Heterogeneous kinetics of the OH-initiated degradation of fenthion and parathion

Fenthion and parathion are two representative kinds of organophosphorus pesticides and widely used in agriculture. They are directly or indirectly released into the atmosphere by spraying or volatilization processes. However, their heterogeneous reactivity toward OH radicals has not yet been well understood. Therefore, this work investigated the heterogeneous kinetics of the OH-initiated degradation of surface-bound fenthion and parathion using a flow reactor. The results showed that OH radicals played an important role in the atmospheric degradation of fenthion and parathion. Their average rate constants were (7.20 +/- 0.77) x 10 -12 and (10.40 +/- 0.60) x 10 -12 cm 3 /(mol center dot sec) at a relative humidity (RH) and temperature of 35% and 20 degrees C, respectively, suggesting that they have relatively short lifetimes in the atmosphere. In addition, a negative RH dependence and a positive temperature dependence of the rate constants were observed. The Arrhenius expressions of fenthion and parathion were k 2 = (1.34 +/- 0.48) x 10 -9 exp[ -(1432.59 +/- 105.29)/T] and k 2 = (1.96 +/- 1.38) x 10 -9 exp[ -(1619.98 +/- 222.02)/T], respectively, and their overall activation energy was estimated to be (11.88 +/- 0.87) and (13.48 +/- 1.83) kJ/mol. The experimental results will update the kinetic data of fenthion and parathion in the atmosphere and be helpful to further understand their atmospheric transportation processes.(c) 2023 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.