COX: DDT RESIDUES IN CALIFORNIA CURRENT SYSTEM 



were eluted with a small amount of 20 ""r ben- 

 zene in hexane into test tubes. The eluates were 

 analyzed individually by the same gas chroma- 

 tographic techniques used for the particulate 

 samples. 



All glassware was combusted at 350° C over- 

 night to remove interfering contaminants. All 

 solvents were nannograde or pesticide quality. 

 A hexane blank was run through the same pro- 

 cedure to detect systematic errors from any of 

 the steps after the initial extraction. No cor- 

 rection was found to be necessary. 



RESULTS AND DISCUSSION 



WHOLE SEAWATER EXTRACTS 



Comparisons of DDT residue concentrations 

 in the particulate samples obtained by the cen- 

 trifugation/filtration method described above 

 (hereafter referred to as the particulate ma- 

 terial) are meaningless when they purport to 

 describe geographical differences since these 

 concentrations change according to the density 

 of the standing crop of the particulate material 

 (Cox, 1970a). Comparisons of the concentra- 

 tions of DDT residues in whole seawater 

 (Tables 1 and 2) reveal some significant geo- 

 graphical differences. Water in the southern 

 California region appears to have a higher DDT 

 residue concentration. Water off Oregon and 

 Washington has lower concentrations, and there 

 is no evidence of high DDT residue levels ad- 

 jacent to the mouth of the Columbia River. The 

 relative uniformity of the DDT residue concen- 

 trations for this northern cruise (Table 1) sug- 

 gests a diffuse source of the residues, possibly 

 from atmospheric fallout. Direct measure- 

 ments of the DDT content of dust in the at- 

 mosphere over the Atlantic Ocean (Risebrough, 

 Hugget, Griffin, and Goldberg, 1968) and mea- 

 surements of DDT residues in rainwater (Tar- 

 rant and Tatton, 1968; Yates, Holswade, and 

 Higer, 1970) implicate aerial transport as an 

 important mechanism of land-sea DDT residue 

 transfer. Published calculations based on an- 

 nual rainfall statistics and probable DDT res- 

 idue concentrations in rainwater predict the 

 concentration of DDT residues in the surface 



mixed layer of the oceans to be 5 x 10^'- g/ml 

 (Smith, 1970). This estimate is within a factor 

 range of 0.5 to 1.1 of the results presented in 

 Tables 1 and 2. 



Atmospheric fallout may be important in 

 areas remote from river systems draining agri- 

 cultural areas or in areas remote from waste 

 dumping of highly populated areas. Sewage 

 outfalls near large centers of population, such as 

 the southern California area, contribute a large 

 share of the DDT residue input to the ocean. 

 When the outfall is below the pycnocline, the 

 DDT residues in the effluent may settle with 

 the particles comprising the solid component 

 of the sewage and thus enter the benthic envi- 

 ronment. This may account for the high DDT 

 levels found in the livers of bottom dwelling 

 fish in the southern California region, as com- 

 pared to pelagic species (figures released by 

 the California Department of Fish and Game 

 in 1970). Sedimentation of organic particulate 

 material from the surface layers represent an 

 additional input to the benthos. 



Input of DDT residues to the mixed layer is 

 represented by the following sources: (1) sew- 

 age input by vertical transport of material from 

 below the pycnocline or by direct input from 

 shallower outfalls, (2) input from terrestrial 

 runoff water which bears fallout particles, and 

 (3) direct input from fallout of particles over 

 the water. The relative importance of these 



Table 1. — DDT residue concentrations in seawater ob- 

 tained by liquid-liquid whole water extracts from tran- 

 sects shown in Figure 1. 



Table 2. — DDT residue concentrations in seawater ob- 

 tained by liquid-liquid whole water e.xtracts from tran- 

 sects shown in Figure 2. 



445 



