Metals speciation in Arctic lake under pollution impact (1980-2019): in-situ measurements, experimental estimates, model calculations

An important fundamental block in the geochemical studies is the evaluation of the equilibrium distribution of metals in water and the influence of environmental conditions on the spetiation. It is important to understand the difference between the behavior of nanoparticles, dissolved particles, colloid particles, and suspended particles. The research deals with study and assess of geochemical processes of metal speciation in Arctic lake in the zone of metallurgical waste and other areas, where natural processes prevail. Consecutive and parallel membrane filtration methods were used to compare of the results of water analysis in the Imandra lake. The membrane pore sizes were: 8 µm, 1.2 µm, 0.45 µm, 0.2 µm. The following filterates characteristics were used: (microfiltration-based) mechanical suspension and oxidized contaminants (>8 μm, 1.2 μm, 0.45 μm, 0.2 μm, 0.1 μm); and (ultrafiltration-based) colloid, bacteria, viruses, etc (less than 0.1 μm).

Industrial effluents lead to the formation of higher concentrations of elements (Ni, Cu, Pb) in their labile forms as were found. In the wastewater-mixing zone, the concentrations of most elements are evenly distributed in depth. In areas that are more distant, there was a significant increase in the concentration of elements in the near-bottom horizon in comparison with the surface waters (Fe by more than 3 times). The obtained results showed that numerous elements had diverse distribution by speciation in the point located closer to the source of wastewaters. This indicates a significant influence of adsorption process on the system balance by such elements as Fe, Cu, and rare earth elements.

The impact of the regional geochemical and anthropogenic speciation and the possible influence of the climatic factor on the metals speciation were showed.   The authors did not have data on the metals speciation in the chosen points for the whole period of monitoring from 1980 until present. However, ElementPhasMigration (certificate 2017662509, Dinu M.I.) software was used to calculate the shares of labile and non-labile metal speciation during the years of the highest pollution (beginning of the 1990s) and during the current period of the ecosystem restoration.    

The software used mathematic modeling of chemical reactions happening in the natural waters and was based on the main laws of analytical and physical chemistry: material balance equation, equilibrium constant, equations of electrical neutrality, equations of proton balance, and competing reactions.

On the one hand, the initial data comprised a significant number of physicochemical parameters of the environment (more than 10 metal ions, рН, content of organic and non-organic anions, etc.). On the other hand, it included diverse mathematical tools for consecutive calculation of acidity constant of organic acids, conditional constants of complexes stability, the share of strong and weak acids in the system, etc. The software solved the tasks on the evaluation of the metal speciation depending on the physical and chemical parameters of the environment and provided the data on the balance speciation of a wide spectrum of elements in the system. The final stage of the calculations included the results verification with the field data.      Financing RFS 18-77-00018