Arsenic Contamination in Groundwater: Geochemical Basis of Treatment Technologies.

Arsenic (As) is abundant in the environment and can be found in both organic (e.g., methylated) and inorganic (e.g., arsenate and arsenite) forms. The source of As in the environment is attributed to both natural reactions and anthropogenic activities. As can also be released naturally to groundwater through As-bearing minerals including arsenopyrites, realgar, and orpiment. Similarly, agricultural and industrial activities have elevated As levels in groundwater. High levels of As in groundwater pose serious health risks and have been regulated in many developed and developing countries. In particular, the presence of inorganic forms of As in drinking water sources gained widespread attention due to their cellular and enzyme disruption activities. The research community has primarily focused on reviewing the natural occurrence and mobilization of As. Yet, As originating from anthropogenic activities, its mobility, and potential treatment techniques have not been covered. This review summarizes the origin, geochemistry, occurrence, mobilization, microbial interaction of natural and anthropogenic-As, and common remediation technologies for As removal from groundwater. In addition, As remediation methods are critically evaluated in terms of practical applicability at drinking water treatment plants, knowledge gaps, and future research needs. Finally, perspectives on As removal technologies and associated implementation limitations in developing countries and small communities are discussed.

Prevalence of metallo-ß-lactamases as a correlate of multidrug resistance among clinical Pseudomonas aeruginosa isolates in Nepal.

Pseudomonas aeruginosa is an opportunistic human pathogen that has developed antibiotic resistance (AR) and causes a range of illnesses, including respiratory pneumonia, gastrointestinal infections, keratitis, otitis media and bacteremia in patients with compromised immune system. The production of metallo-ß-lactamases (MBLs) is one of the major mechanisms of AR in this bacterium with ensuing infections difficult to treat. The main goal of this study was to provide a quantitative estimate of MBLs producing clinical P. aeruginosa isolates among the Nepalese patients and determine if MBL correlates with multi-drug resistance (MDR). Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guideline was followed for meta-analysis of relevant literature using PubMed, Research4Life, and Google Scholar. The prevalence of MBLs in P. aeruginosa from clinical samples was determined using R 4.1.2 for data pooled from studies published until 2021. The meta-analysis of a total of 19 studies selected (of 6038 studies for which titles and abstracts were reviewed) revealed the prevalence of MBLs producing P. aeruginosa (MBL-PA) was 14 % (95 % CI: 0.10-0.19) while MDR isolates among P. aeruginosa was 42 % (95 % CI: 0.30-0.55) in Nepal. Combined Disc Test was predominantly used phenotypic method for confirming MBLs phenotypes among the studies. Sputum was the most common specimen from which MBL-PA was recovered. A significant positive correlation was observed between MDR and MBL production in P. aeruginosa. We conclude that MBL producing strains are widespread among the clinical isolates of P. aeruginosa in Nepal and responsible for emerging MDR strains. It is paramount that antibiotics prescription against the bacterium should be monitored closely and alternative therapeutic modalities against MBL-PA explored.

Understanding COVID-19 Situation in Nepal and Implications for SARS-CoV-2 Transmission and Management.

Background: The pandemic of Coronavirus Disease 2019 (COVID-19), one of the most infectious diseases in the modern history, is caused by Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) and has had a profound health and economic toll, globally. This paper identifies the overall health status associated with COVID-19 pandemic in all 7 provinces of Nepal, a developing country in South Asia, analyzing data from January 2020 to February 2022. It focuses on the SARS-CoV-2 prevalence, transmission through wastewater and other routes, diagnostics, treatment options, and alternative medicines, thereby offering key perspectives for its management. Materials and Methods: Studies regarding coronavirus spanning the 2017 to 2022 period were searched on the web, Nepalese database, and Web of Science. Refined criteria included SARS-CoV-2 in wastewater of Nepal or worldwide. Demographic data (sex, age-group, and geographic location) were also obtained from websites and relevant reports of the Ministry of Health and Population (MOHP) of Nepal, ranging from January 2020 to February 2022. Moreover, trends concerning lockdown, business, and border activities in Nepal between February 2020 and October 2020 were evaluated. The viral dissemination pathways, diagnosis, and available treatment options, including the Ayurvedic medicine, were also examined. Results: Aerosols generated during the hospital, industrial, recreational, and household activities were found to contribute to the propagation of SARS-CoV-2 into environmental wastewater, thereby putting the surrounding communities at risk of infection. When lockdown ended and businesses opened in October 2020, the number of active cases of COVID-19 increased exponentially. Bagmati Province had the highest number of cases (53.84%), while the remaining 6 provinces tallied 46.16%. Kathmandu district had the highest number of COVID-19 cases (138, 319 cases), while Manang district had the smallest number of infections (81 cases). The male population was found to be predominantly infected (58.7%). The most affected age groups were the 31 to 40 years old males (25.92%) and the 21 to 30 years old females (26.85%). Conclusion: The pandemic impacted the public health and economic growth in our study duration. SARS-CoV-2 was prevalent in the wastewater of Nepal. The Terai districts and the megacities were mostly affected by SARS-CoV-2 infections. Working-age groups and males were identified as the highest risk groups. More investigations on the therapeutic and alternative cures are recommended. These findings may guide the researchers and professionals with handling the COVID-19 challenges in developing countries such as Nepal and better prepare for future pandemics.

Per- and polyfluoroalkyl substances in water and wastewater: A critical review of their global occurrence and distribution.

Per- and polyfluoroalkyl substances (PFAS) are a family of fluorinated organic compounds of anthropogenic origin. Due to their unique chemical properties, widespread production, environmental distribution, long-term persistence, bioaccumulative potential, and associated risks for human health, PFAS have been classified as persistent organic pollutants of significant concern. Scientific evidence from the last several decades suggests that their widespread occurrence in the environment correlates with adverse effects on human health and ecology. The presence of PFAS in the aquatic environment demonstrates a close link between the anthroposphere and the hydrological cycle, and concentrations of PFAS in surface and groundwater range in value along the ng L-1-µg L-1 scale. Here, we critically reviewed the research published in the last decade on the global occurrence and distribution of PFAS in the aquatic environment. Ours is the first paper to critically evaluate the occurrence of PFAS at the continental scale and the evolving global regulatory responses to manage and mitigate the adverse human health risks posed by PFAS. The review reports that PFAS are widespread despite being phased out-they have been detected in different continents irrespective of the level of industrial development. Their occurrence far from the potential sources suggests that long-range atmospheric transport is an important pathway of PFAS distribution. Recently, several studies have investigated the health impacts of PFAS exposure-they have been detected in biota, drinking water, food, air, and human serum. In response to the emerging information about PFAS toxicity, several countries have provided administrative guidelines for PFAS in water, including Canada, the United Kingdom, Sweden, Norway, Germany, and Australia. In the US, additional regulatory measures are under consideration. Further, many PFAS have now been listed as persistent organic pollutants. This comprehensive review provides crucial baseline information on the global occurrence, distribution, and regulatory framework of PFAS.

Nanomaterials in the environment, human exposure pathway, and health effects: A review.

Nanomaterials (NMs), both natural and synthetic, are produced, transformed, and exported into our environment daily. Natural NMs annual flux to the environment is around 97% of the total and is significantly higher than synthetic NMs. However, synthetic NMs are considered to have a detrimental effect on the environment. The extensive usage of synthetic NMs in different fields, including chemical, engineering, electronics, and medicine, makes them susceptible to be discharged into the atmosphere, various water sources, soil, and landfill waste. As ever-larger quantities of NMs end up in our environment and start interacting with the biota, it is crucial to understand their behavior under various environmental conditions, their exposure pathway, and their health effects on human beings. This review paper comprises a large portion of the latest research on NMs and the environment. The article describes the natural and synthetic NMs, covering both incidental and engineered NMs and their behavior in the natural environment. The review includes a brief discussion on sampling strategies and various analytical tools to study NMs in complex environmental matrices. The interaction of NMs in natural environments and their pathway to human exposure has been summarized. The potential of NMs to impact human health has been elaborated. The nanotoxicological effect of NMs based on their inherent properties concerning to human health is also reviewed. The knowledge gaps and future research needs on NMs are reported. The findings in this paper will be a resource for researchers working on NMs all over the world to understand better the challenges associated with NMs in the natural environment and their human health effects.

Groundwater pollution: Occurrence, detection, and remediation of organic and inorganic pollutants.

Groundwater pollution is a result of natural and anthropogenic activities. While the elevated levels of various inorganic constituents could be attributed to natural processes, such as geological weathering and aquifer characteristics, many times, anthropogenic activities also substantially pollute the groundwater. On the contrary, the occurrence of organic pollutants is primarily due to various anthropogenic activities. Extensive groundwater mining, the hydraulic connection between groundwater and other surface water bodies, and leaking underground buried infrastructure also contribute to groundwater pollution. Water resources are scarce commodities, and preserving groundwater quality is of critical concern. This paper documents instances of groundwater quality impact during the year 2019 due to both natural and anthropogenic activities throughout the world. PRACTITIONER POINTS: Groundwater pollution problems reported during the year 2019 are reviewed and documented. Occurrence of organic, inorganic, and microbial pollutants in groundwater is reported. Remediation technologies for selected inorganic pollutants are reviewed and documented.

Novel carbon nanotube (CNT)-based ultrasensitive sensors for trace mercury(II) detection in water: A review.

Infamous for "Mad hatter syndrome" and "Minamata disease", mercury (Hg) is ranked high on the Agency for Toxic Substances and Disease Registry's priority list of hazardous substances for its potent neurologic, renal, and developmental toxicities. Most typical exposures are via contaminated water and food. Although regulations and advisories are exercised at various levels, Hg pollution from both natural and anthropogenic sources has remained a major public health and safety concern. Rapid detection of solvated aqueous Hg2+ ions at low levels is critical for immediate response and protection of those who are vulnerable (young children, pregnant and breast-feeding women) to acute and chronic exposures to Hg2+. Various types of sensors capable of detecting Hg in water have been developed. In particular, the novel use of engineered carbon nanotubes (CNTs) has garnered attention due to their specificity and sensitivity towards Hg2+ detection in solution. In this focused review, we describe the sensitivity, selectivity and mechanisms of Hg2+ ion sensing at trace levels by employing CNT-based various sensor designs, and appraise the open literature on the currently applied and "proof-of-concept" methods. Five different types of CNT-based sensor systems are described: potentiometric, DNA-based fluorescence, surface plasmon resonance (SPR), colorimetric, and stripping voltammetric assays. In addition, the recognized merits and shortcomings for each type of electrochemical sensors are discussed. The knowledge from this succinct review shall guide the development of the next generation CNT-based biochemical sensors for rapid Hg2+ detection in the environment, which is a significant first step towards human health risk analysis of this legacy toxicant.

Chemometrics in assessment of seasonal variation of water quality in fresh water systems.

The chemometric techniques were applied for evaluation of the seasonal variation of water qualities at 17 stations along a stretch of the Bagmati river of Nepal for 23 water quality parameters measured during 1999-2003. The application of discriminant analysis confirmed the classification of the water quality measurements into three seasons: pre-monsoon, monsoon, and post-monsoon affording 93.8% correct classification. Factor analysis and box-whisker plots facilitated to investigate the seasonal variation of water quality and the pattern of pollution sources. Application of FA revealed that the influence of water quality parameters changes from season to season. A parameter that is most important in contributing to water quality variation for one season may not be important for another season. Comparison of the discriminant analysis and factor analysis helped to identify the most important water quality parameters, as water temperature, DO, EC, COD, CL, Ca, alkalinity, PO(4)P, and TP, that are most important for seasonal variation and play a significant role in establishment of water quality control strategy.

Adsorption of humic acid onto nanoscale zerovalent iron and its effect on arsenic removal.

Batch experiments were performed to investigate the feasibility of humic acid (HA) removal by synthetic nanoscale zerovalent iron (NZVI) and its interaction with As(III) and As(V), the most poisonous and abundant of groundwater pollutants. High-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD) were used to characterize the particle size, surface morphology of the pristine NZVI and HA-treated NZVI (NZVI-HA), and the zero valence state of the pristine NZVI. It was determined that HA was completely removed by NZVI (0.3 g/L) within a few minutes, at a wide range of initial pH values (approximately 3.0-12.0). Fourier transform infrared (FTIR) and laser light scattering (zeta potential measurement) studies confirmed that NZVI-HA forms inner-sphere surface complexation at different initial pH conditions. The effects of competing anions showed that there was complete removal of HA in the presence of 10 mM NO(-3) and SO4(2-) whereas HA removal was observed 0%, 18% and 22% in presence of 10 mM H2PO4(2-), HCO(3-) and H4SiO4(0), respectively. However, the presence of 2 mM CA2+ and Mg2+ enhanced HA removal from 17 mg g(-1) to 76 mg g(-1) and 55 mg g(-1), respectively. Long-term time-resolved studies of XRD and field emission scanning electron microscopy (FE-SEM) with energy-dispersive X-ray (EDX) revealed the formation of various types of new iron oxides (magnetite, maghemite, and lepidocrocites) during the continuous reaction of HA in the presence of water and NZVI at 1, 30, 60, and 90 days. In addition, the surface-area-normalized rate constant (ksa) of adsorption of As(III) and As(V) onto NZVI was reduced in the presence of HA (20 mg L(-1)), from 100% to 43% and 68%, respectively. Our results show the potential use of NZVI in removing HA and its possible effects on arsenic removal during the application of NZVI in groundwater remediation.

Application of QUAL2Kw for water quality modeling and dissolved oxygen control in the river Bagmati.

A stream water quality model, QUAL2Kw, was calibrated and validated for the river Bagmati of Nepal. The model represented the field data quite well with some exceptions. The influences of various water quality management strategies have on DO concentrations were examined considering: (i) pollution loads modification; (ii) flow augmentation; (iii) local oxygenation. The study showed the local oxygenation is effective in raising DO levels. The combination of wastewater modification, flow augmentation and local oxygenation is necessary to ensure minimum DO concentrations. This reasonable modeling guarantees the use of QUAL2Kw for future river water quality policy options.