Degradation of fenthion and fenthion sulfoxide on grapes on the vines and during refrigerated storage

The degradation of the pesticide fenthion and of the metabolite fenthion sulfoxide were studied on two varieties of Vitis vinifera, “Sideritis” and “Opsimo Edessas”, grown in the vineyard of the Agricultural University of Athens. Vines were sprayed with fenthion according to manufacturer instructions. One part of the sprayed grapes remained on the vines and another part was harvested, packed according to the recommended trade practices and stored in a refrigerator at 0 ± 0.5 °C and relative humidity 80%. It was found that, after spraying, fenthion was very quickly transformed on the grapes into fenthion sulfoxide that had a much slower rate of decomposition. Half-lives for the decomposition of fenthion on the trees were found to be 7.6 days for grapes of Sideritis variety and 5.6 days for grapes of Opsimo Edessas variety. Corresponding values for grapes stored in the refrigerator were 42 and 44.7 days. Percentages of fenthion sulfoxide increased up to the 0th day and then decreased steadily due to the decomposition of the pesticide and its metabolite.