Molecular characteristics, sources and environmental risk of aromatic compounds in particulate matter during COVID-2019: Nontarget screening by ultra-high resolution mass spectrometry and comprehensive two-dimensional gas chromatography.

Aromatic compounds, including many polycyclic aromatic hydrocarbons (PAHs), are suspected carcinogens and may originate from different sources. To investigate the impact of anthropogenic emission reductions on unknown aromatic compounds in particulate matter, we collected samples during the pre-COVID period in 2020, the COVID-19 lockdown period in 2020, and the same period as the lockdown in 2019. Besides the 16 PAHs, other aromatic compounds were analyzed by Fourier transform ion cyclotron resonance mass spectrometry and comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry. Four main compound classes were identified: CH, CHO, CHNO, and CHOS. Hierarchical cluster analysis showed the aromatic compounds varied during the different periods. Compared with before the pandemic, the relative abundances of aromatic compounds with low degrees of unsaturation and long alkyl chains (e.g., alkylbenzenes) increased. These compounds probably mainly arose from fossil fuel combustion and petrochemical industry emissions. The CHO compounds, which were dominated by those with high degrees of oxidation, might originate from secondary organic aerosols. Aromatic aldehydes (e.g., cyclamen aldehyde) and benzoates (e.g., 2-ethylhexyl benzoate) probably with high toxicity deserve more attention. During lockdown, nitro derivatives of condensed PAHs were the main CHNO compounds, and the numbers of homologs decreased perhaps because of significant reductions in NOx and PAHs. CHOS compounds with long carbon chains and low degrees of unsaturation were predominant and the numbers of homologs increased. Five compounds (e.g. 1,3-dimethyl pyrene) were predicted to possibly exhibit persistent and bio-accumulated by EPI Suite model, which need further research. The results provide insight on aromatic compounds and their source appointment in atmospheric particulate matter.

Non-targeted characterization of dissolved organic matter from a wastewater treatment plant by FT-ICR-MS: A case study of hospital sewage

Hospitals generate large volumes of wastewater. Dissolved organic matter (DOM) in wastewater effluent can act as precursors of disinfection by-products, transporter of pollutants, and affect the performance of treatment plants. This study aims to characterize the composition of DOM in medical wastewater and investigate the selectivity of the hospital treatment plant in the removal of DOM. DOM was characterized by Fourier-transform ion-cyclotron resonance mass spectrometry (FT-ICR-MS) and excitation-emission matrix fluorescence spectroscopy (EEMs). DOM of medical wastewater was dominated by aliphatic and highly unsaturated compounds, a feature that is remarkably different from that of natural DOM. In the membrane bioreactor (MBR) unit, more CHNO compounds and highly unsaturated compounds were formed. After disinfection, the highly unsaturated and humic-like compounds were reduced, accompanying a decrease in aromaticity. After reverse osmosis, the highly unsaturated and CHO compounds were concentrated and removed. These steps were complementary in the removal of DOM, suggesting effective transformation and elimination of DOM. This study contributes to a better understanding of the features of DOM in medical wastewater and treatment plant performance in the removal of DOM, which is indispensable for the large-scale design and application of technologies for hospital wastewater treatment, especially in the context of the COVID-19 pandemic.