Evaluation
77
site-specific basis, whereas the HQ method is more generic and is tied
to a single criterion that is assumed to be protective under all exposure
conditions.
The Protocol's hazard estimates closely matched the field evidence
of selenium toxicity to both fish and aquatic birds; the HQ estimates
did not. The inability of HQ to correctly assess hazard reflects the outdated USEPA water quality criterion. Data from the field sites show,
quite clearly, that bioaccumulation of selenium in aquatic food chains
and resultant toxicity to fish and wildlife can occur when concentrations of waterborne selenium are well below the current United States
water quality criterion. This indicates that a revision (lowering) of the
USEPA criterion is necessary, either at a national level, or at a local
site-specific level (see Chapter 7). Even then, there will likely be many
locations where HQ will perform poorly because of the potential for
high selenium bioaccumulation with little detectable elevation in
waterborne concentrations (eg, the sites in Nevada). This situation can
develop because of the presence of ultra-trace amounts «ll-1g SelL) of
dissolved organic selenium that cause disproportionately high
bioaccumulation relative to the inorganic forms of selenium (Besser et
a1. 1989, 1993), or because of a very strong sediment-detrital buildup
of selenium that is possible under certain limnological conditions (Lemly
and Smith 1987; Lemly 1997b). Accounting for this scenario in selenium cycling is essential for accurate hazard assessment. The Protocol
is sensitive to all of the bioaccumulation pathways for selenium, and
its predictions are accurate regardless of waterborne concentrations.
Another problem with HQ analysis, due to its dependence on waterborne selenium, is that it does not accurately evaluate the success of
remediation at contaminated sites. It is possible for waterborne selenium to fall substantially with little or no accompanying reduction in
the overall ecosystem-level hazard to fish and wildlife. For example,
hazard to fish remained high at Belews Lake, NC, because of selenium-laden sediments, even though waterborne concentrations
dropped to near background levels because of site management actions that eliminated selenium inputs (Lemly 1997b). The HQ ratings
suggest that remediation has been successful and no hazard remains,
because waterborne selenium is well below the USEPA criterion. However, this is clearly not the case. The Protocol correctly identified and
rated the hazard that persists at this site; HQ analysis did not. Thus,
there are several important limitations in the application of HQ analysis to aquatic hazard assessment of selenium.
A possible criticism of the Protocol is that it requires considerably
more data than HQ (ie, water, sediments, invertebrates, fish, and birds
for the Protocol; just water for HQ). However, given the serious impacts of selenium on fish and wildlife that have resulted because of
environmental management actions that were based on inadequate
77
site-specific basis, whereas the HQ method is more generic and is tied
to a single criterion that is assumed to be protective under all exposure
conditions.
The Protocol's hazard estimates closely matched the field evidence
of selenium toxicity to both fish and aquatic birds; the HQ estimates
did not. The inability of HQ to correctly assess hazard reflects the outdated USEPA water quality criterion. Data from the field sites show,
quite clearly, that bioaccumulation of selenium in aquatic food chains
and resultant toxicity to fish and wildlife can occur when concentrations of waterborne selenium are well below the current United States
water quality criterion. This indicates that a revision (lowering) of the
USEPA criterion is necessary, either at a national level, or at a local
site-specific level (see Chapter 7). Even then, there will likely be many
locations where HQ will perform poorly because of the potential for
high selenium bioaccumulation with little detectable elevation in
waterborne concentrations (eg, the sites in Nevada). This situation can
develop because of the presence of ultra-trace amounts «ll-1g SelL) of
dissolved organic selenium that cause disproportionately high
bioaccumulation relative to the inorganic forms of selenium (Besser et
a1. 1989, 1993), or because of a very strong sediment-detrital buildup
of selenium that is possible under certain limnological conditions (Lemly
and Smith 1987; Lemly 1997b). Accounting for this scenario in selenium cycling is essential for accurate hazard assessment. The Protocol
is sensitive to all of the bioaccumulation pathways for selenium, and
its predictions are accurate regardless of waterborne concentrations.
Another problem with HQ analysis, due to its dependence on waterborne selenium, is that it does not accurately evaluate the success of
remediation at contaminated sites. It is possible for waterborne selenium to fall substantially with little or no accompanying reduction in
the overall ecosystem-level hazard to fish and wildlife. For example,
hazard to fish remained high at Belews Lake, NC, because of selenium-laden sediments, even though waterborne concentrations
dropped to near background levels because of site management actions that eliminated selenium inputs (Lemly 1997b). The HQ ratings
suggest that remediation has been successful and no hazard remains,
because waterborne selenium is well below the USEPA criterion. However, this is clearly not the case. The Protocol correctly identified and
rated the hazard that persists at this site; HQ analysis did not. Thus,
there are several important limitations in the application of HQ analysis to aquatic hazard assessment of selenium.
A possible criticism of the Protocol is that it requires considerably
more data than HQ (ie, water, sediments, invertebrates, fish, and birds
for the Protocol; just water for HQ). However, given the serious impacts of selenium on fish and wildlife that have resulted because of
environmental management actions that were based on inadequate