Environmental Engineering Reference
In-Depth Information
Audet et al. ( 1992 ) measured DDT residues in osprey eggs from three locations on
the East Coast and compared them with residue levels in the early 1970s. The study
was prompted by the fi nding of an isolated area in Chesapeake Bay with declining
nestling survival. Median DDE levels in 1986 were 2.3 ppm in an area of declining
fl edgling survival (Martin Refuge), 0.65 ppm in coastal Virginia and 0.56 ppm in
southern coastal Massachusetts. Relatively high ratios of DDT to DDE in the eggs
from Massachusetts prompted the authors to suggest recent exposure to DDT from
an unknown source (winter breeding grounds?). Eggs taken in 1972-1973 from the
same area of Massachusetts had DDE residues of 4.2 ppm. The authors concluded that
the 0.65 and 0.56 ppm levels of DDE “were well below reported values associated
with biologically signifi cant effects on eggshell thickness and reproductive success.”
In 1973, the Martin refuge had a median DDE level in eggs of 3.4 ppm with 17%
eggshell thinning, but nonetheless, 1.5 young per active nest. Productivity of 1.5
young per active nest was considered by these authors to be excellent. No reason
was given or suggested for the declining fl edgling survival at the Martin Refuge in
1986. Fledgling survival data were not reported.
Falkenberg et al. ( 1994 ) provided data on a nonmigratory population of osprey
and their prey from the south coast of Australia. Six eggs collected in 1987 had an
average total DDT residue of 0.22 ppm. Total DDT residues in three species of prey
fi sh averaged 0.3 ppm, giving a very low biomagnifi cation factor of 0.73. Shells of
osprey eggs collected in 1987-1988 were no thinner than shells of eggs collected
prior to the DDT era. The biomagnifi cation of DDT into osprey eggs was so low
in this study as to put into question the representativeness of the fi sh samples as a
signifi cant part of the diet eaten by osprey that produced the eggs collected in the
study. The determination of a biomagnifi cation factor is theoretically more certain in
a nonmigrating population. Most likely, the biomagnifi cation factor is small, based
on studies in the 1960s and early 1970s in the U. S., probably less than ten.
In 1997, Ewins published an article about the behavior and history of osprey in
North America. Figure 1 from Ewins ( 1997 ) illustrates the recovery of ospreys in
Wisconsin and the Georgian Bay area of the Great Lakes Region (Fig. 12 ).
Woodford et al. ( 1998 ) reported geometric mean DDE residues of 0.20-0.52 ppm
in osprey eggs collected in 1992-1993 from two breeding areas in central and northern
Wisconsin.
Ewins et al. ( 1999 ) reported on eggs collected between 1980 and 1989 from two
osprey breeding areas in central Michigan. The known age of each female osprey
producing the eggs permitted a study of DDT residues in eggs produced by females
from 3 to 15 years of age. No age-related changes were found. The egg residues
were independent of the age of the female, and DDE averaged 1.2 ppm. Eggshell
thickness increased from 1980 to 1989. Eggs collected from 1980 to 1984 were 5%
thinner and eggs collected from 1985 to 1989 were 3% thinner than eggs collected
prior to the DDT era. Eggs collected from the same areas in 1972-1973 had geomet-
ric mean concentrations of 5.1 ppm DDE and 10% average shell thinning. The
decrease in DDE residues was associated with improved reproduction and popula-
tion increases. Apparently, female osprey in Michigan reached a steady-state DDE
residue level in their tissues in the fi rst 2-3 years of life (most of that time is spent
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