Chemical composition of groundwater used for drinking in conditions of natural deficiency of iodine and selenium and evaluation of its health effect: the case of Bryansk region (Russia).

Chemical composition of drinking water was examined in rural settlements of Bryansk region to reveal its influence on distribution of endemic thyroid diseases among population after the Chernobyl accident (1986) with due regard to different sources of water, the age and composition of water-bearing rocks. Groundwater samples (n = 515 in total) were collected in 156 rural settlements over the region in the period from 2007 to 2017 and analyzed for major cationogenic elements (Ca, Mg, Sr, K, Na, Mn, Zn, Fe, Al, Si) and anions (HCO32-, Cl-, F-, SO42-, NO32-, PO42-) as well as for I- and Se using ICP-AES, potentiometry, photometry and spectrofluorimetry. The results confirmed a low supply of water samples with iodine (Median (Me) = 5.96 µg/L, variation range 0.06-41.2 µg/L) and selenium (Me = 0.18 µg/L, variation 0.001-6.21 µg/L). The concentration levels of iron (64% of examined districts), manganese (36% of examined districts) and strontium (8% of examined districts) appeared to be inconsistent with hygienic standards. The data on chemical composition of drinking water were analyzed for correlation with the medical data on the prevalence of endemic thyroid diseases among the population living in the corresponding rural settlements. Tendencies of relationship between water iodine concentration and the incidence of thyroid diseases caused by iodine deficiency among teenagers aged 8 to 12 have been found. The same trend was found when comparing geochemical data with iodine content in renal excretion in this age group. The influence of some other components of natural waters on the manifestation of thyroid insufficiency has been cartographically assessed.

Endemic diseases of geochemical origin and methodological approaches toward their prevention and elimination.

A new approach to the study of diseases of geochemical origin is presented, which is based on the hypothesis that all such geochemical endemias were not possible in conditions of virgin biosphere and are products of human civilization. Two genetically different types of endemic diseases of geochemical origin are distinguished, each having a specifically spatial structure: (1) diseases of natural origin due to natural element deficiency or excess in the particular zones or areas; (2) diseases of anthropogenic origin related to chemical transformation of the environment in the course of agricultural or industrial production. Anthropogenically provoked diseases of geochemical nature always occur in conditions of already formed natural geochemical heterogeneity. As each type of the endemic disease has a peculiar structure of spatial distribution, the present health risk can be mapped as a genetically two-layer structure, characterizing deviation of the existing geochemical conditions from those ideal for specific species. Parameters of geochemical conditions, which are ideal for humans and domesticated species, should be sought within the areas with undisturbed soil cover, where these species have been formed in their present form. The hypothesis is tested on example of thyroid diseases observed in iodine-deficient areas affected by a nuclear accident with 131I fallout. The developed approach is believed to serve as a practical tool for monitoring and prevention of endemic diseases of geochemical origin.