Investigating the fate and transport behaviour of pesticides in air via bioindicator plants and bulk deposition samplers in southeastern Germany

Plant protection products (PPP) help growers minimise crop losses from pests. For their authorisation in Europe, environmental fate and behaviour must characterised, including possible transport via air, to assess the risk of potential impacts. Recent interest in airborne PPPs has significantly increased but there is a lack of standardisation in measurements and distinction between long-range transport and local off-target movement is often unclear in publications. In the present study, substance-deposition measurements from two bioindicator plants and bulk-deposition samplers, located at different sites in Bavaria, were used to elucidate aspects of different transport mechanisms. Bulk-deposition data, measured at an agricultural and a background site (≥3 km away from agricultural land) showed frequent pesticide detections. However, detection frequencies and measured concentrations in these samples (i.e., precipitation) were significantly lower at the background site compared with the agricultural site. At the background site, the highest measured deposition of a PPP substance corresponded to 0.007% of its maximum registered field-application rate. At the agricultural site, the highest measured deposition was attributed to local spray drift and represented 0.5% of the maximum field-application rate. Bioindicator plants showed that deposition was predominantly influenced by local agriculture, reflecting the extent of land use for the cultivation of different crops and, hence, the likely magnitude of local pesticide spraying. Observed peak depositions to bulk and bioindicator sampling systems corresponded in time with PPP application to crop fields. There was no clear correlation between the bulk- and bioindicator-plant deposition data sets. When investigating pesticide transport via air, special attention should therefore be placed in the selection of the measurement matrices and methodology to address specific research questions.