COX: DDT RESIDUES IN CALIFORNIA CURRENT SYSTEM 



trifuge showed that at least 98% of the imr- 

 ticulate chloropliyll a in the incurrent water is 

 recoverable from the centrifugal pellet in whole 

 particulate form (trappable on GFC filters). 

 This indicates that breakage of cells must be 

 minimal. 



Cause 2 is also a possible explanation. Pfister, 

 Dugan, and Frea (1969) pointed out that chlor- 

 inated hydrocarbons showed quantitative dif- 

 ferences of distribution among particles greater 

 than 0.1.5 /a which were separable by density 

 gradient centrifugation. Although they found 

 no recurrent patterns of distribution among the 

 DDT metabolites they were able to detect, their 

 results suggest large diffei-ences in the pesticide 

 concentrations in the four different density class- 

 es of particles analyzed. The form in which 

 their data are presented, however, does not al- 

 low any conclusions about lower or higher DDT 

 residue concentrations in the material which 

 was collected in the centrifuge, but not included 

 in the net-tow material. 



Odum, Woodwell, and Wurster (1969) found 

 lower DDT residue concentrations associated 

 with smaller detrital particles in a core taken 

 from a sprayed marsh, but it is uncertain if 

 these results may be applied to oceanic seston. 



Cause 3 is a possible explanation on the basis 

 of the mesh size of the zooplankton exclusion 

 filter used in the centrifugation/filtration pro- 

 cedure (0.176 mm) compared to the one used 

 in the processing of the net-tow material both 

 in this report and the earlier published data 

 (0.33 mm). 



EFFECT OF STANDING CROP DENSITY 



The effect of standing crop density, alluded to 

 above, was observed in the analyses of the par- 

 ticulate material. Standing crop densities were 

 calculated for the transects using estimates of 

 the volume of water filtered during the centri- 

 fuge running time and the carbon analyses of 

 the centrifugal pellet. The values for DDT res- 

 idue concentration are plotted vs. the standing 

 crop density in Figure 3. The slope of the re- 

 gression line fitted to the data points from both 

 cruises is ajjproximately — 1, indicating that 

 equal amounts of DDT residues were taken \\\) 



by the algal materials within a given volume 

 of water over the range of standing crop den- 

 sities encountered. This is essentially the same 

 conclusion mentioned earlier (Cox, 1970a). 



PARTICULATE MATERIAL AS A PART 

 OF WHOLE SEA WATER 



Data points from the Vancouver to San Fran- 

 cisco cruise seem to fit the empirical linear re- 

 lationship detailed in Figure 3 much more closely 

 (r — — 0.99) than the data points from the 

 Monterey Bay to southern California cruise (r — 

 — 0.54). This variability is undoubtedly due 

 to the greater variability of the DDT i-esidue 

 concentrations of the whole seawater from the 

 southern California region, where most of the 

 samples were taken. There would be no need 

 to impute causal relationships between the whole 

 seawater concentration and the concentration of 

 DDT residues in the particulate material, if the 

 particulate material represented a major portion 



20 M 60 100 200 



STANDING CROP DENSITY (mgC/m'') 



Figure 3. — DDT concentrations in the particulate 

 samples as a function of particulate carbon standing 

 crop density. Stations 1 and 22 (Table 4) are not in- 

 cluded, since the density of the standing crops could 

 not be computed because there were no measurements 

 of the volume of water filtered in these net-tow samples. 

 Also, for reasons outlined in the text, they may not 

 be comparable to the samples collected by the centrifuge. 

 Transect station 10-11 (Table 4) was omitted because 

 of the possible interference of oil, as described in the 

 text. The remaining 16 values from Tables 3 and 4 

 appear in this figure. Open circles refer to data from 

 Table 3 ; solid circles refer to data from Table 4. 



447 



