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

Abstract

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 (≤ 5 km) 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 (≤ 5 km) 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.

Introduction

Residential proximity to industries that release pollution to air and water is a source of exposure to a high number of toxic substances. In recent years, many studies have been published that have linked such emissions to health problems, such as respiratory (Casella et al., 2005, Dubnov et al., 2007, Lopez et al., 2005, Peled et al., 2005) and cardiovascular disorders (Venners et al., 2003), complications in pregnancy (Brender et al., 2008, Suarez et al., 2007, Tang et al., 2008, Yang et al., 2004) and premature mortality (Hermann et al., 2004, Sarov et al., 2008), among populations residing in the vicinity of these installations. Insofar as cancer is concerned, a number of authors have described associations between certain tumors and proximity to industrial complexes (Casella et al., 2005, Garcia-Perez et al., 2009, Garcia-Perez et al., 2010a, Musti et al., 2009, Parodi et al., 2005, Ramis et al., 2009, Tsai et al., 2009, Viel et al., 2008).

When it comes to assessing public health risks stemming from exposure to industrial pollution, a common choice is to use distance from town or site of residence to pollution source as a proxy of exposure (Biggeri et al., 1996, De Roos et al., 2010, Garcia-Perez et al., 2009, Huang and Batterman, 2000, Johnson et al., 2003, Parodi et al., 2005, Verkasalo et al., 2004). Industries frequently form industrial clusters, with the result that independent analysis of each source fails to give a realistic picture of the possible risk to which the population is exposed. Yet, assessment of whether there is a greater risk in areas with multiple industrial sources than in those with only a single industrial facility continues to be a little studied aspect, in view of the additional analytical complexity posed by this factor. Metal production and processing installations are a clear example of industrial activities which often tend to be concentrated in large industrial areas, as occurs in certain parts of Spain. These types of industries emit a great amount of known or suspected carcinogens (arsenic, cadmium, chromium, tetrachloroethylene, lead and nickel) into the environment. Moreover, many of these facilities use metalworking fluids (MWFs) to cool and lubricate metalworking processes. There is reliable epidemiologic evidence of this chemical substance's carcinogenicity in humans (Savitz, 2003) being related, among other things, with certain tumor sites in the digestive system (esophagus, stomach, colon, rectum, and pancreas) (Canadian Centre for Occupational Health and Safety, 2005).

Hence, the aims of this study were: a) to ascertain whether risk of dying due to malignant tumors of the digestive system (buccal cavity and pharynx, esophagus, stomach, pancreas, liver, gallbladder, and colon-rectum) in populations residing in the vicinity of Spanish metal production and processing installations increased with proximity to a greater number of industrial sources; and, b) to study excess mortality in the environs of specific industrial clusters.