Abstract One of the major sources of OH radical in atmospheric water has been attributed to iron species. However, iron chemistry in aqueous solution is a very complex process due to the existence and the stability of numerous iron species. Given the insolubility of ferric oxyhydroxides and oxides under natural waters conditions, the concentration of iron in equilibrium with these solids is very low and insufficient to drive substantial change in iron speciation or oxidant capacity of the medium. However, the concentration of dissolved iron can substantially increase by the presence of strong complexing agents as siderophores. The so formed iron complexes may absorb solar light and undergo a redox process leading to the reduction of Fe(III) and the formation of oxidant species . The presence of organic Fe-complexing ligands with high stability constants comparable to siderophores ones (K>1020-1022) has been shown in rainwaters[1]. Our hypothesis is that iron could be also complexed by siderophore synthestized by microorgtanisms in cloud waters. To test our hypothesis 450 strains isolated from cloud water at the puy de Dôme station (1465m, France) were identified and screened for siderophore production[2]. Under our conditions 42% of strains were able to produce siderophores. The most frequently encountered genus Pseudomonas was also the most active. A mixture of pyoverdins produced by bacteria isolated from clouds was used to determine the photoreactivity of Fe(III) pyoverdine complexes under simulated cloud conditions. The photolysis of these complexes led to the generation of Fe(II) and hydroxyle formation. Acetate formation was also observed suggesting a fragmentation following ligand-to-metal charge transfer[3]. Finally the presence of pyoverdine in cloud water could impact the composition and oxidative capacity of this environment.
References [1] M. Cheize, G. Sarthou, P.L. Croot, E. Bucciarelli, A.-C. Baudoux, A.R. Baker, Anal. Chim. Acta, 736 (2012) 45‑54. [2] V. Vinatier, N. Wirgot, M. Joly, M. Sancelme, M. Abrantes, L. Deguillaume, A.-M. Delort, Environ. Sci. Technol., 50 (2016) 9315‑9323. [3] M. Passananti, V. Vinatier, A.-M. Delort, G. Mailhot, M. Brigante, Environ. Sci. Technol., 50 (2016) 9324‑9332.