DDT, Chlordane, Toxaphene and PCB Residues in Newport Bay and Watershed: Assessment of Hazard to Wildlife and Human Health - Reviews of Environmental Contamination and Toxicology - page 127

Fig. 23 Threshold for DDE reproductive effects in brown pelicans. Figure 2 in Blus ( 1984 ) repro-
duced with permission from the author and from The Wilson Journal of Ornithology
chain to the fi sh diet of the brown pelican and was deposited in the lipid of the eggs.
DDE residues exceeding 2.5 ppm in eggs were associated with eggshell thinning in
excess of 15%, resulting in decreased hatching success. DDE egg residues below
2.5 ppm, although capable of producing measureable thinning of eggshells, were
not associated with reduced hatching success or any other effect on reproduction.
DDE residues in all populations of brown pelicans in the United States are currently
below the threshold for reduced hatching success.
Brown pelicans in the Southern California Bight were most impacted by DDE
during the 1960s and 1970s. The reason is the much higher contamination levels
from the production wastes of DDT manufacture, compared to agricultural residues
generated throughout the regions populated by brown pelicans. The highly contami-
nated Palos Verdes Shelf provides a continuing source of DDE to the northern
anchovy diet of the breeding colonies of brown pelicans on Anacapa Island. For
example, the Southern California Bight study of 1998 (Allen et al. 2002 ) found total
DDT levels as high as 10.5 ppm in fi sh captured in the Palos Verdes Shelf area.
This aquatic food-chain source explains the slow decline and leveling off of DDE