Introduction: The influence of the interaction of calcium carbonate (CaCO 3 ) and surface-active substances (SAS; surfactants) with different chain lengths and cationic and anionic hydrophilic centers has been analyzed. Results: Laboratory simulations indicate reduced negative influences on cationic SAS nitrification/self-purification processes in the presence of anionic species. This suggests the role of complex ionic formation [anionic SAS * cationic SAS] as a cause of this effect. UV-Vis spectra of lauryl sulfate (LS) and of cetyltrimethylammonium (CTMA), as well as of their mixtures in ratios of 2:1 and 1:1, treated by fine particles of CaCO 3 , display decreased amounts of SAS in analyzed solutions and their presence on the surface of CaCO 3 nanoparticles. UV-Vis spectra reveal the decomposition of the complex [anionic SAS (SAS-An) * cationic SAS (SAS-Ct)] in solutions when CaCO 3 is added. CTMA can be bonded by LS through hydrophobic chains, on the surface of CaCO 3 particles. Therefore, CaCO 3 modifies the nature of LS and CTMA interactions. This leads to an increased degree of toxicity of cationic SAS in aquatic environment. The amounts of CTMA in aqueous solutions are diminished in the presence of ammonium ion NH 4 + (2 mg/L). In the presence of two orders higher concentration of ammonium ion, this effect strongly increases, making the association obvious. The structure of cationic SAS does not influence this effect. The obtained results have been confirmed both by timed natural aquatic sample analysis and laboratory simulations using water from Moldovan small rivers (Isnovat, Raut, and Bic). Conclusions: UV-Vis spectra and laboratory simulations demonstrate the change due to the addition of calcium carbonate. Simulations and laboratory tests of water samples from Isnovat, Bic, and Raut Rivers, establish the cationic SAS negative influence on treatment and self-purification processes.

Abstract. Geometry optimizations at the UBP86/6-311++G** level of electronic structure theory have been performed for DDT, β-hexachlorocyclohexane, and heptachlor organic polychlorides as well for their positive and negative ions. The HOMO composition of these neutral molecules show no participation of the carbon-chlorine atomic orbitals, while LUMO of the calculated molecules include a major contribution of the anti-bonding character atomic orbitals from the two or three carbon-chloride bonds of each calculated molecule. Consequently, the negative ions were the most sensitive structure during the geometry optimization, showing the carbon-chloride bonds cleaving during the electronic structure calculations. Further geometry optimization of the obtained neutral intermediate molecules after the fi rst and second reducing by two electrons show that the electrochemical dehalogenation of the organic poychlorides is sequential.Keywords: poisonous pesticides, organic chlorides, electrochemistry, DFT, carbon-chloride bonds. IntroductionThe electrochemical method for disposal of halogenated organic compounds leads to complete mineralization of organic halides. Generally, the electro-reductive treatments using new, improved electrochemical sensors, lead to partial recovery/recycling of chemicals, are regarded as an advantageous [1]. Methods of chemical and electro-chemical oxidation applied to organic pollutants attain, in most cases, a complete mineralization, being considered to have highenergy requirements [2]. Reduction will not lead to a complete mineralization, but to a complete dehalogenation, with a possible formation of double bonds. This has been proven for organic halides with one [3,4], two [5,6], three [7], four [8] or six [9] halogen atoms in their structure.Dehalogenation reactions of halogen-alkanes have been studied by direct and indirect electrochemical reductions and classical kinetics. The electrochemical redox processes can be divided into two categories: direct (heterogeneous) and indirect or mediated (homogeneous) ones. Direct electrochemical reduction involves electrons accepted directly by the analyte from the cathode surface, while indirect electrochemical reduction occurs between the analyte and an electrogenerated species, which serves as catalyst. Some authors use the term "mediator" as an alternative for catalyst [1]. The catalyst can exist in the electrolyte solution or can be immobilized on the electrode surface, namely CME's or chemically modifi ed electrodes [1,10]. By modifying the surface of the electrodes by adsorption of molecules or ions, the surface reactivity and slow kinetics can be overcome [10].Mechanistically, the halogen atoms are removed in a successive fashion, along with a two electron transfer at more and more cathodic (negative) potentials. This has been proven for polyhalogenated aromatics [11] and remains under question for polyhalogenated aliphatics. The diffi culty of attaining suffi ciently cathodic potentials would explain why complete dehalogenation does not alway...