On October 25, 2019, the US EPA proposed a new tolerance limit for Fenbuconazole in dried and instant tea by changing it from 10 to 30 ppm. Objections and requests for hearing must be received by December 24, 2019.

SAFEGUARDS | FoodNO. 162/19


Fenbuconazole (R,S)-4-(4-chlorophenyl)-2-phenyl-2-(1H-1,2,4-triazole-1-ylmethyl)) butyronitrile is a triazole fungicide used in various agricultural and horticultural applications. It exerts excellent fungicidal activity through inhibition of sterol biosynthesis. Currently, it is approved for use on a wide range of fruits, vegetables, cereals, and ornamental crops [1]. However, this fungicide has been associated with an increase in the incidence of liver adenomas after long term dietary exposure of female mice. In addition, it has been identified as an inhibitor of human aromatase activity which is considered to evaluate cancer risk. Fenbuconazole consists of a pair of enantiomers which can degrade into two major metabolites; RH-9129 and RH-9130 in environment via oxidation process. Both metabolites have the same relative configuration and they differ only in the descriptor (R/S) due to the difference in the order of priority at the stereogenic center [2]

To ensure human food safety, the US EPA has established a tolerance limit by sum of Fenbuconazole and its metabolites including RH-9129, cis-5-(4-chlorophenyl)-dihydro-3-phenyl-3-(1H-1,2,4-triazole-1-ylmethyl)-2-3-H-furanone, and RH-9130, trans-5-(4-chlorophenyl)-dihydro-3-phenyl-3-(1H-1,2,4-triazole-1-ylmethyl)-2-3 H-furanone in various food commodities. Initially, the tolerance limit for this compound in dried and instant tea was set at 10 ppm, based on the data review by the Food Safety Commission of Japan in 1995. With further field study conducted during 2016 and 2017, a new tolerance limit set at 30 ppm has been proposed according with the Organization for Economic Cooperation and Development (OECD) tolerance calculation procedure [3] and shown in Table 1. Monitoring of pesticide enantiomers are mostly carried out by liquid chromatography tandem mass spectrometry (LC-MS/MS). Chiral column, such as cellulose and amylose type, is required to separate the metabolites.

What do the changes mean?

This update has the potential to affect agricultural producers, food manufacturers, and pesticide manufacturers. Any imported foods destined for the United States must not be found to contain Fenbuconazole at levels exceeding the tolerance limit. To ensure compliance with food safety regulations, food producers should seek professional advice.

Common Name Residue Definition Commodity Tolerance Limit (ppm)
(CAS# 114369-43-6)
Sum of Fenbuconazole and its metabolites
Tea, Dried 30 
Tea, Distant Tolerance Limit for Fenbuconazole in Tea 30

Table 1: Tolerance Limit for Fenbuconazole in Tea

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