Assessment of the distribution and ecological risks of heavy metals in coastal sediments in Vietnam's Mong Cai area.

Coastal sediments in the Mong Cai area were collected and analyzed for grain size, heavy metals, total organic carbon, and isotopes (210Pb, 226Ra, δ15N, δ13C) to assess sediment quality. The most common sediments were fine sand in surface sediment, very fine sand in core C1, and very coarse and coarse silt in core C2. 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. The chronology in C1 was 1877-2019 (142 years, 0-5 0 cm), with an average sedimentation rate of 0.71 cm/year. In C2, the chronology was 1944-2019 (75 years, 0-14 cm), with an average sedimentation rate of 0.27 cm/year. These δ13C and δ15N in the sediment reflect the source of the organic matter mix from the marine and terrigenous sediments. All studied heavy metals were lower than the ISQGs, with the exception of As in C1 and C2, which were higher. C1 showed a decline in As over time, while C2 As levels increased between 1996 and 2019. In terms of heavy metal pollution indexes, the geoaccumulation index (Igeo) showed that C1 and C2 were unpolluted to moderately polluted with As, with Li and Pb in C2; the enrichment factor (EF) was moderately enriched with As; the contamination factor (CF) was moderately contaminated (Pb, Cd, Fe, Mo, and Li) in C2 and C1 (Cd, As, Li) and considerably contaminated (As) in C2. The risk factor (ER) of As showed a moderate potential ecological risk in C2. The degree of contamination (CD) ranged from moderate to considerable (C1, C2), and the ecological risk (RI) was low. Although CD ranged from moderate (C1) to considerable (C2), most contamination was concentrated at the bottom of the cores. RI was low. The Mong Cai sediment quality does not currently affect the coastal area's ecosystem and fauna.

The status and distribution of PCBs along the coast of Vietnam.

Polychlorinated biphenyls (PCBs), well-known as an important scientific achievement, are now considered as one of the most persistent organic pollutants (POPs) that need to be strictly controlled and forbidden worldwide (the Stockholm convention on POPs). Vietnam is one of the countries that encounters with serious issues from PCB contamination. This study presented a comprehensive review on the status and contamination of PCBs along the coast of Vietnam. The contaminated PCBs data in the water, sediment and biological samples from 18 provinces along Vietnam coastline were collected from various sources. A comparison in PCBs contamination between Vietnam and other Asian countries was included. The status on PCBs contamination in Vietnam since participated as a party of the Stockholm convention on POPs in 2002 was also assessed. The results showed that Vietnam is facing serious PCBs contamination problems as it evidences the spread and accumulation of PCBs in the marine environment. The implementation of the Stockholm convention on POPs (PCBs in particular) has not yet demonstrated significant effect on the reduction in PCBs contamination in the environment. This information on PCBs contamination in Vietnam urges government to strengthen the mechanism, policy and legislation, the management capacity for PCBs as well as applying advanced and modern technologies in reducing, disposing and eliminating PCBs from the environment.