Unveiling the degradation of lamotrigine in sulfate radical-mediated oxidation: kinetics, influencing factors and transformation mechanisms

Abstract

Lamotrigine (LMG), a widely used anticonvulsant drug, has been frequently detected in aquatic environments due to its limited removal in conventional wastewater treatment. Here, we systematically investigated the degradation of LMG via heat-activated peroxydisulfate (heat/PDS) treatment. The degradation followed pseudo-first-order kinetics, with the observed rate constant (k_obs) increasing at higher PDS doses or elevated temperatures. The apparent activation energy was determined to be 88.7 kJ mol⁻¹. Radical quenching experiments using methanol or tert-butanol indicated that SO₄˙⁻ predominated in LMG degradation. The presence of halides (Br⁻ and Cl⁻), natural organic matter (NOM), ammonium (NH₄⁺), or bicarbonate (HCO₃⁻) generally inhibited LMG degradation, primarily due to their competition for SO₄˙⁻. Detailed transformation pathways were proposed based on quantum chemical calculations and high-resolution mass spectrometry, revealing initial attacks on electron-rich sites of the triazine ring and amino groups, leading to hydroxylated and deaminated products. Both ECOSAR predictions and luminescence bacteria assays showed reduced toxicity for most transformation products relative to LMG, suggesting that degradation of LMG by sulfate radical was a detoxification process. This study demonstrates that heat-activated PDS is an effective strategy for eliminating LMG and attenuating its ecological risk in water.