Therefore, during the cruise of the R/V Akademik Korolev 

 (July-November 1 988 ). a study was undertaken on the kinetics 

 of the oxidative photolysis of a typical carcinogenic PAH — 

 benzol a tpyrene (BaP) — (Clar, 197 1 ) in the Bering Sea and the 

 tropical waters of the Pacific (Table 1 ). 



It is known that the Bering Sea is almost wholly in the 

 subarctic zone, excluding its northern parts, which are in the 

 arctic temperature zones (Izrael & Tsyban, 1987). The main 

 body of its waters is characterized by a subarctic structure 

 whose specific feature is the existence of cold and warm 

 intermediate layers. The upper layer thickness average 

 25-50 m, the salinity being 32.8-33.4%o and the temperature, 

 about 5 to 7°C. According to Izrael and Tsyban ( 1 987), PAH" s 

 are permanent and typical components of these ecosystems. 



TABLE 1 



Exposure of BaP solution in seawater (the 47th cruise of the 

 R/V Akademik Korolev). 



Aiiyust 



Taking into account the low influence of this area from 

 human activities, the physicochemical parameters of the 

 atmosphere above these waters and characteristics of the surface 

 water layer, a study of sunlight photolysis of PAH' sin seawater 



at lower temperatures and low intensity of solar irradiation was 

 of interest. The same experiment was carried out under tropical 

 conditions — that is. at higher temperatures and considerable 

 insolation with a salinity of 35.4%o. 



Methods and Materials 



The surface water samples taken at a depth of to 0.5 m 

 were sterilized by autoclaving for 2 h. cooled, and filtered 

 through main layers of Sterilized cloth into a sterilized dish. 

 The BaP solution in seawater was prepared in 5-1 glass cylindrical 

 reactors whose sides were covered with black paper (water 

 column height 20 cm). Benzol a (pyrene was introduced as an 

 ethanol solution (ethanol content up to 0.01295 ) by constantly 

 mixing with a magnetic stirrer for 15 minutes. The BaP 

 concentration was varied from 0.7 to 6.6 nanomoles mm). 



This solution was exposed to sunlight at the temperatures of the 

 surface water for each given region. Simultaneously, the total 

 solar irradiation dose, Q (MJ/m : per h), was measured 

 pyranometrically (Table I). The experiments were carried out 

 with the following solutions: 



(a) BaP solution in seawater; 



(b) BaP solution in sterilized seawater; and 



(c) BaP solution in sterilized seawater protected from 

 light by black paper (autoxidation). 



The exposures lasted for approximately 3 h in the first half 

 of the day. The solutions were periodically sampled and the 

 BaP concentration measured by chromatography techniques. 

 Conditions of analysis were as follows: 



A 'Jasko' HPLC chromatograph (Japan), a 

 fluorimetric detector, X tx = 295 nm, X cm = 408 

 nm, solvent methanol-water (95:5) isocratic 

 regime, eluent flow-rate 0.7 ml/min using a 

 25 x 0.25 cm ODS column, sample volume was 

 100 ul. 

 Statistical kinetic data processing was performed using the 

 least-squares method. 



Results and Discussion 



From kinetic data (Figs. 2-5. Table 2), it follows that 

 during the first hour of exposure, a decrease in the BaP 

 concentrations in seawater is described by a formal-kinetic 

 equation for the first-order reaction where c and c, are the 

 initial BaP concentration at zero time, and that at a certain time 

 t, k is the constant of the first-order reaction, the dimensions for 

 this constant are per second (s '). 



ln(c,/c,) = kt 



The rate constant values obtained for the Bering Sea areas, 

 the tropical part of the Pacific and the Caroline Atoll (Table 2) 

 are of the same order as those found (Mill et <//.. 1981) by 

 photolysis of BaP in water (X = 366 nm. BaP concentration 

 5x 10 s m, t° = 22-28°C, k = 3.86 ±0.71 x 10V). The half 

 decay time of BaP under these conditions was 0.69 h. In our 

 experiment the average rate constant value per unit Q was 

 (1.1 ±0.1) 10V. 



Irrespective of the areas under study and the sterility 

 of water in those treatments that were subjected to 

 photolysis (Table 2). the initial stage of the process, as 

 mentioned above, is well described by an equation for the first 

 order kinetics. At the same time, according to experimental 

 data (Figs. 2-4), the oxidation of BaP in seawater 

 without sunlight (autoxidation) for the Bering Sea areas and 

 the tropical pari of the Pacific is described by a formal- 

 kinetic of a second-order type (r = 0.90-0.98). The rate 

 constant value of BaP autoxidation in the Bering Sea water 

 at a concentration of 5 x 10 s M (July, t =21°C, 

 Q,, r 0.68 MJ/m" per h) was (0.4 ± 0.01) 10 4 M's ! . but in 

 the tropical part at a concentration of 1.7 x 10 s (October 

 t°=27°C. Q r ,,~3.00 MJ/nr per hi (9.08 ± 1.90) 1() 4 M 's '. 

 respectively. 



198 



