Field scale boscalid residues and dissipation half-life estimation in a sandy soil

The aim of this study was to analyze the environmental fate of the fungicide boscalid in a sandy soil. Boscalid was applied in spring 2010/11 to a cropland site in western Germany. Three years after second application 65 undisturbed soil samples were taken. Boscalid was extracted using accelerated solvent extraction (ASE). Boscalid contents in the plough horizon ranged between 0.12 and 0.53 with a field mean of 0.20 ± 0.09 μg kg−1. These contents were considerably lower compared to calculation using literature DT50 values, whereby a concentration of 16.89 μg kg−1 was expected assuming a literature 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, losses from spray drift and interception can explain the mismatch between calculated and measured concentrations all these uncertainties were taken into account into calculations, but field concentrations and DT50 were still lower as expected. Leaching to deeper horizons was also studied but could not explain the discrepancy either. Moreover, a short-term incubation experiment using 14C labelled boscalid revealed also shorter DT50 values of 297-337 compared to the 345 days taken from literature. However, this DT50 value is still considerably larger compared to the 104-224 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.