The Mineralization Trap: Why Current Standards for Biodegradable Plastic Biodegradation Misread the Soil Carbon Cycle

Given the increasing intentional and unintentional loading of biodegradable plastics into soils, reliance on mineralization alone as a measure of environmental safety is no longer sufficient. To move beyond the mineralization trap, future standards should shift from simplistic disappearance metrics toward carbon fate accounting (Figure 1). A plastic material should be considered successfully biodegraded in soil if its carbon is demonstrably respired as CO2 (catabolism), and/or assimilated into microbial biomass or necromass (anabolism), and/or stabilized within the MAOM fraction. If a carbon atom originating from a biodegradable plastic ultimately becomes part of a microbial cell wall bound to a clay surface, it has completed its transition from a synthetic material to a functional component of the soil ecosystem. Regulatory frameworks must begin to reflect this ecological reality: in living soils, the most valuable carbon is often the carbon that remains.