EFFECTS OF DISSOLVED-OXYGEN AND LIGHT EXPOSURE ON DETERMINATION OF K-OC VALUES FOR PAHS USING FLUORESCENCE QUENCHING

The fluorescence of some polycyclic aromatic hydrocarbons (PAHs) has b een observed to decline over time, potentially leading to overestimati on of PAH-humic binding coefficients (K-OC) determined by fluorescence quenching. This phenomenon was investigated using phenanthrene, anthr acene, pyrene, triphenylene, and a soil humic acid. Fluorescence quenc hing experiments were conducted under ambient conditions and under con ditions that minimized exposure of the samples to UV radiation and dis solved oxygen. All four compounds experienced decays in fluorescence i ntensity when exposed to UV radiation and dissolved oxygen, but anthra cene and pyrene were affected to a much larger extent than phenanthren e and triphenylene. Baseline decays in fluorescence intensity were ref lected in inflated apparent K-OC values, particularly for anthracene a nd pyrene. For example, the apparent K-OC far anthracene when no attem pt was made to limit dissolved oxygen or exposure to UV radiation was 10.9 x 10(4) mL/g of C. When exposure to UV radiation alone was minimi zed, the apparent K-OC decreased by a factor of 2. A similar result wa s found when exposure to dissolved oxygen alone was minimized. When ex posure to both UV radiation and dissolved oxygen was minimized, K-OC w as 3.69 x 10(4) mL/g of C. Photooxidation processes may explain these observations; however, more work is needed to confirm this.