Uptake of the herbicide [C-14] 2,4-D iso-octyl in the vapor-phase by tomato and lettuce plants and some effects on growth and phytotoxicity

Tomato and lettuce plants were exposed to vapour of the herbicide [C-14-phenyl] 2,4-D iso-octyl at concentrations in the range 0 - 450 pg litre-1 for periods of 6, 24 and 72 h in separate experiments using a flowing-air system. The rate of uptake, as indicated by plant content of radiolabel, was both linear with respect to the vapour concentration and independent of the duration of exposure. The uptake rate of tomato was greater than that of lettuce at any given vapour concentration. Uptake by the apical leaves of lettuce was higher than by the older leaves expressed on an area basis; tomato showed no effect of leaf position. Visible symptoms of phytotoxicity were shown by both species 40 days after exposure to the highest doses. Advantages of using the low-volatile ester (iso-octyl) of 2,4-D to reduce vapour drift damage are discussed in terms of plant uptake.