FISHERY BULLETIN: VOL. 69, NO. 2 



45 



40 



SEATTLE 



PORTLAND 



130° 



125° 



Figure 1. — Chart of the transects from Vancouver, 

 British Columbia, to San Francisco Bay, Calif. See 

 Tables 1 and 3 for station data. 



Since only one extracter was used for water ex- 

 traction, the possibility existed for incomplete 

 recovery of the DDT residues in the water pass- 

 ing through the device. Repeated tests of the 

 extraction efficiency using a large carboy of 

 oceanic seawater labelled with low levels of "C- 

 DDT (ca. 5 X 10 ~'- g/ml) gave an extraction 

 efficiency of 83% (±5%) at the flow rate set- 

 tings which were used with apparatus at sea. 

 A Variac setting of 70 was used, which produced 

 an internal recycle rate of 900 ml/hr. The mag- 

 netic stirrer rate, which affects the degree of 

 fracture of the solvent droi)lets, was kept con- 

 stant. 



At the end of a particular run, the contents 

 of the centrifuge tubes were transferred to com- 

 busted 4.25 cm Whatman GFC filter papers" and 

 stored in glass petri dishes at — 15° C until anal- 

 ysis. The samples from one tube were analyzed 

 for particulate carbon by the wet combustion 

 method of Strickland and Parsons (1968). The 

 samples from the other tube were analyzed for 

 DDT residues according to previously described 

 methods (Cox, 1970a). 



At the end of a water extraction run, the 

 flask containing about 100 ml of hexane, the 

 water extract, was removed and stored until 

 processing. The extract was condensed to 100 

 jLiliters after dehydration by passage through 

 an Na2S04 column. The Na2S04 was specially 

 rinsed with solvent and combusted at 350° C 

 to remove interfering impurities normally pre- 

 sent in the reagent salt (Lamar, Goerlitz, and 

 Law, 1966) . The condensed extract was spotted 

 on an alumina chromatoplate, which was de- 

 veloped in 5'^f benzene in hexane, so that the 

 solvent front moved 10 cm from the origin. 

 Centimeter wide zones were stripped from the 

 chromatoplates which corresponded to zones ex- 

 pected to contain p,;/-DDT, DDD, and DDE ac- 

 cording to spots on parallel chromatograms with 

 pure standards. "C-DDT and '^C-DDE were 

 also used to determine Rf zones. These zones 



' The use of trade names is merely to facilitate de- 

 scriptions; no endorsement is implied. 



Figure 2. — Chart of the transects from Monterey Bay, 

 Calif., to the southern California area. See Tables 2 

 and 4 for station data. 



444 



