Abstract
The presence of toxic metals in soil per se, and in soil impacted by mining, industry, agriculture and urbanisation in particular, is a major concern for both human health and ecotoxicology. The dual aim of this study was: to ascertain whether topsoil composition could influence the spatial distribution of mortality due to different types of cancer and to identify possible errors committed by epidemiological studies which analyse soil composition data as a closed number system. We conducted an ecological cancer mortality study, covering 861,440 cancer deaths (27 cancer sites) in 7917 Spanish mainland towns, from 1999 to 2008. Topsoil levels of Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn were determined by ICP-MS at 13,317 sampling points. We transformed the topsoil data in two ways, i.e. log transformation and centred logratio transformation. Principal factor analysis was performed to obtain independent latent factors for the transformed variables. To estimate the effect on mortality of topsoil factor loadings, we fitted Besag, York and Mollié models embedded in geostatistical-spatial models. This model included soil sample locations and town centroids (non-aligned data), fitted using the integrated nested Laplace approximation (INLA) as a tool for Bayesian inference and stochastic partial differential equations (SPDE). All results were adjusted for socio-demographic variables. The results indicated that soil composition could have an influence on the spatial distribution and mortality patterns of cancer. The analysis adjusted for socio-demographic variables showed excess male mortality due to digestive system tumours in areas with soils containing higher Cd, Pb, Zn, Mn and Cu concentrations, bladder cancer in areas with soils containing higher Cd concentrations, and brain cancer in areas with soils containing As. In both sexes, cancer of oesophagus was associated with soils containing a higher lead content, while lung cancer was associated with soils containing a higher copper content. Stress should be laid on the importance of taking into account the compositional nature of the data in this type of analysis.
Highlights
Chemical composition of soil, due to its geological origin, remains stable over time and can contain carcinogens such as heavy metals
The results indicated that soil composition could have an influence on the spatial distribution and mortality patterns of cancer
Mortality data for each of the 8077 (7917 mainland) Spanish towns were drawn from the records of the National Statistics Institute (NSI) for the study period (1999–2008) and computed for 13 types of malignant tumours, with a total of 669,973 deaths due to the tumours analysed
Summary
Due to its geological origin, remains stable over time and can contain carcinogens such as heavy metals. Human exposure to bioavailable carcinogenic components of soil can affect both sexes indiscriminately. Spatio-temporal cancer mortality studies and various cancer atlases in Spain have revealed geographical patterns for some tumours, which display similar spatial distribution in men and women and persist over time (Lopez-Abente et al 2007, 2014). Cancers of the upper gastrointestinal tract (stomach and oesophagus), pancreas, brain, kidney and thyroid all display the above characteristics. High-level exposures to arsenic and heavy metals have been found to be associated with multiple cancer types by numerous epidemiological studies (Naujokas et al 2013). There is far less information, on the health effects of low-dose chronic exposure to many trace metals, and studies on the health effects of metals and metalloids in topsoil belong to this latter category (Centeno et al 2013)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
