Assessment of heavy metals and arsenic contamination in the sediments of the Moulouya River and the Hassan II Dam downstream of the abandoned mine Zeïda (High Moulouya, Morocco)

• The Pb contamination is located exclusively downstream of the tailings; the anthropogenic inputs, from the abandoned tailings, of Pb into the Moulouya stream is highly regarded, despite its natural occurrence.
• The Pb contamination attenuate to the dam Hassan II.
• The Arsenic is present at high levels in all sediments samples, even the dam Hassan II sediment samples are highly contaminated, suggesting a larger scale contamination compared to Pb. This contamination can be attributed to either lithological inputs (Mineralogical features), anthropogenic inputs (agricultural practices), or both sources combined.
• Copper and Zinc are derived from lithogenic sources, the measured concentrations exposed low contamination levels in all sediment samples, therefore both metals have no serious hazard to the studied sediments.

To evaluate the sediment contamination level near the abandoned (PbZn) mine Zeïda, heavy metal concentrations were determined in sediment samples from the Moulouya River, the Ansegmir tributary and the Hassan II Dam located downstream of the abandoned mine. These samples were analysed for their geochemical properties: mineralogy by XRD, carbonate content, pH, particle size and the total concentrations of Pb, Zn, As and Cu elements by ICP-AES. The assessment of the sediment pollution extent was performed by using the multiple pollution indices: contamination factor (CF), pollution load index (PLI) and the geoaccumulation index (Igeo). The Highest CF values (>6) of Pb that have been observed downstream of the tailings promote a high Pb contamination in that specific area. The PLIs results showed that all stations, except for those upstream of the tailings and on the Hassan II Dam, have been found moderately to highly contaminated. The Igeo results confirmed the Pb high contamination but also the extreme As contamination. The potential ecological risk factor results and the comparison with the sediment quality guidelines revealed that the Pb and As levels are potentially toxic to the sediment-dwelling organisms. Based on the multivariate statistical analysis results and the spatial distribution of the sediment contamination level, the pollution of Pb and As have different sources. Pb contamination is located exclusively near and downstream of the tailings. These latter's may be considered as an important point source of Pb into the Moulouya River. The As contamination is derived from a larger scale input sources which can be related to anthropogenic and/or lithogenic effects.