The Mong Cai area, coastal sediments were collected and analyzed for grain sizes, heavy metals, total organic carbon, and isotopes (210Pb, 226Ra, δ15N, δ13C) for assessing sediment quality.Which sediments common were fine sand in surface sediment, very fine sand in core C1, very coarse silt 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. δ13C and δ15N in the sediment reflected the source of the organic matter mix from the marine and terrigenous sediments. Heavy metals were lower than ISQGs, exception of As in C1 and C2 were higher, in C1 showed a decline over time, while in C2 increased between 1996 and 2019. The Mong Cai area was common by sand, accumulation of heavy metals was small, impact of heavy metal pollution on ecosystems was low.

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