The photolysis of three polycyclic aromatic hydrocarbons (PAHs), pyrene, phenanthrene, and naphthalene were studied in waters taken from Gary, Indiana (GIN) and Wilmington, North Carolina (WNC). Direct photolysis of PAHs was observed with pyrene degrading at a faster rate than either phenanthrene or naphthalene. When compared to direct photolysis, phenanthrene degradation increased in GIN water, but decreased in the WNC water due to higher levels of dissolved organic carbon (DOC) for WNC (9.29 mg/L vs 6.73 mg/L for GIN) and less nitrate (0.046 mM vs 0.205 mM) for GIN. The slightly lower rate of phenanthrene degradation in WNC water, corrected for light attenuation effects, is statistically the same as the direct photolysis experiments. We attribute the lower rate of degradation in the presence of WNC water to light screening by DOC, while we believe that the faster reaction rate observed for GIN is the result of nitrate generated hydroxyl radical chemistry. Overall photo-reaction rates decrease for the lower molecular weight PAHs as the fastest naphthalene photolytic rate was roughly two orders of magnitude slower than the photolysis of pyrene.
The photolysis of ibuprofen and caffeine was studied in solutions of fulvic acid isolated from Pony Lake, Antarctica (PLFA); Suwannee River, GA (SRFA); and Old Woman Creek Natural Estuarine Research Reserve, OH (OWCFA). At 10µM initial concentration ibuprofen and caffeine degrade slowly by direct photolysis, but we observed enhanced photodegradation in solutions of each fulvic acid. Quenching studies suggest hydroxyl radical plays a prominent role in both caffeine and ibuprofen photolysis. Spectroscopic techniques reveal the formation of multiple hydrophobic photo-products upon photolysis of ibuprofen, the dominant byproduct identified as 1-(4-isobutylphenyl)ethanol and a minor derivative isobutylacetophenone. Caffeine and ibuprofen photolysis reactions proceed even more quickly in fulvic acid solutions (6 mg/L DOC) at lower, more environmentally relevant concentrations (0.1 μM) where presumably reaction kinetics are controlled by both short and long lived reactive species. When probing the responsible reactive transients under suboxic conditions, fulvic acid mediated photolysis of caffeine and ibuprofen slows suggesting the influence of an oxygen dependent long lived radical (peroxyl or phenoxyl radicals) playing a role at 0.1µM.