EESS talk on "Poisoned groundwater: Arsenic sinks and sources in Mekong Delta sediments"
Event details
| Date | 08.11.2016 |
| Hour | 12:15 › 13:15 |
| Speaker | Dr Yuheng Wang (IDYST-UNIL) & Dr Maria P. Asta Andres, postdocs, EML |
| Location | |
| Category | Conferences - Seminars |
Abstract: Groundwater poisoned by arsenic is common in Southeast Asian deltas and represents a significant health hazard to the health of millions. Althrough extensive research has been carried out to understand the mechanism of As contamination, open questions remain about (a) the persistence of an As(V) signature in the reducing sediment environment, (b) the origin (authigenic or detrital) of individual As-bearing phases, and (c) their role in As cycling. In the present study, we investigate As speciation in redox-preserved sediment cores from the Mekong Delta in Vietnam to obtain a comprehensive view of the As-bearing phases in the sediments and to address the remaining questions. We identified a novel As(V) species associated with graphite-like nanostructures. On the other hand, As-free C nanostructures were identified in suspended particulate matter from the Mekong River, suggesting a riverine origin for the nanostructures but an authigenic origin for the novel As(V) species. We propose that this newly discovered As(V) species might be key to explaining the persistence of pentavalent arsenic in reduced sediments. Additionally, at some depths, the sediment layers also harbor arsenian pyrite and As(III) bound to thiol groups as significant fractions of total As, which correspond to a paleo-mangrove depositional environment. We then probed the potential source(s) of arsenic release in this sediment, and we found that As was released into groundwater mainly as As(III). Interestingly, there was no correlation between the amounts of As and Fe released, suggesting that microbially mediated iron reduction might not be the main mechanism of As release in these reduced sediments. Furthermore, the paleo-mangrove peat layer released the largest fraction of As. In addition, As concentrations in the porewater of the squeezed sediments showed the highest values at the peat layer. These observations suggest that the As species in the peat layer, mainly S-bound As, should be more soluble than O-bound As species. We thus propose that As is likely released from S-bound As pools in the peat layer, most likely NOM-thiol bound As but also possibly As-pyrite, whereas the newly discovered As(V) species acts as a long-term sink for As. This work provides evidences to refine the current model for the origin, deposition, and release of arsenic in the alluvial aquifers of the Mekong Delta.
Short biography: Dr. Yuheng Wang: He obtained his Ph.D. in environmental mineralogy at Université Pierre & Marie Curie (UPMC). He then acquired post-doctoral and teaching experiences at Institut de Physique du Globe de Paris (IPGP), Collège de France, and Ecole Polytechnique Fédérale de Lausanne (EPFL). He is now a post-doctoral researcher in Institute of Earth Surface Dynamics of the University of Lausanne. The main part of his work has focused on the biogeochemistry of arsenic and uranium in iron- and organic-rich reducing environments, e.g. wetlands and deltaic sediments, to decipher the parameters controlling the mobility of these contaminants. Dr. Maria P. Asta Andres: obtained her Degree in Geology in the University of Zaragoza (Spain) in 2001. After finishing her studies, she collaborated with the Geochemical Modelling Group of the Zaragoza University for two years when she got her Diploma Thesis on Geology in 2004 which deals with the study of alkaline waters of granite systems. After that, she stayed during 5-years in the Hydrogeology Group of the Technical University of Catalonia and in the Hydrochemistry Group of the Earth Sciences Institute “Jaume Almera” (CSIC), where she specialized in the modelling of geochemical and hydrogeological processes in acid mine waters and obtained the Ph. Degree (June, 2009). Part of her pre-doctoral research was carried out in the University of Rice in Houston (Texas, USA) and in the U.S. Geological Survey of Boulder (Colorado, USA). Once she achieved her PhD she has been working as a postdoc in different Universitites and research insititutes: in the University of Zaragoza where she worked with the Geochemical Modelling Group of the Zaragoza University in the study of the geochemical processes related to CO2 storage; in the Univesity of California (Merced) with Dr Peggy O’Day where she was invoved in the study of the mechanisms and kinetics of anaerobic abiotic and microbial anaerobic, nitrate-dependent U(IV) oxidation and in the Andalusian Institute of Earth Sciences (CSIC) in Granada (Spain) studying the freshwater carbonates from the Alhama-Jaraba geothermal system to evaluate the relationship between their geochemical and mineralogical composition and the environmental conditions during their formation. Currently she is working in the Ecole Polytechnique Fédérale de Lausanne (Switzerland) studying the main biogeochemical processes involved in the As release from Mekong River Delta sediments.
Short biography: Dr. Yuheng Wang: He obtained his Ph.D. in environmental mineralogy at Université Pierre & Marie Curie (UPMC). He then acquired post-doctoral and teaching experiences at Institut de Physique du Globe de Paris (IPGP), Collège de France, and Ecole Polytechnique Fédérale de Lausanne (EPFL). He is now a post-doctoral researcher in Institute of Earth Surface Dynamics of the University of Lausanne. The main part of his work has focused on the biogeochemistry of arsenic and uranium in iron- and organic-rich reducing environments, e.g. wetlands and deltaic sediments, to decipher the parameters controlling the mobility of these contaminants. Dr. Maria P. Asta Andres: obtained her Degree in Geology in the University of Zaragoza (Spain) in 2001. After finishing her studies, she collaborated with the Geochemical Modelling Group of the Zaragoza University for two years when she got her Diploma Thesis on Geology in 2004 which deals with the study of alkaline waters of granite systems. After that, she stayed during 5-years in the Hydrogeology Group of the Technical University of Catalonia and in the Hydrochemistry Group of the Earth Sciences Institute “Jaume Almera” (CSIC), where she specialized in the modelling of geochemical and hydrogeological processes in acid mine waters and obtained the Ph. Degree (June, 2009). Part of her pre-doctoral research was carried out in the University of Rice in Houston (Texas, USA) and in the U.S. Geological Survey of Boulder (Colorado, USA). Once she achieved her PhD she has been working as a postdoc in different Universitites and research insititutes: in the University of Zaragoza where she worked with the Geochemical Modelling Group of the Zaragoza University in the study of the geochemical processes related to CO2 storage; in the Univesity of California (Merced) with Dr Peggy O’Day where she was invoved in the study of the mechanisms and kinetics of anaerobic abiotic and microbial anaerobic, nitrate-dependent U(IV) oxidation and in the Andalusian Institute of Earth Sciences (CSIC) in Granada (Spain) studying the freshwater carbonates from the Alhama-Jaraba geothermal system to evaluate the relationship between their geochemical and mineralogical composition and the environmental conditions during their formation. Currently she is working in the Ecole Polytechnique Fédérale de Lausanne (Switzerland) studying the main biogeochemical processes involved in the As release from Mekong River Delta sediments.
Practical information
- General public
- Free
- This event is internal
Organizer
- EESS - IIE
Contact
- Prof. Rizlan Bernier-Latmani, EML