Enantioselective degradation of dufulin pesticide in water: Uptake, thermodynamics, and kinetics studies

Fate characteristics of the chiral pesticide dufulin in flooded anaerobic soils and its interaction with soil microorganisms

Dufulin (DFL), a plant antiviral agent synthesized in China, has been widely used to control viral diseases in rice, tobacco, tomato, and other crops. However, its fate in flooded anaerobic soils, which is essential for environmental risk assessment, remains unknown. Using the ¹⁴C tracer technique, the fate of ¹⁴C-labeled DFL isomers in flooded anaerobic soils was systematically investigated in this study. Over the 100-day incubation, a small part of ¹⁴C-DFL enantiomer was mineralized to ¹⁴CO₂ (< 10.44 %) or entered the surface water phase (< 6.69 %), with most of the ¹⁴C (> 80.40 %) remaining in the subsoil. The residues in all tested soils were gradually converted from extractable residues (ERs) to nonextractable residues (NERs). At the end of incubation, the fraction of ¹⁴C-NERs reached 5.38-23.77 %. The half-life (t_1/2) of the DFL parent in soil is relatively long under submerged anaerobic conditions, especially in Fluvo-aquic soil, up to 277.26-315.07 days, which exceeds the risk threshold recommended by the Stockholm Convention (< 180 days). Soil type and microbial activity influenced the fate of DFL in flooded soils and microbial analysis showed that 2.0 mg kg^-1 DFL had no obvious impact on soil bacterial richness and function. Pseudomonas spp. was estimated to be a potentially efficient degrading genus for DFL. No enantioselective behaviors were detected in this study. This research provides a theoretical basis for evaluating the environmental impact and ecological safety of DFL application.

Enantioselective hydrolysis and photolysis of mandipropamid in different aquatic environments - evaluation of influencing factors

The hydrolysis and photolysis of the chiral fungicide mandipropamid were investigated, and the potential enantioselectivity of mandipropamid in solutions was further assessed. The aqueous solutions were filtered and directly injected into the liquid chromatography with tandem mass spectrometry. In the hydrolysis experiments, mandipropamid enantiomers hydrolyzed slowly in aquatic solutions with half-lives > 200 days; nevertheless, rise of the pH and incubation temperature could increase the hydrolysis rates more than 1.1 times (half-lives decreased from 495.1 to 216.6 days). Compared with the hydrolysis results, photolysis was found to be the main degradation pathway for mandipropamid in different solutions (half-lives < 14 h, except in pH = 5.05 buffer solution). Organic solvents were able to accelerate the photolysis of mandipropamid, but acidic solutions and the addition of flavonoids or inorganic salts significantly inhibited the photolysis of mandipropamid. During the hydrolysis and photolysis processes, the configuration of mandipropamid enantiomers was stable and five possible transformation products were identified by high resolution mass spectrometry. Due to the enantiomeric fraction values > 0.5, the hydrolysis and photolysis of mandipropamid were enantioselective, and S-( +)-mandipropamid preferentially disspated in certain aqueous solutions. The systematic evaluation of the hydrolysis and photolysis of mandipropamid enantiomers may provide more accurate data for better assessment of environmental and ecological risks in aquatic ecosystems.