Dissipation of plant protection products from foliage

In the environmental risk assessment for plant protection products in the European Union a default foliar dissipation half-life (DT50) of 10 d is used for the risk assessment of herbivorous birds and mammals feeding on sprayed foliage. This generic DT50 of 10 d is based on a compilation of residue trials conducted over 30 yr ago, in which many compounds and formulations were considered that are not used anymore. We therefore reassessed foliar dissipation based on a data set of 396 residue trials covering 30 compounds. Foliar DT50s were calculated, and potential factors determining dissipation were analyzed, such as crop group, residue zone, and rainfall. The strongest source of variability was found between individual trials. Other factors, including the residue zone and crop group, did not have a significant impact on dissipation. Only heavy rainfall (>6.5 mm/d, i.e., the 95th percentile of rainfall) had a statistically significant influence, although rainfall explained only approximately 5% of the overall variability. Moderate rainfall (≤6.5 mm/d) did not significantly correlate with dissipation and explained only 0.1% of the overall variability. Most importantly, the differences in DT50s between crops and residue zones were neither marked nor statistically significant; hence, trials from different residue zones and crops could be pooled to obtain more robust half-lives. Over all compounds, trials, zones, and crops the geometric mean DT50 was 3.2 d (90th percentile 7.9 d). Environ Toxicol Chem 2018;37:1926-1932. © 2018 SETAC.