Spatial and temporal analysis of the distribution of copper in soils affected by the long-term impact of copper smelter—Aurubis Bulgaria AD

Abstract

This study investigates the spatial and temporal distribution of copper (Cu) in soils affected by long-term atmospheric emissions from a major copper smelter in the Zlatitsa–Pirdop Valley, Bulgaria. The objective is to assess how industrial activity and subsequent technological changes influenced Cu accumulation patterns over a 48-year period (1973–2021). Soil samples were collected along eastward transects at multiple distances from the smelter and analyzed using standard aqua regia digestion followed by atomic absorption spectrometry (AAS) and inductively coupled plasma optical emission spectrometry (ICP-OES) techniques. Three temporal datasets (1973, 1995 and 2021) were compared to evaluate long-term changes in Cu concentrations and spatial distribution. The results show a pronounced shift in contamination patterns over time. In 1973, Cu concentrations exhibited a clear decrease with distance from the emission source, indicating localized deposition. In contrast, data from 1995 and 2021 reveal a more complex spatial pattern, with persistently elevated Cu levels at greater distances from the smelter. This change reflects modifications in emission release height, atmospheric dispersion conditions, and long-term redistribution processes. The study demonstrates that Cu behaves as a persistent and poorly mobile contaminant in surface soils, with limited natural attenuation over decadal time scales. Despite significant improvements in emission control technologies after industrial privatization, historical deposition continues to dominate current soil contamination levels. The findings highlight the combined role of anthropogenic emissions, valley topography, meteorological conditions, and local geochemical background in controlling heavy metal distribution. This study contributes to a better understanding of long-term soil contamination dynamics in industrial mountain-valley environments and provides a basis for environmental monitoring and risk assessment strategies.