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.

Ice is an important physical and chemical sink for various pollutants in cold regions. The photodegradation of emerging fluoroquinolone (FQ) antibiotic contaminants with dissolved organic matter (DOM) in ice remains poorly understood. Here, the photodegradation of ciprofloxacin (CIP) and fulvic acid (FA) in different proportions as representative FQ and DOM in ice were investigated. Results suggested that the photodegradation rate constant of CIP in ice was 1.9 times higher than that in water. When CFA/CCIP ≤ 60, promotion was caused by FA sensitization. FA increased the formation rate of cleavage in the piperazine ring and defluorination products. When 60 < CFA/CCIP < 650, the effect of FA on CIP changed from promoting to inhibiting. When 650 ≤ CFA/CCIP ≤ 2600, inhibition was caused by both quenching effects of 143.9%–51.3% and light screening effects of 0%–48.7%. FA inhibited cleavage in the piperazine ring for CIP by the scavenging reaction intermediate of aniline radical cation in ice. When CFA/CCIP > 2600, the light screening effect was greater than the quenching effect. This work provides new insights into how DOM affects the FQ photodegradation with different concentration proportions, which is beneficial for understanding the environmental behaviors of fluorinated pharmaceuticals in cold regions.

The rapid development of China's industrial economy and implementation of air pollution controls have led to great changes in sulfur (S), nitrogen (N) and base cation (BC) deposition in the past three decades. We estimated China's anthropogenic BC emissions and simulated BC deposition from 1985 to 2015 with a five-year interval using a multilayer Eulerian model. Deposition of S and N from 2000 to 2015 with a five-year interval was simulated with the EMEP MSC-W model and the Multi-resolution Emission Inventory of China (MEIC). The critical load (CL) and its exceedance were then calculated to evaluate the potential long-term acidification risks. From 1985 to 2005, the BC deposition in China was estimated to have increased by 16 % and then decreased by 33 % till 2015. S deposition was simulated to increase by 49 % from 2000 to 2005 and then decrease by 44 % in 2015, while N deposition increased by 32 % from 2000 to 2010 with a limited reduction afterward. The maximum CL of S was found to increase in 67 % of mainland China areas from 1985 to 2005 and to decline in 55 % of the areas from 2005 to 2015, attributed largely to the changed BC deposition. Consistent with the progress of national controls on SO₂ and NOX emissions, the CL exceedance of S increased from 2.9 to 4.6 Mt during 2000–2005 and then decreased to 2.5 Mt in 2015, while that of N increased from 0.4 in 2000 to 1.2 Mt in 2010 and then decreased to 1.1 Mt in 2015. The reduced BC deposition due to particle emission controls partially offset the benefit of SO₂ control on acidification risk reduction in the past decade. It demonstrates the need for a comprehensive strategy for multi-pollutant control against soil acidification.

Acid deposition has been regarded as a serious factor in the deteriorative water environment and ecosystems. Despite the powerful acid emission control measures have been implemented by the Chinese government, many areas (especially Southeast China) are still suffering from acid deposition. The chemical and isotopic (δ³⁴S and ⁸⁷Sr/⁸⁶Sr) compositions of rainwater in Hangzhou, a typical megacity in Southeast China with serious acid rain problem, for one year were studied with the aim to better constrain potential sources and explore the causes of rainwater acidification. Most rainwater samples were acidic, with a VWM pH value of 4.65. SO₄²⁻ was the dominant anion and the main acid ion in rainwater. Sulfur isotope and the quantity equilibrium model revealed that sea salt, crustal, biogenic, and anthropogenic sulfur represented 2.3%, 0.1%, 16.7%, and 80.8% of the SO₄²⁻ source in rainwater, respectively. The back trajectory and strontium isotopes indicated that the base cations (BCs) in rainwater originated mainly from anthropogenic sources. The relatively low neutralizing capacity caused by limited BCs input and emission control measures undermines some efforts to reduce rainwater acidity. This case study demonstrated that a valuable tool to probe the source of acid rain and unravel the mechanism of rainwater acidification can be provided by multiple lines of evidence, including rainwater chemical compositions, stable sulfur isotopes, and stable strontium isotopes.

The release of fine particles from biochar materials applied in the environment may have important environmental implications, such as mobilization of environmental contaminants. In natural environments biochar fine particles can undergo various transformation processes, which may change their surface chemistry and consequently, the mobility of the particles. Here, we show that sulfide reduction can significantly alter the transport of wheat-straw- and pine-wood-derived biochar fine particles in saturated porous media. Counterintuitively, the sulfide-reduced biochar particles exhibited greater mobility in artificial groundwater than their non-reduced counterparts, even though reduction led to decrease of surface charge negativity and increase of hydrophobicity (from the removal of surface O-functional groups), both should favor particle deposition, as predicted based on extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory. Using transport experiments conducted in single-cation background solutions containing K⁺, Mg²⁺ or Ca²⁺ under different pH conditions, we show that the surprisingly greater mobility of sulfide-reduced biochar particles was attributable to the removal of surface carboxyl groups during reduction, as this markedly alleviated particle deposition through cation bridging, wherein Ca²⁺ acted as the bridging agent in linking the surface O-functional groups of biochar particles and quartz sand. These findings show the critical roles of surface properties in dictating the mobility of biochar fine particles and call for further understanding of their transport properties, which apparently cannot be simply extrapolated based on the findings of other (engineered) carbonaceous nanomaterials.

Cadmium cations (Cd²⁺) are extremely toxic to organisms, which limits the remediation of Cd by microorganisms. This study investigated the feasibility of applying biochar to protect bacteria from extreme Cd²⁺ stress (1000 mg/L). An alkaline biochar (RB) and a slightly acidic biochar (SB) were selected. SB revealed a higher Cd²⁺ removal than RB (15.5% vs. 4.8%) due to its high surface area. Addition of Enterobacter sp. induced formation of Cd phosphate and carbonate on both SB and RB surface. However, Cd²⁺ removal by RB enhanced more evidently than SB (78.9% vs. 30.2%) due to the substantial microbial regulation and surficial alkalinity. Thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS) and geochemical modeling (GWB) all confirmed that the formation of stable Cd phosphate on RB was superior to that in SB. These biomineralization, together with biochar pore structure, protect bacterial cells from Cd stress. Moreover, the alkalinity of biochar promoted the formation of carbonate, which strengthened the decline of Cd²⁺ toxicity. The protection by RB was also confirmed by the intense microbial respiration and biomass (PLFA). Furthermore, this protection induced a positive feedback between P-abundant biochar and Enterobacter sp.: biochar provides P source (the most common limiting nutrient) to support microbial growth; bacteria secrete more organic acids to drive P release. This study therefore elucidated the protection of bacteria by P-enriched biochar based on both physic-chemical and microbial insights.

To investigate the removal characteristics of ammonium-nitrogen (NH₄⁺-N), nitrite-nitrogen (NO₂⁻-N), nitrate-nitrogen (NO₃⁻-N), and total nitrogen from groundwater by a degradable composite active medium, kinetics, thermodynamics, and equilibrium adsorption, experiments were performed using scoria and degrading bacteria immobilized on scoria. Removal of NH₄⁺-N, NO₂⁻-N, and NO₃⁻-N was conducted in adsorption experiments using different times, initial concentrations, pH values, and groundwater chemical compositions (Ca²⁺, Mg²⁺, HCO₃⁻, CO₃²⁻, Fe²⁺, Mn²⁺, and SO₄²⁻). The results showed that the removal of nitrogen by the composite active medium was obviously better than that of scoria alone. The removal rates of NH₄⁺-N (C₀ = 5 mg/L), NO₂⁻-N (C₀ = 5 mg/L), and NO₃⁻-N (C₀ = 100 mg/L) by the composite active medium within 1 h were 96.05%, 82.40%, and 83.16%, respectively. The adsorption kinetics were well fitted to a pseudo-second order model, whereas the equilibrium adsorption agreed with the Freundlich model. With changes in the pH, variation in the removal could be attributed to the combined effect of hydrolysis and competitive ion adsorption, and the optimum pH was 7. Different concentration conditions, hardness, alkalinity, anions, and cations showed different promoting and inhibiting effects on the removal of nitrogen. A careful examination of ionic concentrations in adsorption batch experiments suggested that the sorption behavior of nitrogen onto the immobilized medium was mainly controlled by ion exchange. The degrading bacteria on the scoria surface were eluted and analyzed by metagenomic sequencing. There were significant differences in the number of operational taxons, relative abundances, and community diversity among degrading bacteria after adsorption of the three forms of nitrogen. The relative abundance of degrading bacteria was highest after NO₃⁻-N removal, and the diversity was highest after NO₂⁻-N removal. Pseudomonas and Serratia were the dominant genera that could efficiently remove NH₄⁺-N and NO₂⁻-N.

The correlation between endocrine active contaminants in the environment and alterations in reproductive development of Sarotherodon melanotheron from Lagos lagoon has been investigated. Sediment and a total of 155 fish (74 males and 81 females) were collected between November 2014–March 2015 from selected contaminated sites (Ikorodu, Oworonshoki, Makoko and Idumota) and a putative control site (Igbore) along the lagoon. Sediment contaminant analysis revealed, significantly higher concentration of lindane, dieldrin, 4-iso-nonylphenol, 4-t-octylphenol and monobutyltin cation at the contaminated sites. Examination of gross morphological and histological changes of fish gonads showed a 27.4% prevalence of intersex in the sampled fish, of which 78% were males (testes-ova) and 22% were females (ovo-testis). Quantitative PCR (qPCR) of liver transcripts revealed the presence of vitellogenin (vtg) levels in male fish from contaminated sites. Zona radiata proteins (zrp) mRNA levels were significantly higher in females, compared to male fish. In general, significantly lower vtg and zrp transcripts levels were recorded at Igbore (control site), compared with contaminated sites. Principal component analysis (PCA) showed site and sex relationship in biological responses and contaminants, including trace metals, demonstrating that measured endocrine responses in fish were associated with contaminant burden in sediment. In addition, positive relationships were observed in male fish from Idumota, Oworonshoki and Ikorodu with vtg and dieldrin/4-iso-nonyphenol, with higher levels in male fish, compared to females. Further, contaminants from the Makoko, Oworonshoki and Ikorodu sites were positively associated with higher GSI and zrp in females. More importantly, the severity of intersex and changes in vtg transcripts imply a progressive feminization of male fish with concomitant alteration in the reproductive health of fish inhabiting the Lagos lagoon.

The sediment characterisation of wetlands belonging to the Northeastern Region of India particularly regarding the assessment of sediment carbon stock is very scanty. The presently available literature on the wetlands cannot be employed as a common model for managing the wetlands of the Northeastern Region of India as wetlands are a sensitive ecosystem with a different origin or endogenous interventions. Thereby, this research was conducted on Deepor Beel for investigating the spatial and seasonal variation of sediment parameters, the relationship between the parameters and pollution status of the wetland. Results revealed that the study area is of an acidic nature with a sandy clay loam type texture. Organic carbon, total nitrogen and available nitrogen were higher in sediments in the monsoon period. The mean stock of the sediment carbon pool of Deepor Beel is estimated to be 2.5 ± 0.7 kg m−2. The average non-residual fraction percentage (63.2%) of Pb was higher than the residual fraction. Zn content ∼490 mg kg−1 exceeding its effect range medium (ERM) was determined to suggest frequent biological adverse effects. Highest metal enrichment factor (EF) values were shown by Zn and Pb, which ranged between 78 and 255. Risk assessment code (RAC) values of Pb between 21 and 29% indicated its high bio-accessibility risk. Pearson's coefficient matrix revealed a low degree of positive correlation between organic carbon content and metal concentration. Principal component analysis revealed that the first component comprising of EC, basic cations and metals accounted for 62.3% of variance while the second component (OM, OC, TN, AN, AP) and the third component (pH) accounted for 21.8% and 7.0% of the variance, respectively. The present study revealed the adverse impact of human inputs on the Deepor Beel quality status.

A key criterion of the UK Government's policy on sustainable forest management is safeguarding the quality and quantity of water. Forests and forestry management practices can have profound effects on the freshwater environment. Poor forest planning or management can severely damage water resources at great cost to other water users; in contrast good management that restores and maintains the natural functions of woodland can benefit the whole aquatic ecosystem.Forests and forest management practices can affect surface water acidification. Monitoring of water chemistry in ten forest and two moorland acid-sensitive catchments in upland Wales commenced in 1991. The streams were selected to supplement the United Kingdom Upland Waters Monitoring Network (UWMN) with additional examples of afforested catchments. Analysis of 22 years of water chemistry data revealed trends indicative of recovery from acidification. Excess sulphate exhibited a significant coherent decline, accompanied by increases in pH and “charge-balance based” acid neutralising capacity (CB-ANC). Alkalinity and “alkalinity-based” acid neutralising capacity (AB-ANC) exhibited fewer trends, possibily due to the variable responses of the organic - carbonate species to increasing pH in these low alkalinity streams. Whilst total anthropogenic acidity declined, dissolved organic carbon and Nitrate-Nitrogen (NNO₃) concentrations have risen, and the contribution of NNO₃ to acidification has increased.Between-stream variability was analysed using Principal Component Analysis of the trend slopes. Hierarchical clustering of the changes in stream water chemistry indicated three distinct clusters with no absolute distinction between moorland and forest streams. Redundancy analysis was used to test for significant site-specific variables that explained differences in the trend slopes, with rainfall, crop age, base cation concentration and forest cover being significant explanatory variables.