Organohalogen compounds (OHCs) represent a diverse group of organic substances containing fluorine, chlorine, bromine and/or iodine, many of which are well-known for their environmental persistence, bioaccumulation and toxicity. Despite regulations and bans on several problematic OHCs, new compounds continue to emerge as replacements, challenging existing analytical techniques. The concept of the OHC “iceberg” is that we only measure a fraction (“the tip”) of all OHCs in a sample. This thesis aims to quantify the size of the OHC iceberg and apply state-of-the-art analytical techniques to identify the part we cannot see. To achieve this, extractable organohalogen (EOX; where X = F, Cl, or Br) mass balance methods were developed and applied, using a combination of combustion ion chromatography (CIC) and target analyses. Subsequently, high resolution mass spectrometry (HRMS)-based suspect and nontarget screening approaches were applied to further characterize the unknown fractions of EOX.

The lack of standardization for extractable organofluorine (EOF) mass balance methods has raised concerns about data reproducibility. In Paper I, an interlaboratory comparison was conducted to assess the fluorine mass balance method across three laboratories, using both water and sludge samples. The EOF-CIC method demonstrated promising accuracy and robustness, over a wide range of concentrations (60 to 2500 ng/L F). Paper II presents the first multi-halogen mass balance in wastewater treatment plant (WWTP) sludge, a useful approach to prioritize samples for follow-up investigation. Total halogen (TX) and EOX were determined in municipal sewage sludge as well as in standard reference materials (SRMs). Chlorinated paraffins (CPs) made up ~92% of extractable organochlorine (EOCl), while brominated flame retardants accounted for ~54% of extractable organobromine (EOBr) and per- and polyfluoroalkyl substances (PFAS) accounted for only 2% of the EOF. Additionally, unidentified EOF in non-polar CP extracts suggest the existence of organofluorine(s) with chemical properties unlike those of conventional PFAS. In Paper III the unknown fraction of EOF in WWTP sludge was further investigated, focusing on fluoropharmaceuticals and -pesticides. HRMS-based suspect screening was applied and sixteen pharmaceutical substances (including transformation products [TPs]), one pesticide and thirteen conventional PFAS were confirmed at confidence levels 1-4. Although the newly detected organofluorine compounds contained few fluorine atoms, their high concentrations resulted in significant contributions to the EOF. The known EOF fraction increased from 2% to 27% identified, of which ~22% was accounted for by fluoropharmaceuticals. In Paper IV, sludge and SRM extracts from Paper II containing unidentified EOCl and EOBr were reanalyzed using HRMS with ion mobility (IM) separation. Out of 17,982 peaks, 3,890 were prioritized using isotope patterns, collision cross section (CCS) values, and mass defect filters, resulting in the detection of 54 legacy OHCs and 30 unknown OHCs, of which 11 were tentatively identified.