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.