Ecotoxicological Evaluation of Methiocarb Electrochemical Oxidation

Development of a UPLC-MS/MS method for pesticide analysis in paddy water and evaluation of anodic TiO2 nanostructured films for pesticide photodegradation and antimicrobial applications

Pesticide contamination in agricultural water poses serious environmental and public health risks, particularly due to the accumulation of harmful residues that threaten aquatic ecosystems and human health. This study investigated the levels of five pesticides-carbaryl (CBR), methiocarb (MTC), diazinon (DZN), chlorpyrifos (CLO), and cypermethrin (CYPER)-in agricultural water samples from Can Tho City and Hau Giang Province, Vietnam. Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was employed for their detection and quantification. Chlorpyrifos was the most frequently detected pesticide (32.5%), with concentrations ranging from 1.7 to 10.9 ng mL-1. The concentrations of cypermethrin, carbaryl, methiocarb, and diazinon were 2.6-9.4 ng mL-1, 1.3-14.3 ng mL-1, 4.1-7.7 ng mL-1, and 2.8-10.5 ng mL-1, respectively. The persistence of pesticide residues in the water samples highlights the significant contamination concerns in the region. To address this issue, two types of TiO2 nanophotocatalysts-TiO2 nanotube arrays (TNAs) and TiO2 nanowires on nanotube arrays (TNWs/TNAs)-were synthesized for the photocatalytic degradation of the identified pesticides. Under UV-vis irradiation (∼96 mW cm-2), both nanostructures achieved rapid pesticide degradation, with removal efficiencies of up to 99% within 25 minutes. TNWs/TNAs exhibited superior photocatalytic performance, attributed to their increased surface area compared to TNAs. In addition to pesticide degradation, their antibacterial activity was assessed. Under weak UV-vis light (6.3 mW cm-2), both TNAs and TNWs/TNAs achieved 100% antibacterial efficacy against Escherichia coli, significantly higher than the 68% efficacy of UV light treatment alone. Even under dark conditions, TNWs/TNAs demonstrated enhanced antibacterial activity, achieving 63% efficacy compared to 12% for TNAs. These results underscore the dual functionality of TNWs/TNAs as effective photocatalysts for both pesticide degradation and bacterial inactivation, presenting a promising approach for agricultural water treatment.

Special Issue: Advancement in Biomonitoring and Remediation Treatments of Pollutants in Aquatic Environments

A series of negative, attendant circumstances threaten the ecological equilibrium, the quality, and even the existence of the different aquatic ecosystems nowadays more than ever [...]

Methiocarb Degradation by Electro-Fenton: Ecotoxicological Evaluation

This paper studies the degradation of methiocarb, a highly hazardous pesticide found in waters and wastewaters, through an electro-Fenton process, using a boron-doped diamond anode and a carbon felt cathode; and evaluates its potential to reduce toxicity towards the model organism Daphnia magna. The influence of applied current density and type and concentration of added iron source, Fe₂(SO₄)₃·5H₂O or FeCl₃·6H₂O, is assessed in the degradation experiments of methiocarb aqueous solutions. The experimental results show that electro-Fenton can be successfully used to degrade methiocarb and to reduce its high toxicity towards D. magna. Total methiocarb removal is achieved at the applied electric charge of 90 C, and a 450× reduction in the acute toxicity towards D. magna, on average, from approximately 900 toxic units to 2 toxic units, is observed at the end of the experiments. No significant differences are found between the two iron sources studied. At the lowest applied anodic current density, 12.5 A m⁻², an increase in iron concentration led to lower methiocarb removal rates, but the opposite is found at the highest applied current densities. The highest organic carbon removal is obtained at the lowest applied current density and added iron concentration.