COX: UPTAKE, ASSIMILATION. AND LOSS OF DDT RESIDUES 



all patterns of uptake for the 72-hr period. Three 

 arbitrary dry weights of animals (2.0, 3.0, and 

 10.0 mg) were chosen to illustrate different 

 weight effects during uptake. The points cor- 

 responding to these dry weights were taken 

 from regression lines like those shown in Fig- 

 ure 1. The values on the ordinate were con- 

 verted from concentration to total picograms 

 (g X 10-'2) of "C-DDT. After 72 hr of ex- 

 posure, the 10-mg animal did not reach equilib- 

 rium; the 2 and 3 mg animals did reach equi- 

 librium after 72 hr. 



=^ 560 



TIME (hr) 



Figure 2. — Uptake of '^C-DDT by Enphruisia pacifica 

 in a closed system. Equilibrium concentration of '''C- 

 DDT in the water was 20 parts per trillion. The three 

 dry weight values were taken from log-log regression 

 lines for subsamples of 10 animals or more. See text 

 for details. 



EFFECT OF TEMPERATURE 



Temperature appeared to have little effect on 

 initial uptake rates. The Qio for short-term (2 

 hr of exposure) uptake between 5° and 15° C for 

 an animal of a given dry weight was computed 

 by comparing log-log regression functions for 

 two groups of animals exposed to the same nom- 

 inal concentrations of "C-DDT in the medium — 

 one group at 5° C and the other at 15° C. This 

 procedure yielded a Qio of 1.11 for an animal 

 of 2.0 mg dry weight and a Qm of 1.29 for an 

 animal of 10.0 mg dry weight. Both figures 

 suggest a physical process as the limiting step 

 for direct uptake of DDT; the higher figure for 



larger animals may reflect a higher Qio for 

 transfer into the lipid reservoir of the larger 

 animal. 



Del Nimmo (personal communication, 1970) 

 has evidence that DDT residues are transported 

 to internal sites of accumulation by a protein 

 fraction in the haemolymjih of penaeid shrimps. 

 If E. pacifica is comparable in this regard to the 

 penaeid shrimp, then transport of DDT in the 

 circulatory system must not be the rate-limiting 

 step in uptake, since circulatory rates may be 

 expected to have a higher On, than those found. 

 Respiratory rates, which are directly dependent 

 upon circulatory rates, exhibit Qm values in ex- 

 cess of 2.2 in E. pacifica (Paranjape, 1967). 



CONCENTRATION FACTORS 



The short-term uptake concentration factors 

 (the ratio of the concentration of DDT in the 

 animals to the concentration in the water after 

 brief exposure) for "C-DDT changed little over 

 the range of concentrations employed. Table 1 

 summarizes data that were taken from log-log 

 jjlots for animals of 1.0 and 3.0 mg dry weight. 

 It is evident that short-term uptake of DDT for 

 an animal of a given size is proportional to the 

 concentration of the DDT in water. 



Table 1. — Concentration factors after 2 hr e.xposure. 



Equilibrium concentration 

 of •''C-DDT in seawater 



Concentration factor X 103 

 Concentration in animal (dry): 

 concentrotion in water (w/v) 



1 This includes data from one-half hour run. 



LOSS 



If short-term exposure to DDT in the seawater 

 medium of E. pacifica results in surface adsorp- 

 tion, one expects that these adsorbed residues 

 will be lost to the medium if the ambient con- 

 centration of the DDT is lowered. If all the 

 labelled DDT in a short-term experimental ex- 

 posure is adsorbed, the animals would be ex- 

 ])ected to lose eventually all of their label when 

 returned to unlabelled flowing seawater. 



629 



