Abstract
Nonsenescent and senescent leaves of selected coniferous and broadleaf plants contained substantial levels of naturally occurring persistent free radicals (PFRs). These biogenic PFRs (BPFRs) were stable and persistent despite multiple wetting and drying cycles, implying that BPFRs can leach and sorb on soil particles. Results suggest that endogenous chemicals in plants and their transformation byproducts can stabilize unpaired electrons in leaves under ambient conditions. Thus, the vast amount and perpetual supply of leaf litter is an unaccounted natural source of BPFRs. If toxic, inhaling and accidentally ingesting fine soil dust and powder from degraded leaf litter may increase our environmental and health burdens to PFRs. We expect that this finding will generate more studies on natural sources of PFRs, establish their properties, and distinguish them from those formed from combustion and thermal processes.