Understanding pesticide photodegradation & persistence in protected-crop environments.

The need for an improved understanding of the fate of pesticides in food, in agricultural production, and in the wider environment is of growing importance. Pesticide residues are a significant commercial problem for farmers, growers and retailers, since even when below the maximum permissible levels, there are consumer concerns due to perceived threats to health. The effects of pesticides on non-target organisms also causes wider environmental concerns, which extend beyond the agroecosystem, potentially to the global scale in the case of persistent organic chemicals. These societal and environmental drivers inform changes in policy, with developments such as EU directive 91/414/EEC on the authorization/use of Plant Protection Products across Europe, capturing wider concerns but also posing significant challenges for farmers and growers. Despite the clear value of control measures other than pesticides, there is no doubt that pesticides will remain a key element of pest management across all sectors of food production. Thus, concerns around persistance and residues cannot be ignored. There is a particular residue problem with fresh produce such as salads and soft fruit. Fresh produce is a highly valuable sector of agriculture. In 2008 the total value in the UK alone of production of soft fruit and fresh vegetables (from DEFRA http://www.ukagriculture.com/statistics/farming_statistics.cfm) was £331M and £1,101M respectively, substantially greater than oilseed rape (£618M), barley (£882M) or potatoes (£878M). Protected vegetables (i.e. those grown under plastic or glass) alone were worth £282M but this very high-value sector is especially prone to concerns over pesticide residues, as it has a high percentage of tested samples with detectable occurrences of residues. Despite this widely recognised problem, there is little understanding of why pesticide degradation may be slower in protected crops compared to open field conditions. Photochemistry is an important degradation route for many pesticides and we have demonstrated that this is a major loss route for organophosphorus insecticides under natural and simulated light. What is needed, and what this studentship addresses, is a fundamental understanding of approaches to quantifying and predicting degradation under different light conditions; whether those conditions result from agronomic practices (e.g. different cladding materials in protected cropping) or natural variation (for example due to season or latitude). The studentship will develop our initial definition of the degradation action spectrum of fenitrothion. An action spectrum (AS) for a given compound is simply the relationship between the rate of photochemical decay and the spectral irradiance over a given range of wavelengths. AS are widely used in many biological processes, and have the advantage over other methods of quantifying photochemical breakdown (e.g. quantum yield) of being readily applied to 'real systems' such as crop surfaces. We have defined the AS for the degradation of fenitrothion, and by extending the approach to other current-use photoreactive pesticides, the student will gain a wide range of skills that are pertinent both to fundamental and applied science, while generating highly novel knowledge that can be readily applied by our commercial partner and, ultimately by growers. The student will obtain skills in analytical laboratory techniques associated with pesticide analysis & photochemistry, as well as spectroradiometry and the design & delivery of laboratory & field treatments using UV. Extending studies to plant surfaces & bioassays of how pesticide degradation is expressed in terms of changes in pest control performance over time will provide skills in plant/crop biology and plant-pest interactions respectively. Finally, by working with the industrial partner the student will gain experience of field studies on growers' holdings, and direct contact with the industry