This project was part of the First Joint US-USSR Central 

 Pacific Expedition aboard the Soviet Research Vessel, Akademik 

 Korolev. We express our appreciation to the US Fish and 

 Wildlife Service. USA, and the State Committee for 



Hydrometeorology. USSR, who made our participation possible. 

 We also thank H. O'Connor, A. Tsyban, O. Rostovsev, Y. Volodkovich, 

 B. Aleksandrov, L. Polishchuk, S. Kohl, A. Krynitsky, M Wong, and 

 P. Wills. 



2.6 The Role of Solar Irradiation in the 

 Oxidative Transformation of 

 Benzo(a)pyrene 



NATALYA I. IRHA, EHA R. URBAS. and UVE E. K1RSO 

 Institute of Chemistry, Estonian Academy of Sciences, Tallinn, ESSR 



Introduction 



Organic pollutants entering water bodies, including the 

 oceans, contain a wide range of substances. Some of these are 

 quite easily subjected to degradation under the action of natural 

 agents, while many other compounds are stable and persist in 

 various compartments of the ecosystem. Among the persistent 

 compounds are the carcinogens belonging to the polycyclic 

 aromatic hydrocarbon (PAH) group. It has been established 

 that PAH' s enter the ocean in several ways, emissions into the 

 atmosphere as a result of incomplete combustion of fuels, 

 spillage during transportation of oil, and so forth. On the other 

 hand, it is known that there exists a natural occurrence of 

 PAH's (natural background) in the oceans. It is the view of 

 several researchers (Tsyban, 1975; Izrael. 1984; Kirso et ai. 

 1988) that the main mechanism of self-purification of the 

 hydrosphere from carcinogenic PAH' s is biological ( bacterial ) 

 oxidation. However, there are also other mechanisms for 

 removal, including photooxidation under solar irradiation ( Mill 

 etai, 1981; Bockris, 1982). It may be assumed that this process 

 plays a significant role, especially in the surface water layer 

 where the content of soluble oxygen is near \00 c /c saturation 

 (i.e., 10 '■' mol/1). There are numerous factors that modify this 

 process, including the physicochemical characteristics of water 

 ( turbidity , transparency, and the presence of other compounds ) 

 and the air above the sea surface (condition of the atmosphere, 

 i.e., environment and weather conditions). Figure 1 illustrates 

 the characteristic sunlight spectra at the sea surface (Ranby & 

 Rabek. 1978). Photochemical reactions in the marine 

 environment are also moderated by the level of atmospheric 

 pollution with aerosol particles and smoke, as well as changes 

 in ozone and other impurities. Solar irradiation at wavelengths 

 less than 285 nm is to a large extent absorbed by ozone in the 

 upper layer of the atmosphere. Therefore, the active spectra for 

 this process are usually at wavelengths greater than 285 nm. 

 Variations in the characteristics of the ozone layer therefore 

 influence all the photochemical processes occurring on the 

 oceans' surface. 



1000 



UJ 



0.5 



0.1 



ISO 



320 



360 



400 



X,,nm 



Fig. 1 . Seasonal variations in solar spectra at the sea surface. I = July, 



2 = December. E = Spectral Energy; A. = Wavelength (Ranby & 

 Rabek. 1978). 



The extent of these processes and their contribution to self- 

 purification of the marine environment from carcinogenic 

 PAH's are determined by both the value and distribution of 

 solar irradiation energy (Mill et al, 1981; Rabek, 1985)andthe 

 level of pollution of seawater, as well as the concentration and 

 composition of pollutants. The latter may have an influence 

 upon the pattern and intensity of the degradation processes of 

 PAH's (Kirso & Gubergrits, 1971; Gubergrits et al.. 1975). 

 Although systematic studies have been carried out on the 

 photooxidation of individual PAH's in water (Kirso et ai, 

 1971; Gubergrits etai, 1975; Paalme etai, 1976. 1983). there 

 are few data on these processes under natural conditions. 



197 



