Methodology for assessing the stability and evaporation of volatile substances from the soil

When determining the maximum permissible concentrations of volatile substances in the soil, data on their background concentrations, physico-chemical properties, and resistance/toxicity parameters are used. The permissible concentration of volatile matter is experimentally established, at which its entry into the air does not exceed the permissible standards for atmospheric air. This process is associated with certain difficulties caused, first of all, by the complexity of modeling the emission of toxicants from soils in laboratory conditions, and the duration of the process. In this regard, standards for the content of volatile substances in soils have now been established, taking into account their emissions, mainly for pesticides and toxic substances. To eliminate this gap, an economical and simple technique has been developed that allows high accuracy in field and laboratory conditions to study the stability and evaporation rate of volatile substances from soils. To implement the technique, a gas analyzer based on piezosensors of the "electronic nose" type is used. Using the example of dimethylamine the weekly dynamics of changes in concentrations of its vapors above soils, different for typical chernozem and gray forest soil, is shown; the content of the pollutant on geochemical barriers of soils up to 20 cm deep is estimated. Dimethylamine is a relatively stable chemically hazardous substance, whose transformation in the surface layer of soils occurs by a maximum of 52 % in 7 days, and at depth by 21 % during the same time. With significant spills of dimethylamine (0.25 dm3/dm2), the concentration of its vapors decreases in 7 days to 6–8 maximum permissible concentrations set for the air of the working area. It is recommended to examine soils at a depth of 20 cm or more to assess the toxicity of substances, since secondary emission of pollutants is possible.