depths of up to 100 in. However, these also corresponded to 

 background values not exceeding 0.2 ng/1 and averaging 

 0.08 ng/l (Table 1 ). Particularly noteworthy was the absence 

 of BaP in the top 0.5 m of the water column inside the lagoon. 



Without excluding the possibility of PAH biosynthesis in 

 the highly productive coral ecosystem of Caroline Atoll (such 

 as the phenomenon reported for the Clipperton Lagoons; 

 Niassat el <//. . 1 968 ). it may be assumed, with some confidence, 

 that the high rates of photochemical oxidation and microbial 

 transformation of PAH's characteristic of equatorial waters are 

 conducive to the elimination of PAH's from the waters of 

 Caroline Atoll and especially from the surface layer. 



Quite the opposite situation was observed in the Marianas 

 trough region along the Marianas transect (between 142°E and 

 128 K. along 1 1°N) (Fig. 3). Whereas the BaP levels at the 

 extremities of this sector, with one exception, ranged from 

 0.9 to 9.2 ng/l (Table I ). the water column in the central portion 

 of the transect (Stations 122 and 123) contained elevated and 

 even maximum concentrations (up to and over 100 ng/l). As is 

 evident from Fig. 3. high BaP levels from 38 to 104 ng/l were 

 noted not only in the surface layer but also in deeper waters. 

 Thus, the BaP concentration in the upper 100-m water layer at 

 Station 122 averaged 96.2 ng/l. while the average value at 

 1 ,500-2.000 m was 103.5 ng/l. The lowest BaP concentrations 

 occurred at the western end of the transect, where the BaP 



HI', nii.i - i 





Fig. 3. Distribution of benzo(a)pyrene in the waters of the Marianas transect 

 along 1 1°N (between 142°Eand 1 38°E) in the tropical Pacific in 1981 

 and 1988. 



levels at Stations 1 26 and 1 25 in waters up to 2,000 m deep were 

 4.03 and 6.88 ng/l. respectively. The average value for eastern 

 Station 121, at depths from 10 to 2.000 m. was 5.17 ng/l. 



Analysis of rainwater samples taken at 1 1°N along the 

 transect had BaP levels of 7.2, 8.8, and 9.2 ng/l; that was one 

 order of magnitude lower than the levels in rainwater measured 

 along the transect in 1981 (Izrael&Tsyban, 1989). Nevertheless, 

 these findings point to the possible contribution of PAH's to 

 the Marianas sector of the Pacific via long-distance atmospheric 

 transport of organic pollutants. 



High BaP levels (up to over 100 ng/l) were noted in the 

 waters of the Marianas sector during the previous study period 

 in 1981 (Izrael & Tsyban, 1989). These ranged from 80 to 

 1 20 ng/l. However, the pollution in all instances was confined 

 to the top 2 m of the water column with peaks in the surface 

 microlayer (SML). 



Since most of the waters of the Marianas sector lie in the 

 area of influence of the northern branch of the tradewind 

 current, it may be supposed that the invasion of deeper layers 

 by pollutants (including BaP) occurs through downwelling of 

 surface water due to the anticyclonic circulation of water 

 masses in this region. 



The BaP levels in the southwestern South China Sea had 

 a broad range of values from 0.9 to 173 ng/l (Table 1 ). The 

 lowest BaP levels occurred in open waters at Station 127 

 (Fig. 1). Two days of work at this station yielded similar 

 estimates, the BaP levels over most of the water column 

 varying from 0.6 to 2.0 ng/l and averaging 1 .5 ng/l. The bottom 

 layer (at a depth of 61 m) exhibited a very high BaP concentration 

 and with an average value of 1 39.2 ng/l. indicating severe PAH 

 pollution. 



The BaP concentrations in the waters of stations lying 

 close to the eastern coast of Singapore (Stations 1 29 and 131) 

 hadelevated BaP concentrations in the lOto 100-m layerof the 

 water column (averaging 8.2 and 13.2 ng/l, respectively). The 

 maximum BaP lev els were detected in the top 0.5 m layeron the 

 one hand and at the sea bottom on the other. These were as high 

 as 148. 8 ng/l (Table 1). 



This peculiar pattern of BaP level distribution over the 

 water column can be attributed to the influx of PAH's with the 

 oil pollution that impacts the surface waters at the stations in 

 question as well as the deeper waters below. It should be noted 

 that the areas of the South China Sea investigated are busy 

 maritime thoroughfares for vessels carrying both crude oil and 

 refinery products as well as sites of intense offshore drilling 

 activity. 



The potential physiological ability of microflora to 

 transform BaP in the central Pacific was studied in a series of 

 in situ experiments using natural bacterioplankton communities 

 from Caroline Atoll and the southwestern portion of the South 

 China Sea. 



The results of the process simulations expressed in terms 

 of the degree of elimination of the artificially-introduced 

 amount of BaP are shown in Fig. 4. The bacterioplankton of the 

 marine areas investigated were able to transform the 

 polyaromatic hydrocarbon in question. On the whole, the level 

 of microbial degradation reached 57-98% of the mass of BaP 

 introduced into the samples (Table 2). In order to gain deeper 



189 



