In situ investigation into surfactant effects on the clearance of polycyclic aromatic hydrocarbons adsorbed onto soybean leaf surfaces

Abstract

The partitioning of polycyclic aromatic hydrocarbons (PAHs) in agricultural crop leaves, contributes to the exposure of organisms to these chemicals through the dietary pathway. To precisely predict the fate of PAHs and crop safety, the clearance of three-ringed phenanthrene (Phe) and four-ringed pyrene (Pyr) adsorbed individually onto living soybean leaf surfaces, as well as the effects of two surfactants, namely, an ionic surfactant (sodium dodecylbenzene sulfonate, SDBS) and a non-ionic surfactant (polyoxyethyleneglycol dodecyl ether, Brij35), were investigated in situ using the laser-induced nanosecond time-resolved fluorescence (LITRF) method. The effects varied significantly with surfactant types primarily in terms of the elimination rates and the final residues of PAH chemicals. With increasing SDBS and Brij35 concentrations, volatilization rate constants (kC) of both Phe and Pyr initially decreased at fast rates and then at more moderate rates later on, resulting from the plasticizing effect of surfactants adsorbed on leaf surfaces. In addition, the photolysis rate constants (kP) decreased with the presence of SDBS but increased with the presence of Brij35. Overall, the total clearance rates of PAHs (kT) adsorbed onto living soybean leaf surfaces were inhibited by the presence of SDBS but promoted by the presence of Brij35. These observations show that surfactants may significantly alter the clearance of PAHs in agricultural systems, and the potential impact of surfactants on crop safety is closely related to surfactant types in natural environments.