A comparison of equilibrium and kinetic passive sampling for monitoring of aquatic organic contaminants in German rivers
The performances of an equilibrium and a kinetic passive sampler for monitoring a range of organic contaminants (Log KOW from −0.03 to 6.26) were evaluated in the effluent of a wastewater treatment plant, the receiving river Saar as well as the river Mosel in Germany. The polar organic chemical integrative sampler (POCIS) and a new mixed polymer sampler (MPS) were selected as kinetic and equilibrium passive samplers, respectively. Concentrations were described in terms of a time-weighted average concentration (CTWA) from the POCIS measurements and as an equilibrium concentration from the MPS (CEquil-MPS) and POCIS membrane (CEquil-PES) analyses. Twenty-seven compounds could be detected, including eight priority substances of the EU Water Framework Directive. Both sampler types detected a similar range of compounds in the low ng/L to μg/L range, with a high proportion of pharmaceuticals being detected at all sampling sites. To account for uncertainty in the POCIS sampling rates, a range in CTWA was estimated by applying low and high sampling rates. For the compounds that were detected in the POCIS this range was within a factor of 3.5. Interestingly, the MPS extracts showed lower ionisation artefacts than the POCIS extracts during the LC-MS/MS analysis. Finally, total water concentrations (CTotal) were estimated from the dissolved concentrations, literature organic carbon partition coefficients (KOC) and the total organic carbon levels measured in the rivers. For the compounds in this study, negligible differences between CTotal and the passive sampler-derived dissolved concentrations were found with a maximum difference of 15% for diclofenac. Overall, this study demonstrated that the parallel application of kinetic and equilibrium passive samplers can improve the description of water quality.