Impacts of surfactant adjuvants on pesticide availability and transport in soils

Abstract

Surfactants are frequently added to pesticide and herbicide formulations as adjuvants to improve handling, delivery and effectiveness. From a regulatory perspective such additives are generally considered to be inert, and their influence on co-contaminant fate and transport processes has been largely ignored. The objective of this chapter is to illustrate the potential effects of representative surfactant adjuvants on the phase distribution and availability of hydrophobic organic compounds (HOCs), soil water retention and water flow in unsaturated soils. Although the addition of surfactants at concentrations above the critical micelle concentration (CMC) is shown to enhance the total aqueous-phase concentration of HOCs, the free (non-micellar) aqueous phase HOC concentration decreases with increasing surfactant concentration. Results of pressure-saturation studies and one-dimensional column experiments demonstrate that surfactants can substantially reduce soil water retention and alter unsaturated water flow. These findings demonstrate the need to carefully consider the influence of surfactant adjuvants on both soil water characteristics and agrochemical fate and transport in the environment.