Lead, zinc and arsenic contamination of pit lake waters in the Zeida abandoned mine (High Moulouya, Morocco)

Abstract

In the Zeida abandoned mine, pit lake waters exhibit alkaline pH and high conductivity. The concentrations of the total dissolved lead and zinc are very low due to their adsorption on clay minerals and iron oxyhydroxides. Conversely, arsenic concentrations in two lakes (ZL1 and ZA) exceed WHO water quality guidelines. The As content is relatively high in ZL1 and exists mainly as As(V). In ZA, As(III) occurs in low concentration compared to the total dissolved arsenic, while dimethylarsenic acid (H2AsO2(CH3)2, DMA) prevails. This means that arsenic was methylated by organic matter produced by micro-organisms such as chlorella. The sequential extraction of floor sediments in the two lakes shows that the bioavailable arsenic contents change between them. In ZA, the sediments show high concentrations of lead and arsenic compared to the ZL1 sediment since it is surrounded by mining waste tailings, which are rich in these elements. An arsenic leaching test of ZA sediment shows that bioavailable arsenic is distributed in equal proportion between clay/carbonates, sulfide-organic matter and iron oxide phases, while in ZL1, most of the arsenic is linked to hydrous iron oxides.Supplementary material: Information on quality control/quality insurance for the used analytical techniques, and additional figures 9–13 are available at https://doi.org/10.6084/m9.figshare.c.5545316Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues