Distribution and Degradation of ¹⁴C-Ethyl Prothiofos in a Potato Plant and the Effect of Processing

Abstract

Prothiofos and some of its degradation products have been synthesized in our laboratory for investigation purposes. The residual fate of ¹⁴ C-ethyl prothiofos in different parts of potato plant was studied. The highest level of insecticide residues was detected in and on the leaves of potato plants. The residues of prothiofos insecticide were mainly located in the peels of potato tubers (peeling process removed 85% of the total residue after one month of the treatment), small amount penetrated into the pulp of potato tubers. The degradation products in the extracts of both peel and pulp of potato tubers were identified as prothiofos, prothiofos oxon, desethyl prothiofos, O-ethyl-S-propyl phosphorodithioate, O-ethyl phosphorothioate, O-ethyl-S-propyl phosphoric acid, O-ethyl phosphoric acid, despropylthio prothiofos, and prothiofos oxon sulfoxide. In addition 2,4-dichlorophenol was identified as such and in conjugated metabolites.

Potatoes are processed in three ways: frying, boiling, and baking, which is simulated in home preparation. The amount of prothiofos residues was found to decrease on boiling (70%) and further on baking (82%) and frying (100%). The results indicated that frying process is the most effective method for reducing the amount of pesticide residues. Detectable residues were found in boiled potatoes (2.64 ppm), in the boiling water (0.24 ppm), and in the frying oil (0.71 ppm). From these results we concluded that the processed potatoes are safely used for human consumption.

Keywords:

• ¹⁴C-Ethyl prothiofos
• degradation products
• potato plants
• processing and residues

Acknowledgments

We sincerely thank Prof. Dr. Issa Fakhr for his assistance in the synthesis of prothiofos insecticide.

Notes

*Samples taken after the last application

**percentage of the applied dose

***results are expressed as mean ± SD for three determinations of prothiofos level for each sample.

*Results are expressed as mean ± SD for three determinations of prothiofos level for each sample

** related to the original residues.

*Data are mean of two replicates. System 1: n-hexane : ethyl acetate 99.5 : 0.5 (v/v). System 2: n-heptane : ethylacetate 99 :1 (v/v). System 3: n-heptane pure. System 4: n-heptane : chloroform : methanol 9 : 4 : 1 (v/v).

*Data are mean of two replicates. System 1: n-hexane : ethyl acetate 99.5 : 0.5 (v/v). System 2: n-heptane : ethylacetate 99 :1 (v/v). System 3: n-heptane pure. System 4: n-heptane : chloroform : methanol 9 : 4 : 1 (v/v).

*Results are expressed as mean ± SD for three determinations of prothiofos level for each sample.

*Data are mean of two replicates. System 1: n-hexane : ethyl acetate 99.5 : 0.5 (v/v). System 2: n-heptane : ethylacetate 99 :1 (v/v). System 3: n-heptane pure.