Environmental Engineering Reference
In-Depth Information
chronic DDE exposure in birds. The near threshold dietary intake of 0.5 mg/kg-day
in a sensitive carnivorous species is a more appropriate basis for a maximum tolerable
daily intake (TDI) than the square root of the product of the shell thinning LOEL in
ducks and an estimated (5.6 times less) shell thinning NOEL. The TDI is more
appropriately based on 0.5 mg/kg-day and not on the 0.13 mg/kg-day value used by
Environment Canada.
Environment Canada used an uncertainty factor of 10 to account for interspecies
variability. A factor of 10 from ducks to sensitive fi sh-eating raptors is certainly less
protective than a factor of 10 from sparrow hawks to sensitive fi sh-eating raptors.
The Lincer (
1975
) study evaluated the most sensitive chronic endpoint, gender and
life stage in a sensitive species. For example, Newton and Bogan (
1978
) in their
report on the DDE-eggshell thinning dose-response, stated: “The regression of shell
index on log DDE content in the sparrow hawk was similar to those found by other
workers for
Falco peregrinus
,
F. mexicanus
and
Pelecanus occidentalis
.” In Chapter
3 of this report, the dietary threshold for DDE reproductive effects in osprey was
estimated to be 0.3 ppm in fi sh. This level would correspond to exactly one-tenth of
the 0.5 mg/kg-day threshold in the sparrow hawk, which is calculated from a dietary
level of 3 ppm. If one accepts the tenfold uncertainty factor for variability in species
susceptibility, the one remaining variable to consider is the rate of dietary intake.
Environment Canada applied an additional uncertainty factor to the TDI to
account for the species with the maximum food intake per day. They chose Wilson's
storm petrel, with a food intake of 0.94 kg food/kg body weight per day. The choice
of the species with the highest rate of food intake should be limited to species as
sensitive or nearly as sensitive as the most sensitive species. The choice of Wilson's
storm petrel is inappropriate, because petrels have not been shown to be anywhere
near as sensitive as the osprey, brown pelican, peregrine falcon, or other sensitive
species. In addition, Wilson's storm petrel eats fi sh only as a minor part of its diet.
Most of the petrel's diet is at lower trophic levels, explaining, at least in part, the
lower sensitivity of this species to the reproductive effects of DDE.
For example, Coulter and Risebrough (
1973
) measured 43 ppm DDE in ashy
petrel eggs that were thinned only 8-9%. The authors concluded: “The magnitude
of shell-thinning is apparently less than a critical level that would affect reproduc-
tive success.” Henny et al. (
1982b
) measured DDE residues in eggs from Leach's
storm petrel collected in 1979 along the Oregon coast. DDE residue levels averaged
2.5 ppm. Eggshell thinning in Leach's storm petrel measured in eggs collected from
1946 to 1979 did not exceed 8%. Pearce et al. (
1979
) reported residues of DDE in
Leach's storm petrel eggs of 0.75-6.81 ppm. The eggs were collected in 1972 and
1976 off the east coast of Canada. The authors reported measuring shell thickness,
but no data were published. The authors claimed that 12 ppm DDE in eggs produced
20% shell thinning. This conclusion was based on an extrapolation of the residue
shell-thinning data. Again, no data or regression plots were present in the article.
Elliot et al. (
1989
) reported DDE residues in Leach's storm petrel eggs collected off the
Pacifi c coast of Canada in 1970-1985. Residue levels ranged from 0.601 to 2.16 ppm.
Residues in eggs of fork-tailed storm petrel eggs ranged from 1.68 to 2.62 ppm.
The authors cite the 12 ppm DDE critical level reported by Pearce et al. (
1979
).
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