Advancing passive sampling for monitoring organic contaminants in the aquatic environment

Passive sampling has appeared as a promising monitoring technique for organic pollutants in aquatic environments. Passive sampling provides a measure of the bioavailable dissolved concentrations, lower detection limits than grab sampling, allows in situ sampling as well as the possibility of interfacing with mixture toxicity testing. However, to date, this approach has not been fully adopted within regular monitoring programmes, and has limited acceptance outside the scientific community. The research presented in this thesis aims to provide a better understanding of passive sampling techniques for targeting a wide range of organic contaminants for reliable and efficient water monitoring. To accomplish this objective, this thesis covers the development of a novel equilibrium passive sampling device targeting both polar and non-polar contaminants, laboratory calibrations of kinetic and equilibrium passive samplers and field trials in a wastewater treatment plant (WWTP) and the receiving river in southern Germany. Firstly, the partitioning behaviour of a range of environmentally relevant organic contaminants to one of the more widely applied passive sampling receiving phases, Oasis HLB®, was studied as a function of environmental parameters. Secondly, a new mixed polymer passive sampler (MPS) was made by embedding Oasis HLB® in a polydimethylsiloxane (PDMS) matrix in order to enhance the sampler affinity towards the full range of polar and non-polar organic contaminants and to avoid membrane sorption artefacts. This monophasic MPS proved to be advantageous in terms of convenient handling and the possibility of isotropic exchange for the eventual application of the performance reference compounds (PRC) approach for in situ calibration. The sampling performance of the MPS was characterized in a laboratory calibration experiment, and compared to an established kinetic passive sampler, polar organic chemical integrative sampler (POCIS). The POCIS is a widely used kinetic passive sampler, consisting of the same receiving sorbent as the MPS (i.e., Oasis HLB®) but equipped with diffusion-limiting polyethersulfone (PES) membranes. In a laboratory calibration experiment, the equilibrium partition coefficients and sampling rates of a wide range of organic contaminants to both the MPS and POCIS were determined under static and stirred conditions. For the tested analytes (log KOW of -0.03 to 6.26), the POCIS was the more efficient sampler since the relative affinity of the MPS was generally lower. However, the MPS had higher sampling rates for most compounds compared to the POCIS which implies that it can be applied as an equilibrium sampler for providing a “snapshot” of environmental levels. In contrast, the POCIS is a kinetic sampler and provides an integrative measure of environmental levels. Furthermore, equilibrium partitioning to each component of the POCIS (i.e., the Oasis HLB® and PES membranes) was determined. Apolar interactions were found to be the main driving force for sorption to the Oasis HLB®. The extent of sorption to the PES membrane of the POCIS was also determined, allowing a quantitative evaluation of the lag effect. This was found to be particularly relevant for non-polar contaminants. Thirdly, the MPS and POCIS were deployed along the river Saar, river Mosel and the outflow of a WWTP in Germany over five weeks (May-June 2015). The bioavailable dissolved concentrations of 27 organic contaminants, including 8 priority substances of the EU Water Framework Directive, were determined and used to compare the performance of each passive sampler in the field. To advance the applicability of passive sampling within regulatory monitoring programmes, a simple mathematical model was adapted to estimate the total water concentrations of the contaminants from the passive sampling measurements for comparison to environmental quality standard levels. Overall, this thesis describes the characteristics and performance of an equilibrium and a kinetic passive sampling device with regards to the accumulation behaviour of a wide range of relevant aquatic pollutants as along with their overall practicality in the field. This information can contribute to enhancing the reliability of the passive sampling approach for monitoring trace levels of environmental contaminants in aquatic environments as well as the implementation of the produced data within the regulatory context