Implementing Criteria
127
be greater than 10 years, perhaps several decades, due to recycling
of selenium from sediments into benthic-detrital food chains and
associated dietary and reproductive toxicity to fish (Garrett and
Inmann 1984; Lemly 1997).
Similar problems are evident with the use of dilution or mixing
zones, which are areas exempt from ambient criteria. This concept
was developed for application to flowing waters (Stephan et al. 1985).
It has no credible basis for application to selenium in lentic/wetIand
systems because the "dilution zone" may constitute the entire body of
open water. Even in riverine habitats, the notion of mixing zones has
not been supported by data verifying that mixing zones can effectively
dilute a selenium-laden effluent and also be environmentally compatible with fish and wildlife habitat uses, which is a requirement of US
federal statutes such as the Migratory Bird Treaty Act and the Endangered Species Act (Margolin 1979). Selenium strongly bioaccumulates
in food organisms and makes the dilution zone an area of extremely
high exposure for fish and wildlife. Several case studies show that
using mixing zones to dilute seleniferous water creates more biological hazards than it resolves (eg, Skorupa 1998). The apparent benefits
gained by achieving target concentrations in a mixing zone may be
more than offset by detrimental effects that are caused by other aspects of the selenium cycle. The threat of toxic impacts overrides the
need to attempt" dilution as a solution".
Given these flaws, it is important to closely examine the rationale
for, and the distinction between, national and site-specific criteria.
USEPA criteria are intended to provide protection for most aquatic species most of the time, not for all species all of the time (Stephan et al.
1985). Because of this basic caveat and also because there are differences in ecosystem and aquatic species sensitivity to selenium, there
may be a plausible argument for allowing some leeway in meeting
the national criterion. That is, a reasonable averaging of concentrations
over time might be permissible if reproductive assessment indicates
that there are no biological effects (but not 20 I-lg SelL exceedances).
However, at a local level, the national criterion's intent to protect "most
species" still leaves large gaps that could lead to substantial inconsistencies (toxic effects at or below the criterion level for some species,
but no effects for other species even above the criterion). Site-specific
water quality criteria should reflect the sensitivity of local biota and
close the gaps.
Site-specific criteria for selenium should designate a biologically based
concentration limit using the procedure described in this chapter (Figs.
7.1 and 7.2). If full protection of aquatic life is desired, then there should
be no provision for averages, exceedances, or mixing/dilution zones in
the implementation of these site-specific criteria.
127
be greater than 10 years, perhaps several decades, due to recycling
of selenium from sediments into benthic-detrital food chains and
associated dietary and reproductive toxicity to fish (Garrett and
Inmann 1984; Lemly 1997).
Similar problems are evident with the use of dilution or mixing
zones, which are areas exempt from ambient criteria. This concept
was developed for application to flowing waters (Stephan et al. 1985).
It has no credible basis for application to selenium in lentic/wetIand
systems because the "dilution zone" may constitute the entire body of
open water. Even in riverine habitats, the notion of mixing zones has
not been supported by data verifying that mixing zones can effectively
dilute a selenium-laden effluent and also be environmentally compatible with fish and wildlife habitat uses, which is a requirement of US
federal statutes such as the Migratory Bird Treaty Act and the Endangered Species Act (Margolin 1979). Selenium strongly bioaccumulates
in food organisms and makes the dilution zone an area of extremely
high exposure for fish and wildlife. Several case studies show that
using mixing zones to dilute seleniferous water creates more biological hazards than it resolves (eg, Skorupa 1998). The apparent benefits
gained by achieving target concentrations in a mixing zone may be
more than offset by detrimental effects that are caused by other aspects of the selenium cycle. The threat of toxic impacts overrides the
need to attempt" dilution as a solution".
Given these flaws, it is important to closely examine the rationale
for, and the distinction between, national and site-specific criteria.
USEPA criteria are intended to provide protection for most aquatic species most of the time, not for all species all of the time (Stephan et al.
1985). Because of this basic caveat and also because there are differences in ecosystem and aquatic species sensitivity to selenium, there
may be a plausible argument for allowing some leeway in meeting
the national criterion. That is, a reasonable averaging of concentrations
over time might be permissible if reproductive assessment indicates
that there are no biological effects (but not 20 I-lg SelL exceedances).
However, at a local level, the national criterion's intent to protect "most
species" still leaves large gaps that could lead to substantial inconsistencies (toxic effects at or below the criterion level for some species,
but no effects for other species even above the criterion). Site-specific
water quality criteria should reflect the sensitivity of local biota and
close the gaps.
Site-specific criteria for selenium should designate a biologically based
concentration limit using the procedure described in this chapter (Figs.
7.1 and 7.2). If full protection of aquatic life is desired, then there should
be no provision for averages, exceedances, or mixing/dilution zones in
the implementation of these site-specific criteria.