Concentrations, generation and risk characterization of phthalimide in tea-derived from folpet or not?

The fungicide folpet is rapidly degraded into phthalimide (PI) during both thermal processing and analytical procedures in sample preparation; thus, its residue definition has been modified into the sum of itself and PI. Tea is one of the world's most popular nonalcoholic beverages, where folpet is not listed as an applicable pesticide. To demonstrate how serious false-positives and overestimation in dietary risk are caused by the application of a new residue definition, the residue pattern of PI in made tea and processed tea leaves, along with its transfer rate during tea brewing and corresponding dietary risk, were investigated in the present study. The results revealed that PI residue in tea ranged from <10 µg/kg to 180 µg/kg with a median value of 10 µg/kg, 7.3 % of which was over the maximum residue limit established by EU (100 µg/kg, expressed as folpet). The PI residue in green tea was obviously higher than that in black, dark and oolong tea. Simulated heating experiments revealed that PI can arise from improper heating of folpet-free fresh tea leaves, and thus green tea bears a higher risk for its manufacturing employing a comparatively higher temperature. The transfer rate of PI during tea brewing was 104 ± 14 %. Nevertheless, the risk of PI through drinking tea was negligible to humans depending on the risk quotient (RQ) value, which was significantly lower than 1.

De novo formation of phthalimide from ubiquitous phthalic acid derivatives during the drying process of tea (Camellia sinensis) and selected herbal infusions.

It is well documented that under some circumstances phthalimide, a known degradation product of the fungicide folpet, can be formed as an artifact during gas chromatographic analysis. This fact explains one phthalimide source, but does not explain a great number of positive findings in the group of dried plant commodities obtained with an artifact-free analysis. Therefore, in the framework of this study, herbal and tea plants were grown in a glasshouse under the best possible protection against external environmental influences and ensuring the exclusion of the use of folpet. It was demonstrated that relevant amounts of phthalimide are formed during the drying process as part of the routine production of tea and herbals and in the absence of folpet. In this context, the presence of the widespread environmental chemical phthalic anhydride and its impact was investigated. We conclude that phthalimide is no reliable indicator for the active use of folpet.

A method based on precolumn derivatization and ultra high performance liquid chromatography with high-resolution mass spectrometry for the simultaneous determination of phthalimide and phthalic acid in tea.

Phthalimide can be formed from either the degradation of folpet and phosmet, or reaction of phthalic anhydride with primary amino groups. Consequently, the sum of phthalimide and folpet, expressed as folpet-residue definition, is highly prone to false-positive levels of folpet in tea. An analytical method is thus urgently needed to investigate the residue level and source of phthalimide in tea. In this work, we developed an accurate method of determining phthalimide and phthalic acid (the indicator of phthalic anhydride) by acetonitrile extraction and 3-bromopropyltrimethylammonium bromide derivatization coupled with ultra high performance liquid chromatography and high-resolution mass spectrometry. The method was validated, and linearity (correlation coefficients > 0.99) was obtained. Satisfactory recoveries at 10, 20, 50, and 100 µg/kg ranged from 76 to 117%, and the intra- and interday accuracies were <23%. The limit of quantification for phthalimide and phthalic acid was 10 µg/kg. The developed method was further successfully used to determine phthalimide and phthalic acid in some tea samples. The positive rate of phthalimide and phthalic acid detected in the tea samples ranged from 30-75 and 50-90%, respectively.

Quantification of folpet and phthalimide in tea and herbal infusions by LC- high-resolution MS and GC-MS/MS.

Two methods based on a modified QuEChERS sample preparation and either LC coupled to atmospheric pressure ionisation and high-resolution MS or GC coupled to electron ionisation and tripled quadrupole MS have been assessed for the quantification of folpet and phthalimide in tea and other dry herbal infusions. Both methods have been fully validated in green tea and further checked in black tea, verbena and rooibos, and they performed according to the SANTE/11813/2017 criteria at the target LOQ concentration level (50 µg/kg). These methods allow the accurate quantification of folpet in the selected matrices according to the new EU residue definition, which includes phthalimide. Phthalimide is the main metabolite and degradation product of folpet, although according to recent studies, it could be generated from different sources than folpet breakdown, such as food processing or analysis by GC.