Polar organic chemicals (POCs), which include a range of pesticides, pharmaceuticals and personal care products (PPCPs) as well as industrial chemicals, have emerged as a major group of environmental contaminants over the past decade, but relatively little is known about their occurrence and distribution in aquatic systems. The measurement of POCs in aquatic systems generally requires modification of existing methods or development of new methods. Following the success of aquatic passive sampling technologies for the sampling of a range of hydrophobic chemicals, passive sampling tools for POCs have been developed over the last 15 years. Most POC samplers (such as the Polar Organic Chemical Integrative Sampler (POCIS) and ChemcatcherTM) are used with a variety of solid-phase extraction materials to sequester analytes. However, before these technologies can be more widely adopted within routine regulatory monitoring frameworks a number of knowledge gaps need to be addressed. In particular, the ability of polar passive sampling sorbents to accumulate the components of diverse chemical pollutant mixtures and the validity of underpinning models for data interpretation and quantitation require specific attention. In this thesis the development and calibration of a number of new passive sampling tools and calibration of existing ones was undertaken to address some of these knowledge gaps.
In consultation with collaborators from the water industry we identified three types of priority analyte groups that are found in various types of water samples for which little or no passive sampling techniques and/or calibration data were available. These included 19 ionized or polar pesticides and PPCPs, 9 perfluorinated chemicals (PFCs) and a disinfection by-product, N-nitrosodimethylamine (NDMA).
Polar and ionized pesticides and PPCPs were included in the first part of this study (Chapter 2). The comparative performance of a modified POCIS (containing StrataTM-X sorbent) and ChemcatchersTM (containing SDB-RPS or SDB-XC) with a mixture of neutral and ionic chemicals (viz. the 19 ionized or polar pesticides and PPCPs) was investigated. Samplers were calibrated under controlled laboratory conditions for 26 days. The modified POCIS and ChemcatcherTM with SDB-PRS were similar in that approximately half the analytes (16 and 13, respectively) exhibited linear uptake over this time period. A number of ionized chemicals showed nonlinear uptake. The antifungal POC triclosan and the anionic herbicides picloram and dicamba showed negligible uptake in all samplers.
An important aspect of this work was an investigation of the effect of polyethersulfone (PES) membranes on analyte accumulation, often neglected in passive sampling studies. Time profiles of distribution between ChemcatcherTM SDB-RPS disks and PES showed that a significant proportion of diuron and triclosan remained in the membrane, even after 26 days exposure. It was also shown that reducing the membrane pore size from 0.45 to 0.2 µm caused a reduction in sampling rates by about 25%. For chemicals that show appreciable accumulation in PES the use of multi-compartment models may be warranted to fully account for chemical transport.
A new passive sampler containing coconut charcoal sorbent was developed for POCs such as NDMA that have relatively high water solubility, and for which the selection of a suitable sorbent may be difficult (Chapter 3). A significant achievement of this study was the unique breakthrough-column calibration method developed to determine charcoal/water sorption coefficients for NDMA. This method can be also applied to other sorbent-chemical combinations (including chemical mixtures) to achieve a better understanding of sorption processes.
In order to address the sampling of ionic chemicals such as PFCs a modified POCIS containing a weak anion exchange sorbent (Strata-XAWTM) was developed (Chapter 4). PFCs were chosen for calibration of this sampler because no passive sampling tool was available for quantitative estimates of these chemicals in aquatic systems. Laboratory derived Rs’s were between 0.16 - 0.37 L d-1, and t1/2 between 2.2 and 13 d. In addition, a field deployment in Sydney Harbour, Australia was conducted and revealed trace level concentrations from passive samplers (0.1−12 ng L−1), in good agreement with parallel grab sampling (0.2−16 ng L−1), confirming the practical application of this device.
A criticism of passive sampling tools, in particular for polar samplers, has been that the use of sampler calibration parameters derived under laboratory conditions may not be appropriate for estimating field concentrations, as ambient conditions can vary. Therefore, an investigation on the effects of ambient environmental flow rates on chemical Rs’s was undertaken, using the developed modified POCIS (with Strata-XAWTM) and targeting PFCs (Chapter 5). Uptake rates were assessed under 4 different water velocities (0.02 to 0.34 m s-1). Overall, PFC Rs values ranged from 0.09 - 0.29 L d-1. For individual compounds, Rs’s increased from the lowest to highest flow rate employed (by up to a factor of 2) for some PFCs (MW ≤ 464) but not for others (MW ≥ 500). However, for some of these smaller PFCs, Rs’s were increasingly less sensitive to flow rate as this increased within the range investigated. While water velocity effects seemed less pronounced than with samplers for hydrophobic chemicals, the use of in-situ correction methods was recommended to reduce errors associated with TWA concentration estimates. Therefore, a follow-up study investigated two in-situ calibration methods (i.e. performance reference chemicals (PRCs) and the passive flow monitor (PFM)) (Chapter 6). PFMs proved useful and robust to account for in-situ water velocity conditions, while the use of PRCs was unsuccessful.
Overall, results from the work described in this thesis show that the passive sampling technologies investigated can be useful as part of a suite of monitoring tools for most of the analytes. Practitioners need to be aware of instances for which samplers employed proved ineffective. The use of ion exchange sorbents for ionized chemicals and coconut-charcoal for highly polar chemicals demonstrates the potential for expanding the scope of passive sampling tools. More calibration studies would be necessary to encompass additional chemicals because of the chemical-sampler specific nature of sampling behaviour and sorption mechanisms, the latter being especially poorly understood. The break-through column calibration method presented in this study could be useful in this regard.