Water quality has recently emerged as one of the utmost severe ecological problems being faced by the developing countries all over the world, and Bangladesh is no exception. Both surface and groundwater sources contain different contaminants, which lead to numerous deaths due to water-borne diseases, particularly among children. This study presents one of the most comprehensive reviews on the current status of water quality in Bangladesh with a special emphasis on both conventional pollutants and emerging contaminants. Data show that urban rivers in Bangladesh are in a critical condition, especially Korotoa, Teesta, Rupsha, Pashur, and Padma. The Buriganga River and few locations in the Turag, Balu, Sitalakhya, and Karnaphuli rivers have dissolvable oxygen (DO) levels of almost zero. Many waterways contain traces of NO3, NO2, and PO4-3 pollutants. The majority of the rivers in Bangladesh also have Zn, Cu, Fe, Pb, Cd, Ni, Mn, As, and Cr concentrations that exceed the WHO permissible limits for safe drinking water, while their metal concentrations exceed the safety threshold for irrigation. Mercury poses the greatest hazard with 90.91% of the samples falling into the highest risk category. Mercury is followed by zinc 57.53% and copper 29.16% in terms of the dangers they pose to public health and the ecosystem. Results show that a considerable percentage of the population is at risk, being exposed to contaminated water. Despite hundreds of cryptosporidiosis cases reported, fecal contamination, i.e., Cryptosporidium, is totally ignored and need serious considerations to be regularly monitored in source water.

Low pH and aluminum (Al)-toxicity often coexist in acidic soils. Citrus sinensis seedlings were treated with nutrient solution at a pH of 2.5, 3.0, 3.5 or 4.0 and an Al concentration of 0 or 1 mM for 18 weeks. Thereafter, malate, citrate, isocitrate, acid-metabolizing enzymes, and nonstructural carbohydrates in roots and leaves, and release of malate and citrate from roots were measured. Al concentration in roots and leaves increased under Al-toxicity, but it declined with elevating nutrient solution pH. Al-toxicity increased the levels of glucose, fructose, sucrose and total soluble sugars in leaves and roots at each given pH except for a similar sucrose level at pH 2.5–3.0, but it reduced or did not alter the levels of starch and total nonstructural carbohydrates (TNC) in leaves and roots with the exception that Al improved TNC level in roots at pH 4.0. Levels of nonstructural carbohydrates in roots and leaves rose with reducing pH with a few exceptions with or without Al-toxicity. A potential model for the possible role of root organic acid (OA) metabolism (anions) in C. sinensis Al-tolerance was proposed. With Al-toxicity, the elevated pH upregulated the OA metabolism, and increased the flow of carbon to OA metabolism, and the accumulation of malate and citrate in roots and subsequent release of them, thus reducing root and leaf Al and hence eliminating Al-toxicity. Without Al-toxicity, low pH stimulated the exudation of malate and citrate, an adaptive response of Citrus to low pH. The interactive effects of pH and pH on OA metabolism were different between roots and leaves.

After the exploitation of coal mines in the 19th and 20th centuries in northern France, many mining slag heaps (SH) were left without any particular management or monitoring. Currently, the influence of these SHs on the quality of surrounding wetlands is hardly known.The purpose of this work is to determine the water quality in the neighbourhood of two SHs located near the city of Douai and its influence on the distribution of aquatic invertebrates in local wetlands. Our approach involves (1) the spatial and temporal characterization of the water composition (anions, major elements, sulphide, DOC and alkalinity) and of the biological diversity (aquatic invertebrates) and (2), based on this chemical and biological screening, the establishment of relationships between water quality and biodiversity distribution through multivariate data analysis. The results clearly indicate that substantial leaching from the slag heaps occurs, given the very high concentrations of dissolved sulphates (in the range of 2 g L⁻¹). While the pH remains weakly basic, indicating that the leaching water has been neutralized by the highly carbonated regional substratum, high levels of biodegradable organic matter and sulphate contents have been noticed. They sporadically cause significant drops in dissolved oxygen and the occurrence of dissolved sulphides that massively reduce biodiversity, qualitatively and quantitatively. In Summer, oxygen saturation is generally lower due to the higher rate of organic matter degradation, and the risk of anoxic episodes therefore increases. Finally, as wetlands are vulnerable environments, these preliminary results suggest that monitoring and management of these sites must be attempted quickly to avoid the degradation of those valuable habitats.

This study aimed to develop a novel in-situ method to directly remove toxic hexavalent chromium anions from groundwater. The characteristics of Mg/Al-layered double hydroxides (LDH) involving in-situ synthesis and interlayer exchangeable anions can facilitate to remove Cr(VI) from solution. Two different methods of LDH preparation were employed to explore the adsorption efficiency of (di)chromates, such as traditional coprecipitation (CO₃-LDH) and innovative in-situ synthesis (in-situ-LDH). The synthesized LDH samples were characterized using scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and zeta potential. The results demonstrated that the adsorptive amount of Cr(VI) for the in-situ synthesis process dramatically increased with an increase in initial Cr(VI) concentrations from 100 mg/L to 900 mg/L. The kinetic study indicated that the constant rate (k₂) of the pseudo-second-order equation significantly decreased when the initial concentration of Cr(VI) exceeded 500 mg/L. The removal efficiency of Cr(VI) was slightly dependent on solution pH (5.0–12) values. The in-situ-LDH absorbent (339 mg/g) exhibited the significantly higher Langmuir maximum adsorption capacity than CO₃-LDH (246 mg/g). The primary adsorption mechanism was anion exchange; meanwhile, the adsorption-coupled reduction mechanism also played an integral role. The advanced in-situ synthetic method can be developed to efficiently remove toxic hexavalent chromium anions from groundwater.

Nano zero valent iron/Ni bimetal materials (nZVI/Ni) were prepared by borohydride reduction method to remediate toxic Cr(Ⅵ) contaminated in soil leachate. nZVI/Ni was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). Different factors including pH value of soil leachate, reaction time, temperature, humic acid and coexisting anions (SO42-, NO3−, HCO3−, CO32-) were studied to analyze the reduction rate. Results showed that the reduction rate of Cr(Ⅵ) could reach 99.84% under the condition of pH of 5 and temperature of 303 K. pH values and temperature of soil leachate had a significant effect on the reduction efficiency, while humic acid had inhibition effect for the reduction reaction. SO42-, HCO3− and CO32- had inhibition effect for reduction rate, while NO3− barely influenced the reduction process of nZVI/Ni. Moreover, Langumir-Hinshelwood first order kinetic model was studied and could describe the reduction process well. The thermodynamic studies indicated that the reaction process was endothermic and spontaneous. Activation energy was 143.80 kJ mol−1, showing that the reaction occurred easily. Therefore, the study provides an idea for nZVI/Ni further research and practical application of nZVI/Ni in soil remediation.

Recent efforts have been directed towards better understanding the persistency and toxicity of ionic liquids (ILs) in the context of the “benign-by-design” approach, but the assessment of their bioaccumulation potential remains neglected. This paper reports the experimental membrane partitioning of IL cations (imidazolium, pyridinium, pyrrolidinium, phosphonium), anions ([C(CN)3]-, [B(CN)4]-, [FSO2)2N]-, [(C2F5)3PF3]-, [(CF3SO2)2N]-) and their combinations as a measure for estimating the bioconcentration factor (BCF). Both cations and anions can have a strong affinity for phosphatidylcholine bilayers, which is mainly driven by the hydrophobicity of the ions. This affinity is often reflected in the ecotoxicological impact. Our data revealed that the bioconcentration potential of IL cations and anions is much higher than expected from octanol-water-partitioning based estimations that have recently been presented. For some ILs, the membrane-water partition coefficient reached levels corresponding to BCFs that might become relevant in terms of the “B” (bioaccumulation potential) classification under REACH. However, this preliminary estimation need to be confirmed by in vivo bioconcentration studies.

With the extensive application of graphene oxide (GO), it is noticeable that part of GO is directly/indirectly released into the environment and widespread research indicated that it had adverse influences on human health and ecological balance. In this work, a novel nanobelt-like Ca/Al layered double hydroxides (CA-LDH) was synthesized and applied as efficient coagulant for the removal of GO from aqueous solutions. The results indicated that neutral pH, co-existing cations and higher temperature were beneficial to the coagulation of GO. The sequence of cation effect for promoting of GO coagulation was Ca2+ > Mg2+ > K+ > Na+, whereas the effect of anions on GO coagulation was PO43− > CO32− > SO42− > Cl−. Comparing with anions, the cations showed more dominate effect for GO coagulation than anions. Hydrogen bonds and electrostatic interaction were the main coagulation mechanisms for GO coagulation, which were evidenced by FT-IR and XPS analysis. Specifically, for the first time, the reclaimed product of CA-LDH after GO coagulation (CA-LDH + GO) was applied as adsorbents for the secondary application in the removal of heavy metal ions from aqueous solutions. Interestingly, the CA-LDH + GO still had high adsorption capacities, i.e., the maximum adsorption capacities (qmax) for Cu(II), Pb(II), and Cr(VI) were 122.7 mg/g, 221.2 mg/g and 64.4 mg/g, respectively, higher than other similar materials. This paper highlighted the LDH-based nanomaterials are promising materials for the elimination of environmental pollutants and the migration and transformation of carbon nanomaterials in the natural environment.

Ionic mixtures, measured as specific conductivity, have been increasingly concerned because of their toxicities to aquatic organisms. However, identifying protective values of specific conductivity for aquatic organisms is challenging given that laboratory test systems cannot examine more salt-intolerant species nor effects occurring in streams. Large data sets used for deriving field-based benchmarks are rarely available. In this study, a field-based method for small data sets was used to derive specific conductivity benchmark, which is expected to prevent the extirpation of 95% of local taxa from circum-neutral to alkaline waters dominated by a mixture of SO42− and HCO3− anions and other dissolved ions. To compensate for the smaller sample size, species level analyses were combined with genus level analyses. The benchmark is based on extirpation concentration (XC95) values of specific conductivity for 60 macroinvertebrate genera estimated from 296 sampling sites in the Hun-Tai River Basin. We derived the specific conductivity benchmark by using a 2-point interpolation method, which yielded the benchmark of 249 μS/cm. Our study tailored the method that was developed by USEPA to derive aquatic life benchmark for specific conductivity for basin scale application, and may provide useful information for water pollution control and management.

Increasing use of metal and metal oxide nanoparticles [Me(O)NPs] in products means many will inevitably find their way into marine systems. Their likely fate here is sedimentation following hetero-aggregation with natural organic matter and/or free anions, putting benthic, sediment-dwelling and filter feeding organisms most at risk. In marine systems, Me(O)NPs can absorb to micro-organisms with potential for trophic transfer following consumption. Filter feeders, especially bivalves, accumulate Me(O)NPs through trapping them in mucus prior to ingestion. Benthic in-fauna may directly ingest sedimented Me(O)NPs. In fish, uptake is principally via the gut following drinking, whilst Me(O)NPs caught in gill mucus may affect respiratory processes and ion transport. Currently, environmentally-realistic Me(O)NP concentrations are unlikely to cause significant adverse acute health problems, however sub-lethal effects e.g. oxidative stresses have been noted in many organisms, often deriving from dissolution of Ag, Cu or Zn ions, and this could result in chronic health impacts.

Arsenic mobility may increase in liquid phase due to association with colloidal Fe oxides. We studied the association of As with Fe oxide colloids in the effluent from water-saturated soil columns run under anoxic conditions. Upon exfiltration, the solutions, which contained Fe²⁺, were re-aerated and ferrihydrite colloids precipitated. The entire amount of effluent As was associated with the ferrihydrite colloids, although PO₄ ³⁻, SiO₄ ⁴⁻, CO₃ ²⁻ and dissolved organic matter were present in the effluent during ferrihydrite colloid formation. Furthermore, no subsequent release of As from the ferrihydrite colloids was observed despite the presence of these (in)organic species known to compete with As for adsorption on Fe oxides. Arsenic was bound via inner-sphere complexation on the ferrihydrite surface. FTIR spectroscopy also revealed adsorption of PO₄ ³⁻ and polymerized silica. However, these species could not impede the quantitative association of As with colloidal ferrihydrite in the soil effluents.