THE DISSOLUTION AND PHOTODEGRADATION OF KUWAITI CRUDE-OIL IN SEAWATER.2. A LABORATORY PHOTODEGRADATION APPARATUS AND PHOTODEGRADATION KINETICS OF A MODEL SEAWATER SOLUBLE HYDROCARBON (PHENANTHRENE)

A laboratory photodegradation apparatus, incorporating a calibrated xe non lamp, controlled temperature unit and quartz reaction cells design ed to simulate natural irradiation by sunlight, and which is suitable for kinetic studies of hydrocarbon degradation in seawater, is describ ed The apparatus and experimental method was used to determine the pse udo-first order photodegradation constant (k(p)) of phenanthrene (a co mponent present in the seawater-soluble fraction of crude oil) in seaw ater at 25 degrees C. The k(p) values determined in duplicate experime nts were -0.342 +/- 0.003 and -0.317 +/- 0.029 h(-1) with half-lives ( t(1/2)) of 2.03 and 2.19 h. Extrapolation to natural sunlight at latit ude 30 degrees N (Florida midday, midsummer assuming 12 h daylight) ga ve t(1/2) values of 8.6-9.5 h, suggesting that photodegradation is a s ignificantly, fast reaction for removal of phenanthrene from seawater under some conditions, Gas chromatography-mass spectrometry (GC-MS) an d ultraviolet fluorescence spectrophotometry were both suitable method s for monitoring the degradation, but GC-MS was most suitable for the determination of photoproducts. The identifiable products amounted to some 12% of the total products after 7 h irradiation, and their distri bution was consistent with a known mechanism of phenanthrene degradati on involving formation of an unstable and reactive 9,10-epoxide. The p hotolysis method should prove valuable for the determination of k(p) a nd t(1/2) values for a wide range of petroleum hydrocarbons in seawate r.