1. Overlapping redox zones control arsenic pollution in Pleistocene multi-layer aquifers, the Po Plain (Italy)
- Author
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Elisa Sacchi, Rasmus Jakobsen, Veronica Nava, Letizia Fumagalli, Barbara Leoni, John M. McArthur, Chiara Zanotti, Tullia Bonomi, Giuseppe Etiope, Marco Rotiroti, Alessandra Sciarra, Rotiroti, M, Bonomi, T, Sacchi, E, Mcarthur, J, Jakobsen, R, Sciarra, A, Etiope, G, Zanotti, C, Nava, V, Fumagalli, L, and Leoni, B
- Subjects
Environmental Engineering ,Peat ,010504 meteorology & atmospheric sciences ,Pleistocene ,Methanogenesis ,Iron ,Methanogenesi ,Geochemistry ,Aquifer ,010501 environmental sciences ,01 natural sciences ,GEO/05 - GEOLOGIA APPLICATA ,TEAP ,chemistry.chemical_compound ,Groundwater quality ,GEO/08 - GEOCHIMICA E VULCANOLOGIA ,Environmental Chemistry ,Organic matter ,Sulfate ,Waste Management and Disposal ,Holocene ,0105 earth and related environmental sciences ,chemistry.chemical_classification ,geography ,geography.geographical_feature_category ,Pollution ,chemistry ,Environmental science ,BIO/07 - ECOLOGIA ,Groundwater - Abstract
Understanding thefactors that control As concentrations in groundwater is vital for supplying safe groundwaterin regions with As-polluted aquifers. Despite much research, mainly addressing Holocene aquifers hosting young (12,000 yrs) groundwatersare not yet fully understood and so are assessed here through an evaluation of the redox properties of the system in a type locality, the PoPlain (Italy).Analyses of redox-sensitive species and major ions on 22 groundwater samples from the Pleistocene arsenic-affected aquifer in the Po Plain shows that groundwater concentrations of As are controlled by the simultaneous operation of several terminal electron accepters. Organic matter, present as peat, is abundant in the aquifer, allowing groundwater to reach a quasi-steady-state of highly reducing conditions close to thermodynamic equilibrium. In this system, simultaneous reduction of Fe-oxide and sulfate results in low concentrations of As (median 7 μg/L) whereas As reaches higher concentrations (median of 82 μg/L) during simultaneous methanogenesis and Fe-reduction. The position of well-screens is an additional controlling factor on groundwater As: short screens that overlap confining aquitards generate higher As concentrations than long screens placed away from them. A conceptual model for groundwater As, applicable worldwidein other Pleistocene aquifers with reducible Fe-oxides andabundant organic matter is proposed: As may have two concentration peaks, the first after prolonged Fe-oxide reduction and until sulfate reduction takes place, the second during simultaneous Fe-reduction and methanogenesis.
- Published
- 2021