Baseline seasonal investigation of nutrients and trace metals in surface waters and sediments along the Saigon River basin impacted by the megacity of Ho Chi Minh (Vietnam)

Abstract

The Saigon River, Southern Vietnam, crosses one of the most dynamic developing Megacity in Southeast Asia: Ho Chi Minh City (HCMC). The increased economic, industrial, and domestic developments may affect the environmental quality of water and halieutic resources. In this study, we evaluated the seasonal (dry and wet seasons) biogeochemical state of the Saigon River during two snapshot campaigns conducted along the river basin upstream from HCMC; the Saigon River was characterized by slightly acidic (pH 5.7-7.7) and oxygen-depleted water (dissolved oxygen (DO), 0.36-5.18 mg l). Nutrients (N-NH = 0.01-2.41, N-NO = 0.14-2.72, and P-PO = ~0-0.42 mg l), DOC (2.2-8.0 mg l), POC, and trace metal(oid) (As, Cd, Cr, Cu, Zn, and Hg) concentrations were low showing a good quality of the upstream river. In the urban center area, DO dropped to 0.03 mg l accompanied with a rise of nutrient concentrations (e.g., N-NH, up to 17.7 mg l) likely originating from wastewater discharges. Trace metal concentrations also rose sharply (e.g., Cr and Hg rose up to 10-fold higher) in both water and sediments but remained under the World Health Organization (WHO) and Vietnamese concentration guidelines. In the downstream estuarine area, the intrusion of marine waters diluted water flowing from HCMC, leading water quality to return close to the state observed upstream from HCMC. In general, levels of nutrient and metal contaminations along the Saigon River during both seasons appear moderate regarding to Vietnamese and WHO guidelines although the urban area is highlighted as the major contributor for metal(oid) emissions. Finally, we showed that apart from wastewater and industrial discharges that affect the river quality, metal(oid) partitioning between solid and solution is controlled by the change in water geochemistry along the continuum during both seasons, such as DO (e.g., for As and Cr) and pH (e.g., for Pb) which drives their sorption/dissolution dynamics.

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

“…The POCSED content ranges from 0.2 to 1.5% (Table 6). MetalSED concentrations measured in the Tien River (Table 6) are in the same range as previously observed in this system (Cenci and Martin, 2004;Noh et al, 2013) and are in the low concentration range of the main Asian Rivers (Table 4) such as the Yangtze River Estuary (Wang et al, 2015), the Huanghe River Estuary (Wang et al, 2017), the Pearl River Estuary (Zhang et al, 2013), the Ganges-Brahmaputra Rivers (Datta and Subramanian, 1998) and including the Saigon River (Strady et al, 2017). Cenci and Martin (2 0 04) observed that MetalSED in the Mekong Delta varies spatially but not seasonally.…”

“…3) suggesting intense desorption processes from particles occurring in the salinity gradient. This bell-shaped pattern is well documented for CdF as a chloride-induced desorption from the suspended sediments and has been previously observed in the Mekong Delta (Cenci and Martin, 20 04 ) and other estuaries like the Gironde Estuary (Kraepiel et al, 1997;Dabrin et al, 2009), the Pearl River (Wang et al, 2012a), the Saigon River (Strady et al, 2017) and the Huanghe River Estuary (Wang et al, 2016b). For CuF, even if a conservative behaviour is more usual and has been observed in the Mekong Delta (e.g.…”

“…Fo€rstner and Wittmann, 19 79 ;Loring, 19 91 ;Jung et al, 2014). Secondly, although POCSED content is low (0.2%e 1.5%; Table 6), its strong correlation with HgSED, AsSED (r ¼ 0.83 and 0.84, for Hg and As respectively p < 0.01 Table 7) and CoSED, CuSED (r ¼ 0.76 and 0.76 p < 0.01 Table 7) suggest that organic matter is a major carrier for these elements, as it has been observed for Cu in the Saigon River sediments (Strady et al, 2017) and for Hg in the Lower Mekong Basin sediments (Noh et al, 2013;Gue´dron et al, 2014). In the particular case of As, the positive correlation observed between AsSED and POCSED is unusual since As has been documented to be primarily controlled by sorption onto metal oxide surfaces in natural environments (e.g.…”

“…Particulate trace metals on PTFE filters (MetalSPM) and representative sub-samples of surface sediments (MetalSED; 100 mg of dried, powdered and homogenized material) were analyzed by a microwave total extractable acid digestion (NovaWave SCP Sciences ® , IGE-OSUG Laboratory, Grenoble, France; HCl, HNO3, HF; Trace Metal grade Fisher ® ). The protocol is based on the digestion method USEPA 3052 and is fully described in Strady et al (2017). Trace metal concentrations (V, Cr, Co, Ni, Cu, Zn, As, Mo, Cd, Pb, U) were measured by ICP-MS (Elan DRC II Perkin Elmer, TERA Environment Laboratory Fuveau France) while Al, Mn and Fe concentrations were measured by ICP-AES (Varian 7 20 ES, ISTerre-OSUG Laboratory, Grenoble, France) using external calibration for both cases.…”

“…Trace metal concentrations (V, Cr, Co, Ni, Cu, Zn, As, Mo, Cd, Pb, U) were measured by ICP-MS (Elan DRC II Perkin Elmer, TERA Environment Laboratory Fuveau France) while Al, Mn and Fe concentrations were measured by ICP-AES (Varian 7 20 ES, ISTerre-OSUG Laboratory, Grenoble, France) using external calibration for both cases. Total Hg concentrations in sediments THgSED were determined by atomic absorption spectrophotometry after dry mineralization and gold amalgamation by using an automatic mercury analyzer (Altec, Model AMA 254 ISTerre-OSUG Laboratory, Grenoble, France) (Gue´dron et al, 2009;Strady et al, 2017). MetalF concentrations were directly measured by ICP-MS (Elan DRC II Perkin Elmer) using external calibration.…”