Exploring the reproducibility and environmental realism of pesticide fate processes in regulatory systems

Pesticides are vital for controlling agricultural pests and increasing crop yields; however, they can have detrimental effects on the environment and human health. Regulatory laboratory studies need to be carried out to assess the risks of a pesticide before it can be produced and sold. These regulatory studies tend to poorly predict pesticide fate and degradation in the field, likely due to specified test conditions not accurately representing the environment. This thesis focuses on the potential for adding greater environmental realism to regulatory-type tests, using the fungicide isopyrazam in OECD 308- and 309-type studies. Regulatory tests are carried out under dark conditions. Microcosm studies were conducted in the presence of non-UV light to minimise photolysis, yet include phototrophic transformation; there was significantly more biodegradation in illuminated microcosms compared to those carried out in the dark, in which there was little degradation. The effect was more pronounced in water-sediment microcosms compared to water-only microcosms, as the sediment provided a platform for phototrophic biofilm development. Regulatory tests do not consider temporal variation in the microbial composition of environmental inoculum. Experiments carried out over two years showed that the outcome of tests, in terms of both degradation and mineralisation, were variable with inocula collected at different time periods from the same river location. Regulatory tests are also carried out statically. Recirculating microflume experiments showed that flowing water increased dissipation compared to static systems, regardless of light treatment. This suggests regulatory tests are not properly representing flowing aquatic systems, e.g. rivers. Lastly, regulatory tests are carried out on a small scale. Although there was little effect on pesticide decline in different sized microcosms, in the larger microflumes, dissipation occurred even under dark conditions. A number of Operational Taxonomic Units were specific to the microflumes suggesting that, on a larger scale, there was a wider variety of microorganisms that better reflected the environment. This work provides evidence for potential modifications to regulatory tests and insight into non-standard tests that industry could include in regulatory submissions