The Role of Iron Oxide on the Photodegradation of Polycyclic Aromatic Hydrocarbons: Characterization and Toxicity

ABSTRACT

Laboratory experiments were conducted to study the photocatalytic capability of amorphous α-Fe₂O₃ to degrade polycyclic aromatic hydrocarbons (PAHs). Solutions containing 16 US EPA priority PAHs were spiked with Fe₂O₃ and incubated in a climate chamber at stable conditions of temperature (20°C) and light (9.6 W·m⁻²) for 28 days. In addition, samples without Fe₂O₃ were also incubated. PAHs levels were monitored by means of GC–MS, and their toxicity was assessed using Microtox® bioassay. Fe₂O₃ had a significant photocatalytic effect on fluorene, phenanthrene, and benzo(a)pyrene, the photodegradation rate of the latter being 71% and 50% in presence and absence of Fe₂O₃, respectively. On the other hand, photolysis was significantly higher than photocatalysis for benzo(a)anthracene and dibenzo(ah)anthracene. Photodegradation of anthracene was notably the same regardless of Fe₂O₃ presence. Remaining PAHs were not photodegraded, neither with, nor without Fe₂O₃. These results indicated that, in some cases, Fe₂O₃ might act as a shield for PAHs by hindering their photodegradation. Other factors, such as the chemical structure of the Fe₂O₃, and also the absence of the soil matrix components (i.e., humic acid, other metals oxides, and texture) could also play a role. Photodegradation trends were supported by changes of EC₅₀ values, suggesting the formation of more bioavailable or toxic PAHs by-products when Fe₂O₃ and light were present.

KEYWORDS:

• Iron oxide
• Microtox®
• photodegradation
• photocatalysis
• polycyclic aromatic hydrocarbons
• Vibrio fischeri

Acknowledgments

The authors are indebted to Dr. Irene Maijó for her excellent guidance and assistance in GC–MS analysis

Additional information

Funding

This study was supported by the Spanish Ministry of Economy and Competitiveness (Mineco), through the project CTM2012-33079. Montse Marquès received a PhD fellowship from AGAUR (Commissioner for Universities and Research of the Department of Innovation, Universities and Enterprise of the “Generalitat de Catalunya” and the European Social Fund).