2002 Annual Report
Research
Ozone Treatment To Reduce or Remove Pesticides in Fruits and Vegetables
Roger Ruan, Professor
Paul Chen, Senior Research Associate
Zhe Liu, Research Assistant
Funding Source
Private Gifts, Minnesota Agricultural Experiment Station
Objective
The objectives of the present study are to determine the susceptibility
of the organophosphrous pesticides such as malathion to ozonation, evaluate
the effectiveness of ozonation on pesticides degradation compared with
the commonly used chlorination, and apply the method to fruit and vegetable
treatment.
Project Description
Ozonation has been shown to be an effective technique to degrade pesticides
and deactivate a very large number of microorganisms. Compared to chlorination,
ozonation is more powerful in pesticide residue degradation without leaving
any hazardous chemicals. Its application also includes increasing storage
life and sanitizing the surfaces of fruit, vegetables, and other agricultural
products. Since ozone does not remain in the water and surface matrix
very long, there is no concern about consumption of ozone residue in food
products. In this study, we will test our hypothesis using aqueous model
systems first and then further evaluate the feasibility using fruits and
vegetables with surface pesticides residues.
Results
An aqueous model system was developed in order to study the effects of three pH values and chlorination on malathion degradation over a 30 minute period. Aqueous solutions buffered at pH 4.5, 7.0 and 10.7 were prepared and used during testing. For the ozonation study, ozone gas was bubbled into each pH solution with 4 ppm spiked malathion. A 40ml sample was transferred to a separation funnel at 0, 5, 15 and 30 minute intervals, extracted twice with benzene, concentrated using a rotary evaporator, and solved with methanol. The malathion residue was determined using GC-MS. For the chlorination study, an appropriate amount of calcium hypochlorite stock solution was added to each pH solution to bring the final chlorine concentration to 50ppm. The same sampling, sample preparation, and pesticide residue analysis methods were employed in order to make ozonation and chlorination compatible. As a result, the rate of degradation of malathion generally increased at a higher pH. The maximum degradation of malathion by ozonation was observed at an alkaline pH. At pH 7.0, (similar to commercial treatment), almost 80% of the initial amount of malathion was degraded by ozonation in 30 minutes. The 50ppm chlorine treatment resulted in only 55% degradation, indicating that chlorine was less effective than ozonation. The study of ozonation to degrade pesticides on fruits and vegetables will be conducted in the near future.