Contamination, sources and environmental risk assessment of heavy metals in water, sediment and soil around an abandoned Pb mine site in North East Morocco

Metal Mining Contamination is a widespread problem in the world. However, the assessment of abandoned mine metal contamination, especially in Morocco, has not been studied sufficiently. In this study, a total of 83 samples of water, sediments, and soils were collected to investigate the concentrations of heavy metals (HMs) around an abandoned mining area, named: Zeida in North East Morocco. Furthermore, geochemical mapping of these elements has been also conducted. The contamination and environmental risk introduced by the accumulation of HMs has been assessed using numerous ecological indexes, such as: geo-accumulation (Igeo), Potential Ecological Risk Index and Modified Contamination Degree (MCd) to name just a few. Add to that the assessment of water quality using water quality assessment indexes. The results showed that all major elements and HMs of the river and its tributaries were within the Guidelines for Drinking-Water Quality (GDWQ), except for levels of HCO3-, and K+. The hydrochemical facies was dominated by calcium magnesium bicarbonate (CaMg-HCO3), and the concentrations changed in the range (mu g/l): Zn: 14.78-152.00, Cr: 2.56-13.23, Cu: 0.96-12.35, Pb: 0.03-11.26, As: 0.98-3.24, Ni: 0.11-1.34 and Cd: 0.01-0.31, respectively. The spatial distribution of HM concentration and numerous ecological indexes in soil and sediment samples revealed that the highest values were located in and near the tailings, and declined downstream, which classified these sites as very highly contaminated and severely hazardous. Vertically, the soil concentration of HMs accumulated increasingly in relation to depth, and that in fact highlighted their potential mobility. HM concentrations (mg/kg) in sediments were in the range of: Pb: 43.79-9889.30, As: 104.57-289.00, Cr: 25.84-125.00, Zn: 40.78-121.75, Cu: 8.85-36.11, Ni: 1.99-21.00 and Cd: 0.10-0.46, respectively. While the average concentration in the three depths of soil (mg/kg) were in the range of: Pb: 27.00-11,400.00, Zn: 36.00-231.33, As: 42.33-172.00, Cr: 21.67-105.33, Cu: 18.33-143.33, Ni: 13.67-40.33 and Cd: 0.04-1.33, respectively. Multivariate statistical analysis indicated that HMs were related to the dispersion of tailings materials, with the exception of Ni and Cr which were related to lithological source.