FISHERY BULLETIN: VOL. 69, NO. 3 



Table 3. — Calculation of expected DDT residues in different sizes of Eiiphausia pacifica. 



Dry 

 weight 



Equivalent 

 weight 

 carbon 



Carbon 



growth 



incorporation 



efficiency^ 



Cumulative 

 amount 

 nauplius 

 carbon 

 required 



DDT 

 equivalent^ 

 (S X 10-8) 



Assumed 

 DDT 



incorporation 

 efficiency 



Parts per 10^ — dry 



Expected 



DDT 



concentrotion 



OBserved 



DDT 



concentrotion 



1.0 

 2.0 

 3.0 



0.42 

 0.84 

 1.26 



0.30 

 0,15 

 0.10 



mi; 

 1.4 

 4.2 

 8.4 



1.4 

 4.2 

 8.4 



0.62 

 0.62 

 0.62 



0.9 

 1.3 

 1.7 



0.75 

 0.55 

 0.S<5 



' Corbon growth incorporation efficiencies were taken from Table 2 of Lasker (1966); the figures shown ore not means of the values presented by 

 Lasker but are round-figure approximations which take account of the trends shown and of the different range of sizes of animals used in the lab- 

 oratory experiments which yielded these figures. 



2 The DDT equivolent of the food was calculated from nauplius carbon assuming a wet weight DDT concentration in the food of 0.1 ppm, and a 

 carbon weight to wet weight ratio of 0.1. 



ingested DDT determine DDT residue concen- 

 trations in E. pacified. 



DISCUSSION 



For E. pcwitica. there are two important 

 sources of DDT residues — direct uptake from 

 water and assimilation from food. Short-term 

 direct uptake is rapid and appears to be at least 

 partially reversible, suggesting adsorption of 

 DDT to exposed surfaces. Over longer periods, 

 these initially acquired residues are transferred 

 to internal deposition sites. The long-term 

 uptake and loss experiments show that larger 

 animals tend to retain more of the initially 

 acquired DDT, possibly because of greater 

 lipid content. Direct uptake from water is 

 a possible mechanism for accumulation of res- 

 idues if the initially adsorbed residues are con- 

 tinually transferred to internal dejrosition sites. 

 The rate of initial uptake will depend upon the 

 concentration in seawater (Table 1); retention 

 of these initially acquired residues apparently 

 depends on other factors, judging from the lower 

 set of data points in Figure 3. One determina- 

 tive factor may be lipid content; values given by 

 Mauchline and Fisher (1969) indicate that lipids, 

 expres-sed as percentage of body weight, can vary 

 by as much as an order of magnitude in Euphmis- 

 ia spp., according to the body weight of the ani- 

 mal. The four lipid values listed by Mauchline 

 and Fisher (1969) for E. pociticu correspond 

 closely to the DDT concentration values after 2 

 weeks rinsing shown in Figure 3. However, in 

 the absence of concurrent lijiid values for the 

 animals of the lower data points shown in Figure 

 3, no conclusion can be drawn about the relation- 



.ship between retention of '^C-DDT and the per- 

 centage lipid composition of the animals. It is 

 reasonable to assume, nonetheless, that the 

 changes in the lipid content of E. pacifica which 

 accompany reproductive cycles and seasonal 

 feeding changes will have some impact on the 

 DDT residue content, regardless of the source 

 of the DDT residues. 



The second possible source of DDT residues, 

 as previously discussed, is from food. In this 

 case, DDT is almost certainly transported di- 

 rectly in the fat of the food organisms to the fat 

 reservoir of the consumer. Numerous studies 

 indicate that marine organisms do not alter lipids 

 from ingested food (Lasker and Theilacker, 

 1962; Jezyk and Penicnak, 1966; Jeffries, 1970; 

 and others). Comparison of published values 

 of fatty acid comjwsition for E. pacifica (Ya- 

 mada, 1964) with values for its food, micro- 

 zooplankton and j)hytoplankton (Jeffries, 1970), 

 suggests that mass assimilation of fatty constitu- 

 ents along with DDT residues is taking place. 



As has been suggested, food is probably a suf- 

 ficient source of DDT residues in E. pacifica 

 (Table 3). Direct uptake may contribute to 

 DDT residues in E. pacifica, but its role cannot 

 be assessed because of the lack of seasonal data 

 on DDT concentrations in seawater as well as 

 uncertainties about DDT's availability to or- 

 ganisms in the natural environment (Cox, 1971). 



Some basis must be sought to explain the un- 

 expected higher concentrations of DDT residues 

 in the smaller animals. Three possibilities exist: 

 ( 1 ) the food of immature E. pacifica may have 

 higher DDT concentrations, (2) direct uptake 

 from water is more important for the smaller 

 animals because of their higher area: volume 



632 



