VOLUME 54 (2)/August 2025

The Pliocene sediments of the Brusartsi Formation play a role of the bedrock in the Kozloduy lowland. Several important nuclear facilities have been constructed in this area. The upper part of the formation falls into the vadose zone and this part of the sediments is the main natural barrier against eventual radionuclide migration in the geoenvironment. One of the most important parameters used in estimation of mass transport is the distribution (or partition) coefficient Kd. It is one of the most important parameters for the evaluation of the retention capacity of a given soil to adsorb dissolved contaminants. In the current paper the determination of the site-specific Kd values of Ni and Sr for clayey soil from the Brusartsi Formation derived by direct and indirect methods is described.

This study analyzes groundwater quality and its suitability for irrigation purposes. Various 2D models have been created using GIS to illustrate the groundwater chemistry of Bulgaria's hypergenic zone (Ca²⁺, Mg²⁺, Na⁺, SO₄^2–, Cl^–, EC, and TDS), focusing on groundwater with active water exchange. These models are based on data from the Executive Environment Agency of Bulgaria from 2015 to 2019. The author has constructed 2D models representing several indicators of water quality suitable for irrigation, including the Sodium-adsorption ratio (SAR), Magnesium hazard ratio (MHR), Potential salinity (PS), and the (Mg²⁺/Ca²⁺) and (Na⁺/Ca²⁺) ratios. The identified irrigation indicators provide a regional perspective on groundwater quality across Bulgaria. On a macro scale, average values for the individual indices classify shallow groundwater primarily as suitable for irrigation, with a small percentage deemed unsuitable. Its potential to create issues related to soil infiltration capacity and structural degradation, assessed based on salinity and sodium (or alkaline) hazards, is primarily classified as low.

Eight biomass ashes (BAs) generated from agricultural, herbaceous, woody and aquatic biomass types were studied for the occurrence of 14 nutrient elements (NEs) and 6 contaminant elements (CEs) to evaluate their significance for potential soil fertilization. For that purpose, a combination of different mineralogical and chemical analyses, and leaching procedures was used. The data show that the contents of NEs in BAs are highly variable; however, the concentrations of B, Ca, Cl, Cu, K, P, S, and Zn, and, to a lesser extent, Mg, Mn, Mo, Na, and Ni in BAs are perspective for potential soil fertilization or soil conditioners. The inorganic matter of BAs comprises amorphous matter and different minerals among carbonates, silicates, chlorides, sulphates, oxyhydroxides, and phosphates. BAs have high yields of water-soluble solutions with alkaline character, which are favourable for BA use. NEs such as Ca, Cl, K, Mg, Na, P, and S occur significantly in water-soluble and bioavailable salts. Various NEs and CEs in BAs fulfilled the available regulation limits for fertilizing products, excluding some problematic concentrations of Cd, Co, Cr, Fe, Mo, Ni, and P for specific BAs. Therefore, each BA needs to be studied on a case-by-case basis for that purpose. The establishment of advanced regulatory framework for BA utilization as fertilizing products is required to generate strict limit values of NEs and CEs in BA leachates. The water-extractable proportions of elements from BA and their release in time are very important to predict the supply of bioavailable NEs or CEs for crops.