Desphenylchloridazon (DPC), the main metabolite of the herbicide chloridazon (CLZ), is more water soluble and persistent than CLZ and frequently detected in water bodies. When assessing DPC transformation in the environment, results can be non-conclusive if based on concentration analysis alone, because estimates may be confounded by simultaneous DPC formation from CLZ. This study investigated the fate of DPC by combining concentration-based methods with compound-specific C and N stable isotope analysis (CSIA). Additionally, DPC formation and transformation processes were experimentally deconvolved in a dedicated lysimeter study considering three scenarios. First, surface application of DPC enabled studying its degradation in the absence of CLZ. Here, CSIA provided evidence of two distinct DPC transformation processes: one shows significant changes only in 13 C/ 12 C, whereas the other involves changes in both 13 C/ 12 C and 15 N/ 14 N isotope ratios. Second, surface application of CLZ mimicked a realistic field scenario showing that during DPC formation, 13 C/ 12 C ratios of DPC were depleted in 13 C relative to CLZ, while 15 N/ 14 N ratios remained constant. Finally, CLZ depth injection simulated preferential flow and demonstrated the importance of the topsoil for retaining DPC. The combination of the lysimeter study with CSIA enabled insights into DPC transformation in the field that are superior to studies of concentration trends.
*S Supporting InformationFurther details on chemicals, lysimeters, analytical methods, analyte recovery calculations and results of water balance computation, vegetation cover evolution, breakthrough trends, EA-IRMS analyses, soil analyses, CLZ depth injection and nitrogen isotope ratios.