Fluorine in the environment, a review of its sources and geochemistry

Abstract

While F is an essential constituent of some rock-forming minerals such as fluorite and apatite, its major occurrence in the lithosphere is within hydroxysilicate minerals where Foccupies OHlattice sites. The majority of the F occurring in the secondary environment derives from natural weathering processes with some soils derived from F-rich parent rocks containing over 1weight (wt) % F. Other natural sources of F are vulcanicity, wind-blown dust and a minor marine-derived component, with biomass burning, being in part natural, also a source. Several anthropogenic sources of environmental F have also been identified. Of the anthropogenic sources, the application of phosphate fertiliser, which probably adds over 2.3 Mt a-1 F to soils globally, represents the largest. While much of this is strongly retained in soils, some may be transferred to groundwater. In some abandoned mine sites in the UK where fluorite was associated with the mineralisation, soil F contents of up to 8 wt % have been recorded with plants growing on the sites containing up to 1wt % F. The rapid growth of urban areas in India, Pakistan and Bangladesh has resulted in an upsurge of brickmaking in Asia, with these 3 countries plus China accounting for over 75% of global brick production. As a result there is a large number of unregulated brick kilns which emit HF into the surrounding environment. Based on an annual global brick production of 1,500 billion and the F contents of brick clays, it is estimated that about 1.8 Mt a-1 F are released to the environment from brick manufacture. This suggests that brickmaking is the largest source of atmospheric F emissions dwarfing that of coal combustion, 0.2-0.3 Mt a-1 , phosphate fertiliser production, 0.07-0.10 Mt a-1 , aluminium smelting, 0.041 Mt a-1 , and even vulcanicity, 0.3-0.7 Mt a-1. However, it is apparent that atmospheric F emissions are not transported globally and as such their effects are manifested only in the local environment. Emissions from industry sited close to urban centres can impact these environments together with domestic coal combustion and the release of F from high octane fuels in motor vehicles. A more recent source of F in the environment stems from the large number of fluorocarbon compounds in everyday use. Degradation of some of these fluorocarbon compounds together with pyrolysis of fluoropolymers and burning of household refuse has resulted in the deposition of organofluorine compounds such trifluoroacetic acid in the environment.

Formation and In Situ Treatment of High Fluoride Concentrations in Shallow Groundwater of a Semi-Arid Region: Jiaolai Basin, China

“…Fluoride enrichment in groundwater requires the presence of certain hydrochemical conditions [67]. Fluoride content in water is controlled by the solubility of fluorite, which is dependent on the presence of Ca in water [2]. The hydrochemical type of HFGW is generally Na-rich/Ca-poor water [2,9].…”

“…Fluoride is an essential nutrient, and due to its active chemical properties, adopts various forms in the environment. Water-soluble fluoride has a considerable impact on human health, with excessive groundwater fluoride content often resulting in regions of endemic fluorosis [2]. Endemic fluorosis is a geochemical disease occurring in a specific geographical environment [3,4], and since its spatiotemporal distribution is positively correlated with the distribution of groundwater fluoride content, excessive fluoride content in groundwater is considered to be the main cause of regional fluorosis [5].…”

“…Groundwater is an important source of drinking water for human beings and is also the main source of irrigation water for agriculture in many areas. High groundwater fluoride contents can result in excessive uptake of fluoride into the human body through the direct consumption of drinking water, thereby posing a risk to human health [2,[6][7][8][9][10][11]. In addition, the use of high-fluoride groundwater as irrigation water can lead to the build-up of excessive fluoride in crops, thereby posing a risk to the health of the society [12][13][14][15].…”

“…While fluorine is used in industrial processes for the manufacture of steel, aluminum and refrigerants, the majority of fluoride present in groundwater and surface water is of natural origin [17]. The different processes contributing to the formation of high-fluoride groundwater (HFGW) can be summarized as follows: (1) evaporative concentration, (2) leaching enrichment, (3) transgression enrichment, (4) hot water enrichment and (5) anthropogenic pollution [18][19][20][21][22]. HFGW areas formed though evaporative concentration are generally characterized by a flat or low-lying terrain, slow groundwater flow, less well-developed hydrodynamic conditions, shallow groundwater depth and high evaporation.…”

Uso do aplicativo PhotoMetrix no monitoramento da concentração de flúor em sistemas alternativos de abastecimento de água

“…Quando em concentrações adequadas, o flúor contribui para a calcificação do esmalte e é um importante inibidor da cárie dentária (LIMA et al, 2014;PETERSEN, 2016;SHARMA et al, 2017). No entanto, a ingestão de água com níveis acima do permitido, causa um distúrbio chamado de fluorose dental, originada por exposições excessivas ao fluoreto, levando a mineralização defeituosa do esmalte (CANGUSSU et al, 2002;ZOU E ASHLEY, 2014;FUGE, 2019).…”