The Cat Ba is one of the largest Islands offshore North Vietnam, which is characterized by an abundance of coral reefs in the East and Southeast of the island. The surface sediments are considered the basic elements for the coral ecosystem development. In this study, the authors present some new results studying pH, Eh, mineral composition, and grain size as the basic information for environmental assessment of this area. The results show that the pH value of the surface sediment varies from 6.90 to 8.09, with an average of 7.24 while the Eh value of the sediment ranges from -121.10 to -48.20mV,  an average of -68.39mV, demonstrating a reducing environment. The surface sediments have been classified into 8 size classes: the coarse silt > very coarse silt > medium sand, very fine sand > very coarse sand, fine sand > coarse sand, very fine gravel. Most of the sediments are poorly sorted - very poorly sorted, only a few sedimentary samples are well sorted, moderately sorted, and moderately well sorted. The average mineral composition of the surface sediments consists of: 25% quartz, 17% illite, 16% aragonite, 13% kaolinite, 10% calcite, 5% chlorite, 4% gothite, 3% halite, 2% feldspar and less montmorillonite, and dolomite. These results allowed the researcher to interpret that the sediments have been deposited in a relatively calm environment and the terrigenous sediment sources are dominant over the marine sources. Source marine sediment groups are characterized by coarse grains, high pH, and are rich in carbonate minerals, which have been produced by biological materials. In contrast, the terrigenous sediment group is dominated by fine-grained sediments, rich clay minerals, quartz, and gothite. These fine-grained sediments are commonly distributed in the area and are favorable places for pollutant accumulation.

No abstract

The Mong Cai area is located on the border between Vietnam and China, with the Ka Long River forming a natural border. Coastal sediments were collected and analyzed for grain size, heavy metal content, total organic carbon, and isotopes ( 210 Pb, 226 Ra, δ 15 N, δ 13 C) to assess sediment quality.Fine sand was common in surface sediment, with abundant very ne sand in core C1; in core C2, very coarse silt and coarse silt were dominant. The sedimentation rate at C1 ranged between 0.08 and 1.62 cm/year while that at C2 ranged between 0.07 and 0.51 cm/year. The total organic carbon was highest in C2 next to the surface and lowest in C1, with content levels of 1.81%, 0.40% and 0.31%, respectively. δ 13 C in surface sediments ranged from − 27.43 to -17.02‰ and averaged − 24.13‰; δ 15 N ranged from 3.12 to 6.05‰, with an average of 4.96‰; and δ 13 C and δ 15 N in the sediment re ected the source of the organic matter mix from the marine and terrigenous sediments.The sediments' heavy metal contents were lower than ISQGs, with the exception that As in C1 and C2 was higher than the ISQG. The heavy metal distribution was highly concentrated in the Ka Long estuary with low concentration in Ha Coi Bay. The concentration in C1 showed a decline over time, while the Cu, Pb, Zn, Cr, Co, Ni, and Mn contents in C2 increased over time between 1996 and 2019. In terms of heavy metal pollution indexes, Igeo showed C1 and C2 to be unpolluted to moderately polluted with As, with Li and Pb in C2; EF was moderately enriched with As; CF was moderately contaminated (Pb, Cd, Fe, Mo, and Li) in C2 and in C1 (Cd, As, Li) and considerably contaminated (As) in C2. ER of As showed a moderate potential ecological risk in C2. CD ranged from moderate degree contamination to considerable degree contamination (C1, C2). RI had low ecological risks.

The Mong Cai area is located on the border between Vietnam and China, with the Ka Long River forming a natural border. Coastal sediments were collected and analyzed for grain size, heavy metal content, total organic carbon, and isotopes (210Pb, 226Ra, δ15N, δ13C) to assess sediment quality.Fine sand was common in surface sediment, with abundant very fine sand in core C1; in core C2, very coarse silt and coarse silt were dominant. The sedimentation rate at C1 ranged between 0.08 and 1.62 cm/year while that at C2 ranged between 0.07 and 0.51 cm/year. The total organic carbon was highest in C2 next to the surface and lowest in C1, with content levels of 1.81%, 0.40% and 0.31%, respectively. δ13C in surface sediments ranged from − 27.43 to -17.02‰ and averaged − 24.13‰; δ15N ranged from 3.12 to 6.05‰, with an average of 4.96‰; and δ13C and δ15N in the sediment reflected the source of the organic matter mix from the marine and terrigenous sediments.The sediments’ heavy metal contents were lower than ISQGs, with the exception that As in C1 and C2 was higher than the ISQG. The heavy metal distribution was highly concentrated in the Ka Long estuary with low concentration in Ha Coi Bay. The concentration in C1 showed a decline over time, while the Cu, Pb, Zn, Cr, Co, Ni, and Mn contents in C2 increased over time between 1996 and 2019. In terms of heavy metal pollution indexes, Igeo showed C1 and C2 to be unpolluted to moderately polluted with As, with Li and Pb in C2; EF was moderately enriched with As; CF was moderately contaminated (Pb, Cd, Fe, Mo, and Li) in C2 and in C1 (Cd, As, Li) and considerably contaminated (As) in C2. ER of As showed a moderate potential ecological risk in C2. CD ranged from moderate degree contamination to considerable degree contamination (C1, C2). RI had low ecological risks.

During the screening for biological active compounds from the medicinal plant, a species of Euphorbia hirta L. collected from Dan Phuong-Hanoi was utilized for its phytochemical study. From the n-butanol extract, eight compounds, including nonacosan-1-ol (1); β-sitosterol (2); β-sitosterol glucoside (3); quercetin (4); nicotiflorin (5); rutin (6); afzelin (7) and quercitrin (8) have been isolated. Their structures were determined by analysis of IR, MS and NMR (1D and 2D) spectroscopy as well as by comparison with published data.