Risk of dying of cancer in the vicinity of multiple pollutant sources associated with the metal industry

BACKGROUND: Population exposure to emissions from multiple industrial sources, though little studied, is an aspect of great interest from an epidemiologic standpoint. OBJECTIVES: To investigate whether risk of dying due to tumors of the digestive system in populations residing in the vicinity of Spanish metal production and processing installations increases with proximity to a greater number of industrial facilities. METHODS: An ecologic study was designed to ascertain municipal mortality due to malignant tumors of the digestive system (oral cavity and pharynx, esophagus, stomach, pancreas, liver, gallbladder and colon–rectum) during the period 1994–2003, in Spanish regions with the presence of multiple industrial sources in the metal sector. Population exposure to pollution was estimated on the basis of distance from town of residence to pollution source. Using Poisson regression models, we analyzed: the increased risk of dying of cancer with proximity to a given number of sources; and excess mortality in the vicinity of specific industrial clusters. RESULTS: The tumor responsible for the greatest number of regions with increased risk in both sexes was liver cancer (78% of the regions, being statistically significant in Valencia (p-value for trend (p trend)=0.001 in both sexes), Madrid (p trend=0.011 in women) and the Basque Country (p trend=0.002 in men)), followed by colorectal and pancreatic cancers (56% of the regions, being statistically significant in both sexes in Valencia (p trend=0.001) and Zaragoza (p trend=0.018) for colorectal cancer; and Valladolid (p trend=0.019 in men) and Barcelona (p trend=0.049 in women) for pancreatic cancer). Valencia was the province that displayed increased risk with the proximity to metal industries for all tumors studied, while the Basque Country was the Autonomous Region that registered a rising risk trend for liver, stomach and colorectal tumors with proximity (≤5km) to a greater number of sources. CONCLUSIONS: The results could support the hypothesis that mortality due to certain tumors of the digestive system increases with proximity (≤5km) to a greater number of metal industry sources. Nevertheless, in this type of ecologic study, conclusions cannot be obtained in terms of cause and effect, nor can individual inferences be made from grouped data.