In the Antarctic continent, snow and ice are fundamental in the study of the input mechanism of transferring pollutants originating from distant areas through the atmospheres. Various persistent organic pollutants (POPs) and other potential terrestrial biomarkers have been investigated, in particular polycyclic aromatic hydrocarbons (PAHs), pesticides, polychloro biphenyls, polyfluoroalkyl substances (PFASs), polybrominated diphenyl ethers (PBDEs) and polychlorinated dibenzo-p-dioxins and furans. Moreover, during long-range atmospheric transport and after deposition, pollutants may undergo photodegradation and transformation processes (e.g., by microorganisms), and some reaction products could be even more toxic than their parent compounds. Thus, the first objective of this research will be the development of an analytical platform based on liquid chromatography-high resolution mass spectrometry (LC-HRMS) for the determination of the main emerging contaminants, such as PFASs, PBDEs and OH-PAHs, together with their degradation/transformation products, including new/unexpected compounds.
Another important component of Antarctic environment is the dissolved organic matter (DOM), constituted by several thousand compounds. Molecular fingerprints of snowpack DOM indicate that it has both natural and anthropogenic origin. Therefore, the knowledge of DOM composition could provide useful information about pollutants transport, but primarily on bacteria, algae and other microorganisms. Due to its complexity and heterogeneity, DOM characterization is an analytical challenge, since its composition also derives from various and sometimes unknown bacteria/organisms. Thus, the second objective of this project will be the development of an analytical strategy based on LC-HRMS for snow DOM molecular characterization, with attention to both small molecules (untargeted metabolomics approach) and proteins, searched also on the snow filtrate (bottom-up, metaproteomics approach).
Several researches have studied the presence of POPs in Antarctica. One of the reasons to study POPs in Antarctica is that, for example, PAHs are tracers both for biomass and fossil fuel combustion. As reported in a very recent review article [3], both non-alkylated PAH species and alkylated PAHs have been identified in the ice samples: if PAHs are generated primarily during incomplete combustion of oil and coal, alkylated compounds are formed by burning crude and refined oil. The same review [3] reports that information on PAH concentrations in the Antarctic is more scarce as compared to the Arctic. Therefore, there is a need to carry out deep investigations regarding the seasonality and spatial distribution of PAHs in Antarctic snow and ice to gain a comprehensive understanding of their fundamental patterns and to better compare the two polar regions.
Furthermore, the knowledge about POP degradation/transformation products is limited. Indeed, even if photodegradation studies on ice environment have been carried out in laboratory experiments, however they could not fully represent the real situation, in which many microorganisms can contribute to transformation processes. Therefore, only the analysis of snow and ice samples directly collected in Antarctica (that is one of the object of this project) could provide a comprehensive overview of the reaction products. The main difficulty is that while some compounds can be predicted by knowing the common degradation/transformation routes of the main POPs, other compounds can be new or unexpected. For the former group of compounds, including original POPs, a suspect screening approach by LC-HRMS is suitable, whereas for the latter an untargeted approach is mandatory. Therefore, in our opinion, by using our expertise in high resolution mass spectrometry, together with experience in data elaboration, we could give a great contribution to the knowledge of processes occurring to POPs in such snow/ice environment. We also can take advantage of the continuous development and inclusion of emerging environmental substances in the mass spectra databases (e.g., NORMAN MassBank).
More challenging is the molecular characterization of DOM that has been only partially studied in the Antarctic continent. Due to the heterogeneity of DOM sources, it composition may vary significantly depending on sample collection site. Furthermore, DOM transformations by supraglacial microbes are not well understood. Since several thousands of compounds constitute the DOM, a fully elucidation is unfeasible. Previously, some researchers used HRMS to find biomarkers of DOM origin and to classify the detected ions in chemical groups (lipids, proteins, carbohydrates and so on) [9-11, 19-23]. Our aim is to improve the knowledge of substances constituting the DOM by applying our expertise in fractionation (at both SPE level and chromatographic level) and UHPLC-HRMS analysis. In this case, only an untargeted approach can be used to detect the accurate m/z signals of most metabolites. Our improvement respect to the literature will be also the combination of metabolomics data and proteomics data. In fact, proteins will be analyzed both in snow DOM and snow filtrate. The part of protein identification will follow the metaproteomics approach, which involve the identification, function and expression of various proteins present in microbial community, as well as the identification and expression analysis of stress related proteins. Indeed, comparative metaproteomics could provide a powerful tool to study the impact of environmental changes on microbial communities.