The Role of Manganese Dioxide in the Natural Formation of Organochlorines

Abstract

Organochlorines are important environmental contaminants that impact ecosystems, public health, and global warming. Organochlorines are generally regarded as anthropogenic compounds, but they also have natural sources. Here, we report that the commonly occurring manganese(IV) secondary mineral birnessite (δ-MnO 2 ) was found to chlorinate guaiacol (2-methoxyphenol), a moiety in lignocellulose and hence plant-derived natural organic matter (NOM). Environmentally relevant concentrations of birnessite and chloride were incubated together with guaiacol for 18 min at pH 4.0, resulting in the formation of up to 118 μg L −1 of chloroguaiacols. The extent of chlorination was dependent on the chloride concentration. Conducting these reactions under anoxic conditions had little effect on chloroguaiacol formation, suggesting that oxygen is not required in the MnO 2 -mediated chlorination of guaiacol. This study demonstrates that ubiquitous MnO 2 catalyzes the formation of chlorinated NOM, revealing a globally important source of natural organochlorines that has previously been overlooked. The MnO 2 -mediated mechanism can account for the previous detection of organochlorines in forest soils, where accumulation of manganese is known to occur during the decomposition of wood and leaf litter.

Carbon redirection via tunable Fenton-like reactions under nanoconfinement toward sustainable water treatment

“…Meanwhile, PhO • is not susceptible to O 2 attack ( k ≤ ~1.0 × 10 3 M − 1 s − 1 ) 62 , but might be oxidized to a phenoxenium cation (PhO + ) by surface-bound Mn(IV). The presence of PhO + in all the systems was supported by the formation of 4-chlorophenol from nucleophilic addition of Cl – to PhO + 63 (Supplementary Fig. 38 ).…”

Natural Disinfection-like Process Unveiled in Soil Microenvironments by Enzyme-Catalyzed Chlorination

“…There is growing recognition of the ubiquitous occurrence of natural chlorination processes in diverse terrestrial ecosystems for the generation of organochlorines. , These processes have been substantiated in a wide range of environments, including peat bogs, forest soils, pasturelands, agricultural soils, weathering plants, and rhizospheres . Natural chlorination primarily occurs through abiotic redox reactions mediated by metals − or biotic pathways catalyzed by halogenating enzymes . Among these pathways, exoenzymatic processes have been shown to play a pivotal role, particularly in forest soils .…”