Effects of temperature on the dissipation of totaland water-extractable pesticides in Japanese soils

Abstract

We investigated the dissipation of 27 pesticides in five Japanese soils at three temperatures and the variability of activation energies (Ea). The dissipation of total pesticides extracted sequentially using water and acetone was fitted to a single first-order (SFO) model. The Ea values calculated from the dissipation rate constants of the SFO model showed a normal distribution with a median of 61.1 kJ mol-1. The dissipation of water-extractable pesticides (i.e., phytoavailable pesticides) was fitted to a double firstorder in parallel model with two dissipation rate constants: k1 and k2. The Ea values calculated from k1 and k2 showed normal or lognormal distribution, and the medians of the normal distribution calculated from k1 and k2 were 62.8 and 45.2 kJ mol-1, respectively. Furthermore, the method for estimating the biphasic dissipation of phytoavailable pesticides at different temperatures by using the median Ea values of the laboratory experiment was demonstrated in a field experiment.