Uncovering the characteristics of plastic-associated biofilm from the inland river system of Mongolia.

The occurrence and characteristics of plastic debris in aquatic and terrestrial environments have been extensively studied. However, limited information exists on the properties and dynamic behavior of plastic-associated biofilms in the environment. In this study, we collected plastic samples from an inland river system in Mongolia and extracted biofilms to uncover their characteristics using spectroscopic, isotopic, and thermogravimetric techniques. Mixtures of organic and mineral particles were detected in the extracted biofilms, revealing plastic as a carrier for exogenous substances, including contaminants, in the river ecosystem. Thermogravimetric analysis (TGA) indicated the predominant contribution of minerals primarily comprising aluminosilicate and calcite, representing approximately 80 wt% of the biofilms. Differential thermal analysis (DTA) coupled with Fourier transform infrared (FTIR) spectrometry operated at 25°C-600 °C enabled the detection of gaseous decomposition products, such as CO2, H2O, CO, and functional groups (O-H, C-H, C-O, CO, CC, and C-C), released from biopolymers in the extracted biofilms. Dehydration, dehydroxylation, and decarboxylation reactions explain the thermal properties of biofilms. The stable carbon (δ13C) and nitrogen (δ15N) isotope ratios of the biofilms demonstrated variable signatures ranging from -24.1‰ to -27.0‰ and 3.1‰-12.3‰, respectively. A significant difference in the δ13C value (p < 0.05) among the upstream, middle, and downstream research sites could be characterized by available organic carbon sources in the river environment, depending on the research sites. This study provides insights into the characteristics and environmental behavior of biofilms which are useful to elucidate the impact of plastic-associated biofilms on organic matter and material cycling in aquatic ecosystems.

Pb(II) Adsorption of Composite Alginate Beads Containing Mesoporous Natural Zeolite.

Natural zeolite beads were prepared by encapsulating mesoporous zeolite into alginate beads via egg box method and its adsorption properties of Pb(II) ions were investigated in aqueous solution. Crystallinity and size reduction of natural zeolite were enhanced by mechanic modification of the ball milling process. FTIR and SEM-EDS analyses confirmed that mechanically modified zeolite particles were incorporated into alginate hydrogel. The highest adsorption amount of zeolite alginate beads was 87.47 mg/g after 20 h adsorption process. SEM-EDS result confirmed that the adsorption process has occurred on the surface of zeolite alginate beads. Adsorption kinetic data were fitted with Langmuir adsorption isotherm which showed that Pb2+ cation adsorbed into monolayers of adsorbent material. Moreover, we observed that calcium ion released after the Pb2+ adsorption process in the feed solution. Therefore, the adsorption mechanism of zeolite alginate beads explained by complex mechanisms including surface sorption and ion exchange of Pb2+ and Ca2+ in beads.