Photochemical interactions between iron minerals and dissolved organic matter

Abstract

Interactions between iron minerals and dissolved organic matter (DOM) are ubiquitous across environmental systems, but the global effects of photochemical synergies between DOM and iron minerals in surface environments remain to be comprehensively elucidated. Contrary to the assumption that minerals primarily stabilize organic matter, iron minerals also control the release, conversion and mineralization of associated organic carbon through dissolution, phase evolution and photo-oxidation. Concurrently, DOM modulates the photoreduction, transformation and reactivity of iron minerals via light-mediated electron transfer and photochemically generated reactive oxygen species. These mineral–organic interactions are shaped by environmental variables and molecular characteristics that exert a marked influence on the mobility, speciation and transformation of associated contaminants, particularly at dynamic environmental interfaces. This Review focuses on the reactivity, vulnerability and spatial heterogeneity of iron and carbon pools in response to solar radiation and provides an update on how light shapes the coupling of iron and carbon cycles in terrestrial and aquatic surface systems. Field observations integrated with laboratory experiments, and advanced analytical techniques could enable the photochemistry of iron minerals and DOM to provide a framework for improved understanding of the biogeochemical cycling of iron, carbon and contaminants, refining carbon budgets and informing sustainable remediation strategies. Iron minerals and dissolved organic matter contribute to elemental cycling, contaminant dynamics and biogeochemical processes. This Review provides an update on iron mineral–dissolved organic matter photochemistry and highlights research priorities that could improve climate model predictions, the accuracy of carbon budgets and understanding of contaminant behaviour under sunlight.