Activity concentration and distribution of 40K in the soil profile of the Rostov agglomeration

The activity concentration of 40K in soils of Rostov agglomeration was studied. Natural and anthropogenically modified soils of Rostov agglomeration were studied: Haplic Chernozems, Haplic Chernozems (Technic), Urbic Technosols. Activity concentration 40K in soils was measured by gamma-spectrometric method of radionuclide analysis. The total mass fraction of K2O was determined by X-ray fluorescence method on a Spectroscan MAKS-GV instrument. Knowing the total mass fraction of K2O, we calculated its potential radioactivity based on the fact that one gram of natural potassium has an activity concentration of 28.5 Bq. Comparison of the two methods allows estimating the involvement of 40K in biogenic cycles. No significant differences between the actual and calculated activity concentration of 40K in the soil-forming rock were revealed, while in horizons A and B the calculated activity is significantly higher. At the same time, there are no reliable differences between native and their buried analogs. The direct influence of the granulometric composition on the activity concentration of 40K was not established, but in the urban horizons with lightened granulometric composition the average activity of 40K is the lowest by reliably significant values when comparing this index with native, buried horizons and the group of heavy urban horizons. This implies that 40K is more actively involved in biogenic cycles than its stable isotopes. The burial under urban deposits is accompanied by a weak change in the activity concentration of 40K in the profile, while the difference between genetic horizons is leveled out.

Certain patterns of zinc, copper, and lead redistribution across the structural fractions of Chernozems and Urbic Technosols

The purpose of this work was to study the patterns of Zn, Cu, and Pb distribution in soil aggregates of various size fractions. Materials were Calcic Chernozems and Urbic Technosol of the Rostov agglomeration. Soil samples were passed through sieves with different mesh sizes (dry sieving). For the study, particle size fractions of > 10, 7-5, 5-3, 2-1, and < 0.25 mm were sampled, where the total forms of Zn, Cu, and Pb were examined by means of the X-ray fluorescence method. In the Zn content in both Calcic Chernozems and Urbic Technosol peaks in < 0.25-mm particle size fractions, the concentration decreases as particle size grows. Calcic Chernozems display Cu concentrations in mid-size soil particles of 2-1 and 5-3 mm. In Urbic Technosols, the lowest Cu concentration is typically found in particle size fractions of > 10 mm. Pb in Calcic Chernozems is concentrated in mid-size soil aggregates of 2-1 and 5-3 mm. However, Urbic Technosols tend to accumulate silt-fraction lead (< 0.25 mm). A higher zinc concentration in silt-fraction aggregates found in Urbic Technosols in comparison to Calcic Chernozems highlights the anthropogenic origin of a considerable part of this element's soil pool. Excessively high lead content in UR (urbic) horizons leads to the structure degradation and, consequently, to a transformed overall trend of HM distribution across the soil profile in general.