Some reduced carbon species enriched in aromatic functionalities can provide ecosystem services when used as soil amendments. Charcoal has been used for this purpose for millennia. Biochar (biomass intentionally pyrolyzed for soil amendment) has been recently designed to mimic charcoal’s environmental benefits. Here we consider a third family of reduced carbon species that could be used for soil amendment: engineered carbon materials produced from natural gas pyrolysis (i.e. full decomposition of methane into solid carbon and hydrogen). We term these materials generically C0. C0 can be designed to be chemically similar to charcoal or biochar, with the aim of providing similar ecosystem services (improved soil water retention, improved nutrient retention, reduced fertilizer runoff, reduced soil CH4 and N2O production, etc.). Environmental risk assessment is a crucial first step before discussion of use of these materials as soil amendment. Here we begin this process by developing a procedure to assess the release of dissolved materials from C0. We report on the amount and chemistry of dissolved organic carbon (DOC) released by C0 subjected to a range of environmental aging treatments. Specifically, we subjected C0 to 1) 10-day UVA irradiation with light intensity of 50 µW/cm2, mimicking UV-driven reactions likely to occur in natural waters, 2) H2O2 oxidation (30% and 5%), mimicking natural, long-term environmental microbial oxidation, and 3) 10 mg L-1 monochloramine (NH2Cl) oxidation, mimicking reactions that could occur were C0 materials to inadvertently enter drinking water treatment systems. DOC released from C0 was &lt; 2 mg L-1 regardless of aging method. This is significantly lower than DOC released from wildfire-derived charcoal (up to 70 mg L-1), soft wood biochar pyrolyzed at 550 and 700 °C, and commercial biochar under the same oxidation conditions. UVA 10 days is the most oxidizing treatment for C0. UVA-aged C0 had a relatively higher O/C ratio of 0.019±0.006. However, all three aging methods were incapable of significantly oxidizing C0. Next steps involve determining the chemical nature of DOC species released.

Towards a general framework for quantitative assessment of the potential risks associated with soil release of reduced carbon species

ACS Fall 2021

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