Н. Н. Терещенко

The paper presents the results of a chemoecological study of the concentrations of heavy metals (HM) and metalloids (MLD) in water in the eastern region of the lower Mekong Delta (Vietnam) and some physico-chemical characteristic. To measure the concentrations of trace elements, a mass spectrometric method was used. The concentration of dissolved and suspended forms of HM and MLD in water was studied to determine the ecological quality of water. It was found that the main amount of HM and MLD in water was in suspended form. The accumulation ability of suspended matter in relation to HM and MLD was determined. The concentration factors of trace elements in suspended matter varied from n×102 to n×107. Retrace the boundaries of the salinization zone of river waters depending on the distance from the seaside and climatic season. Seven critical and four potency critical trace element were identified.

Investigation of concentrations of organic and inorganic pollutants (hydrocarbons, including oil hydrocarbons, and trace elements-heavy metals and metalloids) in the Ham Luong River in the Mekong Delta was carried out and water quality was assessed by comparing the obtained levels of values with the regulatory limits of concentration. The determination of the total content of hydrocarbons and oil hydrocarbons was made by gas chromatography method; the trace elements were measured by ICP-MS technique after chemical treatment of samples. The content of oil hydrocarbons in the Ham Luong River water ranged from 0.042 to 0.076 mg/l. These values were quite high, exceeding the sanitary standard (0.05 mg/l) for fishery reservoirs, or approaching it, but they were lower compared to Vietnam national standard for domestic supply water (0.1 mg/l). The content of hydrocarbons in suspended matter was in the range of 0.011-0.37 mg/l. The concentrations of 15 trace elements were studied, nine of them (Ni, Fe, V, As, Se, Be, Cd, Sb, Tl) did not exceed any of the established regulatory limits of concentration for surface water. However, concentrations of six trace elements (Pb, Zn, Cu, Co, Ag, Mo) were found to exceed the standard regulatory limits. Among the studied 15 trace elements, critical and potentially critical elements were identified, which are subject to primary monitoring control. Chemoecological studies of water quality are important for monitoring of the ecological and sanitary water state for ensure the quality of consumed natural resources and to preserve the biological diversity of the Mekong Delta ecosystems.

Chemoecological studies were carried out in the water areas of the Kagau and Longtau rivers in the Can Gio Biosphere Reserve (Vietnam). Mass-spectrometry analysis was used to determine the concentrations of 15 microelements (heavy metals and metalloids) in water and bottom sediments. The overall pollution level in the Can Gio rivers was found to be moderate. However, the concentrations of some heavy metals in several cases exceeded the maximum permissible concentration at short-time exposure; also, the limits of safe concentrations at chronic exposure were exceeded for some elements. The concentrations of some heavy elements amount to 30 to 80% of the MPC for water bodies used for fishery. Primarily, these are copper, zinc, arsenic, vanadium, iron, and molybdenum. It was found that, according to the Regulations of Vietnam, the waters of the examined water areas showed concentrations of suspended matter in excess of the standards for category A1 sources, and the concentration of dissolved oxygen in water was below the standard. The obtained results suggest the need to monitor the chemical–ecological conditions of rivers in Can Gio as protected natural objects, which are also used to some extent for social and economic purposes.

Chemoecological studies were carried out in the water areas of the Kagau and Longtau rivers in the Can Gio Biosphere Reserve (Vietnam). Mass-spectrometry analysis was used to determine the concentrations of 15 microelements (heavy metals and metalloids) in water and bottom sediments. The overall pollution level in the Can Gio rivers was found to be moderate. However, the concentrations of some heavy metals in several cases exceeded the maximum permissible concentration at short-time exposure; also, the limits of safe concentrations at chronic exposure were exceeded for some elements. The concentrations of some heavy elements amount to 30 to 80% of the MPC for water bodies used for fishery. Primarily, these are copper, zinc, arsenic, vanadium, iron, and molybdenum. It was found that, according to the Regulations of Vietnam, the waters of the examined water areas showed concentrations of suspended matter in excess of the standards for category A1 sources, and the concentration of dissolved oxygen in water was below the standard. The obtained results suggest the need to monitor the chemical–ecological conditions of rivers in Can Gio as protected natural objects, which are also used to some extent for social and economic purposes.

In the frame of the radioecological monitoring after the Chernobyl nuclear power plant accident, the features of migration and distribution of artificial radionuclides in the North Crimean Canal (NCC) irrigation system were studied. Standard methods of radiochemical analyzes and modern radiospectrometric equipment were used. It was determined that the irrigation system of the NCC retains 43–59% ⁹⁰Sr, 59–60% ^239+240Pu, and 66–70% ¹³⁷Cs of the concentration radionuclides entering to irrigated fields with the Dnieper waters. The NCC irrigation system plays the role of a buffer against the radionuclide pollution of the Karkinitsky Bay (the Black Sea). Differences in the accumulation of radionuclides by agricultural crops were revealed. The ⁹⁰Sr and ^239+240Pu transfer factors (TF) for alfalfa were n × 10⁻² and n × 10⁻¹, respectively. The TF for wheat, corn, and rice for ⁹⁰Sr were n × 10⁻³, and for ^239+240Pu—n × 10⁻². A radioecological assessment on the safety agriculture along the NCC was made: in the absence of an increase in the entry of the Chernobyl origin radionuclides with the Dnieper river waters to the NCC, the levels of activity concentration of artificial radionuclides in cultivated crops will not exceed the maximum permissible concentration for food raw materials in the coming years.

The article is devoted to studing of the features of sedimentation on the bottom of the northwestern shelf and western deep-water area of the Black Sea based on an analysis of our own and published data obtained by bottom sediment radioisotope geochronology. It was determined that the relationship between the mass accumulation rate and primary production was linear, due to the aggregate biogeographic, hydrological, and hydrochemical conditions. The features of bottom sediment formation in the open part of the sea were associated with the presence of hydrogen sulfide (H₂S) in deep waters (deeper than 100–200 m). It was shown that 20 (on the continental slope) and 17 g/(m² year) of particulate organic matter (in the deep-sea basin) entered from the oxygen-containing zone. In this case, the predominant fractions in bottom sediments were mineralized biogenic matter: 54 and 68.5%, respectively, in these areas. The contribution of organic, mineralized biogenic, and lithogenic sedimentary matter to the formation of the mass accumulation rate was estimated, and changes in their ratio with distance from the coast and estuaries were shown. Based on the nature of the formation of the mass accumulation rate, three groups of sea areas were identified in which the ratio of biogenic and lithogenic components in absolute masses reflected a change in their role of these components in bottom sediment formation.