GC × GC–HRMS nontarget fingerprinting of organic micropollutants in urban freshwater sediments

Abstract

Background: Sediments are sinks for organic micropollutants, which are traditionally analysed by gas chromatography-mass spectrometry (GC-MS). Although GC-MS and GC-tandem MS (MS/MS) are preferred for target screening, they provide only limited chromatographic resolution for nontarget screening. In this study, a comprehensive twodimensional GC-high-resolution MS method (GC × GC-HRMS) was developed for nontarget screening and source identification of organic micropollutants in sediments from an urban channel and adjacent lake in Copenhagen, Denmark. The GC × GC-HRMS data were processed by pixel-based chemometric analysis using baseline subtraction, alignment, normalisation, and scaling before principal component analysis (PCA) of the pre-processed GC × GC-HRMS base peak ion chromatograms (BPCs). The analysis was performed to identify organic micropollutants of high abundance and relevance in the urban sediments and to identify pollution sources. Tentative identifications were based on match factors and retention indices and tagged according to the level of identification confidence. Results: The channel contained both a significantly higher abundance of micropollutants and a higher diversity of compounds compared to the lake. The PCA models were able to isolate distinct sources of chemicals such as a natural input (viz., a high relative abundance of mono-, di-and sesquiterpenes) and a weathered oil fingerprint (viz., alkanes, naphthenes and alkylated polycyclic aromatic hydrocarbons). A dilution effect of the weathered oil fingerprint was observed in lake samples that were close to the channel. Several benzothiazole-like structures were identified in lake samples close to a high-traffic road which could indicate a significant input from asphalt or tire wear particles. In total, 104 compounds and compound groups were identified. Conclusions: Several chemical fingerprints of different sources were described in urban freshwater sediments in Copenhagen using a pixel-based chemometric approach of GC × GC-HRMS BPCs. Various micropollutants of anthropogenic origin were identified. Tailored pre-processing and careful interpretation of the identification results is inevitable and still requires further research for an automated workflow.

A non-target screening study of high-density polyethylene pipes revealed rubber compounds as main contaminant in a drinking water distribution system

“…Out of the five tested rubber seals, the highest intensities of the two compounds were observed in the two pipe repair couplings (Figure S5). Previous research focusing on NTS analysis of micropollutants in urban freshwater sediments in Danish water channels also detected the presence of cyclohexyl isocyanate (Lübeck et al, 2020). In addition, the compound was found to migrate from recycled rubber, like rubber carpet padding (Phillips et al, 2018), and together with cyanoethyl ether, in recycled car rubber material (Benson et al, 2019).…”

Recent Advances in GC×GC and Chemometrics to Address Emerging Challenges in Nontargeted Analysis

“…Lubeck and co-workers used PCA with GC×GC-HRMS data to investigate water contamination from two collection sites in Copenhagen, Denamark. 37 Chromatograms were first aligned using a course shift followed by 2DCOW. 22 GC×GC chromatograms of water samples collected from a lake (UTM) and an adjacent water fortress (FSK) are shown in Figure 5Ai.…”

“…Following the general format described earlier, we next describe an example of PCA performed on pixel-level data. Lübeck and co-workers used PCA with GC×GC-HRMS data to investigate water contamination from two collection sites in Copenhagen, Denamark . Chromatograms were first aligned using a course shift followed by 2DCOW .…”

30th Anniversary of comprehensive two‐dimensional gas chromatography: Latest advances

“…Although nowadays many contaminants, such as pesticides, halogenated compounds, and polycyclic aromatic hydrocarbons, are recognized as priority pollutants regulated under environmental laws, contaminants of emerging concerns are not currently under any regulations but might be under investigation for future regulation. In such context, advanced separation methods such as GC×GC presenting enhanced peak capacity and sensitivity are preferable to monitor multi-class contaminants in diverse and complex environmental samples such as water, 71,72 wastewater, 73,74 aerosol, [75][76][77] and oil. 78,79 Meza et al used GC×GC to characterize biologically active micropollutants in hospital wastewater and to evaluate the efficiency of the wastewater treatment for such pollutants removal.…”