Overall effects of topsoil elements on cancer mortality in rural Greece: A modeling approach

This ecological study examines cancer mortality rates in 61 rural Greek municipalities, covering in total 7,305,554 person-years from 2000 to 2015, based on the Hellenic Statistical Authority data. Topsoil concentrations of Mn, Ni, Pb, Be, As and Cd in Greek grazing land samples were obtained from the GEMAS (Geochemical Mapping of Agricultural and Grazing land Soil) project. Municipalities of rural regions with population of up to 20,000 people were selected as the study area and were divided into four quartiles, according to their age-specific cancer mortality rates, to identify the most divergent areas of low/high mortality. Fusion of demographic data with topsoil measurements aimed to reveal their potential association. Towards a univariate analysis, comparing each element individually across the low/high mortality regions revealed significant overlaps in distributions of concentrations for all elements. Machine learning multi-element models were built to predict whether an area would have a low or high cancer mortality rate, based simultaneously and solely on the concentrations of the six elements of the region, for each group. The out-of-sample median accuracy of the model was very high (83.3%) for the 0-29 age group, high (66.7%) for the 30-39, 40-49 and 50-59 age groups, while the accuracy decreased significantly above age of 60. The interaction of Mn, As, Ni, and partially Be, contributes most to the model's prediction for the 0-29 age group, As becomes the main contributor in the 30-39 age group, while all six elements contribute almost equally for the 40-49 group, and the interaction of Ni, Mn and Be becomes important in the 50-59 age group. The findings of this study strongly suggest that topsoil elements may jointly influence the frequency and geographical distribution of cancer.