|M.Sc Student||Zivan Ohad|
|Subject||Atmospheric Levels and Transport of Organophosphates|
Pesticides and their Derivatives at Agricultural
|Department||Department of Civil and Environmental Engineering||Supervisor||Professor Yael Dubowski|
|Full Thesis text|
Pesticides are chemicals used to manage pest organisms for both agricultural and nonagricultural purposes. Once released to the environment, pesticides may degrade and form various transformation products. In order to evaluate the environmental impact of pesticides, it is important to understand their degradation processes and transport. However, most previous studies regarding pesticide degradation focused on processes in bulk water or soil, and not on the atmosphere-surface boundary. In semi-arid or arid climate, applied pesticides are exposed to atmospheric and surface reactions for longer time periods. Furthermore, a significant portion of applied pesticides reaches the atmosphere via spray drift or post-application volatilization and re-suspension. These airborne pesticides continue to be exposed to interactions with solar radiation and atmospheric oxidants.
The present work focuses on the Organophosphorus pesticides (OPs) group, which is still widely used both in the USA and in Israel. Yet, no quantitative atmospheric measurements of pesticide in general and OPs specifically were done in Israel. A major challenge in measuring airborne pesticides is their relatively low concentration and the large temporal and spatial variability.
The overall objective of the present work was to examine primary and secondary drift of organophosphate insecticides and their degradation products from agricultural fields to nearby settlements. For this purpose, atmospheric concentrations of currently used OPs and their degradation products were measured in few settlements that are in close proximity to applied agricultural field.
In addition, atmospheric transformations of Chlorpyrifos (i.e. surface photo-oxidation and evaporation) were studied in order to evaluate the importance of such surface processes on its environmental fate. These were quantified for thin films of Chlorpyrifos and Chlorpyrifos-oxon on different substrates.
Airborne Chlorpyrifos and Dichlorvos were detected during two different application events and in the few days following them, at a settlement located >75m downwind from the applied field. As expected, maximum concentrations were observed during application night, and they decreased gradually in the following days. Chlorpyrifos-oxon was also detected in these applications.
Surface loss rates of Chlorpyrifos and Chlorpyrifos-oxon thin films were found to be significant (t1/2 on the order of few hours). Evaporation and oxidation were on the same order of photolysis degradation. Photo-oxidation of Chlorpyrifos generated Chlorpyrifos-oxon on both tested substrates. The surface loss rate of Chlorpyrifos-oxon was found to be slower than of Chlorpyrifos, while both had lower loss rates on leaves than on glass substrates. In addition, the quantum yields for Chlorpyrifos and Chlorpyrifos-oxon were calculated.