Electrochemical degradation and mechanistic analysis of microcystin-LR at boron-doped diamond electrode

• Degradation mechanism of MC-LR is proposed by experimental and theoretical studies.
• OH radical is the major reactive species for the degradation of MC-LR.
• OH radical reacts with the Adda through substitution and addition reactions.
• OH radical reacts with the Mdha resulting adduct formation.

The electrochemical degradation behavior of microcystin-LR (MC-LR) in aqueous electrolyte at boron-doped diamond (BDD) anode was investigated under neutral pH condition. Hydroxyl radicals (OH) formed were detected by photoluminescence (PL) technique using terephthalic acid as a probe molecule, and it was observed to be predominant reactive specie. The intermediates formed in the MC-LR decomposition reaction were identified by LC–MS/MS, among which, two (m/z 1011.8 and 1029.5) were found to have multiple peaks in total ion current (TIC) chromatogram. The degradation of MC-LR was found to be mainly due to OH attack that involved hydroxylation of MC-LR via substitution/addition with a simultaneous isomerization, oxidation and oxidative bond cleavage reaction processes. The destruction of conjugated double bond of Adda was achieved by different mechanistic steps involving addition and substitution of OH that generated primary by product at m/z 1029.5. The destruction of diene bond of the Mdha, produced an adduct which was observed to be more stable, owing to a very less barrier than its substitution counterpart.