MP3 Ecological Relevance of Photo-enhanced Toxicity
Ballroom G, Level 4
2:10 PM - 5:30 PM, Monday, 10 November 2003
Chair: Barron, Mace ,
(107) Environmental relevance of photoinduced toxicity of PAHs: Aquatic Exposures and the Role of ROS.
Greenberg, B1, 1 University of Waterloo, Waterloo, ON, Canada
ABSTRACT- Polycyclic aromatic hydrocarbons (PAHs) are prevalent in aquatic environments exposed to sunlight. This includes upper layers of sediments, suspended particles and organisms within the water column. PAHs in photic environments are much more toxic and pose a much greater risk than in regions protected from sunlight. There are two primary mechanisms of phototoxicity of PAHs: photosensitization and photooxidation. For photosensitization, the absorbing PAH achieves an excited triplet state and then reacts with ground state triple O2 to produce singlet O2. Singlet O2 is a prevalent reactive oxygen species (ROS) that readily oxidizes organic molecules because the kinetic barrier to reaction is removed. This can result in damage to proteins and lipids. Further, it is a catalytic mechanism as the PAH is returned unaltered to the ground state and the cycle can repeat. PAHs can also be attacked by photochemically produced singlet O2, resulting in PAH oxidation leading to photooxidized PAHs (oxyPAHs). The oxyPAHs are both more water soluble and more cytotoxic than intact PAHs. These two mechanisms provide environmentally relevant routes to increase the risk of PAHs. Numerous research groups in both lab and field trials have observed photoinduced toxicity of PAHs. For instance, using Lake Erie phytoplankton in situ, reciprocity between PAH concentration and exposure time in natural sunlight has been observed. Extrapolation of these data indicates that exposures on the order of 12 h will result in PAH hazards in the nM range. This is well within environmentally relevant PAH concentration ranges. Furthermore, common co-contaminants of PAHs are metals. Such mixtures can lead to synergistic toxicity via an ROS burst. These and other examples of environmentally relevant PAH photoinduced toxicity will be presented.
Key words: Reactive oxygen species, PAHs, Metals, Aquatic toxicology