Laboratory fumigation of wheat flour with sulfuryl fluoride – penetration and fluoride residues

Research on sulfuryl fluoride (SF) in the recent past has been focused on its potential in applications, which were covered by methyl bromide formerly. The fumigation of flour mills is one of the areas of SF use. A lot of publications are focusing the efficacy of SF against stored product pests. However, there are only few data on its behaviour on flour. The present work wants to add some more information about the property of SF to penetrate flour and, in consequence of the SF break down, the fluoride residues. Two different experimental set ups were chosen. In a larger scale experiment different amounts of wheat flour, densely packed in a glass column were exposed to SF. The glass column was connected to a SF reservoir of 2.5 m3. Heights of 110 cm, 30 cm and 15 cm of flour were investigated. In the headspace and on the bottom of the flour the SF concentration was recorded during an exposure of 50 h. In a second experimental set up the SF was pumped through flour in a circuit array, changes in the SF concentration were observed. For both, an initial concentration of 50 gm-3 was chosen. The concentrations were determined with FTIR-spectroscopy methods. After aeration, the fluoride content of the flour samples was determined using a fluoride-selective electrode. The time – concentration curves during the fumigation of flour indicate a decline in the initial concentrations. In case of the first set up, the concentration on the bottom of the flour column increased in a time period, depending on the depth of the flour. It leveled off within a certain time but remained less than the head space concentration on the top. The fluoride contents of the fumigated samples ranged from 7 mg kg-1 to 31 mg kg-1. The results are discussed.