Environmental Engineering Reference
In-Depth Information
collected at Tule Lake NWR in 1972 and 1981 and in northern California from 1952
to 1960 were not signifi cantly different from each other and were not thinner than
eggs collected before 1947 (Table
4
).”
The very next line in Table 16 states that 5.4 ppm DDE caused 2.3% eggshell
thinning and reduced productivity. The research article cited for this data point
(Lindvall and Low
1980
) reported a DDE residue of 6.6 ppm and a thinning of 3.1%.
The authors did not conclude that productivity was reduced. To the contrary, the
authors concluded: “The small amount of eggshell thinning seen in western grebe
eggshells at Bear River MBR appeared to have little or no effect on reproduction,
because no crushed, cracked, or broken eggs were seen during this study. Average
brood sizes of 1.6 in 1973 and 1.8 in 1974 from Bear River compare well with the
Rudd and Herman determination of a normally reproducing population (18).”
The Department of the Interior report also states in Table 16 that less than 1 ppm
DDE produced 6.5% shell thinning in black-crowned night-herons. The reference
for this data point (Findholt and Trost
1985
) reported a linear regression of shell
thickness and log DDE egg residue that had a zero residue intercept of 0.26 mm.
Since pre-DDT era shells in this study were 0.275 mm, the linear regression is likely
to be inaccurate, particularly at low residue levels. A similar phenomenon has been
reported in brown pelican studies. The obvious fallacy in the Table 16 listing is
made clear by the fact that eggs containing 1.01-4.0 ppm DDE had thicker shells
than eggs with less than 1 ppm DDE.
Table 16 states that 0.52 ppm DDE in common goldeneye eggs causes 15.4%
shell thinning and egg breakage. The 15.4% shell thinning is a comparison of 1981
Minnesota colonies with North Dakota and Manitoba eggs collected in 1896 and
1903. The authors (Zicus et al.
1988
) conclusion on egg breakage is as follows:
“The high rate of egg breakage observed for Common Goldeneyes may be related
to eggshell thinning or may be characteristic of the species and perhaps a result of
frequent nest parasitism.”
Finally, Table 16 states that 12 ppm DDE in Leach's storm petrel eggs results in
12% eggshell thinning. The cited reference (Noble and Elliott
1990
) reports only
on raptors and makes no mention of Leach's storm petrel. In the few data points in
Table 16 that were checked against the original publications, the Department of
Interior report repeatedly made errors and misrepresentations of the literature
fi ndings on the effects of DDT on avian reproduction.
Custer et al. (
1999
) reported on cormorant colonies on Cat Island in Green Bay,
Wisconsin. Eggs contained 3.9 ppm DDE and 13.6 ppm PCBs. DDE concentration
correlated with decreased shell thickness and hatching failure (thinning data were
not reported). However, the authors concluded that reproductive performance was
generally good to excellent compared to other locations, including those considered
to have low levels of persistent organochlorine contamination. “Number of young
produced (2.0-2.3 to 12 days of age) was also similar or greater than the 0.7-2.5
young per nest reported in relatively uncontaminated colonies.” “…DDE-
contamination does not seem to be a signifi cant risk factor to double-crested cormo-
rant populations in this region.” A low level of chick deformities was not attributed
to DDE.
Search WWH ::
Custom Search