DDT, Chlordane, Toxaphene and PCB Residues in Newport Bay and Watershed: Assessment of Hazard to Wildlife and Human Health - Reviews of Environmental Contamination and Toxicology - page 130

These assumptions and the procedures for deriving the TRG for DDT in fi sh
were from a protocol document published by the Canadian Council of Ministers of
the Environment ( 1999 ). The Protocol document calls for the use of “…sensitive
endpoints, such as embryonic development, early survival, growth, reproduction,
adult survival, and other ecologically relevant responses.” This Protocol document
states that an uncertainty factor of at least 10 is to be used to account for variability
in species, gender, life stage, and duration of exposure. The Protocol document also
recommends the use of a factor of 5.6 to extrapolate from a LOEL to a no-observable-
effect-level (NOEL), if a NOEL cannot be estimated directly from dose-response
data. Finally, TRGs are to be corrected for the species with the highest food con-
sumption per body mass.
Environment Canada chose to use ducks as the test species and egg shell thinning
as the toxic endpoint for assessing the reproductive effect of DDT on fi sh-eating
avian species. Mallard and black ducks are primarily herbivores. They are also not
particularly sensitive to the reproductive effects of DDE (Peakall et al. 1973 ; Peakall
1975 ). Eggshell thinning below the threshold for hatching failure has been shown in
numerous studies not to be detrimental to avian wildlife. Environment Canada cites,
but does not use, studies done with American kestrels (sparrow hawks). This hawk
species is not fi sh-eating, but does feed on insects and small mammals. Laboratory
and fi eld studies have established a dose-response in eggshell thinning, DDE resi-
dues in eggs, and hatching failure (Porter and Wiemeyer 1969 ; Wiemeyer and Porter
1970 ; Peakall et al. 1973 ). Studies reported by Lincer ( 1975 ) contain concurrent
laboratory and fi eld studies. Residues in diet, eggs and eggshell thinning were used
to correlate the fi eld and laboratory studies. One can see a clear dose-response
between shell thickness and DDE egg residue level (dry weight basis) using the
combined laboratory and fi eld data (Fig. 24 ).
The same data are summarized in Appendix 16 of the Assessment document
(Environment Canada 2000 ) reproduced in Table 27 below. The 0.5 mg/kg-day
level (3 ppm in the diet) produced 15% eggshell thinning, corresponding to a level
just below the threshold for hatching failure, the most sensitive toxic endpoint of