# Influence of Phosphogypsum Dump on the Soil Ecosystem in the Sumy region (Ukraine)
## 3 Results and Discussion
### The Study of the Soil from Different Horizons in the Territory Near the Phosphogypsum Dump  
A subtype of grey forest soils, characterized by a large, deep, fairly loose, granular, and densely permeated humus-accumulative plant root horizon (h humic content from 3%-4% to 6%-8%), formed over a larger area around the dump, which is explained by the predominance of the salinization process. Salinization of the soil with neutral salts (for example, chlorides and sulphates) leads to the formation of a neutral and slightly alkaline reaction of the medium (pH = 7.2), but when exposed to phosphogypsum, which has an acid reaction, the soil pH becomes acidic. Soils are characterized by a lower acidic pH value (on average, from 5.8 to 6.5) and the absence or masking of transitional horizons along the soil profile, weakly expressed by the brown-colored eluvial and well-defined alluvial horizon. The group composition of humus in grey forest soils is characterized by an insignificant predominance of humic acids in the composition of soil humus, and the saturation of the bases with 18-30 mg equivalent per 100 g of soil. In the alluvial horizon, the absorption capacity is markedly increased. The eluvial horizon is fairly dense, mostly of a nut-prismatic structure. Behind the sanitary protection zone of the dump are agricultural lands, where the upper horizons of the soils, primarily the humus-accumulative horizon and part of the eluvial horizon, are impacted by plowing. Although grey forest soils differ from light grey soils, with slightly better agronomic indices, they are united by acid reaction in the upper horizons, unsaturation of bases, and low content of nutrients. Soil humus possesses high sorption properties, forming complex compounds in soils with a high content of heavy metals. An essential factor determining the behavior of chemical elements in soils is the presence of acidic, water-soluble, and therefore mobile fulvic acids, which cause the process of intensive leaching out of the soil profile of many trace elements (Fe, Mn, Zn, Cd, Pb, and Sr), including heavy metals. This process is also characteristic of grey forest soils. The diffractometric analysis of these soils did not reveal the presence of compounds coming from the phosphogypsum dump. The samples from different horizons (H, E\({}_{1}\), E\({}_{2}\), and I) exhibited comparable results, except for the missing phase of calcium carbonate in horizon I. A representative pattern is shown in Figure 6. The patterns confirmed a major presence of silicon oxide (SiO\({}_{2}\)), together with alumino-silicate compounds (illite and nontronite). As mentioned above, calcium carbonate was also present in horizons H, E\({}_{1}\), and E\({}_{2}\). None of the dominant compounds listed in the diffraction pattern of phosphogypsum (calcium sulphate dihydrate and brushite) were found. Figure 6: The X-ray diffraction pattern of a soil sample (sampling point S1) (horizon H). Based on the results from the XRF analysis (Table 3), it can be stated that the samples of soils coming from the profile of Haplic Luvisols soil were mostly not significantly affected by the phosphogypsum dump. From Table 3, a higher concentration of phosphorus and sulfur in the upper horizons can be observed. Moreover, the same results were also achieved in the soil samples located around the phosphogypsum dump (samples S1, S2, and S3). The analysis of soil samples from sampling points S2 and S3 was taken from horizon H, which was generally most susceptible to the anthropogenic influence and the accumulation of pollutants. Strontium is ubiquitous in nature and one of the most abundant of the trace elements in surficial deposits and rocks, acting as a proxy for Ca because both are alkaline earth elements with a similar ionic radius and the same valence [28]. Strontium is easily mobilized during weathering, especially in oxidizing acid environments, and is incorporated in clay minerals and strongly fixed by organic matter.