Environmental Engineering Reference
In-Depth Information
Weseloh et al. (
1983
) reported on the status of double-crested cormorant colonies
in Lake Huron. Six colonies were studied in 1972 and 1973. DDE residues in eggs
averaged 14.5 ppm. Eggshell thickness was reduced an average of 23.9%. Egg
breakage, hatching failure, and population declines were evident.
Fossi et al. (
1984
) reported high levels of DDE in cormorant eggs collected from
the Danube Delta. DDE levels in 13 eggs averaged 9 ppm. Eggshell thickness was
not measured. The authors noted that: “Despite the heavy contamination of the
eggs, however, the population of the colonies of Common Cormorant seems to have
stabilized…”.
King and Krynitsky (
1986
) studied cormorants nesting in Galveston Bay from
1980 to 1982. DDE levels in eggs averaged 1.73 ppm in 1980 and 0.67 ppm in 1981.
Mean shell thickness for the period 1980-1982 was similar to eggs collected prior to
the DDT era. Eggs collected from Galveston Bay in 1970 (King et al.
1978
) were 7%
thinner; eggs collected in 1980 were 5% thinner; eggs collected in 1981 were 3%
thinner; eggs collected in 1982 were 1% thicker. The 3% and 1% effects were not
statistically signifi cant. One eggshell from an egg collected in 1980 was 22% thinner
than in pre DDT era eggs. Although not indicated by the authors, this egg may have
contained the highest residue measured in the 1980 eggs (N = 13). That level was
31 ppm DDE. The authors noted that cormorant populations had remained stable
in recent years.
Dirksen et al. (
1995
) reported a detailed study of organochlorines in cormorants in
the Netherlands. Reproductive effects of DDE were confounded by high levels of
PCBs in adult tissue and eggs. However, the authors concluded that 4 ppm DDE in
cormorant eggs produced 5% shell thinning. They also noted that the threshold for
population reproductive failure and population instability was associated with shell
thinning of 20%. This level of thinning was associated with egg residues of 10 ppm.
In
1998
, the US Department of the Interior published a National Irrigation Water
Quality Program Information Report No. 3 titled: “Guidelines for Interpretation of
the Biological Effects of Selected Constituents in Biota, Water, and Sediment.
DDT.” The US Fish and Wildlife Service participated and presumably wrote the
section on toxicity to avian species. According to the report, “Toxic effect levels for
various types of birds are presented in Table 16.” Beginning on page 70, Table 16
lists various avian species, the DDTs studied, the concentration in eggs, the effects
observed, and the reference. For the double-crested cormorant, a concentration of
10 ppm of DDE in eggs was stated to cause 20% shell thinning. The reference for
this data point is the Pearce et al. (
1979
) article discussed above. This study claims
to have measured shell thinning and to have correlated the shell thinning with DDE
residues. However, no shell thinning data and regression plots are to be found in the
publication. Hence, this data point in the Department of Interior review is based
only on a statement without data or analysis. Comparison of other data points in
Table 16 with the referenced article revealed errors and misinterpretations.
For example, Table 16 lists 1 ppm DDE in Western grebe eggs as causing 1%
shell thinning. The DDE concentration reported in the cited study was 1.4 ppm, not
1 ppm (Boellstorff et al.
1985
). The 1% was reported by Boellstorff et al. (
1985
) to not
be statistically signifi cant. The authors concluded: “Thickness of grebe eggshells
Search WWH ::
Custom Search