In vitro Detection of Folpet and Its Degradation to Phthalimide in Aqueous Solutions and in Yeast Suspensions

¹ Swiss Federal Research Station for Fruit-Growing, Viticulture and Horticulture, 8820 Wädenswil, Switzerland.

Folpet, N-(trichloromethylthio)-phthalimide, hydrolyzes in aqueous solutions to phthalimide, carbon dioxide, hydrochloric acid, and sulfur. Using a slightly modified HPLC method, the decrease in folpet concentration and the simultaneous increase in phthalimide were investigated in different aqueous solutions. If the solution contained Saccharomyces cerevisiae cells, folpet was adsorbed by the yeast cells because of its lipophilic character. When the folpet concentration in the presence of yeast cells was high, only folpet was isolated after an incubation time of two hours, and at low folpet concentration only phthalimide was isolated. We thus conclude that yeast cells influence the decomposition of folpet. The transition from folpet to phthalimide detection took place at 6.7 x 10^-8 mg folpet/yeast cell. In this range the yield of phthalimide was 27% of the original folpet amount. At folpet concentrations higher than 6.7 x 10^-8 mg folpet/yeast cell 70% to 80% of original amount was present as folpet, at lower concentrations 75% to 90% was present as phthalimide. These observations were made in solutions containing intact yeast cells, and the substance phthalimide was stable under these conditions for months. However, if the yeast suspension was heated to 70°C for two hours, neither folpet nor phthalimide was detected. It would, therefore, appear that destroyed yeast cells also affect the decomposition of folpet and phthalimide. We conclude from these results that folpet and phthalimide in aqueous solution can be analyzed quantitatively and qualitatively as long as no microorganisms such as yeasts are present.

Key words: fungicide, folpet degradation, phthalimide, aqueous solutions, yeast, HPLC analysis

Submitted on January 2, 1996