Search

A new conceptual model for supramolecular aggregation of natural organic matter (OM) is proposed. Scientific awareness of OM as natural hydrogels is slowly increasing although in the literature they are primarily categorized as physical hydrogels stabilized only by weak interactions. The supramolecular view of OM is here expanded, based on insight from comprehensive hydrogen bond theory, to include three-center–four-electron near-covalent linkages and introduce a new category of metachemical hydrogels that are neither chemical nor physical hydrogels. Hydrogels are typically classified into chemical (permanent, covalently bonded) or physical (reversible, ionic, hydrophobic, or hydrogen bonded) classes based on crosslinking. However, augmented by contemporary advances in hydrogen bonding theory purporting that not all hydrogen bonds are weak and that some hydrogen bonding motifs result in moderate and strong interactions, the popular supramolecular view of OM is extended to include all types of hydrogen bonds. We propose a new category of hydrogels exists—metachemical hydrogels—as a fundamental component of OM. Strong, near covalent, equally shared hydrogel cross-linkages in the metachemical hydrogel can outcompete water. Here, metachemical (≤1 μm diameter) and physical (>1 μm diameter) hydrogels are described as two primary forms of aggregates observed for OM in a hierarchical 'supramolecular within supramolecular' self-assembling architecture with new information about shear. The metachemical hydrogels are postulated to be encapsulated within a dispersible physical hydrogel scaffold which can form, dissipate, and spontaneously re-form over turbulent/quiescent cycles indicating reversible abiotic self-assembly. The significance of this investigation is to understand the form OM evolved in nature to provide essential functions. The potential for strong intermolecular forces to form a metachemical hydrogel in OM and the concept of a dynamic dual metachemical/physical hydrogel structure was not previously introduced. The metachemical hydrogel construct should inform hydrogen bonded systems in other chemical and biochemical disciplines. Unlabelled Image • The prevailing supramolecular view of OM aggregates is expanded. • A new definition—metachemical hydrogel—is introduced. • Weak, moderate, and strong hydrogen bonds participate in OM self-assembly. • Metachemical and physical hydrogels create hierarchical OM aggregates. • A 'supramolecular within supramolecular' OM architecture is proposed. [ABSTRACT FROM AUTHOR]

Humic substances (HSs) are precursors for the formation of hazardous disinfection by-products (DBPs) during chlorination of water. Various surrogate parameters have been used to investigate the generation of DBPs by HS precursors and the removal of these precursors by activated carbon treatment. Dissolved organic carbon (DOC)- and ultraviolet absorbance (UVA 254 )-based isotherms are commonly reported and presumed to be good predictors of the trihalomethane formation potential (THMFP). However, THMFP-based isotherms are rarely published such that the three types of parameters have not been compared directly. Batch equilibrium experiments on activated carbon were used to generate constant-initial-concentration sorption isotherms for well-characterized samples obtained from the International Humic Substances Society (IHSS). HSs representing type (fulvic acid [FA], humic acid [HA]), origin (aquatic, terrestrial), and geographical source (Nordic, Suwannee, Peat, Soil) were examined at pH 6 and pH 9. THMFP-based isotherms were generated and compared to determine if DOC- and UVA 254 -based isotherms were good predictors of the THMFP. The sorption process depended on the composition of the HSs and the chemical nature of the activated carbon, both of which were influenced by pH. Activated carbon removal of THM-precursors was pH- and HS-dependent. In some instances, the THMFP existed after UVA 254 was depleted. [ABSTRACT FROM AUTHOR]

Abstract: A pilot study for the qualitative detection of methamphetamine at sites within a sewage collection system adjacent to locations suspected to harbor illegal drug activities was investigated and preliminary findings are reported. Sewage samples were collected over a time interval of four weeks using a Polar Organic Chemical Integrative Sampler (POCIS) deployed directly into the sewer line. The POCIS sorbent was extracted and analyzed via high-performance liquid chromatography tandem mass spectrometry (HPLC–MS/MS). Methamphetamine was found in sewage from one of three sampling sites at a concentration greater than the HPLC–MS/MS method detection limit (MDL) of 3ng/mL. The goal of this research was to establish proof-of-concept of the feasibility for sampling and analysis using POCIS devices in the sewage collection system. The data encourage further testing and research. The ability to pinpoint the presence of methamphetamine in the sewer may in the future be used as a forensic tool in law enforcement. [Copyright &y& Elsevier]

Advanced tracking technologies have facilitated the tracking of tourists' movement with high levels of spatial resolution, allowing for the exploration of factors that influence dispersal. However, the degree to which different analytical indices impact the results that they generate, remains under-researched. This study uses a high tempo-spatial resolution data set of location tracking information that was collected in the island state of Tasmania, Australia, using a mobile phone research application. It compares the results that emerge when four different analytical indicators are used to quantify tourist dispersal. The results improve understandings of the role that analytical indicators play in assessing dispersal, along with the underlying factors that influence tourists' dispersal at the state scale. • This study uses a unique high tempo-spatial resolution dataset, using a mobile phone application. • This study assesses how different analytical tools influence the emergence of dispersal factors. • The study assesses the underlying factors that influence tourists' dispersal at the state scale. [ABSTRACT FROM AUTHOR]

The aggregation of humic substances and their interaction with filtration media (membranes, soils) has implications for our understanding of membrane fouling during water treatment, the facilitated transport of contaminants, and the transport of organic matter through the microbial loop. To investigate the aggregation of fulvic and humic acids in low electrolytic conductivity solutions, laboratory studies of simulated environmental water samples as well as actual environmental water samples were examined. Intensity-, volume-, and number-based particle size distributions (PSDs) were obtained by dynamic light scattering. Aggregates were categorized into three ranges, i.e., 10–100 nm, 100–1000 nm, and > 1 μm. Individual biomacromolecules and the aggregates between 10 nm and 1 μm were presumed to be precursors for the formation of a large 5-μm-sized-particle. The self-assembly of the large-in-volume, few-in-number, 5-μm-sized particle was observed in real-time and occurred in unfiltered samples and in samples filtered (0.45 μm) at a nominal size one order of magnitude smaller. The supramicrometer-sized particle formed, dissipated, and spontaneously re-formed over turbulent/quiescent cycles in the presence of sodium azide indicating reversible abiotic self-assembly. Zeta potential analyses demonstrated that colloidal stability increased as concentration increased. DLS studies of the environmental water samples were comparable to those of the simulated laboratory samples. The operational range of the instrumentation used in these experiments was 0.6 nm–6 μm; therefore, aggregates larger than 6 μm may exist in these solutions. [ABSTRACT FROM AUTHOR]