Herbicide Residues in Tobacco Leaves and their Transfer into the Smoke: Urea Herbicides Patoran® and Molipan®

Abstract The herbicides Patoran ( = Metobromuron) and Molipan ( = Monolinuron + Linuron), when applied to the soil previous to planting in concentrations of 4 and 2.5 kgs/ha, respectively, were not toxic to the tobacco plant, but controlled most of the weeds except Veronica persica and Mercurialis annua. In the air-cured tobacco, the Patoran residue was about 1.2 ppm; it was independent of the leaf position and unchanged after fermentation, but higher in the laminae (1.2 ppm) than in the midrib (0.2 ppm). The Molipan residues were higher in the lower (2 ppm) than in the upper leaves (1 ppm) and decreased after fermentation by approximately 40 %; the laminae contained more residues than the midrib. When the tobacco was smoked as cigarettes about 4 % of the Patoran residue was transferred into the mainstream smoke; another 10 % was found in the smoke condensate after pyrolytical degradation to 4-bromoaniline. The transfer rates for the Molipan residues were 2.5 % for monolinuron (plus 10 % recovered as 4-chloroaniline) and 6 % for linuron (plus 20 % recovered as 3,4-dichloroaniline). The retention of these residues from the mainstream smoke by cellulose and cellulose acetate cigarette filters was of the same order of magnitude as the retention of nicotine. Different analytical principles were applied for the residue determinations in tobacco (as azo dyes by spectrophotometry) and in smoke condensate (as bromo-iodo- and chloro-iodo-benzenes by pulsed ECD gaschromatography). The analytical procedures are given in detail.