Metals in surface water of Ukraine: the migration forms,features of distribution between the abiotic components of aquatic ecosystems,and potential bioavailability

We have generalized the results of long-term studies of coexisting forms of a series of metals (Al, Fe, Mn, Zn, Cu, Cr, Pb, Mo, Cd, and V) in surface water bodies of Ukraine, differing in the hydrological regime and the water chemical composition (rivers, reservoirs, lakes, and ponds). The studied metals content has ranged widely, the concentrations of aluminum, iron, and manganese being typically the highest, and the concentration of molybdenum, vanadium, and cadmium being typically the lowest. The ratio between the suspended and the dissolved forms of the metals has been established. Iron and aluminum migrate mostly as part of the suspended matter, whereas the other metals mainly migrate in the dissolved state. The dissolved manganese form predominates in the water bodies under anaerobic conditions. Copper and molybdenum are present almost always in the dissolved state, regardless of the water body type. The data on the relative content of the labile metal fraction (potentially toxic to aquatic organisms) are reported. The relatively low content of this fraction has been found to be majorly owing to the metal ions complexing with natural organic ligands. The humic compounds, the most widespread group of natural organic compounds, play the primary role in the complexation. Even metals with variable oxidation state (Cr, Mo, and V) are found mainly in the form of anionic complexes with the humic substances. Carbohydrates are also involved in the metals binding in the highly bioproductive water bodies, thus increasing the mass fraction of the neutral complexes during the summer and autumn periods. The molecular weight distribution of anionic metal complexes has been discussed; the substantial part of the metals constitutes the compounds with the molecular weight of below 5.0 kDa.     

Hydrochemical Regime of the Kiliya Delta of the Danube River in Retrospective and Modern Conditions: I. Main Indicators of Water Chemical Composition

Russian Journal of General Chemistry - —The article focuses on the changes in the hydrochemical regime of the Kiliya delta of the Danube River, which have occurred during many years of...     

Humic substances in surface waters of the Ukraine

The results of studies of humic substances in water bodies of different types (lakes, rivers, and reservoirs) are given. It is shown that concentration of these natural organic compounds varies in a wide range of values (from 1.2 to 126.5 mg L^?1) due to different sources of their formation. The highest concentrations of humic substances are characteristic for rivers of the Pripyat’ River basin flowing through the wetland. As we move from the north to the south, the content of humic substances is reduced. So, in the Kakhovka Reservoir, closing the Dnieper cascade of reservoirs, the concentration of humic substances is almost thrice as low as in the Kiev Reservoir, which is at the head of the cascade. Seasonal changes of humic substances concentration and the reasons for these changes are discussed. The prevailing fraction in the composition of humic substances is represented by fulvic acids, the content of which reaches 80.8–94.8% of the total. The results of studies of the molecular weight distribution of humic substances and the reasons for changes in the ratio of their individual fractions, depending on the detection method (spectrophotometric and fluorescence methods), are considered. The values of the number average (M _n) and weight average (M _w) molecular weight of humic substances and the degree of polydispersity are calculated. It is shown that M _w varies seasonally. In spring and summer it is lower, but significantly increased in autumn. The reason for this phenomenon is degradation of high-molecular fractions of humic substances under the influence of UV light of solar radiation and increased microbiological activity during the summer season. As a result of these processes high-molecular fractions of humic substances are transformed into fractions with lower molecular weight, which become predominant.     

Potential Complexing Ability of Surface Water Organic Matter: I. Role of Various Groups in Metal Ion Binding

Russian Journal of General Chemistry - The results of experimental studies of the potential complexing ability of dissolved organic matter (DOM) of surface water bodies with respect to Al3+, Fe3+,...     

Potential Complexing Ability of Surface Water Organic Matter: II. Toxicity of Metal-Containing Aquatic Environment

Russian Journal of General Chemistry - The results of biotesting the toxicity of natural water from the upper section of the Kanev reservoir and Lake Verbnoe before and after addition of 500...     

Features of the Hydrochemical Regime of Water Bodies of Urbanized Areas in Summer: I. Biogenic and Organic Substances

Russian Journal of General Chemistry - The article summarizes the results of long-term studies of the hydrochemical regime of some lakes of the Kiev city as an example of the urbanized area water...     

Role of Neutral Fraction of Dissolved Organic Matter in the Migration of Metals in Surface Waters: II. Neutral Metal Complexes in Water Bodies of Different Types

The results of long-term studies on the contents and seasonal dynamics of neutral carbohydrate metal complexes in the surface water bodies of different types (lakes, rivers, reservoirs) are summarized. It is established that the weight fraction of the mentioned complexes characteristically varies significantly depending on the type of the water body and the component composition of dissolved organic substances. In water bodies with a highly colored water, the relative contents of dissolved metals in neutral complexes are low due to their preferential binding to anionic complexes with humic substances. In small eutrophic water bodies with a relatively low content of humic substances, the carbohydrate concentrations are the highest and, accordingly, the weight fractions of metals in their neutral complexes is also very noticeable. The molecular weight distributions of neutral metal complexes are discussed. The neutral complexes with the molecular weight ≤5.0 kDa form a significant part of metals associated with carbohydrates. The seasonal dynamics of these metal complexes are discussed.     

Titanium in natural surface waters: The content and coexisting forms

Results obtained in studying the content and coexisting forms of titanium in surface waters are given. It was established that the titanium concentration lies within 0.0–1180 μg/L in the world’s surface water and within 0.0–573 μg/L in the studied water bodies of Ukraine. The concentration of dissolved and suspended titanium in the water bodies studied also varies within the wide range, 0.0–86.0 and 0.0–534.6 μg/L, respectively. The concentration of its dissolved form in world’s surface water is 0.0–68.7 μg/L. The ratio of dissolved to suspended titanium in water bodies depends on the content of suspended matter and its nature. In river waters, the suspended titanium mostly dominates over the dissolved form. We found that in rivers with the high concentration of suspended matter (6.0–140.6 mg/L), mostly of mineral nature, a fraction of the suspended titanium reaches 62.3–88.6% on the average. A strong correlation between the mass of suspended matter and the concentration of suspended titanium in these surface waters shows that the nature of suspended matter affects the concentration of suspended titanium. The correlation coefficient is between 0.81–0.99 at a significance level of 0.01. The titanium content in the suspended matter and bottom sediments of world’s water bodies makes 0.2–19.8 and 0.1–24.6 mg/g of dry weight of the suspended matter, respectively. In the surface waters studied, its content ranges within 0.0–16.5 mg/g of dry weight of the suspended matter. Taking into account the average values, the titanium content in the suspended matter of the studied rivers, water reservoirs, lakes, and ponds is (mg/g in terms of dry mass): 1.0–7.5, 1.0–4.9, 1.3–3.9, and 1.2–1.3, respectively. The percentage of the adsorbed titanium in the suspended matter of the Kilia Danube delta, Kanev Reservoir, and the Lybid’ River is 91.6–97.3, 67.6–74.4, and 57.1–99.4%, respectively. The acidic (anionic), basic (cationic), and neutral fractions of the dissolved organic substances in the surface waters contained 15.7–89.4, 0.0–33.8, and 0.0–80.7% of dissolved titanium (Ti_diss) (i.e., 44.4, 13.2, and 42.4% of Ti_diss on the average). The presence of dissolved titanium in the anionic fraction shows that titanium forms complexes with humic substances or exists in the form of TiO₂ colloidal particles (nanoparticles) coated with humic substances. In the neutral fraction, a hydrated titanium oxide TiO(OH)₂ may exist as a form of its migration in natural surface waters.     

Potential Transformations of Dissolved Organic Substances and Their Complexes with Metals in Surface Waters under Solar Radiation

Russian Journal of General Chemistry - The article summarizes the results of studies on the molecular weight distribution of humic substances and carbohydrates as the most widespread groups of...     

Features of the Hydrochemical Regime of Water Bodies of Urbanized Areas in Summer: II. Coexisting Forms of Metals

Russian Journal of General Chemistry - The article summarizes the results of studies of coexisting forms of metals (Al, Fe, Mn, Cu, Cr, Zn, and Pb) in some lakes of the Kiev city for the period of...