Example Assessments
97
Esocidae (eg, pike and muskellunge). However, the close similarity of
the relationships for centrarchids and cyprinids (virtual mirror images)
suggests that impacts of terata may be generally consistent, regardless
of fish family. Moreover, extrapolation to other families of fish is not
necessary for many locations in North America, since centrarchids and
cyprinids have characteristics that make them a good indicator or sentinel for other species: they are sensitive to selenium and are widely
distributed (Lee et al. 1980; Lemly 1993).
The TDI can be applied to literally any aquatic habitat because it
consists of impact-based assessment. Impacts (terata) are a function of
selenium concentrations in fish eggs. The events responsible for the
transfer of selenium to fish eggs, that is, bioaccumulation in aquatic
food chains and consumption of contaminated diets by parent fish, can
be highly variable from location to location. These events are influenced by such things as hydrology and landform (the amount and timing of precipitation; stream, lake, or wetland), the chemical form of
selenium (selenate, selenite, organoselenium), and the timing and
amount of selenium inputs relative to spawning periods (Lemly and
Smith 1987). Consequently, the hazard (likelihood of toxic impacts) of
selenium to fish and wildlife is also highly variable. However, the TDI
is based on a measure of existing impact (terata), not potential hazard.
As such, terata are an expression of the sum total of parental exposure,
regardless of the temporal, spatial, or chemical variations that may
exist from site to site. Thus, the applicability of the TDI is not influenced by local environmental conditions that affect selenium dynamics and biological uptake. It makes no difference whether the system is
a fast-flowing stream, in which selenate predominates and
bioaccumulation is low, or a terminal wetland in which high
bioaccumulation from selenite is occurring; population-level impacts
are indicated only if a sufficient amount of terata exists.
Example Assessments
6 composite samples of teratogenic individuals. The investigation reveals that 15% have terata, and the associated selenium
concentrations are 10 to 15 I-lg Se/g. The expected populationlevel mortality is 12 % (85 % normal + 3 % surviving teratogenic =
88% total survival), resulting in a TDI rating of 2. Conclusion:
slight to moderate impact on the population due to teratogenic
effects of selenium. A shift in the relative dominance of fish populations is possible, with selenium-sensitive species replaced by
97
Esocidae (eg, pike and muskellunge). However, the close similarity of
the relationships for centrarchids and cyprinids (virtual mirror images)
suggests that impacts of terata may be generally consistent, regardless
of fish family. Moreover, extrapolation to other families of fish is not
necessary for many locations in North America, since centrarchids and
cyprinids have characteristics that make them a good indicator or sentinel for other species: they are sensitive to selenium and are widely
distributed (Lee et al. 1980; Lemly 1993).
The TDI can be applied to literally any aquatic habitat because it
consists of impact-based assessment. Impacts (terata) are a function of
selenium concentrations in fish eggs. The events responsible for the
transfer of selenium to fish eggs, that is, bioaccumulation in aquatic
food chains and consumption of contaminated diets by parent fish, can
be highly variable from location to location. These events are influenced by such things as hydrology and landform (the amount and timing of precipitation; stream, lake, or wetland), the chemical form of
selenium (selenate, selenite, organoselenium), and the timing and
amount of selenium inputs relative to spawning periods (Lemly and
Smith 1987). Consequently, the hazard (likelihood of toxic impacts) of
selenium to fish and wildlife is also highly variable. However, the TDI
is based on a measure of existing impact (terata), not potential hazard.
As such, terata are an expression of the sum total of parental exposure,
regardless of the temporal, spatial, or chemical variations that may
exist from site to site. Thus, the applicability of the TDI is not influenced by local environmental conditions that affect selenium dynamics and biological uptake. It makes no difference whether the system is
a fast-flowing stream, in which selenate predominates and
bioaccumulation is low, or a terminal wetland in which high
bioaccumulation from selenite is occurring; population-level impacts
are indicated only if a sufficient amount of terata exists.
Example Assessments
6 composite samples of teratogenic individuals. The investigation reveals that 15% have terata, and the associated selenium
concentrations are 10 to 15 I-lg Se/g. The expected populationlevel mortality is 12 % (85 % normal + 3 % surviving teratogenic =
88% total survival), resulting in a TDI rating of 2. Conclusion:
slight to moderate impact on the population due to teratogenic
effects of selenium. A shift in the relative dominance of fish populations is possible, with selenium-sensitive species replaced by