Project objectives:
We propose here to employ a dual isotope approach, using 2H and 13C labeled methyl groups, placed on different methylated As molecules, to unravel As biomethylation
& biovolatilisation pathways. These compounds will be injected in As methylating bacteria, fungi & protozoa cultures and in soil microcosms. The resulting
molecules (including volatiles) will be measured/traced using analytical speciation techniques such as cryotrapping & GC coupled with state of the art IRMS
instruments.
These experiments will shed light on processes that lead to an array of As molecules of varied toxicities and physico-chemical properties being released
in soils. Indeed, such knowledge is essential in order to better assess the threat of As pollution but also in order to potentially use these processes as tools
for soil remediation.
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Project
Summary:
Arsenic (As) is a ubiquitous element found in almost every environmental compartment. Moreover, inorganic As is a Class 1 non-threshold carcinogen and globally,
millions of people are at risk, mainly through drinking tainted water which is also used to irrigate agricultural soils.
As is found in soils in its inorganic form but also as organic As, mostly mono- and dimethylarsenic (MMA(V) and DMAV(V), (III) and (V) being the different oxidation
states). The process leading to these compounds, biomethylation, is biological and it is still not fully understood. Moreover, it is linked to another remarkable
mechanism: biovolatilisation. Microorganisms in soil transform inorganic As to much less toxic methylated compounds, mostly MMA(V) and DMA(V), producing
as well reduced methylated compounds (MMA(III) and DMA(III)) which are even more toxic than inorganic As. Biovolatilisation leads to the production of four
highly volatile As compounds (arsine, mono-, di- and trimethylarsine) and their toxicity is still highly discussed.
Although the products are known, only indirect evidence exists on the different possible pathways, which are still highly debated.
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Professor Paul Bardos