Beyond the Drinking Water Directive: The use of reporter gene assays as an added tool for effect-based monitoring of polycyclic aromatic hydrocarbons and polychlorinated biphenyls in drinking water sources.

Polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) are legacy organic micropollutants (OMPs) that are sporadically detected in drinking water (DW) sources. The European Drinking Water Directive requires EU member states to monitor 5 PAHs in DW and its sources. The Dutch national regulations require 6 additional PAHs to be monitored and 7 polychlorinated biphenyls (PCBs). These indicator compounds act as representatives for large compound classes. PCBs alone comprise 209 congeners, it is evident that conventional chemical target analysis (GC-tQ-MS) alone is not sufficient to monitor these entire compound classes. This study investigated the application of reporter gene assays as effect-based methods (EBMs) to monitor PAHs and PCBs in DW sources. Herein, it was assessed what added value the bioassays can bring compared to the current approach of chemical target analysis for PCBs and PAHs. Regulated and non-regulated PAHs and PCBs were tested in four bioassays to determine the relative potency factors (RPFs) for these compounds. Non-regulated congeners were found to be active in the PAH-CALUX and anti-AR CALUX. An assessment of surface water (SW) spiked with standard mixtures containing PAHs and PCBs confirmed the predictable behavior of the PAH-CALUX. Moreover, the bioassay was able to detect AhR-mediated activity caused by non-regulated PAHs and PCBs, whereas this would have been missed by conventional chemical target analysis. Last, a field study was conducted in Dutch DW sources at six sampling moments. The PAH-CALUX detected AhR-mediated activity at all sampling moments and an ecological effect-based trigger (EBT) value was exceeded on multiple accounts. Combined application of GC-tQ-MS and the PAH-CALUX ensures compliancy with monitoring legislation and provides additional insights into potential hazards to humans and the environment.

The contribution of PFAS to thyroid hormone-displacing activity in Dutch waters: A comparison between two in vitro bioassays with chemical analysis.

Per- and polyfluoroalkyl substances (PFAS) are a group of xenobiotics that are widely distributed throughout the aquatic environment. Many PFAS are possible thyroid hormone (TH) system disrupting compounds, because they have the capacity to -amongst other- inhibit the TH thyroxine (T4) from binding to its transport protein transthyretin (TTR). This study investigated the occurrence of TH-displacing activity in the Dutch water cycle, and more specifically, the contribution of PFAS to this effect. Over one year of monitoring data of 29 PFAS (linear and branched) showed the continuous presence of PFAS in drinking waters and their surface water sources. Secondly, the FITC-T4 and TTR-TRß-CALUX bioassays were mutually compared using positive (HPLC-grade water spiked with PFOA) and negative control samples (HPLC-grade water), as well as relative potency factors (RPFs) of up to 20 PFAS congeners. Both assays were found to be suitable for measuring TH-displacing activity in water samples. As a third aim, a field study was performed in the Dutch water cycle that was comprised of samples from drinking water, surface water, PFAS contaminated sites, and 2 wastewater treatment plants. All samples were analyzed with 1. chemical analysis for 29 PFAS, 2. the FITC-T4 bioassay, and 3. the TTR-TRß-CALUX bioassay. The bioassays mutually showed good correlation (R2 0.85). Bioanalytical equivalent concentrations (BEQ) based on chemically-determined concentrations and RPFs (BEQchem) revealed that analyzed PFAS only explained ≤4.1 % of their activity in water extracts measured by both bioassays (BEQbio). This indicated that as yet unknown compounds contribute to the majority of the measured TH-displacing activity. Moreover, water treatment processes (e.g. DW production from SW) showed a larger contribution of target PFAS to the BEQbio. This could be a first lead to identify unknown compounds that contribute to this activity, and as such, enable the assessment of possible risks associated by the occurrence of TH-displacing activity in water.