7
Developing Site-Specific
Water Quality Criteria
Introduction
The United States Environmental Protection Agency (USEPA) conducted
a comprehensive review of information on selenium ecotoxicology and
issued revised national freshwater criteria for selenium in 1987 (EPA
1987). Since that time, two divergent lines of evidence and thought
have emerged regarding whether the criterion for chronic exposure (5
Ilg SelL) is adequate to protect aquatic life. One line supports the position that the criterion is too high and should be lowered. For example,
Winter Stress Syndrome in fish-a disruption of the normal annual cycle
of metabolic and physiological changes in cold weather-can substantially increase fish sensitivity to selenium and cause concentrations
approaching the criterion value to become toxic (Lemly 1993a, 1996).
Moreover, in the western United States, agricultural irrigation has
caused selenium to bioaccumulate to toxic levels in food chains and to
poison fish and aquatic birds when waterborne concentrations were
well below 5 Ilg SelL (eg, Skorupa and Ohlendorf 1991; Stephens et al.
1992; Hallock and Hallock 1993; Lemly 1995; Hamilton et al. 1996).
The other line of evidence supports the position that the criterion is too
low and should be raised. For example, faunal surveys in Colorado
streams showed abundant fish populations where waterborne selenium
consistently exceeded the criterion. These observations have led some
to conclude that the national criterion is overly conservative, and that
the tolerated level should be raised to as much as 31 Ilg SelL in some
locations (eg, Guglielmone 1995; Canton and Van Derveer 1997; Van
Derveer and Canton 1997). The principal disagreements between these
two schools of thought were recently discussed by Hamilton and Lemly
(1999). They revolve around assumed versus demonstrated biological
effects, and the need to use a Hydrological Unit (HU) as the basis for
setting criteria (see Chapter 6).
The on-going controversy over whether the United States national criterion is too high or too low illustrates a very important point. Regardless
114
Developing Site-Specific
Water Quality Criteria
Introduction
The United States Environmental Protection Agency (USEPA) conducted
a comprehensive review of information on selenium ecotoxicology and
issued revised national freshwater criteria for selenium in 1987 (EPA
1987). Since that time, two divergent lines of evidence and thought
have emerged regarding whether the criterion for chronic exposure (5
Ilg SelL) is adequate to protect aquatic life. One line supports the position that the criterion is too high and should be lowered. For example,
Winter Stress Syndrome in fish-a disruption of the normal annual cycle
of metabolic and physiological changes in cold weather-can substantially increase fish sensitivity to selenium and cause concentrations
approaching the criterion value to become toxic (Lemly 1993a, 1996).
Moreover, in the western United States, agricultural irrigation has
caused selenium to bioaccumulate to toxic levels in food chains and to
poison fish and aquatic birds when waterborne concentrations were
well below 5 Ilg SelL (eg, Skorupa and Ohlendorf 1991; Stephens et al.
1992; Hallock and Hallock 1993; Lemly 1995; Hamilton et al. 1996).
The other line of evidence supports the position that the criterion is too
low and should be raised. For example, faunal surveys in Colorado
streams showed abundant fish populations where waterborne selenium
consistently exceeded the criterion. These observations have led some
to conclude that the national criterion is overly conservative, and that
the tolerated level should be raised to as much as 31 Ilg SelL in some
locations (eg, Guglielmone 1995; Canton and Van Derveer 1997; Van
Derveer and Canton 1997). The principal disagreements between these
two schools of thought were recently discussed by Hamilton and Lemly
(1999). They revolve around assumed versus demonstrated biological
effects, and the need to use a Hydrological Unit (HU) as the basis for
setting criteria (see Chapter 6).
The on-going controversy over whether the United States national criterion is too high or too low illustrates a very important point. Regardless
114