FISHERY BULLETIN: VOL. 69, NO. 2 



of the DDT residues in whole seawater. In 

 fact, the particulate material accounted for 

 less than 10 ':r of the DDT residues in the 

 corresponding whole water extracts (range: 

 1.8^/r to9.99f)- Unless the remaining amount 

 of DDT residues (<909f of the total present) 

 is in soluble form, it must be fixed to particles 

 not collected in the centrifugation/filtration 

 procedure. Typical natural distributions of 

 particulate matter in seawater (Bader, 1970; 

 Beardsley, Pak, and Carder, 1970) suggest that 

 most of the particulate volume and almost all 

 of the particulate surface area is accounted for 

 by particles of less than 2 /x in diameter. Thus it 

 is quite likely that the balance of the DDT resi- 

 dues in whole seawater are fixed to these smaller 

 particles, in view of the hydroi)hobicity and af- 

 finity for interfaces characteristic of the dif- 

 ferent metabolites of DDT. The possibility also 

 exists that it may occur as micelles or aggregates 

 which cannot be taken up by the particulate 

 matter. 



EXPERIMENTAL EVIDENCE 



Two experiments were j^erfoi'med to examine 

 the distribution of DDT residues between sea- 

 water and phytoplankton. In both experiments, 

 '^C-DDT in a 1-ml ethanol carrier was added to 

 GFC filtered oceanic seawater in a 4-liter glass 

 carboy which was stirred by a magnetic stirrer. 

 Repeated subsamples of 25 ml each were taken 

 from the system until successive samples gave a 

 constant "C activity. All counts were made on a 

 Nuclear-Chicago Unilux II scintillation counter. 



Aliquots of a dense suspension of Diinaliella 

 salina culture were added to the carboy from 

 a large separatory funnel with a 25-ml dispen- 

 sing chamber, via a tube connected to the carboy. 

 Sampled and added amounts were such that a 

 constant volume was maintained. After ad- 

 dition of an aliquot of culture, one or two ali- 

 quots of 25 ml each were removed from a tap 

 at the bottom of the carboy. This amount was 

 vacuum filtered onto a GFC-glass-fiber filter pa- 

 per, and counts of '■'C-DDT were made of the 

 filter and of a petroleum ether extract of the 

 filtrate. Cumulative '■'C activity in the filter and 



filtrate equalled amounts present in the 25 ml 

 aliquots (both filter and filtrate) before addi- 

 tion of the algal suspension, when the net 

 amounts of "C-DDT removed from the system 

 by sampling were taken into account. A cor- 

 rection was made for adsorption or possible 

 trapping of small particles of "C-DDT on the 

 filter. The correction factor, expressed as per- 

 cent of total activity per 25-m! aliquot which 

 was on the filter before addition of the algal 

 suspension, was constant in the five replicates 

 taken just before the algal cells were added. 

 This correction factor may have changed during 

 the course of addition of the algal cells, but the 

 techniques used did not allow a distinction be- 

 tween "C activity on the filter which adsorbed, 

 associated with trapped small pai'ticles, or asso- 

 ciated with the algal cells themselves. I be- 

 lieve that this change was small and did not 

 materially afl^ect the outcome of the experiments. 



Figure 4 shows the results of the two experi- 

 ments. In Experiment 1, the seawater used in 

 the carboy was not altered; in Experiment 2, 

 the seawater was specially prepai-ed to increase 

 the load of small (<l-2 fi) inorganic particles, 

 to see what effect this might have on the uptake 

 function. Nuchar-attaclay, a mixture of finely 

 divided charcoal and clay pai-ticles (attapulgite) , 

 was added to 2 liters of GFC-filtered seawater. 

 After shaking, the mixture was refiltered 

 through a GFC filter. It is estimated that only 

 a tiny fraction of the initially added Nuchar- 

 attaclay (initially added amount was 0.1 g) ac- 

 tually got through the filter. The 2 liters of 

 water i)roduced in this way were mixed with 

 another 2 liters of GFC-filtered seawater and 

 jHit into the carboy. Two other conditions were 

 diff"erent in Experiment 2. The culture of Dii- 

 naliella salina used was denser (note that the 

 arrow in Figure 4 indicates that 750 /ng C/liter 

 is reached at a lower volume of culture added). 

 The initial concentration of "C-DDT in Exper- 

 iment 2 was ai)|)roximately 15 ppt. 



The first part of the uptake functions in Ex- 

 l)eriments 1 and 2 aijjieared to be linear, indi- 

 cating that under the conditions ])revailing at 

 the beginning of each experiment, each Diinal- 

 iella cell took up a con.stant amount of the "C- 



448 



