Estudo geoquímico da associação entre fluoreto encontrado na água, no solo e sedimentos de Manacapuru-AM

Abstract

In 2015, the Vigiflúor Network identified wells containing natural fluoride in the water at levels consid-ered optimal for the prevention of dental caries in Manacapuru-AM. The objective of the present study was to carry out a geochemical analysis of the geological units adjacent to the sampled wells within the scope of the Vigiflúor Project, in order to determine the origin of this F- in the water. 22 water samples and 129 soil and sediment samples were collected in the study area, 104 in superficial extracts (0.2 to 5 m) and 25 in deep extracts (58 to 174 m). F- in water and soil was determined with a fluoride electrode. In the soil samples, the concentrations of Total Fluoride (TF) and Soluble Fluoride in water and in acid (SF) were determined. For the analyses, the electrode was calibrated with fluoride standards prepared according to the samples. Data analysis was performed using linear regression with mixed effect (Soft-ware R, version 4.1.3, p<0.05) between fluoride concentrations present in soil/sediments (Soluble Fluoride and Total Fluoride) and in well water. In water, the average was 0.41 ppm F (max: 0.69 ppm F, min: 0.02 ppm F), with 12 wells showing concentrations considered optimal for the control of dental caries (indicating results between 0.51 and 0.69 ppm F) where 11 are wells over 220 m deep. In the soil, the surface extracts showed concentrations ranging from 0.06 to 1.74 μg F/g (FS - H2O), 0.08 to 3.30 μg F/g (FS - HCl) and 0.09 to 22 .24 μg F/g (FT). The concentrations in deep extracts ranged from 0.74 to 3.89 μg F/g (FS – H2O), 0.74 to 4.67 μg F/g (FS – HCl) and 4.02 to 31.71 μg F/g (FT). Regression analysis did not indicate evidence of influence of surface strata on fluoride concentration in water. In the deep strata, a tendency of increase of fluoride in the sediment samples was identified as a function of the depth in the soil. Thus, it is estimated the possibility that geological features related to the mineral composition in deep extracts of this region are a probable cause of the fluoride enrichment observed in the water of the analyzed wells.