Fluoride levels in publicly supplied and bottled drinking water in the Island of Tenerife, Spain

Fluoride Levels in Supply Water from the Canary Islands Region

The Canary Islands, located in the Atlantic Ocean, are an archipelago of volcanic origin which, for decades, has been affected by natural fluoride contamination in the water supply of some of its islands, mainly the island of Tenerife. In addition, recent volcanic eruptions in the archipelago and the increased demand for water supply have led to an increase in the fluoride content in other areas which, historically, were not affected. Fluoride content was determined in 274 water supply samples from the most populated islands of the Canary Islands (Tenerife and Gran Canaria) collected during the months of June 2021 to May 2022. The samples were analysed by fluoride ion selective potentiometry. The highest concentrations in Tenerife were found in the municipalities of Sauzal (7.00 mg/L) and Tegueste (5.39 mg/L), both water samples are over the parametric value of 1.5 mg/L set in the supply water legislation. In the Gran Canaria Island, the highest fluoride levels were found in Valsequillo and Mogán with 1.44 mg/L in both locations, but under the parametric fluoride value abovementioned. Consumption of just 1 L of water per day in the El Sauzal area would result in a contribution rate of 77% for adults and children over 15 years of age (Upper Level value of 7 mg/day) and 108% for children 9-14 years of age (UL value of 5 mg/day). The contribution rates increase considerably, reaching or exceeding 100% of the reference value (UL) with increasing consumption of 1 to 2 L of water per day. Therefore, it is considered that there is a health risk of overexposure to fluoride on the island of Tenerife. In the case of the island of Gran Canaria, it has been shown that even the consumption of 2 litres of water per day does not confer contribution rates that pose a health risk.

Determination of the Fluoride Content in Water of Aqueducts of Cauca (Colombia) by Ion Exchange Chromatography

Water for human consumption is the main source of fluoride exposure. The concentration in water should not exceed 1 mg/L of fluoride since, at higher levels; it increases the risk of dental fluorosis, among other adverse effects. The fluoride content of 149 water samples from different aqueducts in Cauca (Colombia) has been determined by ion exchange chromatography with the aim of fluoride risk assessment. The rural area of the Municipality of Santander de Quilichao registered fluoride concentrations between 0.012 and 0.150 mg/L. The urban area of Santander de Quilichao recorded lower fluoride levels than the rural area (0.027-0.068 mg/L). The urban area of the Municipality of Cajibío registered fluoride levels of 0.082-0.186 mg/L. The highest levels of fluoride were found in Timbío (0.121-0.210 mg/L). The fluoride levels recorded in this study are not considered sufficient to trigger dental fluorosis. Likewise, optimal levels are not considered to protect the child population against dental caries. However, a monitoring plan of fluoride concentrations in water should be implemented to assure the quality and safe of the water.

Effects of fluoride on the histology, lipid metabolism, and bile acid secretion in liver of Bufo gargarizans larvae

In our study, Bufo gargarizans (B. gargarizans) larvae were exposed to control, 0.5, 5, 10 and 50 mg/L of NaF from Gs 26 to 42. At Gs 42, we evaluated the changes of liver histology and the mRNA levels of target genes in liver. In addition, we also examined the composition and content of fatty acids. Histological analysis revealed that fluoride caused liver injury, such as the increase of number of melanomacrophage centres, atrophy of nucleus, dilation of bile canaliculus, and decrease of quantity, degradation and deposition of lipid droplets. The results of RT-qPCR indicated that exposure to 5, 10 and 50 mg/L of NaF significantly decreased the transcript levels of genes related to fatty acid synthesis (FASN, FAE, MECR, KAR and TECR) in liver. Besides, mRNA expression of genes involved in fatty acid β-oxidation (ECHS1, HADHA, SCP2, CPT2, ACAA1 and ACAA2) and oxidative stress (SOD, GPx, MICU1 and HSP90) was significantly downregulated in 0.5, 5, 10 and 50 mg/L of NaF treatment groups. Also, in the relative expression of genes associated with synthesis and secretion of bile acid, BSEP significantly increased at 0.5, 5 and 50 mg/L of NaF while HSD3B7 significantly reduced in 0.5, 5, 10 and 50 mg/L of NaF. Finally, the fatty acid extraction and GC-MS analysis showed that the content of saturated fatty acids (SFAs) was decreased and the content of polyunsaturated fatty acids (PUFAs) was increased in all fluoride treatment groups. Taken together, the present results indicated that fluoride-induced the histological alterations of liver might be linked to the disorder of lipid metabolism, oxidative damage.

Fluoride removal from natural volcanic underground water by an electrocoagulation process: Parametric and cost evaluations

Excessive fluoride content in groundwater can cause serious risks to human health, and sources of groundwater intended for human consumption should be treated to reduce fluoride concentrations down to acceptable levels. In the particular case of the island of Tenerife (Canary Islands, Spain), the water supply comes mainly from aquifers of volcanic origin with a high content of fluorides that make them unacceptable for human consumption without prior conditioning treatment. The treatments that generate a high rejection of water are not acceptable because water is a scarce natural resource of high value. An electrocoagulation process was investigated as a method to treat natural groundwater from volcanic soils containing a hazardously high fluoride content. The operating parameters of an electrocoagulation reactor model with parallel plate aluminum electrodes were optimized for batch and continuous flow operations. In the case of the batch operation, acidification of the water improved the removal efficiency of fluoride, which was the highest at pH 3. However, operation at the natural pH of the water achieved elimination efficiencies between 82 and 92%, depending on the applied current density. An optimum current density of 5 mA/cm² was found in terms of maximum removal efficiency, and the kinetics of fluoride removal conformed to pseudo-second-order kinetics. In the continuous-flow operation, with the optimal residence time of 10 min and a separation of 0.5 cm between the electrodes, it was observed that the current density that would be applied would depend on the initial concentration of fluoride in the raw water. Thus, an initial fluoride concentration of 6.02 mg/L required a current density >7.5 mA/cm² to comply with the legal guidelines in the product water, while for an initial concentration of 8.98 mg/L, the optimal current density was 10 mA/cm². Under these operating conditions, the electrocoagulation process was able to reduce the fluoride concentration of natural groundwater to below 1.5 mg/L according to WHO guidelines with an operating cost between 0.20 and 0.26 €/m³ of treated water.

Long term spatial-temporal dynamics of fluoride in sources of drinking water and associated health risks in a semiarid region of Northern China

There is a concern about the increasing prevalence of health problems related to the ingestion of fluoride (F^-) in the developing world. Drinking water is one important source of F^-, and the concentration of F^- needs to be known to ensure the safety of drinking water. In this study, F^- levels in drinking water were investigated across Taiyuan in Shanxi Province, China. Spatial-temporal distribution characteristics and potential associated health risks were analyzed using GIS. We collected 485 samples from shallow wells without any defluoridation treatments between 2008 and 2016. After analyzing the samples of F^- content we found that mean F^- levels of urban areas (0.61 ± 0.39 mg L^-1), suburban areas (0.70 ± 0.87 mg L^-1) and for all of Taiyuan city (0.63 ± 0.56 mg L^-1) were in optimum range based on the recommendation by USEPA. However, individual locations within industrial areas (e.g. Gujiao District) had higher F^- levels (1.06 mg L^-1). A concerning result showed that 12.37% of tested locations had F^- concentrations larger than 1.0 mg L^-1. We calculated F^- Health Risk Indices (HRIs_F) and found that highest were associated with suburban areas, especially in the year 2009 and 2010. However, from 2008 to 2016, overall F^- levels and HRIs_F of the sampled groundwater in Taiyuan City showed a decreasing trend. HRIs_F in suburban areas was higher than urban areas, possible due to the heavily prevalent coal mining industry in those areas. Specific policies should be formulated to address HRIs_F.

The morphological changes and molecular biomarker responses in the liver of fluoride-exposed Bufo gargarizans larvae

The goal of the current study was to evaluate the negative influences of fluoride on liver of Bufo gargarizans larvae. B. gargarizans larvae were treated with 42.4mgF^-/L for 0, 24, 48 and 72h at Gosner stage 37. The morphological changes and responses of molecular biomarkers involved in lipid metabolism, oxidative stress and apoptosis were examined in liver. Disappearance of cell boundaries, degeneration of hepatic parenchyma cells and significant increase in the number of melanomacrophage centres and the quantity of lipid droplets were found in the liver treated with 42.4mgF^-/L for 72h. In addition, in the relative expression of acetyl CoA carboxylase 1 (ACC-1), fatty acid elongase 1 (FAE-1), sterol carrier protein 2 (SCP-2), and carnitine palmitoyltransferase-1 (CPT-1), decrease was observed after 24, 48 and 72h of 42.4mgF^-/L exposure. Furthermore, the transcript levels of superoxide dismutase (SOD) and glutathione peroxidase (GPx) were downregulated in tadpoles exposed for 24, 48 and 72h to 42.4mgF^-/L, while the transcript level of heat shock protein 90 (HSP90) was upregulated at 42.4mgF^-/L for 72h. Also, mRNA expression of Bcl-2-associated transcription factor 1(BCLAF1) and thyroid hormone receptors (TRα and TRβ) was significantly upregulated in tadpoles treated with 42.4mgF^-/L for 72h. Therefore, our results suggested that the liver injury induced by fluoride might result from disruption of lipid metabolism, oxidative damage and apoptosis.

A review of emerging adsorbents and current demand for defluoridation of water: Bright future in water sustainability

Fluoride contamination of groundwater is a serious problem in several countries of the world because of the intake of excessive fluoride caused by the drinking of the contaminated groundwater. Geological and anthropogenic factors are responsible for the contamination of groundwater with fluoride. Excess amounts of fluoride in potable water may cause irreversible demineralisation of bone and tooth tissues, a condition called fluorosis, and long-term damage to the brain, liver, thyroid, and kidney. There has long been a need for fluoride removal from potable water to make it safe for human use. From among several defluoridation technologies, adsorption is the technology most commonly used due to its cost-effectiveness, ease of operation, and simple physical process. In this paper, the adsorption capacities and fluoride removal efficiencies of different types of adsorbents are compiled from relevant published data available in the literature and represented graphically. The most promising adsorbents tested so far from each category of adsorbents are also highlighted. There is still a need to discover the actual feasibility of usage of adsorbents in the field on a commercial scale and to define the reusability of adsorbents to reduce cost and the waste produced from the adsorption process. The present paper reviews the currently available methods and emerging approaches for defluoridation of water.

Chronic Effects of Fluoride Exposure on Growth, Metamorphosis, and Skeleton Development in Bufo gargarizans Larvae

Bufo gargarizans tadpoles were chronically exposed to waterborne fluoride at measured concentrations ranging from 0.4 to 61.2 mg F^-/L for 70 days from Gosner stage 26 to completion of metamorphosis. The chronic exposure caused a concentration-dependent mortality in all tested fluoride concentrations. Total length, snout-to-vent length (SVL), body mass, and developmental stage of tadpoles were significantly inhibited at 42.6 mg F^-/L. In addition, significant metamorphic delay and increase in size at completion of metamorphosis occurred after exposure to 19.8 mg F^-/L. Moreover, 19.8 mg F^-/L suppressed the bone mineralization of larvae at completion of metamorphosis. However, the bone mineralization could be enhanced by 4.1 mg F^-/L. In conclusion, our results suggested that the presence of high concentrations of fluoride could increase mortality risk, delay metamorphosis, and suppress skeletal ossification in B. gargarizans larvae.

"Borderline" fluorotic region in Serbia: correlations among fluoride in drinking water, biomarkers of exposure and dental fluorosis in schoolchildren

This study explores relation between dental fluorosis occurrence in schoolchildren, residents of Ritopek, a small local community near Belgrade, and fluoride exposure via drinking water. Additionally, fluoride levels were determined in children's urine and hair samples, and efforts were made to correlate them with dental fluorosis. Dental fluorosis and caries prevalence were examined in a total of 52 schoolchildren aged 7-15 years (29 boys and 23 girls). Fluoride levels in three types of samples were analyzed using composite fluoride ion-selective electrode. Results showed high prevalence of dental fluorosis (34.6 %) and low prevalence of dental caries (23.1 %, mean DMFT 0.96) among children exposed to wide range of water fluoride levels (0.11-4.14 mg/L, n = 27). About 11 % of water samples exceeded 1.5 mg/L, a drinking-water quality guideline value for fluoride given by the World Health Organization (2006). Fluoride levels in urine and hair samples ranged between 0.07-2.59 (n = 48) and 1.07-19.83 mg/L (n = 33), respectively. Severity of dental fluorosis was positively and linearly correlated with fluoride levels in drinking water (r = 0.79). Fluoride levels in urine and hair were strongly and positively correlated with levels in drinking water (r = 0.92 and 0.94, respectively). Fluoride levels in hair samples appeared to be a potentially promising biomarker of fluoride intake via drinking water on one hand, and severity of dental fluorosis on the other hand. Based on community fluorosis index value of 0.58, dental fluorosis revealed in Ritopek can be considered as "borderline" public health issue.

Effects of fluoride on development and growth of Rana chensinensis embryos and larvae

The present study examined the adverse effects of fluoride exposure on embryos and larvae of Rana chensinensis. Survival, morphological abnormalities, growth and development, time to metamorphosis and size at metamorphic climax of R. chensinensis were examined. Our results showed that embryos malformation occurred in all fluoride treatments. Morphological abnormalities of embryos are characterized by axial flexures, the extrusion of fin axis, edema, and ruffled dorsal and ventral fin. Additionally, 4.1mg F(-)/L and above could significantly inhibit embryos growth and development. On day 15, total length and weight of tadpole were significantly lower in 19.6 and 42.4 mg F(-)/L treatments compared to control. However, significant reductions in total length and weight were observed only at 42.4 mg F(-)/L on day 30. Moreover, significant metamorphic delay and decrease in the size at metamorphic climax were found in larvae exposed to 42.4 mg F(-)/L. Taken together, embryos of R. chensinensis are more vulnerable to fluoride exposure than their tadpoles. Our results suggested that the presence of high concentrations fluoride might increase mortality risk and a reduction in juvenile recruitment in the field by increasing embryos malformation, delaying metamorphosis and decreasing size at metamorphosis.

Chemical, microbial and physical evaluation of commercial bottled waters in greater Houston area of Texas

Due to the increased demand and consumption of bottled water in the United States, there has been a growing concern about the quality of this product. Retail outlets sell local as well as imported bottled water to consumers. Three bottles for each of 35 different brands of bottled water were randomly collected from local grocery stores in the greater Houston area. Out of the 35 different brands, 16 were designated as spring water, 11 were purified and/or fortified tap water, 5 were carbonated water and 3 were distilled water. Chemical, microbial and physical properties of all samples were evaluated including pH, conductivity, bacteria counts, anion concentration, trace metal concentration, heavy metal and volatile organics concentration were determined in all samples. Inductively coupled plasma/mass spectrometry (ICPMS) was used for elemental analysis, gas chromatography with electron capture detector (GCECD) as well as gas chromatography mass spectrometry (GCMS) were used for analysis of volatile organics, ion chromatography (IC) and selective ion electrodes were used for the analysis of anions. Bacterial identification was performed using the Biolog software (Biolog, Inc., Hayward, Ca, USA). The results obtained were compared with guidelines of drinking water recommended by the International Bottled Water Association (IBWA), United States Food and Drug Administration (FDA), United States Environmental Protection Agency (EPA) and the World Health Organization (WHO) drinking water standard. The majority of the analyzed chemicals were below their respective drinking water standards for maximum admissible concentrations (MAC). Volatile organic chemicals were found to be below detection limits. Four of the 35 brands of the bottled water samples analyzed were found to be contaminated with bacteria.