Relative effects of surfactants and humidity on soil/air desorption of chloroacetanilide and dinitroaniline herbicides

Herbicides are typically applied as formulation mixtures in order to ensure uniform application and improve biocide performance, but little is known about the effects of formulated surfactants on herbicide exchange between soil and the atmosphere. Desorption experiments were performed for seven herbicides from the chloroacetanilide and dinitroaniline families with model anionic-nonionic surfactant mixtures under a range of relative humidity (RH) conditions (3-66%) on two soils. Enhanced desorption of herbicides from soil to the gas phase was observed as the concentration of surfactant mixture or the RH increased. Multiple linear regression models developed to summarize the soil/air desorption behavior of these herbicides revealed that surfactant concentration, relative humidity, and herbicide properties (i.e., K-H, K-OA) all have significant contributions to herbicide desorption. However, the ANOVA results indicated that surfactant concentration only accounted for 1.4% of the variance in desorption, RH accounted for 40-60%, and herbicide properties, logK(H) or logK(OA), accounted for 20-40%. The study results predict that less than a 20% increase (study range 1.5-21.0%) in surfactant concentration could double the atmospheric losses of herbicide from their soil application sites, and about a 60% increase in ambient RH (3-66%) elevated the losses by 10-40 times.