FISHERY BULLETIN: VOL. 69, NO. 



room temperature. Losses of "C-DDT during 

 desiccation were insignificant. Dried animals 

 were removed, weighed on a Cahn electrobal- 

 ance to ± 0.01 mg, placed in scintillation vials 

 with equal volumes of NCS solubilizer (Nuclear- 

 Chicago) , and digested 1 hr at 70° C before in- 

 troduction of scintillation fluid and subsequent 

 counting on a Nuclear Chicago Unilu.\ II scin- 

 tillation counter.' 



Loss experiments were done by taking labelled 

 animals, subsampling them for initial "C-DDT 

 levels, and placing them back in a flowing sea- 

 water tank. Water in the tank had a turnover 

 time of less than 10 min, so lost '^C-DDT was 

 rapidly removed from the system. Groups of 

 animals were removed from the tank at inter- 

 vals and analyzed as described above. 



In addition to work with '■'C-DDT, freshly 

 caught E. iiacifica were processed and analyzed 

 for naturally occurring levels of DDT residues 

 according to published methods (Cox, 1970), 

 except that whole eujihausiids were ground in 

 the homogenizer, rather than algae on filters. 



All direct uptake work was done at concen- 

 trations less than 33 ppt (parts per 10'^) 

 '*C-DDT in seawater, ranging down to 5 ppt. 

 In uptake and loss experiments, individual 

 samples were taken by removing about 10 to 15 

 animals from the experimental system, pro- 

 cessing them, and plotting the results on log- 

 log (full logarithmic) paper and fitting a least- 

 squares regression line to the logarithmically 

 transformed data. Depending upon the extent 

 of the dry weights of the animals taken in each 

 of the described groups, points corres])onding 

 to 1.0, 2.0, 3.0, or 10.0 mg dry weight were taken 

 from the regression line for comparisons. 



RESULTS 



UPTAKE 



Since the lipid constituents of planktonic or- 

 ganisms are not in direct contact with seawater, 

 it is necessary to postulate a two-step process 

 of uptake of DDT residues — first, adsorption on- 



to surfaces in contact with seawater and second, 

 diff'usion or transport of the adsorbed residues 

 into the lipid constituents of the organism. Ini- 

 tial uptake by E. pacifica was rapid; Figure 1 

 shows the results of a 2-hr uptake experiment. 

 Approximately equal numbers of animals were 

 added to two 7-liter jars containing "C-DDT at a 

 low ppt concentration. Two hours later, ani- 

 mals were removed and analyzed. The concen- 

 tration vs. dry weight functions were found to 

 be exponentials, yielding a straight line on the 



100 



XI 

 Q. 



.p.. 



< 



S '0 



u 



z 



S 100 



a 

 a 



\, 



V 



HEAT KILLED 



LOG Y= 2.13-0.97 LOGX 



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-J I I I i I I I 



- Reference to trade name in this publication does not 

 imply endorsement of commercial products by the Na- 

 tional Marine Fisheries Service. 



1.0 K) 



DRY WEIGHT (mg) 



Figure 1. — Uptake of '^C-DDT by Euphausia pacifica 

 of different weights after 2 hr of exposure to labelled 

 medium. 



log-log plot. Initial uptake appeared to be un- 

 related to the animals' activity or respiration 

 since heat-killed animals had the same total 

 uptake as live animals. The amounts of ''C-DDT 

 taken up per animal were almost identical in 

 these experiments (exactly equal amounts would 

 yield a slope of — 1 in the regression function). 

 In a diflFerent series of exijeriments, the slopes 

 of the log-log concentration vs. dry weight func- 

 tions changed from — 1.05 at 2 hr and — 0.99 at 

 8 hr to — 0.67 at 24 hr. This change resulted 

 from increased uptake by larger animals after 

 longer exposure. Figure 2 summarizes the over- 



628 



