Structural characteristics of surfactants and a herbicide were incorporated in the same molecule by forming long-chain alkylamine salts of 2,4-dichlorophenoxyacetic acid [2,4-D]. In water sprays, all of the 2,4-D salts showed surface activities characteristic of surfactants. The application rate of 2,4-D was held constant at 1/16 lb ae/A; salt concentration was varied by varying spray volume. Seventeen salts were herbicidally active on soybeans at a high concentration (1/16 lb ae in 10 gpa of spray) and a few were also active at a lower concentration (1/16 lb ae in 40 gpa). The remaining thirteen salts were relatively inactive in water. Structural features associated with water-active salts of 2,4-D were those which contribute to hydrophilic characteristics of surfactants. Lipophilic structural features contributed to inactivity in water.

The 2,4-D toxicity of fourteen water-active and water-inactive salts of 2,4-D was maximally and equally elicited in one or more of six water and oil spray systems. Differential activities of the salts permitted their classification into six distinct classes—three hydrophilic and three lipophilic. No one of five solution properties—surface tension, interfacial tension, turbidity, specific conductivity, or pH—could be correlated with herbicidal toxicity of a spray. However, a combination of three properties—interfacial tension, turbidity, and specific conductivity—provided some indication of the relative hydrophilic or lipophilic character of a salt and of the 2,4-D toxicity in different sprays. Data suggested that herbicides move into plants by two distinct pathways—one hydrophilic and the other lipophilic.