Soil heavy metal contamination in the vicinity of the abandoned Zelda mine in the Upper Moulouya Basin, Morocco. Implications for airborne dust pollution under semi-arid climatic conditions

For thirteen years, the Zelda mine was one of Morocco's biggest lead reserves. The mining activities produced a huge volume of waste stored as tailings and subjected to meteoric agents. To better understand the impact of the past mining activity on the soil ecosystem in the vicinity of the abandoned mine, several physical and chemical analysis were done to identify the level of soil contamination. A total of 27 surface soil samples were collected from a depth of about 0-20 cm from crop areas and analysed for Pb, Zn, Cu, Co, Cd, and As total concentrations (aqua regia extraction) using the ICP-MS method. Results showed that soils have high to medium levels of metal concentrations, especially close to the tailings, compared to the non-contaminated soil sample taken as a geochemical background reference. Analysis of physicochemical parameters (pH, electrical conductivity, total calcium, phosphorus, potassium, and organic matter) has shown high alkalinity levels related to carbonates, varying organic matter content, and electrical conductivity values ranging from 4.12 to 1466 mu S/cm. Most of the studied soils share the same mineralogical composition that includes: carbonates (Calcite and Dolomite), Quartz, Orthoclase, and Muscovite. Lead mineral phases (cerussite and wulfenite) have been found in 3 samples (ZAM17, ZAM18, and ZAM21). The Illite and the Kaolinite are the main clay minerals. Descriptive and multivariate statistics were carried out to investigate the distribution of the studied metals. Comparing the obtained results with International Standard Limits (ISL), soils especially those close to the mine tailings show high heavy metals content. Pb, Zn, Cu, As, and Cd contents in Zelda soils are usually linked to anthropogenic origins. Results have shown correlation values between As, Cu, and Cd and Pb and Zn indicating that they come from the same origin and react similarly throughout transport.