Distribution of iodine and selenium in soils and groundwater of rural areas in the Oryol region as a risk factor for thyroid cancer

The environmental iodine and selenium deficiency is prevalent in Russia, including the Oryol region, leading to an increased risk of thyroid cancer (TC) among the local population. The aim of the research is to investigate the spatial heterogeneity of the TC incidence in relation to the environmental distribution of iodine and selenium in the Oryol region. Samples were collected from 52 rural settlements (20 cm layer of pasture soils (n = 54) and drinking groundwater (n = 104)). The investigation revealed a high heterogeneity of the concentration of the elements both in soils and in natural water. The concentrations of I and Se were found to be lower in Greyic Phaeozems Albic (median I content: 1,68 mg/kg; Se: 0,155 mg/kg) than in Voronic Chernozems Pachic (I: 2,53 mg/kg; Se: 0,158 mg/kg). The iodine concentrations in all soil samples were lower than the optimal level (5 mg/kg), while Se content was lower than the optimum (0,2–0,7 mg/kg) in 55% of samples. The distribution of the elements in the groundwater is primarily in correlation with particular aquifers. Higher concentrations of iodine are associated with the Frasnian carbonate-terrigenous complex (I: 9,89 μg/l; Se: 0,09 μg/l), while lower concentrations are associated with the Famennian carbonate complex (I: 3,83 μg/l; Se: 0,2 μg/l). Concentrations were found to be below the optimum in 67 % of groundwater samples for iodine (10 μg/l), and in 99 % for selenium (2,5 μg/l). A notable variation in iodine and selenium levels was observed between the districts with low and high TC risk in the region. Based on the data obtained, it is possible to estimate the environmental impact on the TC morbidity.