# Influence of Phosphogypsum Dump on the Soil Ecosystem in the Sumy region (Ukraine)
## 1 Introduction  
Phosphogypsum is a by-product of the chemical reaction called the \"wet process\", whereby sulfuric acid is reacted with phosphate rock to produce the phosphoric acid needed for fertilizer production [1]. The quality and quantity of phosphogypsum generation depends upon the quality of the phosphate rock, the process used to produce phosphoric acid, and the calcium sulphate generated either in di-hydrate (CaSO\({}_{4}\)\(\cdot\)2H\({}_{2}\)O) or hemi-hydrate (CaSO\({}_{4}\)\(\cdot\)1/2H\({}_{2}\)O) form. Production of 1 ton of phosphoric acid generates 5 ton of phosphogypsum [2]. The presence of harmful impurities and their concentration depends on the composition of the phosphate rock. The reaction of the interaction of fluorapatite and acid mixture is:  
\[\text{Ca}_{5}(\text{PO}_{4})_{3}\text{F}+\text{5H}_{2}\text{SO}_{4}+\text{nH}_ {3}\text{PO}_{4}+\text{mH}_{2}\text{O}\rightarrow(\text{n}+3)\text{H}_{3} \text{PO}_{4}+\text{5 CaSO}_{4}\text{-mH}_{2}\text{O}+\text{HF}\]  
Fluorine compounds and sulfur are primary pollutants in industrial emissions generated by the production of wet-process phosphoric acid and phosphate fertilizers. Possible heavy metal pollution inareas of phosphorus-containing fertilizer production is caused by the presence of metals in phosphoric raw materials in the form of ballast elements, as described in a number of works [2; 3; 4; 5; 6; 7; 8; 9]. Phosphogypsum is stocked in large open areas or accumulated in lakes, resulting in a major environmental problem due to the presence of toxic elements dispersed by wind (dust) and water. Metal contamination may affect the functionality, sustainability, and biodiversity of ecosystems [10]. At the same time, estimates on the severity and frequency of acute exposures deriving from old generation facilities are important, so as to estimate the extent of local health impacts. Similarly, much better and more complete data are needed on informal waste management activities and illegal operations, given the likely substantial magnitude of the health burden suffered by the people involved [11]. The main challenges regarding phosphogypsum management are:  
* high fluoride concentration (in the range of 0.5%-1.5%), which can be leached and contaminate groundwater;
* presence of radionuclides;
* occurrence of heavy metals (Cd, Cr, Pb, etc.) that may enter into the food chain through potable water and agriculture products [2]. According to [PERSON] et al. [12], the amounts of mobile contaminants that could be released for every ton of phosphogypsum are approximately \(7\times 10^{2}\) g Sr, \(1.1\times 10^{2}\) g Fe, 55g Y, 30 g Ce, 12 g Cr, 11g Ti, 5 g Zn, 4 g each of Cu and Pb, 3 g each of V and Cd, 2 g each of As and Ni, and 1 g U. Multiplying these amounts by 100 Mt and 20-25 t/ha, it is possible to calculate risk assessments for phosphogypsum for both estuarine zones (e.g., in a hypothetical stack collapse resulting in spilling of waste and in agricultural soils). [PERSON] et al. [13] proposed that in some cases (e.g., Hg and Cd), the high concentrations of soil heavy metals attributed to human activity can be detected at a regional level. While the immense majority of European agricultural land can be considered adequately safe for food production, an estimated 6.24%, or 137,000 km\({}^{2}\), needs local assessment and eventual remediation action. The fluorine compounds emitted by this production can reach the soil by dry deposition, rainfall, or decomposition of plant residues contaminated by fluorine [14]. The fluoride distribution in the environment is controlled by physical-chemical parameters of emission, rain intensity, and soil properties [15]. Fluoride accumulates in the top soil layer because it is retained by the iron, aluminum hydroxide, oxide, and silicate compounds in the soil [16].