Maltene and Asphaltene Contributions to the Formation of Water-Soluble Emerging Contaminants from Photooxidation of Paving Materials

Fossil fuel-derived products commonly used to pave roads, asphalt binder and coal tar pavement sealant, have been shown to readily produce highly oxidized water-soluble photoproducts that are of environmental concern. Previous work has also demonstrated that alkane-insoluble, multicore asphaltenes potentially produce water-soluble species after exposure to photoirradiation. In this work, two main solubility fractions from the asphalt binder and coal tar sealant, maltenes (alkane-soluble) and asphaltenes (alkane-insoluble), are extracted, mixed in various ratios, and photoirradiated to decouple their contributions and determine their individual roles in the generation of water-soluble photoproducts in a solar simulator microcosm. Negative-ion (-) electrospray ionization (ESI) coupled with ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry revealed the relative abundances and molecular compositions of the produced water-soluble species. Moreover, the amount of water-soluble organic carbon was quantified to ascertain the contributions to organic carbon production from each solubility fraction. The results revealed that maltenes, in both asphalt binder and coal tar sealant, produced abundant water-soluble species, with a highly polydisperse molecular composition and a higher dissolved organic carbon concentration compared to asphaltenes. The compositions of the water-soluble photoproducts suggest different photooxidation pathways for both materials, which produce water-solubles with contrasting molecular features. The asphalt binder produced oxidized multicore species, whereas the coal tar sealant yielded single-core oxy-polycyclic aromatic hydrocarbons.