# Determination of Arsenic Species Distribution
###### Abstract
Non-toxic species are arsenocholine, arsenobetaine, and arsenosuclear, the main metabolites of arsenic in marine animals [4]. Under environmental conditions, arsenic is characterized by different ranges of arsenic content in groundwater as a result of water-rock interactions and the gradual entry of arsenic into aquifers and soil. Anthropogenic sources also contribute substantially to pollution, mainly attributable to waste and atmospheric emissions from the mining and processing industries and the energy sector; these emissions result in the accumulation of arsenic-containing waste and pollution of soils and sediments near pollution sources [5; 6]. Furthermore, at the same time, the environmental risks of mine tailings are of particular concern [7; 8; 9; 10; 11]. A lot of research is devoted to finding effective methods for purifying natural waters from arsenic. These methods include the adsorption technique [12; 13]; use of a nanofiltration membrane [14]; biological oxidation followed by As\({}^{\text{V}}\) removal with Fe and Mn dioxide [15; 16]; and with the help of modelling various adsorption processes [17; 18; 19; 20; 21]. Element speciation is fundamental to understanding the toxicity and mobility of chemical elements and is an important addition to the knowledge of the total content of elements, including arsenic. In geochemistry, physicochemical modeling, which is widespread, is used to calculate the content of various forms based on the known chemical composition and physicochemical characteristics of the system under consideration. However, the applicability of this approach critically depends on the availability of reliable thermodynamic data and timely updating of databases. In the case of arsenic, the thermodynamic properties of metal arsenates are well characterized, but metal arsenites are poorly studied, and thermodynamic data for arsenides and arsenic sulfides are practically not studied [22; 23]. Alternative approaches are the determination of arsenic forms using a sequential extraction approach, which allows the extraction of a set of chemical forms with similar physicochemical characteristics, or the direct use of complex analytical methods that make it possible to directly determine specific chemical forms of arsenic [24]. Most of the work on the determination of arsenic species using the step leaching approach was focused primarily on contaminated soils and deposits and mining waste [25; 26; 27; 28; 29; 30]. However, at the same time, there is little work that is directly devoted to the use of step leaching for As-rich waste, which has high arsenic contents and characteristic As-containing minerals [31; 32]. The key feature is the choice of leaching conditions and reagents, taking into account such parameters as geochemical parameters (pH, Eh, total composition, the ratio of Fe, As, and S in the tailings), the age of the tailings, and mineral transformation (oxidation, dissolution, and redeposition) under storage conditions. In addition, there are chemical analysis methods for determining the forms of arsenic in solutions, including high-performance liquid chromatography and capillary electrophoresis in combination with inductively coupled plasma-mass spectrometry (HPLC-ICP-MC/CE-ICP-MS) [24]. Techniques have also been described for the non-chromatographic determination of the arsenic forms arsenic (As\({}^{\text{III}}\)) and arsenate (As\({}^{\text{V}}\)) using the methods of atomic emission spectrometry with hydride generation technique (HG-ICP-AES) [33; 34]. One of the objects on the territory of Eastern Siberia of particular interest is the tailings ponds of the Tuvakobalt plant, which is located in the village Khovu-Aksy (Chedi-Kholsky Kozhuun, Republic of Tuva, Russia). These tailings are recognized as the most environmentally hazardous facilities in the Republic of Tuva and pose a threat of interregional environmental pollution. The tailings have also been repeatedly mentioned in reports on the state of the environment and the media.