Percentage ot initial PCB concentration 



1 2 3 4 5 6 7 



Fig.2 Photochemical breakdown of individual PCB component 1 . 

 A 



Fig. 4. Breakdown of PCB's (dichlorobiphenyls) through microbial and 

 photochemical action: 1) microbial; 2) photochemical: 3) photo- 

 chemical in the presence of PAH's. 



Conclusions 



As a result of human activities, chlorinated hydrocarbons 

 occur in all media constituting the Pacific ecosystems 

 investigated. Levels of HCH isomers in the equatorial Pacific 

 turned out to be lower than in polar areas. This is understandable, 

 given the high volatility of this pollutant. 

 Dichlorodiphenyltrichloroethane levels in certain parts of the 

 Pacific (such as the Caroline Atoll) were found to be similar to 

 those observed in impacted basins, although the concentration 

 of this compound in the equatorial Pacific taken as a whole 

 were not high. Polychlorinated biphenyls occurred in all the 

 water samples studied. It is now clear that despite the slowness 

 of photochemical and microbial breakdown of PCBs, these 

 processes nevertheless play an important role in the self- 

 purification of Pacific Ocean ecosystems. 



Fig. 3. Microbial breakdou n of PCB components in the waters of the Bering 

 Set (A) and central Pacific Ocean (B). 



