V-/EPA
United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/M-86/015 June 1986
ENVIRONMENTAL
RESEARCH BRIEF
Effect of Chlorine on Chromium Speciation in Tap Water
Nancy Sue Ulmer*
Abstract
The 24-hr oxidation of trivalent chromium to hexavalent
chromium is reported in pH 5, 6, 7, and 8 chlorinated tap
water with low levels of alkalinity, chloride, sulfate, and
total organic carbon (TOC). The applicability and use of
analytical methods for hexavalent chromium in the pre-
sence of chlorine are discussed.
Introduction
Chromium may occur in various forms in natural waters as
a result of the weathering of bedrock and soils or the
discharge of chromium-bearing wastes from sources such
as tanneries, cooling towers, animal glue manufacturers,
metal dipping, pickling and electroplating industries, and
sewage treatment plants. The origin, occurrence, and fate
of chromium in water and the oxidation-reduction proc-
esses controlling its speciation during transport and
storage have been the topic of many investigations during
the last decade.
In nature, chromium generally occurs as the stable mineral
chromite (FeO-Cr2Oa); it is usually immobilized in the
trivalent form in bedrock and most soils (1). However,
Bartlett and James (2) have reported the oxidation of
trivalent chromium [Cr(lll)] to hexavalent chromium [Cr(VI)]
in many soils containing manganese. Robertson (3) cited
the occurrence of Cr(VI) at levels exceeding 0.05 mg/L in
ground water in Paradise Valley, Maricopa County, Arizona.
Osaki et al. (4) investigated the speciation of chromium in
the Muromi River of Japan and reported high concentra-
tions of Cr(VI) in the spring and streams of the river's
headwaters as a result of oxidation in the groundwater
sources. Downstream and in the reservoir, the Cr(lll) level
*Drmkmg Water Research Division, Water Engineering Research Laboratory,
Cincinnati, OH 45268
increased because the rate of reduction of Cr(VI) by humic
substances was faster than the rate of oxidation of Cr(lll) by
dissolved oxygen. While studying the Columbia River,
Cranston and Murray (5) observed that 98 percent of the
chromium was in the hexavalent form. An interesting
transport study by Canter and Gloyna (6) revealed that
hexavalent chromium predominated in the non-polluted
river but was reduced to the trivalent form when exposed to
organic pollution. Schroeder and Lee (7) studied chromium
speciation in simulated natural waters and reported that
Cr(VI) was reduced by divalent iron [Fe(ll)], dissolved
sulfides, and certain organic compounds with sulfhydryl
groups. They also noted that Cr(lll) was oxidized by a large
excess of manganese dioxide (MnOa) at a slower rate by
oxygen under conditions approximating those in natural
waters. The factors controlling chromium speciation in
natural waters were summarized by Florence and Batley (1)
as follows:
1. oxygen content and redox potential of the water,
2. presence of dissolved or paniculate organic matter,
and
3. presence of suspended inorganic matter.
Chromium speciation m biological systems has also been
investigated during the last decade. Trivalent chromium
appears to be the predominant species in cells, and its
essential role in maintaining glucose, lipid, and protein
metabolism in mam ma Man systems has been reported (1, 8,
9). Hexavalent chromium, however, appears to diffuse
through cell membranes, oxidize, and then bind with other
biochemical molecules to produce carcinogenic and muta-
genic effects (1, 9).
Cognizant of these of these previous studies, reporting the
toxicity of hexavalent chromium and the conversion
potential of trivalent chromium in nature, the U.S. Envi-
ronmental Protection Agency (EPA) has been reviewing the
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applicability of the current drinking water regulation for
chromium. The advisability of changing the regulation from
a single maximum contaminant level (MCL) basis (total
chromium concentration) to a dual MCL basis (separate
MCL for each of the two valence states) is being considered
(10). To provide a fuller understanding of the potential
trivalent chromium conversion to hexavalent chromium
during and after drinking water treatment, two research
investigations of the effects of chlormation on chromium
speciation in water were conducted. One study, performed
extramurally by Clifford and Chau (11), investigated the
effects of chlorination on chromium speciation in natural
waters and other matrices containing sodium chloride
(NaCI), ammonia (NH3) and humics. A report of this study is
in preparation. Another study was conducted mhouse to
determine the effects of 2 mg/L free residual chlorine on
the speciation of 0.5 mg/L Cr(lll) added to Cincinnati tap
water at initial pH levels of 5, 6, 7, and 8. The approach,
observations, conclusions, and recommendations of the
latter study are reported here
Approach
General Study Design
A large aliquot of Cincinnati tap water was collected, and its
free residual chlorine (FRC) concentration was adjusted to
approximately 2 mg/L. Two 1 -L aliquots of this chlorine-
adjusted tap water were transferred to 1 -L cubitamers and
forwarded to the laboratory for physical and chemical
characterization (alkalinity, arsenic, barium, cadmium,
calcium, chloride, total chromium, color, specific conduc-
tance, copper, fluoride, iron, lead, magnesium, manganese,
mercury, pH, total filterable residue or total dissolved solids,
selenium, silver, sodium, sulfate, turbidity and zinc).
Four exposure study test solutions were prepared by
transferring 2-L aliquots of chlorine-adjusted tap water to
individual containers, adjusting the pH levels to pH 5, 6, 7,
and 8, respectively, adding sufficient Cr(lll) to achieve an
approximate concentration of 0.5-mg/L and then quickly
readjusting the pH levels as necessary. Each of the four test
solutions was then divided into two portions. The first liter
was labeled "initial sample" and immediately subjected to
analysis for alkalinity, total and hexavalent chromium, FRC,
pH, and TOC. The second portion of each of the test
solutions was transferred to an individual 1-L, ground-
glass-stoppered bottle, labeled "final sample," and set
aside in the dark at room temperature for about 24 hr before
analyses were initiated for dissolved oxygen and the
aforementioned six characteristics. The details of the
sample collection and preservation, reagent and test
solution preparation, and analytical methodology are
presented in the following section.
Analytical Approach
The study of the effect of chlorine on the speciation of
chromium in Cincinnati tap water was conducted us ing the
facilities, materials, and equipment of the Inorganics and
Paniculate Control Branch, Drinking Water Research
Division, Water Engineering Research Laboratory.
Reagents, Equipment, and Analytical Methods-
were first cleaned using 1.1 nitric acid (HNOa) and then
rinsed liberally with deionized distilled water All test
solutions and analytical reagents were prepared using
A C.S. reagent grade chemicals and deionized distilled
water unless otherwise specified All samples were col-
lected, preserved, and analyzed according to the specifica-
tions in the analytical methods cited in Table 1.
Preparation of Test Solutions—
The preparation of the special test solutions for the exposure
study was initiated by filling a 5-gal Nalgene®* jug with
Cincinnati tap water (pH ~8 05). Sufficient saturated
chlorine solution, freshly prepared by bubbling gaseous
chlorine into deionized distilled water, was immediately
added to the jug contents to raise the FRC concentration
from 1.37 to 2.04 mg/L. Both FRC levels were determined
amperometrically using the Penwalt Wallace & Tiernan
Series A790 Titrator Four 2-L aliquots of this chlorine-
adjusted Cincinnati tap water were transferred from the
5-gal jug to individual 3-L beakers, and the pH levels were
quickly adjusted to pH 5, 6, 7, and 8, respectively, using
either 1 N sulfunc acid (H2SO.t) or 1 N sodium hydroxide
(NaOH) All pH measurements were performed using an
Orion Model 801 Research lonalyzer pH Meter equipped
with a Metrohm Model AG91 00 combination pH electrode
and calibrated using fresh prepared Beckman Altex pH 4
and 6.86 buffers. Then 20 mL of a freshly prepared
chromium chloride (CrCI3) solution containing 50 mg/L
Cr(lll) was added to each 2-L aliquot, and any additional pH
adjustment required to maintain the pH 5, 6, 7, or 8 levels
was quickly made using 1 N H2S04 or 1 N NaOH. The
increase in each solution volume with the addition of
chromium solution and pH adjustment solution was < 1.05
percent and neglected in subsequent calculations.
Total Chromium Analyses—
All analyses for total chromium were performed by
flameless atomic absorption technology using a Perkm
Elmer Model 4000 Atomic Absorption Spectrometer,
equipped with a Perkm Elmer Model 400 HGA Furnace,
AS-40 Autosampler, background corrector, chromium
hollow cathode lamp, nonpyrolyzed graphite tubes, argon
gas, a 357 9-nm wavelength, and a 0.7-nm slit. The
procedural steps and operating conditions are presented in
Table 2. The instrument was calibrated using six standard
solutions containing 0, 5, 25, 50, 75, and 1 00 /ug/L Cr(VI)
These were prepai ed by appropriate dilution of aliquots of a
stock Cr(VI) solution (0.1414 g K2Cr2O7/L) and preserved
with 1.5 mL concentrated HNOa/L. After electrothermal
atomization, the absorption response of a 20-fjL aliquot of
each of the six solutions was observed, and a calibration
plot relating absorption response and Cr(VI) concentration
was prepared. The total chromium concentration of each
initial and final test solution sample was then determined
by electrothermally atomizing 20 fj\- of a 1.5 dilution
thereof, observing the absorption response, deriving the
corresponding chromium concentration from the calibration
plot, and multiplying by the appropriate dilution factor.
During the exposure study of the four test solutions and all
the related analyses, the laboratory glass and plastic wares
*Mention of trade names or commercial products does not constitute
endorsement or recommendation for use
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Table 1. Analytical Methods Used in Sample Analysis
Characteristic Method
Reference
Comments
Alkalinity
Arsenic
Barium
Cadmium
Calcium
Carbon, total organic
Chloride
Chlorine, free residua/
Chromium, total
Chromium, hexavalent
Chromium, tnvalent
Color
Conductance, specific
Copper
Fluoride
Iron
Lead
Magnesium
Manganese
Mercury
Oxygen, dissolved
pH
Residue, total filterable
(total dissolved solids)
Selenium
Silver
Sodium
Potentiometnc
Flame/ess atomic absorption
Atomic absorption, direct asp/rat/on
Flameless atomic absorption
Atomic absorption, direct aspiration
UV promoted, persulfate oxidation
Potentiometnc, modified
Amperometnc tit ration
Flameless atomic absorption
Revised diphenylcarbazide
color/metric
Calculation
Visual comparison
Wheatstone bridge
Atomic absorption, direct aspiration
Complexone
Atomic absorption, direct aspiration
F/ameless atomic absorption
Atomic absorption, direct aspiration
Atomic absorption, direct aspiration
Manual cold vapor
Membrane electrode
Electrometr/c
Gravimetric
Flameless atomic absorption
Atomic absorption, direct aspiration
Atomic absorption, direct aspiration
SM 403* Automatic titration to carbonate equivalence
point
EPA 2062**
EPA 208 1 NaCI substituted for KCI in reagents
EPA 21 3 2 Instrumental parameters modified
EPA 215 1
SM(1 6) 505B\ With DC 54 Xertex Dohrmann instrument
SM407C Automatic titration using silver, specific ion
electrode
SM 408C
EPA 218 2
SW7196U With standard additions^
Difference between total and hexavalent
chromium
SM 204A With Hellige glass reference discs
EPA 120 1
EPA 220 1
SM413E
EPA 236 1
EPA 239 2
EPA 242 1
EPA 243 1
EPA 245 1
EPA 360 1
EPA 1 50 1
SM 209C
EPA 2702
EPA 272 1
EPA 273 1
SM 325B
Sulfate
Turbidimetnc
EPA 3754
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Table 1. (Continued)
Characteristic Method
Reference
Comments
Turbidity
Zinc
Nephelometric
EPA 180 1
Atomic absorption, direct aspiration EPA 289 1
*SM refers to American Public Health Association, American Water Works A ssociation, and Water Pollution Control Federation Standard
Methods for the Examination of Water and Wastewater 15th edition, unless otherwise specified American Public Health Association,
Washington, DC 1981
**EPA refers to Environmental Monitoring and Support Laboratory Methods for Chemical Analysis of Water and Wastes EPA/600/4-
79/020 US Environmental Protection Agency, Cincinnati, OH March 1983
\SM(16) refers to previously cited SM reference, but 16th ed, 1985
ttSW refers to Office of Solid Waste and Environmental Response Test Methods for Evaluating Solid Waste Physical/Chemical Methods
SW-846 2nd ed US Environmental Protection Agency, Washington, DC July 1982
§See discussion in Trace Analysis, Spectroscopic Methods for Elements J W Wmefordner, ed Vol 46 of Chemical Analysis JohnWiley
& Sons, New York, NY 1946 pp 41-42.
Table 2.
Conditions for Electrothermal Atomization of
Chromium
Step
No
1
2
3
4
Temp
1C)
100
130
WOO
2700
Ramp Time
(sec)
10
2
10
1
Holding
Time
(sec)
10
20
30
6
Argon Flow
Setting
Regular
Regular
Mm if low
Miniflow
Hexavalent Chromium Analyses—
The hexavalent chromium content of each initial and final
test solution was determined by applying the standard
additions technique to the revised diphenylcarbazide
color!metric procedure (see Table 1). Three 100-mL aliquots
of each initial sample and three 50-mL aliquots of each final
sample were processed. To the second and third aliquots in
each set of three were added 0.5 and 1.0 mL, respectively,
of a 4-/jg/mL hexavalent chromium (K2Cr207) solution. The
effective Cr(VI) levels in the second and third aliquots of the
initial and final samples were consequently 0.02 and 0.04
mg/L and 0.04 and 0.08 mg/L, respectively. All aliquots
were then diluted to 101 mL, 2 mLof color reagent (250 mg
1,5-diphenylcarbazide in 50 mL A.C.S. reagent grade
acetone) was added, and the pH was adjusted to 2 0 with
50% sulfunc acid (required volume < 0.5 mL). The
absorbance of each processed aliquot was determined after
1 5 min against that of a reagent blank at 540 nm using a
Beckman B Spectrophotometer equipped with a matched
set of 5-cm cells. The absorbances of each set of three
aliquots were then plotted versus the corresponding
amounts of added Cr(VI) and the linearity of the plot
checked. The Cr(VI) concentration of each test sample was
then calculated by a linear regression analysis of the data
and checked by graphical extrapolation.
Quality Assurance
All laboratory analyses were conducted using the control
measures recommended in the EPA's analytical quality
control manual (12). Accuracy was periodically evaluated
by determining the percent recovery of analyte from
reference samples or from test samples spiked with known
quantities of analyte. Precision was similarly determined
periodically by replicate determinations of analyte, sample
volume permitting. Appropriate Shewhart control charts
and limits were established and maintained
Results and Discussion
Total and Hexavalent Chromium Method
Evaluation and Quality Control
Before initiating the study of the effect of chlorine on the
speciation of chromium in Cincinnati tap water, the
applicability of the methods for determining hexavalent and
total chromium was evaluated First applied was EPA
method 218.5 (13), a flameless atomic absorption technique
for determining dissolved hexavalent chromium after
coprecipitation. Unfortunately, the time this approach
required to isolate and wash the coprecipitate of lead
chromate/lead sulfate exceeded 1 hr. Consequently, the
chlorine action on the trivalent chromium could not be
stopped with sufficient speed or control. The timing of the
diphenylcarbazide colonmetric method for hexavalent
chromium (14), however, proved to be satisfactory, since
only 1 5 to 30 mm elapsed between sample aliquotmg and
initiation of color development. The absorbance of the
developed color, however, was dependent on the concen-
tration of free residual chlorine. A study of samples
containing 0.05 mg/L Cr(VI) in the presence of 0, 0.5, 1.0,
and 2.1 mg/L FRC revealed a 5% color depression with 1
mg/L chlorine and a significant 15% color depression with
2 1 mg/L chlorine. Since the 2-mg/L FRC contents of the
proposed study test solutions might decrease variably with
the degree of reaction with the trivalent chromium, the
method of standard additions, as outlined previously, was
applied to the colorimetric procedure to ensure accurate
hexavalent chromium observations. Solutions containing
0.05 mg/L Cr(VI) in the presence of 0, 0 5, 1.0, and 2.1
mg/L FRC were analyzed to verify the applicability of this
approach The chromium additions to the second and third
sample aliquots in each analysis set were equivalent to
0 10 and 0.20 mg/L, respectively. In each case the observed
hexavalent chromium concentration was 0.05 mg/L. The
accuracy of the approach was thus validated. A solution
containing 0 5 mg/LCr(lll)was also subjected to hexavalent
-------
chromium analysis using the standard additions approach
with the colorimetric procedure. The Cr(VI) additions to the
second and third sample aliquots in this analysis set were
equivalent to 0.02 and 0.04 mg/L, respectively. The
observed hexavalent chromium concentration was 0.0008
mg/L, and confirmed both the specificity of the hexavalent
chromium method and the trivalent chromium speciation in
the CrCh used in preparing the study test solutions.
A flameless atomic absorption technique, EPA method
218.2 (12), was used for determining total chromium. Two
reference solutions were analyzed—EPA No. WS12-1 and
U.S. Geological Survey No. 77 with theoretical chromium
concentrations of 14.3 and 20.3 jug/L, respectively. The
total chromium observations were 15.1 and 20.6 ug/L,
respectively, while the corresponding percent recoveries
were 105.6 and 101.5. The precision of the test solution
preparation [Cr(lll) addition] and the total chromium anal-
yses were evaluated together by determining the total
chromium in the initial and final aliquots of each of the four
study test solutions The mean (M) total chromium concen-
tration was 0.464 mg/L with a standard deviation (s) of ±
0.01 2 mg/L and a coefficient of variation (s/M) of 0.0259.
Influence of Chlorine on Chromium Speciation
The character of the chlorine-adjusted Cincinnati tap water
used in preparing the four test solutions in this study is
presented in Table 3. The analyses revealed that the tap
water had a low alkalinity, chloride, and sulfate, and a pH
above neutral. The primary and secondary inorganic
constituent levels were below the maxim limits specified in
the drinking water regulations.
Table 3. Characterization of Chlorine-Adjusted Cincinnati
Tap Water
Characteristic*
Alkalinity (as CaCOJ
Arsenic
Barium
Cadmium
Chloride
Chlorine, free residual
Chromium, total
Color, c.u.
Conductance, specific.
umhos/cm at 25°C
Copper
Fluoride
Iron
Lead
Magnesium
Manganese
Mercury
pH, units
Residue, total filterable
(total dissolved solids)
Selenium
Silver
Sodium
Sulfate
Turbidity, n t u
Zinc
Observation
36.0
< 0 0005
0.25
< 0002
20 1
204
< OOO5
2
290
< 0.02
0.9
< 0.1
< 0005
7 11
< 003
< 0 0005
a. 05
175
< 0.05
< 0.03
11.
58.
0.08
< 0.02
The character of the four initial and final test solutions is
presented in Table 4. The analyses revealed that the 36.0
mg/L alkalinity level of the chlorine-adjusted tap water was
altered by the final pH adjustment after the Cr(lll) addition
The alkalinity levels of the four initial test solutions with pH
levels adjusted to 5, 6, 7, and 8 were 0,13.6, 30 4, and 36.5
mg/L, respectively. During the subsequent 24-hr exposure
study, these alkalinity levels were not altered significantly,
however. The mean TOC level of the four initial test
solutions was 1.57 ±002 mg/L; it increased slightly to
1.70 ± 0.07 mg/L during the test. This 8-percent increase
probably reflects sampling and analytical variation. The
dissolved oxygen (DO) analyses were performed only on the
final four test solutions because of instrumental mal-
function. In each case, the observed final DO approximated
the aqueous saturation level for the test temperature and
pressure. Thus little, if any, oxygen consumption appears to
have occurred during the test.
FRC, however, declined in each of the four test solutions
during the 24-hr exposure The concentration decreases
ranged from 0.44 to 0.79 mg/L, with changes > 0.65 mg/L
in those solutions with initial pH levels < 6.0
The chromium analyses revealed that the oxidation of
trivalent chromium to hexavalent chromium definitely
occurred in the test solutions prepared from Cincinnati tap
water containing 2 04 mg/L FRC and 0.464 ± 0.01 2 mg/L
Cr(lll) with initial pH levels of approximately 5, 6, 7, and 8.
Because of the time elapsed between initiation of the test
solution exposures and color development in the hexavalent
chromium analyses, the initial and final hexavalent obser-
vations actually represent the 1/2- and 24-hr levels. The
Cr(VI) concentrations in the four initial test solutions were
all low, ranging from 0.007 to 0 019 mg/L. In the 24-hr test
solutions, however, the Cr(VI) levels were more significant
and ranged from 0.094 to 0 1 99 mg/L. The percent Cr(lll)
conversion to Cr(VI) appeared to vary with the initial pH of
the solution (Figure 1) In the 24-hr test solutions with the
initial pH levels of 6 and 8, the observed maximum and
minimum conversions were 43.4 and 20 9%, respectively
Chromium oxidation by chlorine has also been observed by
other investigators. In 1978, Toyama et al. (15) reported
observing the formation of hexavalent chromium in solu-
tions initially containing 10 mg/L Cr(lll) and 20 mg/L
Figure 1. Percent Cr(lll) conversion to Cr(VI) in Cincinnati
tap water containing 0 5 mg/L Cr(lll) and 2.04
mg/L FRC.
"Unit is mg/L unless otherwise noted.
5678
Test Solution Number (Initial solution pH)
5
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Table 4. Periodic Characterization of Test Solutions
Test
Solution
No.
5
6
7
8
Sampling Period
Initial
X
X
X
X
Final
X
X
X
X
pH
499
4.15
603
595
699
6.39
804
7.30
Free Residual
Chlorine
Img/L)
204
1 25
2.05
1.40
2.04
1 60
204
1 59
Total
Cr
0482
0.476
0470
0459
0464
0466
0.447
0.450
Cr(VI)
Img/L)
0007
0126
0.019
0 199
0017
0 139
0012
0094
Alkalinity
fmg CaCOa/L)
0
0
136
132
30.4
29.6
365
36.4
Total
Organic Carbon
Img/L)
1.56
1.65
1.61
1 65
1.56
1.70
1.54
1.80
Dissolved
Oxygen
Img/L)
9.4
9.4
96
95
'Each test solution was originally spiked with 0.5 mg/L Cr(lll)
chlorine (added as sodium hypochlorite) and having pH
levels ranging from < 1 to 1 3 After 2.5 hr, the Cr(VI) levels
varied from 01 to 1.35 mg/L, the highest level being
observed in the solution with an initial pH of 7. Clifford and
Chau (11) have just completed an extensive study of the fate
of chromium in chlorinated water and will soon be reporting
the conversion of Cr(lll) and Cr(VI) in various aqueous
solutions with pH levels ranging from 5 to 10.3.
Although the effects of chlorine on the speciation of
chromium in aqueous solutions have been observed by
several investigators, chlorine apparently has not been
included as a factor in the various diagrams or models of
chromium speciation. In a recent summary of the thermo-
dynamic properties and environmental chemistry of chro-
mium, Schmidt (16) presented a number of illustrations of
the distribution of chromium species at various pH and
redox potential (pE) levels He indicated that the pE/pH
diagram, reproduced here as Figure 2, predicts many, but
not all, of the previously reported chromium speciation
observations in natural waters. He emphasized that some
of the occurrences of chromium species resulted from
chromium complexation and reduction by organic matter,
adsorption and oxidation by manganese oxides in sus-
pended matter, and reduction by hydrogen sulfide (H2S)
Consequently, Schmidt introduced a modified model (Figure
3) to demonstrate the influence of these factors on
chromium speciation in the environment. He further
reported the i ncorporat ion of the chromium thermodynamic
data into the geochemical computer model MINTEQ,
currently being developed by his colleagues at Battelle
Pacific Northwest Laboratory. Perhaps a model for the
speciation of chromium in chlorinated drinking water could
possibly be derived by incorporating the appropriate
chlorine thermodynamic data into this program.
Conclusions and Recommendations
This investigation has demonstrated that trivalent chro-
mium can be oxidized to hexavalent chromium in a tap
water with a low alkalinity, chloride, sulfate, and TOC
content In test solutions with initial pH levels rang ing from
5 to 8, the quantity of Cr(VI) formed from 0 464 mg/L Cr(lll)
Figure 2. pE-pH diagram of aqueous inorganic Crspeciesat
total Cr concentrations of 1 0 8 M (reprinted with
permission, see reference 16).
15
10
10
(Cr)T= 1Cr8M
Cr202(c)
10
12
pH
in 24 hr ranged from 0.094 to 0.199 mg/L (20.9 to 43.4
percent conversion).
Our knowledge and understanding of the conditions under
which trivalent chromium oxidizes to hexavalent chromium
in aqueous solutions containing free residual chlorine
might be enhanced by the incorporation of appropriate
chlorine thermodynamic data into the MINTEQ program
and the development of a model for chromium speciation in
the presence of FRC.
Acknowledgments
Gratitude is expressed to Tom Sorg, Chief, Inorganic and
Paniculate Control Branch, for his encouragement and
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Figure 3. Model of processes controlling the distribution of
Cr in the environment (reprinted with permission,
see references 16 and 17).
Organisms,
Organic Matter
////////////////////////////////T////
Sediment (Soil)
technical suggestions. The author also greatly appreciates
the analytical assistance of Jim Caldwell, William Chaney,
Carl Shadix, and Lou Trombly, all of the aforementioned
Branch. Thanks are also expressed to Brad Smith, Organics
Control Branch, for conducting the TOC determinations.
References
1. Florence, T. M., and Batley, G. E Chemical Speci-
ations in Natural Waters. CRC Critical Reviews in
Analytical Chemistry. 9(3)'262-263, 1980.
2 Bartlett, R , and James, B Behavior of Chromium in
Soils- III Oxidation. J. Environ. Qua/. 8(1}:31-35,
1979
3. Robertson, F. N. Hexavalent Chromium m the Ground
Water in Paradise Valley, Arizona. Ground Water
13(6)-51 6-527, Nov./Dec. 1975.
4. Osaki, S., Osaki, T., and Takashima, Y. Distribution of
Total and Hexavalent Chromium in the Muromi River.
Nippon Kagaku Kaishi. 111800-1801, 1980.
5. Cranston, R. E , and Murray, J W. Chromium Species
in the Columbia River and Estuary. Limnol. Oceanogr.
25(6)-1104-1112, 1980
6. Canter, L. W., and Gloyna, E. F. Transport of
Chromium-51 in an Organically Polluted Environ-
ment. In: Proceedings, 23rd Industrial Waste Con-
ference, Purdue University, May 7-9, 1968. Part I pp.
374-387, 1969.
7. Schroeder, D. C., and Lee, G. F Potential Transforma-
tions of Chromium m Natural Waters. Water. Air, and
Soil Pollution 4:355-365, 1975.
8 Shamberger, R. T. Beneficial Effects of Trace Ele-
ments. In: F. W. Oehme(ed.),Toxicityof HeavyMetals
m the Environment. Part 2 New York, Marcel Dekker,
Inc., 1979, pp 690-691.
9 Norseth.T Health Effects of Nickel and Chromium.//?.
E. DiFerrante (ed ), Trace Metals, Exposure and Health
Effects New York, Pergamon Press, 1979, pp. 135-
141
10 Environmental Protection Agency. National Primary
Drinking Water Regulations. Part IV. Synthetic
Organic Chemicals, Inorganic Chemicals and Micro-
organisms; Proposed Rule. Federal Register. 50(219)
46967, Wed., Nov. 13, 1985.
11 Clifford, D.,andChau, J. M.The Fate of Chromium(lll)
in Chlorinated Waters USEPA Cooperative Agree-
ment No. CR807939 (m preparation), Water Engi-
neering Research Laboratory, Office of Research and
Development, U.S. Environmental Protection Agency,
Cincinnati, Ohio.
12. Environmental Monitoring and Support Laboratory.
Handbook for Analytical Quality Control in Water and
Wastewater Laboratories, EPA/600/4-79/01 9. U.S
Environmental Protection Agency, Cincinnati, Ohio,
March 1979, pp. 6/1-14.
13. Environmental Monitoring and Support Laboratory
Methods for Chemical Analysis of Water and Wastes
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