National and subnational burden of disease attributable to elevated fluoride levels in drinking water apportioned by sex, age group, province, and community type in Iran, 2017 were quantified based on disability-adjusted life years (DALYs). The attributable burden of disease was estimated using four input data: (1) effect size of elevated drinking water fluoride levels for dental and skeletal fluorosis, (2) population distribution of drinking water fluoride levels, (3) the threshold levels of fluoride in drinking water for contribution in dental and skeletal fluorosis, and (4) age-sex distribution of population. The attributable burden of disease was only related to dental fluorosis, because the fluoride levels were lower than the threshold value for skeletal fluorosis (4.0 mg/L) in all of the cases. The national attributable prevalence (per 100,000 people), DALYs, and DALY rate in 2017 were calculated to be 60 (95% uncertainty interval 48-69), 3443 (1034-6940), and 4.31 (1.29-8.68), respectively. The national attributable burden of disease was not significantly different by sex, but was affected by age and community type in a manner that the highest DALY rate was related to the age group 10-14 y (6.06 [1.82-12.21]) and over 66% of the national attributable DALYs occurred in rural communities. The attributable burden of disease occurred only in 10 out of 31 provinces and about 94% of the attributable DALYs were concentrated in four provinces Fars (1967 [592-3964]), Bushehr (414 [124-836]), West Azarbaijan (400 [120-808]), and Hormozgan (377 [113-761]). Implementation of fluoride-safe drinking water supply schemes in the four leading provinces can prevent most of the national health losses and partly compensate the increasing trend of disease burden from oral conditions at the national level.

The present study aims towards fluoride remediation from synthetic water using steam-activated carbon of Aegle marmelos (bael shell/wood apple) (BAC) and Parthenium hysterophorus (PHAC) according to batch sorption techniques. The impact of different parametric conditions viz. initial fluoride concentration (4-12 mg/L), time (0-5 h), temperature (293.15-333.15 K), adsorbent dosage (4-14 g/L), pH (4-9), and RPM (150-350) were considered for both the adsorbents. Maximum defluoridation of 89% was achieved by BAC at a concentration of 10 mg/L, adsorbent dose 6 g/L, pH 5, temperature 313.15 K, agitation speed 250 rpm, and contact time 9 h, whereas PHAC attained maximum removal of 78% at an initial concentration of 8 mg/L, adsorbent dose 10 g/L, pH 4, temperature 313.15 K, and contact time 12 h. Instrumental analysis by SEM, EDX, and FTIR confirmed about the fluoride binding ability of the adsorbents. The Langmuir isotherm model provided the best fit (R2 = 0.9962 and 0.9945) to the removal process with maximum adsorptive uptake of 16.85 and 6.22 mg/g by BAC and PHAC respectively. The adsorption phenomenon was found to obey pseudo-second-order kinetics. The endothermic, spontaneous, and feasible nature of the sorption process was confirmed by the thermodynamic study. The total costs of 1 kg adsorbent preparation were calculated as 1.122 USD and 1.0615 USD which helped us in determining the economic feasibility of the adsorbents in large-scale applications. The growth of Chlorella sorokiniana BTA 9031 was also observed to be affected by the fluoride solution. Comparing the removal efficiencies of both the adsorbents, it can be concluded that BAC shell proved to be an efficient adsorbent over PHAC for fluoride elimination from aqueous solution. Graphical abstract Defluoridation of aqueous solution using biochar derived from Aegle marmelos shell and Parthenium hysterophorus.

Fluoride has both detrimental and beneficial effects on living beings depending on the concentration and consumption periods. The study presented in this article investigated the feasibility of using neem oil phenolic resin treated lignocellulosic bio-sorbents for fluoride removal from water through fixed bed column study. Results indicated that treated bio-sorbents could remove fluoride both from synthetic and groundwater with variable bed depth, flow rate, fluoride concentration and column diameter. Data obtained from this study indicated that columns with the thickest bed, lowest flow rate, and fluoride concentration showed best column performance. Bio-sorbents used in this study are regenerable and reusable for more than five cycles. The initial materials cost needed to remove one gram of fluoride also found to be lower than the available alternatives. This makes the process more promising candidate to be used for fluoride removal. In addition, the process is also technically advantageous over the available alternatives.

Low-cost water defluoridation technique is one of the most important issues throughout the world. In the present study, shale, a coal mine waste, is employed as novel and low-cost adsorbent to abate fluoride from simulated solution. Shale samples were collected from Mahabir colliery (MBS) and Sonepur Bazari colliery (SBS) of Raniganj coalfield in West Bengal, India, and used to remove fluoride. To increase the adsorption efficiency, shale samples were heat activated at a higher temperature and samples obtained at 550 °C are denoted as heat-activated Mahabir colliery shale (HAMBS550) and heat-activated Sonepur Bazari colliery shale (HASBS550), respectively. To prove the fluoride adsorption onto different shale samples and ascertain its mechanism, natural shale samples, heat-activated shale samples, and their fluoride-loaded forms were characterized using scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction study, and Fourier transform infrared spectroscopy. The effect of different parameters such as pH, adsorbent dose, size of particles, and initial concentration of fluoride was investigated during fluoride removal in a batch contactor. Lower pH shows better adsorption in batch study, but it is acidic in nature and not suitable for direct consumption. However, increase of pH of the solution from 3.2 to 6.8 and 7.2 during fluoride removal process with HAMBS550 and HASBS550, respectively, confirms the applicability of the treated water for domestic purposes. HAMBS550 and HASBS550 show maximum removal of 88.3 and 88.5 %, respectively, at initial fluoride concentration of 10 mg/L, pH 3, and adsorbent dose of 70 g/L.