Integrated environmental Assessment of multielement Contamination in Mining-Impacted Soils and Leachates: A Case Study from Northeastern Algeria

Abandoned mining sites are a major source of long-term soil contamination by potentially toxic elements. This study assessed the environmental risk of metal-contaminated soils from the Sidi Kamber mine (northeastern Algeria). Mining residues are spread into the surrounding areas and the Oued Es-Souk, a river that supplies the Guenitra dam.This dam is the main drinking water reserve in the Skikda region..

This study is based on the geochemical and ecotoxicological analysis of 16 soil samples, from four stations distributed along the Oued Es-Souk until the dam. Samples were taken at two depths (0–25 cm and 25–50 cm) during both the dry and wet seasons. in Metal availability was evaluated through simulated leachate analyses, while soil properties (pH, fertility and pseudo-total elemental concentrations) were determined using conventional methods. Ecotoxicological bioassays were conducted to assess the biological effects of both soils and leachates in two plant species (Allium cepa and Lactuca sativa), focusing on seed germination, root elongation, and total biomass production as sensitive indicators of phytotoxicity.  Soil pollution indices, including the Igeo-Geoaccumulation Index and the CF-Contamination Factor were calculated to quantify contamination levels and identify the most critical elements.

The soils showed a very variable conductivity (510–3460 μS/cm) and a pH ranging from neutral to slight acid (5.15–7.54), with a tendency towards acidification during dry season. The leachates, less saline, were systematically acid (pH ~5). The organic carbon and some available nutrients contents were relatively low confirming low soil fertility.

The upstream location had the lowest Zn, Mn, Cu, and Pb concentrations in pseudo-total fraction recorded in wet season (194, 480, 16.5, and 88 mg/kg, respectively).  Despite being the lowest on the site, these levels exceeded benchmarks reported by Dutch Target Values or AFNOR standards. The highest concentrations are located at the surface of the soils and at specific points, reflecting a localized accumulation.  Mobility Index (MI = Av/PT) ranked metals in descending order of mobility: Cd>Zn>Ni>Cu>Pb>Cr>Fe. Contamination Factors confirm a significant polluting heritage: the pseudo-total contents of Zn, Pb and Cd are considerably enriched (CF>10 in many cases) compared to local natural levels. The geoaccumulation index classifies metals into three categories: strong to extreme contamination for Cd and Pb (Igeo>3); moderate accumulation for Zn and S (1<Igeo<2); and low to natural levels for Fe, Mn, Cr and Ni (Igeo=0).

Inhibition index specially on  Lactuca, shows that root growth is much more sensitive than germination. If it is very little affected (indices from -0.06 to +0.01), the length of the roots varies greatly, from a marked inhibition (-33.5% for the most toxic sample) to a significant stimulation (+46.5%). Among all the relationships studied, it is between pH and germination that the negative correlation is the most marked..

Overall, this integrated approach provides a comprehensive framework for assessing the environmental risks associated with abandoned mining.

This work was funded by national funds through FCT – Fundação para a Ciência e a Tecnologia, I.P., under the projects UIDB/04129/2020 and UID/04129/2025 (LEAF) and LA/P/0092/2020 (TERRA).