Spatio-temporal variation of fluoride in groundwater and agricultural soil and crops of Unnao district, UP: Monitoring and assessment

Fluoride in Raw Rice (Oryza sativa): a Global Systematic Review and Probabilistic Health Risk Assessment

Rice (Oryza sativa) is one of the essential staple foods highly consumed globally, with nearly 40% to 45% of the global population estimated to consume rice. Therefore, consumable rice should have low levels of harmful elements. This study investigates fluoride (F¯) content in raw rice (uncooked rice) and evaluates Probabilistic Health Risk Assessment (PHRA) through Monte Carlo simulation (MCS) due to the consumption of F¯ enriched rice. The literature review reveals that limited studies have been conducted on the investigation of F¯ in raw rice. The fluoride (F¯) concentration in raw rice varies across the studied countries, indicating the need for additional studies to facilitate a more accurate comparison. The F¯ content in raw rice varied among the studied countries, making it difficult to definitively state that the concentration of F¯ in one country is higher. However, the concentration of F¯ in raw rice in India is notably elevated. This study also highlighted the importance of investigating the F¯ content in raw rice. The study will be highly helpful for policymakers to formulate guidelines for water used for irrigation.

Co-occurrence of arsenic and fluoride in groundwater of Guide basin in China: Genesis, mobility and enrichment mechanism

Endemic arsenic poisoning and fluorosis caused by primary high arsenic (As) and high fluoride (F-) groundwater have become one of the most serious environmental geological problems faced by the international society. High As and high F- groundwater exists in Neogene confined aquifers in Guide basin, with concentrations of 355 μg/L and 5.67 mg/L, respectively, and showing a co-occurrence phenomenon of As and F- in the groundwater. This poses a double threat to the health of tens of thousands of local residents. In this study, based on the systematic collection of groundwater and borehole sediment samples, analysis of hydrochemistry and isotope indexes, combined with laboratory tests, purpose of this study is to reveal the migration rule and co-enrichment mechanism of As and F- in aquifers, and finally establish a hydrogeochemical conceptual model of the enrichment process of As and F-. The main conclusions are as follows: hydrochemical type of unconfined and confined groundwater in Guide basin is Ca-Na-HCO3 and Na-Cl-HCO3 type, respectively. Main minerals in sediments are quartz and plagioclase. Concentrations of As and F- are lower in unconfined groundwater, but higher in confined groundwater, and which show a gradual increasing trend along the groundwater flow path. The mineralization of natural organic matter in confined aquifer causes iron and manganese oxide minerals containing As to dissolve gradually, which leads to the gradual release of As into groundwater. Large amount of HCO3- produced by mineralization of organic matter precipitate with Ca2+ in groundwater, resulting in reduction of Ca2+ content, promoting the dissolution of fluoride-containing minerals such as fluorite (CaF2), and continuously releasing F- into groundwater. Meanwhile, competitive adsorption reactions in confined aquifers causes more As and F- to be released from mineral surface into groundwater, which gradually migrate and accumulate along groundwater flow. Finally, it is established that a conceptual model for the formation of high As and F- groundwater in the confined aquifer of Guide basin. The research results not only help to improve our understanding of the formation and evolution of groundwater with high As and F- with similar geological background, but also provide scientific basis for rational development and utilization of groundwater, and prevention and control of chronic As and F- poisoning in local and similar areas.

Current progress on fluoride occurrence in the soil environment: Sources, transformation, regulations and remediation

Fluorine is a halogen element widely distributed in nature, but due to excessive emissions from industrial manufacturing and agricultural production, etc., the soil is over-enriched with fluoride and the normal growth of plants is under stress, and it also poses a great threat to human health. In this review, we summarized the sources of fluoride in soil, and then analyzed the potential mechanisms of fluoride uptake in soil-plant systems. In addition, the main influences of soil ecosystems on plant fluoride uptake were discussed, soil management options to mitigate fluoride accumulation in plants were also summarized. The bioremediation techniques were found to be a developmental direction to improve fluoride pollution. Finally, we proposed other research directions, including fluoride uptake mechanisms in soil-plant systems at the molecular expression levels, development of visualization techniques for fluoride transport in plants, interactions mechanisms between soil microhabitats and plant metabolism affecting fluoride uptake, as well as combining abiotic additives, nanotechnology and biotechnology to remediate fluoride contamination problems.

Changes in fatty acids in Brassica juncea L. oil grown under two simulated conditions of fluoride contamination

Rapeseed, the second-most-important vegetable oil source, is cultivated in various areas of India where both groundwater and soil are contaminated with fluoride (F-). Furthermore, the frequent use of F- contaminated groundwater for irrigation leads to accumulation of F- in surface and sub-surface soil. The study aims to compare the morphological and biochemical changes in Brassica juncea L., the variations in its fatty acids (FAs) composition and oil yield, under two regimes of F- contaminated soils: (i) pre-contaminated soil (Tr) and (ii) irrigation with F- contaminated water (Ir). The level of F- (µg g-1) in the plant tissues (root, leaf, and grain) was significantly higher in Ir_10 (18.3, 14.7, and 2.8, respectively) than in Tr_10 (4.3, 2.6, and 0.77, respectively), while the oil yield was significantly lower with Ir_10 (19.5%) than with Tr_10 (44.9%). The phytoremediation potential of F- by Brassica juncea L. is greater in Tr regime than in the Ir regime. The erucic acid content (%), which is detrimental to cardiac health, increased to 67.37% (Ir_10) and 58.3% (Tr_10) from 57.73% (control). Thus, the present study shows that irrigation with F- contaminated water results in greater toxicity and accumulation in plants and is not safe for human health.

Fluoride accumulation characteristics in a northern China apple orchard that has had long-term phosphate fertilization

Phosphate fertilizer can cause fluoride accumulation in the soil and excessive fluoride poses potential risks to soil and food crop safety. However, the effects of fertilization on soil and fruit fluoride accumulations through long-term positioning trials, especially in high-fertilizer application situations such as apple orchards, have received little attention. To close this knowledge gap, we conducted a field experiment to demonstrate the effects among five long-term (13-year) fertilizer treatments on fluoride accumulations at different soil depths and in the fruits of an apple orchard in Baishui, Shaanxi, China. The five treatments included no fertilization (CK); manure application (M); nitrogen and phosphate fertilization (NP); nitrogen, phosphorus, and potassium fertilization (NPK); and groundcover with nitrogen and phosphate fertilization (GNP). The results confirmed that all phosphate fertilizer treatments (NP, NPK, and GNP) had significant increases in total fluoride (TF) and water-soluble fluoride (WF) accumulations in the topsoil (0-20 cm). Among the phosphate fertilizer treatments, NP topsoil accumulated the most TF and WF, 79.4 and 7.7 mg kg^-1 more than CK, respectively, and an average annual TF increase of 6 mg kg^-1. However, the M treatment both experienced reduced fluoride content in the topsoil and had TF and WF contents 8.1 and 0.67 mg kg^-1 lower than CK, respectively. There was no significant difference between all fertilizer treatments and CK in apple fluoride content. Furthermore, TF and WF accumulated mainly in the topsoil and the differences in soil fluoride content among the treatments decreased with soil depth. These findings showed that long-term phosphate fertilization increases the risk of fluoride accumulation in orchard topsoil. Altogether, these results improve the understanding of the characterization of soil and fruit fluoride accumulations in apple orchards under long-term fertilizer conditions and provide new insights into the use of manure as a possible alternative fertilization strategy that reduces fluoride accumulation.

Environmental chemistry, toxicity and health risk assessment of groundwater: Environmental persistence and management strategies

Groundwater is a significant supply of freshwater for the world's population, being used for residence, agricultural, and industrial purposes. One-third of the world's population relies on groundwater for drinking applications. Groundwater pollution is a global issue with serious consequences for human health and the environment. It needs a thorough understanding because access to safe drinking water is a basic human right. However, groundwater quality is being threatened by urbanisation, agricultural activities, industrial activities, and climate change, among others. Pollutants like hydrocarbons, toxic metals, pesticides, microplastics, nanoparticles and other emerging contaminants mean a risk to human health and sustainable socioeconomic development. To ensure sustained groundwater usage to assess, monitor, and regulate groundwater quality issues is essential. Excess withdrawal alters groundwater flow together with contaminants like uranium, radon, radium, salinity, arsenic and fluoride, resulting in mediocre water quality. Consequently, chemical and biological contaminants owing to domestic, industrial, and agricultural practices alter water quality and threaten human health. Controlling and management of groundwater pollution and related health risks require developing vulnerability, hazard, and risk maps.