Impact of copper on halocarbon emissions from soils

We identified a novel copper-catalyzed mechanism to produce ozone-depleting methyl halides abiotically from soils and seawater, with implications for copper use as a pesticide, herbicide and fungicide and the potential for being a globally significant methyl halide source (Jiao et al., 2022).

Most natural methyl halide sources are associated with enzymatic processes in plants or fungi, but there is the possibility that substantial amounts of methyl halides are produced abiotically. Abiotic Fenton-like reactions involving iron (III) have been shown to oxidize organic matter with halides to produce methyl halides, and we have also observed abiotic production in our soil incubations through the stable isotope tracer technique. We decided to test copper instead of iron, and we found that the addition of copper (II) to soils and seawater stimulated surprisingly large emissions of methyl halides. This finding, published in Nature Communications in January 2022, suggested that this abiotic process may be a globally significant source for CH3Br and CH3Cl, as copper is widely used in agriculture in pesticides, herbicides and fungicides. For example, 200 million metric tons of copper sulfate are applied per year in global agriculture . In the United States, it is permitted even in organic agriculture. Copper is also used in anti-fouling paints for boats and leaches out into the surrounding seawater. This novel link between copper and stratospheric ozone has received much attention (Figure 3). This work is not only relevant for methyl halides; it also opens a window into a branch of studies involving abiotic metal ion – organic matter reactions in the environment, and this leads the way to further studies on the environmental impacts of copper.