Microbiology of an abandoned Pb–Zn mine: Impact on environmental metal contamination

Large-scale Zn, Pb, Cu, Fe and Ag mining ceased over 70 years ago in the Aran Valley (Catalonia, Spain). Some of the abandoned mining relics (e.g. tunnels, processing facilities and tailings dumps) exhibit elevated concentrations of metals in the associated water systems, thus posing a health risk in the neighboring ecosystem. In this study, the largest underground zinc mine in the area was chosen as a field site to showcase the processes affecting metal mobility in the environment. The precipitation of hydrozincite (Zn5(CO3)2(OH)6) that occurs along the walls and ground of galleries where water flows serves as a metal (e.g. Zn, Ni, Cd) polishing mechanism. We focus on the microbiology at the site and its potential impact on metal mobility. Microbial DNA was sampled from several locations inside and outside of the mine and subsequently sequenced. This is used to further determine the relative diversity of each community to make comparisons between indoor and outdoor locations. By way of DNA sequencing of local communities, microbial batch experiments, and morphological comparisons to samples known to be a product of biomineralization, it is confirmed that the mineral forms abiotically at the mine.We would like to thank the CCiTUB and IDAEA-CSIC research group for the analysis and tech support. We thank Jordi Bellés, Natàlia Moreno, Rafael Bartrolí and Mercè Cabanas (IDAEA), David Artiga, Maite Romero and Xavier LLovet (SCT-Barcelona University) for analytical assistance. This work has been financed by the CGL2017-82331-R project (Spanish Ministry of Economy and Competitiveness), with contribution of FEDER founds, and 2017SGR 1733 project (Catalan Government). IDAEA-CSIC is a Centre of Excellence Severo Ochoa (Spanish Ministry of Science and Innovation, Project CEX2018-000794-S funded by MCIN/AEI/10.13039/501100011033). We also thank the Editor and two anonymous reviewers for their helpful comments on this manuscript.Peer reviewe