FISHERY BULLETIN: VOL. 69, NO. 2 



sources is not known, but it is quite likely that 

 sources (1) and (2) account for the higher DDT 

 residue concentration in the whole seawater 

 samples taken off southern California. 



PARTICULATE MATERIAL 



Results of the analyses of the particulate ma- 

 terial are shown in Tables 3 and 4. Transect 

 10-11 (Table 4) yielded an abnormally high 

 value when compared to the other values for 

 pai-ticulate material. During transect 10-11, 

 visual observations were made of oil globules 

 at the sea surface. The abnormally high value 

 may have been caused by inclusion of a small 

 globule of this material in the particulate ma- 

 terial for transect 10-11, after entrainment in 

 the seawater system of the vessel. This value 

 has been deleted from further data presenta- 

 tions. 



Table 3. — DDT residue concentrations in organic par- 

 ticulate material collected by continuous-flow centrifu- 

 gation and collection of the centrifugal pellet on GFC- 

 glass-fiber filter papers. Transects shown in Figure 1. 



Tronsect 

 stations 



Total volume 

 filtered (liters) 



Wt. of carbon 



in centrifugal 



pellet (g X lO-S) 



DDT concentration 



ng DDT resi- 



dues/g carbon (ppm) 



Table 4. — DDT residue concentrations in organic par- 

 ticulate material collected by continuous-flow centrifu- 

 gation and collection of the centrifugal pellet on GFC- 

 glass-fiber filter papers. Transects shown in Figure 2. 



Transect 

 stations 



Total volume 

 filtered (liters) 



Wf. of carbon 



in centrifugal 



pellet (g X 10— « 



DDT concentration 



ng DDT resi- 



dues/g carbon [ppm) 



^ These samples were obtained by using a net; see text for details. 



On the May cruise to southern California 

 (Figure 2), two phytoplankton '/t-m net tows 

 (35-/a effective ai)erture) were taken at stations 

 1 and 22, and analyzed along with the particulate 

 material samples. These tows consisted of 10 

 successive vertical hauls from 1.5 m to the sur- 

 face at station 1 and one oblique haul from 10 m 

 to the surface at station 22. The station 1 value 

 is in approximate agreement with earlier pub- 

 lished DDT residue concentrations for net phy- 

 toplankton samples (27 ppm per unit of carbon 

 converts to 0.27 ppm wet weight; compare to 

 values given by Cox, 1970a) . This value is con- 

 siderably higher than the values listed in Tables 

 3 and 4 for particulate material. At station 22, 

 the ship was stopped for an investigation of a 

 dense phytoplankton bloom, which consisted 

 principally of Rhizosoleuia spp. No measure- 

 ments of chloro]jhyll were made, but the water 

 was visibly discolored due to the high concen- 

 tration of algal cells in parallel streaks at the 

 surface. The concentration of DDT residues in 

 net-tow material fi-om this bloom was consider- 

 ably lower than in the sample taken at station 1 

 (0.012 ppm wet weight compared to 0.27 ppm). 

 This may be explained by the fact that the 

 standing crop density was much higher at sta- 

 tion 22 than at station 1. 



The generally lower values in the particulate 

 material compared to net-tow material (except 

 in the case of station 22 as discussed above) 

 could result from at least three causes: (1) 

 loss of materials by cells bursting during the 

 centrifugation (filtration as a cause of bursting 

 of cells is well known, but cannot account for 

 a difference in this case since the net-tow samples 

 [Cox, 1970a and this report] were vacuum fil- 

 tered through GFC papers as well), (2) inclu- 

 sion of smaller particulate material having a 

 lower intrinsic DDT residue concentration, or 

 (3) exclusion from the centrifuge of larger zoo- 

 plankters which would be trapped by the phyto- 

 plankton net. 



Cause 1 represents one reasonable source of 

 loss of DDT residues from the particulate ma- 

 terial, if in fact they should have higher DDT 

 residue concentrations than those reported here- 

 in. However, experiments with the same cen- 



446 



