EPA's Vessel General Permit and Small Vessel General

criteria and procedures for site-specific adjustments.
To achieve these goals and as part of the remedy for these problems, the EPA initiated an
interagency project with the USFWS and the U.S. Geological Survey (USGS) to address issues
of 1) a methodology for translation of a tissue guidelines to protective site-specific dissolved Se
concentrations (implementation of tissue criteria); 2) inclusion of protection of wildlife species
(i.e., federally-listed species) in regulatory methodologies; and 3) site-specific criteria
development for the Bay-Delta (USEPA 1999).
A methodology for ecosystem-scale modeling of Se is now available (Presser and Luoma 2010b,
a). Analysis from this biodynamically-based methodology showed, in general, that:
� A crucial factor ultimately defining Se toxicity is the link between dissolved and
particulate phases at the base of the food web (i.e., Kd);
� Collection of particulate material phases and analysis of their Se concentrations are key
to representing the dynamics of the system;
� Bioaccumulation in invertebrates is a major source of variability in Se exposure of
predators within an ecosystem, although that variability can be explained by invertebrate
physiology (i.e., TTFinvertebrate);
� TTFfish is relatively constant over the range of species considered here; and
� Se concentrations are at least conserved and usually magnified at every step in a food
web.”
The ecosystem-scale model developed by Presser and Luoma (Presser and Luoma 2010b, a)
reveals the importance of understanding the biodynamics of selenium in aquatic environments to
more accurately predict selenium toxicity. Conventional methods that relate water column
selenium concentrations to tissue concentrations using bioaccumulation factors (BAFs), as was
used in in the BE, have a high degree of uncertainty (Presser and Luoma 2010b). We
reevaluated the risk assessment for selenium to examine how the analysis might benefit from a
more informed, ecosystem-scale approach. We adapted the model used to support criteria
development to estimate tissue concentrations (referred to as ECT values in the BE) from
concentrations of selenium in water (Table 31). For this evaluation we selected parameter
estimates (Kd’s and TTFs; Table 32) that were developed by Presser and Luoma (Presser and
Luoma 2010a) for the San Francisco Bay-Delta system, as well as, estimates used to represent a
hypothetical estuary (Presser and Luoma 2010b). We incorporated effects estimates for fish and
bird reproduction (i.e. larval edema/skeletal defects and hatchability) and survival that were
derived by the USFWS and used by Pressor and Luoma (Presser and Luoma 2010a) to predict
water concentrations necessary for protecting sensitive listed fish and bird species in the San
Francisco Bay-Delta.
Our revaluation indicates that EPAs, BAF-based, analysis likely underestimates risks of
selenium exposure to listed species. As previously mentioned, EPA concluded (based on their
original loading estimates) that risks to listed species from selenium discharged by vessels would
be negligible for some taxa and remote for others. In contrast, risk quotients calculated using the
ecosystem-scale approach ranged from 2.05 to 79.8 (Table 33), indicating that significant effects
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