Chemical mechanisms of nitrite formation and chemical aspects of pollution

Abstract

The present article provides the results of comprehensive field observations and laboratory analyses aimed at a detailed study and identification of the patterns of chemical mechanisms of nitrite formation in the waters of the Araz River. These processes develop under the influence of various sources of anthropogenic pollution, including industrial and agricultural effluents, and are accompanied by significant changes in the hydrochemical composition of the aquatic environment, reflected in the concentrations of major ions, redox potential, and thermal characteristics of the river. The studies were conducted in different seasons of the year at three key sites -in the Sadarak, Ordubad, and Beylagan districts - which made it possible to assess the spatio-temporal dynamics of pollution.Sampling was carried out in compliance with GOST/AZS standards, and chemical analysis was performed using spectrophotometric, titrimetric, and ion-exchange methods. Concentrations of nitrites, nitrates, chlorides, and other inorganic substances were determined, as well as redox potential (ORP) values. The results showed that the highest concentrations of nitrites (0.145 mg/L), nitrates (12.8 mg/L), and chlorides (238 mg/L) were recorded in the Sadarak district, which is associated with high water mineralization and active chlorine oxidation processes. In the Ordubad district, concentrations were minimal due to dilution of river water by tributaries and partial adsorption of ions onto sediments. In the Beylagan district, a repeated increase in nitrite content (up to 0.132 mg/L) was noted, probably due to the inflow of polluted transboundary tributaries.Correlation analysis revealed significant positive relationships between nitrite and chloride content (r = 0.78, p < 0.05), as well as between nitrites and nitrates (r = 0.72, p < 0.05). The mechanisms of formation include the interaction of nitrogen oxides with water and the formation of intermediate chlorine-nitrogen compounds followed by hydrolysis. The scientific novelty of the study lies in establishing a direct relationship between mineralization and nitrite accumulation under transboundary impact conditions. The practical significance consists in substantiating measures to reduce the chloride–nitrate load on the upper reaches of the river, including the modernization of treatment facilities and the tightening of control over discharges.