98
5. Teratogenic Deformity Index for Fish
tolerant species. Resultant long-term changes in fish community ecology are anticipated.
(2) Collect and examine 300 juvenile and 200 adult fish of the same
species. Assess the prevalence of teratagenic deformities and
measure selenium concentrations in individuals with terata
(whole-body samples; 6 juveniles and 6 adults). The investigation reveals that 8% have terata, and the associated selenium
concentrations are 20 to 30 Ilg Se/g. The expected populationlevel mortality is 2% (92% normal + 6% surviving teratogenic =
98% total survival), resulting in a TDI rating of 1. Conclusion:
negligible impact on the population due to teratogenic effects of
selenium. No shift in fish populations or community-level ecology is expected.
(3) Sample 1000 larval, 200 juvenile, and 100 adult fish of the same
species. Determine the prevalence of teratogenic deformities and
measure selenium concentrations in teratogenic individuals (6 composite samples for larvae; 6 each, whole-body samples for juveniles and adults). The investigation reveals that 35% of larvae have
terata, and 3% of juveniles and adults have terata; selenium concentrations are 10 to 30 Ilg Se/g. The expected population-level
mortality is 28% for larvae (65% normal + 7% surviving teratogenic =72% total survival) and 0.6% for juveniles and adults (97%
normal + 2.4% surviving teratogenic =99.4% total survival). Resulting TDI ratings are 3 for larvae and 1 for juveniles/adults. Conclusion: major impact on the population due to teratogenic effects
of selenium on larvae. Extirpation of selenium-sensitive species is
likely. Population and community-level ecology will be substantially altered; collapse of the fishery is possible.
Conclusions
There are several reasons to use the TDI for impact assessment of selenium. First, the sensitivity of TDI is unaffected by variations in the
environmental mixture of selenium species. Terata are produced by a
rather uniform process regardless of what chemical form(s) of selenium the parent fish were exposed to. Thus, the TDI can be applied
with confidence to any aquatic habitat. Second, terata-based assessment provides a conclusive cause-effect linkage between the contaminant and the fish. Because of this linkage, TDI is particularly useful for
verifying selenium-induced impacts on reproductive success, since poor
reproduction can be caused by many other things as well: for example,
fluctuating water levels, nest predation, food shortages, poor recruit-
5. Teratogenic Deformity Index for Fish
tolerant species. Resultant long-term changes in fish community ecology are anticipated.
(2) Collect and examine 300 juvenile and 200 adult fish of the same
species. Assess the prevalence of teratagenic deformities and
measure selenium concentrations in individuals with terata
(whole-body samples; 6 juveniles and 6 adults). The investigation reveals that 8% have terata, and the associated selenium
concentrations are 20 to 30 Ilg Se/g. The expected populationlevel mortality is 2% (92% normal + 6% surviving teratogenic =
98% total survival), resulting in a TDI rating of 1. Conclusion:
negligible impact on the population due to teratogenic effects of
selenium. No shift in fish populations or community-level ecology is expected.
(3) Sample 1000 larval, 200 juvenile, and 100 adult fish of the same
species. Determine the prevalence of teratogenic deformities and
measure selenium concentrations in teratogenic individuals (6 composite samples for larvae; 6 each, whole-body samples for juveniles and adults). The investigation reveals that 35% of larvae have
terata, and 3% of juveniles and adults have terata; selenium concentrations are 10 to 30 Ilg Se/g. The expected population-level
mortality is 28% for larvae (65% normal + 7% surviving teratogenic =72% total survival) and 0.6% for juveniles and adults (97%
normal + 2.4% surviving teratogenic =99.4% total survival). Resulting TDI ratings are 3 for larvae and 1 for juveniles/adults. Conclusion: major impact on the population due to teratogenic effects
of selenium on larvae. Extirpation of selenium-sensitive species is
likely. Population and community-level ecology will be substantially altered; collapse of the fishery is possible.
Conclusions
There are several reasons to use the TDI for impact assessment of selenium. First, the sensitivity of TDI is unaffected by variations in the
environmental mixture of selenium species. Terata are produced by a
rather uniform process regardless of what chemical form(s) of selenium the parent fish were exposed to. Thus, the TDI can be applied
with confidence to any aquatic habitat. Second, terata-based assessment provides a conclusive cause-effect linkage between the contaminant and the fish. Because of this linkage, TDI is particularly useful for
verifying selenium-induced impacts on reproductive success, since poor
reproduction can be caused by many other things as well: for example,
fluctuating water levels, nest predation, food shortages, poor recruit-