission factors, which are representative for the industrial sectors. Furthermore, this code is used when the emission calculation methods is obtained from published references [14,15].
Code E: emission data are based on non-standardised estimations derived from best assumptions or expert judgement.
In this first approach, analysis of the EPER 2001 pollution data reveals that industrial air pollution is more intense for substances grouped under: "Environmental themes" in Andalusia, Aragon, Asturias, Castile la Mancha, Catalonia and Galicia; "Metals and compounds" in Andalusia, Catalonia and the Basque Country; "Chlorinated organic substances" in Andalusia, Castile & Leon, Catalonia, Madrid Autonomous Region, Extremadura and the Basque Country; "Other organic compounds" in Andalusia; and "Other compounds" in Andalusia, Castile & Leon and the Basque Country.
On the other hand, industrial pollution discharged directly into water proved more intense for substances grouped under: "Environmental themes" in Andalusia and Aragon; "Metals and compounds" in Andalusia, Aragon, Cantabria, Catalonia and the Basque Country; "Chlorinated organic substances" in Andalusia, Cantabria and Catalonia; "Other organic compounds" in Andalusia and Cantabria; and "Other compounds" in Asturias and the Basque Country.
Lastly, industrial pollution discharged indirectly into water (via sewage treatment plants) was more intense for substances grouped under: "Environmental themes" in Andalusia; "Metals and compounds" in Aragon, Cantabria, Galicia and the Basque Country; "Chlorinated organic substances" in Catalonia and Basque Country; "Other organic compounds" in Andalusia, Catalonia and the Basque Country; and "Other compounds" in Andalusia, Catalonia and the Basque Country.
In Spain, a total of 655 towns have at least one EPER registered facility (excluding farms) in their administrative limit. A total of 215 towns have at least one pollutant facility located within two kilometres from their town centroid (centre point of town) with a population estimated at 500,000 inhabitants. These figures have been calculated after a thorough quality control of the facility UTM coordinates provided by EPER.
As it can be observed from the EPER, a few single industrial plants are responsible for the highest percentage of emissions (Tables 3, 4 and 5). Identification of a small number of high emission plants should elicit implementation of adequately designed health studies in their surrounding.
Analysis of the comparative percentage emissions of pollutant substances released to air in the 15 European Union countries shows that Spain features as a polluter in 32 substances. In percentage terms it ranks: as the leading polluter in 10 of these (arsenic, copper, chromium, nitrogen dioxide, hexachlorobenzene, hydrofluorocarbons, nickel, sulphur oxides, PM10 and zinc); as the second-leading polluter in 3 more (ammonia, cadmium and fluorine); and as the third-leading polluter and in a further 7 (non-methane volatile organic compounds, dioxins and furans, polycyclic aromatic hydrofluorocarbons, lead, tetrachloroethylene, trichloroethylene and trichloromethane). According to data released by EPER in 2004, Spain would be the leading polluter in almost one third of all EPER-registered pollutant substances released into the air and ranks among the top three leading polluters in two-thirds of all such substances. It should be noted that this situation can reflect differences in reporting between countries.
With regard to release of substances to air, in which Spain is pre-eminent vis-à-vis the remaining European countries, hexachlorobenzene & a secondary product formed during the manufacture of other chemical substances – has been classified by the IARC as a possible carcinogen to human beings (group 2B) . Its principal health effects stem from ingesting products highly contaminated with this substance . Zinc, whose principal exposure occurs when eating food, drinking water or breathing air polluted with this compound , has not been classified by the IARC in terms of carcinogenicity , but can nonetheless cause a number of disorders. The IARC has concluded that some nickel compounds are carcinogenic to humans (group 1) and that metallic nickel is possibly carcinogenic to humans (group 2B) . Its most harmful effects are seen when large amounts of compounds of this substance are inhaled . The IARC has decided that chromium compounds (VI) are carcinogenic to humans (group 1)  and may increase the risk of contracting lung cancer. The principal health effects follow on from inhaling high levels of this compound . Some studies conducted in Spain have found evidence of risk posed to the population living near industries that release some of these compounds [20-22].
The EPER contains data on the main pollutant emissions to air and water reported by over 10000 medium- and large-sized industrial installations in 17 European countries. Online information searches can be made via the EPER web page, according to type of industrial plant, industrial activity, area, year and pollutant. It is a user-friendly register, from which, not only tables, but also crude data on pollutant emissions and interactive maps can be obtained. This tool enables useful information to be generated in a public health/environmental pollution context, with similar limitations than other registries as, for instance, Toxic Release Inventory (TRI register) in US [23,24]. It should be noted here that the 2001-based data used for this study were in fact published in February 2004, and that in the last two years there may have been corrections by industries to the emission reports submitted for said year. This gives rise to slight discrepancies between the information reported in this paper and that shown on the EPER-Spain web page.
In relation to public health, there has been growing interest in the development of useful statistical methods for detection of patterns of health events linked with pollution sources in recent years. The information obtained through EPER and PRTR would allow to study the consequences of pollutant foci in population health applying focused clustering methods [25,26]. Raised incidence of the health outcomes in the target population living near to the source or directional preference related to a dominant wind direction may provide evidence of such a link .
Some authors reported statistically significant associations between lung cancer risk and residential proximity to smelters, complex industrial areas, and other emission sources. There was some evidence that leukaemia and lymphomas occurred in the neighbourhoods that contained industrial sites [1,4,5] The modelling of distance effect to sources of pollution under isotropic or anisotropic assumptions is complex and there are very limited examples in the literature. To date, most pollution source studies concentrate on incidence or mortality of a single disease [26,27].
The EPER is scheduled to be upgraded and replaced by the European Pollutant Release and Transfer Register (PRTR), which will include more comprehensive information on industrial pollution from 91 substances and 65 industrial activities, as well as information on waste management by industrial installations. It will also compile pollutionreports from a range of sources, such as road traffic, aviation, shipping and agriculture. The reports will be annual (rather than triennial as envisaged under the EPER), with the first becoming available in 2007. As from 2009, the PRTR will be accessible by Internet and will have replaced the EPER.