Influence of HLB of polysorbate surfactants on mobility of methazole in plants and soil

Abstract

Methazole-¹⁴C and/or its C-labeled metabolites moved acropetally in the treated leaves of cotton (Gossypium hirsutum L., 'Deltapine') and prickly sida (Sida spinosa L.). The mobility pattern was not altered with polysorbate surfactants with different HLB (Hydrophilic-Lipophilic Balance) values. Total uptake and distribution of ¹⁴C increased with increasing concentration of methanol as a solvent and decreasing HLB values of surfactants. More ¹⁴C was translocated in cotton than in prickly sida. The effects of surfactants were masked by the drastic solvent action of 100% methanol. When the solvent effect was subtracted, the surfactant with HLB 8 caused greatest enhancement of translocation of ¹⁴C in both species.

Scanning electron photomicrographs showed that polysorbate surfactant (HLB 4.3) eroded cotton leaf surfaces severely at the 1% (w/w) level. Reticulated and etched patterns were observed on cotton leaf surfaces treated with water soluble surfactants. Trichomes on the leaves of prickly sida appeared not to be affected by the surfactants. The leaves of prickly sida were less affected than those of cotton by the surfactants. Surface deposits of formulated methazole were different in appearance from those of technical methazole.

The influence of polysorbate surfactants on the leaching of methazole-¹⁴C in Landisburg-Greendale silt loam soil was examined. When the herbicide was applied with surfactants (1:4, w/w, all HLB values), leaching of methazole was not affected. However, ratios of 1:1 and 4:1 (herbicide/surfactant) caused slight and significant retardation of movement, respectively. The influence of HLB of polysorbate surfactants was minimal.