Natural attenuation of lead by microbial manganese oxides in a karst aquifer
Newsome, L; Bacon, CGD; Song, H; et al.Luo, Y; Sherman, DM; LLoyd, JR
Date: 21 September 2020
Article
Journal
Science of the Total Environment
Publisher
Elsevier
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Abstract
Lead is a toxic environmental contaminant associated with current and historic mine sites.
Here we studied the natural attenuation of Pb in a limestone cave system that receives
drainage from the ancient Priddy Mineries, UK. Extensive deposits of manganese oxides
were observed to be forming on the cave walls and as coatings in the ...
Lead is a toxic environmental contaminant associated with current and historic mine sites.
Here we studied the natural attenuation of Pb in a limestone cave system that receives
drainage from the ancient Priddy Mineries, UK. Extensive deposits of manganese oxides
were observed to be forming on the cave walls and as coatings in the stream beds. Analysis
of these deposits identified them as birnessite (δ-MnO2), with some extremely high
concentrations of sorbed Pb (up to 56 wt. %) also present. We hypothesised that these cave
crusts were actively being formed by microbial Mn(II)-oxidation, and to investigate this the
microbial communities were characterised by DNA sequencing, enrichment and isolation
experiments. The birnessite deposits contained abundant and diverse prokaryotes and fungi,
with ~5 % of prokaryotes and ~10 % of fungi closely related to known heterotrophic Mn(II)-
oxidisers. A substantial proportion (up to 17 %) of prokaryote sequences were assigned to
groups known as autotrophic ammonia and nitrite oxidisers, suggesting that nitrogen cycling
may play an important role in contributing energy and carbon to the cave crust microbial
communities and consequently the formation of Mn(IV)-oxides and Pb attenuation.
Enrichment and isolation experiments showed that the birnessite deposits contained Mn(II)-
oxidising microorganisms, and two isolates (Streptomyces sp. and Phyllobacterium sp.)
could oxidise Mn(II) in the presence of 0.1 mM Pb. Supplying the enrichment cultures with
acetate as a source of energy and carbon stimulated Mn(II)-oxidation, but excess organics in
the form of glucose generated aqueous Mn(II), likely via microbial Mn(IV)-reduction. In this
karst cave, microbial Mn(II)-oxidation contributes to the active sequestration and natural
attenuation of Pb from contaminated waters, and therefore may be considered a natural
analogue for the design of wastewater remediation systems and for understanding the
geochemical controls on karst groundwater quality, a resource relied upon by billions of
people across the globe.
Camborne School of Mines
Collections of Former Colleges
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