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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 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 KOW) 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.