Abundance of microplastics in sediments from the urban river in Mongolia

Microplastics (MPs) are ubiquitous pollutants of the aquatic environment; however, the behavior of these materials in freshwater environments is largely unknown. The present study aimed to identify types of MPs and quantify their concentration in the river bottom sediment in the Tuul River, northern central part of Mongolia. The goal was also to analyze and evaluate the behavior of MPs. Six sampling plots were chosen as the research objectives, which were close to the junctions between tributaries and the main river of Tuul in the capital of Mongolia,Ulaanbaatar. All sediment samples contained MPs with an average concentration of 603±251 items kg−1. The major morphotype was synthetic fibers, which originated from polyester and polyamide polymers. While the size of MPs ranged between 28.4 µm and 3409.1 µm, most of these materials varied between 100 and 200 µm. Furthermore, the finer the particle sizes of sediments, the higher the number of detected MPs. Distribution of the MPs in the study area indicates that the point-source of MPs such as wastewater treatment plant strongly affects their concentration. However, domestic wastes (i.e., plastic litter) impact the distribution of MPs as non-point sources

Occurrence of arsenic in the riverbed sediments of the Selenga river system

Over the past few decades, anthropogenic activities have concentrated in the transboundary Selenga River basin, especially in the two-thirds of it located in the Mongolian territory. In this study, we measure the concentration of arsenic (As) in riverbed sediments and the mobilization and accumulation of this metalloid in sediments of the Selenga River system. Higher concentrations of As were detected in the sediments collected from the Orkhon River system than those from downstream of Selenga River in Russia. The observed difference indicates that the Orkhon River watershed is highly affected by anthropogenic activities involving soil excavation. In particular, high concentrations of As (3.6-4.9 mg kg^), in comparison with the average for the entire Selenga River system (2.8 mg kg^), were detected in sediment samples collected downstream of gold mining areas and near Darkhan City. Around this city, As pollution might be related to the combustion of coal with high As content. Gold mining is a main source of As pollution in rural areas. Notably, the content of fine fractions in sediment samples collected downstream of the Zaamar mining area was half that measured in samples collected upstream of it. However, no correlation was observed between As concentration and fine particle content in sediment samples collected throughout the whole research area, suggesting that the proportion of fine particle sediments is not a controlling factor in As distribution in the riverbed. Heavy and coarse particles released by mining sites seem to quickly deposit on the riverbed near their source. However, fine particles can co-precipitate at river junctions due to changes in water quality. These deposition processes can limit the extent to which As pollution can spread in a large area, but redissolution of As from secondary minerals is now recognized as a key factor in the widespread groundwater As contamination observed around the world

Adsorption Properties of Au(III) and Cu(II) from Aqueous Solution Using Chemically Treated Sheep Wool

Au(III) and Cu(II) adsorption from aqueous solution were carried out using sheep wools with chemical treatments, by NaOH, Na2S, NaHSO3, and NaBH4 aqueous solution. The fibrous wool was transformed into a film like structures after the chemical treatment using Na2S. The sheep wool and the chemically treated sheep wool adsorbed selectively Au(III) from Au-Cu binary aqueous solution and the presence of copper ion had no effect on the Au(III) adsorption. Au(III) adsorbed substantially at low pH range. The kinetic experimental data fitted well with the pseudo-second-order kinetic model and the adsorption amount of Au(III) increased with time and reached a plateau after 12 h. The kinetic analysis suggests that rate determining step of Au adsorption would be chemisorption due to the formation of a monolayer on the wool surface. Sheep wool is a low cost, eco-friendly material, and has a high capacity of adsorption, and could be used as a biosorbent for precious and heavy metals by modification of appropriate chemical treatment

Plastic-associated metal(loid)s in the urban river environments of Mongolia

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

Bacterial Communities of Three Saline Meromictic Lakes in Central Asia

<div><p>Meromictic lakes located in landlocked steppes of central Asia (~2500 km inland) have unique geophysiochemical characteristics compared to other meromictic lakes. To characterize their bacteria and elucidate relationships between those bacteria and surrounding environments, water samples were collected from three saline meromictic lakes (Lakes Shira, Shunet and Oigon) in the border between Siberia and the West Mongolia, near the center of Asia. Based on in-depth tag pyrosequencing, bacterial communities were highly variable and dissimilar among lakes and between oxic and anoxic layers within individual lakes. <i>Proteobacteria</i>, <i>Bacteroidetes</i>, <i>Cyanobacteria</i>, <i>Actinobacteria</i> and <i>Firmicutes</i> were the most abundant phyla, whereas three genera of purple sulfur bacteria (a novel genus, <i>Thiocapsa</i> and <i>Halochromatium)</i> were predominant bacterial components in the anoxic layer of Lake Shira (~20.6% of relative abundance), Lake Shunet (~27.1%) and Lake Oigon (~9.25%), respectively. However, few known green sulfur bacteria were detected. Notably, 3.94% of all sequencing reads were classified into 19 candidate divisions, which was especially high (23.12%) in the anoxic layer of Lake Shunet. Furthermore, several hydro-parameters (temperature, pH, dissolved oxygen, H₂S and salinity) were associated (P< 0.05) with variations in dominant bacterial groups. In conclusion, based on highly variable bacterial composition in water layers or lakes, we inferred that the meromictic ecosystem was characterized by high diversity and heterogenous niches.</p></div

Number of shared OTUs in Lakes Shira, Shunet and Oigon, visualized by a heat map.

<p>Relative abundance of OTUs were standardized to the total number of OTUs (per-lake basis).</p

Relative abundance of bacterial communities at the phylum level according to depth in Lakes Shira, Shunet and Oigon.

<p>Relative abundance of bacterial communities at the phylum level according to depth in Lakes Shira, Shunet and Oigon.</p