Sunlight Produces Water-Soluble Chemicals from Asphalt

Published March 29, 2021

Relative abundances of water-soluble oxygen-containing compounds, where Ox on the horizontal axis denotes the summed abundances of all compounds containing x oxygen atoms. Data are shown after 24, 72, and 168 hours of simulated sunlight irradiation of road asphalt binder.

Road asphalt is made from aggregate (rocks) mixed with a "binder” from the residue remaining after extraction of gasoline and oils from petroleum crude oil. Until recently, this binder was thought to be chemically unreactive. Maglab scientists subjected a thin film of asphalt binder to simulated sunlight in the laboratory and used ultrahigh resolution mass spectrometry to reveal thousands of new, water-soluble chemicals that could be released into the environment by rainfall.

What did scientists discover?

MagLab users found that some chemicals in road asphalt oxidize under simulated sunlight. Compounds with higher oxygen content are more water soluble. As such, these new compounds, created by exposure to sunlight, could leach out of road asphalt during rainfall to cause pollution in the water system.

Why is this important?

Until recently, the tar in asphalt was thought to be essentially chemically inert and therefore environmentally benign. This new research reveals thousands of new, water-soluble chemicals that could be released into the environment by rainfall. The toxicity of the new compounds is being investigated.

Who did the research?

S. F. Niles¹, M. L. Chacón-Patiño², S. P. Putnam³, R. P. Rodgers², and A. G. Marshall^1,2

¹Department of Chemistry and Biochemistry, Florida State University; ²Ion Cyclotron Resonance Program, National MagLab; ³Department of Chemistry and Biochemistry, University of South Carolina

Why did they need the MagLab?

The unique ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometers at the MagLab were required to identify the thousands of different chemicals, before and after irradiation. The analysis revealed that irradiation produces abundant new compounds containing many more oxygen atoms ‒ and therefore much higher solubility in water ‒ than the original asphalt. The collaboration has been expanded to include investigators at M.I.T. who will assess the toxicity of the new compounds.