EPA's Vessel General Permit and Small Vessel General

known to leach from vessel hulls and can cause exceedances of water quality standards. For
example, significant leaching of copper from the hulls of sailboats, powerboats, and cruise ships
has been documented (Srinivasan and Swain 2007).
While some metals, including copper, nickel and zinc, are known to be essential to organism
function, many others, including thallium and arsenic, are non-essential and/or are known to
have only adverse impacts. Exposure to metals at toxic levels (which is partially dependent on
the essentiality of the metal) can cause a variety of changes in biochemical, physiological,
morphological, and behavioral patterns in aquatic and aquatic-dependent organisms. In the
aquatic environment, elevated concentrations of dissolved metals can be toxic to many species of
algae, crustaceans, and fish because it is this dissolved form of the metal that is most readily
available and taken up and internalized by an organism. Additionally, metals may not be fully
eliminated from blood and tissues processes, and may bioaccumulate in predatory and
scavenging organisms further up the food chain, including fish, birds, reptiles, and mammals.
One of the key factors in evaluating risk from exposure to metals is the bioavailability of the
metal to an organism. As indicated above, some metals have a strong tendency to adsorb to
suspended organic matter and clay minerals, or to precipitate out of solution, thus removing the
metal from the water column. The tendency of a given metal to adsorb to suspended particles is
typically controlled by the pH and salinity of the waterbody, as well as the organic carbon
content of the suspended particles. If the metal is highly sorbed to particulate matter, then it is
likely to not be in a dissolved form that aquatic organisms can process, i.e., bioavailable.
Accordingly, the protection of aquatic life for metals is typically expressed in the dissolved metal
form.
In contrast, evaluation of total metals is more appropriate for aquatic-dependent animals where
the primary route of exposure is assumed to be through the consumption of aquatic organisms,
and where the digestive process is assumed to transform all forms of metals to the dissolved
phase, thus increasing the amount of biologically available metals. This latter is also applicable
in aquatic animals exposed to metalloids such as arsenic and selenium.
EPA describes effects of aluminum, arsenic, cadmium, chromium, lead, nickel, and zinc that
result in measured changes to survival, growth, and reproduction. In addition, each of these
elements may result in sublethal effects to aquatic and aquatic-dependent wildlife that may affect
a species’ fitness, either alone or in combination with other physiological or environmental
stressors. Exposure to metals may result in a wide range of effects to endpoints such as
behavior, enzyme activity, blood chemistry, osmoregulation, respiration, disease resistance, and
other physiolological parameters. In many cases, these effects have been found to occur at
concentrations lower than those used in established aquatic life criteria (Eisler 2000).
One example of a particular sensitive endpoint is avoidance behavior in fish, observed at
concentrations as low as 23.9 ug/L nickel and 10 ug/L zinc in rainbow trout (Eisler 2000). Other
sublethal effects of metals were recorded at concentrations generally consistent with those
observed to effect survival, growth, and reproduction.
While abundant data are available for metal effects in most aquatic species, information on
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