8.6.1 Solar Oxidation of Benzo(a)pyrene 



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



Institute of Chemistry, Estonian Academy of Sciences. Tallinn. USSR 



Introduction 



The extent of photochemical 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 (Rabek, 1985; Mill 

 etal.. 198 1 ) and the level of pollution of seawater, as well as the 

 concentration and composition of pollutants. The latter may 

 have an intluence 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 & Gubergrits, 1971; Gubergrits et al., 1975; 

 Paalme et al.. 1976. 1983b), there are few data on these 

 processes under natural conditions. Therefore, during the 

 cruise of the RA' Akademik Korolev (July-November 1988) a 

 study was undertaken on the kinetics of the oxidative photolysis 

 of a typical carcinogenic PAH — benzo(a)pyrene [BaP] (Car, 

 1971) in the Bering Sea (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 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. 



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's in 

 seawater at lower temperatures and low intensity of solar 

 irradiation was of interest. 



Methods and Materials 



Detailed descriptions of the techniques used in carrying 

 out these experiments are described in Subchapter 2.6 of 

 Residts of the First Joint US-USSR Central Pacific E.xpedition 

 (BERPAC). Autumn 19H8 (Nagel, 1992). Experimental 

 conditions are described in Table 1. 



Results and Discussion 



From kinetic data (Table 2; Figs. 1 , 2) it follows that during 

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

 in seawater is described by a fonnal-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 '). 



TABLE 1 



Exposure of BaP solution in seawater 

 (the 47th cruise of the RJM Akademik Korolev] 



August 



53°58'N/176°28'W 

 53°58'N/176°28'W 



14.1 



15.7 



1.48 

 1.09 



341 



