Among agents of the reducing nature, reduced sulfur compounds occupy a special place in natural waters. The role of reduced sulfur compounds in the natural aquatic environment and bottom sediments is shown in a large number of works [1]. In general, attention is paid to the study of marine waters [2]. The presence of reduced sulfur compounds in the oxygenated waters - thermodynamically inexplicable phenomenon, indicating the dynamic nature of the processes of their formation and oxidation. Among the identified reducing substances there are thiol compounds, allocated by microalgae. The greatest influence on the aerobic process provides hydrogen sulfide in natural waters. Hydrogen sulfide in the natural aquatic environment is formed with the participation of sulfate-reducing microorganisms. Sulfate ions can not be restored to sulfide chemically under such conditions. 2Н+(Н+) СН2О + SO4= → 2CO2 + Н2S (НS-) + 2H2O Constant acid-base dissociation pKa is ≈ 7, so the content of H2S, HS- in a neutral aqueous medium is approximately the same. Hydrogen sulfide hardly reacts with O2 and hydrosulfide HS- oxidation has induction period and includes a mechanism involving autocatalysis with poly sulfides. Contrary to the authors of [3], small additions of hydrogen peroxide (10-5 M) in the aerated water do not lead to an acceleration process of auto-oxidation of sulfide. In contrast to the reaction with oxygen, HS- interaction with H2O2 proceeds without an induction period. The presence of oxygen in the reaction medium has no influence on the reaction kinetics. Pic. 1. Effect of dissolved oxygen on reacting HS- with Н2О2. Initial concentration: Na2S – 1∙10-4 М; phosphate buffer – 2∙10-3 М; Н2О2 – 6∙10-4 М. Thus, no H2O2 or hydrosulfide oxidation products of hydrogen peroxide is not involved in the oxidation of HS- autocatalysis by molecular oxygen. Addition of small amounts (10 -5 M) in the reaction solution of ferrous ions (Mohr salt) had no effect on the kinetics of the oxidation of hydrogen sulfide by hydrogen peroxide. This suggests non-catalytic mechanism of interaction HS- with H2O2. Additives OH radical scavenger - tertiary butyl alcohol have no effect on the rate of oxidation of hydrogen sulfide by hydrogen peroxide. This demonstrates the 2-electron mechanism of the process: Н+ HS- + Н2О2 → S0- + 2Н2О The main complexing agent for hydrogen sulfide in natural waters are ferrous ions, forming complexes with HS- as cluster FeS [4] [5]. At a ratio of 1: 1, HS- interaction with Fe2+ occurs by mixing the reactants to form micro colloid (nano) particles with concentration of iron sulfide ≤ 10-4 M: HS-+ Fe2+ → FeS + H+ Pic. 2. The effect of small additives Fe2+ and tert-butanol at the rate of oxidation of hydrogen sulfide with hydrogen peroxide. Initial concentration: sulfide – 1∙10 -4 М; phosphate buffer – 2∙10-3 М; Н2О2 – 6∙10-4 М; Fe2+ – 1∙10-5 М; tert-butanol – 1∙10-2 М. Sediments are potential source in the aquatic environment, not only reducing equivalents in the form of H2S / HS-, but also as part of the iron sulfide. Iron sulfide which in turn effectively reacts with hydrogen peroxide. Reduced sulfur compounds effectively react with copper ions in the water layer. For example, glutathione [6] and a number of other amino thiols [7] found that the Cu + ions react with reduced sulfur compounds (RSN) to form a high-strength mono-complex (1: 1) resistant to O2 action and effective react with H2O2. Oxygen reacts with a bis-complexes Cu +, which are formed only under a large excess of thiol ligand. The monovalent copper (microcell) associated mono-thiolate complex becomes biologically unavailable, giving rise to toxic properties of the aquatic environment to aquatic organisms in the step of forming respiratory enzymes.