Online fluxes of pesticides over bare soil in France with a PTRMS: results from French the Online-PTR4-Pest study

In agriculture, plant protection products (i.e. pesticides) protect crops from pests, weeds and diseases. However, pesticides introduced into our environment can also contaminate the air, partly due to volatilisation after pesticide application. Measuring volatilisation in field crops requires trapping techniques, which are costly and time-consuming. There is therefore a strong need for metrological developments to implement (1) analysers that can measure pesticide concentrations continuously over a short period of time, (2) the monitoring of pesticide emissions over a sufficiently long period to capture the entire volatilisation period and (3) the acquisition of data sets in little-explored situations, particularly in wine-growing practices.

The aim of the Online-PTR4-Pest project was to develop the measurement of concentration and volatilisation for three pesticides using proton transfer mass spectrometry (PTR-MS). This technique should eventually enable real-time measurement of pesticide concentrations in the air, as well as field measurement of pesticide volatilisation (using inverse modelling or possibly turbulent covariance methods).

Three pesticides were selected: Prosulfocarb, Pendimethalin (two herbicides used in field crops) and Cyflufenamide (a vine fungicide). Several analysers were used: gas chromatography with thermodesorption mass spectrometry (TD-GC-MS) and PTR-MS. Measurement of the two herbicides was validated using the highly sensitive PTR-Qi-TOF-MS (a time-of-flight mass spectrometer with a proton transfer ionisation source and quad used as an ion guide). Gas-phase calibration is a key stage in the metrological development of PTR-MS measurements. A permeation calibration system was developed and successfully tested, enabling the PTR-MS to be calibrated over a concentration range of 3 ppt to 10 ppb for prosulfocarb and 1 ppt to 3 ppb for pendimethalin.

A three-week field campaign was carried out at the ‘BioEcoAgro’ cross-border joint research unit of INRAE in Mons, with measurements on wheat plots. Air concentrations of Proculfocarb and Pendimethalin were quantified (using both analytical chains and a time step of 5 minutes). These air concentrations varied between 0 and 15 µg m 3 for Prosulfocarb and 0 to 3 µg m 3 for Pendimethalin. Volatilisation fluxes for these two herbicides were estimated using two different methods (aerodynamic gradient and inverse modelling). Over the first few days of field measurements, volatilization of Prosulfocarb was around ten times higher than that of Pendimethalin, regardless of the method used. However, the two methods gave different volatilisation values, as the inverse modelling method was made more uncertain by the applications of these pesticides in the surrounding fields. Finally, the Volt'air-Veg model of pesticide volatilisation was tested on the two datasets. The feasibility of measuring gaseous pesticides in the air in real time using a PTR-MS has been demonstrated.