Arsenic/Organic matter/Fe(III) oxide interactions. Can wetlands be source of arsenic for aquifers? – ARSENORG

The project will be conducted in three steps: (1) the identification of the As speciation in solid phases within wetland soils, (2) the study of the As release processes involved the organic-rich context of the wetland soil and (3) the resulting As speciation in wetland soil solution. Each of these tasks will be developed by using in situ (field) and laboratory experiments. Solid analyses using cutting-edge technologies such as NanoSIMS, EXAFS and ESR (electron spin resonance) will be performed to access to the very fine interactions between As, Fe and organic matter. Bacterial communities and respective functions of interest involved in the release and redox behavior of As will be also determined through genomics. This project is both a prerequisite for managing and protection of soil and water resources in relation to As contamination and a source of needed fundamental knowledge on the true involved mechanisms and related occurring processes.

The aim of this project is whether the organic matter in wetlands can really be a key factor in controlling the As mobilization and transfert from wetlands to the underlying aquifers. The 3 studies proposed here will allow understanding: (i) if organic matter is only a source of labile C for Arseno-oxidant and/or Arseno-and ferro-reducing bacteria which are suggested to be involved in As and Fe release in contaminated aquifers or (ii) if organic matter plays a direct role in controlling the As speciation . In addition, this project will allow the quantification and modeling of the As distribution between Fe-nanoparticles and organic matter in mixed colloids. Finally, the use of the technique of the Fe(III)-oxides coated slide will allow to (i) quantify organic matter impact on the As release from the bioreduction of Fe(III)- oxides in field conditions, (ii) to determine the nature and influence of secondary mineral carrier of As and Fe, (iii) to identify the nature and function of bacterial consortia involved in the As solubilization from the bioreduction of Fe(III)-oxides.

Worldwide, millions of people currently consume water containing unacceptable levels of As, which are responsible for the increase of many diseases. In many countries, even in Europe, the arsenic concentrations are not yet systematically analyzed, although the tests are becoming widespread. The mechanisms of contamination of shallow aquifers are still hotly debated. However, no solution can be proposed until the process of solubilization and mobility of As are not fully understood. In this context, this proposal will significantly improve our knowledge on the mobilization of As in wetlands recently proposed as a source of As for contaminated aquifers

Proposal main deliverables
Task 1 Peer reviewed publications 2
conferences 1
Task 2 Peer reviewed publications 3
conferences 1
Task 3 Peer reviewed publications 3
conferences 1

Arsenic (As) is probably the environmental contaminant that is responsible for the highest risk of morbidity and mortality worldwide. The major source of contamination has to be related to high As concentrations in groundwaters. However, the origin of such high amount of As remains a matter of debate. Recent studies suggested that As is not only an in situ aquifer product, but could derives instead from reduction processes occurring at near- surface and notably in flood plains and wetlands. To get further information, this proposal is therefore focused on the redox biogeochemistry of As in wetlands. We propose to unravel the complex interactions occurring between Fe(III)-oxides, As and organic matter in wetland soils and soil solutions. The project will be conducted in three steps: (1) the identification of the As speciation in solid phases within wetland soils, (2) the study of the As release processes involved the organic-rich context of the wetland soil and (3) the resulting As speciation in wetland soil solution. Each of these tasks will be developed by using in situ (field) and laboratory experiments. Solid analyses using cutting-edge technologies such as NanoSIMS, EXAFS and ESR (electron spin resonance) will be performed to access to the very fine interactions between As, Fe and organic matter. Bacterial communities and respective functions of interest involved in the release and redox behavior of As will be also determined through genomics. This project is both a prerequisite for managing and protection of soil and water resources in relation to As contamination and a source of needed fundamental knowledge on the true involved mechanisms and related occurring processes.