Calibration of a passive sampling device for time-integrated sampling of hydrophilic herbicides in aquatic environments

Two types of solid-phase materials, a styrenedivinylbenzene copolymer sorbent (embedded in a SDB-XC Empore (TM) disk) and a styrenedivinylbenzene copolymer sorbent modified with sulfonic acid functional groups (embedded in a SDB-RPS Empore disk), were compared as a receiving phase in a passive sampling device for monitoring polar pesticides. The SDB-XC Empore disk was selected for further evaluation, overlayed with either a polysulfone or a polyethersulfone diffusion membrane. The target herbicides included five nonionized herbicides (simazine, atrazine, diuron, clomazone, and metolachlor) and four phenoxy acid herbicides (dicamba, (2,4-dichlorophenoxy)acetic acid [2,4-D], (4-chloro-2-methylphenoxy)acetic acid [MCPA], and triclopyr) with log octanol/water partition coefficient (log K-OW) values of less than three in water. Uptake of these herbicides generally was higher into a device constructed of a SDB-XC Empore disk as a receiving phase covered with a polyethersulfone membrane compared to a similar device covered with a polysulfone membrane. Using the device with a SDB-XC Empore disk covered with a polyethersulfone membrane, linear uptake of simazine, atrazine, diuron, clomazone, and metolachlor was observed for up to 21 d, and daily sampling rates of the herbicides from water in a laboratory flow-through system were determined. The uptake rate of each nonionized herbicide by the Empore disk-based passive sampler was linearly proportional to its concentration in the water, and the sampling rate was independent of the water concentrations over the 21-d period. Uptake of the phenoxy acid herbicides (2,4-D, MCPA, and triclopyr) obeyed first-order kinetics and rapidly reached equilibrium in the passive sampler after approximately 12 d of exposure. The Empore disk-based passive sampler displayed isotropic kinetics, with a release half-life for triclopyr of approximately 6 d.