Hiroshi Hasegawa

Molecular interactions governing viscosity non-ideality in ACN–tertiary alkanolamine mixtures were investigated across the full composition range at 303.15–323.15 K.

Freshwater salinization is an emerging environmental stressor that significantly influences aquatic contaminant cycling; however, its impact on phytoplankton-mediated arsenic (As) biotransformation remains poorly understood. This study investigates how salinity-driven physiological responses regulate arsenate (As(V)) uptake and speciation in three freshwater phytoplankton species (Scenedesmus acutus, Pediastrum duplex, and Staurastrum paradoxum) across a controlled salinity gradient (0–10‰). Cellular responses were evaluated through growth kinetics, photosynthetic efficiency (Y(II)), intracellular electrolyte composition, and antioxidant (thiol and pigment) biosynthesis. Furthermore, single-cell inductively coupled plasma mass spectrometry (SC-ICP-MS) and speciation analyses were employed to quantify intracellular As metabolism. The results reveal that in the salt-sensitive species (P. duplex and S. paradoxum), elevated salinity induced substantial inorganic ion influx and subsequent generation of reactive oxygen species (ROS). This stress activated glutathione (GSH)-based antioxidant defenses but concurrently suppressed As methylation, indicating a metabolic trade-off between oxidative stress mitigation and As biotransformation. Conversely, the salt-tolerant S. acutus maintained tight ionic homeostasis and upregulated carotenoid-based photoprotection. This adaptation preserved photosynthetic efficiency and facilitated the sustained conversion of inorganic As into less toxic, higher-order organic species despite osmotic stress. The findings demonstrate that species-specific osmotic and redox regulation mechanisms dictate As cycling under saline stress, highlighting a critical link between progressive freshwater salinization and altered contaminant bioaccumulation in aquatic ecosystems.

A thiuram disulfide–modified cellulose adsorbent (TDMC) was developed for the highly selective recovery of silver ions from aqueous solutions. The adsorbent was synthesized by introducing thiuram disulfide functional groups onto a cellulose backbone to selectively adsorb Ag(I). Batch adsorption experiments were conducted to evaluate the adsorption performance and selectivity under various conditions. The maximum adsorption capacity of TDMC for Ag(I), estimated from the Langmuir model, was 3.61 mmol g⁻¹ at pH 1.0. Remarkably, TDMC exhibited outstanding selectivity toward Ag(I) even in the presence of high concentrations of competing metal ions. When Ag(I) coexisted with Cu(II), Pb(II), Zn(II), Ni(II), Ca(II), K(I), Mg(II), and Na(I) at 2000-fold higher total concentrations, the adsorption percentage of Ag(I) remained 99.0%, comparable to that under single-metal conditions, whereas those of other ions were below 2.5%. X-ray photoelectron spectroscopy revealed that adsorbed Ag atoms were bonded to sulfur atoms of the thiuram disulfide groups. Furthermore, fast atom bombardment mass spectrometry was performed on a low-molecular-weight thiuram–Ag(I) complex that exhibits spectroscopic features similar to those of Ag–TDMC, allowing us to determine the molecular weight and structural characteristics of the complex. These findings demonstrate that TDMC possesses an exceptional ability to selectively capture Ag(I) through specific Ag–S coordination, providing a simple and efficient approach for silver recovery.

Platinum (Pt), extensively used in automotive catalytic converters and anti-cancer drugs, has led to elevated concentrations in the environment. Monitoring Pt levels in coastal ecosystems is crucial as excessive accumulation may cause ecotoxicological impacts. In this study, Undaria pinnatifida, a common edible macroalgae in Japan known for its high affinity for platinum group elements, was evaluated as a biomonitor for monitoring Pt concentrations and assessing its anthropogenic influences in coastal areas. An analytical protocol using inductively coupled plasma mass spectrometry (ICP-MS) was developed and optimized for Pt quantification in macroalgal tissues. The optimal digestion conditions included 0.24 mL/g of hydrofluoric acid and the addition of 7 mL/g of hydrochloric acid, which effectively reduced white precipitate formation and improved Pt recovery. The established method demonstrated excellent sensitivity, achieving a method blank of 16 ppt and a detection limit of 5 ppt, surpassing previously reported approaches. Applying this optimized protocol, tissue-specific Pt concentrations were determined in different parts of U. pinnatifida collected from various coastal zones. The results revealed significant spatial variations in Pt concentrations among plant organs: concentrations in blades, stipes, and sporophylls decreased from the outer bay to the inner bay, while holdfasts concentrations exhibited the opposite trend. These findings suggest distinct Pt accumulation behaviors between above-ground and below-ground tissues of U. pinnatifida, underscoring its potential for monitoring spatial variations of Pt in coastal environments. Graphical abstract