Impact of Heavy Metal Content on Soil Physicochemical Properties, Soil C : N : P Stocks and Stoichiometric Ratios in Mine Soils: Northeast of Algeria

Despite its abandonment, a former Zn–Pb mine in northeastern Algeria continues to emit contaminants into the surrounding environment, contributing to local soil degradation. This study assesses the impact of heavy metal contamination on soil quality, focusing on nutrient balance and pollution levels. The analysis covered physicochemical properties such as pH, electrical conductivity, organic matter, soil organic carbon, total nitrogen, total phosphorus, elemental stocks (C, N, P), and concentrations of trace metals (Pb, Zn, Fe, Cd, Cu, Ni). Standardized indices evaluated contamination levels using a combination of geochemical enrichment (enrichment factor) and ecological risk (geoaccumulation index, contamination factor, and ecological risk index). Results show that most soil samples are classified as Arenosols, with those nearest to the mine exhibiting a highly acidic pH (2.4), elevated salinity (1463 µS/cm), and increased organic content along with heavy metals, mainly Pb (2813 mg/kg) and Zn (337.45 mg/kg). The imbalances in elemental ratios reflect significant disruptions in nutrient cycling. Pollution indices categorize the area as extremely polluted, with Pb presenting the highest ecological threat, followed by Cd, Cu, Zn, and Ni. These findings underscore the ongoing environmental risks associated with abandoned mining activities.