Spatial variation and risk assessment of trace metals in water and sediment of the Mekong Delta

Abstract

The Mekong Delta, is home to 17 million inhabitants and faces numerous challenges relating to climate change, environmental degradation and water issues. In this study, we assess trace metals concentrations (Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, Hg, Pb) in the water, suspended particulate matter and surface sediments of the Tien River, the Northern branch of the Mekong Delta, during both dry and rainy seasons. Metal concentrations in the dissolved and suspended particle phases remain in the low concentration range of the main Asian Tropical River. During transportation in the riverine part, we evidenced that V, Cr, Co, As and Pb are dominant in the particulate phase while Mo, Ni and Cu dominate in the dissolved fraction. In the salinity gradient, dissolved U, V, Mo exhibit conservative behaviour while Ni, Cu, As, Co and Cd showed additive behaviour suggesting desorption processes. In the surface sediment, metal concentrations are controlled by the particle-size, POC contents and Fe, Al and Mn - oxy(hydr)oxides. Calculated Enrichment Factor and Geoaccumulation Index evidenced As enrichment while the calculated mean effect range median quotients evidenced a low to medium ecotoxicological potential effects range in the surface sediments.

Spatial and Temporal Variation of Dissolved Heavy Metals in the Mun River, Northeast Thailand

“…Although Mn was abundant in the whole drainage basin, its fluxes into the Mekong River were small. The elemental fluxes of Cu and Zn are negligible, but Cu might have a significant impact on the dissolved heavy metals in the Mekong River, the background values of which are 0.96 µg/L-3.96 µg/L in the wet season and 0.63 µg/L-1.41 µg/L in the dry season [46,47].…”

Trace metals partitioning between particulate and dissolved phases along a tropical mangrove estuary (Can Gio, Vietnam)

“…The filtrate was transferred into pre-cleaned 50 mL polypropylene, immediately acidified to pH < 2 using concentrated suprapur ® HNO3 (HNO3/sample ¼ 1/1000 (v/v)) for dissolved trace metals MD, while the filters were kept in pre-cleaned plastic petri dishes for suspended particulate trace metals analysis (MP). Both samples were maintained in cool box during sampling campaign and stored at 4 ○ C in the laboratory for dissolved metal and at -18 ○ C for particulate metal (Strady et al, 2017b). Filters were then freeze dried, weighed and preserved at room temperature until analysis.…”

Spatial Variations of Trace Metals and Their Complexation Behavior with DOM in the Water of Dianchi Lake, China

“…Cu and Fe in natural waters and effluents are significantly influenced not only by DOM concentration but also by the aromaticity of DOM [20,26]. The assessment of DOM optical properties may be useful to understand the trace metal-DOM interaction and metal bioavailability in natural and effluent water systems [10]. In surface water, the proportion of total metals in DOC mainly depended on the amount of dissolved metals and was intimately related to molecular size and the percentage of substitutable aromatic rings in DOM (R 2 = 0.64, p ≤ 0.01; Figure 6).…”

“…The bound phase and distributions of different metal species in various aquatic environments differed from each other. U, V and Mo exhibited conservative behavior, while Ni, Cu, As, Co and Cd showed additive behavior in desorption processes in the Mekong Delta [10]. Cd and Zn enhanced settling with bio-detritus of upwelling waters, Pb, Co and Ni were evidenced to associate through adsorption of Fe-Mn oxides nodules onto clay minerals, whereas Cu precipitated as Cu sulfides during reducing reactions in the coast along Southwest India [11].…”