Acute toxicity assessment and QSAR modeling of zebrafish embryos exposed to methyl paraben and its halogenated byproducts

Feasibility of in situ bioelectro-Fenton reactions facilitated by bio-transformed Fe minerals in microbial peroxide production cell: Organic pollutant degradation and phytotoxicity

A microbial peroxide producing cell (MPPC) was developed and systematically optimized through electrochemical performance evaluations, along with profiling of pH and hydrogen peroxide (H2O2) dynamics in the catholyte. Following MPPC optimization, the biogenic transformation of poorly-crystalline ferrihydrite was investigated in the presence of an acclimated microbial consortium derived from the anolyte and biofilms. The degradation kinetics and mechanism of simazine (SMZ) were examined via a bioelectro-Fenton process using various iron (Fe) catalysts, including ferrihydrite, goethite, hematite, and Ferric-citrate. Additionally, the degradation pathway of SMZ was elucidated, followed by a toxicological assessment of SMZ and its degradation byproducts. Notably, in situ H2O2 production reached 1,315 μM within 24 h (equivalent to 27.3 mg L-1 h-1), accompanied by a gradual increase in pH from 3.8 to 8.2. To enhance the bioelectro-Fenton reaction, the catholyte pH was adjusted to 4, and Fe catalysts were introduced. Principle-based kinetic parameters, including the apparent pseudo-first-order rate constant for H2O2 decomposition, steady-state hydroxyl radicals (•OH) concentration, and the second-order rate constant for SMZ degradation, were systematically determined. The degradation of SMZ proceeded via •OH-mediated reactions, involving dealkylation, hydroxylation, and dechlorination pathways. Phytotoxicity evaluations using Arabidopsis thaliana revealed that SMZ significantly inhibited plant growth and leaf bleaching, whereas its degradation products exhibited markedly reduced toxicity. The extent of toxicity mitigation was directly correlated with the progression of the bioelectro-Fenton process. Overall, the comprehensive analysis of degradation kinetics, reaction mechanisms, and toxicological impacts presented in this study supports the practical application of bioelectro-Fenton systems integrated with optimized MPPC catholytes for effective in situ remediation of persistent organic pollutants.