Differential contributions of reactive oxygen species in iron-modified biochar-activated oxidation systems to environmental DNA degradation

Environmental DNA (eDNA) has emerged as a global contaminant due to its potential health risks. Although catalytic degradation has been explored for eDNA removal, no study has systematically compared its degradation efficiency and mechanisms under different oxidant systems. This study examined the catalytic degradation of herring sperm DNA (hsDNA) using iron-modified biochar (FBC) activated by persulfate (PS), urea hydrogen peroxide (UHP), and peroxymonosulfate (PMS). The FBC400/PMS system achieved the fastest hsDNA degradation, removing 93.1% of hsDNA within 90 min. Quenching experiments and electron paramagnetic resonance spectroscopy showed that singlet oxygen (¹O₂) dominated in the FBC400/PMS and FBC400/PS systems, whereas hydroxyl radicals (•OH) dominated in the FBC400/UHP system. Gel electrophoresis and atomic force microscopy confirmed that all systems induced hsDNA strand breakage. The degradation pathways of thymine, a representative DNA base, were further elucidated. In the FBC400/PMS system, ¹O₂ and SO₄^•-synergically attacked thymine C₅=C₆, generating dimer and ring-opening products. In the FBC400/UHP system, •OH dominated the competitive pathway of dihydroxylation and methyl oxidation. In the FBC400/PS system, ¹O₂, SO₄^•-, and •OH synergically drove the C₅ and C₆ hydroxylation and ring opening. These findings offer new insight into eDNA degradation by FBC-activated oxidants and emphasized the importance of selecting an appropriate oxidant system.