1.1 Background
9
Aluminum toxicity to aquatic organisms is caused primarily by inorganic
forms of Al rather than organically complexed Al (Al o ; Driscoll et al. 1980, Baker
and Schofield 1982, Havas 1985). There is limited evidence of biological effects
at Al i less than 50 μg/L (~2 μM). Free Al concentrations (Al 3+ ; roughly equivalent to Al i concentrations at pH values substantially below 5.0) between 50 and
200 μg/L have been shown to reduce the growth and survival of various species
of fish (Muniz and Levivestad 1980, Baker and Schofield 1982). Concentrations
of Al i greater than 200 μg/L are generally considered to have toxic effects on the
majority of freshwater fish species (Table 1.2).
Sensitivity of surface waters to eutrophication and the nutrient status
of lakes and streams are typically evaluated on the basis of concentrations of
P and N. These nutrients can be assessed as total N or total P or as one or more
of the various forms that commonly occur in surface waters, such as nitrate
(NO 3
− ) and soluble reactive P (SRP). The US EPA has provided guidance to states
for setting nutrient criteria for total N and P concentrations in US lakes (US
EPA 2000a) and streams and rivers (US EPA 2000b). Different nutrient criteria
are being developed for each of 14 different nutrient ecoregions throughout the
country. Nutrient ecoregions are based on aggregations of level III Omernik
ecoregions (Omernik 1987; http://www.nps.gov/plants/sos/pdf/SOS%20
Omernik%20Level%20III.pdf).
In some areas, the concentrations of potentially toxic substances in surface
waters may be of concern. This issue is likely to be of greatest interest in areas
downwind of substantial emissions sources of pesticides or where atmospheric
deposition of Hg (or another trace metal) is known to be elevated. Monitoring
of pesticides in surface waters may be advisable on lands directly downwind of
intensive agricultural development.
Studies of Hg concentrations in fish tissue may be warranted in areas that
are downwind of known Hg emissions sources, especially where such areas
TABLE 1.2 GENERAL GUIDELINES a FOR EVALUATING THE LIKELIHOOD
OF AL TOXICITY IN FRESHWATERS
Concentration of
Inorganic Monomeric Al
Expected Response of Aquatic Biota
<50 μg/L
Biological effects not likely to most forms of aquatic biota
50 to 200 μg/L
Reduced growth and survival of various species of fish,
including brook trout, and likely other aquatic life-forms
> 200 μg/L
Adverse effects likely for most freshwater fish species
a These are general guidelines. Variability is high with species, life stage, and various
aspects of water chemistry, including Ca 2+ concentration, dissolved organic carbon
(DOC), and total fluoride (F) concentration.
9
Aluminum toxicity to aquatic organisms is caused primarily by inorganic
forms of Al rather than organically complexed Al (Al o ; Driscoll et al. 1980, Baker
and Schofield 1982, Havas 1985). There is limited evidence of biological effects
at Al i less than 50 μg/L (~2 μM). Free Al concentrations (Al 3+ ; roughly equivalent to Al i concentrations at pH values substantially below 5.0) between 50 and
200 μg/L have been shown to reduce the growth and survival of various species
of fish (Muniz and Levivestad 1980, Baker and Schofield 1982). Concentrations
of Al i greater than 200 μg/L are generally considered to have toxic effects on the
majority of freshwater fish species (Table 1.2).
Sensitivity of surface waters to eutrophication and the nutrient status
of lakes and streams are typically evaluated on the basis of concentrations of
P and N. These nutrients can be assessed as total N or total P or as one or more
of the various forms that commonly occur in surface waters, such as nitrate
(NO 3
− ) and soluble reactive P (SRP). The US EPA has provided guidance to states
for setting nutrient criteria for total N and P concentrations in US lakes (US
EPA 2000a) and streams and rivers (US EPA 2000b). Different nutrient criteria
are being developed for each of 14 different nutrient ecoregions throughout the
country. Nutrient ecoregions are based on aggregations of level III Omernik
ecoregions (Omernik 1987; http://www.nps.gov/plants/sos/pdf/SOS%20
Omernik%20Level%20III.pdf).
In some areas, the concentrations of potentially toxic substances in surface
waters may be of concern. This issue is likely to be of greatest interest in areas
downwind of substantial emissions sources of pesticides or where atmospheric
deposition of Hg (or another trace metal) is known to be elevated. Monitoring
of pesticides in surface waters may be advisable on lands directly downwind of
intensive agricultural development.
Studies of Hg concentrations in fish tissue may be warranted in areas that
are downwind of known Hg emissions sources, especially where such areas
TABLE 1.2 GENERAL GUIDELINES a FOR EVALUATING THE LIKELIHOOD
OF AL TOXICITY IN FRESHWATERS
Concentration of
Inorganic Monomeric Al
Expected Response of Aquatic Biota
<50 μg/L
Biological effects not likely to most forms of aquatic biota
50 to 200 μg/L
Reduced growth and survival of various species of fish,
including brook trout, and likely other aquatic life-forms
> 200 μg/L
Adverse effects likely for most freshwater fish species
a These are general guidelines. Variability is high with species, life stage, and various
aspects of water chemistry, including Ca 2+ concentration, dissolved organic carbon
(DOC), and total fluoride (F) concentration.