Photooxidation/adsorption of arsenic (III) in aqueous solution over bentonite/ chitosan/TiO2 heterostructured catalyst

Arsenic in drinking water: overview of removal strategies and role of chitosan biosorbent for its remediation

Accessibility to clean drinking water often remains a crucial task at times. Among other water pollutants, arsenic is considered a more lethal contaminant and has become a serious threat to human life globally. This review discussed the sources, chemistry, distribution, and toxicity of arsenic and various conventional technologies that are in option for its removal from the water system. Nowadays, biosorbents are considered the best option for arsenic-contaminated water treatment. We have mainly focused on the need and potential of biosorbents especially the role of chitosan-based composites for arsenic removal. The chitosan-based sorbents are economically more efficient in terms of their, low toxicity, cost-effectiveness, biodegradability, eco-friendly nature, and reusability. The role of various modification techniques, such as physical and chemical, has also been evaluated to improve the physicochemical properties of biosorbent. The importance of adsorption kinetic and isotherm models and the role of solution pH and pH_PZC for arsenic uptake from the polluted water have also been investigated. Some other potential applications of chitosan-based biosorbents have also been discussed along with its sustainability aspect. Finally, some suggestions have been highlighted for further improvements in this field.

The ZrO2 NPs enhanced the risk of arsenate by promoting its accumulation and reducing its detoxification during food chain transfer from Daphnia magna to zebrafish

Arsenic (As) can co-occur with zirconium dioxide nanoparticles (ZrO₂ NPs) in aquatic environments, but their combined influence along the aquatic food chain is barely explored. This study constructed water flea Daphnia magna - zebrafish Danio rerio to evaluate the impact of ZrO₂ NPs on the accumulation, trophic transfer, transformation, and detoxification of arsenate (As(V)). The zebrafish were fed D. magna exposed to As(V), ZrO₂ NPs, or As(V) + ZrO₂ NPs for 20 d. Results demonstrated that ZrO₂ NPs significantly facilitated total As and As(V) sorption in D. magna and in tissues of zebrafish. ZrO₂ NPs enhanced the transformation of inorganic arsenic (iAs) to monomethylated acid (MMA), while decreased synthesis of arsenobetaine (AsB) in tissues, leading to iAs increased. Co-exposed As(V) and ZrO₂ NPs facilitated upregulation of absorption-related genes (aqp7) and As biotransformation-related genes (gst, gss), and detoxification and oxidative stress-related genes (mt2, cat, sod1 and sod2). Therefore, genetic expression coupling with biotransformation for the first time demonstrated that As(V) combined with ZrO₂ NPs led to increased harm to D. magna and zebrafish and amplified the ecological risks of As(V) along the aquatic food chain. Attention should be paid to the combined toxicity of As(V) and ZrO₂ NPs in aquatic environment.

Arsenic removal approaches: A focus on chitosan biosorption to conserve the water sources

Globally, millions of people have no access to clean drinking water and are either striving for that or oppressed to intake polluted water. Arsenic is considered one of the most hazardous contaminants in water bodies that reaches there due to various natural and anthropogenic activities. Modified chitosan has gained much attention from researchers due to its potential for arsenic removal. This review focuses on the need and potential of chitosan-based biosorbents for arsenic removal from water systems. Chitosan is a low-cost, abundant, biodegradable biopolymer that possesses unique structural aspects and functional sites for the adsorption of contaminants like arsenic species from contaminated water. The chitosan-based biosorbents had also been modified using various techniques to enhance their arsenic removal efficiencies. This article reviews various forms of chitosan and parameters involved in chitosan modification which eventually affect the arsenic removal efficiency of the resultant sorbents. The literature revealed that the modified chitosan-based sorbents could express higher adsorption efficiency compared to those prepared from native chitosan. The sustainability of the chitosan-based sorbents has also been considered in terms of reusability. Finally, some recommendations have been underlined for further improvements in this domain.

The Electrophysiological Correlates of Phoneme Perception in Primary Progressive Aphasia: A Preliminary Case Series

Aims: This study aimed to investigate phoneme perception in patients with primary progressive aphasia (PPA) by using the event-related potential (ERP) technique. These ERP components might contribute to the diagnostic process of PPA and its clinical variants (NFV: nonfluent variant, SV: semantic variant, LV: logopenic variant) and reveal insights about phoneme perception processes in these patients.

Method: Phoneme discrimination and categorization processes were investigated by the mismatch negativity (MMN) and P300 in eight persons with early- and late-stage PPA (3 NFV, 2 LV, 2 SV, and 1 PPA-NOS; not otherwise specified) and 30 age-matched healthy adults. The mean amplitude, the onset latency, and the topographic distribution of both components in each patient were compared to the results of the control group.

Results: The MMN was absent or the onset latency of the MMN was delayed in the patients with the NFV, LV, and PPA-NOS in comparison to the control group. In contrast, no differences in mean amplitudes and onset latencies of the MMN were found between the patients with the SV and the control group. Concerning the P300, variable results were found in the patients with the NFV, SV, and PPA-NOS, but the P300 of both patients with the LV was delayed and prolonged with increased mean amplitude in comparison to the control group.

Conclusion: In this preliminary study, phoneme discrimination deficits were found in the patients with the NFV and LV, and variable deficits in phoneme categorization processes were found in all patients with PPA. In clinical practice, the MMN might be valuable to differentiate the SV from the NFV and the LV and the P300 to differentiate the LV from the NFV and the SV. Further research in larger and independent patient groups is required to investigate the applicability of these components in the diagnostic process and to determine the nature of these speech perception deficits in the clinical variants of PPA.