Environmentally persistent free radicals (EPFRs) are produced during biochar pyrolysis and, depending on biochar application, can be either detrimental or beneficial. High levels of EPFRs may interfere with cellular metabolism and be toxic, because EPFR-generated reactive oxygen species (e.g., hydroxyl radicals (center dot OH)) attack organic molecules. However, center dot OH can be useful in remediating recalcitrant organic contaminants in soils. Understanding the (system-specific) safe range of EPFRs produced by biochars requires knowing both the context of their use and their overall significance in the existing suite of environmental radicals, which has rarely been addressed. Here we place EPFRs in a broader environmental context, showing that biochar can have EPFR concentrations from 108-fold lower to 109-fold higher than EPFRs from other environmental sources, depending on feedstock, production conditions, and degree of environmental aging. We also demonstrate that center dot OH radical concentrations from biochar EPFRs can be from 104-fold lower to 1017-fold higher than other environmental sources, depending on EPFR type and concentration, reaction time, oxidant concentration, and extent of environmental EPFR persistence. For both EPFR and center dot OH concentrations, major uncertainties derive from the range of biochar properties and the range of data reporting practices. Controlling feedstock lignin content and pyrolysis conditions are the most immediate options for managing EPFRs. Co-application of compost to provide organics may serve as a postpyrolysis method to quench and reduce biochar EPFRs.

Disinfecting Aspergillus flavus represents a promising strategy to mitigate aflatoxin contamination in agricultural soils and crops. In this study, the efficient disinfection of Aspergillus flavus using a g-C3N4/alpha-Fe2O3 heterojunction under visible light irradiation, along with the roles and mechanisms of the main reactive oxygen species involved in the disinfection process were demonstrated. The g-C3N4/alpha-Fe2O3 exhibited a high photocatalytic disinfection efficiency of up to 91 %, with hydroxyl radicals (center dot OH) identified as the main active species. The production of chitin in the cell walls of Aspergillus flavus was mainly interfered with center dot OH, leading to the destruction of cellular components such as carbohydrates, proteins, and lipids during the disinfection process. The metabolic interference induced by center dot OH resulted in cell structural damage and the release of essential intracellular constituents, ultimately leading to the death of Aspergillus flavus. These findings provided valuable insights into Aspergillus flavus control that was beneficial for its future agricultural applications.