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 125

Fig. 21 Decline in DDT and
metabolites in eggs of brown
pelicans collected in South
Carolina from 1969 to 1977.
Data from Figure 1 in Blus
et al. ( 1979b )
thinning of 18% or greater had been reported to be associated with reproductive
failure and population declines. An DDE egg residue of 5 ppm was associated with
18% shell thinning by regression analysis (Fig. 22 ). Using the sample egg method,
reproductive effects occurred at 3 ppm, with a threshold between 2.5 and 3 ppm
DDE (Fig. 23 ). The critical level of 3 ppm is associated with eggshell thinning of
16% from the regression analysis of 813 eggs plotted in Blus's Figure 1.
I n 1985 , King et al. reported on studies from 1975 to 1981 on colonies of brown
pelicans in Texas. During this period, nesting pairs increased from 18 to 57.
Fledgling rates were considered adequate in all years except 1975. DDE levels were
about half those measured in 1970 and ranged from 0.9 to 2.3 ppm. “Current levels
of DDE apparently pose a minimal threat to pelican reproduction.” “Mean eggshell
thickness was 4-14% thinner than normal, but we found no evidence that shell
thinning adversely affected reproduction.” DDE residues in a major food item,
the gulf menhaden, were measured at an average of 0.06 ppm in 11 fi sh in 1980. “DDT
and metabolite residues may have been magnifi ed 23 times from fi sh (0.06 ppm) to
pelican eggs (1.36 ppm), but interpretation of this apparent biomagnifi cation is
complicated by the migratory habits of the pelicans and their prey.”