Due to its very rich and varied geological heritage, the Moroccan subsoil contains many mining deposits that are subject to large-scale exploitation and extraction (mainly phosphates, base metals and precious metals) assigning to this sector an important role in the country's economic development. However, the exploitation of these mineral resources can present serious negative influence on the environment. Indeed, mining activities can disrupt natural environments in several ways, e.g. by altering landscapes, depositing large amounts of hazardous tailings and discharging polluted liquid and atmospheric effluents. Thus, it causes significant environmental damage with negative impacts on air, water and soil quality as well as the loss of biodiversity. Growing concerns about the consequences of mining activities, particularly mining waste, have led many researchers to assess the extent of the environmental damage they have caused. This review summarizes the most important research finding published on the environmental impact assessment of mining industries. Particular attention is paid to some metal ore mines, mainly abandoned ones, occurring across Morocco. The results of the environmental assessments have shown that the abandoned tailings dumps have caused severe contamination of the environment and its compartments. However, the major impact was observed in soils around the mining zones. Thus, particularly in sulphide-rich mines, such as Kettara, Draâ Lasfar, Ouixane, Axara and Sétolazar mines, the tailings with high acid-generating potential have led to a significant pH level decrease (down to pH 2) and to a severe metal contamination of soils. In many affected areas, toxic metal concentrations exceed standard levels admitted for agricultural soils (1.5 mg of Cd kg-1, 300 mg of Cu kg-1, 150 mg of Pb kg-1 and 300 mg of Zn kg-1). Currently, this pollution continues to spread through these sites to the environment due to the lack of proper remediation of these mining lands. The persistence of this situation, therefore, poses a risk not only to the environment but also to the health and safety of the local population living near these sites.

The mining industry is of major importance to Morocco’s economy. However, the abandoned pyritic mines are a source of potentially toxic elements that can cause the disruption of the surrounding ecosystems, constituting a huge threat to wellbeing and human health. The present study aimed to analyze the physical and chemical characteristics of different types of tailings and to investigate the microbial populations of acidophilic bacteria involved in the oxidation of pyrite. Coarse and fine tailings collected from different zones of the mine (dike and pond) at two different depths (oxidized and non-oxidized residues) were analyzed for their pH, electrical conductivity, total organic carbon, total nitrogen, available P, major elements, and pseudo-total metal concentrations. The abundance of acidophilic bacteria was determined, and some acidophilic bacterial strains were isolated and tested for their metal tolerance. Tailings showed a pH ≈ 2, very low nutritional content, and high concentrations of Cu, As, Zn, and Pb, which were higher in the non-oxidized samples. The microbial counts of iron- and sulfur-oxidizing bacteria were higher than heterotrophic bacteria, with the highest numbers detected in the oxidized fine tailings. The five acidophilic bacteria isolated from the tailings were affiliated to genera Alicyclobacillus and Sulfobacillus, commonly found in this kind of environment.