Examining Committee

Dr. Lisa Duizer, Chair 
Dr. Keith Warriner, Advisor 
Dr. William Lubitz, Advisory Committee Member  
Dr. Lawrence Goodridge, Department Member 

TITLE:  The Use of Advanced Oxidation Processes in the Degradation of the Pesticide Chlorpyrifos and Reduction of Microbial Contamination on Apples
 
ABSTRACT: Chlorpyrifos is a widely used insecticide in apple production but there are concerns that residues ingested by consumers can lead to chronic neurological conditions. A method based on Advanced Oxidation Process (AOP) was validated for the degradation of chlorpyrifos on apples and inactivating Escherichia coli O157:H7, along with Aspergillus niger spores. AOP is a process that generates free-radicals from the UVC (at 254 nm) mediated degradation of hydrogen peroxide and ozone thereby leading to highly oxidative species. The use of gaseous ozone alone was found to be ineffective in chlorpyrifos degradation and was therefore excluded from AOP use. Response surface methodology (RSM) was used to find that the degradation of chlorpyrifos was primarily dependent on UV-C dose and hydrogen peroxide temperature but not hydrogen peroxide concentration. Maximal degradation of chlorpyrifos on apples was achieved through an AOP treatment applying 68.4 kJ/m² UV dose and 1.22% v/v H₂O₂ at 66°C that resulted in 94 μg degradation (47% of the initial concentration) of the pesticide with < 0.004 μg accumulation of the degradative photoproduct, chlorpyrifos-oxon. The same treatment supported a >6.56 log CFU reduction in E. coli O157:H7 and >6.56 log CFU reduction of A. niger spores. In conclusion, this study has demonstrated that an AOP-based process can degrade chlorpyrifos and address microbiological hazards associated with apples.