Abstract
Particulate organic matter (POM) is distributed worldwide in high abundance. Although insoluble, it could serve as a redox mediator for microbial reductive dehalogenation and mineral transformation. Quantitative information on the role of POM in the natural occurrence of silver nanoparticles (AgNPs) is lacking, but is needed to re-evaluate the sources of AgNPs in soils, which are commonly considered to derive from anthropogenic inputs. Here we demonstrate that POM reduces silver ions to AgNPs under solar irradiation, by producing superoxide radicals from phenol-like groups. The contribution of POM to the naturally occurring AgNPs is estimated to be 11–31%. By providing fresh insight into the sources of AgNPs in soils, our study facilitates unbiased assessments of the fate and impacts of anthropogenic AgNPs. Moreover, the reducing role of POM is likely widespread within surface environments and is expected to significantly influence the biogeochemical cycling of Ag and other contaminants that are reactive towards phenol-like groups.
Highlights
Particulate organic matter (POM) is distributed worldwide in high abundance
The natural formation of anthropogenic silver nanoparticles (AgNPs) at soil surface was mimicked with a sand depth of 1 mm[22] and exposure of the samples to natural sunlight irradiation for 10 h outdoors (Fig. 1a)
The formation of AgNPs was confirmed by the characteristic peak of surface plasmon resonance (SPR) at ~400 nm on ultraviolet (UV)–visible (Vis) spectrometry[18] (Fig. 1c)
Summary
Particulate organic matter (POM) is distributed worldwide in high abundance Insoluble, it could serve as a redox mediator for microbial reductive dehalogenation and mineral transformation. By providing fresh insight into the sources of AgNPs in soils, our study facilitates unbiased assessments of the fate and impacts of anthropogenic AgNPs. the reducing role of POM is likely widespread within surface environments and is expected to significantly influence the biogeochemical cycling of Ag and other contaminants that are reactive towards phenol-like groups. Considering that POM is distributed worldwide in high abundance[3,5], typically comprising >50% of soil organic matter in mineral soils and >70% of that in lithified sediments[4], identifying the mechanisms underlying its reactivity will provide new insight into its role in the cycling of numerous trace metals within surface environments. AgNPs in terrestrial environment, and to conduct unbiased assessments of fate and impacts of anthropogenic AgNPs
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