Potential arsenic-chromium-lead Co-contamination in the hilly terrain of Arunachal Pradesh, north-eastern India: Genesis and health perspective

Land use alters the alignment of Arsenic and Chromium co-contamination in the unconsolidated aquifer under reducing environments of the Mid-Gangetic Plains

The Indo-Gangetic Plain, well known for its alluvial landscape and dense human settlement, is facing rapid industrialization and urbanization, leading to high stress on its aquifers. Arsenic and chromium co-occurrence in shallow aquifers is a growing global concern, influenced by redox conditions, geochemistry, and human activities. We aim to address the influence of the suburban and urban land use on the co-contamination of As and Cr, using various geostatistical tools, models, and indices. Among twenty-six (n = 26) groundwater samples, the majority of water types were found to be Mg2+-HCO3- and Na+-K+ exhibiting carbonate weathering and evaporation enrichments, with saturation indices exhibiting the supersaturation of calcite and dolomite. Probability exceedance implied inverse correlation between contaminant concentrations and the probability of their likelihood of regulatory thresholds. Factor analysis indicates that the natural alignment of contaminants, particularly As and Cr, is maintained under suburban land use but significantly altered in urban settings. No specific trend of As was observed in suburban areas, but in urban settings, it showed a positive correlation with Total organic carbon (TOC) and Sulphate (SO₄2-), indicating anthropogenic influences like subsurface leaching and also justify the results of factor analysis. An integrated cluster heatmap has identified a trifecta of As, Cr, and lead (Pb), closely linked to pH, DO, and K+, highlighting the effects of increased anthropogenic activities in alluvial floodplains. Finally, a conceptual model was developed to clarify the common processes in these environments, facilitating the creation of universal management strategies for aquifers impacted by As and Cr co-contamination.

Mixture effects of arsenic and chromium on erythrocytic nuclear abnormalities and expression of DNA repair, tumor suppressor and apoptotic genes in liver of zebrafish

The present study investigated the individual and mixture effects of Arsenic (As) and Chromium (Cr) at their environmental concentrations in zebrafish (Danio rerio). After 15, 30 and 60 days of exposure, increased frequencies of erythrocytic nuclear abnormalities (ENAs) were noticed. After 60 days of exposure, DNA damage was observed in liver and base excision DNA repair (BER) and mismatch DNA repair (MMR) pathways were studied to know the cellular responses. Altered expression of BER (ogg1, apex1, creb1, polb) and MMR (mlh1, msh2, msh6) genes indicated inhibition of DNA repair. Downregulation of tumor suppressor genes (p53 and brca2) occurred in mixture group. Downregulation of bax, caspase9 and decreased bax/bcl2 ratio indicated prevention of intrinsic apoptotic pathway in treated groups. Results indicated As and Cr-induced predisposition to genomic instability and carcinogenesis in zebrafish. Overall, this study confirmed the additive genotoxic effects of As and Cr in zebrafish erythrocytes and in liver after chronic exposure.

Arsenic and Chromium Induced Toxicity on Zebrafish Kidney: Mixture Effects on Oxidative Stress and Involvement of Nrf2-Keap1-ARE, DNA Repair, and Intrinsic Apoptotic Pathways

In polluted water, cooccurrences of two carcinogens, arsenic (As) and chromium (Cr), are extensively reported. Individual effects of these heavy metals have been reported in kidney of fishes, but underlying molecular mechanisms are not well established. There is no report on combined exposure of As and Cr in kidney. Thus, the present study investigated and compared individual and combined effects of As and Cr on zebrafish (Danio rerio) kidney treating at their environmentally relevant concentrations for 15, 30, and 60 days. Increased ROS levels, lipid peroxidation, GSH level, and decreased catalase activity implied oxidative stress in treated zebrafish kidney. Damage in histoarchitecture in treated groups was also noticed. The current study involved gene expression study of Nrf2, an important transcription factor of cellular stress responses along with its negative regulator Keap1 and downstream antioxidant genes nqo1 and ho1. Results indicated activation of Nrf2-Keap1 pathway after combined exposure. Expression pattern of ogg1, apex1, polb, and creb1 revealed the inhibition of base excision repair pathway in treatments. mRNA expression of tumor suppressor genes p53 and brca2 was also altered. Expressional alteration in bax, bcl2, caspase9, and caspase 3 indicated apoptosis (intrinsic pathway) induction, which was maximum in combined group. Inhibition of DNA repair and induction of apoptosis indicated that the activated antioxidant system was not enough to overcome the damage caused by As and Cr. Overall, this study revealed additive effects of As and Cr in zebrafish kidney after chronic exposure focusing cellular antioxidant and DNA damage responses.

Investigating the efficiency of fixed bed column containing Fe3O4-ZIF8@eggshell membrane matrix in concurrent adsorption of arsenic and nitrate from water

In the current work, the behavior of a fixed bed column (FBC) containing an innovative nanocomposite, Fe3O4-ZIF8@eggshell membrane matrix (F-ZIF8@EMM), was investigated in the concurrent elimination of arsenic and nitrate, as two potentially harmful elements (PHEs) in drinking water. Flow rate (6-10 mL/min), column height (10-20 cm), reaction time (30-180 min), pH (5-10), primary content of arsenic (25-100 µg/L), primary content of nitrate (100-200 mg/L), and nanocomposite dose (0.25-1 mg/L) were examined as different operational effects on the simultaneous uptake of arsenic and nitrate from actual water via the as-fabricated novel nanocomposite through various experiments. Characteristics of F-ZIF8@EMM were analyzed via X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), and Brunauer-Emmett-Teller (BET) analyses. The consequences illustrated that the optimal parameters were: flow rate (6 mL/min), primary content of arsenic (100 µg/L), primary content of nitrate (150 mg/L), bed height (20 cm), and pH (7). The simultaneous elimination efficiency of nitrate and arsenic was 90 % under optimal conditions. The FBC fed with water containing arsenic and high nitrate could operate for 440 min with a qm of 226 mg/g. After fitting, different models were identified, with the concurrent uptake of nitrate and arsenic was the optimum fit with the Thomas model (R2 = 0.9998). Analysis of the cost of the process displayed that it should be estimated to be approximately 0.005$ per liter of safe drinking water. This study demonstrates the stability and high efficiency of the newly structured adsorbent after 10 consecutive adsorption cycles. It also validates the significant capacity of the as-made composite F-ZIF8@EMM in the concurrent uptake of nitrate and arsenic. Consequently, the application of FBC technology has shown promise in enhancing this process.

Growth-dependent cr(VI) reduction by Alteromonas sp. ORB2 under haloalkaline conditions: toxicity, removal mechanism and effect of heavy metals

Bacterial reduction of hexavalent chromium (VI) to chromium (III) is a sustainable bioremediation approach. However, the Cr(VI) containing wastewaters are often characterized with complex conditions such as high salt, alkaline pH and heavy metals which severely impact the growth and Cr(VI) reduction potential of microorganisms. This study investigated Cr(VI) reduction under complex haloalkaline conditions by an Alteromonas sp. ORB2 isolated from aerobic granular sludge cultivated from the seawater-microbiome. Optimum growth of Alteromonas sp. ORB2 was observed under haloalkaline conditions at 3.5-9.5% NaCl and pH 7-11. The bacterial growth in normal culture conditions (3.5% NaCl; pH 7.6) was not inhibited by 100 mg/l Cr(VI)/ As(V)/ Pb(II), 50 mg/l Cu(II) or 5 mg/l Cd(II). Near complete reduction of 100 mg/l Cr(VI) was achieved within 24 h at 3.5-7.5% NaCl and pH 8-11. Cr(VI) reduction by Alteromonas sp. ORB2 was not inhibited by 100 mg/L As(V), 100 mg/L Pb(II), 50 mg/L Cu(II) or 5 mg/L Cd(II). The bacterial cells grew in the medium with 100 mg/l Cr(VI) contained lower esterase activity and higher reactive oxygen species levels indicating toxicity and oxidative stress. In-spite of toxicity, the cells grew and reduced 100 mg/l Cr(VI) completely within 24 h. Cr(VI) removal from the medium was driven by bacterial reduction to Cr(III) which remained in the complex medium. Cr(VI) reduction was strongly linked to aerobic growth of Alteromonas sp. The Cr(VI) reductase activity of cytosolic protein fraction was pronounced by supplementing with NADPH in vitro assays. This study demonstrated a growth-dependent aerobic Cr(VI) reduction by Alteromonas sp. ORB2 under complex haloalkaline conditions akin to wastewaters.

Characterization of trace and heavy metal concentration in groundwater: A case study from a tropical river basin of southern India

This study investigates the hydrogeochemistry of groundwater samples collected from the Shiriya River Basin (SRB), a tropical watershed located in Kasaragod, Kerala, southern India, with a special focus on trace elements. Fifty-four groundwater samples were collected from deep aquifers, which constitute weathered and fractured granitoids and mafic rocks, and the groundwater is tapped by bore wells from a fractured zone at a depth range of 60-100 m. Concentrations of Sr, Li, Ba, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Cd, Ag, Au, Te, Pb, Re, and PGEs in groundwater were determined by using Q-ICPMS. Out of the 25 analysed trace elements in groundwater, only Sr (489.6 μg/L), Ba (226 μg/L), Li (11.76 μg/L) Mn (396.8 μg/L), Ni (68 μg/L) and Fe (2438.5 μg/L) show anomalous values. The PGEs and the majority of trace elements show values within the permissible limit. Raman spectral studies reveal the presence of celsian in aquifer rocks and are the source of Ba in groundwater. Further, XRF data of the rocks show a high enrichment of Fe and Mn in mafic dyke, basalt, and syenite, and Ba and Sr in granite, pegmatite, and granitic gneiss. Therefore, this study proved that the source of these elements is geogenic, i.e., they are released from the crystalline aquifer through rock-water interaction under alkaline conditions. The results of this study show that the groundwater of the basin has enough metals such as Na, K, Mg, Ca, Mn, Fe, Co, Cu, and Zn, which are good for health. Nevertheless, a few metals (Fe, Mn, Ba, Sr, Li, Ni) that may exert toxic effects on humans are also present in the groundwater of the SRB. As groundwater is found to be a dependable source of drinking water in such watersheds, a comprehensive study on the hydrogeochemistry of all watersheds in tropical regions is recommended.