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Abstract
Objectives Few studies have focused on pleural mesothelioma and environmental exposure in individuals residing around an industrial source of asbestos. The aim of this study is to determine whether residential distance and wind conditions are related to the risk of developing pleural mesothelioma.
Methods In this retrospective cohort study carried out in an area of Barcelona province (Catalonia, Spain), 24 environmental pleural mesothelioma cases were diagnosed between 2000 and 2009. We calculated the age-standardised incidence rate ratios of developing this disease in the population studied, taking into account the residential distance from the plant. For cases living within a 500-m radius of the plant, the geographical location in relation to the factory was also assessed.
Results The incidence rate of environmental pleural mesothelioma was higher in the population living within 500 m of the plant than in those living in a radius of 500–2000 m and much higher than those living at 2000–10 000 m. The highest incidence rate ratio for pleural mesothelioma (161.9) was found in the southeast quadrant of the 500-m area, coinciding with the predominant wind direction.
Conclusions Residential distance from an industrial source of asbestos and local wind conditions have a considerable impact on the risk of developing environmental pleural mesothelioma.
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Introduction
In a recent study,1 we described the main epidemiological features of asbestos-related diseases in relation to a large asbestos cement plant located in the province of Barcelona (Catalonia, Spain) that acted as a source of asbestos contamination over a period of 90 years. This cement plant, the first in Spain, began production in 1907 and was the only existing industry of this type up to 1950. It consumed a third of the entire volume of asbestos imported by Spain until it was closed in 1997. During its working period, an average of 1250 persons were employed at the plant and 14 446 tons of asbestos (80% white, 15% blue and 5% brown) were used per year. This enormous volume of raw asbestos arrived by train to the factory, which was located in the center of 1 (Cerdanyola del Vallès) of the 12 towns in the area studied, and was ground up during the manufacturing process. A risk of developing asbestos-related diseases was documented in the workers exposed to asbestos at the plant, and in persons living with them and in the population residing in the surrounding area.
The aim of this study is to determine whether residential distance and meteorological conditions are related to differences in the risk of developing pleural mesothelioma.
Methods
This is a retrospective cohort study whose information was obtained from the medical records of patients diagnosed with pleural mesothelioma between 2000 and 2009 attended to in the area's primary care centers and the referral hospital. All patients had been living in the area around an asbestos cement plant in the province of Barcelona for some time while the plant was functioning (1907–1997) and up to the time of the diagnosis. Patients who worked in the cement plant or lived with an asbestos worker were excluded.
Clinical and epidemiological data were recorded on a case report form specifically designed for the study, as is described in detail in a previous publication.2 Diagnostic pathological features for mesothelioma were required in all cases. The duration of exposure was established as the time living in the plant area between 1907 and 1997. The latency period was the time from the start of exposure, defined as the year that patients established their residence in the asbestos cement plant area, to the diagnosis.
The patient's place of residence was determined from primary healthcare documentation and plotted on a topographic map drawn to scale, to establish the distance from the plant's central source of asbestos emission to the patient's home. Taking into consideration that the factory and its warehouses occupied a considerable area, the investigators, together with the factory workers, considered the central emission point to be the asbestos mill and the railway platform where asbestos arriving by train was unloaded. Concentric circles were drawn around the emission point at a radius of 500, 2000 and 10 000 m, and patients were classified according to their residential distance from this point. In cases living within 500 m of the plant, we established the position of their home according to the four cardinal points (dividing the circumscribed area into quadrants) and documented the number of years they lived there while the plant was functioning. In addition, we specifically investigated whether any of the environmental cases lived within 500 m of two other industries in the area that manipulated asbestos, a brake factory and a factory producing thermal insulation and electrical material.
The predominant winds in the area blew from west to east and southeast at a mean annual speed of 1–2 m/s. This information was obtained from the Catalan Meteorologic Service and the Climatic Atlas of Catalonia, which is published by the Department of Environmental Management from readings taken at the meteorological station in Parc Tecnològic del Vallès, located in Cerdanyola, the town in which the asbestos cement plant was located.3
Statistical analysis
The information regarding population was obtained from data provided by the Institut d'Estadística de Catalunya (IDESCAT, Statistics Institute of Catalonia) in 2005.4 We used the 2005 population as an estimation of the mean population between 2000 and 2009. χ2 and Anova tests were performed to compare sex, mean age and exposure time between sector exposure groups. Significance was set at a p value of <0.05. Age-standardised incidence rate (IR) was calculated by direct standardisation, using the European standard population. The 95% CI was calculated with the exact Poisson method for a small number of cases. Incidence rate ratios (RRs) were calculated in relation to the most distant zone from the source (>2000 m to 10 000 m). Research ethics committee approval was obtained from Catalonian Health Institute.
Results
A total of 24 pleural mesotheliomas were identified. No environmental pleural mesotheliomas were detected within 500 m of the two other industries within the study area that worked with asbestos. Mean age was 69.3 (SD: 10.2) years, 15 (62.5%) patients were men and 13 (54.2%) were non-smokers. The mean duration of exposure and latency periods were 29.2 (SD: 18.0) years and 47.2 (SD: 17.1) years, respectively. Age, sex and exposure time showed no significant differences between sectors (<500 m, 500–2000 m, >2000–10 000 m, and the quadrants southwest, northeast and southeast at <500 m) (p>0.05).
The IRs and the RRs for pleural mesothelioma are shown in table 1. The IR was higher in the population living within 500 m of the plant than in those living in the area of 500–2000 m, and much higher than in those residing in the >2000–10 000-m sector.
Age-standardised incidence rate per 100 000 person-years and incidence rate ratios of environmental pleural mesothelioma in relation to the residential distance and position to the asbestos plant
The IR in the closest sector was 56.5-fold greater than in the farthest sector. Furthermore, within the closest sector, individuals living in the eastern quadrants and particularly those in the southeast quadrant presented a much higher RR of mesothelioma than those living in the west quadrants of the plant. The RR in the southeast quadrant was 161.9.
Discussion
The findings of this study suggest that fluffed asbestos dispersed into the ambient air created an important environmental risk of pleural mesothelioma in neighborhood residents living around the asbestos cement plant investigated. In a recent study in Japan. Kuramatani and Kumagai5 described a higher risk of mesothelioma death with respect to the expected deaths in persons living within 600 m of a large asbestos cement plant. According to our findings, the risk varied depending on the distance of homes from the focal point of asbestos emission. In two other studies,6 ,7 however, significant higher risk with closer proximity to the industrial source was not observed. These discrepancies could be explained because of the statistical power of the study, the population and size of the studied area, the industries' capacity for contamination and the existence of other industrial sources of contamination, among others. In the present study, there were no cases of pleural mesothelioma around two other factories in the area in which asbestos was used. This is not surprising considering that in the asbestos cement plant a large volume of raw, fluffed asbestos was manipulated in the open air, while the other two factories worked with much smaller amounts of processed asbestos in closed areas. The land in the area under study is not a natural source of asbestos.8 It is unlikely that transport of packed raw asbestos to the plant by highway would be a determinant contribution to mesothelioma risk in this case, since the main means of transport was by freight train and unloading was done directly at the plant site. In the areas around the plant, asbestos cement residuals were only sporadically used to stabilise road surfaces between 1959 and 1974.9
A low wind speed can facilitate asbestos deposit and contamination near the source of emission, whereas intense winds disperse asbestos fibres a greater distance.10 The mild winds in the area of our study may have facilitated a higher concentration of fibres near the plant and contributed to the high risk of pleural mesothelioma in the neighborhoods nearby. Although it is recognised that wind direction determines the concentration of asbestos fibres in a specific area,10 only one study has considered that this meteorological factor could be related to pleural mesothelioma deaths by environmental exposure.5 The authors reported a significantly elevated standardised mortality ratio up to 2200 m from the factory in the same direction in which the wind predominantly blew. In our study, the RR of pleural mesothelioma was very high in the northeast and southeast quadrants of the 500-m sector, coinciding with the study area's predominant wind direction. The fact that no statistically significant differences in age, sex and exposure time were found in different sectors, makes it unlikely that these variables influence our findings.
The results of this study show that the residential distance from a contaminating industrial source of asbestos and the predominant wind conditions in the area can have an influence on the risk of developing environmental pleural mesothelioma.
What this paper adds
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Little is known if residential distance from a contaminating industrial source of asbestos and the wind conditions in the area can have an influence on the incidence rate ratios of developing pleural mesothelioma.
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The rate ratio of pleural mesothelioma was higher the closer the distance from the asbestos cement plant and in the same direction in which the wind predominantly blew.
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Residential distance and wind conditions in an area where there was a contaminating industrial source of asbestos could have implications for clinical practice and public healthcare policies.
Acknowledgments
The City Hall of Cerdanyola kindly provided the population data for each quadrant within a radius of 500 m from the focal point of asbestos emission. The authors thank Celine Cavallo for English language support and Rosa Llòria for technical assistance in the writing and preparation of the manuscript.
Footnotes
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Contributors JT: Contributed to the study design and hypothesis, clinical assessment, data interpretation, and drafting and revising the manuscript. Guarantor of the paper. CA: Contributed to the statistical analyses, data interpretation, and drafting and revising the manuscript. Guarantor of the paper. XM-A: Contributed to the clinical assessment, data management, and manuscript revision. RA-H: Contributed to the clinical assessment and manuscript revision. MR-M: Contributed to the study design and hypothesis, data interpretation, and manuscript revision. Guarantor of the paper. IG-A: Contributed to the clinical assessment and manuscript revision. IK: Contributed to the clinical assessment and manuscript revision. GC: Contributed to the clinical assessment, data management, and manuscript revision. MG: Contributed to the clinical assessment, and manuscript revision. JC-S: Contributed to the statistical analyses, data interpretation, and manuscript revision. RO: Contributed to the clinical assessment, data interpretation, and drafting and revising the manuscript. Guarantor of the paper.
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Funding This study was funded by the Institut d'Investigacions en Atenció Primària (IDIAP) Jordi Gol (exp.AJ/05/0314), the Fondo de Investigaciones Sanitarias de la Seguridad Social (exp.IP06/0063) and the Programa de Intensificación de la Actividad Investigadora en el Sistema Nacional de Salud (I3SNSexp.INT07/208).
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Competing interests None.
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Patient consent Obtained.
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Ethics approval IDIAP Jordi Gol.
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Provenance and peer review Not commissioned; externally peer reviewed.