Dark Formation of Hydroxyl Radical in Arctic Soil and Surface Waters

Abstract

Hydroxyl radical (•OH) is a highly reactive and unselective oxidant in atmospheric and aquatic systems. Current understanding limits the role of DOM-produced •OH as an oxidant in carbon cycling mainly to sunlit environments where •OH is produced photochemically, but a recent laboratory study proposed a sunlight-independent pathway in which •OH forms during oxidation of reduced aquatic dissolved organic matter (DOM) and iron. Here we demonstrate this non-photochemical pathway for •OH formation in natural aquatic environments. Across a gradient from dry upland to wet lowland habitats, •OH formation rates increase with increasing concentrations of DOM and reduced iron, with highest •OH formation predicted at oxic-anoxic boundaries in soil and surface waters. Comparison of measured vs expected electron release from reduced moieties suggests that both DOM and iron contribute to •OH formation. At landscape scales, abiotic DOM oxidation by this dark •OH pathway may be as important to carbon cycling as bacterial oxidation of DOM in arctic surface waters.

Indirect Photochemistry in Sunlit Surface Waters: Photoinduced Production of Reactive Transient Species

“…elevated [COH] levels, which could be important in the transformation of dissolved compounds. [134,135] As far as the H 2 O 2 -independent formation of COH by irradiated CDOM is concerned, the detailed pathways are still to be elucidated. For instance, while some excited triplet states are able to oxidize water and/or OH À to COH, [136,137] this is not a general feature of triplet-state reactivity.…”

Sorption, photodegradation, and chemical transformation of naproxen and ibuprofen in soils and water

“…These products were not observed in this study; the ketone and alcohol analogs observed here were less polar than the parent PhAC. Recent reports of dark hydroxyl radical formation in arctic soils (Page et al, 2013) indicate the possibility that hydroxyl radical mediated transformation could contribute to soil transformation as it does with DOM-mediated phototransformation.…”

Biological Formation of Organic Substances from Particulate Organic Matter

“…Note that rates of superoxide production normalized to the proportion of metabolically active cells is detected to vary between 0.02  0.02 amol cell −1 hour −1 (mean ± standard error) and 19.4  5.2 amol cell −1 hour −1 [1]. Such biological formation of H 2 O 2 subsequently could be link with dark formation of hydroxyl radical (HO • ) in Arctic soil and surface waters [13,14].…”