Dissipation kinetics of fenamidone, propamocarb and their metabolites in ambient soil and water samples and unknown screening of metabolites

A fenamidone and propamocarb dissipation study was carried out applying ultra high-performance liquid chromatography coupled to Orbitrap mass spectrometry (UHPLC-Orbitrap-MS). Dissipation kinetics were evaluated in different types of soils and in water under different conditions (sunlight or darkness). In addition, a plant protection product containing both compounds was applied at two doses: (i) single and (ii) double dose in soils, and (i) single and (ii) fivefold dose in water. The fenamidone and propamocarb concentration decreased during the monitored period (100 days), obtaining high persistence in the case of water studies (DT₅₀ > 50 days) and low to medium persistence in soils (DT₅₀ < 50 days). No Observed Effect Concentration (NOEC) and concentration causing 50% lethality (EC50) were calculated and showed that fenamidone could cause toxic effects in soil and water organisms due to very high NOEC values (0.013 mg/L for aquatic invertebrates) while propamocarb did not cause any lethality. Fenamidone and propamocarb metabolites were also monitored with acetophenone and RPA-411639 ((5)-5-methyl-2-(methylthio)-3-(4-S nitrophenyl)amino-5-phenyl-3,5-dihydro-4H-imidazole-4-one) being the main metabolites for fenamidone. These metabolites obtained concentration values of up to 25% initial fenamidone content which can be a risk for the environment and fauna but, despite the toxicity of these compounds, they have not been studied yet. Metabolite 175 m/z and propamocarb n-desmethyl were the main propamocarb metabolites with values of 3% of initial propamocarb content. Three new propamocarb metabolites were detected in water samples and one in soil, highlighting the capabilities of the proposed methodology for monitoring known metabolites and identifying new ones in environmental studies.