Online pesticide concentration and fluxes measurements over crops with a PTRMS shows unexpected volatilisation rates

Pesticide usage has been expanding since the 1950s. Their use has been known to harm human and environmental health for decades. Pesticide volatilisation to the atmosphere is a known process which is however not well documented, especially for periods beyond a few days after pesticide application. This is partly due to the difficulty to measure gaseous pesticides concentration in the atmosphere continuously for long time periods. Indeed, current state-of-the-art measurements is made by thermo-desorption gaseous chromatography involving semi-manual sampling with cartridges. In this study, we report first monthly outdoor online measurement of concentrations and volatilisation of one fungicide and two herbicides by proton transfer reaction, quadrupole injection, time of flight, mass spectrometry (PTR-QI-TOF-MS). The fungicide Chlorothalonil was measured over a wheat field in spring, while the herbicides Prosulfocarb and Pendimethalin were measured over a bare soil in autumn. Comparison with state-of-the-art TD-GC-MS and calibration by a home-made permeation system proved the PTRMS to be adapted for pesticides measurements. Maximum measured concentrations ranged from 12 ppt for Chlorothalonil to 600 ppt Prosulfocarfb. Maximum daily volatilisation fluxes ranged from 35 ng m-2 s-1 for Chlorothalonil to 350 ng m-2 s-1 for Prosulfocarb. We found that volatilisation of Chlorothalonil lasted more than three weeks, leading to up to 50% of the applied quantity volatilised, a duration and an amount much larger that what has been reported before. Volatilisation of pesticides may contribute much more significantly than expected to atmospheric burden, and be wet and dry deposited over larger areas. Further PTRMS pesticides measurements should be done to gain insight into pesticide transfer to the environment, and better characterize human exposure to these harmful compounds.