Environmental Fate of Pesticides - Transport, Transformation and Eco Toxicological Effects

Abstract

Pesticides are a tool to ensure a sound harvest to foster human nutrition and economic income for farmers. Besides this benefit, pesticides have the potential to harm the environment due to their (eco)toxic effects and their fate in the environement related to their physical-chemical properties. When applied to agricultural fields, several mechanisms in terms of transport, retention and degradation take place. Pesticides do not stay at the target area where they are sprayed but are transported via air or water flow and reach non-target areas continuing their toxic effects. The velocity and extent of the relocation is driven by the adsorption coefficient kf of each compound. A high sorption potential leads to retention in soil enabling degradation processs. The persistence of a pesticide displayed as DT50 (dissipation time) governs the time period of the pesticide’s (eco)toxic effects. The more persistent the compound, the longer this period lasts. The applied pesticide (parent compound=PC) can be transformed into another compound (transformation product=TP) in the environement by slightly changing the molecule structure. This transformation is enabled by phytolysis, hydrolysis, chemical and microbiological degradation in all compartments. The number of generated TPs from a PC cannot be assessed due to the high number of options. Nevertheless, most TPs are more mobile and persistent than their PC causing high concentration peaks and positive findings even years after the application of the related PC. The (eco)toxicity of TPs greatly varies and has to be assessed individually; it can partly be higher than their PC’s (eco) toxicity. Besides the wanted toxic effect to target organisms at target areas, unwanted effect on non-target organisms and at non-target-areas. Direct effects occur at organism/species/population levels and are obvious such as impairment or even poisoning of certain species leading to changes in the community composition. The recovery of the species can last from short-term to long-term or can be irreversible. While these direct effects are detectable/measureable, indirect effects are challenging to observe and to quantify. They affect the ecosystem and its functions. Indirect effects include the loss of shelter and foraging areas by changes in the structure and diversity of habitats. Further, food resources vanish due to changes in the community composition and cause further loss species