Heating effect on chromium speciation and mobility in Cr-rich soils: A snapshot from New Caledonia
2024
Thery, Gaël | Juillot, Farid | Calmels, Damien | Bollaert, Quentin | Meyer, Michael | Quiniou, Thomas | David, Magali | Jourand, Philippe | Ducousso, Marc | Fritsch, Emmanuel | Landrot, Gautier | Morin, Guillaume | Quantin, Cécile
In the context of global warming, wildfires are expected to increase in both frequency and intensity in the forthcoming decades. Among the environmental and ecological wildfires-induced impacts, the risk of freshwater pollution by soilborne trace metals deserves a more extensive and accurate assessment because of its potential threat to human health. This study aims to contribute to this evaluation by investigating the influence of laboratory soil heating on chromium solid speciation (including redox state) and mobility in Ferralsols, Cambisols, Vertisols and Regosols holding varying amounts of this trace metal in New Caledonia (South Pacific). A first result is that soil heating from 400 °C induces a partial Cr(III) oxidation to Cr(VI) in all the studied soils, confirming recent findings and extending them to a wider range of soil types. A second result is that the rate of heat-induced Cr(III) oxidation to Cr(VI) appears to depend on chromium speciation. This latter parameter might thus represent the primary driver of chromium reactivity in burned soils. Finally, a third result is the confirmation that most of the Cr(VI) formed in the heated soils is highly mobile. Heat-induced Cr(III) oxidation to Cr(VI) in burned soils thus represents a significant risk towards freshwater quality. At the local scale, this risk might concern a large range of drinking water catchments since the soils investigated in this study encompass a wide portion of the pedological diversity in New Caledonia. At a broader scale, considering the wide occurrence of Cr-bearing pedological settings worldwide, the potential threats to freshwater systems resulting from the occurrence of highly toxic Cr(VI) in burned soils should be considered as a global emerging risk towards water quality that requires further assessment.
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