Currently, plastic and microplastic pollution have become a common problem in many countries around the world, especially in developing countries, including Vietnam. Salt is the main ingredient in most of the spices used, but microplastic contamination has also been reported in seasalt samples in Vietnam. This paper presents the observation results of microplastic concentrations in some spice-salt samples that were purchased in the market in Hanoi, Viet Nam. The analysis results showed that the microplastic concentrations in the spice-salt samples varied in a wide range, from 320 to 1880 items/kg spice-salt. Microplastic fibers accounted for the majority (99%), whereas fragment forms accounted for a negligible proportion (1%). Microplastics were observed with a wide variety of colors, of which blue, red, and black were predominant. The results contribute to assessing the level of microplastic contamination in spice-salts in Hanoi city, Vietnam in order to give warnings and propose solutions to prevent and minimize microplastic contamination in spice-salt, for protecting the health of human consumers.

This study investigated the variation of the cyanobacterium Raphidiopsis raciborskii population under the influence of physicochemical parameters from May 2019 to April 2020 in the Buon Phong reservoir. The correlations between these parameters were explored by using Principal Component Analysis (PCA) and Pearson correlation analysis. The cylindrospermopsin (CYN) toxin in isolated strains from the reservoir was confirmed by using High-performance liquid chromatography (HPLC) analyses. R. raciborskii presented throughout the year in the reservoir with a biovolume from 0.12 to 9.14 mm3 L-1. Four R. raciborskii strains (CBP2, CBP3, CBP4, and CBP5) were successfully isolated and confirmed to produce CYN by the HPLC results. The highest concentration in isolated strains was 0.345 μg g-1 DW in the CBP4 strain. The PCR results of genes responsible for CYN biosynthesis showed that the PCR amplicons of cyrB and CyrC were amplified in two toxic strains (CBP2 and CBP3), while the amplicons of both cyrB and cyrC were not observed in two remaining toxic strains. In addition, such abiotic factors as temperature and nutrients played major roles in the abundance of R. raciborskii. Moreover, the biovolume of R. raciborskii positively correlated with the CYN concentrations in the Buon Phong reservoir.

Microplastics (MPs), referring to plastic items ranging from 1 to 5000 µm long, are polluting the terrestrial and aquatic environments and are becoming a threat to the health of ecosystems, biota, and humans. Rivers are major carriers of these materials from the terrestrial environment to the oceans. In the present study, the occurrence of MPs in a peri-urban river was investigated. The Day river system is a good example of a peri-urban river strongly influenced by human activities in the whole basin. Water samples were collected from the downstream of the Day river, including Cau Que, Cau Do, and Do Thong, in the rainy and dry seasons using a plankton sampling net for identifying microplastic concentration, size, shape, color, and polymer composition. Microplastic abundance in the surface water ranged from 269,693±60,624 to 863,005±131,925 items/m3. The microplastic concentration in the rainy season was higher than that in the dry season. MPs abundance was increased at a site near urban areas with high human activity. The microplastic shape was collected in different seasons did not change significantly, with microplastic fibers as the major items, accounting for above 92% of the total items. Many fibers microplastics collected in this study were in small sizes of 300-1000 µm and 1000-2000 µm, occupying 78.5-85.7% of the total microplastic items. Purple was the most common color of microplastics. Polyethylene (PE) and polypropylene (PP) were major polymer types of the selected items in the surface water samples downstream of the Day River.

In this research, rice husk-derived biochar (BC) was evaluated to determine the suitable conditions for the methylene blue (MB) solution adsorption. The characterization of BC was identified by the methods of FT-IR, Raman, and point of zero charges (PZC). The adsorption studies were carried out with BC at different activation conditions (raw BC, HNO3 25% for 4 hours, NaOH 25% for 4 hours, H2O at 90°C for 2 hours and 4 hours, HNO3 25% at 90°C for 2 hours and 4 hours). The activated material then went through an adsorption assessment. Activated BC with NaOH 25% showed its preeminence compared to the other six conditions when reaching the maximum efficiency after the first hour of adsorption. The investigation revealed that the adsorption capacity of the material depends on the activation methods, including pH, activation agent, temperature, and time. The adsorption of BC was consistent with the pseudo-first-order kinetic model and the Langmuir isotherm model, with high correlation coefficients (R2: 0.9838 and 0.9975, respectively). Therefore, it can be concluded that the use of rice husk is feasible for the removal of MB from aqueous solutions.