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SUMMARY:EESS talk on "Poisoned groundwater: Arsenic sinks and sources in M
 ekong Delta sediments"
DTSTART:20161108T121500
DTEND:20161108T131500
DTSTAMP:20260428T074411Z
UID:01432d027fe115f6ae543142324d40816c3c1ce74c25e42f45af55be
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr Yuheng Wang (IDYST-UNIL) & Dr Maria P. Asta Andres\, postdo
 cs\, EML\nAbstract: 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 pe
 rsistence 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 sp
 eciation in redox-preserved sediment cores from the Mekong Delta in Vietna
 m 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) speci
 es associated with graphite-like nanostructures. On the other hand\, As-fr
 ee C nanostructures were identified in suspended particulate matter from t
 he Mekong River\, suggesting a riverine origin for the nanostructures but 
 an authigenic origin for the novel As(V) species. We propose that this new
 ly 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 i
 nto groundwater mainly as As(III). Interestingly\, there was no correlatio
 n between the amounts of As and Fe released\, suggesting that microbially 
 mediated iron reduction might not be the main mechanism of As release in t
 hese reduced sediments. Furthermore\, the paleo-mangrove peat layer releas
 ed the largest fraction of As. In addition\, As concentrations in the pore
 water of the squeezed sediments showed the highest values at the peat laye
 r. These observations suggest that the As species in the peat layer\, main
 ly S-bound As\, should be more soluble than O-bound As species. We thus pr
 opose 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.\n\
 nShort biography: Dr. Yuheng Wang: He obtained his Ph.D. in environmental 
 mineralogy at Université Pierre & Marie Curie (UPMC). He then acquired po
 st-doctoral and teaching experiences at Institut de Physique du Globe de P
 aris (IPGP)\, Collège de France\, and Ecole Polytechnique Fédérale de L
 ausanne (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 or
 ganic-rich reducing environments\, e.g. wetlands and deltaic sediments\, t
 o decipher the parameters controlling the mobility of these contaminants. 
 Dr. Maria  P. Asta Andres: obtained her Degree in Geology in the Universi
 ty of Zaragoza (Spain) in 2001. After finishing her studies\, she collabor
 ated with the Geochemical Modelling Group of the Zaragoza University for t
 wo 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 sta
 yed during 5-years in the Hydrogeology Group of the Technical University o
 f Catalonia and in the Hydrochemistry Group of the Earth Sciences Institut
 e “Jaume Almera” (CSIC)\, where she specialized in the modelling of ge
 ochemical and hydrogeological processes in acid mine waters and obtained t
 he 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. Ge
 ological Survey of Boulder (Colorado\, USA). Once she achieved her PhD she
  has been working as a postdoc in different Universitites and research in
 sititutes: in the University of Zaragoza where she worked with the Geochem
 ical Modelling Group of the Zaragoza University in the study of the geoche
 mical 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 m
 echanisms and kinetics of anaerobic abiotic and microbial anaerobic\, nitr
 ate-dependent U(IV) oxidation and in the Andalusian Institute of Earth Sci
 ences (CSIC) in Granada (Spain) studying the freshwater carbonates from t
 he Alhama-Jaraba geothermal system to evaluate the relationship between t
 heir geochemical and mineralogical composition and the environmental cond
 itions during their formation. Currently she is working in the Ecole Polyt
 echnique Fédérale de Lausanne (Switzerland) studying the main biogeoch
 emical processes involved in the As release from Mekong River Delta sedim
 ents.
LOCATION:GR A3 31 http://plan.epfl.ch/?room=GR%20A3%2031
STATUS:CONFIRMED
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