Translocation of 14C-dieldrin from small droplets on cotton leaves

Dieldrin (HEOD) spread from dried residues formed from droplets of emulsions and crystalline suspensions applied to the upper surfaces of cotton leaves (Gossypium species). The amounts of radiolabelled insecticide reaching defined areas of leaf-surface bearing adhesive tape (Sellotape) were measured quantitatively by scintillation counting. Autoradiography supported these results in demonstrating the extent of insecticide movement in the leaf. Up to one-fifth of the applied dose spread more than 8 mm across the leaf surface within a day (lateral movement). Penetration to the lower surface (vertical movement) took place within 4 days, depending on the leaf thickness, which itself was greatly affected by the growing conditions. During this process some dieldrin formed a derivative, possibly a hydroxydieldrin, and some was sorbed at the sites of the lysigenous secretory glands within the leaf. Dieldrin spreads from a deposit (representing that left by a spray droplet) on cotton leaf in all directions to a greater extent and more rapidly than previously supposed.