Accuracy of Hazard Ratings
69
occur even though each of the individual components was rated "moderate". The rationale for this "weighting" is that 3 distinct routes of
exposure are possible for selenium: water, planktonic food chain, and
detrital food chain. Based on field evidence of bioaccumulation and
toxic effects, the hazard of all 3 together should be greater than if each
is present separately. Thus, the aggregate hazard for the ecosystem as
a whole can be greater than the hazard for individual components.
This is analogous to synergism, that is, the parts (the hazard scores for
the components) are not simply additive.
The Protocol should not be used if data are missing for more than 1
ecosystem component. Accepting only 3 components could mean that
data for both fish and birds were absent. The objective of the Protocol
is to estimate ecosystem-level hazard by focusing on bioaccumulation
in fish and aquatic birds. If one of these components is missing, the
predictive power of the assessment will not be as strong as if both are
included, but the assessment will still have validity. However, if both
are missing, the procedure does not meet its objective and, therefore,
is invalid. One other precaution is necessary. An extraneous ecosystem component should never be substituted for one that was specified
for use in the Protocol (for example, zooplankton should not be substituted for benthic macroinvertebrates), because the hazard profiles were
constructed for use with the indicated ecosystem components only.
Substitutions will invalidate the results.
Depending on the needs of the investigator, the Protocol can be applied to data collected for a single sampling site or to pooled data from
a monitoring effort covering a large area. The Protocol can thus address several levels of landscape scale and provide site-specific, as well
as regional, assessment of selenium hazard. Comparisons can be made
between locations and years, and follow-up assessments can be made
to evaluate the success of management actions and cleanup activities
at selenium-contaminated sites.
Accuracy of Hazard Ratings
Comparison to Other Methods
The Protocol is an important new method for assessing selenium hazards to aquatic life. It is designed for application across a wide range of
habitat types and environmental conditions. In order for this objective
to be met, it must provide hazard ratings that are verified in the field
and are more accurate than those generated by other methods. Prior to
its development, the other major technique available was the USEPA's
Hazard Quotient (HQ) procedure (EPA 1992). The HQ technique is generally considered to be a good method to use when there is a USEPA
69
occur even though each of the individual components was rated "moderate". The rationale for this "weighting" is that 3 distinct routes of
exposure are possible for selenium: water, planktonic food chain, and
detrital food chain. Based on field evidence of bioaccumulation and
toxic effects, the hazard of all 3 together should be greater than if each
is present separately. Thus, the aggregate hazard for the ecosystem as
a whole can be greater than the hazard for individual components.
This is analogous to synergism, that is, the parts (the hazard scores for
the components) are not simply additive.
The Protocol should not be used if data are missing for more than 1
ecosystem component. Accepting only 3 components could mean that
data for both fish and birds were absent. The objective of the Protocol
is to estimate ecosystem-level hazard by focusing on bioaccumulation
in fish and aquatic birds. If one of these components is missing, the
predictive power of the assessment will not be as strong as if both are
included, but the assessment will still have validity. However, if both
are missing, the procedure does not meet its objective and, therefore,
is invalid. One other precaution is necessary. An extraneous ecosystem component should never be substituted for one that was specified
for use in the Protocol (for example, zooplankton should not be substituted for benthic macroinvertebrates), because the hazard profiles were
constructed for use with the indicated ecosystem components only.
Substitutions will invalidate the results.
Depending on the needs of the investigator, the Protocol can be applied to data collected for a single sampling site or to pooled data from
a monitoring effort covering a large area. The Protocol can thus address several levels of landscape scale and provide site-specific, as well
as regional, assessment of selenium hazard. Comparisons can be made
between locations and years, and follow-up assessments can be made
to evaluate the success of management actions and cleanup activities
at selenium-contaminated sites.
Accuracy of Hazard Ratings
Comparison to Other Methods
The Protocol is an important new method for assessing selenium hazards to aquatic life. It is designed for application across a wide range of
habitat types and environmental conditions. In order for this objective
to be met, it must provide hazard ratings that are verified in the field
and are more accurate than those generated by other methods. Prior to
its development, the other major technique available was the USEPA's
Hazard Quotient (HQ) procedure (EPA 1992). The HQ technique is generally considered to be a good method to use when there is a USEPA