Generally, abstracted groundwater is aerated, leading to iron (Fe²⁺) oxidation to Fe³⁺ and precipitation as Fe³⁺-(hydr)oxide (HFO) flocs. This passive groundwater treatment practice is not considered a barrier for arsenic (As) because of its widely varying removal efficiencies (15-95%), depending on Fe/As ratio. Arsenic is typically present as arsenite [As(III)] species in anaerobic groundwater, used for drinking water. However, the oxidized arsenate [As(V)] species is preferably removed, because of the negative charge and therefore, rapid oxidation of As(III) is desired. Oxidation of As(III) can be achieved by dosing chemical oxidants, but recent studies have also demonstrated the potential of biological As(III) oxidation in conventional rapid sand filtration (RSF), combined with aeration. The presented study aimed to study biotic As(III) oxidation and removal in pilot-scale biological RSF columns using local materials as a low-cost, chemical-free and robust method for As safe water availability. This study also studied the interaction of As with Fe, phosphate, and ammonium in a contaminated region of Rajshahi, Bangladesh. The results depicted that 230 µg/L (99%) As(III) oxidized to As(V) in the RSF; however, removal was limited to 210 µg/L, probably due to the inefficient use of native-Fe for adsorption. This limiting factor resulted from rapid Fe²⁺ oxidation and precipitation of HFO flocs before As(III) oxidation. Further optimization is therefore required to avoid complete Fe²⁺ oxidation-precipitation before As(III) oxidation to achieve total As removal, reaching the WHO guideline value of 10 µg/L. Therefore, with the optimized operation, the biological RSF system could be used as an economical, user-friendly, and chemical-free solution for As safe drinking water supply.

Ecological integrity and human well-being are the major concerns of rapidly growing communities. The vital components like water and soil are under increasing threat of degradation due to rapid industrialization and urbanization. It brings the necessity to examine the quality status of these entities for sustainability, especially in the pollution hotspots. One of such hotspots of Ambur in Vellore District, TN is chosen for the study. Thuthipattu village, a rural area in Ambur, the interest of our study where number of tanneries, chromate factories, and pharmaceuticals are thronging in 2.24 km² area. Earlier studies indicated severe water contamination in the study area though no other environmental parameters (soil, vegetable, crops) have been investigated to identify the extent of the contamination and their inter-relationships. This study examined the land use patterns for the past two decades and shown the industrial evolution occurred in the study area. Demarcation was done on the basis of contamination criticality by Remote sensing tools. Further, 22 water, 30 soil, 16 vegetable samples from the village were collected covering each of the demarcated areas. Water samples are analyzed for physicochemical parameters and heavy metals. Six different WQI is applied and compared to find the potability of the water. After digestion, heavy metal analysis in the soil and vegetable samples were done to assess the distribution, sources, and ecological risks. Further indices like I_geo, EF, BF, CF, and PI are evaluated to determine the bioavailable pollutants in the environment. Result shows significant heavy metal contamination in water and soil samples especially chromium and zinc which are close to the industries. Though the supply water is suitable for drinking but other sources are much polluted. Also crops grown in the study area are found to be polluted. Suggesting detailed investigation in the study area frequently for quality check.

The Ganges Delta is a key area where elemental contamination of groundwater constitutes a human catastrophe. The delta plain geomorphology comprises a large number of abandoned meander bends or oxbow lakes (Donselaar et al., 2017; Ghosh et al., 2021) characterized by an anoxic environment in the lower part of the lake water column (hypolimnion). Here we present the critical role of these abandoned-river channels forming oxbow lakes. The geomorphological the juxtaposition of (a) abandoned channels (or: oxbow lakes) where the cocktail of organic matter and sediment leads to the release of various elements, (b) the topographically higher point bars where the released elements accumulate in the aquifer and provide a blueprint to explain the origin and localization of elemental toxicity. Dissolved organic matter (DOM) is implicated in the mobilization of elements via microbial metabolic processes. Organic matter (OM) is preserved in this environment and provides a perfect environment for microbial oxidation and mobilization of Fe-oxides. Additional deposition of human-introduced sewage wastes adds to a rich source of nutrients to the indigenous microbial communities.
A multidisciplinary approach was effective in understanding the geomorphology of river meanders, forming abandoned channels, which act as a growth bed for biomass. While acting as an incubator for primary production (lake vegetation dynamics), and subsequent organic debris accumulation (anoxic, hypolimnion water column), where selective preferential preservation of organic carbon compound (anoxic sediment base) occur. We have described how organic compound infiltration, deposition and abundance depends on their hydrophobicity, molecular weights and bioavailability and further, due to diagenetic alteration (microbial metabolic oxidation). Different classes of surface derived organic carbon from vegetation with anthropogenic inputs, can have different effects on the mineral weathering and in controlling the downstream cationic fluxes such as Fe, Mn, As, F etc. and contamination of aquifers in various river plains across the world.

Rapid urbanization and industrialization leading to an increase in groundwater contamination is a serious environmental concern in India in recent years. The risk of groundwater contamination is highly pronounced in and around the Ranipet industrial area causing a threat to human health and a balanced ecosystem. In this study, 40 groundwater samples were collected in and around the industrial area of Ranipet which is largely producing Chromium and Chromium-based chemicals. The heavy metal contamination and water quality index (WQI) were evaluated to determine groundwater quality and related human health risk assessment using the model proposed by USEPA for adults. The result indicates that the groundwater in the study area was alkaline with a mean value of 7.22 due to the presence of high carbonates and bicarbonates in the samples. WQI ranges from 42.7 – 117.97 in which only 10% of groundwater samples were good for consumption while 35% to 50% falls under moderate to poor category and 5 % is unsuitable for drinking purpose. The content of heavy metal in the groundwater is found to be below the USEPA and WHO standards except for Chromium which exceeded the acceptable limit i.e., 0.05 mg/L. The human health risk assessment indicates that the chronic daily intake of groundwater for the adult in the study area is in the order of Cr>Fe>Pb>Cd indicating chromic toxicity. It was also observed the carcinogenic risk is higher than the acceptable limit (1×10^-6) as a result of higher Chromium intake via ingestion. The outcome of the present study will support the stakeholders in decision-making towards regional sustainable groundwater management. Keyword: Groundwater, Water quality index, Heavy metal, Carcinogenic risk.

Heavy metals attained global focus for their extreme toxicity, persistence in aquatic environments and their bio-accumulation into plants and living organisms along with their adverse health effects. Present study area, Puliyanthangal Lake lies in Ranipet municipality surrounded by tanneries, ceramics, pigments and paints, pharmaceuticals, refractories and chromate chemicals receives industrial effluents and domestic wastes from surrounding areas. Hence to identify the bioavailability and mobility of metals in Lake bed sediments and soil from surrounding area, Sequential Extraction Procedure (SEP) was performed by modified BCR (Community Bureau of Reference) method. Concentrations of Al, Cd, Cr, Cu, Fe, Mn, Pb and Zn in and around the Puliyanthangal Lake were determined. Also, to perceive the contamination trend, size fractions of soil/sediments were performed in four sizes i.e., 300µ, 150µ, 50µ and 22µ and Sequential Extraction Procedure is applied to each fraction. Results indicated metals in the bio-available fractions are high when compared to residual fractions indicating contamination. Also, metal concentration increased with reduction in soil fraction size. Al, and Fe show strong correlations with TOC (Total Organic Carbon) indicate their distribution under influence of TOC.

The widespread geogenic occurrence of arsenic (As) in shallow depth groundwater wells is a severe drinking water quality problem worldwide, and about 200 million people are exposed to As-contaminated drinking water sources. This problem is too extreme in South-East Asia, especially in Bangladesh and West Bengal, India, where millions of shallow wells have been installed for water supply. Therefore, it is essential to provide As-safe water through awareness building, screening, and providing safe sources or treatment. In 2000, with the help of the World Bank, Unicef, and Department of Public Health Engineering (DPHE), Bangladesh, an extensive campaign conducted to screen >10 million tubewells and marked as red and green to identified As-contaminated and safe wells. Recent studies also mentioned that tubewell platform color could be considered a user-friendly, cost- and chemical-free alternative for As and Mn screening tools compared to available field As-test kits. Furthermore, In As-contaminated areas, where As-safe water is not accessible using shallow (<70 m) wells or surface water, the alternative solutions could be the use of Intermediate Deep Aquifer (IDA: 70-150 m) and Deep Aquifer (>150 m) wells that commonly contains a low level of As and Mn or treating contaminated water before supply. Within practiced treatment methods, such as Pond sand filter, Rainwater harvesting, Arsenic removal filter, and Bishudhya filter, As co-removal with groundwater native-iron could be the preferable option without using additional adsorbents or chemicals. A recent pilot-scale study demonstrated that the combination of anoxic storage followed by aeration and rapid sand filter could be used as a cost-effective, chemical-free, and local resources-based alternative for As-safe drinking water accessibility. Therefore, it is evident that the mitigation measures need to be developed based on local resources, perceptions, and local conditions.