Fluoride Pollution

Groundwater availability depends on its accessibility, as well as on its quality. A principal component analysis (PCA) has been used to link the occurrence of natural (fluoride) and human (nitrate) pollutants with the hydrological dynamics in the Selva Basin (NE Spain) as a means to analyze quality problems and provide strategies for water resources exploitation. Statistical results show that both pollutants are independent, and they are related to groundwater fluxes of different spatial scales. Fluoride is linked to regional groundwater systems, while nitrate is related to local recharge produced within the basin. PCA thus permits relating a potential occurrence of pollutants to specific characteristics of the hydrogeological system. It also becomes an approach to assess its vulnerability by identifying key parameters related to pollution. Such a statistical outcome is of interest for water resources planning with the aim to avoid locating production wells in areas that show hydrogeological or hydrochemical features associated with either type of pollution.

The systematic and comprehensive geochemical analysis of fluoride (F) in twenty agricultural soil samples was carried out to understand spatial variability, mechanism of retention and release, and the areas of potential risk due to high concentrations of F in soil around Sidhi District, Central India. The spatial variations in physico-chemical parameters revealed significant difference in the methods of cultivation due to geomorphological constraints, availability of surface water and ground water etc., in the study area. The north and small pocket in central Sidhi were rich in fertile soils due to availability of surface and ground water. The southern and eastern Sidhi were rainfed areas, hence, the monocropping system by traditional methods showed less impact on the soil physico-chemical parameters. The soil F varied from 366.94 to 1178 mg/kg and 2-4 times greater than the background soil value (320 mg/kg) of the world. The pollution indexes were > 1 indicating prevalence of elevated soil fluorine.

The purpose of this work was to elucidate the repercussion of changing pH, incubation time and As(V) competition on fluoride (F −) sorption on forest and vineyard soil samples, pyritic, and granitic materials, as well as on the by-products pine sawdust, oak wood ash, mussel shell ash, fine and coarse mussel shell, and slate processing waste fines. To reach this end, the methodological approach was based on batch-type experiments. The results indicate that, for most materials, F − sorption was very high at the start, but was clearly diminished when the pH value increased. However, oak wood ash and shell ash showed high F − sorption even at alkaline pH, and pine sawdust showed low F − sorption for any pH value. Specifically, F − sorption was close to 100% for both ashes at pH <6, and around 70% at pH 10, while for forest soil it was close to 90% at pH <2, and around 60% at pH values near 8. Regarding the effect of incubation time on F − sorption, it was very low for both soils, pyritic material, granitic material, and both kinds of ashes, as all of them showed very rapid F − sorption from the start, with differences being lesser than 10% between sorption at 30 min and 1 month of incubation. However, sawdust and slate fines sorbed 20% of added F − in 30 min, remaining constant up to 12 h, and doubling after 30 days. And finally, mussel shell sorbed 20% at 30 min, increasing to close to 60% when incubation time was 30 days. This means that some of the materials showed a first sorption phase characterized by rapid F − sorption, and a slower sorption in a second phase. As regards the effect of the presence of As(V) on F − sorption, it was almost negligible, indicating the absence of competition for sorption sites. In view of that all, these results could aid to appropriately manage soils and by-products when focusing on F − removal, in circumstances where pH value changes, contact time vary from hours to days, and potential competition between F − and As(V) could take place.

The purpose of this work was to elucidate the repercussion of changing pH, incubation time and As(V) competition on fluoride (F) sorption on forest and vineyard soil samples, pyritic, and granitic materials, as well as on the by-products pine sawdust, oak wood ash, mussel shell ash, fine and coarse mussel shell, and slate processing waste fines. To reach this end, the methodological approach was based on batch-type experiments. The results indicate that, for most materials, F sorption was very high at the start, but was clearly diminished when the pH value increased. However, oak wood ash and shell ash showed high F sorption even at alkaline pH, and pine sawdust showed low F sorption for any pH value. Specifically, F sorption was close to 100% for both ashes at pH &lt; 6, and around 70% at pH 10, while for forest soil it was close to 90% at pH &lt; 2, and around 60% at pH values near 8. Regarding the effect of incubation time on F sorption, it was very low for both soils, pyritic ma...

The purpose of this work was to elucidate the repercussion of changing pH, incubation time and As(V) competition on fluoride (F) sorption on forest and vineyard soil samples, pyritic, and granitic materials, as well as on the by-products pine sawdust, oak wood ash, mussel shell ash, fine and coarse mussel shell, and slate processing waste fines. To reach this end, the methodological approach was based on batch-type experiments. The results indicate that, for most materials, F sorption was very high at the start, but was clearly diminished when the pH value increased. However, oak wood ash and shell ash showed high F sorption even at alkaline pH, and pine sawdust showed low F sorption for any pH value. Specifically, F sorption was close to 100% for both ashes at pH &lt; 6, and around 70% at pH 10, while for forest soil it was close to 90% at pH &lt; 2, and around 60% at pH values near 8. Regarding the effect of incubation time on F sorption, it was very low for both soils, pyritic ma...

Aluminium smelters are major sources of F emission to the environment. We studied, in laboratory experiments, the sorption and desorption of fluoride on organic and mineral horizons of soils located within 2 km from one of these factories, situated in the northern coast of Galicia (NW Spain). The soils, developed from granite, are acid (pH H 2 O 3.9-5.5), rich in organic matter (4-16 % C in the A horizon) and most A horizons have high Al saturation in the exchange complex. All samples showed a notable F sorption, between 1,066 and 1,589 mg kg-1 , after adding 200 mg F L-1 , which accounts for 53-80 % of F added. The sorption was slightly higher in the A horizons than in the respective organic horizons (differences of up to 194 mg kg-1). The fluoride sorption upon addition of 200 mg F L-1 correlated significantly (p \ 0.05) with soil pH in water (r =-0.77), iron extracted by acid ammonium oxalate (r = 0.68), aluminium plus iron extracted by acid ammonium oxalate (r = 0.63), exchange aluminium (r = 0.52) and clay percentage in soil (r = 0.76). The F sorption fitted to both Langmuir and Freundlich models. Desorbed F accounted for only 12-22 % of sorbed fluoride and correlated (p \ 0.05) negatively with non-crystalline (extracted by acid ammonium oxalate) Fe (r =-0.51) and clay content (r =-0.74) and positively with organic matter (r = 0.69) and with the effective cation exchange capacity of the soil (r = 0.50).

Aluminium smelters are major sources of F emission to the environment. We studied, in laboratory experiments, the sorption and desorption of fluoride on organic and mineral horizons of soils located within 2 km from one of these factories, situated in the northern coast of Galicia (NW Spain). The soils, developed from granite, are acid (pH H 2 O 3.9-5.5), rich in organic matter (4-16 % C in the A horizon) and most A horizons have high Al saturation in the exchange complex. All samples showed a notable F sorption, between 1,066 and 1,589 mg kg-1 , after adding 200 mg F L-1 , which accounts for 53-80 % of F added. The sorption was slightly higher in the A horizons than in the respective organic horizons (differences of up to 194 mg kg-1). The fluoride sorption upon addition of 200 mg F L-1 correlated significantly (p \ 0.05) with soil pH in water (r =-0.77), iron extracted by acid ammonium oxalate (r = 0.68), aluminium plus iron extracted by acid ammonium oxalate (r = 0.63), exchange aluminium (r = 0.52) and clay percentage in soil (r = 0.76). The F sorption fitted to both Langmuir and Freundlich models. Desorbed F accounted for only 12-22 % of sorbed fluoride and correlated (p \ 0.05) negatively with non-crystalline (extracted by acid ammonium oxalate) Fe (r =-0.51) and clay content (r =-0.74) and positively with organic matter (r = 0.69) and with the effective cation exchange capacity of the soil (r = 0.50).

The systematic and comprehensive geochemical analysis of fluoride (F) in twenty agricultural soil samples was carried out to understand spatial variability, mechanism of retention and release, and the areas of potential risk due to high concentrations of F in soil around Sidhi District, Central India. The spatial variations in physico-chemical parameters revealed significant difference in the methods of cultivation due to geomorphological constraints, availability of surface water and ground water etc., in the study area. The north and small pocket in central Sidhi were rich in fertile soils due to availability of surface and ground water. The southern and eastern Sidhi were rainfed areas, hence, the monocropping system by traditional methods showed less impact on the soil physico-chemical parameters. The soil F varied from 366.94 to 1178 mg/kg and 2-4 times greater than the background soil value (320 mg/kg) of the world. The pollution indexes were > 1 indicating prevalence of elevated soil fluorine.

The Sidhi District is situated on the Northeastern boundary of the Madhya Pradesh State, India which lies over a transitional area between the Indo-Gangetic plain in the north and the Deccan plateau in the south and the remotest district of Madhya Pradesh The systemic and comprehensive analysis of twenty composite samples of rainfed and irrigated agricultural soil around Sidhi district. The pH of soil samples varied from 6.6 to 8 especially and recorded higher values in the irrigated soils. The EC and CEC showed large spatial variation in the irrigated soils. The results showed alterations in the biogeochemical relationships between physico-chemical parameters. In rain fed areas, the high Si/Al and low Fe/Al ratios showed silicate nature of agricultural soils along with low iron loss from primary silicates.

Soil contamination by atmospheric fluorides was studied in the vicinity of an aluminum smelter. Soil profiles at various distances from the emission source were sampled and the samples analyzed for total and water-extractable F. Both measurements, in particular the water-extractable fraction, reflected the gradient of F exposure. The F concentration of the soil solution exhibited a similar dependence upon distance from the emission source. Over a distance of 8.8 km the total F concentration decreased from 2,700 to 616 #g F g-t, the waterextractable fraction from 292 to 10 #g F g-t, and the F concentration in the soil solution from 8.2 to 0.3/~g F mL-t. Within an extensively sampled profile, the total F concentration was more-or-less constant, whereas the water-extractable fraction increased significantly with depth. A soil column experiment was conducted in the field in order to estimate the rate of F accumulation and translocation. The F fluxes into and out of the main root zone were estimated to be in the order of 7.7 4-3.5 and 5.4-4-2.1 g F m-2 year-t, respectively, which is roughly an equivalent of 5070 of the F stored in a comparable uncontaminated profile.

Aluminium smelters are major sources of F emission to the environment. We studied, in laboratory experiments, the sorption and desorption of fluoride on organic and mineral horizons of soils located within 2 km from one of these factories, situated in the northern coast of Galicia (NW Spain). The soils, developed from granite, are acid (pH H 2 O: 3.9-5.5), rich in organic matter (4-16% C in the A horizon) and most A horizons have high Al saturation in the exchange complex. All samples showed a notable F sorption, between 1066 and 1589 mg kg -1 , after adding 200 mg F L -1 , which accounts for 53-80% of F added. The sorption was slightly higher in the A horizons than in the respective organic horizons (differences of up to 194 mg kg -1 ). The fluoride sorption upon addition of 200 mg F L -1 correlated significantly (p<0.05) with soil pH in water (r = -0.77), iron extracted by acid ammonium oxalate (r = 0.68), aluminium plus iron extracted by acid ammonium oxalate (r = 0.63), exchange aluminium (r = 0.52) and clay percentage in soil (r = 0.76). The F sorption fitted to both Langmuir and Freundlich models. Desorbed F accounted for only 12-22% of sorbed fluoride and correlated (p<0.05) negatively with non-crystalline (extracted by acid ammonium oxalate) Fe (r = -0.51) and clay content (r = -0.74) and positively with organic matter (r = 0.69) and with the effective cation exchange capacity of the soil (r = 0.50).

Aluminium speciation was studied in aqueous extracts of forest soils in the vicinity of an aluminium smelter in Galicia, NW Spain. Two soil depths (0-10 and 10-20 cm) were sampled within a 3.5 km radius around the factory. Forest soils samples far away from the factory were used as a control. Aqueous extracts (1:10 soil:water ratio) were analyzed for pH, electrical conductivity (EC), dissolved organic carbon (DOC), sulphate, Ca, Mg, Na, K, free and total fluoride, and aluminium species. The pH of the extracts ranged between 4.50 and 7.85, the EC was always under 0.35 dS/m, DOC ranged between 0.14 and 1.64 mmole C/L, and sulphate between 1.36 and 14.10 mg/L. Most of these values fall within normal ranges for natural Galician soils. Total fluoride concentrations ranged between 0.18 and 1.19 mg/L and tended to be lower in subsurface layers and at greater distances from the factory. Free fluoride and free/total fluoride ratio correlated positively (P < 0.01) with pH. Total aluminium concentrations in the extracts ranged between 0.04 and 3.24 mg/L. Acid-soluble (colloidal, polymeric and/or organically complexed) aluminium often accounted for more than 50% of the total Al. Non-labile (organic monomeric) aluminium constituted 6 to 83% of the total Al and 30 to 96% of the reactive Al. Labile (inorganic monomeric) aluminium was a very small fraction of the total Al in extracts at pH > 5 but prevailed in some more acid samples. Most labile Al in the vicinity of the factory was bound to fluoride and the activity of Al 3+ was extremely low. In control samples Al 3+ and hydroxylated complexes appeared together with lower concentrations of Al-F complexes.

Available phosphorus levels and P sorption capacity were investigated in soils derived from coal mine spoils at As Pontes (Galicia, NW Spain), currently in the process of reclamation. Clays and shales, often in conjunction with pyrite and other sulphides, are the main constituents of the spoils; many are extremely acid as a result of oxidation of sulphides. Reclamation tasks consisted of topsoiling, chemical and organic fertilizing or various amendments. Two depths (O-15 and 15-30 cm) were sampled and analysed at each sampling site. In total, 140 samples were collected ranging in pH-H,O from 2.7 to 8.4. Olsen P values ranged between 1 and 54 mg. kg-'. The phosphorus sorption index (PSI), determined according to Bathe and Williams (1971), ranged between 2.4 and 55.1. Multiple correlation between PSI and several soil parameters was investigated using a stepwise linear regression method. Four soil parameters (oxalate-extractable Fe and Al, pH in KC1 and organic carbon) were shown to explain 79% of the variance in log PSI. The correlation equation found was: log PSI = 3.562 + 0.519 x log(A1 + Fe),-0.065 x pH-KC1 + 0.247 x log(org. C).

Iron (Fe), a micronutrient, is currently being determined using extractants that were developed for homogeneous temperate soils. Considering the fact that tropical soils are largely heterogeneous and may not conform to conditions that apply to temperate soils, there was a need to have an extractant that will be able to meet the requirements of tropical soils. The Fe content of twenty soils across the humid zone of South-Western Nigeria were determined by Diethylenetriamine pentaacetic acid (DTPA), 0.1 N hydrochloric acid (HCl) and sodium hypochlorite (NaOCl) buffer methods. The test crop was maize (Zea mays L.). There was a significant (p<0.05) positive correlation between dry matter and Fe content in the plants. Iron extracted by NaOCl buffered at various pH levels was highly correlated (p<0.01) with Fe extracted by the conventional extractants (DTPA and 0.1 N HCl). A weak positive non significant (p>0.05) correlation with plant Fe uptake for NaOCl buffered at pH 8.0 was found to be superior to those of DTPA and 0.1 N HCl. Because of its availability and the simplicity of the extraction procedure, NaOCl buffered at pH 8.0 could be used as a replacement for DTPA and 0.1 N HCl.

The systematic and comprehensive geochemical analysis of fluoride (F) in twenty agricultural soil samples was carried out to understand spatial variability, mechanism of retention and release, and the areas of potential risk due to high concentrations of F in soil around Sidhi District, Central India. The spatial variations in physico-chemical parameters revealed significant difference in the methods of cultivation due to geomorphological constraints, availability of surface water and ground water etc., in the study area. The north and small pocket in central Sidhi were rich in fertile soils due to availability of surface and ground water. The southern and eastern Sidhi were rainfed areas, hence, the monocropping system by traditional methods showed less impact on the soil physico-chemical parameters. The soil F varied from 366.94 to 1178 mg/kg and 2-4 times greater than the background soil value (320 mg/kg) of the world. The pollution indexes were > 1 indicating prevalence of elevated soil fluorine.

The systematic and comprehensive geochemical analysis of fluoride (F) in twenty agricultural soil samples was carried out to understand spatial variability, mechanism of retention and release, and the areas of potential risk due to high concentrations of F in soil around Sidhi District, Central India. The spatial variations in physico-chemical parameters revealed significant difference in the methods of cultivation due to geomorphological constraints, availability of surface water and ground water etc., in the study area. The north and small pocket in central Sidhi were rich in fertile soils due to availability of surface and ground water. The southern and eastern Sidhi were rainfed areas, hence, the monocropping system by traditional methods showed less impact on the soil physico-chemical parameters. The soil F varied from 366.94 to 1178 mg/kg and 2-4 times greater than the background soil value (320 mg/kg) of the world. The pollution indexes were > 1 indicating prevalence of elevated soil fluorine.

The aim was to determine whether the addition of F to an acid soil reduces the concentration of free Al3+ and other forms that have been shown to be toxic to plants. The ability of two different extracts to reflect Al speciation in the soil solution was also investigated. Addition of F (0-5.2μmolg−1) to an acid soil (pH 4.15, soil solution) increased the pH and total concentrations of Al and F in the soil solution whereas Al3+ remained constant or decreased. Soil solution pH, total soluble Al and Al extracted by 0.01 m CaCl2 are not good predictors of the likelihood of aluminium toxicity in soils containing soluble fluoride.

Four extracting solutions (1 M NH4Cl, 0.02 M NH4Cl, 0.01 M CaCl2, and water) have been tested to determine mobile fluoride in forest and cropped soils having high fluoride contents resulting from emissions by an aluminum smelter in Galicia, NW Spain. Seventy-two acid forest soil samples and 47 cropped soil samples were analyzed. Linear regression analysis was performed by SPSS 9.0 statistical package. Significant correlations (P < 0.01) were found between fluoride concentrations in different extracts provided that soils had similar pH and exchange aluminum (Al) and calcium (Ca) values. The 1 M NH4Cl, 0.02 M NH4Cl, and 0.01 M CaCl2 extractants were more efficient than water in extracting fluoride from acid forest soils, due to displacement of exchange aluminum and, therefore, Al-bound fluoride. Highest extractions were achieved by 1 M NH4Cl, due to its higher ionic strength. Water extracted more fluoride than salt solutions from cropped soils, usually fertilized and limed, and consequently having high (>10 cmolec kg−1) exchange Ca values. When extracting cropped soils by NH4Cl and CaCl2, the CaF2 solubility product is presumably reached due to displacement of exchangeable calcium, and fluoride is removed from solution. Water extractions seem adequate to estimate mobile F from soils high in exchange Ca (>10 cmolec kg−1), while salt solutions seem suitable for soils high in exchange Al (>1 cmolec kg−1).

The aim of this study was to evaluate the effects of the particle size (2-4 mm, 0.5-2 mm, 0.25-0.5 mm and less than 0.25 mm) of magnesium limestone and the method of application (in a single dose or split in three yearly doses), on the forms of Al in the solid and liquid phases of an acid Galician soil destined for pasture production. Monitoring the experimental plots over a period of 3 years showed that the plots treated with a single application of the finest limestone (<0.25 mm) exhibited the highest pH and the lowest concentrations of exchangeable Al, with less than 10% Al saturation throughout the period of study. The average values of pH in water along the period of study were 5.30 in the most effective treatment and 5.06 in control plots. The average values of aluminium saturation were 6.5% in the most effective treatment and 16.9% in control plots. One year after liming, the plots treated with a single application of the finest limestone presented also the highest concentrations of weakly stable organo-aluminium complexes in the solid phase and of organically bound Al in the soil solution, as well as the lowest concentrations of labile Al, while no Al3+ (considered the most toxic Al species) was detected. Over time non-crystalline inorganic Al tended to precipitate, apparently at the expense of exchangeable Al and/or Al bound to the organic matter. The application of the finest limestone split in three doses (until completion of 3 t ha(-1) in the third year of the study) was less effective than the application of a single dose. The plots treated with the coarsest limestone (between 2 and 4 mm) and the control plots provided similar results for all parameters throughout the three years of the study. In the former the exchangeable Al was higher than 20% and the concentration of labile Al was the highest of all plots.

Atmospheric emissions of fluoride from an aluminium smelter-alumina refinery located on the northern coast of Galicia, NW Spain, increase the content of fluorine in soils and vegetation in the vicinity of the complex. The effects of the addition of fluoride solutions on the chemical properties of soil samples from the area surrounding the complex were investigated in laboratory experiments. Addition of fluoride to soils resulted in increases in pH and concentrations of Fe, Al, and organic matter in the equilibrium solutions and decreases in concentrations of Ca, Mg, and K. No consistent effects were observed on the Cu, Mn, or Zn concentrations. Most of the Al in solution was bound to organic matter. Within the fraction “labile aluminium”, the concentration of Al-OH complexes decreased and the Al-F complexes increased, especially AlF3 and AlF−4, which are less toxic than Al3+ and Al-OH species.