'Scripps Institution of Oceanography. 

 ^Mexico. 



a 50:50 acetone-hexane solution, the extracts dried 

 over anhydrous Na2S04, and dried in vacuo. The 

 residues were taken up in 50 /xl of hexane and 

 treated identically as the above water samples. 



Aliquots of the isooctane solutions were injected 

 into a Hewlett-Packard model 5750B gas chroma- 

 tograph equipped with a Ni^s electron capture 

 detector and a 6-foot glass column packed with 

 either 1.5% OV-17 and 1.95% QF-1 or 5% SP2401 on 

 100/200 mesh Supelcoport. Column temperature 

 was 195°C. An alkaline (KOH, NaOH) precolumn 

 for saponification of DDT residues was used to 

 give confirmatory identification (Miller and Wells 

 1969). Retention times and peak heights were 

 compared with standard mixtures of p,p'DDT, 

 p.p'DDE, and Aroclor 1254. Reagent and appara- 

 tus blanks were essentially zero, and reextraction 

 of the water sample with hexane showed no addi- 

 tional traces of DDT residues or PCB's. The 

 minimum detectable amounts of p,p'DDT, 

 p.p'DDE, and PCB's (as Aroclor 1254) are 5x10'- 

 g, 3 X 10-'^ g, and 1 x lO"'" g, respectively. 



Results and Discussion 



In the North Central Pacific Gyre (Table 2), the 

 concentration of DDT residues in surface films 

 and subsurface waters was less than 0.03 ng/liter 

 for all samples, while the PCB content was two 

 orders of magnitude higher, and PCB's were al- 

 ways present. A higher concentration of PCB's in 

 the surface films as compared to the subsurface 



Table 2.-Concentrations of PCB's, p.p'DDT, and p,p'DDE in 

 surface films and subsurface waters. All values in nanograms per 

 liter. 



'These lower limits are greater than the absolute minimum 

 amounts detectable due to sample splitting during analysis. 



waters was significant but not striking, largely 

 because well-defined surface films were not 

 present at the time of sampling. 



In the California and Mexican coastal waters, 

 both PCB and DDT residue concentrations in the 

 surface films were slightly higher (as would be 

 expected) than in the 1-2 m subsurface waters of 

 the nearshore California Current (Cox 1971). 



The available data in the literature pertaining 

 to the chlorinated hydrocarbon content of surface 

 films and subsurface waters is collected in Table 3. 

 This table does not include a considerable amount 

 of unpublished data taken in conjunction with 

 outfall studies and pollution problems in general. 



446 



