Environmental Engineering Reference
In-Depth Information
reached a steady-state with the more rapidly declining residues in the aquatic
environment. If we assume that in time the DDE residue in the eggs would also
decline 27-fold, the fi nal egg residue would have a geometric mean of 1.7 ppm.
Would this level be a no-effect level for reproductive effects in the brown pelican?
To answer this question, let us review in chronological order some of the key
studies of the effects of DDT on various populations of brown pelicans during and
after the DDT era. The recovery of brown pelicans following the ban of DDT in
1972 provides a measure of dose-response and thresholds for the reproductive
effects of DDT. Some of the earlier studies have been reviewed by Ware (
1975
).
Risebrough et al. (
1967
) reported the accumulation of DDT in higher trophic
levels along the California coast. “Fish from California coastal waters contained
more residue, but in general total concentrations were 10-20% of those in the birds.”
Bird species included Cassin's auklet, western gull, pelagic cormorant, Brandt's
cormorant, brown pelican, common murre, ancient murrelet, red phalarope, rhinoc-
eros auklet, sooty shearwater and slender-billed shearwater. Whole bird tissue con-
tained from 1.0 to 15.4 ppm DDT. Western gull and Cassin's auklet eggs contained
6.5 ppm and 10.8 ppm, respectively. Fish included northern anchovy, English sole,
Pacifi c jack mackerel, and hake. DDT levels in fi sh ranged from 0.2 to 2.8 ppm,
with one sample of northern anchovy taken off Terminal Island, Los Angeles
containing 12.7 ppm DDT.
In a 1969 conference at Oregon State University, Keith (
1969
) stated that scientists
now have data to show that DDT is causing eggshell thinning in birds. Pelicans on
Anacapa Island off the southern California coast produced good numbers of young
in 1962, 1963 and 1966. In 1968 they were clearly in trouble, and in 1969 their
reproductive effort was for all practical purposes a complete failure. In the same
conference, Risebrough (Terriere et al.
1969
) stated in a panel discussion that DDT
levels in northern anchovies were low around San Francisco Bay compared to
5-15 ppm in waters off southern California. “We are aware of certain massive “hot
spots”: Clear Lake, California, Lake Michigan and evidently the Southern California
coast.” DDT stored in fat is toxicologically inert unless mobilized due to mobilization
of fat stores. In a separate paper at the conference, Risebrough et al. (
1969
) spoke of
recent fi ndings, summarized as follows:
The DDT congener
p
,
p
-DDE was the major cause of eggshell thinning in raptorial
and fi sh-eating birds (Risebrough et al.
1969
). The peregrine falcon, bald eagle and
osprey were in decline due to DDE eggshell thinning. There was no evidence of
thinning in eggshells of species that prey mostly on mammals, such as the Red-tailed
hawk, golden eagle and great horned owl. Brown pelicans had declined 50% in the
past 4 years at Point Reyes. Brown pelican and double-crested cormorant reproduc-
tion on the Channel Islands and Islas Coronados near San Diego were decimated in
1969. Western gull eggs on Anacapa Island in 1969 were normal. Some eggshell
thinning is evident in ashy petrel and murre from the Farallon Islands. A “No effect”
level has not been established for eggshell thinning. The relationship between
DDE residues and eggshell thinning is linear with an absence of a “no effect” range
of concentrations. DDE plus DDD in eggs from white pelicans, at levels ranging
from less than 0.5 to 6 ppm, were associated with signifi cant eggshell thinning.
′
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