Sources of Oxygenated Polycyclic Aromatic Hydrocarbons (OPAHs) in soils – a compound-specific stable isotope approach

• Applicant: Professor Dr. Wolfgang Wilcke
• Subject Area: Soil Sciences
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 537676254

Oxygenated polycyclic aromatic hydrocarbons (OPAHs) can be produced during combustion of organic materials or secondary transformations of parent-PAHs in the environment. Several OPAHs show a higher toxicity, bioavailability, and mobility in soil than their parent-PAHs. To assess the environmental risk arising from PAH and OPAH contamination requires the understanding of the production of OPAHs. Thus, there is a need to distinguish the primary (i.e., combustion-derived), secondary photochemical, and secondary microbial sources of OPAHs and to improve our understanding of the transformation of PAHs to OPAHs in soils. We aim to provide a novel stable isotope ratio-based tool to distinguish between the OPAH sources in aerosol and soil at the example of the parent compound-derivative pair anthracene (ANTH) and 9,10-anthraquinone (9,10-AQ), the frequently most abundant OPAH. We will test five hypotheses: (i) Primary and secondary 9,10-AQ can be distinguished with the help of their compound-specific C and H isotope ratios (d13C and d2H values). (ii) Photochemically produced 9,10-AQ shows a specific 2H value. (iii) The differences in the d13C and d2H values of 9,10-AQ from the three sources (primary, secondary photochemical, secondary microbial) allow for the solution of a three-end-member mixing model. (iv) The contribution of biologically produced 9,10-AQ increases with microbial activity in soil measured as CO2-evolution from plant-free microcosms and the contribution of photochemically produced 9,10-AQ is higher in rural than in urban soils. (v) When the soil microorganisms are poisoned, no OPAHs are produced from parent-PAHs during incubation. To test the five hypotheses, we will realize three work packages (WPs). Each WP includes an experimental and an observational component. In the first WP, we will characterize the d13C and d2H values of ANTH, benz(a)pyrene [B(A)P] as an entirely combustion-derived reference PAH and 9,10-AQ in the total in the atmosphere suspended particles (TSPs) from primary emissions (combustion of biomass and fossil fuels). In the second WP, we will determine d13C and d2H values of 9,10-AQ from photochemical secondary formation in the atmosphere and in the third WP from microbial secondary transformation in the soil. We will collect TSPs from the emissions of experimental biomass and fossil fuel combustion and from urban and rural atmosphere. We will expose ANTH sorbed to a muck aerosol to solar irradiation in glass spheres. Moreover, we will conduct microbial turnover experiments in microcosms with rural soils to which ANTH will be spiked. We will study the vertical distribution and compound-specific d13C and d2H values of ANTH, B(A)P, and 9,10-AQ in moder-type forest organic layers where the microbial turnover of PAHs progresses with depth. In all TSP and soil samples, we will determine PAH and OPAH concentrations and compound-specific d13C and d2H values of ANTH, 9,10-AQ, and partly also B(A)P.

• DFG Programme: Research Grants