Dr. Silvina FIORESSI

Researcher: Dr. Silvina Fioressi

Institution: Department of Sciences & Technology, University of Turabo

Project Title: Photochemistry and bioactivity of polycyclic aromatic hydrocarbons adsorbed on model surfaces

AABRE Cluster: Molecular Medicine

Mentor: Dr. Rafael Arce, University of Puerto Rico - Rio Piedras

Collaborators and Consultants:

• Dr. Nicholas Geacintov, New York University

Abstract:

Polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs are ubiquitous atmospheric pollutants associated to the airborne particulate matter. Many of them present mutagenic activity and their presence in the atmosphere have been related with an increase in cancer incidence, particularly lung cancer. PAHs can be formed from any incomplete combustion process under oxygen deficient conditions of fossil fuels or any organic material. Human exposure to PAHs can occur through several pathways, these include inhalation from ambient air and internal absorption from food and water. During their residence in the atmosphere, PAHs &re susceptible to thermal and photochemical reactions with air or with other copollutants. For example, PAHs can react with nitrogen oxides to form mono- and di-nitro derivatives. These reactions are of particular interest because both types of contaminants are often emitted simultaneously from combustion sources and could react directly at the point of emission. Moreover, the nitro-PAHs are often much more potent carcinogens than the parent PAHs. In the presence of oxygen, PAHs react photochemically forming oxidized derivatives like diones, alcohols and poly-alcohols, among others. These oxygenated PAHs are in many cases, more harmful to human health than their precursors. In this project we propose to study the photochemistry, spectroscopy and mutagenic properties of nitrated and oxygenated derivatives of polycyclic aromatic hydrocarbons adsorbed on model surfaces and in solution with the purpose of providing information on its ultimate environmental and biomedical fate. Benzo[e]pyrene (BeP) and benzo[a]pyrene (BaP) will be studied as representative PAHs, whereas silica gel and alumina will be selected as models of the respirable particles. The specific aims pursued can be summarized as the followings:

1. Determine the experimental conditions that favor the transformation of the PAHs to the corresponding nitrated and oxygenated derivatives. The effect of the physical and chemical properties of the adsorbent (substrate composition, surface loading, water content, presence of acidic and basic additives) on the photo reactivity of BeP and BaP towards nitrogen oxides and oxygen will be studied. Thermal reactions that may occur on the surface will be also explored.
2. Isolate and characterize the major products (particularly nitro-PAHs and oxygenated derivatives of the PAHs) adsorbed on silica gel and alumina and also in solution using HPLC coupled with MS and UVvisible absorption detection. Establish a possible photo degradation mechanism for the products formation adsorbed on the different surfaces and compare it with the photochemical behavior in solution.
3. Investigate the photophysical properties of adsorbed PAH's derivatives and study the interactions between the PAH and its microenvironment because these will influence its reactivity. Spectroscopic techniques such as UV-visible spectroscopy, fluorescence, laser flash photolysis and electron spin resonance will be used to achieve this aim.
4. Generate enough amounts of the major products to test their toxicological properties. The optimal conditions to produce the PAH's derivatives determined in aim 1 will be reproduced at semi-preparative scale to obtain significant amounts of the products. These will be purified chromatographically and collected in the appropriate solvent for further analysis of their mutagenicity.
5. Evaluate the mutagenic properties of the nitrated and oxygenated derivatives produced by reaction of BeP and BaP with nitrogen oxides and oxygen under simulated atmospheric conditions. The bacterial mutagenic activity of the isolated products will be determined by the Ames Salmonella typhimurium assay. This will help to establish if atmospheric reactions with nitrogen oxides and oxygen increase the toxicity of PAHs and to establish a realistic risk assessment for the human exposition to these pollutants and the biomedical consequences.