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The widespread distribution of plastic debris in riverine environment is one of the major concerns of environmental pollution because of its potential impact on the aquatic ecosystem. In this study, we investigated the accumulation of metal(loid)s on polystyrene foam (PSF) plastics collected from the floodplain of the Tuul River of Mongolia. The metal(loid)s sorbed on plastics were extracted from the collected PSF via sonication after peroxide oxidation. The size-dependent association of metal(loid)s with plastics indicates that PSFs act as vectors for pollutants in the urban river environment. The mean concentrations of metal(loid)s (i.e., B, Cr, Cu, Na, and Pb) indicate a higher accumulation of the metal(loid)s on meso-sized PSFs compared with macro- and micro-sized PSFs. In addition, the images from scanning electron microscopy (SEM) indicated not only the degraded surface of plastics showing fractures, holes, and pits but also the adhered mineral particles and microorganisms on the PSFs. The interaction of metal(loid)s with plastics was probably facilitated by the physical and chemical properties of altered surface of plastics through photodegradation, followed by an increase in surface area by size reduction and/or biofilm development in the aquatic environment. The enrichment ratio (ER) of metals on PSF samples suggested the continuous accumulation of heavy metals on plastics. Our results demonstrate that the widespread plastic debris could be a carrier of hazardous chemicals in the environment. Considering that the negative impacts of plastic debris on environmental health are major concerns to be addressed, the fate and behavior of the plastics especially their interaction with pollutants in aquatic environments should be further studied. [Display omitted] • Relatively high concentrations of metal(loid)s were detected in meso-sized PSFs. • Adhered mineral particles and microorganisms were detected on PSFs. • Metals were quantified for extracts through digestion of field-collected PSFs. • Interaction between PSF and metal(loid)s could be dominated by surface complexation. [ABSTRACT FROM AUTHOR]

The physicochemical properties of oyster shell-derived adsorbents prepared by calcination at different temperatures were characterized by elemental analysis, specific surface area, particle size distribution, X-ray diffraction, and scanning electron microscopy. The pH value in natural oyster shell increased from 9 to 12.7 following calcination above 750 °C. All of the oyster shell-derived adsorbents exhibited a BET surface area that ranged from 1.8 to 64.6 m 2 /g. Clearly, the proportion of particles within the ranges 25–50 μm and 50–100 μm increased after calcination, regardless of calcination temperature. The adsorption equilibrium and kinetics of cadmium (Cd) were investigated, and the mechanisms of sorption discussed. Experimental equilibrium data were fitted to a Langmuir adsorption isotherm model. Most Cd adsorption occurred during the initial hours of contact time, and a pseudo-second-order kinetic model best fitted the adsorption process. Cd sorption profiles indicated an initial, low Cd sorption region (25.25–32.36 mg/g) that was associated with calcination temperatures of up to 650 °C for 2 h, and a second region that contributed to high Cd sorption from 750 °C, with the maximum sorption capacity reaching a value of 1666.67 mg/g at 900 °C. The high Cd-removal capacity of oyster shell-derived adsorbents above 750 °C is attributed to their enhanced specific surface area, their material porosity, the bulk precipitation of Cd hydroxide and otavite on shell fragments, the formation of ettringite as a secondary precipitate, and ion exchange via Ca ions. This study highlights the effectiveness of calcined oyster shells in Cd removal from highly contaminated water and wastewater. [ABSTRACT FROM AUTHOR]

Microplastic (MP) surfaces are common sites for microbial colonization and promote biofilm formation in aquatic environments, resulting in changes to the surface properties of MPs and their interaction with pollutants. Although the diversity of microbial communities adhering to MPs has been well documented in aquatic environments, surface changes in MPs due to microbial colonization are still poorly understood. In this study, we aimed to evaluate the variations in the chemical structure and components of biofilms on the surface of polystyrene microplastics (PS-MPs) collected from the shore of the Tuul River in Mongolia, using micro-Fourier transform infrared (micro-FTIR) spectroscopy. We applied a spectral subtraction approach, and the differences in spectra between peroxide-treated and untreated PS-MP particles enabled us to obtain the structural features of biofilms that developed on the plastic surface. In addition, the surface photooxidation status of the sampled PS-MPs was calculated from the subtracted spectra of peroxide-treated and pristine PS-MPs. Various functional groups of N-containing organic substances from bacterial and fungal communities were detected in the obtained biofilm spectra. Based on the spectral characteristics, biofilm spectra were classified into four groups by applying principal component analysis (PCA). A wide range of carbonyl indices (CIs: 0.00–1.40) was found in the subtracted spectra between peroxide-treated and pristine PS-MPs, revealing that different levels of surface oxidation progressed by physical influences such as solar radiation and freeze-thaw cycles. Furthermore, lignocellulose and silicate were found on the PS-MP surface as allochthonous attachments. Considering the variation in residence time of PS-MPs, they attract plant residues and mineral particles through the development of biofilms and travel together in the river environment. Given that the dynamic behavior of MPs can be greatly affected by changes in their surfaces, further studies are needed to emphasize their link to organic matter dynamics. • The MP-associated biofilms were evaluated by using IR spectral features. • Biofilm development characterizes the surface status of PS-MPs. • Differentiation of biofilm spectra was successfully carried out by PCA. • A wide range of CIs demonstrate the alteration of surface properties of MPs. • Hetero-aggregates of PS-MPs were found with organic and inorganic particles. [ABSTRACT FROM AUTHOR]

Abstract: Ultrafiltration fractions of three soil humic acids were characterized by viscometry and high performance size-exclusion chromatography (HPSEC) in order to estimate shapes and hydrodynamic sizes. Intrinsic viscosities under given solute/solvent/temperature conditions were obtained by extrapolating the concentration dependence of reduced viscosities to zero concentration. Molecular mass (weight average molecular weight () and number average molecular weight ()) and hydrodynamic radius () were determined by HPSEC using pullulan as calibrant. Values of and ranged from 15 to and from 9 to (g mol-1), respectively. Polydispersity, as indicated by , increased with increasing filter size from 1.5 to 2.4. The hydrodynamic radii () ranged between 2.2 and 6.4 nm. For each humic acid, and [η] were related. Mark–Houwink coefficients calculated on the basis of the relationships suggested restricted flexible chains for two of the humic acids and a branched structure for the third humic acid. Those structures probably behave as hydrated sphere colloids in a good solvent. Hydrodynamic radii of fractions calculated from [η] using Einstein''s equation, which is applicable to hydrated sphere colloids, ranged from 2.2 to 7.1 nm. These dimensions are fit to the size of nanospaces on and between clay minerals and micropores in soil particle aggregates. On the other hand, the good agreement of values obtained by applying Einstein''s equation with those directly determined by HPSEC suggests that pullulan is a suitable calibrant for estimation of molecular mass and size of humic acids by HPSEC. [Copyright &y& Elsevier]