Field Scale Boscalid Residues and Degradation Half-Life Estimation in a Sandy Soil.

The aim of this study was to analyze the environmental fate of the fungicide Boscalid (2-Chlor-N-(4′-chlorbiphenyl-2-yl)nicotinamid) in a sandy soil. Boscalid was applied in spring 2010 and 2011 to an experimental study site located in western Germany. Three years after the second application 65 undisturbed soil samples were taken from the plough horizon down to a depth of 30 cm. Boscalid was extracted from the soil samples using accelerated solvent extraction (ASE). The Boscalid contents in the plough horizon ranged between 0.12 and 0.53 µg kg^-1 with a field mean of 0.20 ± 0.09 µg kg^-1. These contents were considerably lower compared to those calculated based on DT₅₀ values taken from literature, whereby a Boscalid concentration of 16.89 µg kg^-1 would have been expected assuming a literature mean DT₅₀ value of 345 days. Therefore, the measured field Boscalid concentration only yields 1.2 % of the expected value. To test whether the unknown extraction efficiency of Boscalid by ASE can explain the mismatch between theoretically expected and measured concentrations extractability was assumed to range between 20 and 100, whereby even the lowest assumed extractability still showed much lower Boscalid concentrations as expected. Leaching to deeper soil horizons was also investigated but could not explain the discrepancy between measured and calculated concentrations either. Moreover, a short-term incubation experiment using ¹⁴C labelled Boscalid revealed also shorter DT₅₀ values of 297 to 337 days compared to the 345 days taken from literature. However, this DT₅₀ value is still considerably larger compared to the 104 to 182 days that were calculated based on the field experiment. Our results indicate that Boscalid dissipation under field conditions is much faster at agricultural sites with sandy soil type as expected from laboratory incubation experiments.