Polychlorinated Dibenzodioxins and Polychlorinated Dibenzofurans - Organic Pollutants: An Ecotoxicological Perspective - page 158

Because of the concern over human health hazards associated with PCDDs,
many toxicity tests have been performed on rodents. Some toxicity data are given for
2,3,7,8-TCDD as follows:
Acute oral LD 50 /rat: 22-297 μg/kg (Different strains were tested)
Acute oral LD 50 /mice: 114-2570 μg/kg (Different strains were tested)
Acute oral LD 50 /guinea pig: 0.6-19 μg/kg
A variety of toxic symptoms were shown, the pattern differing between species.
There were often long periods between commencement of dosing and death. There
were also large species differences in toxicity, the guinea pig being extremely sus-
ceptible, the mouse far less so. However, the critical point is that 2,3,7,8-TCDD is
an exceedingly toxic compound even to the mouse. With such differences in toxicity
between closely related species, it seems probable that there will be even larger dif-
ferences across the wide range of vertebrate species found in nature.
2,3,7,8-TCDF is not very toxic to the mouse (acute oral LD 50 < 6000 μg/kg) but is
highly toxic to the guinea pig (acute oral LD 50 5-10 μg/kg). Symptoms of toxicity in
the guinea pig were similar to those found with 2,3,7,8-TCDD. Thus, the selectivity
pattern was similar to that for 2,3,7,8-TCDD, but toxicity was considerably less (see
Environmental Health Criteria 88).
7.6 ecoLogIcaL effectS reLated to teQS for 2,3,7,8-tcdd
Estimates of TCDD toxicity in field studies have depended on the estimates of TEQ
values in an attempt to relate Ah-receptor-mediated toxicity caused by total PHAHs
to effects on individuals and populations. Although some encouraging progress
has been made, there have also been a number of problems. Not infrequently, TEQ
values determined by bioassay have considerably exceeded values calculated from
chemical data using TEFs. These discrepancies have not been explicable in terms of
antagonistic effects, and the balance of evidence suggests that environmental com-
pounds other than the PHAHs determined by analysis have contributed to the mea-
sured TEQ values. This has been observed in studies on fish (Giesy et al. 1997) and
white-tailed sea eagles ( Haliaetus albicilla ) (Koistinen et al. 1997). In the study on
fish, as much as 75% of the measured TEQ could not be accounted for using chemi-
cal data. The results of a number of studies are summarized in Table 7.3.
The results for the double-crested cormorant and the Caspian tern in the Great
Lakes both show a relationship between TEQs and reproductive success. They
were obtained during the late 1980s, at a time when DDE-related thinning of egg-
shells had fallen and TEQ values were based on PCBs alone. However, in certain
areas PHAH levels remained high, and populations of these two species were still
depressed. These investigations suggested that populations were still being adversely
affected by PHAHs as a consequence of Ah-receptor-mediated toxicity. The data
for white-tailed sea eagles from the Baltic coast also relate to an area where, at the
time of the investigation, there was evidence of reduced breeding success in the local
population—at a time when the species was increasing elsewhere in Scandinavia.
The TEQs in the most highly contaminated individuals were high enough to support
the suggestion that PHAHs were contributing to lack of breeding success.