Development of a passive sampling device for hydrophilic organic pesticides in aquatic environments
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NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- The experimental aspects of this thesis deal with the development of a passive sampling device for measuring hydrophilic organic herbicides in. the aquatic environment. The target herbicides included five non-acidic herbicides (simazine, atrazine, diuron, clomazone, and metolachlor) and five acidic herbicides (dicamba, (2,4-dichlorophenoxy)acetic acid [2,4-D], ( 4-chloro-2-methylphenoxy)acetic acid [MCPA], triclopyr and bensulfuron-methyl) with log octanol/water partition coefficient (log Kow) values less than three in water. Chapter 1 of the thesis presents a literature review. This includes information on the usage of the target hydrophilic herbicides in Australia and details on the routine analysis methods for determination of these herbicides in aqueous environments. Chapter 2 focuses on the optimisation of the separation of the ten target herbicides by high-performance liquid chromatography (HPLC) with a photodiode array (PDA) or a ultra-violet (UV) detector. An artificial neural network (ANN) was employed to model the chromatographic response surface for the linear gradient separation of the ten target herbicides. The ANN was trained using the pH of the mobile phase and the slope of the acetonitrile/water gradient as input variables. Nine experiments were required to generate sufficient data to train the ANN to accurately describe the retention times of each of the herbicides within a defined experimental space of mobile-phase pH range 3.0 to 4.8 and linear gradient slope 1 to 4% acetonitrile/min. The modeled chromatographic response surface was then used to determine the optimum separation within the experimental space. This approach allowed the rapid determination of experimental conditions for baseline resolution of all ten herbicides. Chapter 3 focuses on the development of sample preconcentration methods for the target compounds in the aquatic environment. Liquid-liquid extraction (LLE) with dichloromethane, solid-phase extraction (SPE) using Oasis® HLB cartridges or SBD-XC Empore™ disks with Filter Aid 400 were compared for the extraction efficiency of these herbicides in different water matrices, especially water samples from contaminated agricultural drainage water containing high concentrations of particulate matter. Herbicides were then separated and quantified by HPLC-UV. Chapter 4 presents the results of experiments carried out.to develop an Empore™ disk-based passive sampling device for the target hydrophilic herbicides. The herbicide uptake or sampling rate of passive sampling devices depended on the configuration of the passive sampler, the properties of the receiving phase, the overlying diffusion membrane and the properties of the compound being sampled. Two types of Empore™ solid-phase materials, a styrenedivinylbenzene copolymer sorbent (embedded in a SDB-XC Empore™ disk), and a styrenedivinylbenzene copolymer sorbent that was modified with sulfonic-acid functional groups (embedded in a SDB-RPS Empore™ disk) were compared as a receiving phase in a. device for uptake of the target herbicides. The SDB-XC Empore™ disk proved to be the superior receiving phase and was then further evaluated with either a polysulfone or polyethersulfone diffusion-limiting membrane. Uptake of the target herbicides was generally higher into a device constructed of a SDB-XC Empore™ disk covered with a polyethersulfone membrane. This device showed linear uptake of the non-acidic (simazine, atrazine, diuron, clomazone, and metolachlor) for up to 21 days. Daily sampling rates of the herbicides from water in a laboratory flow-through system were determined. 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 days of exposure. The Empore™ disk-based passive sampler displayed isotropic kinetics, with a release half-life for triclopyr of approximately six days. Chapter 5 details the evaluation of the developed device for monitoring the nonacidic target herbicides in the field. The herbicide uptake depended on the configuration of the passive sampler, the properties of the receiving phase, the overlying diffusion membrane, the properties of the compound being sampled and also the aqueous environment conditions during deployment, such as biofouling and water turbulence. Calculations of time-weighted average water concentrations of the herbicides during the deployment period were based on the sampling rates of the passive sampling devices determined in the laboratory. The field sampling rates were adjusted by the application of a correction factor determined from the release of monolinuron as a performance reference compound (PRC). The field study was undertaken in the Murrumbidgee Irrigation Area (MIA) (Leeton, NSW, Australia). Daily water extractions of 24-hour composite water samples collected at two sites were performed by SPE using SDB-XC Empore™ disks with Filter Aid 400. Empore™ disk-based passive samplers, consisting of a SDB-XC Empore™ disk as a receiving phase and a polyethersulfone membrane as a diffusion membrane, were deployed at the same sites. Over a two-week study period, the daily aqueous concentrations of herbicides from 24-hour composite samples detected at two sites increased after run-off from a storm event and were in the range of: 0.1 to 17.8 μg/L, < 0.1 to 0.9 μg/L and 0.2 to 17 .8 μg/L at site l; < 0.1 to 3.5 μg/L, < 0.1 to 0.2 μg/L and< 0.2 to 3.2 μg/L at site 2 for simazine, atrazine and diuron, respectively. The release half-life for monolinuron from the device in the laboratory was 106 days compared to 34 days at site 1 and 31 days at site 2 in the field. The differences in the release rates of monolinuron were used to compensate for variations in the environmental conditions. The time-weighted average (TWA) herbicide concentrations determined from the recovered passive sampling devices after 7, 10 or 13 days were generally within twofold of the mean of the daily drainage-water concentrations of simazine, atrazine and diuron for each corresponding period.
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