Collection and Analysis of Pesticide Residue Data for Pollen and Nectar Final Report.
The authors characterized pesticide residue levels and decline over time in pollen, nectar, and other plant matrices, in an effort to tease apart the reasons underlying variability in residue levels, drawing from 125 studies covering 30 pesticides, all conducted since 2010.
Residue concentrations were normalized by converting values to Residue Unit Doses (RUD), calculated as the measured residue concentration (in mg/kg) divided by the relevant application rate (in kg/ha) used in each trial. RUDs were not calculated for studies that involved more than one application. For studies that measured residue levels over time, dissipation rates were also calculated (DT50 – or time for 50% residue decline and DT90 - time for 90% residue decline).
The data is relevant primarily for foliar applications. Results from only one granular application trial was included and no seed treatment results were included due to the authors’ exclusion of RUD values they considered unreliable. The active ingredients with the most data included clothianidin (24 studies) flupyradifurone (13 studies), and cyantraniliprole (29 studies).
Sampling Matrix: Median RUD values in pollen were significantly higher than in nectar (28.6 vs. 2.4) and higher than median foliage RUDs (17.1). In addition, pollen collected directly from flowers showed significantly higher RUDs than pollen collected from bees or traps.
Crop related differences: Residue levels in rapeseed notably exceeded the residue levels in Phacelia tanacetifolia and other types of crops, both for pollen and nectar.
Substance related differences: Only some active ingredients had enough independent studies to compare substance differences, and only three insecticides were included in the analysis. Of these, the pyrethroid alpha-cypermethrin demonstrated far higher RUDs than any other substance, but statistical analyses are impeded due to the small number of studies. [These conclusions provide some insight into exposure potential for bees from but not into the risk, since toxicity levels are not discussed.]
Persistence: Calculated foliar DT50 values were, in most cases, less than 2 days for both pollen and nectar, but in some cases the DT50 value in pollen was estimated to be approximately 4 days, much lower than the EFSA default value of 10 days [note that the data as presented is skewed toward fungicides and excludes all of the neonics, diamides, and flupyradifurone]. However, for the single granular study on clothianidin included, no decline was observed in samples taken up to 25 days after the start of flowering.
The results revealed no correlation of the residue decline values between nectar and pollen with the respective values in soil and water.
