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Substituted diphenylamine antioxidants (SDPAs) and synthetic phenolic antioxidants (SPAs), widely used in rubber and consumer products, pose growing environmental concerns. This study evaluated the occurrence and release of 43 SDPAs and 4 SPAs in raw leachate and treated effluent from 18 municipal landfills across China. Results showed 17 SDPAs and 1 SPA (AO4703) were detected in raw leachate. DPG, AO4703, and C8/C8-DPA dominated, accounting for 90.6 ± 5.20 % of total antioxidant concentrations (SAOs, median: 6638 ng/L). Landfill size had the most universal influence on antioxidant concentrations (9/14 targets affected, P = 0.001 or P<0.05), while operational status (open/closed) and regional industrial structure also played roles. SAOs correlated positively with COD, TOC, and heavy metals (P<0.01), and AO4703 showed a strong negative correlation with pH (r=-0.71, P<0.01). Among treatment processes, the two-stage MBR + NF + RO process achieved the highest SAOs removal rate (>98 %), but over 75 % of treated effluents still contained 18 antioxidants (SAOs median: 200 ng/L), with AO4703 and C8/C8-DPA remaining persistent. This study confirms landfills as critical sources of persistent antioxidants, highlighting the need for stricter monitoring, optimized multi-stage treatment, and source control to mitigate ecological risks.