12 3 4 t, hour 



F ; ig. 4. Kinetics of BaP degradation under sunlight irradiation in the tropical 

 part of the Pacific (coordinates: 09°54'N I56°23'W): a) in sterilized 

 seawater; b) in non-sterilized seawater; and c) by autoxidation (w/o 

 light). 



2 t, hour 



Fig- 5. Kinetics of BaP degradation under sunlight irradiation in the lagoon 

 of the Caroline Atoll (coordinates: 09°54'N I5fv2.vwi: al j„ 

 sterilized seawater; bi in nonsterilized seawater: c) by autoxidation 

 lu/o light). 



by x3 the rate tor the Bering Sea area at similar initial 

 BaP concentrations (2.44 x 10 i: mole s '). For comparison, 

 it may he pointed oui thai at the initial concentrations of 10 " M, 

 the initial rate of sunlight photolysis of BaP in the Caroline 

 Atoll is much higher than that found for BaP autoxidation 

 in water under laboratory condition 1.67 x 10 i: and 

 0.3 x 10 - |: mole s '. respectively (Kirso et al., 1983). 



Thus, experimental data, as expected, gave evidence of a 

 dependence of BaP degradation on the location of exposure, 

 intensity of solar UV-irradiation, and temperature of the 

 environment, and data agreed well w ith the results obtained by 

 Graupera and associates (Graupera et al., 1988). Obviously, 

 during photolysis of BaP by sunlight in seawater, the existence 

 ofmicroimpurities, inorganic components, salinity, and general 



water composition all have a major impact on photochemical 

 reactions in different areas of the world oceans. A comparison 

 of experimental kinetic parameters and literature data (Mill 

 et al., 1981 ) suggests that proceeding from the values of k at 

 T"- of BaP under similar conditions of its photolysis in water 

 (X = 366 nm and concentration of 5 x 10 s M) the value of 

 quantum yield evp (the number of molecules subjected to 

 transformation as a result of adsorption of one energy quantum ) 

 is almost equal to <p - 5.4 x 10" 4 — that is, less than one (Mill 

 et al.. 1981). Consequently, the processes under study are 

 complex, involving competing chemical reactions. Thus, the 

 degradation of BaP is initiated directly or indirectly and proceeds 

 under solar irradiation. 



Photochemical reactions were investigated with soluble 

 oxygen in the presence of different inorganic and organic- 

 components in water bodies. Zafiriou (Zafiriou et al.. 1989) 

 presented the following scheme for generation of free radicals 

 in the marine environment: 



O, + hv > initiation of radicals R' 



R- + R,NO > RNO\ R : NOH, R : NOR 



seawater + O, + hv - - > initiation > oxygen con- 

 taining radicals 



seawater + : + hv > superoxide 



0.+ NO - - >00 * NO* H + - -> * NO, - -> 2 



seawater + *0 ; + hv — > H * O * OH product 

 seawater + H * O * OH + hv - - -> *0 2 + H : *0 



According to (Mopper et al.. 1989) the concentration of 

 high-energy ( more than 4 kcal/mole ) oxygen-containing radicals 

 in seawater is low and makes for hydroxyl groups (OH) — for 

 example, in subtropical coastal areas 1 1.9 x 10 ls M and for 

 open sea 1.1 x 10 IB M, correspondingly. Consequently, it may 

 be assumed that BaP (and other PAH's) is subjected to 

 photodegradation due mainly to secondary photochemical 

 reactions w ith different reactive radicals formed directly under 

 the action of light quanta or indirectly (see the scheme). 

 According to our results, the rate of BaP transformation depends 

 primarily on the sunlight intensity. Obviously, then, the 

 mechanism of photochemical oxidation of organic xenobiotics 

 of the PAH type is not different in northern and southern areas 

 (i.e., the amount of oxidizing particles sufficient for 

 transformation is generated whose excess favors the first-order 

 reaction [pseudomonomolecular] relative to BaP). 



A study of the influence of inorganic salts and micro- 

 impurities on the photochemical processes in the marine 

 ecosystems requires further research. 



To sum up, it should be pointed out that the experiments 

 (under natural conditions) were carried out with only one 

 reference PAH. ben/o( a)pyrene, and in the marine environment 

 many other PAH"s are present (see Fig. 6). To estimate the 

 reactivities of other PAHs undergoing photooxidation in 

 seawater. the data obtained by Paalme et al. (1988) were 

 considered. It appears that the rate of the process for individual 

 homologs differs by factors of over 140 (Fig. 6). Anthracene 

 and its derivatives are easily oxidized, while the more condensed 

 systems — for example, coronene — remain more stable. It 

 may be assumed that as a result of photochemical oxidation, the 

 quantitative ratio of PAH's m the marine environment shifts 

 low, ml the heavier homologs. 



200 



