Humic Substances as Electron Acceptors and Electron Shuttlers in Anaerobic Marine Sediments

摘要

Humic substances are a class of yellow to black colored organic molecules that are recalcitrant and ubiquitous in the environment. Previous research has shown that humic substances can act as electron acceptors in the anoxic oxidation of acetate by Fe(III)-reducing microorganisms. The reduced humic substances were then able to transfer the excess electrons to Fe(III) abiotically. Our hypothesis was that quinone moieties within the humic substances are the primary reducible group. Using electron spin resonance, the organic radical concentration of the humic substances has been shown to increase up to six-fold after incubation with Geobacter Metallireducens. A direct positive correlation exists between the change in organic radicals and the molar concentration of Fe(III) reduced abiotically by the reduced humic substances from many environments. These findings support the hypothesis that quinone moieties are the electron accepting groups within the humic substances. These findings are very important in understanding the reduction of Fe(III) and other metals in anoxic environments, as well as the oxidation of organic contaminants in polluted environments such as marine sediments.