United States
Environmental Protection
Agency
Environmental Research
Laboratory
Duluth MN 55804
Research and Development
EPA/600/S3-86/023 May 1986
AEPA Project Summary
The Effects of Variable
Hardness, pH, Alkalinity,
Suspended Clay, and Humics
on the Chemical Speciation
and Aquatic Toxicity of
Copper
Henry Nelson, Ouane Benoit, Russ Erickson,
Vince Mattson, and Jim Lindberg
The effects of variable hardness, pH,
alkalinity, humics, and suspended clay
on the chemical speciation of copper
and its toxicity to fathead minnow lar-
vae in Lake Superior water were inves-
tigated. Two proposed methods (toxic-
ity factors and chemical speciation) for
predicting LC50 values in specific natu-
ral waters from laboratory toxicity data
and the average site-specific values of
general water quality parameters were
evaluated. The accuracy of the cupric
ion selective electrode in determining
Cu+z activities in ambient and chemi-
cally altered Lake Superior water was
also determined.
Increases in calcium and magnesium
hardness at constant ambient Lake Su-
perior alkalinity (approximately
1 x 10~3 eg/L) increased LC50 values in
terms of total, dissolved, and free cop-
per (Cu+2 activity) as did increases in
sodium. Increases in pH from 6.6 to 8.7
at ambient Lake Superior alkalinity in-
creased the total and dissolved copper
LCSOs. However, the free copper LC50
increased from pH 6.6 to 7.3, remained
constant from pH 7.3 to 8.0, and then
decreased from pH 8.0 to 8.7. At ap-
proximately three times the ambient
Lake Superior alkalinity (3 x 10~3 eg/L),
the total and dissolved copper LCSOs
increased monotonically, and the free
copper LC50 decreased monotonically
with increasing pH from 7.1 to 8.5. In-
creases in alkalinity from about one-
third to six times the ambient alkalinity
of Lake Superior did not significantly
affect the total and dissolved copper
LCSOs but decreased the free copper
LCSOs.
The differences between LC50 values
for some waters with higher than ambi-
ent Lake Superior alkalinity and pH are
because of changes in the proportions
of inorganic copper species with differ-
ent toxicities/unit concentration. How-
ever, the differences between LC50 val-
ues for waters with lower than ambient
alkalinity and pH and for waters at am-
bient alkalinity and pH but different
hardnesses cannot be explained by
changes in the proportions of inorganic
species. In such cases, it is likely that
changes in general water quality
parameters such as pH and hardness,
change the toxicity/untt concentrations
of one or more toxic copper species.
By adding humics or suspended clay
or both to Lake Superior water total
and dissolved copper LCSOs increased,
but free copper LCSOs generally de-
creased even though they did not ap-
preciably affect pH or alkalinity. The de-
crease in the free copper LC50 caused
by adding humics and/or clay may have
been because of increases in the toxic-
ities/unit concentrations of inorganic
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copper species due to a possible in-
crease in the stress on the organisms. It
is also possible that some copper humic
and copper clay complexes are directly
toxic to fathead minnow larvae.
Changes in the toxicities/unit concen-
tration of toxic copper species along
with changes in the values of general
water quality parameters such as pH or
alkalinity indicate that the chance of de-
veloping a chemical speciation method
for deriving site-specific criteria is low.
Developing a toxicity factors method,
which empirically derives from labora-
tory data multi-variable equations re-
lating LC50 values to general water
quality parameters such as pH and
hardness, is more feasible but is still
being evaluated.
The ratio of Cu+z activities deter-
mined by the ion selective electrode to
Cu+2 activities predicted from inputing
dissolved copper into the REDEQL
chemical equilibrium computer pro-
gram (assuming no organic or clay
complexation) varied from 0.85 to 1.15
for 12 of the 18 test waters to which no
humics or clay were added. The four
test waters for which the ratios were
less than 0.85 had ambient Lake Supe-
rior or lower pH and/or alkalinity. Most
of the test waters for which the ratios
were close to one had greater than am-
bient Lake Superior pH or alkalinity or
both. These observations along with
the observed dependence of the slope
of the cupric ion electrode response on
various parameters showed that a sub-
stantial proportion of copper may be
bound by organics in Lake Superior
water at ambient or lower pH and/or
alkalinity even though the TOG of Lake
Superior water averages only 1 ppm.
The reason may be because of the high
stability constants for the formation of
many copper-organic complexes and to
a reduction in the competition between
OH", CO3~2, and organic ligands for
Cu+2 at ambient or lower pH and/or
alkalinity.
This Project Summary was devel-
oped by EPA's Environmental Research
Laboratory, Duluth, MN, to announce
key findings of the research project that
is fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
The aquatic toxicities of metals are
shown to be partially dependent upon
the values of general water quality
parameters such as temperature, dis-
solved oxygen, hardness, pH, alkalinity,
total organic carbon (TOO, and sus-
pended solids (1-20). Since the average
values of such parameters can vary over
the range of natural waters normally en-
countered (21), there is interest in for-
mulating protocols by which site-
specific criteria for metals can be
derived (22). EPA is currently assessing
whether protocols for formulating site-
specific criteria based on non-site labo-
ratory toxicity data bases and on aver-
age site-specific values of general water
quality parameters can be developed.
Such protocols are more cost effective
than those that perform toxicity tests at
each site.
Developing protocols for site-specific
criteria depends on which water quality
parameters significantly affect metal
toxicity. It also depends upon the devel-
opment of one or more methods by
which the toxicity of metals in a site
water can be estimated (e.g., the LC50
values for an appropriate sensitive spe-
cies) from non-site laboratory toxicity
data bases and average site-specific val-
ues of those general water parameters
that significantly affect toxicity.
For the past year, scientists at EPA's
Environmental Research Laboratory—
Duluth (ERL-Duluth) have conducted
toxicity tests to determine the effects of
five general water quality parameters
(hardness, pH, alkalinity, humics, and
suspended solids) on the toxicity of cop-
per to fathead minnow (Pimephales
promelas) larvae. The tests were de-
signed to determine which of those gen-
eral water quality parameters exert a
significant effect on copper toxicity. Ad-
ditionally, the tests are being used to
determine if copper toxicity can be pre-
dicted for fathead minnow larvae found
in site waters resulting from laboratory
toxicity tests and from average site-
specific values of general water quality
parameters that are found to signifi-
cantly affect toxicity.
Currently, scientists at the lab are
evaluating two proposed methods for
estimating copper LC50 values in site
water:
a) Toxicity Factors Method—in-
volves empirically deriving one or
more equations relating the LC50
or a LC50 related transformation to
one or more general water quality
parameters (or transformations)
such as pH and hardness.
b) Chemical Speciation Method—in-
volves determining the relative
concentration and toxicity/unit
concentration of the various cop-
per species present.
Recommendations
Results of copper toxicity tests show
that differences in copper toxicity be-
tween different test waters cannot be
fully explained by changes in the pro-
portions or concentrations or inorganic
copper species alone. Also, changes in
the toxicities/unit concentration of toxic
copper species and/or changes in the
proportions or concentrations of toxic
copper-organic complexes probably oc-
cur. Although it is impossible from the
current data to determine the relative
contributions of changes in toxicities/
unit concentration and changes in the
proportions or concentrations of toxic
copper-organic complexes to toxicity
changes, either case is extremely detri-
mental when developing a chemical
speciation method. It is likely that
changes in several of the general water
quality parameters do change the toxic-
ities/unit concentration of some of the
toxic copper species. We could not suc-
cessfully determine the toxicities/unit
concentration of copper species from
multiple linear regression, using data
from test waters in which no obvious
changes in the toxicities/unit concentra-
tion had occurred. Therefore, we rec-
ommend that efforts to develop a chem-
ical speciation method be dropped in
favor of developing a toxicity factors
method. That does not necessarily
mean that all work with the cupric ion
selective electrode should be dropped.
Some linear combinations of the con-
centrations of copper species calculated
from electrode measured Cu activities
could be a useful measurable form of
copper on which to base LCBOs in devel-
oping a toxicity factors method.
If copper-humic and copper-clay com-
plexes are shown to be relatively non-
toxic, efforts could be concentrated on
developing a toxicity factors method
which uses, if possible, a measurable
form of copper that will decrease or
eliminate the dependence of the LC50
values on humic and suspended clay
concentrations. Even if such a method is
developed, it may not be well received if
the measurable form of copper chosen
is more difficult to determine than dis-
solved copper. Therefore, as a possible
alternative, EPA should consider using
dissolved copper as the measurable
form of copper on which a toxicity fac-
tors method should be based. Of
course, dissolved copper LCBOs are de-
pendent upon humic and suspended
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clay concentrations. Furthermore, the
types and characteristics of humics and
clay vary so much, it would be difficult
to model such effects. If EPA decides to
use dissolved copper as the measurable
form of copper on which to base the
toxicity factors method, it should be re-
alized that any resultant criteria derived
would probably be extremely conserva-
tive. Nevertheless, if current equations
relating total and dissolved copper
LC50s to hardness can be extended to
multivariable equations relating total or
dissolved copper LCSOs to other general
water quality parameters such as pH,
any resultant criteria should be less con-
servative than they are now.
The effects of alkalinity on copper tox-
icity are small compared to hardness.
Therefore, since hardness and alkalinity
are so closely correlated in natural wa-
ters, it might be useful to break hard-
ness into carbonate hardness which
would include any effect of alkalinity
and non-carbonate hardness instead of
considering alkalinity as a separate vari-
able.
A multivariate equation relating
LCBOs to hardness and pH or possibly
carbonate hardness, non-carbonate
hardness, and pH should be based on
the results of toxicity tests run in waters
which have typical combinations of car-
bonate hardness, non-carbonate hard-
ness, and pH values. Generally, waters
will have a hardness equal to or greater
than alkalinity so that most waters will
have some non-carbonate hardness.
Most waters will have a pH somewhat
lower than that expected if they are in
equilibrium with the atmosphere.
Therefore, the tests should be run in
waters at several different hardnesses
equal to the alkalinity covering the
range of alkalinity normally encoun-
tered in natural waters, and at pHs
equivalent to equilibrium with the at-
mosphere. Additionally, tests should be
run in waters with non-carbonate hard-
ness added in the form of Ca+2 and
Mg+2 chloride and sulfate salts, and pH
lowered with C02 bubbling. The base
waters in which the hardness is equal to
the alkalinity and the pH equivalent to
that of equilibrium with the atmosphere
should be made with mixtures of cal-
cium and magnesium bicarbonates at a
Ca+2/Mg + 2 ratio typical of natural
waters and then aerated. Since recent
work showed that chloride and sulfate
salts may exert different effects on tox-
icities, the non-carbonate hardness
should be added in ratios of CI~/S04~2
salts similar to the Cl /S04 2 ratios typ-
ically seen in natural waters. Because
the effects of Na+ and K+ are not well
known, the use of Na+ and K+ salts
should be avoided. The use of such salts
is not necessary if hardness is divided
into carbonate and non-carbonate hard-
ness and the effects of alkalinity are
considered jointly with hardness in the
form of the carbonate hardness. Typical
combinations of carbonate hardness,
non-carbonate hardness, and the pH
can be determined from national sur-
veys of freshwaters such as the U.S. Ge-
ological Survey entitled Quality of
Rivers of the United States, 1975 Water
Year. Typical ratios of Ca+2/Mg+2 and
Cr/S04~2 can also be determined from
such sources.
Bibliography
1. J. Cairns Jr., A. Health and B.
Parker. "The Effects of Temperature
Upon the Toxicity of Chemicals to
Aquatic Organisms." Hydrobiolgia
47(1), 135-171 (1975)
2. U. Forstner and G. Wittman. Metal
Pollution in the Aquatic Environ-
ment, P. 273-280. Springer-Verlag
Publishers. Berlin, Heidelberg, New
York (1979)
3. W. A. Spoor. "Water Quality and
Pollutant Toxicity" Internal Report
for U.S. EPA Environmental Re-
search Laboratory, Duluth MN.
4. K. Warwood and F. Beamish. "The
Effect of Copper, Hardness and pH
on the Growth of Rainbow Trout
(Salmo Gairdenri)." J. Fish Biol. 13,
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of Test Water on the Toxicity of
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8. R. Andrew. "Toxicity Relationships
to Copper Forms in Natural
Waters." Chap. 6 in Toxicity to Biota
of Metal Forms in Natural Water
Proc. Workshop of the International
Joint Commission's Great Lakes
Research Advisory Board (1975)
9. R. Andrew, K. Bresinger and G.
Glass. "Effects of Inorganic Com-
plexation on the Toxicity of Copper
to Daphnia Magna." Water Res. 77,
309-315 (1977)
10. R. Howarth and J. Sprague.
"Copper Lethality to Rainbow Trout
in Waters of Various Hardness and
pH." Water Res. 12, 455-462 (1978)
11. C. Chakoumakos, R. Russo and R.
Thurston. "Toxicity of Copper to
Cutthroat Trout (Salmo clarki)
under Different Conditions of Alka-
linity, pH and Hardness." Environ.
Sci. + Technol. 13, 213-219 (1979)
12. V. Magnuson, D. Harriss, M. Sun,
D. Taylor and G. Glass. "Relation-
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ACS Symposium Series 93, Ameri-
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D.C. (1979)
13. K. Warwood and F. Beamish.
"Effects of Copper, pH and Hard-
ness on the Critical Swimming Per-
formance of Rainbow Trout (Salmo
Gairdneri)." Water Res. 12, 611-619
(1978)
14. G. Pagenkopf. "Gill Surface Interac-
tion Model for Trace-Metal Toxicity
to Fishes: Role of Complexation, pH
and Water Hardness" Environ. Sci.
Technol. 17(6), 342-347 (1983)
15. U. Borgmann, "Metal Speciation
and Toxicity of Free Metal Ions to
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Mancy. "Effects of Organic Pollu-
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Chapter 7 in Toxicity to Biota of
Metal Forms in Natural Waters.
Proc. Workshop of the International
Joint Commission's Great Lakes
Research Advisory Board (1975)
17. P. Zitko, W. V. Carson and W. G.
Carson. "Prediction of Incipient
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10(5), 265-271 (1973)
18. R. Cook and R. Cote. "The Influence
of Humic Acids on the Toxicity of
Copper and Zinc to Juvenile At-
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19. U. Borgmann and K. Ralph.
"Complexation and Toxicity of Cop-
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Technique." Water Res. 17(11),
1697-1703 (1983)
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"Aspects of Water Quality and the
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21. U.S. Geological Survey. Quality of
Rivers of the United States, 1975
Water Year (1976)
22. U.S. Environmental Protection
Agency "Guidelines for Deriving
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Agency (1982)
Henry Nelson is with Science Applications International Corp., McLean, VA; the
EPA authors Duane Benoit, Russ Erickson. and Vince Mattson are with the
Environmental Research Laboratory, Duluth. MN 55804; and Jim Lindberg is
with the University of Wisconsin, Superior, Wl.
A. R. Carlson is the EPA Project Officer (see below).
The complete report, entitled "The Effects of Variable Hardness, pH, Alkalinity,
Suspended Clay, and Humics on the Chemical Speciation and Aquatic Toxicity
of Copper," (Order No. PB 86-171 444/A S; Cost: $ 16.95, subject to change) will
be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Research Laboratory
U.S. Environmental Protection Agency
6201 Congdon Blvd.
Duluth. MN 55804
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
EPA/600/S3-86/023
0000329 PS
U S ENVIR PROTECTION AGENCY
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