Effects of Benefin Vaporizing from Soils on Tobacco (Nicotiana tabacum) Foliage

Abstract

In closed vapor exposure chambers, foliar injury on tobacco (Nicotiana tabacumL. ‘Speight G-28’) seedlings was caused by vapors arising from soils in which technical grade benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine) or its commercially-formulated emulsifiable concentrate had been incorporated. The emulsifier alone did not cause injury. Dosages of the herbicide ranged from 0.84 to 6.72 kg/ha or 13.1 to 104.8 ppmw in the concentration in soils, and the lowest dosage was sufficient to induce the foliar injury. Leaves which developed during the exposure were markedly shortened, narrowed, and thickened, distorted in shape, and had an extremely poor lamina expansion and abnormal venation pattern. Severity of the foliar injury increased as the herbicide dosage and soil moisture increased, and as the soil organic matter content decreased. Leaves which were partially expanded before the exposure were affected much less. When exposed to vapors of14C-benefin, plant seedlings readily absorbed radioactive materials by its entire foliage including the stem tip with a few tiny developing leaves. More than half of the14C absorbed and adsorbed during a 3-day exposure was recovered by CHCl3wash of leaves and appeared to be retained by the wax and cutin layers, and also by lipoidal secretion substances of the numerous trichomes on the leaf surface. There was a small fraction of unabsorbed or loosely retained14C material on the surface of the leaves and stem tip, which was removed by water. That not recovered from H2O and CHCl3washes appeared to be distributed in the internal tissues. Little acropetal translocation appeared to occur from the expanded leaves toward the stem tip. There was no translocation of14C-benefin into roots of plants where only a single leaf was exposed to the radioactive vapors.