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In the present investigation, perennial grass ( Saccharum ravannae L.) based activated biochar was synthesized for possible application in both arsenic (As) and fluoride (F − ) removal from aquous solution using optimization technique response surface methodology (RSM) based on central composite design (CCD). Influence of initial concentration, adsorbent dose and contact time on removal efficiency of As and F − adsorption was investigated. Activated biochar was characterized by proximate and ultimate analysis, FTIR, XRD, Raman, SEM-EDX, BET, pH and electrical conductivity. Isotherm and kinetics models were also investigated. Results obtained from CCD showed that the best local maximum for As removal was at initial ion concentration 100 mg L −1 , adsorbent dosage 0.2 g 50 mL −1 and contact time 60 min with removal percentage of 72.1 for As and for F − the removal percentage was 24.3 at initial ion concentration of 25 mg L −1 , adsorbent dosage of 0.2 g 50 mL −1 and contact time 60 min. [ABSTRACT FROM AUTHOR]

Considerable lacunae exists in As and F − co-contamination investigation in the Brahmaputra and Gangetic floodplains. Therefore we selected Diphu a township in the Karbi Plateau rising from the Brahmaputra floodplains for evaluation of As and F co-occurrence, correlation with coexisting ions of the aquifer system and elucidation of potential processes for releasing As and F − in the groundwater. Our initial appraisal used generic plots for identification of hydro geochemical processes and major water types. Subsequently, As and F − co-occurrence with pH, depth, HCO 3 − , SO 4 2− , Ca 2+ and Fe were probed for possible correlation followed by hierarchical cluster analyses to identify key processes for co-occurrence. Finally, saturation indices of groundwater minerals were calculated using MINTEQA2 to elucidate prospective As and F − release into groundwater. Results indicate F − and As presence in Ca–HCO 3 rich water along with positive correlation between Ca 2+ and F − possibly due to limestone reserves in adjoining areas. Multivariate analyses suggest the presence of high concentrations of PO 4 3− , and H 4 SiO 4 either individually or in combination can enhance the mobility of both As and F − and possibly abet conditions conducive for co-contamination of aquifers. Initial release of As and F − from the parent rock seems driven by the anthropogenic activities while mobilization depends on chemical interactions and individual affinities of the elements. The results of speciation highlight further mobilization of As and F − into the groundwater which in turn require regular attention for sustainable management of scarce water resource present in the area. [ABSTRACT FROM AUTHOR]

• Arsenic is removed with bilayered oleic acid functionalized iron oxide nanoparticles. • Maximum monolayer sorption capacity (q max) was 32.8 μg g−1 for As(V) in 120 min. • As(V) adsorption was heterogeneous and pseudo second order model fitted the data. • Antagonism of common anions follows the order: Cl– < SO 4 2– < NO 3 – < F– < PO 4 3–. • Adsorbent exhibited good As(V) removal performance from the cocktail mixture. Groundwater, one of the significant potable water resources of the geological epoch is certainly contaminated with class I human carcinogenic metalloid of pnictogen family which delimiting its usability for human consumption. Hence, this study concerns with the elimination of arsenate (As(V)) from groundwater using bilayer–oleic coated iron–oxide nanoparticles (bilayer–OA@FeO NPs). The functionalized (with high–affinity carboxyl groups) adsorbent was characterized using the state–of–the–art techniques in order to understand the structural arrangement. The major emphasis was to examine the effects of pH (5.0–13), contact times (0–120 min), initial concentrations (10–150 μg L–1), adsorbent dosages (0.1–3 g L–1), and co–existing anions in order to understand the optimal experimental conditions for the effective removal process. The adsorbent had better adsorption efficiency (∼ 32.8 μg g–1, after 2 h) for As(V) at neutral pH. Adsorption process mainly followed pseudo–second–order kinetics and Freundlich isotherm models (R2∼0.90) and was facilitated by coulombic, charge–dipole and surface complexation interactions. The regeneration (upto five cycles with 0.1 M NaOH) and competition studies (with binary and cocktail mixture of co–anions) supported the potential field application of the proposed adsorbent. [ABSTRACT FROM AUTHOR]

Arsenic (As) and fluoride (F−) are the two most conspicuous contaminants, in terms of distribution and menace, in aquifers around the world. While the majority of studies focus on the individual accounts of their hydro-geochemistry, the current work is an effort to bring together the past and contemporary works on As and F− co-occurrence. Co-occurrence in the context of As and F− is a broad umbrella term and necessarily does not imply a positive correlation between the two contaminants. In arid oxidized aquifers, healthy relationships between As and F− is reported owing desorption based release from the positively charged (hydr)oxides of metals like iron (Fe) under alkaline pH. In many instances, multiple pathways of release led to little or no correlation between the two, yet there were high concentrations of both at the same time. The key influencer of the strength of the co-occurrence is seasonality, environment, and climatic conditions. Besides, the existing primary ion and dissolved organic matter also affect the release and enrichment of As–F- in the aquifer system. Anthropogenic forcing in the form of mining, irrigation return flow, extraction, recharge, and agrochemicals remains the most significant contributing factor in the co-occurrence. The epidemiological indicate that the interface of these two interacting elements concerning public health is considerably complicated and can be affected by some uncertain factors. The existing explanations of interactions between As–F are indecisive, especially their antagonistic interactions that need further investigation. "Multi-contamination perspectives of groundwater" is an essential consideration for the overarching question of freshwater sustainability. Image 109 • First review on co-occurrence perspectives of Arsenic and Fluoride in the groundwater. • As and F co-occurrences is quite common yet concealed owing to one being dominant. • Arid areas are more suitable for co-occurrence with few reports in the Alluvium plains. • Local hydro-geochemical processes and seasonality greatly affect co-contamination. • Co-contamination can have severe health and socio-economic impacts around the World. [ABSTRACT FROM AUTHOR]

Abstract The study attempts to understand arsenic (As) mobilization in a shallow aquifer with depth variation while focusing on the potential co-occurrence of As with priority metals (zinc and lead), using a pilot scale multilevel groundwater monitoring system (MGWS). Groundwater samples (n = 72) were collected bi-weekly (every 15 days) from the multilevel sampler (4.6, 9.2 and 13.8 m depths), installed at Tezpur, Sonitpur district of Brahmaputra floodplain (BFP), Assam, India, for a period of 1 year (August 2013–July 2014). Both geogenic and anthropogenic influences were found to affect the studied unconfined aquifer. At 4.6 m, weathering dominated due to interaction with CO 2 and infiltrating water. Prevalent high pH (7.9–8.6) at all three depths in association with strong oxidizing condition (at 4.6 m) during the drier months seem to play a crucial role in desorption based As release. Multivariate analyses revealed that redox potential (ORP) remains the primary controller of As release at all three depths. With depth, stronger anoxic conditions resulted in the dominance of reductive hydrolysis leading to a co-occurrence scenario of As (max 4.6 μgL−1) with Zn (max 2514 μgL−1) and Pb (max 740 μL−1) with influences of anthropogenic modes of activities like agriculture and dry deposition from a brick kiln. Multi-element enrichment is an emerging concern but the bigger picture would be to understand the peculiarities of individual aquifers, as a generalization can lead to missing a ton of information. In this regard, long-term multilevel monitoring can help in the predictive understanding of the vertical stratification and co-occurrences of multi-metals that can subsequently be applied for water production at the safer depths. Graphical abstract Image 1 Highlights • Multilevel groundwater monitoring in the Indian alluvium plain for arsenic mobilization. • ORP emerged as the single most important governing feature of arsenic release with depth. • Secondary anthropogenic forcing supplements reductive hydrolysis of Fe/Mn(hydr)oxides. • Supersaturated states of hydrozincite attributed to the elevated levels of Zn at all depths. • Co-occurrence of Zn, Pb, Mn and As aggravate the health and environmental implication. [ABSTRACT FROM AUTHOR]

The widespread presence of arsenic (As) and fluoride (F−) in groundwater poses substantial risks to human health on a global scale. These elements have been identified as the most prevalent geogenic contaminants in groundwater in northern Mexico. Consequently, this study aimed to evaluate the human health and ecological risks associated with the content of As and F− in the Meoqui-Delicias aquifer, which is in one of Mexico's most emblematic irrigation districts. Concentrations of As and F− were measured in 38 groundwater samples using ICP-MS and ion chromatography, respectively. Overall, these elements showed a similar trend across the aquifer, revealing a positive correlation between them and pH. The concentration of As and F− in the groundwater ranged from 5.3 μg/L to 303 μg/L and from 0.5 mg/L to 8.8 mg/L, respectively. Additionally, the levels of As and F− surpassed the established national standards for safe drinking water in 92% and 97% of samples, respectively. Given that groundwater is used for both agricultural purposes and human activities, this study also assessed the associated human health and ecological risks posed by these elements using Monte Carlo simulation and Species Sensitivity Distribution. The findings disclosed a significant noncarcinogenic health risk associated with exposure to As and F−, as well as an unacceptable carcinogenic health risk to As through water consumption for both adults and children. Furthermore, a high ecological risk to aquatic species was identified for F− and high to medium risks for As in the sampling sites. Therefore, the findings in this study provide valuable information for Mexican authorities and international organizations (e.g., WHO) about the adverse effects that any exposure without treatment to groundwater from this region represents for human health. [Display omitted] • As and F− in groundwater exceeded Mexican drinking standards in 92% and 97% of cases, respectively. • Probabilistic model suggests an 82% chance for adults, 95% for children to exceed safe As levels. • A high ecological risk to aquatic species was identified for F- and high to medium risks for As. • Excessive As and F- in drinking water linked to cancer, cognitive issues, posing widespread health risks. [ABSTRACT FROM AUTHOR]

A sequential extraction procedure (SEP), batch desorption experiments and the concept of partition coefficient were applied on seven sediment samples from the Subansiri-Dikrong-Ranganadi River System (SDRS), a subset of the upper Brahmaputra floodplain (BFP), to understand leaching of arsenic (As) and fluoride (F−). Sediment samples were collected during monsoon and post-monsoon seasons from each of three river banks to distinguish the effect of annual cyclic flooding events on As content and mobilization. SEP revealed that the readily leachable chemisorbed As phase and amorphous Fe (hydr)oxides were the principal contributors to mobilized As during the monsoon season. Constant flushing of the rivers removed most of the physisorbed and chemisorbed As during the monsoon. A submerged anoxic condition toward late monsoon resulted in Fe (hydr)oxides becoming the dominant source of removable As during the post-monsoon season. Iron in the sediments was positively correlated with F− during both monsoon and post-monsoon seasons. This suggests that Fe (hydr)oxides are a host for F− and a correlation between reductive hydrolysis and F−. Removal of Fe (hydr)oxides from the sediments significantly reduced As retention/leaching capacity. Arsenic desorption was especially high from raw sediments of the Ranganadi River owing to the fact that it had the highest amount of As associated with Fe (hydr)oxides, which falls sharply in the post-monsoon season due to a prolonged submerged state leading to reductive dissolution. However, as leached F− is being constantly flushed out by the SDRS, F− contamination may not pose a problem in the current or futuristic scenarios. Unlabelled Image • Subansiri-Dikrong-Ranganadi River System (SDRS) sediments were studied for As, F mobilization. • Sequential extraction, desorption and partitioning coefficient were coupled to study As-F sorption. • Fe (hydr)oxides, a potential secondary host of F−, lead to its co-leaching with As. • Leached F is being flushed regularly and thus not leading to its enrichment. [ABSTRACT FROM AUTHOR]

The present work focuses on understanding the provenance, prevalence and health perspective of As and F − along with possible co-occurrence of uranium (U) in the aquifers of the Brahmaputra floodplains (BFP), India. Groundwater ( n = 164) and sediment samples ( n = 5) were obtained from the upper, middle and lower BFP. Energy dispersive spectroscopy (EDX) revealed the presence of As, U and Fe in the sediment matrix. Regression analysis showed a weaker relationship between As and F − co-occurrence. Hierarchical cluster analysis (HCA) and principal component analysis (PCA) suggested reductive dissolution of Fe (hydr)oxides responsible for As release in the BFP, especially in the upper and lower BFP. Bicarbonate appeared to compete with As oxyanions for adsorption on positively charged surfaces leading to As release. Arsenic desorption in presence of PO 4 3− , F − and HCO 3 − at elevated pH appeared greatest in the upper BFP, suggesting the highest potential for co-occurrence. Co-occurrence, were mainly in isolated aquifers of the upper BFP owing to desorption of adsorbed As and F − from Fe (hydr)oxides at higher pH. Weathering and dissolution of clay minerals in the upper BFP, and competitive desorption in presence of HCO 3 − and PO 4 3− in the middle and lower BFP, respectively, explain variabilities in F − release. Amorphous Fe (hydr)oxides like ferrihydrite act as sinks of U. Concentrations of As and F − will likely increase in the future as projected from the saturated levels of goethite and ferrihydrite. Hazard indices (HI) revealed that children (3–8 years) were at greater health risk than adults. [ABSTRACT FROM AUTHOR]

In the recent times, multi-metal co-contamination in the groundwater of various parts of the globe has emerged as a challenging environmental health problems. While arsenic (As) has been reported with high fluoride and at times with uranium; and Cr & Pb are also found in aquifers under high anthropogenic impacts. The present work probably for the first time traces the As–Cr–Pb co-contamination in the pristine aquifers of a hilly terrain that are under relatively less stress from the anthropogenic activities. Based on the analyses of twenty-two (n = 22) groundwater (GW) samples and six (n = 6) sediment samples, it was found that Cr being leached from the natural sources as evident from 100% of samples with dissolve Cr exceeding the prescribed drinking water limit. Generic plots suggests rock-water interaction as the major hydrogeological processes with mixed Ca2+-Na+-HCO 3 - type water. Wide range of pH suggests localized human interferences, as well as indicative of both calcite and silicate weathering processes. In general water samples were found high only with Cr and Fe, however all sediment samples were found to contain As–Cr–Pb. This implies that the groundwater is under-risk of co-contamination of highly toxic trio of As–Cr–Pb. Multivariate analyses indicate that the changing pH as the causative factor for Cr leaching into the groundwater. This is a new finding for a pristine hilly aquifers, and we suspect such condition may also be present in other parts of globe, and thus precautionary investigations are needed to prevent this catastrophic situation to arise, and to alert the community in advance. [Display omitted] • We trace the As–Cr–Pb co-contamination in the pristine aquifers of a hilly terrain. • Wide range of pH suggests localized human interferences, calcite and silicate weathering. • Groundwater had high Cr and Fe, however all sediment samples contained As–Cr–Pb. • Groundwater is under-risk of co-contamination of highly toxic trio of As–Cr–Pb. • Precautionary investigations are needed to prevent this catastrophic situation to arise. [ABSTRACT FROM AUTHOR]

The upper Brahmaputra floodplain (UBF) is highly enriched with geogenic contaminants, mostly the Arsenic (As), owing to its sensitive geomorphology, aquifer groundwater (GW) dynamics, huge sediment deposition along with natural and anthropogenic disturbance significantly accelerate the As leaching rate into the groundwater, leading to an increase the health risk. Concerning the above active processes in the Lakhimpur district of UBF, current work aims to investigate seasonal dynamics of As contamination and associated health hazard for local community. To carry out this study, 51 GW samples analyzed which reveal the seasonal variation in As concentrations with the minimum average concentration in the monsoon season (4.7 μg.L−1) and the maximum in the post-monsoon season (18.5 μg.L−1) with 50% of the samples exceeding permissible limits. The differences in the local geological conditions and the GW flow may contribute to the spatial variations in mean As concentration in the study area. Also, the active GW recharge process identified in post-monsoon season accelerates the As leaching in the area's aquifers. Further, results indicate higher As levels associated with a pH range of 6–7 favours As desorption from minerals under reducing conditions. The hazard index indicates that the children population has high carcinogenic risk compared to adult populations. Furthermore, the study highlights the social risk potential arising from public health crises due to As exposure. Overall, results indicate high As concentrations in region with moderate seasonal variability and demand a dire attention for long-term monitoring to provide sustainable water resources to safeguard the people at risk. [Display omitted] • Effect of upstream/downstream was investigated on As contamination in the groundwater. • Four-fold increase in mean arsenic(As) concentration was reported in post-monsoon season. • Active groundwater (GW) recharge process was identified in the post-monsoon season. • Mainly rock-water interaction mechanism triggers the elevation of As concentration in GW. • Children's population was more vulnerable to carcinogenic risk compared to adults. [ABSTRACT FROM AUTHOR]

Dissolved arsenic typically results from chemical weathering of arsenic rich sediments and is most often found in oxidized forms in surface water. The mobility of arsenic is controlled by its valence state and also by its association with iron oxides minerals, the forms of which are both influenced by abiotic and biotic processes in aqueous environment. In this study, speciation methods were used to measure and confirm the presence of reduced arsenic species in the surface water of Frenchman creek, a gaining stream that crosses the Colorado-Nebraska border. Selective extraction analysis of aquifer and stream bed sediments shows that the bulk of the arsenic occurs with labile iron-rich oxy(hydroxide) minerals. Total dissolved arsenic in surface and groundwater ranged from ~3–18 µg L−1, and reduced arsenic species comprise about 41% of the total dissolved arsenic (16.0 µg L−1) in Frenchman creek. Leachable arsenic in the aquifer sediment samples ranged up to 1553 µg kg−1, while samples from Frenchman creek bed sediments contained 4218 µg kg−1. Dynamic surface and groundwater interaction sustains arsenite in iron-rich surface headwaters, and the implied toxicity of reduced arsenic in this hydrogeological setting, which can be important in surface water environments around the globe. [Display omitted] • The occurrence of persistent and mobile As(III) in a gaining stream is investigated. • Co-occurrence of reduced iron-(oxyhydr)oxides implicates reduced zones along the creek. • Groundwater, surface water interaction sustains reduced arsenic in the headwater. • Reduced toxic arsenic forms are stabilized and enriched in streambed sediments. • Arsenic from groundwater can be possible source of arsenic in surface water. [ABSTRACT FROM AUTHOR]