Fish embryo toxicity assessment of o-dianisidine in Clarias gariepinus and its electrochemical treatment in aquatic samples using super conductive carbon black

Abstract

The present study tested fish embryo toxicity (FET) of o-dianisidine (o-dian) on African catfish (Clarias gariepinus) and its electrochemical treatment through electro-oxidation of real aquatic samples for the first time. The o-dian exposed groups exhibited embryonic malformations, hatching retardation and mortality in a dose- and time-dependent manner compared to the control group even for 5 mg L⁻¹ o-dian, in spite of being under the permissible limit. The LC₅₀ values (with 95% confidence limits) of o-dian for larvae were estimated to be 42.614 (36.851–50.766), 35.327 (29.632–43.819) and 19.442 (15.448–24.539) mg L⁻¹, respectively from 24 to 72 hours post-fertilization (hpf). Subsequently, the electrochemical uptake and treatment of o-dian was successfully demonstrated using a super conductive carbon black (CL-08) modified glassy carbon electrode in pH 2 phosphate buffer solution (PBS). The saturation surface coverage, Γ_s and adsorption constant, K_a values, evaluated using curve fitting for the Langmuir isotherm model, were 88.354 nmol cm⁻² and 48.6 × 10³ M⁻¹ respectively. The calculated % yields of o-dian uptake on the electrode surface were 33, 43, 40 and 34. UV-Vis spectra of the electro-oxidized real samples showed 56, 36, 39 and 86% reductions of the o-dian absorbance peak at 363 nm respectively. The electrochemically treated real samples showed an efficient increase in the survival rate of African catfish larvae (p < 0.05).