According to the results of the comparative study performed of the littoral sediments sampled in small inlets of Kandalaksha Bay (the White Sea in the Russian Arctic), the metals (Fe, Mn, Cu, Zn, Pb, Cr, and Li) occur mainly in a biogeochemical-stable mineral-incorporated form, which comprises 77–99% of the total metal content. The ratio of the liable form, which is easily extracted by a weak acid, is on average 3.2% for the total Fe, 2.0% for Mn, 1.7% for Cr, 5.6% for Pb, 5.8% for Zn, 6.5% for Cu, and is negligible for Li. The concentrations of the most studied trace metals are below the threshold level according to the environmental quality guidelines (the sediment analysis). The ratio of the metal forms evidences the natural origin of the elevated concentrations of both Zn and Cr in the sediments.

This data article refers to the paper entitled “Multi-element signatures in solid and solution phases in a tropical mixing zone: A case study in the Cai River estuary, Vietnam” (Koukina et al., 2021), which considers the fate of major, trace, and rare-earth elements transported through the estuarine geochemical filter of the typical tropical estuary. The present work contributes to the local geochemical baselines as a background for long-term monitoring of potential hazardous elements. Therefore, the dataset covers the abundance, enrichment, and partitioning parameters of 53 chemical elements in the water, suspended particulate matter, and bottom sediment samples collected in the Cai River estuary and the adjacent part of the Nha Trang Bay (South China Sea) between July and August 2013. The total filtered, particulate, and sedimentary elements were determined by atomic emission and inductively coupled plasma mass spectrometry (ICP-AES; ICP-MS). The environmental indices (the enrichment factor and geoaccumulation index) and partition coefficients were calculated from the total element contents. The data provided is essential for the comprehensive environmental assessment of the anthropogenic impact on the coastal ecosystem as well as for the evaluation and modelling of element fractionation and mobility at the estuarine gradients.

The distribution of particulate form of organic carbon (POC), Al, Fe, Ti, Li, Zn, Pb, U, Sc, Sn, Bi, Zr, Ba, As, Sr, W, V, Co, Cu, Ni, Mo, Cr, Mn, Ba, Sn, Sb, Hg, and Ag in the Cai river and Nha Trang Bay generally followed the distribution of total suspended matter (SPM) and was characterized by the most significant loss in the frontal zone of the estuary with highest horizontal gradients within the salinity interval of 8–20‰. The most part of these elements are supplied to the estuary with the Cai river discharge. Sedimentary Al, Fe, Ti, Li, Sc, Co, Cs, Zr, Cr, Zn, Co, Ni, Cu, Pb, Sn, and V are most likely controlled by the accumulation of their most fine-grained host minerals in sea floor depression of the bay. Sedimentary Bi, W, As, U, and Mo are mainly deposited with the coarse river material near the river mouth. The distribution of Ca, Sr, Mn, and Ba is largely controlled by the total inorganic carbon (TIC) content in the sediments. Metal form study revealed the highest percent contents of the labile forms for Mn, Co, and Pb in the sediments. The high levels of weak acid-soluble Pb and Co (30% and 43% of the total content in sediment, on average, respectively) contributes to a contamination problem in the Nha Trang Bay which arises from the Cai River discharge.