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Methyl parathion (MP) is a typical organophosphorus pesticide that is widely used worldwide, and hydrolysis, oxidation and reduction are the main abiotic degradation processes. Manganese dioxide (MnO 2 ) and organic acid can participate in various geochemical processes of pollutants, a reaction system was constructed to degrade MP using δ-MnO 2 and oxalic acid. The δ-MnO 2 /oxalic acid reaction system could efficiently degrade MP, and the removal rate of MP (20 μM) reached 67.83% within 30 h under the optimized conditions (pH 5, [δ-MnO 2 ] = 2 mM, [oxalic acid] = 100 mM). MP was hydrolyzed by substitution reactions of S N @P and S N @C, and reduced by conversion of the nitro groups (-NO 2 ) in MP and its hydrolysates to amino groups (-NH 2 ). The primary active substance produced in the reaction system was the complexes dominated by Mn(III)-oxalic acid. This study provides a scientific basis for the degradation of organophosphorus pesticides using MnO 2 and an organic acid. The results have important theoretical significance and application value for pollution control and remediation of organophosphorus pesticides., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)