Spatial Distribution and Contamination Assessment of Soils Affected by the Baikal Pulp and Paper Mill Sludge Impoundments (Baikal Region, Russia)

This study evaluates the impact of the sludge impoundments at the Solzan site of the former Baikal Pulp and Paper Mill at Lake Baikal on soil chemistry. Concentrations of 16 elements were analyzed in the surface soil layer both near and at a distance from the sludge impoundments. Chemical analysis was performed using atomic absorption spectrometry. The results showed that, based on the coefficient of variation (CV), element concentrations in soils near the impoundments exhibited moderate (29–49%) variability for Al, V, Cd, Cr, Pb, Ca, and Ni; high (53–68%) for Sr, Mn, Co, Mg, Fe, and As; and extreme (109–317%) for Cu, Hg, and Zn. At a distance from the impoundments, the variability was substantially lower: Al (19%); V, Mn, Fe, Pb, Cr, Mg, Cd, Co, and Ni (24–48%); Ca, Sr, Hg, Cu, and As (50–90%); and Zn (121%). The level of anthropogenic impact was assessed using contamination indices calculated relative to the local reference levels. According to the contamination factor (CF), most of the samples exhibited low to moderate contamination. However, localized significant (Co, As, Hg, Cu, Pb) and very high (Zn, As, Cu, Hg) contamination was recorded near the impoundments, as well as significant (Cu, As, Sr) and very high (As, Zn) contamination at a distance. The pollution load index (PLI) indicated multi-element contamination in some samples, both near and at a distance from the impoundments. The enrichment factor (EF) suggested minimal to moderate enrichment for most of the samples. Nevertheless, individual samples exhibited significant (Cr, Co, V, Ni, Zn, Cd, Al, Pb, Hg, As, Cu), very high (Hg), and extremely high (As) enrichment near the impoundments, as well as significant enrichment (Cu, Zn, As) at a distance. These findings expand the theoretical understanding of element distribution, accumulation, and migration patterns in environmental compartments during the post-operational phase of major industrial contamination sources. Furthermore, they hold practical significance for planning future reclamation and environmental protection measures.