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Hydrogels were produced from mixtures of polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), and acrylic acid (AAc) using γ-radiation at doses of 3, 7, and 10 kGy and the effect of the variation in concentration of AAc within 0%–3% (w/v) on the gelation, swelling, crosslinking, thermal properties, crystallinity, mechanical properties, and surface morphology of the hydrogels were characterized and their adsorptive removal properties for methylene blue (MB) was investigated. The swelling trend was pH-dependent which was dictated by the dominance of two competing factors namely, crosslink density and hydrophilicity. Although thermal analysis showed that the presence of AAc decreased the thermal stability of the hydrogels, SEM images exhibited gradual morphological changes establishing the role of AAc as a crosslinker, and thus increasing the elastic moduli, toughness, and crystallinity of the hydrogels. However, correlation between the characterization results revealed that, in spite of AAc occupying some of the crosslinking sites within PVA–PVP networks, at low concentration (1% w/v), it could not polymerize enough to contribute to the crosslinks. FTIR spectral analysis revealed a possible gelation mechanism along with the points of interaction among the gel-components. MB adsorption capacity of the hydrogels reached a maximum of 117 mg/g following pseudo-second-order kinetics through film diffusion mechanism while the adsorption isotherm resembled most with that of Langmuir.

The interaction between water vapor and natural/anthropogenic airborne particles deposits a massive amount of trace elements in the ecosystem. As the principal source region of the Indian monsoon originated from the Bay of Bengal, atmospheric trace elements in Bangladesh have impacted atmospheric wet deposition along the pathway, even reaching the headwaters in the Asian water tower. However, no study reports the atmospheric wet deposition of trace elements at the spatiotemporal scale. Thus, this study investigated the concentration, sources, and deposition of eighteen trace elements (Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Rb, Sr, Mo, Cd, Sn, Sb, Ba, and Pb) from 232 precipitation samples at four sites in Bangladesh. Results showed that the VWM concentrations of the eighteen measured trace elements ranged from 0.03 to 535.6 μg L

Dhaka is one of the highly populated cities in the world. Increased urbanization and population growth in Dhaka are mostly dependent on groundwater, with 78% of the supply water coming from the Plio-Pleistocene Dupi Tila aquifer. This research was conducted with the objectives of identifying ion chemistry, hydrochemical processes and their relationship to groundwater quality and finding out the impact of over-exploitation on Dupi Tila aquifer. Three consecutive semi-confined aquifers have been delineated up to the explored depth: the Upper Dupi Tila aquifer (UDA), Middle Dupi Tila aquifer (MDA) and Lower Dupi Tila aquifer (LDA). Hydrogeochemical processes and water quality have been inferred from bivariate plots, correlation of major ions, piper plot and stable isotopes analysis. The total dissolved solids show an increasing downwards trend from an average of 267 mg/l in UDA to an average of 284 mg/l in LDA. Waters in all three aquifers as well as surface water (SW) are mainly of Ca/Mg-HCO

This investigation concentrates on the possibility of using gamma radiation for the decomposition of textile wastewater and reuse as irrigation water. The real wastewater sample was irradiated at four different radiation doses of 3, 5, 8, and 10 kGy. After irradiation at 8–10 KGy, physicochemical parameters, i.e., pH, turbidity, EC, total suspended solids (TSS), total dissolved solids (TDS), biological oxygen demand (BOD5), and chemical oxygen demand (COD) have decreased sharply and approached to the expected value. At maximum 10 KGy radiation dose, 59.0 % BOD5 and 71.6 % COD removal have been achieved, accelerating the enhancement in biodegradability index (BOD5/COD, 0.43). Ammonium and total nitrogen have improved up to 87.0 % and 94.5 % after irradiation at 10 KGy doses. These treated textile wastewater samples were reused to grow Capsicum frutescens plants to inspect the fertility responses. When Capsicum plants were nourished by textile wastewater irradiated at 8–10 kGy, the dry masses of the fruits, moisture content, root length, average plant height, average number of leaves, and total number of fruits were increased in comparison to those plants nourished by simply water and raw wastewater. The elemental analysis confirmed that the heavy metals concentration in Capsicum fruits decreased gradually with higher radiation doses. Helpful macro and micronutrients for plant production such as Na, K, and Mg were raised at a sufficient level of 47.7 %, 23.5 %, and 63.8 % for 10 KGy, whereas the highest 50.0 % increase in Ca concentration was found for 8 KGy fruit samples.

This study aims to appraise the spatial variations and pathways of groundwater contaminations and associated health risks in the Surma basin, Bangladesh using geostatistics, Fuzzy GIS technique and health risk modelbased on ninety groundwater samples. The results show that the mean concentrations of As, Fe, Mn and NO3 are below the Bangladesh water quality standard, whereas As, Fe and Mn concentrations exceed World Health Organization guideline values in several sampling sites. The compositional study identifies weathering of source rocks, reductive dissolution of Fe and Mn-oxyhydroxide minerals and various anthropogenic inputs as the key sources of groundwater contamination. The kriged maps show the elevated risks of Fe, Mn and NO3 concentrations from the south to northern parts and As concentration from the north to southwestern parts of the Surma basin. The results of fuzzy GIS maps confirm the outcomes of kriged maps. Cross validation results show better performance of indicator kriging over probability kriging. The results also show a spatial heterogeneity with As, Fe, Mn and NO3 concentrations, indicating the low to medium risk categories. A health risk assessment is performed using hazard quotient (HQ) and hazard index (HI). The HQ values imply that the risk of contamination through oral ingestion pathway is medium to high levels for both adults and children as the trace elements show HQ values more than one. It is found that drinking water of several upazilas exhibits high contamination and that children are more susceptible to the non-carcinogenic and carcinogenic risks than adults in the study area.

Groundwater development in coastal aquifers of southwest Bangladesh is challenged by both natural and anthropogenic activities resulting in a landward migration of marine waters and increase in the risk of seawater intrusion. In some cases, infiltration of dissolved evaporite salts in the shallow aquifer and presence of connate water in the deep aquifer (DA) are the sources of groundwater salinity other than modern seawater intrusion. A detail investigation of these sources is imperative for a sustainable development and management of coastal aquifers. This work investigates the hydrogeochemical processes affecting groundwater chemistry by interpreting conventional plots, ionic delta, HFE-diagram, stable isotopes, and geochemical modelling. There are three hydrogeological units delineated in this area: upper shallow aquifer (USA) (3-, but in shallow aquifers Cl-. The main water type based on the classification of Stuyfzand (1989) is the brackish to saline NaCl type in the shallow aquifers. The Br-/Cl- ratio and relatively enriched δ18O values in these NaCl waters suggest an origin derived from evaporate dissolution. Reverse cation exchange during intrusion, replacing Na+ with Ca2+, results in CaCl and CaMix water types. These waters infiltrate into the LSA. The water in the DA is mainly fresh NaHCO3+ type which originated by cation exchange from infiltrating fresh water. Ca2+ was replaced by Na+ due to the cation exchange, the water became undersaturated with respect to calcite and secondary calcite dissolution caused elevated bicarbonate concentrations. Near the present-day shoreline and at larger depths, the NaHCO3+ type water mixes with connate water, increasing salinity. The enriched δ18O values in the DA suggest an origin in a warmer climate, implying that this water has infiltrated a long time ago, much farther inland, probably during the Holocene climatic optimum. It can be expected that the salinization of the shallow aquifers will continue to increase if evaporite deposition and seasonal flooding occur. For a sustainable use of the groundwater resource in this coastal region and to prevent from even further worsening of water quality in its shallow aquifers, it is advised to develop future exploitations in the DA.Key words: Groundwater chemistry; Stable isotope; Evaporite; Cation exchange; Calcite dissolution.

To investigate the hydrogeochemical characteristics of groundwater 23 shallow, 30 intermediate and 38 deep wells samples were collected from Sylhet district of Bangladesh, and analyzed for temperature, pH, Eh, EC, DO, DOC, Na+, K+, Ca2+, Mg2+, Cl−, SO42−, NO3−, HCO3−, SiO2−, Fe, Mn and As. Besides, 12 surface water samples from Surma and Kushiyara Rivers were also collected and analyzed to understand the influence into aquifers. Results revealed that, most of the groundwater samples are acidic in nature, and Na–HCO3 is the dominant groundwater type. The mean value of temperature, EC, Na+, K+, Ca2+, Mg2+, Cl−, NO3− and SO42− were found within the range of permissible limits, while most of the samples exceeds the allowable limits of Fe, Mn and As concentrations. However, relatively higher concentration of Fe and Mn were found in deep water samples and reverse trend was found in case of As. The mean concentrations of As in shallow, intermediate and deep wells were 39.3, 25.3 and 21.4 µg/L respectively, which varied from 0.03 to 148 µg/L. From spatial distribution, it was found that Fe, Mn and As concentrations are high but patchy in northern, north-western, and south-western part of Sylhet region. The most influential geochemical process in study area were identified as silicate weathering, characterized by active cation exchange process and carbonate weathering, which thereby can enhance the elemental concentrations in groundwater. Pearson’s correlation matrix, principal component analysis and cluster analysis were also employed to evaluate the controlling factors, and it was found that, both natural and anthropogenic sources were influencing the groundwater chemistry of the aquifers. However, surface water has no significant role to contaminate the aquifers, rather geogenic factors affecting the trace elemental contamination. Thus it is expected that, outcomes of this study will provide useful insights for future groundwater monitoring and management of the study area.

The hydrogeochemical processes in the multilayer aquifers of southwest (SW) coastal area of Bangladesh provide important information for quantifying hydrochemical differences between different aquifers. Hydrogeochemical processes affecting groundwater chemistry in this coastal area have been evaluated by interpreting conventional plots, ionic delta, HFE-diagram, stable isotopes and geochemical modelling. The median TDS distribution of the aquifers has an increasing trend from below 1000 mg/l in the deep aquifer (DA) to 2622 mg/l in lower shallow aquifer (LSA) and 7012 mg/l in upper shallow aquifer (USA). Na+ is the dominant cation in all the aquifers. HCO3− is the dominant anion in DA with high median concentration (495 mg/l), which is more than double than that in LSA (214 mg/l) and USA (159 mg/l). The groundwater in the DA is freshened NaHCO3+ type due to cation exchange process that enhances second stage of calcite dissolution. Few NaCl+ type DA waters found in the SW corner of the study area indicate the presence of connate water confined in the inter-basin during the Holocene transgression. The stable isotopes indicate that the DA waters have been deposited during warmer periods. In contrast, both the LSA and USA are dominated by NaCl- type water; some CaCl- type waters have also been found in these aquifers, indicating salinization. The salinization processes consist of infiltration of redissolved evaporite salts, reverse cation exchange, and mixing with marine influenced flood water. Thus, the knowledge of different processes controlling freshening and salinization will help properly manage and preserve the environmental characteristics in the aquifer systems of SW Bangladesh as well as similar complex coastal geological settings.

The quantitative and qualitative characterization of ions and inorganic nitrogen in precipitation assists in understanding the accompanying sources and chemistry of regional precipitation. A total of 212 event-based precipitation samples were collected from four sites in Bangladesh in 2017 to investigate the physicochemical characteristics, sources, and deposition of atmospheric ionic constituents and inorganic nitrogen. During the entire monitoring period, 5.7% of the total samples were acidic (i.e., pH Cox's Bazar > Dinajpur > Sylhet, whereas the anthropogenic species exhibited the order of Dinajpur > Satkhira > Sylhet > Cox's Bazar, underlining the local and regional impacts of these species in Bangladesh. Based on the source apportionment, the sources were categorized as marine (Na+ and Cl−), terrigenous (Ca2+, Mg2+, and HCO3−), fossil fuel combustion (NO3− and SO42−), agriculture (NH4+), and biomass burning (K+). The Cl− in Sylhet and Satkhira suggests additional sources associated with anthropogenic activities. The back-trajectory analyses and the National Centers for Environmental Prediction's final (NCEP FNL) datasets illustrate the presence of significantly diverse air masses with contributions from various sources in the monsoon and non-monsoon climates. Both the amount of precipitation and the ionic quantity governs the fluxes in Bangladesh. The Na+ % and SAR lie under the safe category suggesting a good precipitation water quality for agriculture and soil in Bangladesh, while the deposition of inorganic nitrogen has resulted in a value above the threshold line (10 kg ha−1 y−1). Thus, this study conveys a comprehensive picture of the ionic composition, providing a baseline dataset to assess the atmospheric environment in this lowland region.

This study aims to appraise the spatial variations and pathways of groundwater contaminations and associated health risks in the Surma basin, Bangladesh using geostatistics, Fuzzy GIS technique and health risk modelbased on ninety groundwater samples. The results show that the mean concentrations of As, Fe, Mn and NO