Environmental Engineering Reference
In-Depth Information
Ohlendorf et al. (
1988
) reported geometric mean DDE levels of 6.93 ppm in 22
Caspian tern eggs from San Francisco Bay and 7.64 ppm in ten Caspian tern eggs
from Elkhorn Slough in 1982. In comparing these levels with levels from other reports,
the authors stated that: “Caspian Terns in the Great Lakes (Struger and Weseloh
1985
)
experienced good reproductive success when mean DDE concentrations in eggs
were generally similar to—and PCBs generally higher than—concentrations we
found in California.”
Blus and Prouty (
1979
) concluded that geometric mean DDE levels in 44 least
tern eggs (
Sterna antillarum browni
) from South Carolina in 1972-1975 were low
(0.33-0.63 ppm with a range of 0.19-1.22 ppm) and posed no identifi able threat to
the species. Eggshells were 2-7% thinner than shells of eggs collected prior to the
DDT era.
Hothem and Zador (
1995
) reported an overall geometric mean of 0.936 ppm
DDE in nonviable least tern eggs collected from San Diego Bay in the mid-1980s.
Factors such as putrefaction and desiccation in nonviable eggs do not cause loss
of DDT, but can produce changes in fresh weight, and therefore the concentration of
DDT. Hothem and Powell (
2000
) sampled 14 least tern eggs from three locations in
the San Diego area. The eggs were taken after the breeding season. Although not
stated, these eggs also were most likely nonviable. Geometric mean concentrations of
DDE in eggs from the three sites ranged from 0.23 to 0.56 ppm. Hothem and Powell
(
2000
) concluded as follows: “Similar or higher mean concentrations in least terns
(0.19-1.22
ʼ
g/g) from South Carolina (Blus and Prouty
1979
) and in Forster's terns from
Texas (1.6
g/g) (King et al.
1991
) were not thought to pose a threat to reproduction.
Likewise, DDE should not pose a threat to either species in our study.”
ʼ
DDT and Cormorants
. Eleven cormorant colonies were studied by Anderson et al.
(
1969
) in the upper midwest and central Canadian provinces in 1965. DDE residue
levels were as high as 45 ppm in cormorant eggs with an average of 10.4 ppm. Egg size,
weight and thickness varied between the locations. Egg laying is a mechanism for
excretion of DDT. Egg residues are more closely related to residues stored in lipid than
recent dietary intake. Eggshell thickness was decreased 8.3%. Increases in shell thick-
ness during rebreeding suggest that low DDT levels in local diets were more important
than reductions in DDT from utilization of lipid stores during breeding. One population
of cormorants, with a 25% decline in eggshell thickness, had recently decreased to
nearly zero. The authors claim that the eggshell thinning-DDE regression is linear to
zero concentration of DDE. A minimal effect level could not be established. Figure
6
illustrates the eggshell thinning dose-response in cormorants.
Faber and Hickey (
1973
) reported on a 1969-1970 survey of egg residues and
eggshell thinning in fi sh-eating birds from the upper Great Lakes states and Louisiana.
The authors suggest that signifi cant decreases in shell thickness will be found in
virtually all fi sh-eating birds in these parts of America. “We are uncertain about the
biological signifi cance of decreases in shell thickness below 10%. Certainly,
widespread eggshell breakage does not occur with changes below this magnitude.”
The level of DDE residue necessary to cause eggshell thinning varies greatly among
species. Double-crested cormorants developed eggshell thinning of approximately
12% at 17.5 ppm total organochlorine residues.
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