ORNL
Oak Ridge
National
Laboratory
Operated by
Union Carbide Corporation for the
Department of Energy
Oak Ridge, Tennessee 37830
EPA
United States
Environmental Protection
Agency
Office of Research and Development
Health Effects Research Laboratory
Cincinnati, Ohio 45268
EPA-600/1-78-026
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-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3 Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL HEALTH EFFECTS RE-
SEARCH series. This series describes projects and studies relating to the toler-
ances of man for unhealthful substances or conditions. This work is generally
assessed from a medical viewpoint, including physiological or psychological
studies. In addition to toxicology and other medical specialities, study areas in-
clude biomedical instrumentation and health research techniques utilizing ani-
mals — but always with intended application to human health measures.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
-------
ORNL/EIS-106
EPA-600/1-78-026
June 1978
Contract No. W-7405-eng-26
REVIEWS OF THE ENVIRONMENTAL EFFECTS OF POLLUTANTS: IV. CADMIUM
by
Anna S. Hammons, James Edward Huff, Helen M. Braunstein,
John S. Drury, Carole R. Shriner, Eric B. Lewis,
Bradford L. Whitfield, and Leigh E. Towill
Information Center Complex, Information Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee 37830
operated by
Union Carbide Corporation
for the
Department of Energy
Technical Reviewer
Ernest C. Foulkes
University of Cincinnati
Cincinnati, Ohio
Interagency Agreement No. D5-0403
Project Officer
Jerry F. Stara
Office of Program Operations
Health Effects Research Laboratory
Cincinnati, Ohio 45268
June 1978
Prepared for
HEALTH EFFECTS RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
-------
Printed in the United States of America. Available from
National Technical Information Service
U.S. Department of Commerce
5285 Port Royal Road, Springfield, Virginia 22161
Price: Printed Copy $11.00; Microfiche $3.00
This report was prepared as an account of work sponsored by an agency
of the United States Government. Neither the United States Government nor
any agency thereof, nor any of their employees, contractors, subcontractors,
or their employees, makes any warranty, express or implied, nor assumes any
legal liability or responsibility for any third party's use or the results
of such use of any information, apparatus, product or process disclosed in
this report, nor represents that its use by such third party would not
infringe privately owned rights.
This report has been reviewed by the Health Effects Research Laboratory,
U.S. Environmental Protection Agency, and approved for publication. Approval
does not signify that the contents necessarily reflect the views and policies
of the U.S. Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation for use.
-------
CONTENTS
Figures v
Tables ix
Foreword xvi
Acknowledgments xvii
Abstract xix
1. Summary 1
1.1 Discussion of Findings 1
1.2 Conclusions 4
2. Physical and Chemical Properties and Analysis 6
2.1 Summary 6
2.2 Physical Characteristics 7
2.3 Chemical Characteristics 8
2.3.1 Cadmium in Air 8
2.3.2 Cadmium in Water 10
2.3.3 Cadmium in Soils 22
2.3.4 Cadmium in Biological Systems 26
2.4 Analysis for Cadmium 27
2.4.1 Considerations in Analysis 27
2.4.2 Analytical Procedures 28
2.4.3 Comparison of Analytical Methods 38
3. Biological Aspects in Microorganisms 50
3.1 Summary 50
3.2 Metabolism 50
3.2.1 Bacteria 50
3.2.2 Yeast 51
3.2.3 Plankton 51
3.3 Effects 51
3.3.1 Bacteria 51
3.3.2 Algae 53
3.3.3 Protozoa 54
3.3.4 Fungi 54
4. Biological Aspects in Plants 58
4.1 Summary 58
4.2 Metabolic Processes 58
4.2.1 Uptake and Absorption 58
4.2.2 Translocation, Distribution, and Accumulation .... 67
4.2.3 Elimination 80
4.3 Effects 80
5. Effects of Cadmium on Aquatic Animals and Birds 90
5.1 Summary 90
5.2 Fish and Other Aquatic Organisms 90
5.2.1 Metabolism 90
5.2.2 Effects 95
5.3 Birds 101
5.3.1 Metabolism 103
5.3.2 Effects 108
6. Effects on Terrestrial Mammals Including Man 113
6.1 Summary 113
6.2 Metabolism 114
iii
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IV
6.2.1 Uptake and Absorption 114
6.2.2 Transport and Distribution 119
6.2.3 Excretion 125
6.2.4 Biological Half-Time 128
6.2.5 Normal Levels 129
6.2.6 Blood, Urine, and Feces as Indicators of
Body Burden 134
6.3 Effects 134
6.3.1 Mechanisms of Action 134
6.3.2 Toxic Effects 137
7. Environmental Distribution and Transformation 170
7.1 Summary 170
7.2 Trends in Production and Usage 171
7.3 Distribution of Cadmium in the Environment 175
7.3.1 Sources of Pollution 175
7.3.2 Distribution in Air 179
7.3.3 Distribution in Soils 189
7.3.4 Distribution in Water 193
7.3.5 Distribution in Sediments 199
7.4 Environmental Fate 200
7.4.1 Mobility and Persistence in Air 200
7.4.2 Mobility and Persistence in Soil 202
7.4.3 Mobility and Persistence in Water and Sediments . . . 204
7.5 Waste Management 204
8. Environmental Interactions and Their Consequences 217
8.1 Summary 217
8.2 Environmental Cycling of Cadmium 217
8.3 Food Chains 217
8.3.1 Cadmium in Foods 217
8.3.2 Cadmium in Cigarettes 223
8.3.3 Terrestrial Ecosystems 223
8.3.4 Aquatic Ecosystems 227
9. Assessment of the Effects of Cadmium in the Environment 239
9.1 Introduction 239
9.2 Nature, Sources, and Extent of Cadmium Pollution 239
9.2.1 Analytical Problems 239
9.2.2 Domestic Production and Import 240
9.2.3 Uses of Cadmium 240
9.2.4 Flow into the Environment 240
9.3 Cadmium in the Human Food Chain 243
9.4 Toxicity and Health Effects of Cadmium 244
9.5 Standards for Environmental and Occupational Exposures . . . 245
9.6 Environmental Hazards Posed by Present and Projected
Concentrations of Cadmium in the Environment 247
9.7 Research Needs 248
9.7.1 Improvement in Identification and Analysis of
Low Concentrations of Cadmium 248
9.7.2 Development of Measures to Minimize and to
Adequately Dispose of Wastes 248
9.7.3 Further Information Related to Biological Effects . . 249
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FIGURES
2.1 The vapor pressures of cadmium and zinc vs temperature. ... 7
2.2 The solubility of cadmium vs pH at different carbonate
concentrations at 20°C 12
2.3 The distribution of cadmium complexes in solution in the
presence of increasing concentrations of various ligands. . 14
2.4 Rates of sorption of cadmium on hydrated oxides of Mn(IV) ,
Fe(III), and Al(III) 18
2.5 Corrosion of cadmium as a function of pH in carbonate-free
solutions 19
2.6 Effect of total carbonate species concentration on rate of
cadmium corrosion 20
2.7 Effect of external galvanic coupling on rate of cadmium
corrosion 21
2.8 Diagrammatic representation of a silicate clay crystal. ... 23
2.9 Percent 109Cd retained by montmorillonites in 0.01 M
Ca(N03)2 23
2.10 Adsorption of cations by humus colloids 24
2.11 Influence of pH on the cation exchange capacity of
montmorillonite and humus 25
2.12 Fitting a two-site mechanism to observed complexing of
Cd2+ by captina humic acid 26
2.13 Correlation of absorbency with concentration of cadmium and
of silver-titratable mercapto groups 27
3.1 Effect of cadmium concentration on li'C02 evolution by
Esaheriahia coli (108 cells) 53
3.2 Growth rate of Selenastnm eapricornutim as a function of
cadmium concentration in culture medium 54
4.1 Mean cadmium concentrations in radish tops and roots grown on
unlimed (pH 4.1) and limed (pH 5.5) soils containing various
concentrations of added cadmium 60
4.2 Cadmium content of plants grown in 200 mg cadmium per
1000 g soil 69
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vi
4.3 Uptake of 109Cd by fescue grass and by three species of mosses
following application as CdCl2 in simulated rainfall .... 72
4.4 Uptake of 109Cd by fescue grass and by three species of mosses
following application as CdO in simulated rainfall 73
5.1 Toxicity of cadmium in hard water to rainbow trout 98
5.2 Uptake of 109Cd by chipping sparrows (feeding on tagged bird
seed) 103
5.3 Biological turnover of 109Cd by chipping sparrows following
21 days of feeding on tagged bird seed 104
6.1 Fraction of particles deposited in the three respiratory
tract compartments as a function of particle diameter. . . . 115
6.2 Concentrations of cadmium in plasma and blood cells in mice
given a single subcutaneous injection of 109CdCl2 and
killed various times after injection 120
6.3 Whole-body retention of 115mCd in rats following a single
exposure by different routes of administration 129
6.4 Cadmium content in renal cortex as a function of age,
exposure, and geographical location 131
6.5 Cadmium content in liver as a function of age, exposure,
and geographical location 132
6.6 Cadmium content in renal cortex as a function of age and
geographical location 133
6.7 Effect of oral cadmium administration on milk production of
lactating holstein cows 138
7.1 Schematic flowsheet for recovery of cadmium as a by-product
of zinc and lead recovery 172
7.2 Societal flow of cadmium in the United States, 1968 173
7.3 Rates, routes, and reservoirs of cadmium in the environment. . 179
7.4 Location of U.S. deposits of lead, lead-zinc, and zinc-
lead ore 180
7.5 Location and approximate outputs (1968) of major U.S. zinc
production mines 180
7.6 Surface geochemical cycle of cadmium 201
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vii
8.1 Cadmium concentrations of surface waters, soils, and foods
and estimated dose levels resulting in various symptoms
and effects in humans 218
8.2 Cadmium content in various food samples collected in
October 1968 and June 1969 in Annaka City, Japan, compared
with unpolluted samples 222
8.3 Generalized food web for man showing cadmium introduction
and movement 223
8.4 Cadmium concentration in cigarettes of different ages 224
8.5 Metal cadmium concentrations (ppm dry weight) in selected
trophic levels of a deciduous forest ecosystem in East
Tennessee 227
8.6 Mean activity in stream ecosystem components after labeling
with 109CdCl2 234
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TABLES
2.1 Some properties of cadmium and its important compounds .... 9
2.2 Solubility products of various compounds 11
2.3 Stepwise formation constants of various cadmium complexes. . . 12
2.4 Effect of chloride concentration on solubility of cadmium
precipitates 16
2.5 Percent recovery of metal salts from platinum crucibles after
heating at various temperatures for one hour 28
2.6 Comparison of atomic absorption spectroscopy results on
New York City particulate sample on filter paper prepared
by wet digestion and dry ashing 30
2.7 Commonly used instrumental methods for the analysis of
cadmium 33
2.8 Interlaboratory study on trace level analysis of cadmium by
atomic absorption spectrometry 40
2.9 Composition of water metals sample used in interlaboratory
comparison 41
2.10 Summary of interlaboratory data on manganese, silver, and
cadmium analyses of water samples 42
2.11 Comparison of cadmium concentrations in coal, fly ash, fuel
oil, and gasoline by analytical method and by laboratory . . 43
3.1 Cadmium concentrations causing toxicity to various
microorganisms 52
4.1 Estimates of cadmium concentrations in some plant tissues. . . 59
4.2 Concentrations of 109Cd in Japanese millet derived from two
chemical forms of cadmium at three levels of calcium
carbonate 61
4.3 Correlation coefficients between levels of cadmium and levels
of other elements in the same plant part 62
4.4 Cadmium content of pasture species from adjacent fertilized
and unfertilized pastures 64
4.5 Influence of cadmium contamination of soil on cadmium content
of various parts of eight crops 65
ix
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X
4.6 Distribution of cadmium in cereal plants grown in pot
culture 66
4.7 Cadmium content of and uptake by vegetable species grown in
pot culture 68
4.8 Extractable cadmium and zinc contents of roadside soil and
vegetation as a function of distance from traffic and depth
in the profile 71
4.9 Cadmium content of woody plants growing in New Haven,
Connecticut 74
4.10 Concentrations of cadmium in components of a spruce forest in
central Sweden polluted by a local industrial source .... 75
4.11 Distribution of cadmium in the components of aboveground
biomass in Calluna and Eriaa ecosystems 76
4.12 Mean cadmium concentrations in tree, shrub, and grass samples
from six vegetation-type areas in Missouri 78
4.13 Mean cadmium concentrations and ash yields in tree and shrub
samples from mineralized areas in Colorado 79
4.14 Phytotoxic effects exerted by cadmium on seedling plants of
economic importance in Illinois 81
4.15 Cadmium concentrations in nutrient solutions producing 50%
growth reduction in some crops 81
4.16 Effect of cadmium contamination of soil on yield of various
parts of eight crops 82
5.1 Cadmium uptake by marine organisms 91
5.2 Distribution of cadmium in organs of rainbow trout reared in
cadmium solution (0.0048 ppm) 92
5.3 Cadmium concentrations in bluegill tissues after an 11-month
chronic exposure 93
5.4 Average cadmium concentrations in fish from upper Clark Fork
River in western Montana 94
5.5 Cadmium levels in organisms from the Illinois River 95
5.6 Acute doses of cadmium from some aquatic organisms 96
5.7 Cadmium toxicity to some aquatic organisms 97
5.8 Chronic toxic effects of cadmium to aquatic organisms 99
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xi
5.9 Cadmium toxicity to fiddler crabs as a function of salinity
and temperature 100
5.10 Comparison of the acute toxicity of a copper, cadmium, and
zinc mixture with that of individual metals to fathead
minnows 101
5.11 Spawning and hatching success of fathead minnows at various
concentrations of copper, cadmium, and zinc 102
5.12 Percentages of whole-body cadmium in chickens at sacrifice. . 105
5.13 Cadmium residues in starlings in the United States, 1971. . . 106
5.14 Concentrations of cadmium in livers of eight adult puffins
from the British Isles 108
6.1 Cadmium levels in organs of Finnish males and females at
autopsy 122
6.2 Tissue distribution of 109Cd 14 days after oral or intra-
venous administration to goats 124
6.3 Cadmium excretion in urine of normal, unexposed individuals . 125
6.4 Cadmium in hair from boys living in urban areas 127
6.5 Cadmium concentration in whole blood from "normal" persons
and exposed workers 130
6.6 Cadmium and zinc values in human liver and kidney 136
6.7 Concentrations of cadmium in kidney cortex of workers exposed
to cadmium oxide dust in relation to morphological kidney
changes seen at autopsy or biopsy 142
6.8 Zinc and cadmium concentrations in water and snow 145
6.9 Changes in glutamic oxaloacetic transaminase activity
following intravenous injection of cadmium into rabbits . . 147
6.10 Cadmium levels in liver and kidney with respect to lung and
other cancers 149
6.11 Cadmium levels in liver and kidney with respect to lung
cancer and/or emphysema 150
6.12 Cadmium teratogenicity in hamsters 151
6.13 Symptoms of itai-itai disease 153
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xii
7.1 Natural abundance of zinc and cadmium 171
7.2 Projected U.S. demand for cadmium and zinc in 2000 based
on use in 1968 174
7.3 Approximate material balance for cadmium in the United States
in 1968 176
7.4 Cadmium released from various sources in the United States . . 178
7.5 Cadmium concentrations in U.S. urban air, 1969 182
7.6 Nonurban sites showing less than 0.001 yg cadmium per
cubic meter of air in 1969 188
7.7 Cadmium in sedimentary recks 190
7.8 Cadmium in igneous rocks 190
7.9 Cadmium in soils 191
7.10 Cadmium in waters 194
7.11 Cadmium concentrations and flows in selected rivers 195
7.12 Regional summary of cadmium in U.S. surface waters 196
7.13 Locations at which U.S. Public Health Service mandatory
upper limit for cadmium in drinking water was exceeded . . . 197
7.14 Cadmium cycling budget in Walker Branch watershed, Oak Ridge,
Tennessee, 1974 198
7.15 Range of metal contents in digested sewage sludge 206
7.16 Average concentrations of metals in raw sludge 206
7.17 Concentration of cadmium in several industrial sludges .... 207
8.1 Cadmium content and zinc to cadmium ratio in some foods. . . . 220
8.2 Concentrations of cadmium added to field plots as
109Cd(N03)2 in four grassland community food chain
components 225
8.3 Observed retention of cadmium in sediment, shells, and
organisms of a synthetic marine microcosm 230
8.4 Residues of total cadmium in fish from New York State
waters, 1969 231
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xiii
.5 Cadmium in organisms from waters of the Southampton and The
Solent areas of England 233
.6 Distribution of 284 yCi 115mCdCl2 in microcosms 27 days
after tagging 234
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FOREWORD
A vast amount of published material is accumulating as numerous
research investigations are conducted to develop a data base on the
adverse effects of environmental pollution. As this information is
amassed, it becomes continually more critical to focus on pertinent,
well-designed studies. Research data must be summarized and interpreted
in order to adequately evaluate the potential hazards of these substances
to ecosystems and ultimately to public health. The Reviews of the Environ-
mental Effects of Pollutants (REEPs) series represents an extensive com-
pilation of relevant research and forms an up-to-date compendium of the
environmental effect data on selected pollutants.
Reviews of the Environmental Effects of Pollutants: IV. Cadmium
includes information on chemical and physical properties; pertinent
analytical techniques; transport processes to the environment and sub-
sequent distribution and deposition; impact on microorganisms, plants,
and wildlife; toxicologic data in experimental animals including metabo-
lism, toxicity, mutagenicity, teratogenicity, and carcinogenicity; and an
assessment of its health effects in man. The large volume of factual
information presented in this document is summarized and interpreted in
the final chapter, "Environmental Assessment," which presents an overall
evaluation of the potential hazard resulting from present concentrations
of cadmium in the environment.
The REEPs are intended to serve various technical and administrative
personnel within the Agency in the decision-making processes, i.e., in
the development of criteria documents and environmental standards, and
for other regulatory actions. The breadth of these documents makes them
a useful resource for public health personnel, environmental specialists,
and control officers. Upon request these documents will be made available
to any interested individuals or firms, both in and out of the government.
Depending on the supply, the document can be obtained directly by writing
to:
Dr. Jerry F. Stara
U.S. Environmental Protection Agency
Health Effects Research Laboratory
26 W. St. Clair Street
Cincinnati, Ohio 45268
R. J. Garner
Director
Health Effects Research Laboratory
xv
-------
ACKNOWLEDGMENTS
The authors are especially grateful to William Fulkerson, Energy
Division, Oak Ridge National Laboratory, for reviewing preliminary drafts
of this report and offering valuable comments and to Gerald U. Ulrikson,
Manager, Information Center Complex, and Jerry F. Stara, EPA Project
Officer, for providing consistent guidance and support. The efforts of
J. Michael Fielden and Lilabeth S. Cockrum, who collected the bulk of the
literature used in this review, are gratefully acknowledged. Gratitude
is also expressed to Carol A. Brumley and Anita B. Gill, editors, and
Patricia B. Hartman and Donna M. Stokes, typists, for preparing the manu-
script for publication. The authors also appreciate the cooperation of
the Toxic Materials Information Center, the Toxicology Information Response
Center, and the Environmental Mutagen Information Center of the Information
Center Complex.
Appreciation is expressed to Bonita M. Smith, Karen L. Blackburn, and
Donna J. Sivulka for EPA in-house reviews and editing and for coordinating
contractual arrangements. The efforts of Allan Susten and Rosa Raskin in
coordinating early processing of the reviews were important in laying the
groundwork for document preparation. The advice of Walter E. Grube was
valuable in preparation of manuscript drafts. The support of R. John
Garner, Director of Health Effects Research Laboratory, is much appre-
ciated. Thanks are also expressed to Carol A. Haynes and Peggy J. Bowman
for typing correspondence and corrected reviews.
xvii
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ABSTRACT
This report is a comprehensive, multidisciplinary review of the health
and environmental effects of cadmium and specific cadmium derivatives. More
than 500 references are cited.
Background levels of cadmium are typically low. The highest concentra-
tions are most likely found in localized regions of smelters or in industri-
alized urban areas. Cadmium is introduced into the environment mainly during
extraction, refining, and production of metallic cadmium, zinc, lead, and
copper; through the wastes generated during other metallurgical processes
such as electrolytic plating; through the reprocessing of scrap metal such
as cadmium-plated steel; following disposal by combustion; or as solid wastes
from consumer items such as paints, nickel-cadmium batteries, and plastics.
Other sources of cadmium in the environment are cadmium-containing fungicides,
phosphate fertilizers, and municipal sewage sludges.
The cadmium body burden in animals and humans results mainly from the
diet. In the United States, the normal intake of cadmium for adult humans
is estimated at about 50 yg per day. Tobacco smoke is a significant addi-
tional source of cadmium exposure. The kidneys and liver together contain
about 50% of the total cadmium body burden.
Acute cadmium poisoning is primarily an occupational problem, generally
from inhalation of cadmium fumes or dusts. In the general population, inci-
dents of acute poisoning by inhaled or ingested cadmium or its compounds are
relatively rare.
The kidney is the primary target organ for toxicity from prolonged low-
level exposure to cadmium. No causal relationship has been established be-
tween cadmium exposure and human cancer, although a possible link between
cadmium and prostate cancer has been indicated. Cadmium has been shown to
be teratogenic in rats, hamsters, and mice, but no such effects have been
proven in humans. Cadmium has been reported to increase the frequency of
chromosomal aberrations in cultured Chinese hamster ovary cells and in
human peripheral leucocytes. More recent studies on individuals exposed
to cadmium showed no statistically significant difference in the frequency
of chromosomal aberrations from those individuals not exposed to cadmium.
A suggested role of cadmium in cardiovascular disease has not been proven.
The major concern about environmental cadmium is the potential effects
on the general population. There is no substantial evidence of hazard from
current levels of cadmium in air, water, or food. However, because cadmium
is a cumulative poison and because present intake provides a relatively
small safety margin, there are adequate reasons for concern over possible
future increases in background levels.
This report was submitted in partial fulfillment of Interagency
Agreement No. D5-0403 between the Department of Energy and the U.S. Environ-
mental Protection Agency. The draft report was submitted for review in
September 1975. The final report was completed in July 1977.
xix
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SECTION 1
SUMMARY
1.1 DISCUSSION OF FINDINGS
Cadmium is a soft, bluish-silver-white metal which is harder than tin
but softer than zinc; it melts at 321°C and boils at 765°C (Section 2.2).
Cadmium is relatively rare, occurring most commonly as an impurity in the
commercially important zinc ore sphalerite (zinc sulfide) (Section 7.2).
Major uses for cadmium are in electroplating, pigment production, plastics
stabilizers, alloys, and nickel-cadmium batteries. Minor uses include
electrical contact production, curing of rubber, use in fungicides, and use
in solid-state systems (Section 7.2).
Present background levels of cadmium are typically low. For example,
uncontaminated soils contain 0.4 ppm cadmium or less, and many open rural
waters contain less than 1.0 ppb (Section 7.3). Cadmium content of air in
rural or uncontaminated urban areas is usually below detection levels. The
highest concentrations of cadmium are generally found in localized regions
of smelters or in industrialized urban areas. Distribution and concentra-
tions vary with season and distance from the source. In the vicinity of
smelters, soil contains about 10 to 100 ppm; waters near industrial areas
contain about 1 to 100 ppb. Most of the cadmium in natural waters is con-
tained in sediments and suspended particles. Cadmium in urban air varies
from below detectable limits to 0.150 yg/m3 with means usually near 0.005
to 0.015 yg/m3.
Background levels are exceeded because of mining, refining, and process-
ing procedures and as a result of municipal waste disposal. Major sources
of industrial liquid and solid wastes containing cadmium are electroplating
(liquid slurry and sludge), nickel-cadmium battery manufacturing (sludge from
baths), paint manufacturing (sludge), and paint in old containers (residues
to municipal dumps). Cadmium dusts and fumes from metal extraction, refin-
ing, and processing industries constitute a major pollution source of atmos-
pheric cadmium. Lesser sources of cadmium pollution are combustion of fos-
sil fuels, phosphate fertilizers with a high cadmium content, wearing of
tires, and combustion of lubrication oil. Threshold limit values for cadmium
exposure in industrial air in the United States as established by the
American Conference of Governmental Industrial Hygienists are 50 yg/m3 for
cadmium fume and 200 yg/m3 for cadmium dust.
A variety of analytical methods sensitive to as low as 1 ppb are
available for determining cadmium in environmental media (Section 2.4.2):
spectrophotometric colorimetry, emission spectroscopy, atomic absorption
spectrophotometry, neutron activation, polarography and anodic stripping
voltammetry, spark-source mass spectrometry, and isotope dilution mass
spectrometry. At present, however, no one method satisfies the requirements
for accuracy, reliability, and sensitivity while at the same time being
simple, rapid, inexpensive, and requiring small samples. Thus, no single
analytical method can be characterized as superior for the analysis of
cadmium in every circumstance.
-------
Zooplankton and phytoplankton apparently can remove and concentrate
trace metals from water by direct absorption.. Cadmium is toxic at different
concentrations to several species of bacteria, yeast, and fungi. Generally,
cadmium levels causing toxic effects in bacteria (0.2 to 6 ppm) are several
times higher than concentrations normally detected in industrially polluted
waters (1 to 100 ppb) (Sections 3.1 and 7.3.4).
Cadmium accumulation in plants at present background levels is usually
less than 1 ppm. Little is known about cadmium concentrations needed to
reduce plant yields; however, plants growing in contaminated soils contain
abnormally high cadmium levels which may be detrimental to growth. Cadmium
contamination of soils can result from industrial sources such as smelters
or from the use of phosphate fertilizers and sewage sludge. Increased up-
take of cadmium by plants directly increases dietary cadmium levels in
animals and humans.
'' Cadmium may be transported to all regions of the plant, but it most
often accumulates in the roots. Cadmium content in plants usually reflects
environmental cadmium levels. Several factors may stimulate uptake of cad-
mium by plants: increased soil acidity, increased soil temperature, the
presence of small amounts of zinc, or oxidation of insoluble cadmium sulfide
by soil microorganisms (Section 4.2.1). In controlled experiments, cadmium
produces five major effects on plants: altered ion absorption and release,
altered stomatal function, reduced chlorophyll content, reduced cell turgor,
and reduced photosynthesis.
Cadmium levels found in animal tissues under normal conditions are
usually not high enough to be considered toxic. The primary concern aris-
ing from environmental exposure of animals and man centers on effects from
low-level chronic exposure. Little information is available on cadmium
levels in wild or domestic animals. Evidence suggesting that cadmium con-
centrates in food chains is fragmentary. Cadmium accumulation in shellfish
generally is higher than cadmium accumulation in fish (Section 5.2.1.1).
In the nonoccupational environment, oral intake represents the primary
source of the cadmium accumulated in the body; most food and water supplies
contain some cadmium (Section 6.2.1.2). The average daily cadmium intake
for persons on American diets can be reasonably estimated at about 50 yg
from all sources. In the United States, cigarette smokers and persons
occupationally exposed to atmospheric cadmium have higher cadmium body
burdens than nonsmokers or persons not occupationally exposed (Sections
6.2.1.1 and 8.3.2). Generally, little cadmium has been detected in new-
borns. Levels increase with age and vary among individuals, depending on
diet, environment, and smoking habits (Section 6.2.5.2). Although cadmium
has been found in kidneys and other organs in populations all over the
world, it does not appear to be a micronutrient.
Cadmium is absorbed through both the respiratory and gastrointestinal
tracts. Nutritional factors such as protein or vitamin D deficiencies may
increase cadmium absorption. Cadmium is transported from the site of
absorption via the bloodstream; most of the cadmium in the bloodstream of
exposed workers can be found in the red blood cells (Section 6.2.2.1).
-------
Chronically exposed workers maintain the highest blood cadmium levels;
these concentrations have been shown to slowly decrease in workers after
exposure stops. Half-times for cadmium in blood approximate six months.
One-third of the total cadmium body burden is in the kidneys (Section
6.2.2.2). Liver and kidneys together contain about 50% of the total body
burden, which generally lies between 15 and 30 mg for a 70-kg person. Bio-
logical half-times for cadmium based on body burden and excretion data for
groups from various countries are estimated at 13 to 47 years (Section
6.2.4). Cadmium is excreted primarily through urine and feces.
The protein metallothionein (thionein plus a bound metal) contains
many sulfhydryl groups; it is synthesized in response to metal exposure
and binds a major portion of cadmium in the tissues (Section 6.3.1.1). The
precise function of metallothionein, if any, in cadmium metabolism remains
uncertain. Cadmium also reacts with many other ligands, including several
important enzyme systems. The nature of the ligands determines the toxicity
of the metal; thus, the nephrotoxicity of cadmium is increased by low-
molecular-weight sulfhydryl compounds. Some toxic effects of the metal
arise from its competition with zinc at the level of zinc-requiring enzymes;
certain acute effects of cadmium can indeed be prevented or reduced by
excess zinc. Selenium is also an effective cadmium antagonist.
Acute cadmium poisoning via inhalation continues to be an occupational
rather than an environmental hazard (Section 6.3.2.2.1). Inhaled freshly
generated cadmium fume is the most toxic form. Acute cadmium poisoning due
to ingestion is rare (Section 6.3.2.2.2); use of cadmium in food or drink
containers is prohibited.
Signs and symptoms of acute cadmium poisoning generally begin one-half
to one hour after ingestion and include: (1) severe nausea, vomiting,
diarrhea, abdominal cramps, and salivation; (2) headache, muscular cramps,
vertigo, and (rarely) convulsions; (3) exhaustion, collapse, shock, and
death; or (4) gradual appearance of kidney and liver damage resulting in
death in one to two weeks from acute renal failure.
The critical organ with respect to prolonged, low-level exposure to
cadmium is the kidney. Itai-itai disease, believed by many investigators
to result from chronic cadmium exposure due to industrial contamination of
the environment, reflects primarily renal tubular dysfunction plus osteo-
malacia and osteoporosis (Section 6.3.2.4.7).
Proteinuria and kidney stones are commonly found in cadmium workers.
Other renal changes may include glucosuria, amino aciduria, and decreased
urine concentrating ability. No critical level of cadmium in the renal cor-
tex has been generally accepted, but at approximately 200 ppm wet weight
kidney damage may be observed. Moderate, apparently reversible anemia has
been associated with occupational exposure to cadmium oxide dusts and fumes
(Section 6.3.2.3.2.2).
Hypertension can be induced experimentally in certain animal species
by administration of cadmium; some epidemiological data indicate a positive
-------
correlation between hypertension and cadmium in humans; however, a rela-
tionship between the two has not been proven.
Experimental animal data suggest that cadmium may cause testicular
damage in humans; however, no direct evidence exists (Section 6.3.2.4.2).
Limited data indicate a possible correlation between cadmium exposure and
cancer of the prostate (Section 6.3.2.4.4). Although no teratogenic effects
of cadmium have been reported in humans, cadmium has been shown to be terato-
genic in rats, mice, and hamsters. Cadmium-induced mutagenesis has not been
experimentally demonstrated; however, an increased number of chromosomal ab-
normalities were found in peripheral leukocytes from itai-itai patients and
in cultured human leukocytes exposed to cadmium sulfide.
The major concern surrounding environmental cadmium stems from poten-
tial effects on the general population from chronic, low-level exposure.
Emphasis is placed on the effects of soil contamination on plant uptake of
cadmium and the resultant effect on animals and humans through diet.
1.2 CONCLUSIONS
1. No one method is uniquely superior for the analysis of cadmium in
various materials.
2. Background levels of cadmium are generally low; higher concentra-
tions occur near smelters or in industrialized urban areas. The
metal may be present at relatively high concentrations in a variety
of industrial and municipal wastewaters.
3. Cadmium is a relatively volatile metal, and significant amounts are
contributed to the atmosphere from smelting operations and the com-
bustion of fossil fuels.
4. Cadmium may move among air, biomass, soil, and water; much of the
cadmium in water finds its way into sediments.
5. Although cadmium moves within the ecosystem, significant biomagni-
fication along the food chain seems limited; some mollusks are an
exception.
6. In sufficient concentration, cadmium is toxic to all forms of life,
including microorganisms, higher plants and animals, and man.
7. Information is lacking on the concentrations of cadmium necessary
to reduce plant yields, but in general the cadmium levels in plants
reflect that in soil. Actual uptake by a given species depends on
pH and other chemical characteristics of the soil.
8. Cadmium uptake by plants, especially mosses, may also reflect the
concentration of the element in air.
9. Application of cadmium-containing fertilizers and sewage sludges to
agricultural lands may lead to significant increases in the cadmium
content of the crops.
-------
10. Cadmium in the body of animals and man under normal conditions is
derived primarily from the diet; most food and water supplies contain
at least traces of the element.
11. An additional contribution to the body burden of cadmium in the
general population is made by cigarette smoking.
12. In the occupational setting, significant pulmonary uptake of cadmium
dusts or fumes may further elevate the body burden.
13. The biological half-life of cadmium is very long so that its con-
centration in the body increases with age; the metal therefore
acts as a cumulative poison.
14. The primary target organ of cadmium is the kidney; a major portion
of renal (and hepatic) cadmium is present in the form of metallo-
thionein, a low-molecular-weight metalloprotein of undefined function.
15. Cadmium readily reacts with sulfhydryl groups and may compete, espe-
cially with zinc, for binding sites on proteins. In this manner,
the metal may inhibit a variety of enzymatic reactions.
16. A primary role of cadmium is suspected in some human diseases, includ-
ing itai-itai disease; whether the metal plays a part in the etiology
of human hypertension, carcinogenesis, mutagenesis, or teratogenesis
remains uncertain.
-------
SECTION 2
PHYSICAL AND CHEMICAL PROPERTIES AND ANALYSIS
2.1 SUMMARY
Cadmium possesses the size, charge, and Group II behavior of calcium
and the ccmplexing properties of zinc. Adsorption reactions, complex for-
mation with different ligands, the volatility of the element, and the water
solubility of its salts are important factors controlling distribution in
the environment. In natural waters, for instance, the presence of carbon-
ate, hydroxide, or sulfide ions may be instrumental in removing cadmium
from solution, while ammonia, chloride, or cyanide may maintain the solu-
bility of cadmium. In soils, cadmium mobility and accessibility appear to
depend on adsorption by humic material and clays coated with hydrous oxide.
Adsorption by humic matter is sjtrpngly pH dependent. All fractions of the
soil communicate with one another and with natural waters, providing the
pathway for movement of free cadmium ions. Organocadmium compounds are
unstable in air and water, preventing their presence in the natural
environment.
/The exact chemistry of cadmium in vivo is still uncertain. The metal
is bound to a variety of proteins, especially the low-molecular-weight
thioneins in liver and kidney.
A variety of analytical techniques are available for the determination
of cadmium in environmental matrices down to the 1-ppb level. Although
this level of sensitivity is adequate for most samples, it frequently can
be achieved only at the expense of costly, time-consuming preconcentration
steps. There is a continuing need for more rapid and inexpensive methods
which do not require pretreatment of the samples. Flameless atomic absorp-
tion spectrometry, anodic stripping voltammetry, and differential pulse
polarography represent excellent advances in this direction, but procedural
standardization of these relatively new techniques is required.
Errors associated with the analysis of cadmium at concentration levels
near 1 ppb may result as much from sampling techniques, sample storage, and
handling procedures as from instrumental variance. Information relative to
these factors is not currently available for sample matrices commonly en-
countered in environmental work. Standard methods similar to those published
for water and wastewater should be explored and widely adopted.
Essentially all published determinations of cadmium in environmental
samples refer to total cadmium; in general, no attempt is made to identify
particular cadmium species which may exist in the sample. Although the
chemistry of cadmium is relatively simple, numerous complexes exist, and
some may have relevance to the impact of cadmium on the environment.
-------
2.2 PHYSICAL CHARACTERISTICS
Cadmium is a soft, bluish-silver-white metal, harder than tin but
softer than zinc; it can be cut with a knife (Chizhikov, 1966). Cadmium
has low melting and boiling points (321°C and 765°C respectively); the vapor
pressure or the liquid metal between these temperatures is shown in Figure
2.1. Although imperceptible at ambient temperature, the vapor pressure of
metallic cadmium rises rapidly with increased temperature; an orange-yellow
vapor is emitted. This vapor may be discharged during metal refining or
during combustion of fossil fuels or other materials and represents a major
source of atmospheric cadmium (Goeller, Hise, and Flora, 1973; Hise and
Fulkerson, 1973). Upon contact with air, cadmium vapor is oxidized to CdO
(Section 2.3.1).
ORNL-DWG 71-13842
760
e
E
LJ
tr
=>
CO
CO
Ld
tr
a.
0.76
0.0002
0.0001
0.076
300 400 500 600 700 800 900 1000
TEMPERATURE (°C)
Figure 2.1. The vapor pressures of cadmium and zinc vs temperature.
Source: Baes, 1973, Figure III-3, p. 35.
-------
Some properties of cadmium and of its important compounds are shown in
Table 2.1. The solubility of many of these compounds is noteworthy in con-
nection with the chemical behavior of cadmium in the aqueous environment
(Section 2.3.2).
2.3 CHEMICAL CHARACTERISTICS
The chemistry of cadmium is inseparable from that of zinc. Cadmium is
universally associated with zinc in natural deposits; both possess the same
outer-electron configuration [ndl°(n + l)s2] and participate qualitatively,
if not quantitatively, in the same hydrolysis and complexation reactions.
An unknown amount of cadmium occurs as an impurity in zinc and escapes to
the environment whenever zinc escapes. In fact, estimations of cadmium
concentrations (in the absence of direct data) are often possible from the
fairly constant cadmium-to-zinc abundance ratio (Hem, 1972).
The corrosion behavior of cadmium and zinc in air and water are impor-
tant in dictating some of the uses of these metals and, thereby, their prev-
alence in the environment. Cadmium corrodes slightly in air but forms a
protective surface film that prevents further corrosion; zinc behaves simi-
larly. This low corrosion renders both zinc (with its customary cadmium
impurity) and cadmium industrially valuable as protective surface platings
for corrosion-susceptible steel.
Zinc and cadmium react readily with acids to produce hydrogen:
Zn + 2H+ = Zn2+ + H2 ,
Cd + 2H+ = Cd2+ + H2 ,
but the analogous reaction with pure water at ambient temperatures is
exceedingly slow (Baes, 1973). Thus, until the introduction of copper and
plastic water pipe, zinc (containing cadmium) was used widely to galvanize
iron water pipe. Some of this piping is still functional, posing a possible
contamination problem, particularly in soft-water areas (Section 2.3.2.4 and
Table 6.8).
2.3.1 Cadmium in Air
Although the exact forms of cadmium in air are still uncertain, pre-
sumably cadmium oxide constitutes the largest portion of airborne cadmium
(Friberg et al., 1974). Cadmium vapor, emitted during man-moderated thermal
processes, is converted to the oxide on contact with air,
Cd + %Q2 = CdO .
CdO is also directly released into the air during a variety of combustion
processes such as cigarette smoking (Menden et al. , 1972).
Likewise, cadmium sulfate, which does not occur naturally, is a con-
version product found in atmospheric emissions from thermal processes involv-
ing materials containing cadmium and sulfur (International Agency for Research
-------
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10
on Cancer, 1973). The sulfide is readily prepared in the laboratory by heat-
ing a mixture of cadmium (or cadmium oxide) and sulfur,
Cd + S = CdS ,
whereas the sulfate is the primary stable product of the oxidation of cadmium
sulfide at elevated temperatures (Chizhikov, 1966),
CdS + 202 = CdSO<. .
Cadmium chloride can be generated and released into the atmosphere by
the incineration of polyvinyl chloride plastic to which organic cadmium
stabilizers are added (International Agency for Research on Cancer, 1973).
Cadmium can appear in air as dust, fumes, and mist as a by-product of the
refining of zinc, copper, or lead (McCaull, 1971). Dusts of cadmium sulfide
have been reported in refinery working atmospheres (International Agency for
Research on Cancer, 1973). Cadmium is present in the atmosphere mostly in
the form of particulate matter composed of cadmium oxide and cadmium oxide-
iron oxide (from zinc refining) with some cadmium sulfide, cadmium sulfate,
and cadmium chloride.
2.3.2 Cadmium in Water
The concentration of cadmium in natural waters may be determined by the
solubility of cadmium compounds, by the formation of cadmium complexes, and
by the removal of cadmium through adsorption.
2.3.2.1 Solubility — Although the solubility of cadmium compounds has been
postulated to be the single most important natural process governing cadmium
distribution and availability in the aqueous environment (Posselt and Weber,
1971), Harris, Helz, and Cory (1975), Bailey, Helz, and Harris (1975), and
Hem (1972) concluded that it is unlikely that precipitation of inorganic
compounds controls the cadmium concentration in natural waters. The solu-
bility product constant (^Sp)> a molar measure of solubility, is the product
of the solute ion concentrations in a saturated solution of the substance.
For example, for cadmium carbonate (CdC03),
xsp = [Cd2+][(co3)2-] ,
where the square brackets refer to molar concentrations of the ions.
The solubility products of some environmentally important cadmium
compounds are listed in Table 2.2 along with those of additional Group II
metals. Posselt and Weber (1971) stated that hydroxide and carbonate ions
at alkaline pH may limit the amount of cadmium in solution because of the
low solubilities of the corresponding cadmium compounds. In regard to water
treatment applications, Posselt (1971) suggested that the effect of carbon-
ate on the solubility of cadmium is dramatic. Thus, cadmium removal via
carbonate precipitation appears promising, provided that attainment of
equilibrium proceeds at a practical rate. Posselt (1971) concluded that
slow attainment of equilibrium is probably the most significant factor in
many applications of thermodynamic solubility relationships, particularly
-------
11
TABLE 2.2. SOLUBILITY PRODUCTS OF VARIOUS COMPOUNDS
Cation, Hydroxides, M(OH)2 Carbonates, MC03 Sulfides, MS
M2 + log ([M2+][OH-]2) log ([M2+][C032-]) log ([M2+][S2-])
Magnesium
Calcium
Zinc
Cadmium
Mercury
Mg2 +
Ca2 +
Zn2 +
Cd2 +
Hg2 +
-10.9
-5.43
-17.0
-14.4
(-25.5)
-5.4
-8.35
-10.20
-12.01
-24.5
-28.9
-52.7
Source: Adapted from Baes, 1973, Table III-2, p. 37.
in precipitation reactions. Posselt's conclusions emphasizing the impor-
tance of solubility in the distribution of cadmium compounds in the aqueous
environment were based on laboratory studies conducted under conditions
approaching saturation. After completion of field studies, Hem (1972)
concluded that it appears unlikely that many river waters approach satura-
tion in respect to cadmium carbonate. Hem (1972) also suggested that bio-
logical factors and/or adsorption by stream sediments may affect the levels
of heavy metals in natural waters.
2.3.2.1.1 Hydroxide and carbonate — Knowledge of the behavior of cadmium
in hard or soft water is important in evaluating the risk of cadmium inges-
tion from drinking water (Section 6.3.2.3.2). Cadmium carbonate dissolu-
tion or deposition depends not only on the thermodynamic relationship between
solid and dissolved CdC03 and its ions, but also on solubility equilibria
involving hydroxide ions. For instance, at low metal ion concentrations,
cadmium forms at least four soluble hydroxide species (Posselt and Weber,
1971): CdOH+, Cd(OH)2, Cd(OH)3~, and Cd(OH)<,2~, each of which is described
by a formation (equilibrium) constant defined by stepwise equilibria as out-
lined in Section 2.3.2.2 and enumerated in Table 2.3. Use of the measured
solubility product and equilibrium constants (as described by Posselt and
Weber, 1971) allows the calculation of dissolved cadmium concentrations in
a solution containing both carbonate and hydroxide (Figure 2.2). The derived
cadmium concentrations are applicable only in the absence of sulfide or
complex-forming ions such as chloride. Sulfide ions remove cadmium by forma-
tion of insoluble cadmium sulfide (Section 2.3.2.1.3), whereas complex-
forming ions maintain cadmium in solution (Section 2.3.2.2). The solid
curves in Figure 2.2 correspond to the total C02 concentration (the sum of
dissolved carbon dioxide, bicarbonate, and carbonate) in moles per liter.
The uppermost solid curve corresponds to zero carbonate, indicating control
by the hydroxide equilibrium:
Cd2+ + 20H" = Cd(OH)2 (solid) .
Precipitation of Cd(OH)2 reportedly occurs at a pH greater than 7.5 and at
-------
12
TABLE 2.3. STEPWISE FORMATION CONSTANTS OF VARIOUS CADMIUM COMPLEXES
[CdL]
[CdL2]
[CdL3]
[CdL,,]
i_io_ gjdi.ua 9 ij
Cyanide, CN~
Pyrophosphate, P2
Hydroxide, OH~
Ammonia, NH3
Sulfate, S042"
Iodide, I~
Nitrite, N02~
Bromide, Br~
Chloride, Cl~
Fluoride, F"
[Cd2+][L]
300,000
07"~ 10,000
8,500
550
130
120
63
57
35
3
[CdL][L]
140,000
200
(1,000)
150
5.9
16
4
5
[CdL2][L]
36,000
(180)
30
140
6
10
1
[CdL3][L]
4,000
22
10
30
2
Source: Adapted from Baes, 1973, Table III-4, p. 41.
ORNL-OWG 71-13843
1 1 1
0 TOTAL CARBONATE (moles/liter)
Figure 2.2. The solubility of cadmium vs pH at different carbonate
concentrations at 20°C. Source: Baes, 1973, Figure III-6, p. 47.
-------
13
a hydroxide-to-cadmium ion ratio greater than or equal to 0.05 (Posselt
and Weber, 1971).
This precipitation may be suppressed by the presence of relatively
large concentrations of complex-forming anions such as iodide, bromide, or
chloride (Posselt and Weber, 1971). In fact, even hydroxide becomes a
complexing ligand at pH values greater than 9.5 (Figure 2.3) so that, in
the absence of carbonate, the cedmium concentration cannot be reduced below
0.5 ppm (Figure 2.2). This greatly exceeds (about 50 times) the U.S. Public
Health Service maximum of 0.01 ppm for drinking water (Posselt and Weber,
1971). Reduction to the 0.01-ppm cadmium level, indicated by the dashed
line in Figure 2.2, is attained only at dissolved carbonate concentrations
greater than 10"3 mole/liter. Since the carbonate content of hard water
rarely exceeds 4 x 10"3 mole/liter (U.S. Environmental Protection Agency,
1974), water hardness alone does not appear to provide a dependable means
for reduction of cadmium concentrations in water to desirable levels. Addi-
tions lly, only equilibrium thermodynamic considerations have been applied
here, and these may easily be overruled by kinetic factors that can hinder
deposition of cadmium as the carbonate. Posselt and Weber (1971), in fact,
found the final rate of attainment of equilibrium in the precipitation of
soluble cadmium from alkaline carbonate solutions rather slow and highly
irreproducible.
Hem (1972) compared observed cadmium concentrations in 80 samples of
river water with cadmium solubilities calculated from graphs similar to
Figure 2.2. The conclusion was drawn that not many river waters are likely
to approach saturation with respect to cadmium carbonate. Further evidence
that inorganic precipitation does not control the cadmium concentration was
provided by Bailey, Helz, and Harris (1975) and Harris, Helz, and Cory (1975).
2.3.2.1.2 Carbonate solid solution — Baes (1973) discussed the likelihood
of solid-solution formation, Cd2 replacing Ca2+ in precipitated CaC03 and
other calcium-bearing minerals, as a result of similarity in size and charge
of the two ions. Although Baes considered the exchange in terms of removal
of cadmium from natural waters, solid solutions of Cd2+ in CaC03 may be even
more important as a possible reservoir for dissolution of cadmium (Bondietti
et al. , 1974), considering the very low concentration to be maintained as a
drinking water standard.
2.3.2.1.3 Sulfide — If sulfide is present in solution, cadmium should pre-
cipitate as solid cadmium sulfide according to the solubility product constant
in Table 2.2: KS = 1.2 x 10"29. In the event of simultaneous discharge of
zinc and cadmium into sulfide-containing waters, the Zn2+ to Cd2+ ratio in
water at equilibrium would be about 25,000, the ratio of the solubilities of
the sulfides (Baes, 1973). Because of the biological antagonism between zinc
and cadmium, this high Zn2+ to Cd2+ ratio may be as important as the absolute
Cd2+ intake in preventing cadmium toxicity (Section 6.3.1.2). In fact, as
determined by inspection of the solubility product ratios (Table 2.2), the
Zn2+ concentration in carbonate-containing waters may also exceed that of
Cd2 (by a factor of 65). In soft water, where solubility of cadmium is
presumably a function of [OH~], the Cd2+ concentration may be greater than
that of Zn2+, even at a high pH.
-------
14
in
^r
CO
o
o
NOiirnos NI wmiAiavo iwioi jo
-------
15
According to Hem (1972), precipitation of sulfides may be an important
factor in the control of cadmium and zinc in water systems, with the reduced
mud in the bottom of some types of lakes and reservoirs constituting a sink
for deposition of these metals. Bowen (1966), however, pointed to the activ-
ity of aerobic bacteria in oxidizing insoluble sulfides in soils to sulfates,
which liberates the cation in a soluble form.
2.3.2.2 Complex Formation — An important property of the Cd2 + ion is its
ability to complex with negatively charged ions or ligands to form soluble
complexes. Complex formation constitutes a serious competitive process
which can reduce the extent of precipitation and adsorption, the prime mech-
anisms for natural removal of cadmium from water systems.
The consecutive addition of ligands (L) is controlled by the stepwise
formation constants C^n) enumerated for a number of ligands in Table 2.3:
[CdL+]
Cd2+ + L" = CdL+ , Kl =
CdL+ + L~ = CdL2 , K2 =
CdL2+ + L~ = CdL3 , K3 =
CdL3 + L = CdLA2~ , K,, =
[Cd2+][L-]
[CdL2]
[CdL+][L-]
[CdL3~]
[CdLa][L-]
[cdu2-]
[CdL3-][L-]
Chloride, cyanide, and ammonia form cadmium complexes of environmental
importance: chloride because it is prevalent in natural waters and cyanide
and ammonia because they appear in industrial wastes and effluents.
2.3.2.2.1 Chloride — Complex formation with chloride becomes a significant
factor in solubility considerations at chloride levels greater than 10~3
mole/liter (Hahne and Kroontje, 1973). The distribution of chloride
complexes for chloride ion concentrations in the range from 1 x 10"* to
1 mole/liter is shown in the upper right of Figure 2.3. At 0.1 mole/liter
chloride, 85% of the cadmium in solution exists as chloride complexes. The
effect of this complex formation on the solubility of some cadmium precipi-
tates is given in Table 2.4. /Clearly, dramatic increases in cadmium solu-
bility occur as the chloride concentration increases from 0.01 mole/liter
to 1 mole/liter. The phosphate salt, which is important when considering
cadmium in fertilizer application (Section 7.3.3), shows nearly a 40-fold
increase in solubility on contact with a solution of high salinity — a
condition encountered in soils as a result, for instance, of runoff from
roads from application of chloride salts for snow and ice removal.
-------
16
TABLE 2.4. EFFECT OF CHLORIDE CONCENTRATION ON
SOLUBILITY OF CADMIUM PRECIPITATES
Cadmium values
Precipitate
Cd3(PO<,)2
CdS
Cd(OH)2
I0~u M
chloride
1.001
1.001
1.001
lO'2 M
chloride
1.130
1.107
1.070
1 M
chloride
39.83
21.55
7.745
Values represent the ratio of cadmium
dissolved from various salts in the presence of
a given chloride concentration to the amount
dissolved in absence of chloride.
Source: Adapted from Hahne and Kroontje,
1973, Table 4, p. 450.
2.3.2.2.2 Ammonia — Complex formation of cadmium with ammonia is somewhat
stronger than with chloride (Table 2.3 and Figure 2.3). However, because
ammonia is rarely present in more than minute amounts — usually at levels
much lower than chloride (even in industrial wastes) — its role in forming
soluble complexes of cadmium is probably less than that of chloride (Posselt
and Weber, 1971). However, since chloride ion and ammonia are independent
entities in aqueous solution, their ability to form complexes with cadmium
is additive. ./At pH 9, the calculated solubility of cadmium carbonate is
increased fivefold in the simultaneous presence of 0.1 mole/liter chloride
ion and 0.005 mole/liter NH3 (Posselt and Weber, 1971). In the case of
ammonia,
Cd2 + + nNH3 = Cd(NH3)n2+ (n = 1, 2, 3, or 4) ,
the divalent cadmium ion is still available to associate with the anion of
tie insoluble cadmium salt brought into solution by the presence of ammonia.
2.3.2.2.,3 Cyanide — Cyanide ion is one of the strongest complexing ligands
known. Its appearance in waste streams along with cadmium is a result of
electroplating operations, which consume about one-half the cadmium used in
the United States (Hem, 1972). Watson (1973) cited a report which stated
that cadmium ions are impossible to precipitate as cadmium hydroxide or oxide
in the presence of cyanide; pretreatment to destroy this complexing agent is
required before cedmium removal in wastewater treatment. This is not sur-
prising since the magnitude of the cyanide association (Table 2.3) exceeds
that of chloride by almost 10,000-fold. Fortunately, cyanide can be rapidly
and easily broken down (Watson, 1973), allowing removal of cadmium from
wastewater following prior destruction of cyanide.
-------
17
2.3.2.3 Adsorption — Cadmium in water can be adsorbed by clays and muds,
by humic and organic materials, and by hydrated oxides of iron and manga-
nese. The phenomenon is of prime importance not only as a mechanism for
natural removal of soluble cadmium, but also for chemical treatment of
industrial waste streams (Watson, 1973). The discussion of aqueous sorption
(adsorption and/or absorption) by clays and humic substances, however, is
included in Section 2.3.3 since the sorption behavior in aqueous sediments
is similar to that in soils.
Hydrated oxides of manganese and iron are widespread in clays, soils,
and sediments, both as coatings on other minerals and as discrete oxide
particles (Jenne, 1968). Although little is known about the surface^area
of the many different naturally formed oxides of iron and manganese, prepared
hydrated oxides have large surface areas (200 to 300 m2/g), a property un-
doubtedly important in their adsorption ability^XJenne., 1968) . Laboratory
studies of the rate of sorptive uptake of cadmium by the hydrated oxides of
manganese, iron, and aluminum have been reported by Posselt and Weber (1971).
Results in Figure 2.4 show that the attainment of sorption equilibrium is
very rapid (within 10 min), although rates with aged crystals (for example,
in the natural environment) may be much slower (hours, perhaps, rather than
minutes). Considerable competition with the sorption process would be ex-
pected from ligands with strong complexing capability (for example, cyanide)
or from certain organic or humic substances. The sorptive affinity of
manganese dioxide for cadmium wss superior to that of hydrated iron oxide,
but the latter was considered useful at pH values greater than 6. The
utility of hydrated aluminum oxide in sorptive removal of cadmium from water
was considered doubtful since the sorptive capacity was reported as inferior
and the range of applicable pH was limited (Posselt and Weber, 1971). This
is not so with aluminum-hydroxide-coated montmorillonite clays, which retain
cadmium strongly (Section 2.3.3.1).
2.3.2.4 Corrosion Behavior — Widespread concern has been expressed about
the appearance of cadmium in drinking water as a result of corrosion of
galvanized iron water pipes (Baes, 1973; Friberg et al., 1974; National
Academy of Sciences, 1974; Posselt and Weber, 1971) (Table 6.8 and Section
6.3.2.3.2.3). A more serious situation is likely to exist in cases where
galvanized pipes are coupled to copper or brass pipes and fittings; this
condition may enhance the rate of corrosion (dissolution of zinc and cadmium)
as a result of galvanic effects (Posselt and Weber, 1971). Such galvanic
currents between different metals have been implicated in acute cadmium
poisoning arising from consumption of soft drinks from a vending machine
(Emmelin, 1973); the cadmium was released into the stored water from a high-
cadmium alloy used to solder the top and sides of the brass storage tank.
Laboratory studies of the aqueous corrosion chemistry of cadmium
(Posselt and Weber, 1974) have identified some cadmium corrosion promoters
and inhibitors; a high oxygen content and the coupling of cadmium to copper
promote corrosion, whereas a high pH and the presence of carbonate inhibit
it. Coupling cadmium directly to less-noble zinc has little effect on the
corrosion behavior.
-------
18
ORNL-DWG 77-5279
c
.0
O
tn
O
-------
19
and their sum,
2Cd + 02 + 4H+ = 2Cd2+ + 2H20
E = 1.63 V.
o
The action is thermodynamically favorable by 1.63 V, but because the reaction
requires 2 moles of hydrogen ion for each mole of cadmium oxidized, oxygen
attack is decreased sharply by increasing the pH, as shown in Figure 2.5.
Cadmium dissolution is reduced by more than an order of magnitude upon
increasing the pH from 8.3 to 10.5.
ORNL-DWG 77-5280
50
40
£
o
to
C/)
o
o
<
o
30
20
0
0
•
://
• s ^r
—*—•—T——'I
40
20 30
TIME (min)
Figure 2.5. Corrosion of cadmium as a function of pH in carbonate
free solutions. Source: Adapted from Posselt and Weber, 1974,
Figure 8.2, p. 301. Reprinted by permission of the publisher.
In addition to pH and oxygen concentration, carbonate concentration
and copper coupling are important factors in cadmium corrosion; carbonate
reduces the corrosion rate. This reduced corrosion rate is thought to occur
by gradual formation of a protective film (probably solid CdC03) that causes
-------
20
a progressive decrease in the cadmium dissolution rate as the film thickens
with time. The decrease was interpreted by Posselt and Weber (1974) in
terms of an initial and a secondary rate of corrosion; the average primary
and secondary rate constants are shown as the upper and lower curves, re-
spectively, of Figure 2.6. The higher the concentration of carbonate, the
more effective it is in decreasing the corrosion rate.
O 'c
co c
CC CM
-------
21
the process as occurring by successive deposition and dissolution of copper
frcm one corrosion site to the next:
WATER
Figure 2.7 shows an almost tenfold increase in the corrosion rate when
cadmium is galvanically coupled to copper.
ORNL-DWG 77-5282
Figure 2.7. Effect of external galvanic coupling on rate of cadmium
corrosion. Source: Adapted from Posselt and Weber, 1974, Figure 8.9,
p. 311. Reprinted by permission of the publisher.
Coupling to less-noble zinc, which should reverse the galvanic effect,
somewhat suppresses corrosion but definitely does not eliminate it (Figure
2.7). This may be due to enhanced passivation of zinc relative to cadmium,
which effectively enobles zinc to virtual equality with cadmium (Pourbaix,
1973).
In summary, corrosion of cadmium contained within zinc-galvanized pipe
is minimized by hard water and high pH and enhanced by galvanic coupling to
copper pipes and fittings. The corrosion proceeds by oxygen reduction,
which is hindered at high pH.
-------
22
2.3.3 Cadmium in Soils
/Behavior of cadmium in soils is important in terms of biological
availability, including especially uptake by plants/^ Shacklette (1972)
found that the cadmium concentration in normally grown plants is determined
by the inherent ability of a plant species to absorb cadmium and by the
cadmium concentration in the environment. Studies in solution culture
indicated to Van Hook et al. (1973) the importance of the solution chemistry
of cadmium in determining cadmium availability to plants. Evaluation of the
total amount of cadmium in scils may be important; dissolved cadmium is in
dynamic equilibrium with the solid soil and removal of cadmium from the soil
solution leads to replenishment from the solid soil due to ionic dissociation
(see reviews discussed by Bowen, 1966).
Soils are composed of several fractions: (1) the inorganic mineral
portion made up of coarse or colloidal matter; (2) the organic portion,
which contains decomposing tissue and humic material; (3) the soil solution
or aqueous portion; (4) the air fraction; and (5) the living organisms.
Cadmium undoubtedly interacts chemically with all of these but most notably
with the colloidal inorganic and humic portions. Solubility interactions
and complex formation within the soil solution would be expected to resemble
those in other aqueous media (Section 2.3.2). Likewise, interactions with
hydrated oxides of manganese, iron, and aluminum — part of the inorganic
colloidal fraction of soil — also are expected to be similar to those seen
in aquecus solution (Section 2.3.2.3).
2.3.3.1 Clay Minerals — It is important to consider the clay mineral portion
of soils in estimating the role of adsorption processes in the availability
of heavy metals. Silicate clays are characterized by shape and size of their
particles and by their ion exchange properties (Brady, 1974). Unlike sand
particles, which are more or less spherical, clay particles are laminated,
that is, made up of layers of plates or flakes often no more than a few
angstroms thick and 1 to 2 u across; these dimensions result in a ratio of
breadth to thickness of approximately 10,000. Consequently, Brady (1974)
conservatively estimated the active surface area due to the clay fraction
of an acre-furrow slice of a representative clay loam soil to exceed the
land area of Illinois by 40 or 50 times. /The sheetlike structure of the
clay particles gives rise to an intrinsically produced negative surface
charge to which positive cations are attracted (Figure 2.8). Both the
external and internal surfaces provide sites for cation adsorption, result-
ing in a clay colloid particle (micelle) that behaves like a huge anion.
The action of the internal surfaces is not only interesting but also is of
practical importance. The interplatelet lattice dimension in clay minerals
such as vermiculite and montmorillonite is about 1.4 A (Bowen, 1966). Clays
of this type swell when wet, allowing ions such as K+ (radius, 1.33 A) and
NHi,+ (radius, 1.48 A) to permeate between layers. On drying, the layers
come together again and are held tightly in place by electrostatic forces;
the ions are fixed in place. The retention of cadmium on coated and uncoated
montmorillonite is shown in Figure 2.9. Clays coated with hydrated oxides
(a common natural occurrence) have increased adsorption and retention of cad-
mium even under the competitive influence of Ca2+, a behavior not unlike
that observed in aqueous solution (Section 2.3.2.3).
-------
23
ORNL-DWG 77-5669
ENLARGED EDGE OF CRYSTAL
Ca** Mg** H* K*
K* H* Ca** H* Ca
Na* H* Ca++ Mg** H
H* Ca** K* H* Ca** Mg**
Ca** H+ Ca** H+ Ca** H*
H* K* Ca" Mg** Ca** H* ,
Ca** H* K* Ca** H* Ca**X>>
| Ca** H* Mg** H* Ca** K*
+ +•
+ •+•
+ +
+ -f
EXTERNAL
SURFACES
INTERNAL
SURFACES
Figure 2.8. Diagrammatic representation of a silicate clay crystal,
Source: Brady, 1974, Figure 4.2, p. 74.
o Na-MONTMORILLONITE
• Ca-MONTMORILLONITE
0 ALUMINUM HYDROXIDE COATED
Ca-MONTMORILLONITE 614
« IRON HYDROXIDE COATED
Ca-MONTMORILLONITE 222
* AI-MONTMORILLONITE 33
a Fe-MONTMORILLONITE 43
DISTRIBUTION COEFFICIENT (Kt), DEFINED
AS FRACTION OF '09Cd ADSORBED PER GRAM
DIVIDED BY THE FRACTION IN SOLUTION (ml)
ORNL-OWG 73-8695R
EQUILIBRIUM
a IN 001 M
Co (N03)2
59
(04
NUMBER OF WASHES - 0 01 M Ca (N03)2
Figure 2.9. Percent 109Cd retained by montmorillonites in 0.01 M
Ca(N03)2. Source: Brantley et al., 1974, Figure 5.2.26, p. 210.
-------
24
2.3.3.2 Humus — Another important soil constituent involved in cadmium
adsorption is humus, which binds very strongly to particles of clay (Bowen,
1966). This combined organo-clay fraction largely controls the adsorption
of cadmium in soil (Brantley et al., 1974). The cation exchange capacity
/of humus depends markedly on pH (Bowen, 1966) due to the weakly acid prop-
erties of the adsorbing phenolic (ZI>—0") and carboxyl ( — COO") groups
(Figure 2.10). Although only surface adsorption is shown, adsorption occurs
ORNL-DWG 77-5673
CENTRAL UNIT
of a
HUMUS COLLOID
(mostly C and H)
Ca+
-COO"
COO"
o-
COO"
o-
COO"
o-
C007
NEGATIVE CHARGES
H+
NH4+
ADSORBED IONS
Figure 2.10. Adsorption of cations by humus colloids. Source:
Brady, 1974, Figure 4.10, p. 94.
within the micelle as well (Brady, 1974). A comparison of the effect of pH
on the cation exchange capacity of organic colloid humus and montmorillonite
clay is shown in Figure 2.11. The exchange capacity is a measure of the
negative charge, which, in turn, determines the adsorption ability of the
micelle. The adsorptive capacity of humus is approximately halved as the
pH is lowered from 9 to 4, whereas that of clay is almost independent of pH.
Soils become acidified by various means. For instance, release of
sulfur dioxide during combustion of sulfur-containing fuel is held respon-
sible for the high acidity of ^rainwater and the resultant acidification of
Swedish soils (Marx, 1975).^/Interestingly, the deleterious effect of sulfur
dioxide thus can be extended to a possible second-order effect — the release
by acidification of heavy metals from soils, making them available for plant
uptake (Section 4.2.1). ,'
Three categories of humus exist: fulvic acid, humic acid, and humin.
These differ in chemical and physical makeup but are similar with regard to
cation adsorption and release (Brady, 1974). Consequently, laboratory
adsorption studies may be facilitated by utilizing only one fraction, usually
the humic or fulvic acid fraction (Gamble and Schnitzer, 1974). Bondietti et
al. (1974) concluded that humic acids provide at least two types of adsorp-
tion sites, each with a different adsorption energy and coverage capacity, as
shown in Figure 2.12. The total cadmium binding capacity in their test solu-
tion (i.e., the maximum concentration of complexed ion) equalled 3.58 x 10"
-------
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220
ORNL-DWG 77-5668
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180
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Q, 120
100
80
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111
2 60
40
20
ORGANIC COLLOID.
MONTMORILLONITE.
pH-dependent charge
Permanent
charge
4.0
5.0
6.0
SOILpH
8.0
Figure 2.11. Influence of pH on the cation exchange capacity of mont-
morillonite and humus. Source: Brady, 1974, Figure 4.11, p. 100.
mole/liter attained at free Cd2+ concentrations above 10 3 M. At lower Cd2 +
concentrations, the adsorption is very strong, although only a small portion
of the available adsorption sites are occupied. As stated above, this is
interpreted in terms of different adsorption sites with different affinities.
In conclusion, adsorption phenomena are involved in the behavior of cad-
mium in bcth soils (or sediments) and aqueous media. Cadmium is held most
strongly by the organic-clay portion of soil, although clays coated with
hydrated oxides may possess an equally high affinity for the metal. Adsorp-
tion power of humic matter is strongly pH dependent, whereas that of clay is
-------
26
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SITES PRESENT
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IO"6
FREE Cd2
10"1
(moles/liter)
10~4
10"3
Figure 2.12. Fitting a two-site mechanism to observed complexing of
Cd2+ by captina humic acid. Source: Bondietti et al., 1974, Figure
5.2.21, p. 190.
virtually pH independent. The role of carbonate and hydroxide (lime) in
immobilizing cadmium as insoluble compounds in soil may be as important as
in aqueous media.
2.3.4 Cadmium in Biological Systems
2.3.4.1 Organocadmium Compounds — Organic compounds of cadmium can be pre-
pared in the laboratory but have not been observed in the natural environ-
ment; alkyl cadmium compounds are unstable in air and in water. Dimethyl-
cadmium rapidly absorbs oxygen from air and is converted to a glassy mass
that explodes when touched (Sheverdina and Kocheshkov, 1967). In water,
dialkylcadmium sinks to the bottom of the container in the form of large
drops, which are gradually converted to the hydrocarbon and cadmium hydroxide.
The reaction is accompanied by a characteristic crackling noise (Sheverdina
and Kocheshkov, 1967). Wood (1974), on the basis of the same approach as
that used with methylmercury, concluded that cadmium is not methylated in
soils and sediments; microbial methylation of cadmium has so far not been
observed. Nevertheless, it is worth noting that the nephrotoxicity of
methylcadmium chloride after intraperitoneal injection into cats may be
greater than that of inorganic cadmium (Chang and Sprecher, 1976).
-------
27
2.3.4.2 Biological Cadmium — Research into the action of cadmium in cells
and tissues indicates that Cd2+ is the active form (Berry, Osgood, and
St. John, 1974). Once within the system, cadmium may be bound to any one
of a large number of soluble or structural proteins as well as to compounds
of lower molecular weight. The low-molecular-weight, metal-binding pro-
teins (metallothioneins) deserve special mention.
'' Methallothioneins are characterized by a high content of the sulfhydryl
amino acid cysteine and of strongly bound metal ions such as cadmium and
zinc (Friberg et al., 1974; Kagi and Vallee, 1960; Nordberg et al., 1972).
Cadmium has a high affinity for sulfhydryl groups (Torchinskii, 1974), and
as many as seven ions may be bound to each molecule of thionein. To further
confirm that cadmium in metallothionein is bound via the cysteine residues,
Kagi and Vallee (1960) reported a strong correlation between the light
absorption by metallothionein at 250 nm and the presence of sulfhydryl groups
and bound cadmium (Figure 2.13).
ORNL- DWG 77-5283
1.0
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2
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ul
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.
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-------
28
Piscator, and Nordberg, 1971; Friberg et al., 1974, 1975; Fulkerson and
Goeller, 1973); progress and problems of cadmium analysis were reviewed
especially by Friberg and his collaborators. No one method is best for
cadmium analysis in every application; sample load, equipment availability,
and cost are key considerations in method selection. Detection limits,
sample matrix, specificity, analysis time, and accuracy must also be con-
sidered. These and other factors pertinent to the selection of an analyti-
cal method and the evaluation of reported analytical data are summarized
here.
Sample handling and sampling techniques assume even greater importance
in analytical schemes for trace metals than they do in other analytical
determinations. Correctly prepared standards may be invalidated by adsorp-
tion of the metal on container walls or by leaching of contaminants from
the container material. This problem is obviously aggravated by prolonged
storage of such solutions before use. The composition of samples may be
altered drastically by contaminated reagents used in various pretreatment
procedures such as dissolution, digestion, or extraction. Care should be
taken to employ only reagents of the highest purity. Even then, the quantity
added should be the minimum required to accomplish the purpose so that
unnecessary buildup of contaminants is avoided. A process control to monitor
additions from reagents is required. Thermal processing of samples contain-
ing cadmium should be carefully controlled. Although cadmium is not as vola-
tile as mercury or arsenic, it is, nevertheless, appreciably volatile, par-
ticularly as the chloride (Table 2.5), and caution must be exercised to avoid
losses during preliminary operations with the sample.
TABLE 2.5. PERCENT RECOVERY OF METAL SALTS FROM PLATINUM CRUCIBLES AFTER HEATING AT
VARIOUS TEMPERATURES FOR ONE HOUR
Metal
Cadmium
Copper
Zinc
Lead
weight
(Pg)
10
20
40
50
Recovery (%)
400°C
77
96
87
78
Chloride
500°C
56
96
87
54
600°C
17
71
62
21
400°C
102
104
99
100
Nitrate
500°C
100
98
97
102
600°C
83
77
88
96
400°C
100
102
96
102
Sulfate
500°C
100
100
97
102
600°C
96
56
97
96
Source: Adapted from Kometani et al., 1972, Table I, p. 618. Reprinted by permission of the
publisher.
2.4.2 Analytical Procedures
2.4.2.1 Preparation and Storage of Standard Solutions — Among plastic
materials tested, teflon, polyethylene, and polypropylene adsorb the
smallest amount of cadmium from aqueous solution, but polyethylene and
polypropylene are also known to supply traces of contaminants to solutions
(Shults, Lyon, and Carter, 1973, p. 428). Definitive data are needed to
-------
29
establish optimum sample handling and storage procedures. A safe procedure
is to prepare a stock standard solution of 10~s M or greater, using quartz
or borosilicate glassware with nitric acid as a solvent. To prevent pre-
cipitation or adsorption of cadmium, the nitric acid should provide a final
pH below 1 when dilutions are made of the stock solution (McFarren and
Lishka, 1968). Acid-washed (10% nitric acid) and previously equilibrated
glassware should be used for dilutions. Dilution flasks should always be
used with solutions that have similar concentration levels. Alternatively,
a stock solution of 1000 ppm cadmium in 1 N nitric acid may be prepared in
borosilicate glassware (Sandell, 1959), and small volumes of this solution
may be micropipetted directly. Stock solutions containing 1000 ppm cadmium
are commercially available.
2.4.2.2 Preparation and Storage of Samples — Cadmium metal and salts are
readily soluble in acid media; nitric acid is superior to hydrochloric and
sulfuric acids. In contrast to zinc, alkaline media are generally not
satisfactory. For organic and biological materials, a nitric acid digestion
under reflux is usually adequate. This process may be followed by evapora-
tion with perchloric or sulfuric acid, which in essence completes the oxida-
tion of organic material, removes nitric acid, and provides a cadmium
solution amenable to analysis by most methods.
Evaporation to dryness, particularly in the presence of HC10<,, should
be avoided; explosive mixtures may be formed. Dissolution under reflux,
low-temperature ashing, and freeze drying are recommended techniques for
controlling solution volumes. Comparison of results using wet digestion
and dry ashing techniques are shown in Table 2.6. To avoid losses by vola-
tilization, samples should be dissolved or digested at low temperatures.
It is important to collect and handle aqueous samples as carefully as dilute
stock or standard solutions.
,'
/ Airborne cadmium normally occurs as suspended aerosol particles —
probably oxides, chlorides, and sulfates (Hise and Fulkerson, 1973, p. 206).
Usually, sampling is done by collecting the particulates on a micropore
filter through which a measured volume of air is passed. Collected partic-
ulates are then dissolved in acid media and subsequently handled as an
aqueous solution. Alternatively, collected particulates may be analyzed
directly on the filter by x-ray fluorescence (Bennett, Wagman, and Knapp,
1975).
2.4.2.3 Concentration and Separation — Analysis of samples containing cad-
mium in the low parts-per-billion range generally requires a procedure to
concentrate the cadmium or to separate it from potential interferences,
regardless of the analytical techniques subsequently employed. Simple
separation procedures such as evaporation or precipitation often suffice,
but more specific techniques are usually required to eliminate interfering
constituents. The ideal procedure should accomplish both objectives.
2.4.2.3.1 Precipitatioii — Thioacetamide quantitatively precipitates the
sulfides of a number of heavy metals from acid solutions. This technique
is effective for solutions containing cadmium in concentrations of 5 yg/liter
or more (Burrell, 1974, p. 127). Although thioacetamide precipitation
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30
TABLE 2.6. COMPARISON OF ATOMIC ABSORPTION SPECTROSCOPY
RESULTS ON NEW YORK CITY PARTICULATE SAMPLE ON FILTER
PAPER PREPARED BY WET DIGESTION AND DRY ASHING
Metal
Metal content
(ng/cm2)
Wet digestion
HC10<,-HN03
Dry ashing,
500°C
Cadmium
Chromium
Cobalt
Copper
Iron
Lead
Manganese
Nickel
Vandium
Zinc
33, 39
25
N.D.,a
7.6 x 102, 7.4 x 102
46.5 x 102
62.0 x 102, 63.6 x 102
42, 42
1.2 x 102, 1.4 x 102
3.7 x 102
2.17 x 102, 2.17 x 102
22, 33
25
N.D.,a
7.9 x 102, 7.6 x 102
49.6 x 102, 46.5 x 102
66.7 x 102, 63.6 x 102
53, 64
1.2 x 102, 1.2 x 102
4.3 x 102
21.7 x 102, 21.7 x 102
a.
N.D. — not detected.
Source: Adapted from Kometani et al., 1972, Table IV,
p. 618. Reprinted by permission of the publisher.
increases sensitivity and eliminates matrix effects, the technique is not
widely used because of the excessive time and attention required. (Note:
Thioacetamide is listed by the National Institute for Occupational Safety
and Health as a possible carcinogen.)
2.4.2.3.2 Solvent extraction — Liquid-liquid solvent extraction is probably
the single most useful separation method for all chemical analyses (Andelman,
1971, p. 39). Its versatility is exemplified by the variety of its applica-
tions with cadmium. Cadmium can be extracted from aqueous into organic media
either as an ion-association or a chelate complex. In general, ion-association
complexes are used for milligram and larger quantities of cadmium, while
chelate complexes are used for trace quantities.
Quaternary ammonium salts of long chain amines, when dissolved in an
organic solvent, can extract a variety of metals as anlonic-association
complexes. Cadmium can be extracted quantitatively by tetrahexylammonium
iodide into methyl isobutyl ketone from acidic solutions. Cadmium is readily
stripped from the organic phase with the appropriate aqueous solution, thus
providing a convenient technique for concentration and separation of the metal
from a variety of environmental media (Maeck et al., 1961).
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31
Extraction with dithizone (diphenylthiocarbazone) is probably the most
widely used separation technique for cadmium. Typically, the cadmium dithi-
zonate is extracted into carbon tetrachloride or chloroform from an alkaline
aqueous medium containing suitable metal buffers and masking agents. Cadmium
is them recovered for analysis from the organic phase with strong acid
(Sandell, 1959, p. 355).
Under conditions similar to those cited above, cadmium can be extracted
into carbon tetrachloride as the diethyldithiocarbamate (Sandell, 1959,
p. 352). In alkaline solution, metals which form sufficiently strong com-
plexes with cyanide ions remain in the aqueous phase. Similarly, cadmium
can be extracted into methyl isobutyl ketone as the pyrrolidine dithiocarba-
mate (Yeager, Cholak, and Meiners, 1973). The latter solvent is compatible
with flame atomic absorption spectrographic techniques.
2.4.2.3.3 Chromatographic methods — Numerous chromatographic separation
methods have been applied to cadmium in recent years. Alumina, paper, cation
and anion exchange resins, and chelating agents, as well as zinc sulfide,
have been used. The ion exchange resin technique is particularly convenient.
For example, Dowex-1 (an anion exchange resin) sorbs cadmium, zinc, and bis-
muth from a solution of 0.1 M HC1 and 10% NaCl, but rejects iron(III),
copper, manganese, aluminum, nickel, cobalt, chromium(III), rare earths,
titanium, beryllium, and the alkaline earth ions. Washing the resin with a
solution of 2 M NaOH and 2% NaCl solution removes zinc, lead, and some
bismuth. The cadmium and remaining bismuth can be removed with 1 M HNOs
(Kolthoff and Elving, 1961, p. 192). Collection and concentration of trace
elements on ion exchange resins in the field and subsequent elution and
analysis in the laboratory preserve the sample while avoiding the adsorp-
tive losses or contamination that can occur during storage. This technique
deserves greater consideration than it is presently given (Environmental
Instrumentation Group, 1973a).
2.4.2.3.4 Electrodeposition— One of the most convenient methods for effect-
ing the separation of cadmium from other metals is electrolytic deposition
on either a platinum or mercury electrode. The electrolysis can be per-
formed in neutral, weakly acid, or alkaline media. The completeness of the
separation depends on the difference between the reduction potentials of
the metals to be separated. To assure the quantitative separation of cad-
mium from such metals as zinc, copper, and lead, it is advisable to perform
the electrolysis at an electrode whose potential is controlled at an optimum
value. For example, cadmium can be quantitatively separated from zinc by an
electrodeposition from sulfuric or hydrochloric acid at a mercury electrode
that is controlled at -0.85 V versus a saturated calomel reference electrode
(Kolthoff and Elving, 1961, p. 184). Cadmium is collected as an amalgam
which can be back-electrolyzed at a more positive potential to achieve
greater purity, if desired (Section 2.4.2.4.3). Electrodeposition can be
used with pyrolytic graphite as the working electrode, followed by neutron
activation analysis, or with platinum, gold, or copper electrodes for spark-
source spectrometric analysis.
2.4.2.4 Methods of Analysis — Cadmium can be determined by a variety of
analytical procedures. Those which are currently important or show future
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32
promise are described in this section. Emphasis is placed on performance
and limitations of each procedure rather than on minute details. Table 2.7
lists common instrumental methods for the analysis of cadmium. Sensitivity,
precision, accuracy, and optimum concentration ranges of samples vary not
only among different methods, but also among various models of particular
instruments. The tabulated data must therefore be considered representative
rather than definitive.
Several of the terms used in Table 2.7 are defined variously in the
literature. Sensitivity (Column 4) denotes the smallest quantity that can
be determined reliably by the designated technique or instrumentation. In
analytical methods utilizing continuous sampling, such as atomic absorption
spectrometry, sensitivity usually means the concentration of analyte that
yields an absorption of 1% or an absorbance of 0.0044. These data cannot be
compared with sensitivities given for methods using noncontinuous sampling
techniques, such as flameless atomic absorption spectrometry (Burrell, 1974,
p. 76). Column 6 gives the precision of each method as relative standard
deviation (i.e., the standard deviation of a set of samples expressed as a
percentage of the mean). It also indicates sample concentration because
the reported precisions of trace-level analyses strongly depend on sample
size. Column 7 records accuracies of various methods in terms of percentage
recovery from spiked samples. Literature values for the accuracy of a given
method vary widely, and only a few interlaboratory or interprocedural com-
parisons are available. In general, however, only conservative literature
reports are cited; under ideal conditions, even more favorable results
may be expected.
2.4.2.4.1 Spectrophotometric analysis — Spectrophotometric procedures are
based on measuring light absorbed by a sample at a particular wavelength.
The most popular method for determining trace levels of cadmium has been
extraction with dithizone followed by a Spectrophotometric reading (American
Public Health Association, American Water Works Association, and Water
Pollution Control Federation, 1971, p. 77). Although tedious and time-
consuming, this technique can be both sensitive and specific. The extrac-
tion procedure depends on the type of sample being processed as well as the
type of matrix and interferences that might be present. In general, extrac-
tion is performed at pH greater than 12 with cyanide and/or tartrate present
to prevent hydrolysis of the cadmium and to control precipitation and ex-
traction of other metals. The dithizone-chloroform extract is washed first
with dilute sodium hydroxide, then water, and the optical absorbance of the
cadmium dithizonate is measured at 520 nm. Lead, zinc, and bismuth are not
extracted and do not interfere. Accurate results depend on the use of high-
purity dithizone and chloroform. As an alternative procedure, the cadmium
dithizonate is acidified with 0.5 M HC1, and the color intensity of liberated
dithizone is measured at 620 nm.
The dithizone method is useful for processing a variety of liquid and
solid samples, especially when preconcentration is needed or when high
levels of other cations may be present. It is now being superseded, how-
ever, by the more sensitive and convenient technique of atomic absorption
spectrometry.
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35
2.4.2.4.2 Spectroscopic methods — These useful methods for determining
cadmium include emission spectroscopy, flame and flameless spectrometry,
and spark-source mass spectrometry.
Emission spectroscopy has been used a great deal for rapid qualitative
or semiquantitative analysis of cadmium in a variety of liquid and solid
sample forms, especially metals, alloys, ores, and homogeneous solids which
require multielement determinations (Environmental Instrumentation Group,
1973a, p. 14). Liquid samples are usually deposited on metal or graphite
electrodes and dried before analysis. Atoms or atomic ions form by excita-
tion of the sample in an electrical arc, spark, or plasma. The energy of
the excited atoms or ions is emitted as discrete radiation or as bands of
radiation for molecular forms. Spectra consist of sharp lines for which
the wavelength and intensity are characteristic of the element. Comparison
of spectra of known and unknown materials provides qualitative identification
of elements in the sample. For quantitative analysis, the usual practice is
to measure the ratios of line intensities of the element under study and
compare them to those of a known element. The known element may be part of
the sample or may be added to the sample and thus be subjected to the same
conditions as the element of interest. This minimizes the influence of pro-
cedural variables. For accurate work the ratios are compared with standards
prepared by the same techniques. Accuracy is about 10% if the standard
addition technique is used and the concentration is approximately 0.1%
(Environmental Instrumentation Group, 1973a, p. 14). Emission spectroscopy
using plasma excitation of the sample is more sensitive than conventional
direct or alternating current arc or spark sources (Environmental Instru-
mentation Group, 1973&, p. 6).
Flames can be used to volatilize, atomize, or excite many elements,
which can then be determined by the amount of light emitted from or absorbed
by these elements in selected zones of the flame (flame spectrometry). Cad-
mium can be determined by atomic emission, atomic absorption, and atomic
fluorescence modes of operation. Usual detection limits reported for these
techniques are 50, 10, and 0.2 yg/liter respectively (Shults, Lyon, and
Carter, 1973, p. 435). Atomic absorption is most often used and is rapidly
becoming the accepted method for determining cadmium at the trace level.
Though not as sensitive as anodic stripping voltammetry, this method has the
definite advantage of being faster and less tedious. The cadmium lines at
228.8 nm and 326.1 nm are usable; the 228.8-nm line is more intense and pre-
ferred for analysis. Detection limits can be improved either by using a
long optical (flame) path length or by preconcentration. The former approach
has been reported to provide detection limits under 1 yg/liter (Environmental
Instrumentation Group, 1973a, p. 14). The latter approach— extraction plus
direct aspiration of the extract into the flame — provides detection limits
comparable to those of anodic stripping techniques. The atomic absorption
technique is useful for all types of samples, particularly trace-level deter-
minations of cadmium in fresh and marine waters, industrial effluents, and
biological materials. The atomic fluorescence technique needs further
development to gain wide acceptance in the determination of trace levels of
cadmium in environmental samples.
Conventional flame spectrometry techniques normally convert 2% to 8% of
the sample to the atomic state (Environmental Instrumentation Group, 1973a,
-------
36
p. 5). In some instances, efficiency and sensitivity can be improved by
replacing the flame with a carbon, graphite, or tantalum-ribbon furnace in
which the sample is sequentially dried, ashed (if necessary), and heated to
incandescence (flameless spectrometry). Smoke or salt particles produced
during the heating steps can cause scattering and attenuation of light
intensities. In addition, flameless techniques generally produce an absorb-
ance peak of relatively short duration compared to the "steady" signal
obtained from a flame. Nevertheless, direct analysis of cadmium at the
level of 1 ng/liter is now feasible for some samples (Environmental Instru-
mentation Group, 1973a, p. 14), and rapid extension of the technique to new
types of samples continues. The flameless atomic absorption technique may
be used to analyze all types of samples; however, it is probably most effec-
tive for the direct analysis of solid biological and environmental samples
without prior processing.
Cadmium may be determined by exciting the sample with a radio-frequency
spark, followed by separation of the resulting cadmium ions according to
their mass (spark-source mass spectrometry). This technique is applicable
to virtually any matrix, but results are only semiquantitative. The method
can be accurate within ±5%, however, when used with an isotope dilution
technique (Shults, Lyon, and Carter, 1973, p. 435). In this procedure,
106Cd is added to the sample, and isotopic equilibrium is established
between the added 106Cd and the "normal" cadmium in the sample. In most
cases, isotopic equilibrium is easily attained by refluxing the sample with
a perchloric acid—nitric acid mixture. This treatment also serves to oxi-
dize any organic matter present in the sample. Once isotopic equilibrium
is reached, any technique that permits the transfer of 1 to 10 ng of cadmium
from the solution to the surface of a suitable substrate (electrode) may be
used. Solvent extraction may be employed, if necessary, to concentrate the
cadmium before transfer to the substrate. Extraction with dithizone is
suitable. High extraction efficiencies are not required since the analysis
at this point depends only on establishing a ratio between two isotopes —
for example, 11£>Cd and 106Cd. This procedure is more time-consuming and
expensive than some of the methods discussed previously; however, it is
virtually free from matrix effects and has the advantage of allowing anal-
ysis for many elements simultaneously. When the isotope dilution technique
is used, the method has a detection limit of about 1 yg cadmium per liter.
It is attractive for samples requiring multielement determinations at low
trace-element concentrations.
2.4.2.4.3 Electrochemical techniques — Cadmium can be determined by a
variety of electrochemical techniques. The most popular methods are polar-
ography and anodic stripping voltammetry. In polarography, the current-
voltage curve for electrolysis at a small mercury drop is obtained. The
curve is sigmoidal: height reflects the concentration of electroactive
material present and location (potential) reflects the identity of the
material. Conventional polarography can easily be used to determine cad-
mium at the 1 yg/g level, with precision and accuracy of approximately ±3%.
With sophisticated instrumentation, lower concentrations can be analyzed
(Shults, Lyon, and Carter, 1973, p. 433). For example, 0.1 yg/g solutions
can be analyzed by "derivative" polarography, and 0.01 yg/g solutions can
be analyzed by "pulse" polarography. Conventional polarography techniques
-------
37
are useful in analyzing metal-bearing liquid wastes and effluents and sur-
face water samples containing relatively high concentrations of cadmium.
Natural water samples and other environmental liquids containing cadmium
in the parts-per-billion range cannot be analyzed without preconcentration.
The latter samples may, however, be satisfactorily processed by "derivative"
and "pulsed" polarographic techniques. This technique differs from ordinary
polarography because the current is measured twice during each drop, and
the difference is recorded. Well-defined signals are obtained from concen-
trations of cadmium as small as 4 ppb (Osteryoung and Osteryoung, 1972).
Anodic stripping voltammetry is a sensitive electrochemical technique
for determining cadmium. Cadmium is electrodeposited under strictly con-
trolled experimental conditions (e.g., stirring rate and electrode potential),
and the resulting cadmium amalgam is electrolytically dissolved to determine
the amount of cadmium electrodeposited. The dissolution or "stripping" step
can be accomplished in several ways. Voltammetric stripping involves the
measurement of stripping current as a function of electrode potential,
whereas coulometric stripping measures the amount of charge required to
dissolve the amalgam. In either mode of operation, solutions containing
1 yg cadmium per liter can be analyzed with an accuracy of about ±10%
(Shults, Lyon, and Carter, 1973, p. 433). With care, this technique can be
used routinely. Zinc and cadmium-to-zinc ratios can also be determined.
Because of great sensitivity, the anodic stripping voltammetry technique
can be1 used to analyze most freshwater samples without preconcentration.
^With suitable sample preparation, this technique is also useful for
industrial wastes, biological materials, dusts, alloys, and ores.
In recent years, ion-selective electrodes have been developed which
respond to various cations and anions. Such an electrode is available for
measuring cadmium concentration. Although sensitivity is not sufficient
for monitoring cadmium in natural waters, it may be suitable for monitoring
cadmium in waste materials and other special situations. Semilogarithmic
response extends down to about 1 Mg/g cadmium (Shults, Lyon, and Carter,
1973, p. 434). Interference by copper, lead, silver, and mercury may be
severe, and since only the activity of the free metal ion is measured, any
complexed metal will go undetected.
2.4.2.4.4 Neutron activation analysis — Neutron activation analysis is one
of the most sensitive modern analytical techniques for the determination of
trace elements. Samples and krown standards are irradiated in a nuclear
reactor during which time neutrons are captured by various nuclides in the
sample. Radioactive isotopes are usually produced, making it possible, by
appropriate measurement techniques, to identify the daughter activities and
relate them to the parent isotope. By comparison with the activity induced
in the standards, the amount of sought isotope can be calculated. The in-
duced activity, and hence the sensitivity for determining the parent nuclide,
is proportional to the neutron flux, to the nuclear cross section of the
atoms, and to the amount of the parent isotope present. Neutron fluxes of
1012 to lO1** per square centimeter per second are easily available in modern
reactors; therefore, for reasonable length irradiations (a few seconds to a
few days) most elements can be determined at the level of 10~8 to 10~10 g
(Shults, Lyon, and Carter, 1973, p. 437). The commonly used reaction for
-------
38
activation analysis is lli'Cd(n, y)il5Cd. Since ilifCd has a cross section
of 1.1 x 10"24 cm2 and produces a 53.5-hr half-life decay for ll5Cd, which
has only 25% branching through a measurable gamma ray, sensitivity for non-
destructive neutron activation analysis of cadmium is not as great as for
some other elements. Cadmium can be determined nondestructively at the
level of 10~7 to 10~9 g in matrices that do not activate significantly.
Chemical separation of cadmium allows sensitivities several orders of magni-
tude greater than this. The technique is applicable to all types of samples,
usually in their existing state. Aqueous samples may require concentration
by evaporation, precipitation, solvent extraction, electrodeposition, or ion
exchange. -'Minimum detectable concentrations of cadmium are relatively high
for river water (0.05 ppm) and seawater (16 ppm) because of interference
from major constituents, such as sodium (Environmental Instrumentation Group,
1973a, p. 15).
The determination of cadmium by neutron activation analysis is rela-
tively expensive; it is economically competitive with other techniques only
when nondestructive methods must be applied or when several elements are
determined simultaneously, thus reducing the analytical cost per element.
2.4.2.4.5 X-ray fluorescence — Recent developments in x-ray sources and
instrumentation have resulted in increased acceptance of x-ray fluorescence
as an analytical method for the simultaneous detection of several elements
in a wide range of samples. X-ray fluorescence may be induced by excita-
tion sources such as electron beams, high-energy x rays, or alpha, beta,
and gamma radiation from radioisotope sources. When the sample is irradi-
ated, a series of characteristic x-ray lines are then emitted as the ejected
electron is replaced by an electron from an outer orbital of the excited
atom. Two techniques are used to resolve the spectra. Wavelength-dispersive
spectrometers employ analyzing crystals to resolve the fluorescence spectra.
Alternatively, energy-dispersive spectrometers utilize solid-state detectors
in conjunction with multichannel analyzers.
X-ray fluorescence has not been the best method for determining cad-
mium in trace-level samples. Cadmium is only poorly excited by conventional
x-ray sources; thus, a sensitivity of a few parts per million is the best
that can be expected. Watanabe, Berman, and Russell (1972) stated that cad-
mium cannot be determined simultaneously with other elements because special
targets and analyzing crystals are required. However, Bennett, Wagman, and
Knapp (1975) analyzed air pollution particulate samples collected on mem-
brane filters for cadmium. A spectrometer system with a 16-crystal mono-
chromator was capable of determining up to 30 elements simultaneously. The
detection limit for cadmium was 6 pg/cma and was attributed to a combina-
tion of low background and efficient excitation of the cadmium Ka line by
a chromium target x-ray tube. The method is nondestructive, requires no
pretreatment, and may be completed with nominal counting times of 100 sec.
2.4.3 Comparison of Analytical Methods
Until the last decade, the spectrophotometric method utilizing dithi-
zone was the most widely used technique for determining cadmium. As dis-
cussed above, the method must be combined with extraction procedures to
-------
39
achieve adequate sensitivity and specificity. During the last few years,
however, this method has been largely replaced by atomic absorption spec-
trometry. The latter method usually requires extraction of cadmium as the
ammonium pyrrolidine dithiocarbamate complex into methyl isobutyl ketone,
followed by aspiration into an air-acetylene flame. However, many aqueous
samples containing 25 to 250 yg cadmium per liter can be analyzed satisfac-
torily without pretreatment. The spectrophotometric method using dithizone
is neither sensitive nor specific for measuring cadmium in natural water
samples, although it can be made so by extraction methods.
The chief need in analysis of environmental samples of cadmium is
greater sensitivity so that sample pretreatment can be minimized or elimi-
nated. Fortunately, several such techniques are emerging from developmental
laboratories and are becoming generally available. Flameless atomic absorp-
tion spectrometers equipped with a graphite furnace, a carbon rod, or a
tantalum ribbon rather than a flame may extend the detection limit of cad-
mium by a factor of 10 to 1000 (Environmental Instrumentation Group, 1973Z?,
p. 16). Direct analysis of water and biological samples is feasible with
minimal pretreatment and greatly simplifies the procedure. The anodic
stripping voltammetry technique can often determine cadmium in the low
parts-per-billion range without sample pretreatment. Differential pulse
polarography is 100 to 1000 times more sensitive than classical polarography,
permitting analysis of cadmium at the level of 1 to 100 ppb. Preparation of
biological samples for atomic absorption spectrometry was described by
Gross et al. (1975) and special solutions for analyzing blood by anodic
stripping voltammetry have been reported (Environmental Science Associates,
Inc.).
Two somewhat older analytical techniques are available for analyses
of cadmium in the parts-per-billion range: spark-source mass spectrometry
with isotope dilution and neutron activation analysis. These established
methods are not, in general, economically competitive with the methods
described above, unless simultaneous determinations of a number of other
elements are required.
The x-ray fluorescence method allows multielement analysis, requires
minimal sample handling, and is essentially nondestructive. The technique
is useful in many applications such as particulate samples collected from
ambient air and source emission streams. However, low sensitivity and
general inconvenience prevent x-ray fluorescence from being the best method
for determining cadmium at trace levels (Watanabe, Berman, and Russell,
1972).
'2.4.3.1 Standardization — Trace-level determinations of cadmium are required
in an extensive variety of samples: biological specimens such as plants,
animal tissues, bone, and blood; soils and sediments; geological specimens;
industrial wastes and products, including sludges, dusts, and filter deposits;
metals and alloys; paints and pigments; plastics; and various fresh and
marine water supplies. Reliable analyses require (1) standard procedures for
collection, preparation, and storage of these specimen types and (2) standard
methods for concentrating or separating the contained cadmium for determination
by one of several analytical techniques. Standardization, however, is only
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40
beginning; earliest efforts have been directed toward development of proce-
dures for groundwater, surface water, domestic and industrial waste efflu-
ents, and treatment process samples. Thus, Standard Methods for the Exami-
nation of Water and Wastewater, 13th ed., 1971, published jointly by the
American Public Health Association, the American Water Works Association,
and the Water Pollution Control Federation, prescribes standard sample
handling techniques and analytical procedures for many metals, including
spectrophotometric and atomic absorption techniques for cadmium at the trace
level. More recently, the U.S. Environmental Protection Agency published
the Handbook for Analytical Quality Control in Water and Wastewater Labora-
tories, 1972, defining standards useful in many aspects of the work. In a
companion volume, Manual of Methods for Chemical Analysis of Water and
Wastes, 1974, the U.S. Environmental Protection Agency established standard
procedures for determining many constituents of water samples, including
the analysis of trace levels of cadmium by atomic absorption spectrometry.
Much work remains to be done in this area. One of the most pressing needs
is to make standard materials representative of environmental samples more
available. Secondary standards, based on analysis rather than synthesis,
should be available for comparison of procedures as well as for interlabora-
tory comparisons.
2.4.3.2 Interlaboratory Comparison — Relatively few interlaboratory com-
parisons of cadmium analyses at the trace level have been reported. In one
study, conducted by the Quality Assurance Laboratory Branch of the Methods
Development and Quality Assurance Research Laboratory, Cincinnati, Ohio,
six synthetic concentrates containing varying levels of aluminum, cadmium,
chromium, iron, manganese, lead, and zinc were added to natural water
samples (U.S. Environmental Protection Agency, 1974). Samples were distrib-
uted to various laboratories for analysis by atomic absorption spectrom-
etry. The statistical results for cadmium detection are given in Table 2.8.
The precision and accuracy obtained among laboratories established the
adequacy of the atomic absorption spectrometry method for cadmium down to
1 ppb for sample types described.
TABLE 2.8. INTERLABORATORY STUDY ON TRACE LEVEL ANALYSIS
OF CADMIUM BY ATOMIC ABSORPTION SPECTROMETRY
Number
of
labs
74
73
63
68
55
51
True
value
(Mg/liter)
71
78
14
18
1.4
2.8
Mean
value
(yg/liter)
70
74
16.8
18.3
3.3
2.9
Standard
deviation
(yg/liter)
21
18
11.0
10.3
5.0
2.8
Accuracy
(% bias)
-2.2
-5.7
19.8
1.9
135
4.7
Source: U.S. Environmental Protection Agency, 1974,
102.
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41
In an earlier study (McFarren and Lishka, 1968), the Analytical Ref-
erence Service, Cincinnati, Ohio, prepared water samples having the composi-
tion given in Table 2.9. The samples were distributed to 79 participating
TABLE 2.9. COMPOSITION OF WATER METALS
SAMPLE USED IN INTERLABORATORY COMPARISON
, ,,i Concentration
Compound Metal , /n_ x
* (mg/liter)
K2A12(SO,.K«24H20
Copper metal
Fe(NH<,)2(SO<,)2-6H20
KMnOz,
Zinc metal
AgN03
Cadmium metal
K2Cr207
Pb(N03)2
Al
Cu
Fe
Mn
Zn
Ag
Cd
Cr
Pb
0.50
0.47
0.30
0.12
0.65
0.15
0.05
0.11
0.07
Source: Adapted from McFarren and
Lishka, 1968, Table I, p. 254. Reprinted by
permission of the publisher.
laboratories for analysis of nine designated metals by procedures specified
in Standard Methods for the Examination of Water and Wastewater, 12th ed.
For analysis of cadmium, the indicated methods were spectrophotometry, using
dithizone, and polarography. The results for cadmium are listed in Table 2.10.
The dithizone method, giving poor precision but excellent accuracy, is
obviously superior on both counts to the polarographic technique. However,
both methods suffer when compared with the more modern atomic absorption
technique previously described.
In a study by the U.S. Environmental Protection Agency in which trace
elements in fuels were monitored (von Lehmden, Jungers, and Lee, 1974),
nine laboratories using similar analytical methods were asked to determine
the concentration of 28 elements, including cadmium, in the same fuel as
well as in fly-ash matrices. The analytical methods used included neutron
activation analysis, atomic absorption spectrometry, spark-source mass
spectrometry, optical emission spectrometry, anodic stripping voltammetry,
and x-ray fluorescence. The cadmium results are listed in Table 2.11. The
wide range of concentrations illustrates the difficulties in determining
trace elements in different matrices and again emphasizes the need for
standard reference materials certified in trace-element concentrations.
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42
TABLE 2.10. SUMMARY OF INTERLABORATORY DATA ON MANGANESE, SILVER, AND CADMIUM
ANALYSES OF WATER SAMPLES
Method
of
analysis
Persulfate
Periodatea
Spectrograph
Atomic absorption
Formaldoxime
Dithizone
Spectrograph
Dithizone
Polarograph
Number
of
analyses
33
14
4
3
3
14
3
44
4
„ Standard Mean
Mean , ...
, ,... , deviation error
(mg/liter) (mg/llter) (mg/liter)
Manganese,
0.118
0.150
0.113
0.127
0.180
Silver, 0.
0.049
0.090
Cadmium , 0 .
0.053
0.040
0.12 mg/liter
0.031
0.054
0.022
0.025
0.069
15 mg/liter
0.030
0.066
05 mg/liter
0.013
0.034
0.00
0.03
0.01
0.01
0.06
0.00
0.06
0.00
0.01
Relative
standard
deviation
(%)
26.3
36.0
19.4
19.6
38.4
61.0
73.5
24.5
68.0
Relative
error
(%)
0.0
25.0
8.3
8.3
50.0
66.6
40.0
0.0
20.0
a.
Standard method.
Source: Adapted from McFarren and Lishka, 1968, Table V, p. 258. Reprinted by permission
of the publisher.
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43
TABLE 2.11.
COMPARISON OF CADMIUM CONCENTRATIONS IN COAL, FLY ASH, FUEL OIL, AND GASOLINE
BY ANALYTICAL METHOD AND BY LABORATORY
Sample
matrix
Coal
Fly ash
Fuel oil (No. 6)
Premium gasoline
Analytical method
Spark-source mass spectrometry"
Spark-source mass spectrometry
Spark-source mass spectrometry
Optical emission spectrometry^
Optical emission spectrometry
Nuclear activation analysis (instrumental)
Nuclear activation analysis (instrumental)
Spark-source mass spectrometry
Spark-source mass spectrometry '
Spark-source mass spectrometry
Spark-source mass spectrometry
Optical emission spectrometry^
Optical emission spectrometry"^ e
Neutron activation analysis (instrumental)
Spark-source mass spectrometry^
Spark-source mass spectrometry*
Optical emission spectrometry/
Optical emission spectrometry?
Atomic absorption spectrometry
Spark-source mass spectrometry
Optical emission spectrometry.
Optical emission spectrometry
Neutron activation analysis (instrumental)
Atomic absorption spectrometry
Spark-source mass spectrometry
Anodic stripping voltammetry^
Laboratory
code
1
3
6
1
3
3
4
1
1
3
6
1
1
4
1
3
1
1
1
1
1
1
4
1
3
7
Analysis
S amp 1 e
code^ , , .
(ug/g)
6.
<1 .
0.7
<30
<10
<3
<40
<3
<6
2
2.3
<50
<100
<90
G-10
G-10
G-10
G-10
G-10
G-l
G-l
(pg/ml)
0.003
0.83
0.4
1.
<0.2
0.001
<0.1
<1.
<20
<0.15
0.023
0.006
,The nine participating laboratories were coded to maintain anonymity.
Comparison includes two samples (G-l and G-10) of the same brand name collected from the pumps of two
different retail service stations.
Analysis on sample direct.
Direct current arc on sample direct.
Duplicate sample submitted for spark-source mass spectrometry and optical emission spectrometry
analysis only.
J|450°C ashing followed by ash analysis.
•f ^SOi,—HN03 dissolution , dried , and analyzed .
•HC1 extraction preparation.
Analysis of residue after combustion of sample.
Source: Adapted from von Lehmden, Jungers, and Lee, Tables I-IV, pp. 240-243. Reprinted by permission
of the publisher.
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44
SECTION 2
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45
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Mass. 01803.
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Shacklette, I.C.T. Nisbet, and S. Epstein. 1974. Environmental
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24. Fulkerson, W., and H. E. Goeller, eds. 1973. Cadmium, the Dissipated
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Tenn. 473 pp.
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46
25. Gamble, D. S., and M. Schnitzer. 1974. The Chemistry of Fulvic Acid
and Its Reactions with Metal Ions. In: Trace Metals and Metal-Organic
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26. Goeller, H. E., E. C. Rise, and H. B. Flora II. 1973. Societal Flow
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27. Gross, S. B., E. A. Pfitzer, D. W. Yeager, and R. A. Kehoe. 1975.
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29. Harris, R. L., G. R. Helz, and R. L. Cory. 1975. Processess Affecting
the Vertical Distribution of Trace Components in the Chesapeake Bay.
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30. Hem, J. D. 1972. Chemistry and Occurrence of Cadmium and Zinc in
Surface Water and Groundwater. Water Resour. Res. 8(3):661-679.
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32. International Agency for Research on Cancer. 1973. IARC Monographs
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chemical Properties. J. Biol. Chem. 236(9):2435-2442.
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to Pollution Evaluation. Environ. Res. 8:92-106.
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37. Kolthoff, I. M., and P. J. Elving. 1961. Treatise on Analytical
Chemistry, Part II, Analytical Chemistry of the Elements, Vol. 3.
Interscience Publishers, New York. 380 pp.
38. Kometani, T. Y., J. L. Bove, B. Nathanson, S. Siebenberg, and
M. Magyar. 1972. Dry Ashing of Airborne Particulate Matter on
Paper and Glass Fiber Filters for Trace Metal Analysis by Atomic
Absorption Spectrometry. Environ. Sci. Technol. 6(7):617-620.
39. MacLeod, K. E., and R. E. Lee, Jr. 1973. Selected Trace Metal
Determination of Spot Tape Samples by Anodic Stripping Voltammetry.
Anal. Chem. 45(14)=2380-2383.
40. Maeck, W. J., G. L. Booman, M. E. Kussy, and J. E. Rein. 1961.
Extraction of the Elements as Quaternary (Propyl, Butyl, and Hexyl)
Amine Complexes. Anal. Chem. 33(12):1775-1780.
41. Marx, J. L. 1975. Air Pollution: Effects on Plants. Science
187:731-733.
42. McCaull, J. 1971. Building a Shorter Life. Environment 13(7):3-41.
43. McFarren, E. F., and R. J. Lishka. 1968. Evaluation of Laboratory
Methods for the Analysis of Inorganics in Water. Adv. Chem. Ser.
73:253-262.
44. Menden, E. E., V. J. Elia, L. W. Michael, and H. G. Petering. 1972.
Distribution of Cadmium and Nickel of Tobacco during Cigarette
Smoking. Environ. Sci. Technol. 6(9)=830-832.
45. National Academy of Sciences. 1974. Geochemistry and the Environ-
ment, Vol. 1, The Relation of Selected Trace Elements to Health and
Disease. Washington, D.C. 113 pp.
46. Nordberg, G. F., M. Nordberg, M. Piscator, and 0. Vesterberg. 1972.
Separation of Two Forms of Rabbit Metallothionein by Isoelectric
Focusing. Biochem. J. (Great Britain) 126:491-498.
47. Osteryoung, J. G., and R. A. Osteryoung. 1972. Pulse Polarographic
Analysis of Toxic Heavy Metals. Am. Lab. 4(7):8-16.
48. Posselt, H. S. 1971. Environmental Chemistry of Cadmium in Aqueous
Systems. Ph.D. Dissertation. University of Michigan, Ann Arbor,
Mich. 189 pp.
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of Cadmium in Aqueous Systems. University of Michigan, Ann Arbor,
Mich. 178 pp.
50. Posselt, H. S., and W. J. Weber, Jr. 197^. Studies on the Aqueous
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Arbor, Mich. pp. 291-315.
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48
51. Pourbaix, M. 1973. Lectures on Electrochemical Corrosion. Plenum
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-------
SECTION 3
BIOLOGICAL ASPECTS IN MICROORGANISMS
3.1 SUMMARY
Zooplankton and phytoplankton can absorb and concentrate trace metals
present in water. Cadmium can be found adsorbed to exoskeletons of zoo-
plankton in bottom sediments. It is concentrated by several species of
algae, some of which tolerate high concentrations of cadmium in the labora-
tory. Because cadmium is present in water, its effects on microorganisms
must be elucidated in order to permit evaluation of hazards as the metal
enters the food chain.
In a small number of studies, cadmium was found to be toxic in varying
concentrations to several species of bacteria, yeast, and fungi. In general,
cadmium levels needed to cause toxic effects in bacteria (0.2 to 6 ppm) are
several times higher than concentrations generally detected in waters pol-
luted with industrial waste. The small amount of available data concerning
yeast and fungi does not permit a comparison of toxic levels with concen-
trations in the environment. Anaerobic digestion of sludge is inhibited by
soluble cadmium, as influenced by pH, and by the concentrations of sulfide
and carbonate ions. Several fungicides contain cadmium compounds as the
active ingredient, but little is known about mode of action or lethal
concentrations.
3.2 METABOLISM
3.2.1 Bacteria
Information available on the relationship of cadmium to bacterial
metabolism is limited. Mitchell (1974) stated that metabolism of cadmium
by bacteria has not been detected in natural habitats. Kondo, Ishikawa,
and Nakahara (1974) reported that Staphyloaoceus aureus, a common human
pathogen, contains a specific gene in the penicillinase plasmid that con-
fers resistance to cadmium toxicity. Experimentally, a 2-ppb concentration
of cadmium chloride proved toxic to the plasmid-negative strain, while a
concentration of 200 ppb was needed before a toxic effect on the plasmid-
positive strain was seen. This resistance was attributed to some mech-
anism which retained the cadmium ion outside the cell by conformational
changes of the cytoplasmic membrane and/or to a recognition mechanism
allowing the cell to distinguish between toxic cadmium ions and beneficial
calcium ions. The bacteria not carrying the plasmid incorporated cadmium
ions into the cell. This incorporation was temperature dependent and did
not occur at 4°C. Kondo, Ishikawa, and Nakahara (1974) concluded that
cadmium ions could not penetrate resting cells of 5. awceus and suggested
that cadmium ions may uncouple oxidative phosphorylation in the cytoplasmic
membranesY Chopra (1971) reported earlier that most of the cadmium ions
taken up by the cadmium-sensitive cells were bound to a structure within
the cell and were not merely adsorbed to the surface.
50
-------
51
Cadmium increased the swelling of Pseudomonas aevuginosa cells which
had been pretreated with alkali (Bernheim, 1973). These treated cells
also showed an increased efflux of potassium in the presence of cadmium.
Bernheim postulated that cadmium can react with membrane phospholipids
since it precipitates phospholipids from solution.
3.2.2 Yeast
Some research has been done on effects of cadmium on respiration in
yeasts. Cadmium ions at a concentration of 1.5 to 150 yM (0.17 to 17 ppm)
stimulated the oxidation of reduced nicotinamide adenine dinucleotide
(NADH) by Saacharomyoes aerevisiae mitochondria (Subik and Kolarov, 1970).
The cadmium-stimulated respiratory rate exceeded state 3 oxidation of NADH
but was sensitive to antimycin A inhibition. Even though stimulation was
found over a wide range of concentrations, greatest stimulation occurred
between 5 and 15 yM. Cadmium inhibited citrate oxidation to a lesser ex-
tent than succinate oxidation (Subik and Kolarov, 1970). The authors sug-
gested that the effect of cadmium involves reaction with SH groups and is
associated with an increased cation permeability of the mitochondrial inner
membrane, previously reported by Blondin, Vail, and Green (1969). Cells
of bakers' yeast, grown in broth containing 10 ppm cadmium, showed a con-
spicuous endoplasmic reticulum in electron micrographs (Lindegren and
Lindegren, 1973) in contrast to cells grown in absence of the metal. Only
a few mitochondria with signs of cristae were observed, and no normal cris-
tate mitochondria were seen. Cells grown in cadmium broth were replated on
normal agar; 30% of the colonies formed were "petite" and respiratory defi-
cient. The authors concluded that the cadmium ion produced a nonlethal
modification of the mitochondria, which caused them to lose respiratory
capacity.
3.2.3 Plankton
Only scattered data are available concerning the effects of cadmium on
plankton. Abdullah, Royle, and Morris (1972) suggested that phytoplankton
and zooplankton are natural agencies for removal and control of trace
metals. When the concentration of trace metals increased, a corresponding
decrease of plankton took place, suggesting a concentration-effect relation-
ship. Knauer and Martin (1973) also reported an inverse relationship
between cadmium concentration and phytoplankton productivity. This connec-
tion, however, was obscured by changes in cadmium concentration caused by
ocean swells. Studies by Rice, Leighty, and McLeod (1973) suggest that,
for the most part, accumulation of trace metals by plankton is due to sur-
face adsorption and ion exchange processes.
3.3 EFFECTS
Cadmium toxicity to microorganisms is summarized in Table 3.1.
3.3.1 Bacteria
Knowledge concerning the effects of cadmium on bacteria is limited.
The few reported studies determined the sensitivity of the test organism
-------
52
TABLE 3.1. CADMIUM CONCENTRATIONS CAUSING TOXICITY TO VARIOUS MICROORGANISMS
Organism
Toxic
concentration
Reference
Eschenahi-a coli.
StaphyloGOcous aureus
Plasmid-positive
Plasmid-negative
Selenastvum capricornutum
Chaetoaeros galvestonens-is
Cyclotella nana
Phaeodaotylum tricornutwn
Tetrahymena pyriformis
Thraustochytrium striatum
6 ppm Cd as CdCl2
0.2 ppm CdCl2
2 ppb CdCl2
0.65 ppm Cd
0.1 ppm (not toxic)
0.1 ppm (not toxic)
0.1 ppm (not toxic)
1.67 ppm CdSO<.a
0.112 ppmC
1.12 ppm as CdCl
d
Zwarun, 1973
Kondo, Ishikawa, and
Nakahara, 1974
Barlett, Rabe, and Funk,
1974
Hannan and Patouillet, 1972
Hannan and Patouillet, 1972
Hannan and Patouillet, 1972
Carter and Cameron, 1973
Schneider, 1972
Schneider, 1972
a.
Lethal threshold concentration.
^Algicidal concentration.
.Suppressed zoospore activity.
Suppressed sporangia activity.
d
to cadmium and, for the most part, did not delve into the mode of action
responsible for the toxic effects. As in the case of the interaction
between zinc and cadmium in higher animals, the toxic action in bacteria
may also involve zinc enzymes such as carboxypeptidase (Zwarun, 1973).
The effects of various concentrations of cadmium on Esc'kevidh'ia coli,
were investigated by measuring li*C02 production using i;*C-glucose as
substrate (Figure 3.1) (Zwarun, 1973); the organism exhibited a high
tolerance for cadmium. At concentrations below 0.6 ppm cadmium as CdCl2,
no effect on li*C02 production was observed. However, with a tenfold
increase in cadmium concentration to 6 ppm, an inhibitory threshold level
was reached and 14C02 production began to decrease. The decrease in C02
evolution could be correlated with a reduction in the number of surviving
cells. Zwarun (1973) suggested that cadmium might be associated with the
cell wall and outer membrane and that only a small percentage of cadmium
taken up actually penetrates into the cytoplasm.
Studies have shown that cadmium interferes with anaerobic digestion
of sludge. Mosey (1971), for example, found cadmium inhibition to be both
quick acting and only partially reversible. Inhibition was a function of
contact time and shock-dose concentration. A contact time of only 5 min
produced inhibition, and concentrations of 50 to 300 ppm proved toxic. A
shock-dose concentration was more toxic than gradual accumulation to the
same concentration. Mosey (1971) proposed that in the case of the gradual
accumulation group, slow precipitation of the metal occurred until the
-------
53
ORNL-DWG 77-5284
0.025
0.020
CJ
ji
Q
U-l
5
o
0.015
0.010
CJ
0.005
• 6 mg Cd per liter
Q 0 to 0.6mg Cd per liter
34
TIME (hr)
Figure 3.1. Effect of cadmium concentration on litC02 evolution by
Escherich-ia eoli, (10s cells). Source: Adapted from Zwarun, 1973,
Figure 2, p. 355.
neutralizing capacity of the sludge had been exhausted. Sulfide was found
to obviate the cadmium effect with an optimum molar ratio for neutraliza-
tion of 1.0. The resultant product from this reaction was insoluble
cadmium sulfide. Cadmium toxicity to anaerobic microorganisms depends on
pH above 7.0; at higher pH values, insoluble cadmium carbonate is formed.
Mosey, Swanwick, and Hughes (1971) reported that the neutralization of
cadmium toxicity depends on the total soluble sulfide rather than the free
sulfide ion concentration.
3.3.2 Algae
Cadmium produces algicidal and algistatic effects on the freshwater
unicellular green alga Selenastrum eaprieornutum. Growth rate begins to
decrease at a concentration of 50 ppb; higher concentrations both depress
growth rate and prolong the lag phase (Figure 3.2). At 650 ppb cadmium
was algicidal (Bartlett, Rabe, and Funk, 1974). Earlier studies by Hannan
and Patouillet (1972), however, involving the marine algae Phaeodaatylum
triaornutum, Cyslotella nana, and Ckaetooeros galvastonensis demonstrated
that cadmium at a concentration of 0.1 ppm is not toxic. Species speci-
ficity may be responsible for such differences.
-------
54
32
28
24
20
i 16
o
12
— CONTROL 50ppb 6°PPb
ORNL-DWG 77-5385R
1 2345678
TIME (days)
Figure 3.2. Growth rate of Selenastmm eaprieornutian as a function
of cadmium concentration in culture medium. Source: Adapted from
Bartlett et al., 1974, Figure 3, p. 182. Reprinted by permission of the
publisher.
3.3.3 Protozoa
Even though protozoa occupy an important part of the food chain, the
effects of heavy metals have been ignored. Carter and Cameron (1973) de-
veloped an assay using Tetrahymena pyr-iformis, a filter-feeding ciliated
protozoan, as the test organism for heavy-metal toxicity. Of the metals
tested — cadmium, cobalt, lead, mercury, and zinc — cadmium was the most
toxic. Concentrations of cadmium sulfate from 0.84 to 3.33 ppm killed at
least 20% of the cells within 30 min; 3.33 to 10.00 ppm killed all cells.
The lethal threshold was 1.67 ppm.
Because a rapid and reliable bioassay is needed for the determination
of harmful effects of trace metals in water, such single cell techniques
may prove very useful. It is worth noting that cell cultures from higher
animals have also been used for this purpose (Christian et al., 1973).
3.3.4 Fungi
Cadmium has been used in various fungicides, especially in turf grass
fungicides and sprays for fruit trees. The nature of the cadmium effect
is not known.
-------
55
A study to determine the adequacy of using the water mold Thpausto-
ohytviwn stnatturi as a test organism for pollutants in seawater was
carried out by Schneider (1972). A concentration of 0.112 ppm cadmium
completely suppressed zoospore activity, and only below 11 ppb cadmium
could normal zoospore activity be found. At a concentration of 1.12 ppm
cadmium, some sporangia were observed and some were still viable when
subcultured.
-------
56
SECTION 3
REFERENCES
1. Abdullah, M. I., L. G. Royle, and A. W. Morris. 1972. Heavy Metal
Concentration in Coastal Waters. Nature (Great Britain) 235:158-160.
2. Bartlett, L., F. W. Rabe, and W. H. Funk. 1974. Effects of Copper,
Zinc and Cadmium on Selenastrum oaprieornutum. Water Res. (Great
Britain) 8:179-185.
3. Bernheim, F. 1973. Effect of Na Salts of Organic Acids on Acid
Induced Swelling and K Loss in Pseudomonas aeruginosa and Effect of
pH on Actions of Mercuric, Cadmium, and Zinc Salts. Cytobios (Great
Britain) 8:7-13.
4. Blondin, G. A., W. J. Vail, and D. E. Green. 1969. The Mechanism
of Mitochondrial Swelling: II. Pseudoenergized Swelling in the
Presence of Alkali Metal Salts. Arch. Biochem. Biophys. 129:158-172.
5. Carter, J. W., and I. L. Cameron. 1973. Toxicity Bioassay of Heavy
Metals in Water Using Tetrahymena pyriformis. Water Res. (Great
Britain) 7:951-961.
6. Chopra, I. 1971. Decreased Uptake of Cadmium by a Resistant Strain
of Staphyloooaaus aureus. J. Gen. Microbiol. (Great Britain)
63:265-267.
7. Christian, R. T., T. E. Cody, C. S. Clark, R. Lingg, and E. J. Cleary.
1973. Development of a Biological Chemical Test for the Potability of
Water. Am. Inst. Chem. Eng. Symp. Ser. 70:15-21.
8. Hannan, P. J., and C. Patouillet. 1972. Effect of Mercury on Algal
Growth Rates. Biotechnol. Bioeng. (Great Britain) 14:93-101.
9. Knauer, G. A., and J. H. Martin. 1973. Seasonal Variations of
Cadmium, Copper, Manganese, Lead, and Zinc in Water and Phyto-
plankton in Monterey Bay, California. Limnol. Oceanogr.
18(4)=597-604.
10. Kondo, I., T. Ishikawa, and H. Nakahara. 1974. Mercury and Cadmium
Resistance Mediated by the Penicillinase Plasmid in Staphylocooous
aureus. J. Bacteriol. 117(1) :l-7.
11. Lindegren, C. C., and G. Lindegren. 1973. Mitochondrial Modifica-
tion and Respiratory Deficiency in the Yeast Cell Caused by Cadmium
Poisoning. Mutat. Res. (Netherlands) 21:315-322.
-------
57
12. Mitchell, R. 1974. Metals as Pollutants. In: Introduction to
Environmental Microbiology. Prentice-Hall, Inc., Englewood Cliffs,
N.J. p. 226.
13. Mosey, F. E. 1971. The Toxicity of Cadmium to Anaerobic Digestion:
Its Modification by Inorganic Anions. Water Pollut. Control (Great
Britain) 70:584-598.
14. Mosey, F. E., J. D. Swanwick, and D. A. Hughes. 1971. Factors
Affecting the Availability of Heavy Metals to Inhibit Anaerobic
Digestion. Water Pollut. Control (Great Britain) 6:2-12.
15. Rice, H. V., D. A. Leighty, and G. C. McLeod. 1973. The Effects
of Some Trace Metals on Marine Phytoplankton. In: Grit. Rev.
Microbiol. 3:27-49.
16. Schneider, J. 1972. Niedere Pfilze als Testorganismen fur Schadstoffe
in Meer- und Brackwasser Die Wirkung von Schwermetallverbindungen und
Phenol auf Thraustochytriwn striatim (Lower Fungi as Test Organisms of
Pollutants in Sea and Brackish Water: The Effects of Heavy Metal
Compounds and Phenol on Thraustochytrium str-iatwn). Mar. Biol. (West
Germany) 16:214-225.
17. Subik, J., and J. Kolarov. 1970. Metabolism of Cadmium and Effects
of Divalent Cations on Respiratory Activity of Yeast Mitochondria.
Folia Microbiol. (Czechoslovakia) 15(6):448-458.
18. Zwarun, A. A. 1973. Tolerance of Escheriahia aoli to Cadmium.
J. Environ. Qual. 2(3):353-355.
-------
SECTION 4
BIOLOGICAL ASPECTS IN PLANTS
4.1 SUMMARY
Background concentrations of cadmium in plants appear to be less than
1 ppm. Generally, plants accumulate this element when environmental back-
ground levels are exceeded. Cadmium is readily transported to all regions
of the plant and often accumulates in the roots. No natural means for elim-
ination of cadmium from living plant tissue is known.
Cadmium concentrations which reduce plant yields are variable and
largely unknown. Cadmium interferes with stomatal function, chlorophyll
production, ion absorption and desorption, and photosynthesis.
4.2 METABOLIC PROCESSES
The concentration of cadmium in plants is determined by the ability of
the plant species to take up the metal and by the cadmium concentration in
the environment. Plant cadmium content usually reflects environmental cad-
mium content. When the cadmium content of soil is higher than background
levels, the cadmium content of plant tissue tends to be increased (Table 4.1),
4.2.1 Uptake and Absorption
Studies on plants grown in soil or nutrient solution indicate that
cadmium may be absorbed by either roots or foliage and incorporated into
plant tissue. Although conditions regulating this uptake are not well under-
stood, several determining factors are known and are discussed in this sec-
tion. In general, it can be stated that cadmium is accumulated by a wide
variety of plant species to an extent dependent upon the cadmium concentra-
tion of the substrate (Bingham et al., 1975), its pH, and other factors.
For example, John (1972) applied lime to soil supporting radish plants
(Eaphanus sativus') and found a decrease in cadmium uptake (Figure 4.1).
The pH of unlimed soil was 4.1; after application of lime the pH rose to
5.5. Cadmium uptake by both tops and roots was significantly higher from
unlimed (low pH) soil.
Similar results have been obtained for a variety of plants (John,
VanLaerhoven, and Chuah, 1972; Lagerwerff, 1971; Lagerwerff and Specht,
1971; Linnman et al., 1973; Williams and David, 1973). Francis and Rush
(1973) evaluated the availability of cadmium chloride (water soluble) and
cadmium oxide (water insoluble) to Japanese millet (Echinochtoa frumentaaea)
at three liming levels (Table 4.2). After 26 days, cadmium concentrations
in plants grown in presence of CdCl2 were two to three times higher than in
those exposed to CdO; the availability of cadmium in both cases was greatest
at low pH. A second harvest after an additional 63 days revealed no signif-
icant difference in cadmium content from either form in limed treatments
but greater concentrations from CdCl2 in unlimed treatments. Francis and
Rush (1973) suggested that the cadmium originally applied became less
58
-------
59
TABLE 4.1. ESTIMATES OF CADMIUM CONCENTRATIONS IN SOME PLANT TISSUES
Reported or estimated
cadmium concentration
(ppm, dry wt)
Plant or plant part
In environments
presumably having
normal cadmium
levels
In environments
having greater than
normal cadmium
levels
Marine algae
Mosses (bryophytes)
Lichens (fruticose type)
Grasses
Grains
Corn (Zea mays)
Rice (polished)
Barley, wheat, and oats
Vegetables
Asparagus
Beet root
Cabbage leaves
Carrots
Chinese cabbage
Eggplant fruit
Kale
Leafy vegetables used as pot herbs or
salads
Leeks
Lettuce
Potatoes
Spinach
Turnip roots
Turnip leaves
Tomatoes
Trees , deciduous
Leaves
Stems (branches)
Trees, coniferous
Leaves
Stems
Epiphytes (Spanish moss)
Floating aquatic plants (duckweed)
Marine flowering plants (Zostera marina)
0.1-1
0.7-1.2
0.1-0.4
0.03-0.3
0.1
0.1-0.5
0.05
0.05
<0.35
1
0.3-0.5
0.3-0.5
0.05-0.3
0.6-1.2
0.1-2.4
0.1-1.3
0.1-0.9
0.1
0.23
8-340
1
0.6-40
2
0.5
0.1-1.5a
8
0.24
6-12
8
41
8
3-50
14
4-16
0.6-2
5
15
2
4-17
0.14-1.5
0.05-1
0.03-1.5
1
17
Original data given in wet weight; because the water content of grains is very
low, these values were not converted to a dry weight basis.
Source: Adapted from Shacklette, 1972, Table 3, p. 24.
-------
60
ORNL-DWG 77-5256
400 n
300-
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100-
RADISH TOPS FROM
UNLIMED SOIL
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.X^RADISH TOPS ,XRADISH ROOTS FROM
X
-------
61
TABLE 4.2. CONCENTRATIONS OF 109Cd IN JAPANESE
MILLET DERIVED FROM TWO CHEMICAL FORMS OF
CADMIUM AT THREE LEVELS OF CALCIUM CARBONATE0
109Cd concentration
CaCOs level (pCi/mg dry wt)
(tons/ha)
First harvest,
-,-,,. Leaves Heads
total plant
Derived from CdCl-
0
11
22
0
11
22
46.4 a
45.4 a
29.5 b
Derived from
26.3 be
15.7 d
18.1 ad
14.9 a
3.6 bo
4.0 bo
CdO
6.8 b
2.6 o
2.2 o
4.6 a
0.79 c
0.46 c
2.4 b
0.62 c
0.56 c
Average of three replicates. Numbers
followed by identical letters within the same
column are not statistically different at the 5%
level as tested by Duncan's multiple range test.
Concentration of cadmium in soil <20 ppb; speci-
fic activity 1.91 Ci/g.
Source: Adapted from Francis and Rush,
1973, Table V. Reprinted by permission of the
publisher.
The influence of zinc on cadmium uptake has also been studied. Haghiri
(1974) found that addition of 5 to 50 ppm zinc to soil significantly in-
creased the cadmium concentration of soybean (Glyc'ine max) shoots; con-
versely, at 100 ppm, zinc reduced cadmium uptake. Lagerwerff and Biersdorf
(1972) used complete nutrient solutions with 2, 20, or 100 ppb cadmium com-
bined with 20, 100, or 400 ppb zinc to determine whether zinc affects cad-
mium uptake in radishes. In addition, plants grown in a greenhouse at 100%
relative humidity (to decrease transpiration) were compared with those grown
outdoors near a highway. In both cases, cadmium uptake at 2 and 20 ppb cad-
mium decreased with increasing zinc content, while at the 100 ppb cadmium
concentration higher zinc concentrations resulted in increased cadmium up-
take. This was thought to be the result of root damage because growth was
also decreased at high cadmium concentrations. Because high zinc concentra-
tions are also detrimental to growth, this study was criticized by Smith and
Huckabee (1973) for lacking a control of zinc without cadmium. Subsequently,
Van Hook et al. (1974) concluded that increased cadmium uptake by plants in
the presence of zinc cannot be attributed simply to root damage. Significant
correlations between concentrations of cadmium and of a variety of other
elements, including zinc, were found under various conditions in tops and
roots of radish and lettuce (John, VanLaerhoven, and Chuah, 1972). These
results are collected in Table 4.3.
-------
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Hutchinson and Czyrska (1972) found that zinc concentrations up to 0.08
ppm in solution increased cadmium uptake by aquatic plants. Francis and
Rush (1973) also found enhanced cadmium uptake by plants in the presence of
zinc. Nutrient solutions containing 5 ppm zinc resulted in higher plant cad-
mium concentrations than did solution's containing 1 ppm zinc. Zinc increased
cadmium concentrations in stem and leaf tissues but decreased that in roots.
Nitrogen added as ammonium nitrate significantly lowered net tracer uptake
by foliage but not by root or stem. Significantly higher cadmium concentra-
tions appeared in the upper leaves at all nitrogen concentrations employed,
suggesting that cadmium translocation occurred early in leaf development.
In these experiments, selenium was also tested; concentrations of 0.1 ppm
severely reduced foliar cadmium concentrations.
Investigations of cadmium-zinc interactions also include studies on
effects of high cadmium concentrations on zinc accumulation. Bingham et al.
(1975) determined that the zinc concentration of plant tissues was signifi-
cantly reduced at higher cadmium treatment rates. Various species of plants
were grown to harvest stage on soil pretreated with municipal sewage sludge
(1%) moistened with variable amounts of cadmium sulfate. For field beans,
the leaf zinc dropped from 47 yg/g for control plants to 24 yg/g for plants
grown in soil treated with 160 yg of cadmium as cadmium sulfate per gram of
soil. Seed zinc concentrations also decreased in these field bean plants.
However, the plants showed no signs of zinc deficiency. Bingham et al.
(1975) were unable to offer an adequate explanation for the reduced zinc
levels in plants grown in presence of high cadmium sulfate levels.
A survey of the cadmium content in wheat led Huffman and Hodgson (1973)
to conclude that superphosphate fertilizers do not affect plant cadmium
levels. No significant differences were found between cadmium levels in
plants of the eastern United States, an area of heavy superphosphate usage,
and in those of the Midwest, an area of little usage.
More recently Reuss, Dooley, and Griffis (1976) tested cadmium uptake
by radish, lettuce, and peas from phosphate fertilizer applied over a range
equivalent to 0 to 0.087 yg cadmium per gram of soil. These cadmium con-
centrations represent those commonly found in phosphate fertilizers. Plants
grown on a calcareous silt loam soil (pH 8.4) accumulated marginally detect-
able amounts of cadmium, even at the highest level tested. However, plants
grown on a coarse-textured acid soil (pH 4.5) reached cadmium levels of
3.55, 6.01, and 0.53 ppm in radish roots, lettuce tops, and pea seeds re-
spectively. These investigators cautioned that although "the biological
significance to consumer organisms is not clear, ... it does not appear
that it can be dismissed as unimportant."
Williams and David (1973) analyzed vegetation from adjacent fertilized
and unfertilized fields (Table 4.4). A top-dressing of superphosphate re-
sulted in increased cadmium content of grasses and clover. Controlled studies
with superphosphate showed that the cadmium content of oats was 0.02 ppm on
unfertilized soil and 0.28 ppm on fertilized soil. Corresponding concentra-
tion ranges for subterranean clover and lucerne were 0.10 to 1.34 ppm and
0.03 to 0.60 ppm respectively. The cadmium content of 21 Australian phos-
phatic fertilizers analyzed by Williams and David (1973) ranged between 18
-------
64
TABLE 4.4. CADMIUM CONTENT OF PASTURE SPECIES FROM ADJACENT
FERTILIZED AND UNFERTILIZED PASTURES
Unfertilized pasture
Fertilized pasture
Species
Native grasses
(Danfhonia, Themeda)
Phalaris
Subterranean clover
Cadmium
content
(ppm)
0.028
0.020
0.048
Total
superphosphate
applied
(kg/ha)
2500
2500
2060
2060
2800
2800
Species
Phalaris
Subterranean clover
Phalaris
Subterranean clover
Ryegrass
Subterranean clover
Cadmium
content
(ppm)
0.060
0.324
0.072
0.164
0.153
0.411
Source: Adapted from Williams and David, 1973, Table 11, p. 53. Reprinted by
permission of the publisher.
and 91 ppm. Swedish fertilizers have been shown to contain 0.1 to 28 ppm
cadmium (Stenstrb'm and Vahter, 1974), while American brands ranged from 3.48
to 14.3 ppm (Yost et al., 1973) and from 7.4 to 156 ppm cadmium (Reuss,
Dooley, and Griffis, 1976).
Oats cultured by John, Chuah, and VanLaerhoven (1972) in contaminated
(46.4 ppm cadmium) and uncontaminated (1.3 ppm) soil contained 16.1 and 0.51
ppm cadmium respectively. John (1973) measured cadmium in plants grown on
soil containing either 0, 40, or 200 mg cadmium per 1000 g soil. As soil
cadmium increased, uptake by oats increased. The highest accumulation oc-
curred in roots, the lowest in grain (Table 4.5).
Williams and David (1973) examined the distribution of cadmium in cereal
plants from contaminated and uncontaminated soils (Table 4.6). Five to eight-
een percent of the cadmium in plant tops was in the grain. Less than 0.2% of
the added cadmium was found in the grain of wheat, oats, and Hungarian rice
and about 1% was found in that of Taichung rice. The harvested oat grain
included the glumes, which analysis from one sample revealed to contain 25%
of the "grain" cadmium.
Uptake of cadmium by barley (Hordeum vulgare) from nutrient solutions
(cadmium content, 1 ppm) was studied by Cutler and Rains (1974). The cadmium
content of both roots and shoots increased over a 28-day growth period.
Roots accumulated 250 ppm and shoots 56 ppm. Page, Bingham, and Nelson
(1972) found increased uptake by barley and other plants growing in solution
culture when the cadmium concentration was raised over the range of 0.1 to
10 ppm. Plants varied in their tolerance to cadmium, but in all species
studied the leaves accumulated the metal to much higher concentrations than
that present in the culture solution.
Traynor and Knezek (1973) tested the response of corn (Zea mays) to
contaminated soil. As cadmium increased from 0 to 562 ppm, cadmium content
-------
65
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67
in plants increased from below the detection limit to 133 ppm. Prince (1957)
analyzed corn grown in four soil types: Sassafras sandy loam, Norton loam,
Washington loam, and Cossayuna loam. Leaves accumulated up to 2.43 ppm cad-
mium; content increased with age of the plants. Cadmium concentrations in
soil were not given.
4.2.2 Translocation, Distribution, and Accumulation
4.2.2.1 Crop Plants
4.2.2.1.1 Grains — Cadmium content of wheat from unpolluted areas of the
eastern and midwestern United States was determined by Huffman and Hodgson
(1973). Only 3 of 33 samples contained greater than 0.5 ppm, and the highest
concentration was 0.71 ppm. In greenhouse studies, Haghiri (1973) found that
wheat tops accumulated cadmium when the metal was applied to soil. Cadmium
uptake by wheat from soil containing sewage sludge (cadmium content, 10 ppm)
applied at rates of 0, 6.5, 19, 58, and 175 tons/ha was determined by Linnman
et al. (1973). Applications at all but the highest rate increased cadmium
uptake; maximum accumulation was 257 ± 9 ppb. The concentration of cadmium
in whole wheat was 50 ppb, while that in bran was threefold higher at 148
ppb. In a similar study, Stenstrbm and Lb'nsjo (1974) applied sludge (5.2
ppm cadmium) to several soils and determined the radiocadmium uptake by
wheat; isotopic equilibration of added tracer with sludge cadmium is assumed.
Uptake of tracer increased with increasing sludge addition, and 0.0033% of
the cadmium originally in sludge was recovered in the mature crop. The
authors estimated that when sludge containing 15 ppm cadmium was applied at
a level of 1 metric ton/ha, it would increase the grain cadmium by 2.2%.
They concluded that even a limited annual application of sludge may give
rise to intolerable concentrations of cadmium in agricultural crops.
Other researchers have found that the cadmium content of grains increased
by several hundred percent when the grains were grown on sewage sludge.
Hinesly, Jones, and Ziegler (1972) observed a 240% increase in the cadmium
content of corn grain at harvest, from 0.30 to 1.03 ppm, as from 0 to 1 in.
(2.54 cm) of anaerobically digested sewage sludge was applied to the soil.
Applications were made as frequently during the growing season as drying
conditions of the sludge would permit. Dowdy and Larson (1975) found a 150%
increase of cadmium in corn grain as sludge applications increased from 0 to
450 tons/ha. Sabey and Hart (1975) found a 190% increase in the cadmium
content of wheat grain, from 0.066 to 0.190 ppm, as the sludge application
rate increased from 0 to 100 metric tons/ha (dry weight). In this case, the
municipal sewage sludge was added to a Truckton loamy sand in the field.
For additional information on land application of sewage sludge, see Sections
4.2.2.1.2 and 7.5.
4.2.2.1.2 Vegetables and fruits — Haghiri (1973) compared root and foliar
uptake of cadmium by soybean. Root uptake was 15 times more efficient, in-
dicating that absorption of airborne cadmium is not as environmentally
important as absorption from contaminated soils. Regardless of the method
of application, the cadmium content of plant parts in this study decreased
in the following order: stem > leaves > pods > beans. In the same study,
the following uptake of cadmium by vegetables was observed on soil contain-
ing 10 ppm of the metal: lettuce (Laotuaa sativa), 27.10 ppm; radish top
-------
68
(Raphanus sativus), 16.13 ppm; celery stalk (Apium graveolens), 14.87 ppm;
celery leaves, 10.77 ppm; green pepper (Capsiaum frut e so ens') , 6.28 ppm; and
radish roots, 5.93 ppm. Williams and David (1973) also tested vegetable up-
take of cadmium from soil (Table 4.7). The cadmium content of the edible
portion was less than that of the nonedible portion in every case.
TABLE 4.7. CADMIUM CONTENT OF AND UPTAKE BY VEGETABLE
SPECIES GROWN IN POT CULTURE
Species
Peas
Beans
Tomato
Radish
Cabbage
Treatment
Nil ,
Super
CdCl2C
Nil
Super
CdCl2
Nil
Super
CdCl2
Nil
Super
CdCl2
Nil
Super
CdCl2
Cadmium content
(ppm)
Edible
portion
0.063
0.233
0.238
0.018
0.054
0.071
0.074
0.157
0.339
0.136
0.656
1.140
0.076
0.220
0.408
Nonedible
portion
0.089
0.265
0.555
0.103
0.187
0.252
0.214
0.596
0.922
0.237
1.020
1.560
Total
cadmium
uptake
(ug/pot)
1.03
3.77
6.58
1.03
2.05
2.77
3.10
9.46
15.43
1.47
6.78
11.09
1.08
3.48
6.10
Added
cadmium
taken up
3.3
2.8
1.2
0.9
7.6
6.1
6.3
4.8
2.9
2.5
Moisture
content of
fresh edible
material
at harvest
76
86
93
91
80
, Plant tops only except for radish, which included roots.
2 g superphosphate, adding 85 pg cadmium per pot.
CCdCl2, 200 yg per pot.
Source: Adapted from Williams and David, 1973, Table 10, p.
permission of the publisher.
53. Reprinted by
Turner (1973) grew vegetables in nutrient solution containing 0 to
1.00 yg cadmium per milliliter. The cadmium content of all species tended
to increase with increasing cadmium treatment. Tomato (Lyeopersieum escu-
lentwri) was a high accumulator (0.3 to 158.0 ppm), while carrot (Daueus
aarota) was a low accumulator (0.2 to 2.2 ppm). John (1973) determined up-
take of cadmium by vegetables from contaminated soil (Table 4.5). At the
higher level of soil contamination, the mean cadmium concentration of plant
parts in general was significantly higher than control values. The accumula-
tion of cadmium in underground plant portions was dramatic (Figure 4.2).
Uptake of cadmium by radish was measured by John (1972). In unlimed
soil, radish roots accumulated 174.3 ppm cadmium, which was 34.2 times the
level in control plants. Radish tops accumulated 402.8 ppm. Lagerwerff
-------
69
CADMIUM CONTENT (ppml
§ 8 8 S §
ORNLDWG77 5286
• 6121 5 CARROT ROOTS
- 16474 BROCCOLI ROOTS
• 16282 LETTUCE ROOTS
• 1571 2 PEA ROOTS
1356 7 CAULIFLOWER ROOTS
• 667 7 LETTUCE LEAVES
• 663 2 OAT ROOTS
• 490 5 SPINACH ROOTS
•3980 RADISH TOPS
294 4 CARROT TOPS
— 268 5 BROCCOLI LEAVES
-239 3 SPINACH LEAVES
• 198 6 CAULIFLOWER LEAVES
1770OAT LEAVES
123 3 RADISH TUBERS
— 116 9 PEA VINES
— 116 5 OAT STALKS
- 960 OAT HUSKS
• 33 6 OAT GRAINS
• 298 CAR ROT TUBERS
• 28 2 PEA PODS
197 PEA SEEDS
Figure 4.2. Cadmium content of plants grown in 200 mg cadmium per
1000 g soil. Source: Adapted from John, 1973, Figure 1, p. 14. Reprinted
by permission of the publisher.
(1971) also found that cadmium accumulation was greater in radish tops than
in roots. Turner (1973), measuring accumulation only in tops, found 144.2
ppnrln plants grown in nutrient solutions containing 1.0 ppm cadmium.
Kobayashi (1972) sampled vegetables at varying distances from a zinc refin-
ery in Japan and concluded that root uptake of cadmium from contaminated
soil appeared to be the principal source of plant cadmium, as opposed to
foliar absorption from polluted air. Shacklette (1972) criticized this
observation: "The vegetable analyses show relatively low amounts of cad-
mium in plant parts that have a low surface-to-volume ratio (asparagus stems,
pumpkin, tomato, and eggplant fruit), in parts that are surrounded by protec-
tive outer structures (corn and bean seeds), and in plant parts that grow
underground (potatoes, radish roots, taro potatoes, and turnip roots).
Leaves, in contrast, have a high surface-to-volume ratio and were shown to
usually contain much larger amounts of cadmium." Schroeder et al. (1967)
tested a wide variety of plants and plant products for cadmium content. The
cadmium content of vegetables ranged from below the detection limit to 0.45
ppm; fruits showed 0.01 to 0.14 ppm, and nuts 0.03 to 0.07 ppm (all values
based on variable wet weights; cadmium content based on wet weights gives
an indication of dietary cadmium intake).
Ross and Stewart (1969) sprayed apple trees with an aqueous solution
of cadmium chloride (43 ppm cadmium) once a year for three years. Cadmium
residues in foliage declined slowly from an initial concentration of about
25 yg/100 cm2 to about 13 yg/100 cm2 at the times of harvest. The initial
cadmium concentration in apples was about 38 yg per ten apples, each of the
first two years, whereas harvest residues were 95 yg in 1964 and 65 yg in
-------
70
1965. In 1967, the initial cadmium content in fruit after spraying was
82 yg per ten apples; the content declined to 69 yg after a month but in-
creased to 90 ug at harvest. The higher initial concentration in 1967 was
due to increased apple size. Peels contained more cadmium than did pulp.
Thus, cadmium residues persist in foliage during the growing season and may
be translocated from foliage to fruit.
As in grains, vegetables and fruits grown in soil treated with sewage
sludge also show increases in cadmium content. A 300% increase in the cad-
mium content of tomato fruit was observed by Dowdy and Larson (1975) as the
applied sludge increased from 0 to 450 tons/ha. The increase in cadmium
content of pea fruit was 33% and the cadmium content of carrots, radishes,
and potatoes increased by 140%, 140%, and 90% respectively. Under the same
conditions, the cadmium content of leaf lettuce increased 340%; Dowdy and
Larson (1975) concluded that lettuce is an accumulator of metals.
4.2.2.1.3 Herbs — Gordee, Porter, and Langston (1960) exposed peppermint
(Mentha piper-ita) plants to tracer cadmium. Plants were harvested after 4,
24, 48, and 72 hr. Remaining pots were than flushed with water to remove
tracer and additional plants were collected at 7 and 14 days. Accumulation
was not evident during the first 4 hr, but it. increased throughout the remain-
ing 68 hr. The 7- and 14-day harvests revealed that cadmium is translocated
from older to newer plant growth and remains mostly in the vascular tissue.
Thus, crop plants normally accumulate only moderately high levels of
cadmium. When background cadmium levels in soils are raised, however, plant
uptake is significantly increased. Accumulated cadmium tends to be retained
in the roots.
4.2.2.2 Noncrop Plants
4.2.2.2.1 Herbaceous plants — The consideration of mosses, lichens, and
vascular plants in this section does not imply that methods of uptake in
these plants are identical. Uptake in mosses is through sorption by rhi-
zoids; in lichens, the fungal mycelium is responsible for uptake. Since
mosses and lichens have no true roots, their methods of uptake should not be
equated with that of vascular plants. Huckabee and Blaylock (1973) sampled
mosses and grasses in a relatively uncontaminated area to determine near-
background levels of cadmium. The mean cadmium content of the mosses DiaTa-
nwn and ~P~lijtT-lohwn was 0.421 and 0.383 ppm respectively. Festuaa and Andro-
pogon grasses averaged 0.279 and 0.210 ppm. Huffman and Hodgson (1973)
determined the cadmium concentration in grasses from rural areas of the
United States to be 0.17 ppm. Selected Alaskan grasses contained slightly
less than 0.1 ppm (Kubota, Rieger, and Lazar, 1970).
Retention of 109Cd by old field vegetation was studied by Matti,
Witherspoon, and Blaylock (1975). Approximately 10% of l09CdC!2 applied in
simulated rainfall was retained after 24 to 48 hr. Seven days later, after
three rainfalls, retention decreased to 7.3% of the total applied cadmium.
Cadmium content in grasses near four heavily traveled highways decreased
with increased distance from the pavement (Lagerwerff and Specht, 1970).
-------
71
TABLE 4.8. EXTRACTABLE CADMIUM AND ZINC CONTENTS OF ROADSIDE SOIL AND VEGETATION AS A
FUNCTION OF DISTANCE FROM TRAFFIC AND DEPTH IN THE PROFILE13
Site Metal
I. East of U.S. 1, near Cadmium
Plant Industry Sta-
tion, Beltsville,
Md. ; 20,000 cars Zinc
per day
II. East of Victory Road, Cadmium
Cincinnati, Ohio;
10,600 cars per day
Zinc
Distance
from
road
(m)
8
16
32
8
16
32
8
16
32
8
16
32
Metal content
(mg/kg dry wt)
Grass
1.25
0.75
0.58
64.5
50.0
41.2
0.63
0.38
0.25
92.4
82.7
72.5
0-5 cm
0.65
0.31
0.17
192
112
43
1.04
0.86
0.66
55.5
38.0
17.4
Soil
5-10 cm
0.44
0.18
0.12
98.2
28.3
22.1
0.80
0.66
0.52
27.3
17.1
7.9
10-15 cm
0.23
0.11
0.08
30.3
20.0
16.2
0.54
0.48
0.30
3.5
3.2
1.3
Average of duplicate samplings and analyses.
Source: Adapted from Lagerwerff and Specht, 1971, Table 1, p.
mission of the publisher.
88. Reprinted by per-
Another study by Lagerwerff and Specht (1971) conducted near heavily traveled
(20,000 cars per day) and moderately traveled (10,600 cars per day) highways
had similar results (Table 4.8). Soil was also collected at 6 m (0.75 ppm
cadmium) and 180 m (0.10 ppm cadmium) from the heavily used highway and
seeded with bromegrass. Cultures were grown in either their natural environ-
ment or an artificial environment containing particulate-free air. The cad-
mium content of grass grown in natural air was 1.4 times higher than that in
grass grown indoors in the low-cadmium soil; exposure to particulates of the
natural environment increased the cadmium content 1.8 times.
Goodman and Roberts (1971) determined the cadmium content of moss
(Hypnum supressiforme) and grass (Festuoa ¥ubr>d) in polluted and unpolluted
areas. The cadmium content of moss was 1.0 to 9.5 ppm in the polluted area
and 1.0 to 1.8 ppm in the unpolluted area. Corresponding grass contents
were 1.3 to 40.0 ppm and 0.7 to 0.8 ppm. Huckabee, Stella, and Olmstead
(cited in Smith and Huckabee, 1973) studied 109Cd uptake by mosses (Eur-
hynohium hians, Brachy theciwn rivulare, and Sharpiella striatella) and a
grass (Festuca elatior). Both soluble and insoluble forms of cadmium were
used; in both cases mosses retained at least ten times more cadmium than did
grass (Figures 4.3 and 4.4).
Mosses were sampled at ten paired sites along highways by Shacklette
(1972). One site for each pair was 45.7 to 61.0 m (15 to 20 ft) from the
highway, the other 304.8 to 1828.8 m (100 to 600 ft) away. Samples near the
highway contained a mean level of 5.6 ppm cadmium; those away from the high-
way averaged 5.2 ppm (difference not statistically significant). The author
noted that dust present on the samples could not be completely removed by
-------
72
104
ORNL-DWG 72-11321R
MOSSES
103 —
ui
en
CM
102
o
J3
Q.
Q.
101
10°
N
Cd CI2
FESCUE GRASS
0
8 12 16 20
TIME (days)
24
28
32
Figure 4.3. Uptake of Cd by fescue grass and by three species of
mosses following application as CdCl2 in simulated rainfall.
and Huckabee, 1973, Figure VI-ll, p. 285.
Source: Smith
washing and may have obscured larger differences. A U.S. Geological Survey
study (Shacklette, 1972) which monitored Spanish moss (Tillandsia usneoides),
a vascular plant and not a true moss, throughout the southeastern United
States revealed that the cadmium content of the plant was related to the
degree of air pollution in the sampling location.
-------
73
105
ORNL-DWG 72-11320R
104
LJ
(f)
CM
T3
0
_Q
Q.
Q.
103
102
10'
CdO
x:
x
MOSSES
: FESCUE
20
TIME (days)
27
Figure 4.4. Uptake of 109Cd by fescue grass and by three species of
mosses following application as CdO in simulated rainfall. Source: Smith
and Huckabee, 1973, Figure VI-12, p. 286.
Samples of moss (Hypmm oupressi forme) from a polluted area of Sweden
contained 30 ppm cadmium; lichen (Parmelia physodes) contained 12 ppm
(Tyler, 1972). Hairgrass (Desehampsia flexuosa') contained 7.6 ppm in leaves
and 11 ppm in combined samples of roots and rhizomes. Tyler et al. (1973)
found values of 0.30 g cadmium per hectare in mixed mosses and 0.36 g cad-
mium per hectare in lichens in a heath ecosystem.
-------
74
Jaakkola, Takahashi, and Miettinen (1973) compared the cadmium content
of lichens growing near a zinc smelter with those from an unpolluted area.
Samples taken near the smelter approximately six months after smelting began
contained about 1 ppm cadmium. Samples from the unpolluted area contained
only about 0.1 to 0.2 ppm. Shacklette (1972) tested a species of fruticose
lichen (Cladonia rangiferina) growing over a dolomite deposit and found
approximately 0.19 ppm cadmium.
Lounamaa (1956) sampled vegetation in Finland to determine cadmium
content. Fifteen of sixteen species of lichens growing on silicic rock
contained 10 to 300 ppm cadmium in ash, while the remaining species con-
tained 30 to 600 ppm in ash. Eight of nine species of mosses contained 1 to
10 ppm. The remaining mosses, collected in a contaminated area, contained
100 ppm cadmium in ash. For ferns, the highest cadmium concentration in
fronds was 30 ppm, but an accumulation of as much as 100 ppm (mean = 22) was
found in the ash of subterranean plant parts.
Cearley and Coleman (1973) exposed southern naiad (Najas guadalupensis)
to CdSOi,. Exposure levels ranged from 0.0005 ± 0.0001 ppm (control) to
0.83 ± 0.12 ppm cadmium. As the exposure level increased, cadmium accumula-
tion by the plants increased. After 21 days the plants subjected to the
highest exposure contained 5429.3 ±60.6 ppm cadmium compared with 7.1 ± 0.1
ppm in the control. Uptake of CdN03 by duckweed (Lerma valdivLana) and
aquatic fern (Salvinia natans) from water culture was evaluated by Hutchin-
son and Czyrska (1972). As the cadmium content of the solution culture
increased from 0.00 to 1.00 ppm, cadmium content of duckweed rose from 7.2
to 1475.5 ppm and that of aquatic fern rose from 2.1 to 6400 ppm.
4.2.2.2.2 Woody plants — Smith (1973) examined leaf and twig tissue from
six tree species in New Haven, Connecticut (Table 4.9). As a check, 25
TABLE 4.9. CADMIUM CONTENT OF WOODY PLANTS GROWING IN NEW HAVEN, CONNECTICUT0
Species
Pin oak, Quercus
palustpis Muenchh.
Sugar maple, Acer
saechccnan Marsh.
Norway maple, Aaer
platanoides L.
Eastern hemlock, Tsuga
canadensis (L.) Carr.
Yew, Taxus spp.
Norway spruce, Pioea
abi.es (L.) Karst.
Total
trees
sampled
24
14
64
16
20
8
Average
distance from
nearest street
(m)
1.4
1.8
2.0
3.7
3.8
4.8
Tissue
Organ
Leaves
Twigs
Leaves
Twigs
Leaves
Twigs
Leaves
Twigs
Leaves
Twigs
Leaves
Twigs
analyzed
Number
of trees
12
12
7
7
32
32
8
8
10
10
4
4
Cadmium content
(ppm dry wt)
Mean and
standard error
2.3 + 0.2
2.3 ± 0.2
1.0 ± 0.1
0.8 ± 0.1
1.1 ± 0.1
0.7 + 0.1
0.9 ± 0.1
1.2 ± 0.2
1.2 ± 0.2
2.0 ± 0.4
0.7 ± 0.2
0.8 ± 0.2
Range
1.5-3.0
1.0-3.0
0.5-1.5
0.5-1.5
0.5-2.0
0.5-2.0
0.5-1.0
0.5-1.8
0.5-2.5
0.5-4.1
0.5-1.0
0.5-1.0
,Branch samples were collected during the fall of 1970 approximately 2 m above the ground.
Washed growth of the previous growing season only.
Source: Adapted from Smith, 1973, Table II, p. 633. Reprinted by permission of the publisher.
-------
75
sugar maple samples were obtained from remote areas of Vermont and New
Hampshire. Twigs and leaves of the remote samples contained 0 to 5 ppm cad-
mium; New Haven samples contained 0.5 to 4.1 ppm. Smith concluded that New
Haven trees contained "normal" cadmium concentrations. Mixed tree species
from Alaska were found to contain 0.4 to 0.5 ppm cadmium in leaves and twigs
(Kubota, Rieger, and Lazar, 1970). Huckabee and Blaylock (1973) found that
needles of eastern hemlock (Tsuga canadensis) contained a mean of 0.083 ppm
cadmium; twigs contained 0.326 ppm. Tyler (1972) determined cadmium distri-
bution in an area polluted by industry (Table 4.10) and concluded that an
increase in heavy-metal deposition results in metal accumulation in the more
exposed, permeable portions of the ecosystem such as mosses, lichens, humus,
and rough bark of twigs. Anderson et al. (1974) reported the following
values for samples from three deciduous species: leaves, 0.16 to 0.38 ppm;
twigs, 0.05 to 0.93 ppm; branches, 0.03 to 0.39 ppm; bole, 0.2 to 0.33 ppm;
and roots, 0.15 to 0.34 ppm. A coniferous species contained 0.48 ppm in
leaves, 0.26 ppm in twigs, 0.30 ppm in branches, 0.21 ppm in bole, and 0.30
ppm in roots.
TABLE 4.10. CONCENTRATIONS OF CADMIUM IN COMPONENTS OF A SPRUCE FOREST IN
CENTRAL SWEDEN POLLUTED BY A LOCAL INDUSTRIAL SOURCE
Species
Spruce, Piaea dbies
Cowberry, Vaaaini-wn vitis idaea
Bilberry, Vacainiwn myrtillus
Hair grass, Desaharrrpsia flexuosa
Epiphytic lichens, Pannelia physodes
Mosses , Hypnwn aupressiforme
Humus layer (raw humus)
Plant part
Roots, <5 mm diam
Roots, >5 mm diam
Wood
Bark
Twigs
1st year
2nd year
3rd year
4th year
5th-7th year
Needles
1st year
2nd year
3rd year
4th year
5th-7th year
Needle liter
Aboveground biomass
Aboveground biomass
Leaves
Leaf litt. r
Roots and rhizomes
Cadmium
content
(ppm dry wt)
2.7
1.5
<0.1
2.5
5.4
4.6
4.2
3.3
2.7
0.6
0.4
0.5
0.5
1.0
24
3.2
4.4
7.6
12
11
12
30
44
Enrichment
ratio
6.8
7.5
13
14
12
10
7.5
6.0
3.0
1.5
1.4
1.4
2.4
63
17
13
10
15
16
30
33
40
Ratio of cadmium concentration at this site to that at a similar site with no local
deposition.
Source: Adapted from Tyler, 1972, Table 1, p. 59. Reprinted by permission of the
publisher.
-------
76
Elm (Ulmus glabra) leaves were analyzed from branches either facing or
opposing a smelter (Little and Martin, 1972). Cadmium concentrations were
higher in leaves from the sheltered side due to natural slowing of wind
speed by the tree and, thus, greater metal precipitation. A comparison of
washed and unwashed leaves revealed that only 28% of the total cadmium was
removed by detergent washing, indicating partial cadmium penetration into
the leaf. Smith (1973) found no significant difference between washed and
unwashed leaves. Little (1973) found that about 67% of the cadmium content
of oak (Querous Tobwc} leaves was removed after washing and boiling in
deionized water, but only 15% to 20% was removed from willow (Salix alba)
and hawthorn (Crataegus monogyna) leaves. The cadmium content of unwashed
leaves collected about 400 m from a zinc and palladium smelter was 6.04 ±
0.98 ppm for hawthorn, 6.82 ± 1.33 ppm for oak, and 7.85 ± 1.24 ppm for
willow.
Metal distribution in the aboveground portion of two heath ecosystems
(Calluna vulgaT-is and Eriea tetral-ix) was studied by Tyler et al. (1973).
Calluna contained a total of 0.73 g cadmium per hectare; Er-Loa contained
0.69 g/ha. The distribution of cadmium within each species is given in
Table 4.11.
TABLE 4.11. DISTRIBUTION OF CADMIUM IN THE COMPONENTS OF ABOVEGROUND
BIOMASS IN CALLUNA AND ERICA ECOSYSTEMS
Species
Plant
part
Age
Cadmium
content
(g/ha)
Calluna vulgaris
Calluna ecosystem
Short shoots and leaves
Short shoots and leaves
Short shoots and leaves
Long shoots and leaves
Long shoots and leaves
Long shoots and leaves
Empetmm nigrum
Mosses and lichens
Other species
Current year
Last year
Older
Current year
Last year
Older
0.73
0.13
0.19
0.02
0.05
0.08
0.26
0.10
0.30
0.06
Erica ecosystem
Erica tetralix
Mosses and lichens
Other species
Leaves
Leaves
Leaves
Shoots
Shoots
Shoots
Current year
Last year
Older
Current year
Last year
Older
0.69
0.11
0.09
0.02
0.13
0.11
0.23
0.36
0.12
Source: Adapted from Tyler et al., 1973, Table 5, p.
Reprinted by permission of the publisher.
261.
-------
77
In a U.S. Geological Survey study (Shacklette, 1972), plants were
sampled in six vegetation-type areas remote from major pollution sources
in Missouri. The terminal 15 to 20 cm (6 to 8 in.) of stem was analyzed
for cadmium content (Table 4.12). Soil samples from the area contained
1 ppm cadmium. According to Shacklette (1972), the data indicate that plant
cadmium content is determined by the ability of the species involved to take
up cadmium rather than by the amount of cadmium present in the soil.
Lounamaa (1956) found that conifer needles usually contained less cadmium
(slightly less than 10 ppm in ash) than twigs (about 30 ppm). Needles and
twigs from trees growing on silicic rock contained more cadmium than those
on ultrabasic or calcareous rock. For deciduous species, most leaf speci-
mens contained less cadmium than did twigs. For "dwarf shrubs," 80% of the
stem samples contained more cadmium than did the leaves.
Hanna and Grant (1962) determined the mineral composition of 12 species
of woody plants growing on two different soil types regarded as having
"normal" cadmium levels. The following cadmium contents were found in
plants: Aaer vubrwn, 1.7 ppm (mean of four samples); A. saachaifinwn, 0.10
ppm; A. saaoharum, 0.21 ppm; Ilex opaaa, 5.2 ppm (mean of four samples);
Kalmia lati.folia, 0.43 ppm (mean of two samples); P-ier-is japoni-ca, 1.2 ppm
(mean of five samples); Pinus strobus, 0.9 ppm (mean of three samples);
Querous palustris, 2.4 ppm (mean of four samples); and Tsuga canadensis,
0.6 ppm (mean of two samples). After analysis of data for the two soil
types, the authors concluded that greater variation occurred among different
species growing on the same soil than in the same species growing on dif-
ferent soils. No data were presented on the soil cadmium levels. Fertiliza-
tion was minimal and the only soil property reported was pH.
Data from a U.S. Geological Survey study of trace elements in plants
growing near mineral deposits (Curtin and King, cited in Shacklette, 1972)
are shown in Table 4.13. Stem ash generally contained more cadmium than
leaf ash, indicating uptake from the soil rather than deposition from the
air. If the source of cadmium had been airborne particles, stems, according
to Shacklette (1972), would have contained less cadmium than leaves due to
a lower surface-to-volume ratio. Cadmium in soil humus of the sampling area
ranged from <1 to 10 ppm.
Blaylock et al. (1973) used cadmium in a tree inoculation study.
Cadmium as 109CdCl2 was promptly translocated from trunk (point of inocu-
lation) to foliage of eastern red cedar (Juniperus vi.rgini.ana). Approxi-
mately 65% of the cadmium reached the crown, of which 0.1% was leached by
rain (20.8 cm total) over an eight-week period. Of the cadmium leached
from the crown, 2.7% was absorbed by understory vegetation.
In summary, noncrop plants contain insignificant cadmium levels unless
soil content exceeds background levels. Mosses tend to be cadmium accumu-
lators and may be potential indicators of atmospheric concentrations. Woody
plants accumulate cadmium in twigs. Generally, cadmium levels in noncrop
plants do not appear to represent an environmental hazard.
-------
78
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4.2.3 Elimination — Gordee, Porter, and Langston (1960) determined that
cadmium is not eliminated from peppermint. According to Shacklette (1972),
there appears to be no natural means by which cadmium is eliminated from
living plant tissue. No other references to cadmium elimination by plants
were found.
4.3 EFFECTS
In general, the fact that a given cadmium concentration is toxic to
plants depends on many largely unknown factors (Shacklette, 1972). Page,
Bingham, and Nelson (1972), using nutrient solutions, found the yield of
tops of beetroot, carrot, lettuce, radish, and Swiss chard to be essentially
unaffected by cadmium levels of 0.01 to 0.10 ppm. Yield of tomato plants
was severely reduced at 0.01 ppm. At a concentration of 1 ppm, cadmium
reduced yields of tops of all species tested to 30% to 50% of controls.
Chaney (1973) suggested that this work with nutrient solutions cannot easily
be extrapolated to soils.
In greenhouse experiments using municipal sewage sludge moistened with
cadmium sulfate, Bingham et al. (1975) observed that cadmium-sensitive
plants such as spinach, soybean, curlycress, and lettuce were injured by
soil cadmium levels of 3 to 4 ppm. In contrast, tomato and cabbage toler-
ated soil cadmium levels of approximately 170 ppm without apparent injury.
Rice exhibited no ill effects at soil cadmium levels as high as 640 ppm.
Thus, when comparing solution cultures (Page, Bingham, and Nelson, 1972)
with soil cultures, critical cadmium concentrations may differ. In addi-
tion, results obtained in a particular soil are not necessarily applicable
to other soils or soil mixes (Bingham et al., 1975).
Table 4.14 lists some phytotoxic effects exerted by cadmium on several
economically important plants (Yopp, Schmid, and Hoist, 1974). These data
indicate that a general reduction in yield is the usual symptom of phyto-
toxic cadmium levels. Page, Bingham, and Nelson (1972) determined cadmium
concentrations in nutrient solutions which resulted in a 50% growth reduc-
tion in some crops (Table 4.15). Significant differences are seen in the
sensitivities of different species.
The effects of cadmium applied to soil on various crop yields were
studied by John (1973). At a high rate of cadmium application, yields of
most plant parts were depressed (Table 4.16). The yield of marketable
portions (especially oat grain) was reduced more than that of roots. In
other work, John (1972) found that as the amount of cadmium applied to soil
increased from 0 to 100 ppm, yield of radish tops decreased from 1.59 to
1.00 g per pot and yield of roots decreased from 1.58 to 0.61 g per pot
(number of plants per pot not given). Dry weight of corn plants grown in
sandy soil decreased from 0.70 g per plant in the control to 0.25 g per
plant when 562 ppm cadmium was added to the soil (Traynor and Knezek, 1973) .
A cadmium concentration of 0.01 ppm in rooting solution inhibited frond
production of duckweed (Hutchinson and Czyrska, 1972). A concentration of
0.05 ppm reduced growth 35% over a one-week period; at 0.5 and 1.0 ppm cad-
mium, plants ceased growth and eventually died. Similar results occurred
-------
81
TABLE 4.14. PHYTOTOXIC EFFECTS EXERTED BY CADMIUM ON SEEDLING PLANTS
OF ECONOMIC IMPORTANCE IN ILLINOIS"
Plant
Soybean
Winter wheat
Lettuce
Radish
Celery
Green pepper
Beet (root)
Swiss chard
Tomato
Carrot
Entire
Source:
permission of
Growing
medium
Defined soil type
Defined soil type
Defined soil type
Defined soil type
Defined soil type
Defined soil type
Defined nutrient medium
Defined nutrient medium
Defined nutrient medium
Defined nutrient medium
plant affected in all cases.
Adapted from Yopp, Schmid,
the publisher.
Minimum
phytotoxic
concentration
of cadmium
(ppm)
2.5
2.5
2.5
2.5
2.5
2.5
1.0
0.1
0.1
1.0
and Hoist, Table
Phytotoxic
symptoms
Reddish brown veins in
youngest trifoliate
leaves; growth retar-
dation
General growth retardation
General growth retardation
General growth retardation
General growth retardation
General growth retardation
General growth retardation
General growth retardation
General growth retardation
General growth retardation
I, p. 74. Reprinted by
TABLE 4.15. CADMIUM CONCENTRATIONS IN NUTRIENT SOLUTIONS
PRODUCING 50% GROWTH REDUCTION IN SOME CROPS
Plant
Cabbage
Tomato
Barley
Pepper
Sweet corn
Lettuce
Red beet
Field bean
Turnip
Cadmium concentration
(pg/ml)
Concentration
Range .
, producing 50%
tested u j
growth depression
0-10 9.0
0-10 4.8
0-10 5.6
0-10 2.0
0-10 1.2
0-10 0.9
0-10 0.2
0-1.0 0.2
0-1.0 0.2
Concentration
of cadmium
in leaf at
50% growth
depression0"
(Pg/g)
800
570
120
160
230
320
290
22
290
Visible
symptoms
associated
with 50%
growth
depression
No specific symptoms were
associated with reduced
growth.
Chlorosis
No specific symptoms were
associated with reduced
growth .
Chlorosis
Reddish orange coloration
of leaf margin, necro-
sis, and chlorosis
Chlorosis
Wilting
Wilting
Chlorosis
Oven dry weight, 70°C.
Source: Adapted from Page, Bingham, and Nelson, Table 2, p. 290.
-------
TABLE 4.16.
82
EFFECT OF CADMIUM CONTAMINATION OF SOIL ON YIELD
OF VARIOUS PARTS OF EIGHT CROPS
Plants
Crop
per pot
Lettuce 6
Spinach 8
Broccoli 3
Cauliflower 3
Pea 3
Oat 12
Radish 8
Carrot 10
Growth
. , Plant
period
,, .. part
(days) v
35 Leaves
Roots
55 Leaves
Roots
60 Leaves
Roots
70 Leaves
Roots
95 Seeds
Pods
Vines
Roots
100 Grains
Husks
Leaves
Stalks
Roots
45 Tops
Tubers
130 Tops
Tubers
Roots
Control
17.50 a
0.91 a
10.96 a
0.51 a
95.93 a
2.46 a
103.67 a
1.78 a
27.45 a
10.59 a
19.64 a
1.98 a
42.57 a
5.56 b
20.84 a
29.90 a
3.75 a
8.24 a
7.10 a
18.95 a
41.72 a
0.96 a
Dry weight
(g/pot)a
40 mg Cd
per kilogram
of soil
18.82 a
0.99 a
0.39 b
0.02 b
122.50 a
4.08 a
100.83 a
1.47 a
16.98 a &
7.45 a
14.43 a
1.08 a
27.28 b
8.31 a
21.50 a
39.17 a
3.18 a
6.25 b
5.12 a
16.92 a
38.27 a
0.81 a
200 mg Cd
per kilogram
of soil
1.55 b
0.36 a
0.16 b
0.02 b
35.20 *
2.09 a
3.17 b
0.17 Z>
0.21 b
0.84 &
2.47 b
0.56 &
18.37 fc
6.85 a 2>
18.72 a
23.28 a
2.88 a
1.47 e
0.48 b
1.50 b
1.52 2>
0.13 b
Values followed by the same letter do not differ significantly at the 5% level.
Source: Adapted from John, 1973, Table 2, p. 11. Reprinted by permission of the
publisher.
with aquatic fern. Cearley and Coleman (1973) reported that southern naiad
exhibited toxicity symptoms (reduced chlorophyll content, turgor, and stolon
development) as cadmium concentrations were raised from 0.007 to 0.83 ppm.
Haghiri (1973) noted that cadmium was toxic to wheat at the lowest
concentration tested (2.5 ppm). Imai and Siegel (1973) reported that growth
of red kidney bean embryos was inhibited by concentrations greater than 3
ppm in nutrient media. Broad beans (Viaia fdbd) lost turgor 2 to 3 hr after
exposure to 0.5 x 10"3 M or 1 x 10"3 M concentrations of CdCl2 (Nosseir,
1970). The cadmium altered normal ion absorption and release. Similar but
less pronounced effects were recorded for kidney beans.
Puerner and Siegel (1972) found that 10 ppm cadmium added to rooting
media of cucumbers (Cueumis sativus") produced severe root damage and induced
shoots to spiral 180° around their own axes. Cadmium chloride (5 x 10~A A/)
-------
83
applied to endocarp surfaces of excised immature tissue or intact seedlings
of peas (Pisum sat-ivwn') resulted in an increased production of pisatin
(Hadwiger, von Broembsen, and Eddy, 1973), a phytoalexin produced in response
to certain plant pathogens. A concentration of 6 x 10~A M cadmium increased
RNA synthesis. Cadmium acetate applied to tobacco leaves results in a
decrease in leaf dry weight and leaf sap phosphorus (Verma, 1971).
Huang, Bazzaz, and Vanderhoef (1974) found that soybeans grown in nutri-
ent solution were sensitive to cadmium. Concentrations as low as 18 micro-
moles reduced fresh weight by approximately 35% and caused a 71% decline in
nitrogenase activity. A lower nodule carbohydrate content caused by inhibi-
tion of photosynthesis was also noted. Cadmium nitrate is a potent inhibi-
tor of photosynthesis in isolated chloroplasts of maize (Bazzaz, 1974).
Absorption and fluoresence studies revealed that cadmium results in a 20%
to 30% decrease in the chlorophyll A to chlorophyll B ratio. Bazzaz,
Carlson, and Rolfe (1974) determined that a leaf tissue concentration of
0.93 ppm cadmium reduced photosynthesis by 50% in detached sunflower
(Helianthus annuus~) leaves. The primary mode of action was interference
with stomatal function.
In conclusion, cadmium levels which affect plant metabolism are
highly variable and virtually unknown for field crops. In controlled
experiments cadmium has produced decreases in plant yield. Major effects
reported in the literature include (1) altered ion absorption and release,
(2) altered stomatal function, (3) reduced chlorophyll content, (4) reduced
cell turgor, and (5) reduced photosynthesis. Generally, plants exposed to
normal background levels are not known to experience any major inhibitory
effects. Plants near cadmium sources, however, may contain abnormal cad-
mium levels detrimental to growth.
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84
SECTION 4
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23. Jaakkola, T., H. Takahashi, and J. K. Miettinen. 1973. Cadmium
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of Ions by Broad and Kidney Beans. Adv. Front. Plant Sci. (India)
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Fruit and Foliage following a Cover Spray of Cadmium Chloride.
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48. Smith, R. H., and J. W. Huckabee. 1973. Ecological Studies of
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SECTION 5
EFFECTS OF CADMIUM ON AQUATIC ANIMALS AND BIRDS
5.1 SUMMARY
Fish.kills and excessive levels of pollutants in seafood illustrate
the disposal problem for industrial and other wastes. Animals are valuable
indicators of environmental pollution, and periodic sampling of trace
metals in fish from waters into which industrial wastes are dumped helps
to evaluate pollution control measures.
In fish, cadmium is absorbed through gills and/or the digestive tract.
Concentration of the metal in tissues resembles that in other species
(Section 6): levels are highest in kidneys and liver and low in muscle.
Scallops concentrate cadmium from seawater to a great extent — by a factor
of about 100 in one study. Shellfish, in general, accumulate cadmium to a
greater extent than fish. Accumulation of cadmium may continue over the
organism's lifetime. In bass and bluegill, equilibrium is reached between
water and tissue cadmium concentrations.
Toxicity of cadmium can vary with water hardness and temperature and
presence of other metals. A cadmium concentration of 0.008 to 0.010 ppm
killed 50% of rainbow trout after seven days in hard water at a temperature
of 11.0°C to 12.5°C. Cadmium is generally more toxic to fiddler crabs at
higher temperatures and lower salinities.
Birds also take up cadmium mainly by ingestion. About 8% of ingested
cadmium was absorbed by chipping sparrows. The tissue distribution is
similar to that in other organisms mentioned, with kidneys and liver con-
taining the highest concentrations. Cadmium levels in birds are generally
low; 72% of starling samples collected across the United States contained
less than 0.05 ppm whole-body weight. Levels in Cooper's hawk eggs were
generally low but were significantly higher in eggs from unsuccessful nests
than from successful ones. Toxic effects in birds are similar to those in
other species and include growth retardation, anemia, and testicular
hypoplasia.
5.2 FISH AND OTHER AQUATIC ORGANISMS
5.2.1 Metabolism
5.2.1.1 Uptake and Absorption — Fish and other aquatic animals absorb
cadmium through gills and/or through the gastrointestinal tract. Because
in the natural situation it is impossible to differentiate between the two
routes of uptake, they are considered together in this section.
Mount and Stephan (1967) exposed bluegills to cadmium in a flow-through
system for 90 days. They reported that there was substantial accumulation
of cadmium in kidney, liver, gill, and gut, with lesser accumulation in
spleen and none in muscle or bone.
90
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91
Eisler, Zaroogian, and Hennekey (1972) examined cadmium uptake by
adult mummichogs, scallops, and oysters and by subadult lobsters. All
species were collected from Rhode Island waters and acclimated for 28 days
in flowing, unfiltered seawater at 16°C to 20°C before separation into
control and experimental groups. Cadmium (0.01 ppm as CdCl2) was then
added to the seawater of the experimental group for 21 days. Control sea-
water contained 0.001 ppm cadmium. As shown in Table 5.1, some marine
organisms accumulate cadmium even when it is present at a very low con-
centration in water.
TABLE 5.1. CADMIUM UPTAKE BY MARINE ORGANISMS
Species
Cadmium content
(ppm wet wt)
Experimental Control
Increase
over control
Crassostrea virginioa
(whole system meats)
Aquipecten -i
(scallop, sum of
soft parts
EomaTus ameri-canus
(lobster, sum of parts)
Fundulus heteroalitus
(whole mummichog)
1.49
2.46
0.72
0.48
0.33
1.15
0.51
0.33
352
114
41
45
Source: Adapted from Eisler, Zaroogian, and Hennekey, 1972,
Table 1, p. 1368. Reprinted by permission of the Journal of the
Fisheries Research Board of Canada.
Cearley and Coleman (1974) reported that cadmium uptake by large-
mouth bass and bluegills established a steady state between water and
tissue concentrations after two months. Maximum whole-body burden of cad-
mium in bass was eightfold and fifteenfold greater than controls at ex-
posures of 0.008 and 0.08 ppm cadmium respectively. Because the fish
continued to grow, the absolute amount of cadmium per whole fish continued
to increase although the amount per unit weight remained constant.
Kumada et al. (1973) found that maximum cadmium concentrations in
rainbow trout exposed to cadmium levels in water of up to 0.0048 ppm oc-
curred after 10 to 20 weeks. Cadmium concentrations as high as 300 times
that in water were achieved. Total body content of cadmium decreased only
moderately in ten weeks following transfer to cadmium-free water. These
results are shown in Table 5.2.
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92
TABLE 5.2. DISTRIBUTION OF CADMIUM IN ORGANS OF RAINBOW
TROUT REARED IN CADMIUM SOLUTION (0.0048 ppm)
Time
elapsed
/ i \a
(weeks)
30
40
Tissue
Muscle
Skin
Liver
Kidney
Digestive tract
Gill
Bone
Residue
Muscle
Skin
Liver
Kidney
Gill
Bone
Residue
Cadmium
Wet
sample
0.12
0.59
7.3
20
9.5
0.85
1.6
0.04
0.32
4.4
16
0.63
0.38
1.3
content
Dry
sample
0.40
1.8
37
100
38
1.1
3.1
0.14
0.84
19
75
2.1
0.66
1.6
(ppm)
Ash
5.2
18
350
1100
240
1.2
31
2.2
11
230
860
11
0.80
27
The fish were exposed to cadmium for 30 weeks and
then put in flowing water free of cadmium for 10 weeks.
Source: Adapted from Kumada et al., 1973, Table 3,
p. 162. Reprinted by permission of the publisher.
Rainbow trout fed cadmium in food (up to 100 ppm of diet) also had
increased levels of cadmium in their tissues (Kumada et al., 1973). On a
dry weight basis, the maximum whole-body cadmium concentration was less
than one-tenth that in the diet. Liver and kidney contained the most cad-
mium. Unlike cadmium absorbed from water, cadmium absorbed from the diet
was rapidly eliminated when the fish were switched to cadmium-free diets.
In whole fish, cadmium levels dropped by 90% on a relative basis (parts
per million) and by 80% on an absolute basis in eight weeks after cadmium-
free diets were started. Kidney levels remained high, suggesting a pos-
sible role of these organs in cadmium excretion.
Eaton (1974) reported information regarding the sites of deposition
of cadmium in bluegills exposed for 11 months. He found (Table 5.3) that
at each of the cadmium concentrations examined, the highest cadmium resi-
dues were found in the liver. Cadmium concentrations in intestine and
cecum were somewhat lower and also increased with water concentration.
In contrast, kidney cadmium did not increase with exposure levels.
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93
TABLE 5.3. CADMIUM CONCENTRATIONS IN BLUEGILL TISSUES AFTER AN 11-MONTH CHRONIC EXPOSURE
Measured
cadmium
concentration
in water
(ppm)
0.0023
(control)
0.031
0.080
0.239
0.757
2.14
Number
of fish
examined
18 L
0 D
18 L
0 D
9 L
4 D
2 L
6 D
0 L
16 D
0 L
18 D
Cadmium content (ppm)
Gill
Trace0
34
(22-51)
37
(18-60)
21
(3-47)
45
(38 and 53)
23
(15-26)
40
(22-73)
80
(38-211)
Intestine
and
cecum
Trace
73
~(49-99)
140
(73-327)
210
(104-378)
349
(274 and 424)
302
(113-461)
173
(67-336)
377
(131-756)
Liver
Trace^
201
(138-298)
325
(218-472)
343
(126-614)
538
(496 and 581)
335
(146-422)
275
(114-458)
440
(172-755)
Kidney
Trace
188
(96-305)
213
(170-293)
157
(44-275)
218
(169 and 268)
85
(7-208)
125
(42-344)
145
(67-295)
,Fish that lived to the end of the test (L) or died during it (D).
Mean concentration with range in parentheses.
o
Less than 5 ppm.
Less than 10 ppm.
Source: Adapted from Eaton, 1974, Table 4, p. 733. Reprinted by permission of the
publisher.
5.2.1.2 Normal Levels — Because aquatic organisms take up cadmium and
fish and shellfish are an important food source for many people, they
potentially could contribute to the human body burden of cadmium. Fish
from cadmium-contaminated waters may have higher cadmium levels in tissues
and organs than fish from uncontaminated water; however, the results are
not always clear-cut.
For example, fish from the Holston River in Knox County, Tennessee,
taken near the outfall of a zinc beneficiation mill contained 0.023 to
0.23 ppm cadmium in muscle and 0.47 to 2.9 ppm cadmium in kidneys (wet
weight), while fish from a nearby lake with no known source of cadmium
except normal background sources had 0.02 to 0.056 ppm cadmium in muscle
and 0.2 to 2.0 ppm cadmium in kidneys (Huckabee et al., 1971, personal
communication cited in Smith and Huckabee, 1973). The maximum values may
reflect the industrial activity, but the variability makes definite con-
clusions impossible. A survey of cadmium in fish from the upper Clark
Fork River in western Montana gave the values shown in Table 5.4 (Van
Meter, 1974). Mining is common in this part of Montana.
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94
TABLE 5.4. AVERAGE CADMIUM
CONCENTRATIONS IN FISH FROM
UPPER CLARK FORK RIVER IN
WESTERN MONTANA
Cadmium content
c . (ppm wet wt)
Species ^ __
Muscle Liver
Trout
Whitefish
Sucker
Sculpin
Shiner
Squawfish
0.19
0.20
0.60
0.69
0.65
0.79
0.30
0.32
0.53
Arithmetic mean of all
samples.
Source: Adapted from
Van Meter, 1974, Table 2,
p. 14.
Cadmium levels in whole fish of three species from the Great Lakes
(Lucas, Edgington, and Colby, 1970) averaged 0.094 ppm (range of 0.062 to
0.140 ppm). Concentrations varied among fish of the same species and with
collection site. Liver cadmium concentrations in ten other species from
the Great Lakes averaged 0.4 ppm (range of 0.06 to 1.4 ppm) and were highest
in goldfish from Lake Erie.
Mathis and Cummings (1973) examined levels of cadmium and other metals
in organisms from the Illinois River. Results are given in Table 5.5.
Bottom sediment contained a mean of 2.0 ppm cadmium (range of 0.02 to 12.1
ppm) and the water a mean of 0.0006 ppm (range of 0.0001 to 0.002 ppm).
Bottom-dwelling organisms contained the most cadmium in this study; worms
had the highest levels, while fish muscle had the least. There was no
significant difference (P = 0.05) between muscle cadmium concentrations in
carnivorous and omnivorous fish.
Cadmium concentration is much higher in shellfish than in fish. This
is true of various kinds of shellfish from around the world (Smith and
Huckabee, 1973). The cadmium content of various species of saltwater shell-
fish from Japan ranged from less than 0.01 ppm in the octopus to 0.85 ppm
in the oyster (Smith and Huckabee, 1973).
Seals, although mammals, are discussed in this section because they
are aquatic organisms feeding on fish and other seafoods. Cadmium levels
in seals from several areas around Britain were determined between 1968 and
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95
TABLE 5.5. CADMIUM LEVELS IN ORGANISMS FROM
THE ILLINOIS RIVER
Species
Number
of
samples
Cadmium level (ppm)
Mean Range
Clams
Fusoonaia flava 17 0.69
Amblema plioata 25 0.38
Quadrula quadrula 20 0.56
Tubificid annelids 11 1.1
Carnivorous fish
Esox luaius 4 0.022
Microptevus salmoides 7 0.022
UoTone chrysops 2 0.024
Lepisosteits platostomus 2 0.030
Micropterus dolorrrieui 1 0.005
Omnivorous fish
Ictiobus cyprinellus 12 0.032
Dorosoma oepedianum 12 0.033
Moxostoma maoro'lep-idotwn 4 0.017
Carp-lodes cyprinus 22 0.024
Cyprinus oavpio 14 0.035
0.36-1.17
0.15-1.41
0.31-1.37
0.5-3.2
0.013-0.031
0.004-0.060
0.004-0.038
0.004-0.085
0.001-0.055
0.005-0.068
0.005-0.031
0.004-0.046
0.011-0.069
Source: Adapted from Mathis and Cummings, 1973, Tables
II-V, pp. 1575-1577.
1972 by Heppleston and French (1973) . Kidney levels were relatively high
(up to 22 ppm wet weight as determined by atomic absorption spectrophotom-
etry) and increased with age as in humans (Section 6). Brain and liver
levels were below 1 ppm. Cadmium levels (yg/g kidney wet weight ± standard
deviation) were: Fame Island, 5.3 ± 4.0; Outer Hebrides, 11.6 ± 7.5; and
Shetland, 2.2 ± 2.0.
5.2.2 Effects
Cadmium produces both acute and chronic effects in aquatic animals;
these are considered in this section. Discussion of mechanisms is post-
poned to Section 6.3.1 because similar molecular mechanisms are presumably
involved in all species.
5.2.2.1 Acute — The acute toxicity of cadmium to various aquatic organisms
is given in Tables 5.6 and 5.7. Cadmium toxicity varies with concentration,
water characteristics, and experimental conditions. Because of these varia-
bles, it is difficult to evaluate the relative sensitivities of different
-------
96
TABLE 5.6. ACUTE DOSES OF CADMIUM FOR SOME AQUATIC ORGANISMS
Species
Acute dose LC50
(ppm)
b
Test conditions
Pimephales pPamelas
Lepomis macroahifus
Lebistes reticulatus
Lepomis oyane'llus
Salmo gairdneifii
Crassostrea virginica
Fundulus hetevoalitus
5 Static acute bioassay; hard
water; CdCl2
0.9 Static acute bioassay; soft
water; CdCl2
1.05 Static acute bioassay; soft
water; CdCl2, concentration as
cadmium
72.6 Static acute bioassay; hard
water; CdCl2, concentration as
cadmium
1.94 Static acute bioassay; soft
water; CdCl2, concentration as
cadmium
1.27 Static acute bioassay; soft
water; CdCl2, concentration as
cadmium
2.84 Static acute bioassay; soft
water; CdCl2, concentration as
cadmium
66.0 Static acute bioassay; hard
water; CdCl2, concentration as
cadmium
0.008-0.01 Continuous flow, acute bioassay;
(7 days) hard water
30 (1 day) Continuous flow, acute bioassay;
hard water
0.12 (4-8 In flowing water; 20°C; salinity,
weeks) 31 ppt; CdCl2«2.5H20
27.0 20-22°C; no feeding during the
96 hr; aerated water
The units used are those presented in the original publication. In
some cases it is impossible to deduce whether the concentration is expressed
in terms of the element or the compound tested. Very abbreviated descrip-
tions of the conditions of the test are presented. The purpose of the compi-
lation is to indicate the range of concentrations and species used.
days, unless specified.
Source: Adapted from National Academy of Sciences and National Academy
of Engineering, 1973, Table 1, p. 451. Data collected from several sources.
-------
97
TABLE 5.7. CADMIUM TOXICITY TO SOME AQUATIC ORGANISMS
Compound Organism
CdCl2 Agonus cataphractus
Cavdium edule
Crangon crangon
Fundulus heteroelitus
Fundulus heteroclitus
Pagurus longiearpus
Palaemonetes vulgaris
Asterias forbesi
Mya arenaria
Carcinus maenus
Urosalpinx cinerea
Fundulus majalis
Mytilus edulis
Cyprinodon variegatus
Nassarius obsoletus
Nereis virens
CdSOi, AoToneuria
Ephemerella
Hy dropsy che
Field
study
BSA
BSA
BSA
L
BSA
BSA
BSA
BSA
BSA
BSA
BSA
BSA
BSA
BSA
BSA
BSA
BSA
BSA
BSA
Toxicity
of active,
ingredient
(ppm)
33 (T4)
3.3 (T4)
1.0 (T2)
50 (SB2)
55.0 (T4)
0.32 (T4)
0.42 (T4)
0.82 (T4)
2.2 (T4)
4.1 (T4)
6.6 (T4)
21.0 (T4)
25.0 (T4)
50.0 (T4)
10.5 (T4)
11.0 (T4)
32 (T14)
2 (T4)
32 (T10)
BSA — bioassay, static, acute; L — laboratory
bioassay.
^T — TLm; SB — sublethal effect. The numbers within
parentheses following these designations indicate the time
in days when the effect was observed.
Source: Adpated from Kemp et al., 1973, Appendix A,
pp. A-53 to A-58. Data collected from several sources.
-------
98
species. Rehwoldt et al. (1971) examined the acute toxicity of cadmium to
12 fish species in soft water (55 ppm as CaC03). The 96-hr LCSO values in
these static bioassays varied from 0.11 to 2.8 ppm cadmium. Eisler (1971)
reported on the acute toxicity of cadmium to 13 species of marine animals
tested at 20°C and 20% salinity. In general, the fish were more resistant,
with 96-hr LC50 values that ranged from 21 to 51 ppm cadmium. The Crustacea
were the most sensitive, with 96-hr LC50 values ranging from 0.32 to 4.1 ppm
cadmium; mollusks and sandworms were intermediate in sensitivity. Biesinger
and Christensen (1972) reported a 48-hr LC50 value of 0.065 ppm cadmium for
Daphnia magna tested in Lake Superior waters. Ball (1967) found a one-day
LC50 value of 30 ppm cadmium; results, as shown in Figure 5.1, suggested a
seven-day minimum toxic dose of 0.008 to 0.01 ppm.
ORNL-DWG 77-5288
§J
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20,000
10,000
1000
0.01
0.1 10 10
CADMIUM CONCENTRATION (ppm)
100
Figure 5.1. Toxicity of cadmium in hard water to rainbow trout.
Source: Adapted from Ball, 1967, Figure 1, p. 805. Reprinted by permission
of the publisher.
5.2.2.2 Chronic — Chronic toxicity tests are desirable for estimating long-
term safe concentrations of cadmium for aquatic life. Pickering and Cast
(1972) reported on the chronic toxicity of cadmium in hard water to the fat-
head minnow. A complete life cycle was studied and the effects on survival,
growth, and reproduction were measured. At the higher concentrations mortal-
ity slowly increased. The most sensitive effect was on the developing em-
bryos. A cadmium concentration of 0.057 ppm was lethal to some embryos and
many surviving larvae were inactive and deformed, whereas 0.037 ppm cadmium
did not produce any adverse effects on survival, growth, or reproduction.
Eaton (1974) studied the chronic toxicity of cadmium in hard water to
the bluegill. He reported a slow cumulative mortality at all but the lowest
cadmium concentration. Continuous exposure in water containing 0.080 ppm
cadmium was toxic to bluegills, as judged from effects on larvae and from
mortality among adult fish exposed for several months; no effects were pro-
duced by cadmium at a concentration of 0.031 ppm.
The chronic toxicity of a mixture of copper, cadmium, and zinc to the
fathead minnow was reported by Eaton (1973). He found that the chronic
-------
99
toxicity of the mixture attributable to copper appeared to be increased,
but that attributable to cadmium was reduced. The effects thought to be
due to zinc were similar to those observed in the single chronic exposure.
Biesinger and Christensen (1972) studied the effects of various metals
on survival, growth, reproduction, and metabolism of Daphn-ia magna. Cadmium
was the most toxic of the heavy metals. In soft Lake Superior waters they
found a three-week LCSO value of 0.005 ppm cadmium. A cadmium concentra-
tion of 0.0007 ppm depressed reproduction by 50%; a concentration of
0.00017 ppm caused no apparent effects.
5.2.2.3 Mode of Action — Table 5.8 shows some chronic effects of cadmium
and suggests some possible modes of action. Gardner and Yevich (1970) ex-
posed the killifish (Fundulus heteroolitus) to 50 ppm cadmium in seawater
at 37% salinity. They found pathological changes in the intestinal tract
as early as 1 hr after exposure, in the kidney after 12 hr, and in the gill
filaments and respiratory lamellae after 20 hr. They also found that
eosinophils increased to a level 45% above normal.
TABLE 5.8. CHRONIC TOXIC EFFECTS OF CADMIUM TO AQUATIC ORGANISMS
Species
Chronic
dose
(ppm)
Test conditions
Daphnia magna
Australorbis glabratus
Sewage organisms
Cvassostrea virgin-Loa
Fundulus heteyoolitus
0.0026
0.05-0.10
142
0.1-0.2
50
27
Threshold of immobilization
Produced distress syndromes;
distilled water
50% inhibition of 02 utili-
zation
20-week exposure; little
shell growth, lost pigmen-
tation of mantle edge;
coloration of digestive
diverticulae
Pathological changes in
intestinal tract, kidney,
and gills; changes in eo-
sinophil lineage
Inhibition of some liver
enzymes
Source: Adapted from National Academy of Sciences and
National Academy of Engineering, 1973, Table 2, p. 462.
-------
100
Jackim, Hamlin, and Sonis (1970) studied the effects of metal expo-
sure on liver enzymes in the killifish (Fundulus heteroelitus). Changes
in enzyme activity produced by exposure to 27 ppm cadmium in seawater were
not necessarily the same in magnitude or direction as those produced in
vitro. Fish that survived this cadmium exposure had a significant change
in activity of acid phosphatase, xanthine oxidase, and catalase.
Hiltibran (1971) reported on 16 effects of cadmium on oxygen and phos-
phate metabolism of bluegill liver mitochondria. He found that low levels
of cadmium severely interrupt energy production in vitro by blocking oxygen
uptake. Oxidation of lactate by the gills of rainbow trout that survived
a 24-hr exposure to 1.12 ppm cadmium (50% to 70% survival) was inhibited
by over 50% (Bilinski and Jonas, 1973). No detectable effect on oxidation
was seen at lower doses although mortality was increased.
5.2.2.4 Alteration of Toxicity — Water conditions such as temperature and
salinity might be expected to influence toxicity of cadmium to aquatic
organisms, either directly by changing the organism's metabolic rate or
indirectly by altering the solubility of the cadmium compound. O'Hara (1973)
examined the effect of temperature and salinity on the toxicity of cadmium
to the fiddler crab and in general found greater toxicity at higher tempera-
tures and lower salinities. Table 5.9 lists the cadmium level that killed
50% of the crabs (TL ) for various salinities and temperatures.
TABLE 5.9. CADMIUM TOXICITY TO FIDDLER
CRABS AS A FUNCTION OF SALINITY
AND TEMPERATURE
Salnity
(%)
10
20
30
Time
(hr)
48
96
144
192
48
96
144
192
240
48
96
144
192
240
TLm (ppm)
10°C 20°C
32.2
51.0 21.3
15.7 11.8
46.6
23.0
52.0 16.5
42.0 9.5
37.0
29.6
21.0
47.0 17.9
30 °C
11.0
6.8
4.0
2.9
28.0
10.4
5.2
3.7
3.5
33.3
23.3
7.6
6.5
5.7
a
Concentration lethal to 50% of
crabs.
Source: Adapted from O'Hara, 1973,
Table 1, p. 150.
-------
101
Cadmium toxicity may be altered by the presence of other metals
(Section 6.3.2) — a situation likely to exist in most waterways where cad-
mium is present. With this in mind, Eaton (1973) exposed fathead minnows
to mixtures of cadmium, copper, and zinc and compared the toxicities with
those of the individual metals. A lethal threshold was reached when each
metal was present at a concentration of 40% or less of its individual lethal
threshold. The toxicity due to cadmium in the mixture was less than expect-
ed from its individual toxicity. Table 5.10 gives acute toxicity levels of
the individual metals and of the mixture.
TABLE 5.10. COMPARISON OF THE ACUTE TOXICITY OF A
COPPER, CADMIUM, AND ZINC MIXTURE WITH THAT OF
INDIVIDUAL METALS TO FATHEAD MINNOWS
Toxicity determination
Measured acute test value
( Ma
_ _
Copper Cadmium Zinc
Copper, cadmium, and zinc
mixture, lethal threshold
value 145 320 2050
Copper, 96-hr TLm value 430
Cadmium, lethal threshold
value 7200
Zinc, lethal threshold value 5030
VMean of daily composited samples.
As little or no mortality took place after three
days of exposure, this is considered a close approxima-
tion of the lethal threshold value.
Source: Adapted from Eaton, 1973, Table 7, p. 1735.
Reprinted by permission of the publisher.
The effect of pollutants on spawning and hatching success is an impor-
tant consideration in long-term survival of a species in polluted water.
Table 5.11 shows the decrease in number of spawnings and number of embryos
with increasing concentrations of metals in a mixture of cadmium, copper,
and zinc (Eaton, 1973).
5.3 BIRDS
Birds are good indicators of environmental pollution for several
reasons. "The varied diets of different birds in an area (e.g., seed and
grain, rodents and other small animals, or fish) permit a sampling of cad-
mium contamination of several aspects of the environment. A declining
-------
102
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103
population trend for a species may also indicate the presence of a toxic
substance in the area. In addition to bird muscle, organs, and feathers,
eggs can also be analyzed for cadmium.
5.3.1 Metabolism
5.3.1.1 Uptake and Absorption — Birds take up and absorb cadmium via the
same routes as other organisms; ingestion contributes the major part of
total uptake (Section 6.2.1). Little information is available on actual
rates of uptake in birds. Anderson and Van Hook (1973) fed 109Cd-tagged
birdseed to chipping sparrows (167 nCi/g birdseed) for 21 days. Cadmium
concentrations at 21 days (nCi/g live weight) were: feather, 8; liver,
14; kidneys, 29; and gut, 75. Approximately 8% of the cadmium available
in the food was absorbed. Figure 5.2 shows whole-body uptake over the
21-day period. Figure 5.3 shows decrease in whole-body cadmium with time
after 109Cd-tagged birdseed was discontinued. After an initial rapid drop
in total burden, the remaining cadmium decreased slowly with a half-life
of 99 days. The whole-body cadmium level was only about 0.007 ppm live
weight; no mention was made of toxic effects.
15
ORNL-DWG 73-3797
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-------
104
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225
90
45
ORNL-DWG 72-1Z82IR
v,.,
i -|—
= — f
— J
$ 1
3 5 10 15 20 25 30 35 40
TIME (days)
Figure 5.3. Biological turnover of 109Cd by chipping sparrows
following 21 days of feeding on tagged bird seed. Points represent means
of eight observations (± standard error). Source: Adapted from Anderson
and Van Hook, 1973, Figure 2, p. 245.
5.3.1.2 Transport and Distribution — Tissue and organ distribution of
cadmium in birds is similar to that in other animals discussed in Section
6.2.2; therefore, transport is probably also similar, although no specific
information is available.
Distribution of cadmium in three-month-old female leghorn chickens was
determined following 12 weeks of daily intraperitoneal injections of trace
amounts of [115Cd] cadmium acetate (average cadmium dose of 0.010 mg/kg
body weight) (Dyer, Born, and Kessler, 1974). Three weeks after the last
injection radioactivity in tissues was determined. The results are shown
in Table 5.12. Because only small amounts of radioactive cadmium had been
given, levels are expressed as percentage of whole-body level rather than
parts per million of tissue sample. Eggs were laid during the three-week
period between the last cadmium injection and sacrifice. On the average,
each egg contained approximately 0.1% of the total body cadmium with 80%
in yolk, 15% in white, and 5% in shell. The percentage of whole-body cad-
mium and distribution within the eggs did not change from the first to last
egg laid during the three-week period.
5.3.1.3 Normal Levels — Cadmium levels normally found in bird tissues
would be expected to vary depending on diet and environmental conditions in
a given area. For example, Martin and Nickerson (1973) surveyed cadmium
levels in starlings from areas in the United States selected to give a
broad coverage of environmental conditions and human activities. Analyses
were made on homogenized samples of ten birds (minus skin, beaks, feet, and
wings first joint out from body) by atomic absorption spectrophotometry.
-------
105
TABLE 5.12. PERCENTAGES OF WHOLE-BODY
CADMIUM IN CHICKENS AT SACRIFICE
Percentage of
Tissue whole-body cadmium
per gram ± std deviation
Liver
Kidney
Pancreas
Spleen
Intestines
Ceca
Stomach
Gizzard
Shell glands
Ovaries
Gut fat
Carcass
0.90
1.88
0.61
0.30
0.11
0.16
0.15
0.05
0.04
0.03
0.03
0.02
± 0.33
± 0.24
± 0.21
± 0.09
±0.30
± 0.07
±0.04
± 0.02
± 0.03
± 0.02
±0.00
±0.00
Source: Adapted from Dyer, Born,
and Kessler, 1974, Table 1, p. 122, by
courtesy of Marcel Dekker, Inc.
Values ranged from not detectable (<0.005 ppm) to 0.24 ppm. Seventy-two
percent of the samples contained 0.05 ppm or less. Table 5.13 lists the
data. It is worth noting that little difference was seen between samples
from rural and urban areas.
Cadmium levels in eggs may provide useful information about cadmium
levels in birds and their diets. Assuming that the data of Dyer, Born,
and Kessler (1974) on cadmium levels in leghorn chicken eggs as percentage
of total body burden are applicable to other species (0.1% of total body
burden in each egg) , it would be possible to quantitate cadmium levels in
other species by collecting representative samples of their eggs.
Cadmium levels in the eggs of Cooper's hawks in the Arizona and New
Mexico area were determined by Snyder et al. (1973). Cadmium was found in
20 of 24 eggs (limit of detection, 0.015 to 0.024 ppm) with a mean level in
those with detectable cadmium of 0.120 ppm (standard error = 0.023 ppm).
Overall cadmium levels were quite low; however, levels in eggs from un-
successful nests were significantly higher than in eggs from successful
nests (P < 0.01).
A decline in the puffin population in the British Isles led to a search
in the birds and their eggs for residues of some organic contaminant or for
a particularly high content of heavy metal(s) (Parslow, Jefferies, and
French, 1972). Levels of the various pollutants were not unusually high
when compared to those in other seabird species with the possible exception
-------
TABLE 5.13.
106
CADMIUM RESIDUES IN STARLINGS IN THE
UNITED STATES, 1971
State
Alabama
Arizona
Arkansas
California
Colorado
Connecticut
Delaware
Florida
Georgia
Idaho
Illinois
Indiana
Iowa
Kansas
Louisiana
Maine
Maryland
Massachusetts
Minnesota
Michigan
Mississippi
Missouri
Nebraska
City
or
county
Mobile
Phoenix
Stuttgart
Bakersfield
Duplicate analysis
Los Angeles
Sacramento
Greeley
Connecticut River Valley
Dover
Gainesville
Atlanta
Boise
Chicago
Evansville
Highland
Des Moines
Garden City
Baton Rouge
Gray
Patuxent
Duplicate analysis
Quincy
Twin Cities
Lansing
Starkville
Maiden
North Platte
Type
of
site
Urban
Rural
Rural
Urban
Urban
Urban
Rural
Rural
Rural
Rural
Urban
Rural
Urban
Rural
Urban
Urban
Rural
Rural
Rural
Urban
Urban
Urban
Urban
Rural
Rural
Rural
Cadmium
(ppm, whole-
body wet wt)
<0.05
0.11
0.10
0.24
0.11
0.06
<0.05
0.05
<0.05
0.09
<0.05
<0.05
<0.05
0.06
<0.05
NDa
0.05
<0.05
<0.05
<0.05
<0.05
<0.05
0.08
0.12
<0.05
<0.05
<0.05
(continued)
-------
107
TABLE 5.13 (continued)
State
Nevada
New Jersey
New Mexico
New York
North Carolina
North Dakota
Ohio
Oklahoma
Oregon
Pennsylvania
South Carolina
South Dakota
Tennessee
Texas
Utah
Vermont
Virginia
Washington
West Virginia
Wisconsin
City
or
county
McGill
Reno
New Brunswick
Duplicate analysis
Carlsbad
Farmington
Duplicate analysis
Albany
Jamestown
Raleigh
Mandan
Columbus
Tishomingo
Corvallis
Wilsonville
Pittsburgh
Columbia
Pierre
Duplicate analysis
Nashville
Hillsboro
San Antonio
Salt Lake City
Champlain Valley
Blacksburg
Spokane
Yakima
Elkins
Horicon
Type
of
site
Rural
Rural
Urban
Rural
Rural
Urban
Urban
Urban
Rural
Rural
Rural
Rural
Rural
Urban
Urban
Rural
Urban
Rural
Urban
Rural
Rural
Rural
Rural
Rural
Rural
Urban
Cadmium
(ppm, whole-
body wet wt)
<0.05
<0.05
<0.05
<0.05
<0.05
0.12
0.10
0.08
<0.05
NDa
0.08
<0.05
<0.05
0.09
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
<0.05
0.06
<0.05
<0.05
<0.05
<0.05
0.12
<0.05
ND — not detected.
Source: Adapted from Martin and Nickerson, 1973, Table 1,
pp. 69-70.
-------
108
of cadmium. The cadmium concentrations in the livers of breeding birds
from two declining colonies (St. Kilda and Clo Mor) were higher than in
livers of puffins from other areas and in livers of other seabirds exam-
ined. Table 5.14 shows a comparison of liver cadmium levels in puffins
from eight areas. Only 3 of 55 other seabird livers (17 species) had cad-
mium levels above 12 ppm. No reason for the high cadmium levels in puffins
from St. Kilda and Clo Mor was shown.
TABLE 5.14. CONCENTRATIONS OF CADMIUM IN
LIVERS OF EIGHT ADULT PUFFINS FROM
THE BRITISH ISLES
Locality
Cadmium concentration
in liver
(mg/g dry wt) Total (yg)
Angus
Aberdeen
Northumberland
Fame Islands
St. Kilda
Clo Mor
5.5
6.8
3.3
7.5
2.9
8.4
12.9
22.3
8
21
12
26
10
38
49
127
Source: Adapted from Parslow, Jefferies,
and French, 1972, Table VII, p. 28. Reprinted
by permission of the publisher.
5.3.2 Effects
Cadmium-induced effects in birds are similar to those produced in
other animals as discussed in Section 6.3. In general, the danger to birds
is one of chronic exposure to low levels of cadmium, and most work with
birds has been with chronic exposures.
Richardson, Spivey Fox, and Fry (1974) fed Japanese quail 75 mg cad-
mium per kilogram diet from hatching to four or six weeks and compared the
effects with those of zinc and iron deficiencies. At four weeks both cad-
mium-containing and zinc-deficient diets produced growth retardation and
testicular hypoplasia. Bone marrow hypoplasia and severe anemia occurred
in birds fed cadmium-containing or iron-deficient diets. Hypertrophy of
both heart ventricles was apparent at six weeks in cadmium-treated birds.
Left-ventricular hypertrophy occurred in four weeks in iron-deficient
quail. Ascorbic acid in the diet (1%) prevented cadmium-induced effects.
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109
Similar effects occurred in adult male white leghorn chickens given
2 mg cadmium sulfate per kilogram body weight daily intraperitoneally for
15 to 22 days or a total dose of over 60 mg cadmium per bird (Sturkie, 1973).
There was no effect on blood pressure or leucocyte counts, but anemia, en-
larged hearts, and myocardial infarction occurred. The hematocrit decreased
from an average of 36% before treatment to 19% after 15 cadmium injections.
Thirty-four days after the last cadmium injection the hematocrit had in-
creased to 26%, still significantly below normal.
Although cadmium delayed testicular development in the study by
Richardson, Spivey Fox, and Fry (1974), testicular damage in birds or other
organisms with abdominal testes has not always been reported (Section
6.3.2.4.2; Johnson and Turner, 1972; Johnson and Walker, 1970). Suscepti-
bility differs among avian species. Testicular damage was produced in ring
doves 20 days after intramuscular injection of 6.6 mg cadmium per kilogram
body weight (Richardson, Spivey Fox, and Fry, 1974), but in domestic pigeons
a single subcutaneous injection of 0.5 mg cadmium chloride per kilogram body
weight produced damage (Sarkar and Mondal, 1973).
Johnson and Walker (1970) compared the effect of cadmium on carbonic
anhydrase activity in rat and domestic fowl testes. Carbonic anhydrase
activity was studied because it is a zinc enzyme. Inhibition of carbonic
anhydrase activity was similar in both species either in vivo or in vitro;
however, testicular damage was apparent only in the rat. Thus, in the rat
the inhibition of carbonic anhydrase is not correlated with cadmium damage
to the testis. Cadmium increased blood flow in rat but not in domestic
fowl testes (Johnson and Turner, 1972); this supports the now generally
accepted belief that a primary effect of cadmium is on the testicular
vascular system (Richardson, Spivey Fox, and Fry, 1974).
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110
SECTION 5
REFERENCES
1. Anderson, S. H. , and R. I. Van Hook, Jr. 1973. Uptake and Biological
Turnover of 109Cd in Chipping Sparrows, Spizella passerina. Environ.
Physiol. Biochem. (Denmark) 3:243-247.
2. Ball, I. R. 1967. The Toxicity of Cadmium to Rainbow Trout (Salmo
ga-ivdnevii Richardson). Water Res. (Great Britain) 1:805-806.
3. Bilinski, E., and R.E.E. Jonas. 1973. Effects of Cadmium and Copper
on the Oxidation of Lactate by Rainbow Trout (Salmo gaivdne^ii) Gills.
J. Fish. Res. Board Can. (Canada) 30(10):1553-1558.
4. Biesinger, K. E. , and G. M. Christensen. 1972. Effects of Various
Metals on Survival, Growth, Reproduction, and Metabolism of Daphnia
magna. J. Fish. Res. Board Can. (Canada) 29:1691-1700.
5. Cearley, J. E., and R. L. Coleman. 1974. Cadmium Toxicity and
Bioconcentration in Largemouth Bass and Bluegill. Bull. Environ.
Contam. Toxicol. 11 (2):146-151.
6. Dyer, R. D., G. S. Born, and W. V. Kessler. 1974. The Distribu-
tion of Intraperitoneally Injected Cadmium-115m in Chickens.
Environ. Lett. 7(2):119-124, Marcel Dekker, Inc., N.Y.
7. Eaton, J. G. 1973. Chronic Toxicity of a Copper, Cadmium and
Zinc Mixture to the Fathead Minnow (Pimephales promelas Rafinesque).
Water Res. (Great Britain) 7:1723-1736.
8. Eaton, J. G. 1974. Chronic Cadmium Toxicity to the Bluegill
(Lepomis macvoch-imis Raf inesque). Trans. Am. Fish. Soc. 103(4) :729-735,
9. Eisler, R. 1971. Cadmium Poisoning in Fundulus heteroclitus (Pisces:
Cyprinodontidae) and Other Marine Organisms. J. Fish. Res. Board Can.
(Canada) 28(9):1225-1234.
10. Eisler, R., G. E. Zaroogian, and R. J. Hennekey. 1972. Cadmium
Uptake by Marine Organisms. J. Fish. Res. Board Can. (Canada)
29(9):1367-1369.
11. Gardner, G. R., and P. P. Yevich. 1970. Histological and Hemato-
logical Responses of an Estuarine Teleost to Cadmium. J. Fish Res.
Board Can. (Canada) 27(12):2185-2196.
12. Heppleston, P. B., and M. C. French. 1973. Mercury and Other
Metals in British Seals. Nature (Great Britain) 243:302-304.
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Ill
13. Hiltibran, R. C. 1971. Effects of Cadmium, Zinc, Manganese,
and Calcium on Oxygen and Phosphate Metabolism of Bluegill Liver
Mitochondria. J. Water Pollut. Control Fed. 43(5):818-823.
14. Jackim, E. , J. M. Hamlin, and S. Sonis. 1970. Effects of Metal
Poisoning on Five Liver Enzymes in the Killifish (Fundulus
heteroalitus). J. Fish. Res. Board Can. (Canada) 27(2):383-390.
15. Johnson, A. D., and P. C. Turner. 1972. Early Actions of Cadmium
in the Rat and Domestic Fowl: VI. Testicular and Muscle Blood
Flow Changes. Comp. Biochem. Physiol. A (Great Britain) 41:451-456.
16. Johnson, A. D., and G. P. Walker. 1970. Early Actions of Cadmium
in the Rat and Domestic Fowl Testis: V. Inhibition of Carbonic
Anhydrase. J. Reprod. Fertil. (Great Britain) 23:463-468.
17. Kemp, H. T., R. L. Little, V. L. Holoman, and R. L. Darby. 1973.
Water Quality Criteria Data Book, Vol. 5, Effects of Chemicals
on Aquatic Life. U.S. Environmental Protection Agency, Washington,
D.C. 489 pp.
18. Kumada, H., S. Kimura, M. Yokote, and Y. Matida. 1973. Acute and
Chronic Toxicity, Uptake and Retention of Cadmium in Freshwater
Organisms. Bull. Freshwater Fish. Res. Lab. (Japan) 22(2):157-165.
19. Lucas, H. F., Jr., D. N. Edgington, and P. J. Colby. 1970. Concen-
trations of Trace Elements in Great Lakes Fishes. J. Fish. Res.
Board Can. (Canada) 27:677-684.
20. Martin, W. E., and P. R. Nickerson. 1973. Mercury, Lead, Cadmium,
and Arsenic Residues in Starlings — 1971. Pestic. Monit. J.
7(l):67-72.
21. Mathis, B. J. , and T. F. Cummings. 1973. Selected Metals in
Sediments, Water, and Biota in the Illinois River. J. Water
Pollut. Control Fed. 45(7):1573-1582.
22. Mount, D. I., and C. E. Stephan. 1967. A Method for Detecting
Cadmium Poisoning in Fish. J. Wildl. Manage. 31(1):168-172.
23. National Academy of Sciences and National Academy of Engineering.
1973. Water Quality Criteria 1972. U.S. Environmental Protection
Agency, Washington, D.C. 594 pp.
24. O'Hara, J. 1973. The Influence of Temperature and Salinity on
the Toxicity of Cadmium to the Fiddler Crab, Uca pugilator>.
Nat. Oceanic Atmos. Adm. (U.S.) Fish. Bull. 74(1) :149-153.
25. Parslow, J.L.F. , D. J. Jefferies, and M. C. French. 1972. Ingested
Pollutants in Puffins and Their Eggs. Bird Study (Great Britain)
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112
26. Pickering, Q. H., and M. H. Cast. 1972. Acute and Chronic
Toxicity of Cadmium to the Fathead Minnow (Pimephales promelas).
J. Fish. Res. Board Can. (Canada) 29(8) : 1099-1106.
27. Rehwoldt, R., L. Menapace, B. Nerrie, and D. Alessandrello. 1971.
The Effect of Increased Temperature upon the Acute Toxicity of
Some Heavy Metal Ions. Bull. Environ. Contam. Toxicol. 8(2):91-96.
28. Richardson, M. E., M. R. Spivey Fox, and B. E. Fry, Jr. 1974.
Pathological Changes Produced in Japanese Quail by Ingestion of
Cadmium. J. Nutr. 104(3):323-338.
29. Sarkar, A. K., and R. Mondal. 1973. Injurious Effect of Cadmium
on Testis of Domestic Pigeon and Its Prevention by Zinc. Indian
J. Exp. Biol. (India) 11:108-109.
30. Smith, R. H., and J. W. Huckabee. 1973. Ecological Studies of
the Movement, Fate, and Consequences of Cadmium. In: Cadmium,
the Dissipated Element, W. Fulkerson and H. E. Goeller, eds.
ORNL/NSF/EP-21, Oak Ridge National Laboratory, Oak Ridge, Tenn.
pp. 278-322.
31. Snyder, N.F.R., H. A. Snyder, J. L. Lincer, and R. T. Reynolds.
1973. Organochlorines, Heavy Metals, and the Biology of North
American Accipiters. BioScience 23(5):300-305.
32. Sturkie, P. D. 1973. Effects of Cadmium on Electrocardiogram,
Blood Pressure, and Hematocrit of Chickens. Avian Dis. 17:106-110,
33. Van Meter, W. P. 1974. Heavy Metal Concentration in Fish Tissue
of the Upper Clark Fork River. Montana University Joint Water
Resources Research Center, Bozeman, Mont. 37 pp.
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SECTION 6
EFFECTS ON TERRESTRIAL MAMMALS INCLUDING MAN
6.1 SUMMARY
This chapter describes effects of cadmium on higher organisms includ-
ing man. The toxic potential of cadmium, as determined from industrial
exposures and animal experiments, is very clear. However, dose-response
data for human exposure are scarce. Some estimates of dose levels likely
to result in various symptoms and effects in humans are identified in Sec-
tion 8, along with cadmium concentrations in surface waters, soils, and
food.
Human epidemiological data are often deficient in dose information;
exposures often include more than one toxic substance, and previous disease
and smoking histories may not be known. Controlled animal experiments are
therefore essential in providing useful information, in spite of possible
problems in extrapolating from animal to man.
In adult humans cadmium is primarily absorbed following inhalation or
ingestion; about 25% to 50% of the cadmium retained in the lungs is absorbed,
and an average of 6% may be absorbed following ingestion. Once cadmium is
absorbed, about 50% is stored in the kidneys and liver. Immediately after
an acute exposure most of the cadmium is in the liver, but with time kidney
levels increase until one-third of the body burden is located in this organ.
Cadmium is excreted primarily through urine and feces; however, excre-
tion is slow and the half-time of absorbed cadmium in humans is very long —
of the order of several decades. The daily dietary intake of cadmium exceeds
excretion, leading to an accumulation of cadmium with age. If the concentra-
tion reaches about 200 ppm wet weight in the renal cortex, kidney damage may
result.
Cadmium reacts with sulfhydryl groups and thus can alter activity of
many enzymes, including those involved in energy production. The actual
symptoms of cadmium toxicity differ with route and extent of exposure.
Acute inhalation exposure causes pulmonary problems. Acute ingestion leads
to symptoms mimicking food poisoning and may cause death through shock with-
in 24 hr or from renal failure within one to two weeks. Chronic cadmium
inhalation may lead to chronic bronchitis or emphysema after a few years,
and maximum permissible exposures have been established in recognition of
this risk. The maximum legal atmospheric concentration in the United States /
for an 8-hr-day exposure period is 0.1 mg/m3 for cadmium fume and 0.2 mg/m3 /
for cadmium dust, although lower limits have recently been recommended.
Other effects such as proteinuria, anemia, liver damage, and possibly hyper-
tension may result from long-term cadmium exposure via either inhalation or
ingestion. Nutritional factors such as calcium and vitamin D deficiencies
can accentuate cadmium effects as may be the case in itai-itai disease in
Japan.
113
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114
-\
The toxicity of cadmium is well recognized, and acute poisoning from
inhalation of cadmium fumes or from ingestion of grossly cadmium-contaminated
food or drink is rare. The greatest danger lies in long-term, low-level ex-
posure to cadmium, especially in conjunction with low-level exposure to other
toxic trace metals in the environment. This chapter emphasizes experimental
and epidemiological data concerning uptake and accumulation of cadmium in
the bcdy and the actual or possible effects of this accumulation.
6.2 METABOLISM
6.2.1 j/ptake and Absorption
6.2.1.1 Inhalation — Cadmium in the air is generally present as an aerosol;
therefore, deposition of inhaled cadmium in the respiratory system should be
a function of particle size. Absorption of cadmium following deposition is
a function of the solubility of the cadmium compound and the rate of clear-
ance. Deposition, retention, and clearance of particulate matter from the
respiratory system are discussed itv'Air Quality Criteria for Partiaulate
Matter (U.S. Department of Health, Education, and Welfare, 1969). Figure 6.1
summarizes deposition in the three respiratory compartments with respect to
particle size (Hise and Fulkerson, 1973). In general, deposition in the
lungs varies inversely with particle size, being roughly 50% for particles
with mean mass diameters of 0.1 y and 10% for particles with mean mass diam-
eters of 5 y. Deposition in the tracheobronchial system is also an inverse
function of particle size, whereas deposition in the nasopharyngeal compart-
ment varies directly with particle size (Figure 6.1)./Unfortunately, coal-
fired power plants and other high-temperature combustion sources emit the
highest concentrations of cadmium in the smallest particles (<1 y) , which are
most likely to reach the alveolar region of the lungs (Natusch, Wallace, and
Evans, 1974).
Particles deposited in the tracheobronchial compartment should be
cleared relatively fast by ciliary activity, while those reaching the lung
may have half-times ranging from a few days to a year (Task Group on Lung
Dynamics, 1966). Particles cleared from the lung and tracheobronchial system
are usually swallowed; larger particles are cleared more rapidly than smaller
ones (Hise and Fulkerson, 1973). However, precise data are lacking on clear-
ance of particles from the respiratory system (Task Group on Metal Accumula-
tion, 1973).
Several studies from 1944 to 1947 concerned clearance of cadmium chlo-
ride aerosol or cadmium oxide fumes from the lungs of Experimental animals.
The half-time of an inhaled cadmium chloride aerosol in dog lungs was about
five days; however, the particle size was not given (Harrison et al., 1947).
In another study, one-fourth of the cadmium chloride initially retained in
mice lungs was present at 48 hr (Gerard, 1944, as cited in Harrison et al.,
1947). Retention of cadmium oxide fumes in the lungs of mice, guinea pigs,
rabbits, dogs, and monkeys was about 11% with a range of 5% to 20%. The
widely varying exposure.conditions make meaningful conclusions about clear-
ance rates impossible. It is worth noting that cadmium itself, at a con-
centration as low as 6 x 10"6 M, significantly inhibits ciliary activity of
hamster trachea in vitro (Adalis et al., 1977). /Such inhibition of normal
pulmonary clearance mechanisms may be of considerable importance.
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115
ORNL-DWG 72-288
NASOPHARYNGEAL
10'
MASS MEDIAN DIAMETER
10'
Figure 6.1. Fraction of particles deposited in the three respiratory
tract compartments as a function of particle diameter. Source: Rise and
Fulkerson, 1973, Figure VI-4, p. 212.
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116
Higher cadmium levels in the organs of persons occupationally exposed
to airborne cadmium and in the organs of cigarette smokers [cigarettes
contain about 1 to 2 yg of cadmium per cigarette (Section 8.3.2) (Menden et
al., 1972)] than in the organs of nonoccupationally exposed, nonsmoking
persons demonstrate that absorption of cadmium occurs through the lungs
(Adams, Harrison, and Scott, 1969; Barrett and Card, 1947, Bonnell, 1955;
Lewis et al., 1972a). These epidemiological data do not permit quantitative
determinations of absorption rates; however, according to data from smokers,
cadmium absorption through the lungs is probably in the range of 25% to 50%,
whereas animal experiments have shown an absorption of 10% to 40% of inhaled
cadmium (Friberg et al., 1974; Nordberg, 1974).
In general, estimates of body burden and tissue levels have not always
distinguished between smokers and nonsmokers. In the population studied by
Lewis et al. (1972Z?) , total body burden in smokers of around 60 years of age
averaged 30 mg; that in nonsmokers averaged only 12 mg.
Because of the undoubted risk of excessive cadmium intake through the
lungs, especially in industrial settings, the legal limits for time-weighted
average concentrations at the work place in the United States were set at
0.1 mg/m3 for cadmium fume and at 0.2 mg/m3 for cadmium dust (Occupational
Safety and Health Act, Document 29 CFR 1910). The American Conference of
Governmental Industrial Hygienists in 1976 recommended that both levels be
reduced to 0.05 mg/m3; a recent criteria document on cadmium prepared by
the National Institute of Occupational Safety and Health (1976) proposed a
further lowering to 0.04 mg/m3. (See also the work of Lauwerys et al.,
1974, discussed in Section 6.3.2.3.2.1.)
6.2.1.2 Ingestion — With the exception of occupationally exposed persons or
smokers, the cadmium body burden of the general population is acquired mainly
through the diet. Most foods and water supplies contain cadmium (Sections 7
and 8). Duggan and Corneliussen (1972) cited an average daily intake of cad-
mium through foods of 50 yg; this value varies with area of residence and
individual choice of food. Cadmium intake from water should be negligible
compared with intake from food, except in areas where industrial contamina-
tion of the water supply has occurred.
In regard to ingestion of aqueous and solid cadmium, Pribble and Weswig
(1973) have suggested the possibility that aqueous cadmium constitutes a
different hazard to human health than does dietary cadmium. They observed
that weanling brown rats which received 5 mg cadmium (as CdCl2) per liter
distilled drinking water accumulated cadmium in the kidneys at a rate 2.5
times that seen in rats receiving 5 mg cadmium (as CdCl2) per kilogram in
solid food. For a specified period the rats consumed 1.5 times more water
than solid food. The investigators suggested, however, that this does not
adequately explain the 2.5-fold difference in accumulation rates between the
test groups. A combination of factors, including the physical state of the
digestive tract during ingestion, may account for the differential absorption
of the metal. Absorption of cadmium from the gastrointestinal tract has been
reported as 1% to 75%; however, an average absorption of 6% is probably the
most realistic figure (Rahola, Aaran, and Miettinen, 1972).
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117
Tipton, Stewart, and Dickson (1969) and Tipton and Stewart (1969) used
atomic absorption measurements to determine the daily cadmium intake in the
diet and the daily excretion in urine and feces of three persons for 140 to
347 days. They reported a mean daily intake of 170 yg cadmium, resulting
in a fecal excretion rate of 40 yg/day and a urinary excretion rate of
100 yg./day. These values indicated an absorption of .74% of dietary cadmium.
The authors apparently were aware of analytical problems referred to by
Fulkerson and Goeller (1973) as potentially arising from the presence of
high salt concentrations in urine; therefore, there is little reason to
suspect that the high cadmium values reported for intake and urinary excre-
tion represent artifacts.
The possible analytical complications in the previous study were, how-
ever, completely avoided in a radioactive tracer experiment with five male
volunteers aged 19 to 50 years (Rahola, Aaran, and Miettinen, 1972). Each
subject received 4.8 to 6.1 yCi of -"-^Cd mixed with a calf kidney suspen-
sion in a single dose (total ingested cadmium about 100 yg). Average absorp-
tion was about 6.0% with a range of 4.7% to 7.0%. Kitamura (1972, as cited
in Friberg et al., 1974) reported a gastrointestinal absorption of less than
10% in humans. A low absorption of ingested cadmium (about 2%) has also
been found in animal studies (Decker, Byerrum, and Hoppert, 1957; Moore,
Stara, and Crocker, 1973). No significant differences were found in absorp-
tion of cadmium given to rats as [ mCd] cadmium sulfate, chloride, or
acetate in a single oral dose (Moore, Stara, and Crocker, 1973). The
absorption values given above can be modified by dietary factors. For
example, low calcium or protein intake doubles the cadmium absorption in
animal experiments (Schroeder et al. , 1967). The Japanese experience with
itai-itai disease (Section 6.3.2.4.7) possibly indicates that dietary
factors can also increase cadmium absorption in humans. Ten percent or more
of ingested cadmium may be absorbed in humans in the presence of a calcium
or protein deficiency (Friberg et al., 1974). Vitamin D was also shown to
increase cadmium uptake into the tibia of rachitic chickens when cadmium was
given orally but not when it was injected (Worker and Migicovsky, 1961),
indicating an effect on intestinal absorption. Absorption can vary with the --
particular cadmium salt ingested. Twice as much cadmium was found in the
livers of rats given cadmium sulfate as in rats given comparable amounts of
cadmium as cadmium stearate (Friberg et al., 1974).
Miller et al. (1967) gave three holstein cows 3.0 g each of cadmium
as CdCl2 daily in two equal doses in gelatin capsules for two weeks. During
the second week, an average of 82% of the cadmium given to the cows was excret-
ed in the feces. Cadmium in the urine was below the limits of detection —
0.5 ppm of urine by atomic absorption spectrometry. Assuming that the fecal
samples taken were representative of total feces, cadmium absorption over the
two-week period was equivalent to about 12 ppm of the cow's weight. Excre-
tion through milk was very low, and all samples collected during and after
cadmium administration had a cadmium level less than 0.1 ppm of milk, the
limit of detection. Total cadmium excreted in milk was less than 0.022% of
administered cadmium, possibly up to ten times less (Section 6.2.3.4).
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118
Miller, Blackmon, and Martin (1968) gave 2.5-month-old goats single
tracer doses of 109Cd as CdCl2, either orally or intravenously. About 90%
of the oral dose was excreted in the feces within five days, a value compa-
rable to that reported in the previous study for cows and similar to those
for other mammals. Following intravenous administration, however, only 5.6%
of the dose was excreted in the feces in five days. Only significant frac-
tions of the cadmium administered either way were excreted in the first
seven days.
6.2.1.3 Placental Transfer — The effectiveness of the placental barrier in
preventing cadmium from reaching the fetus apparently varies with the dose
and route of administration (Friberg et al., 1974). Thus, when cadmium is
administered via routes that provide rapid and quantitative absorption (i.e.,
intravenously or intraperitoneally) and at relatively high dosage rates — 0.5
to 2.0 mg/kg and above — significant fetal cadmium accumulations or terato-
genic effects are observed (Barr, 1973; Ferm and Carpenter, 1968; Mulvihill,
Gamm, and Ferm, 1970; Tanaka et al., 1972) (Section 6.3.2.4.5). In contrast,
cadmium in small doses, even when given intravenously, was not observed to
accumulate in fetal tissues of mice (Berlin and Ullberg, 1963).
Experiments reported in preliminary form (Choudhury et al., 1977)
showed that cadmium given to pregnant rats in drinking water caused signifi-
cant biochemical and behavioral changes in the offspring. The oral adminis-
tration of cadmium to the mothers in these studies did not add significant
amounts of the metal to the body burden of the neonates.
Large doses of cadmium (2.5 to 12 mg/kg) administered subcutaneously
at various times during gestation in rats have generally caused fetal anom-
alies or deaths (Barr, 1973; Chernoff, 1973; Parizek, 1964, 1965). Fetal
cadmium levels were not reported in the above studies although destruction
of the placenta occurred at 2.5 mg cadmium per kilogram (Friberg et al.,
1974; Parizek, 1965).
Cadmium levels in fetal tissues have been studied by Ishizu et al.
(1973). These workers injected a single subcutaneous dose of cadmium (2.5
mg/kg as cadmium chloride) on day 7 of gestation; fetuses were taken on
day 18. The dose was sufficient to cause teratogenic effects. Although
cadmium concentrations in the placentas of treated mice increased tenfold,
similar fetal cadmium levels were observed for both groups. From these
results the authors concluded that placental transfer of cadmium per se
might not be necessary to produce adverse fetal effects. Rather, they
suggested that the cadmium effect might be exerted on the placenta. However,
because cadmium levels in the fetuses were only measured approximately 11
days after a single injection, the results of these studies do not exclude
the possibility of significant placental transfer of cadmium and, thus, a
direct effect on the fetus. This possibility is further reinforced by the
observation of Ferm, Hanlon, and Urban (1969), who studied the distribution
of cadmium in fetal tissues 24 and 96 hr after a single injection of the
metal into pregnant hamsters; levels after 96 hr were significantly lower
than those observed after 24 hr.
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119
These experimental results indicate that the placenta is not a complete
barrier against cadmium. As pointed out by Chernoff (1973), the placenta
may block the transfer of small amounts of maternally administered cadmium,
but larger doses will enter the fetus. For example, Barr (1973) found that
a dose of cadmium capable of inducing teratogenesis when given intraperi-
toneally was not able to induce anomalies when given subcutaneously. Mea-
surements of cadmium in human fetal tissues support the observation of
Chernoff (1973). Indeed, in areas where maternal cadmium intake is consid-
ered greater than "normal," the cadmium body burden of fetuses will generally
also be higher (Chaube, Nishlmura, and Swinyard, 1973; Henke et al., 1970, as
cited in Friberg et al., 1974).
6.2.1.4 Other^ Routes of Uptake — Cadmium in solution has been shown to pene-
trate guinea pig skin (Skog and Wahlberg, 1964) as well as rabbit and mouse
skin (Kimura and Otaki, 1972); presumably it also would penetrate human skin
in the unlikely case of cutaneous exposure. Various types of injection
(subcutaneous, intraperitoneal, intravenous, and intramuscular) are only of
interest from an experimental viewpoint. Moore et al. (1973) compared the
initial absorption of cadmium administered by different routes to rats: 93%
for intraperitoneal injection, 91% for intravenous injection, 41% for inhala-
tion, and 2.3% for ingestion.
6.2.2 Transport and Distribution
6.2.2.1 In Blood — Whether absorbed from the respiratory or gastrointestinal
tract, cadmium is distributed in and transported by the blood. Experimental
data on initial distribution and transport in the blood are derived from
animal studies. Blood values determined in humans reflect a long-term
balance since exposure continues from birth. Acute exposure potentially
provides more meaningful data on early blood distribution, but acute ex-
posures usually occur with persons exposed occupationally to higher cadmium
levels than is the general population, thus complicating the interpretation.
The ratio of cadmium in plasma to that in cells of persons with no known
exposure to cadmium, except that normally acquired through diet and air,
was 1^9. in a study by Szadkowski (1972, cited in Friberg et al., 1974). The
mean blood cadmium level in this study of 18 individuals was 3.5 ng/g, as
determined by atomic absorption spectrophotometry after extraction. A wide
variation in "normal" blood levels appears in the literature (Section 6.2.5);
however, an average normal level in whole blood or serum is probably well
below 10 ng/g. Chronically exposed workers have higher blood cadmium levels
than normal workers (Sections 6.2.5.1 and 6.2.6), and more cadmium is found
in cells than in plasma. A mean plasma-to-cell cadmium distribution ratio
of 0.5 was reported for 22 exposed workers (Friberg et al., 1974). These
observations are in agreement with results determined experimentally in
animals.
Several studies using dogs, rabbits, or rats show that during the first
i hours after intravenous injection of cadmium, blood cadmium is found mainly
/ in the plasma — 98% at 0.5 min and 99% at 8.5 min after injection in rats
(Perry et al., 1970) and 90% to 80% at 9 min and at 1 hr after injection in
rabbits (Kench et al., 1962, as cited in Friberg et al., 1974). Clearance
from the blood is initially quite fast during the first 10 min after injection
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120
but is followed by a slower clearance phase (Walsh and Burch, 1959). Intra-
peritoneal and subcutaneous injections gave similar results (Friberg et al.,
1974).
Cadmium concentrations in red cells and plasma of mice were monitored
following subcutaneous injection of 1 mg/kg 109CdCl2 (Nordberg, 1972).
Results are shown in Figure 6.2. Red cells were hemolyzed and fractionated
on G-75 Sephadex to determine cadmium distribution. Twenty minutes after
injection most of the cadmium was in a high-molecular-weight fraction with
only a minor amount in the hemoglobin fraction and essentially none in the
metallothionein fraction. Up to 4 hr after injection most cadmium in plasma
was in fractions corresponding to albumin or larger proteins.
ORNL-DWG 77-5289
2000
1000
500
200
100
o
I—
<
o
z
o
o
<
o
2 —
96
Figure 6.2. Concentrations of cadmium in plasma and blood cells in
mice given a single subcutaneous injection of 109CdCl2 and killed various
times after injection. Vertical bars indicate ranges of two or three mice
and circles are mean values. Source: Adapted from Nordberg, 1972,
Figure 1, p. 11. Reprinted by permission of the publisher.
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121
Twenty-four hours after injection, cadmium in blood is found mainly in
the cells and appears in a low-molecular-weight protein fraction, probably
metallothionein (Friberg et al., 1974). Insufficient metallothionein is
probably available to handle acutely injected cadmium; metallothionein will
therefore be involved only to a minor degree in transport of cadmium during
the first hours after injection (Friberg et al., 1974). Nevertheless,
Friberg et al. (1974) concluded that proteins, such as metallothionein, hemo-
globin, and others, may play important roles in cadmium metabolism.
Following initial clearance of cadmium from the blood, a subsequent
increase in blood cadmium levels has been seen in animals. For example, the
blood cadmium concentration in rats 16 days after an intravenous injection
of [115Cd] cadmium sulfate was twice the level at one day (Niemeir, 1967, as
cited in Friberg et al. , 1974). Increases in blood cadmium after an initial
decrease were also shown in goats and hamsters (Perm, Hanlon, and Urban,
1969; Miller et al., 1967). This increase probably reflects a release of
cadmium from the liver into the blood.
Distribution of cadmium in the blood of animals receiving repeated cad-
mium injections is similar to that seen in exposed workers. More cadmium
appears in the cells than in the plasma. Rabbits given subcutaneous injec-
tions of [115Cd] cadmium sulfate at 0.65 mg/kg six days a week for four or
ten weeks had blood cadmium levels of 450 and 1000 ng/g respectively (Friberg,
1952; Friberg et al., 1974). Cadmium was not detected in the plasma.
Similar results were obtained when rabbits were subcutaneously given 13
injections of 2.1 mg/kg cadmium sulfate or 19 injections of 1.8 mg/kg cad-
mium sulfate. The red blood cells contained 18 and 10 times more cadmium,
respectively, than the plasma (Truhaut and Boudene, 1954, as cited in
Friberg et al., 1974).
The concentration of cadmium in blood has been shown to decrease in
workers after exposure stops (Rogenfelt, personal communication cited in
Friberg et al., 1974). The half-time in blood was about six months. These
observations have been confirmed in animal studies.
6.2.2.2 Organ Distribution — Many studies on cadmium distribution in organs
of various groups around the world have been published — for example, reviews
by Friberg et al. (1974) and Nordberg (1972) and a report by Forssen (1972).
Actual values in the organs vary, but the relative distribution among organs
is quite similar. Kidneys and liver accumulate far more cadmium than any
other organs. Over half of the total body burden may be found in these two
organs, with perhaps one-third in the renal cortex.
Table 6.1 lists cadmium levels in 43 different organs taken at autopsy
from males and females who had lived their entire lives in Finland. Ages
ranged from birth to 70 years; death resulted from causes other than disease.
Only 20 subjects were involved and cadmium levels were not determined in all
organs of all subjects; however, relative distribution agrees with that ob-
tained in other studies. The ratio of cadmium concentration in kidney to
that in liver in this Finnish study was about 10. In the United States,
mean ratios between 11 and 15 were found for individuals between ages 20
and 59 grouped in ten-year age intervals (Schroeder and Balassa, 1961),
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122
TABLE 6.1. CADMIUM LEVELS IN ORGANS OF FINNISH MALES AND FEMALES AT AUTOPSY
Organ
Parietal lobe
Gray matter
White matter
Hypothalamus
Aorta
Myocardium
Vena cava
Larynx
Trachea
Lung
Upper lobe
Middle lobe
Lower lobe
Esophagus
Stomach
Duodenum
Je j unum
Ileum
Cecum
Sigmoid colon
Rectum
Pancreas
Liver
Gall bladder
Kidney
Urinary bladder
Testis
Prostate
Ovary
Uterus
Vagina
Breast
Adrenal
Thyroid
Spleen
Lymph nodes
Thymus
Bone marrow
Number
of
samples
20
20
16
18
20
14
19
18
19
19
18
18
18
18
18
17
18
18
18
19
20
12
19
18
12
12
5
5
5
4
16
17
20
6
7
20
„ , Cadmium
Number
concentration
° . ('% in ash)fc
positive
Ash
(% of dry wt)
findings Median Min Max
0 <
1 <
0 <
0 <
1 <
2 <
0 <
1 <
10 0.002
10 0.002
11 0.002
1 <
3 <
7 <
5 <
4 <
4 <
2 <
2 <
12 0.002
14 0.007
4 <
17 0.072
6 <
3 <
1 <
2 <
0 <
0 <
0 <
11 0.002
12 0.003
1 <
0 <
0 <
1 <
: 0.002
=
: <
: 0.002
: 0.004
=
: 0.004
: 0.017
: 0.009
: 0.014
: 0.003
: 0.005
: 0.006
: 0.013
: 0.004
: 0.005
: 0.003
: 0.005
• 0.009
: 0.019
- 0.005
: 0.281
: 0.006
: 0.006
: 0.007
: 0.003
' <
:
= <
' 0.006
; 0.017
; 0.003
' <
=
: 0.007
7.08
6.35
6.73
2.79
5.03
3.46
12.02
4.88
5.78
5.70
5.22
4.27
4.52
4.78
4.78
4.75
3.62
3.86
2.84
4.25
5.40
4.62
5.66
2.79
6.57
4.74
5.75
5.35
4.86
0.98
2.77
4.16
5.60
3.16
6.09
27.72
(continued)
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123
TABLE 6.1 (continued)
Organ
Skeletal muscle
Articular cartilage
(knee)
Costal cartilage
Bone (rib)
Skin
(mid-ventral)
Fat (under skin
mid-ventral)
Hair
Number
of
samples
19
19
19
20
13
8
6
, Cadmium
Number
, concentration ,
of ,„,: ^\h As n
(% in ash)0 .a
positive (% of dry wt)
findings , .
6 Median
1 <
0 <
0 <
0 <
0 <
3 <
2 <
Min Max
< 0.004 4
< < 27
< < 25
< < 33
< < 1
< 0.004 0
< 0.003 1
.03
.98
.98
.76
.15
.22
.36
Samples dry ashed in quartz crucibles at 200°C for some hours, then at 450°C
overnight. Lowest positive value used was 0.002% in ash.
"< — value below detection limit.
Median.
Source: Adapted from Forssen, 1972, Table 3, pp. 105-126. Reprinted by permis-
sion of the publisher.
whereas seven groups, each with a mean age of 60 years, had ratios between
9 and 14 (Morgan, unpublished data cited in Friberg et al., 1974).
Cadmium distribution between liver and kidney varies in some circum-
stances. During or immediately after exposure, the liver may contain as
much or more cadmium than the kidneys, which could explain why occupationally
exposed workers usually have lower kidney-to-liver cadmium ratios than un-
exposed workers (Friberg et al. , 1974).
Rats given intravenous injections of [H^Cd] cadmium nitrate (0.65 mg/kg)
had 62% to 70% of the injected dose in liver and only 1.6% to 2.4% in kidneys
at 4 hr to five weeks after injection (Decker, Byerrum, and Hoppert, 1957).
Similar results were obtained following intravenous injection of [H^Cd] cad-
mium nitrate (0.2 to 0.4 mg/kg) into dogs. The liver concentration was much
greater than the kidney concentration during the first 24 hr , but after three
to four weeks the kidney levels were 50% to 100% of the liver levels (Burch
and Walsh, 1959).
The route of administration can have an effect on cadmium distribution
in tissues. Table 6.2 shows tissue distribution of cadmium two weeks after
oral or intravenous administration into goats. Cadmium may be transported
in blood in a different form when absorbed from the digestive tract than
when injected, and it may also be metabolized differently.
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124
TABLE 6.2. TISSUE DISTRIBUTION OF
1 O9
Cd 14 DAYS AFTER ORAL
OR INTRAVENOUS ADMINISTRATION
TO GOATS0
Tissue
Cadmium
concentration
of dose per kg)
» ctlllf -L CU
Hair
Skin
Testicles
Tibia
Joint
Shaft
Kidney
Muscle
Liver
Heart
Spleen ,
Duodenum
Oral
dose
0.11
0.02
0.02
0.07
0.04
1.13
0.03
0.88
0.02
0.05
1.04
Intravenous
dose
1.9
1.3
2.3
1.9
0.9
49.2
0.6
129.9
3.0
17.2
4.3
All tissue data expressed on a
fresh weight basis.
^First 1.83 m of small intes-
tine.
Source: Adapted from Miller,
Blackmon, and Martin, 1968, Table 1,
p. 1838. Reprinted by permission of
the publisher.
Miller et al. (1969) determined the effect of added stable cadmium in
the diet on the distribution of trace amounts of 109Cd in goats. Four- to
six-month-old male goats were fed 100 ppm cadmium as CdCl2 in the diet start-
ing seven days before a single oral tracer dose of 109Cd and continuing until
sacrifice 14 days after the tracer dose. This level of cadmium was near the
upper limit before toxic symptoms appeared. Total body retention of the
tracer dose was 0.3% to 0.4% and, with the exception of reduced retention of
109Cd in some sections of the gastrointestinal tract, there was no signifi-
cant difference in tissue distribution between goats receiving 100 ppm stable
cadmium and those that did not. The rate of daily excretion following
absorption also remained unaffected, decreasing in both experimental and
control goats during the second week after dosing from 20% of body burden on
day 8 to less than 5% of remaining body burden on day 14.
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125
6.2.3 Excretion
Cadmium is excreted primarily in urine and feces, with minor amounts
potentially excreted in hair, sweat, skin, milk, and saliva (Friberg et
al. , 1974; Rise and Fulkerson, 1973).
6.2.3.1 Urinary Excretion — Urinary excretion of cadmium varies; however,
an average value of 1 to 2 yg/day is commonly reported for normal, unexposed
individuals (Table 6.3). No, or only a slight, relationship has been found
between age and urinary excretion of cadmium (Suzuki and Taguchi, 1970;
Szadkowski, Schaller, and Lehnert, 1969). Another study, however, showed a
rise in urinary excretion (0.5 to 2 yg/liter) from age 5 to 35 with a level-
ing off until age 55, when excretion slowly fell (Friberg et al. , 1974;
Nordt/erg, 1972; Tsuchiya, 1967). The youngest subject in the study of
Suzuki and Taguchi (1970) was 16 years old, possibly masking the relationship.
Despite a large individual scatter, Nordberg (1972) found an increase in
urinary cadmium with total body burden on a group basis in mice; total body
burden increases with age. Table 6.3 lists the urinary excretion of cadmium
from normal, unexposed individuals.
TABLE 6.3. CADMIUM EXCRETION IN URINE OF NORMAL, UNEXPOSED INDIVIDUALS
Country
Analytical
method
Number of
individuals
Age
range
(years)
Cadmium level
(tig/liter)
,, Standard
Mean . . . Range
deviation
United States
Japan (Gifu)
West Germany
Sweden
Spectrographic after
dithizone extrac-
tion
Atomic absorption
after extraction
Dithizone
Atomic absorption
after extraction
with chelating
agent into organic
solvent
154
46
40
41
56
37
40
43
14
10°
10
4-6
9-10
14-15
20-29
30-39
40-49
50-59
34-63
20-40
1.59
0.47
0.65
0.72
0.99
13
76
75
1.0
2.1
0.34
0.25
0.45
0.50
0.63
1.06
1.33
1.38
<0.5-10.8
Polluted area.
Source: Adapted from Friberg et al., Cadmium in the Environment, 2nd ed., Table 4:7,
pp. 66-67, (c) CRC Press, Inc., 1974. Used by permission of CRC Press, Inc.
There is no clear relationship between urinary cadmium excretion in
exposed workers and degree of exposure. In exposed workers, urinary excre-
tion of cadmium varies from 0 to 1000 yg/day (Adams, Harrison, and Scott,
1969; Truhaut and Boudene, 1954, as cited in Friberg et al., 1974). Workers
-------
126
who have absorbed "enough" cadmium (defined in Section 6.3.2.3.2.1) to pro-
duce kidney damage and proteinuria have higher cadmium levels in urine than
exposed persons without proteinuria. Some workers with proteinuria studied
by Adams, Harrison, and Scott (1969) excreted 30 to 170 ug/liter cadmium in
their urine, whereas other workers in the same study, without proteinuria,
had less than 2 yg/liter.
Urinary excretion of cadmium usually decreases after exposure stops,
but not in a regular, predictable pattern. Unpublished data from Piscator
(cited in Friberg et al., 1974) showed large individual variations in uri-
nary cadmium in workers one or two years after cadmium exposure ceased.
Some workers showed an increase, some a decrease, and some no change.
6.2.3.2 Fecal Excretion — The amount of cadmium excreted by the intestines
cannot be determined from fecal cadmium levels since unabsorbed cadmium from
the diet passing through the digestive tract will add to any cadmium actually
being excreted by the intestines. Therefore, fecal cadmium levels reported
for humans give no information about intestinal excretion. Fecal excretion
of cadmium in normal, unexposed persons averaged 31 yg/day in a study by
Essing et al. (1969) and 42 yg/day in another study by Tipton and Stewart
(1969).
Less than 0.1% of the retained oral dose of 115mCd in humans was
excreted in feces (Rahola, Aaran, and Miettinen, 1972). The mechanisms of
fecal cadmium excretion in humans are not known. High concentrations of
cadmium in bile from autopsy samples indicate an enterohepatic circulation
of cadmium (Tsuchiua et al., 1972, as cited in Friberg et al. , 1974). How-
ever, experiments with rats given [109Cd] cadmium sulfate intraperitoneally
or [109Cd] cadmium chloride subcutaneously, while indicating excretion via
bile with some recirculation, showed that only about 5% of the fecal excre-
tion could be accounted for by this route (Caujolle, Oustrin, and Silve-Mamy,
1971; Nordberg and Robert, unpublished data cited in Friberg et al., 1974).
Nordberg (cited in Friberg et al., 1974) exposed mice to 0.025 or 0.25 mg
cadmium per kilogram body weight five days a week for five months and found
that the main part of fecal excretion of cadmium was correlated with daily
dose. However, since the average fecal cadmium was higher after exposure
stopped than before exposure began (14.2 yg/24 hr, standard deviation ±11,
versus 5.1 ± 3.1 ug),yfart of the fecal excretion must be related to body
burden. /
6.2,3.3 Excretion in Hair — Schroeder and Nason (1969) examined cadmium
levels in hair as a function of age, sex, and hair color. Results showed
some differences in cadmium content with color (males had less cadmium in
black hair than other colors, and women had less cadmium in gray than other
colors), with age, and with sex (female gray hair had less cadmium than male
gray hair). Concentration of cadmium in hair probably does not reflect
tissue stores under normal conditions (Schroeder and Nason, 1969).
Hammer et al. (1971) found a positive correlation in ten-year-old boys
between cadmium levels in hair and community exposure to cadmium. Boys
from five cities ranked according to trace-metal contamination in the area
were used as subjects (Table 6.4).
-------
127
TABLE 6.4. CADMIUM IN HAIR FROM BOYS
LIVING IN URBAN AREAS
Exposure XT
, . Number of
ranking ,
,. . S determinations
of citya
I.
II.
III.
IV.
V.
High
High
Lowc
Low
Low
45
25
37
21
37
Cadmium
content
of hair^
(ppm)
2.1
1.5
1.0
1.0
0.7
Ranking determined by combining
aerometric, geologic, and industrial
data..
Geometric mean.
G
Low approximates usual U.S. urban
level.
Source: Adapted from Hammer et al.,
1971, Table 3, p. 86. Reprinted by per-
mission of the publisher.
More recent studies cited by Friberg et al. (1975) indicate that levels
of cadmium in hair in the United States range from 1 to 2 ppm, varying in
part with age and sex of the individual. Lower values have been reported
from Europe and Japan; European values averaged about 0.5 ppm. No obvious
differences in analytical methodology or in exposure to cadmium as reflected
in levels of the metal in liver and kidney can account for this discrepancy.
The usefulness of cadmium levels in hair as an index of total body burden
of cadmium remains, therefore, in question.
6.2.3.4 Excretion in Milk — In terms of the clearance of cadmium from the
body, only the fecal and urinary routes appear to be of significance.
Because excretion into milk, however, may be a major source of dietary cad-
mium, it deserves special mention. Indeed, according to Pinkerton et al.
(1973) , excretion in human or bovine milk can contribute 25% to 50% of the
total human dietary uptake in the first years of life.
The studies of Miller discussed in Section 6.2.2.2 have shown that
absorption of cadmium following ingestion is relatively low in ruminants
and that only a small fraction of this cadmium is excreted in milk. Cad-
mium levels in cow milk from cities around the United States were found to
average between 0.017 and 0.030 ppm as determined by atomic absorption
spectrophotometry (Murthy and Rhea, 1968). The national weighted average
-------
128
was 0.026 ± 0.004 ppm. Although low, this value is more than twice the
level established for cadmium in drinking water (U.S. Department of Health,
Education, and Welfare, 1962). These values, if accurate, could be of
concern to those who ingest large quantities of milk. A person consuming
1 qt of milk daily would ingest 30% to 50% of what is considered the average
daily intake of cadmium from this one source (Section 6.2.1.2). In spite of
the importance of extraction in the analysis for cadmium (Friberg et al.,
1974), adequate control experiments have shown no reason to assume that the
above data on milk are too high (Murthy, 1974). More recently, somewhat
lower values were reported by Bruhn and Franke (1974) using extraction pro-
cedures on 315 samples of California milk; an average concentration of
0.0060 ppm (standard deviation, 0.0040 ppm) was found.
A study in the United Kingdom by the Ministry of Agriculture, Fish-
eries, and Food (1973), based on extraction and atomic absorption techniques,
reported a mean concentration for all milk samples of less than 0.002 ppm, a
value ten times less than that reported by Murthy and Rhea (1968). Cornell
and Pallansch (1973) used pulse polarography with internal standards and
found natural concentrations of cadmium in dried, skimmed cow milk of 0.7 to
2.9 ppb. On a fresh milk basis, this value would correspond to a level 100
times lover than that observed by Murthy and Rhea (1968).
6.2.4 Biological Half-Time
The biological half-time of absorbed cadmium in the body is very long
and, as a result, accumulation is essentially continuous throughout life.
Newborn babies, for example, have an average cadmium concentration of about
0.002 ppm in liver and 0.010 ppm in kidney, whereas values in 50-year-old
men averaged about 3 ppm in liver and 30 to 50 ppm in renal cortex (Nordberg,
1974).
An exact biological half-time for cadmium in the human body cannot be
determined from available experimental data. Rahola, Aaran, and Miettinen
(1972) gave ll5mCd orally (4.8 to 6.1 yCi/100 g in calf kidney suspension)
to five men. After an initial rapid decrease in whole-body retention during
the first week, probably representing unabsorbed cadmium, a slower elimina-
tion phase was seen. The slow decrease in whole-body retention was only
followed for two months, and the estimated half-time of this slow phase
could be anywhere from 130 days to infinity.
An estimate of csdmium half-life in the human body can be made on a
group basis by comparing bcdy burden and excretion. Based on data from
various countries, a half-time of 13 to 47 years was obtained by Friberg
et al. (1974). Similar biological half-times were calculated on theoretical
models. All human data favor a very long biological half-time.
Figure 6.3 shows whole-body retention of 115mCd in rats following a
single exposure by different routes. Except for differences in the initial
rapid decay, route of administration did not significantly influence the
rate of elimination and biological half-life (Moore et al., 1973).
The toxicological significance of experimentally established values
for the biological half-time of cadmium is thrown into doubt by the facts
-------
129
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that (1) different half-lives for cadmium have been observed in different
tissues, and even within one tissue the chemical form of the retained metal
is known to change with time, and (2) the half-life is affected by the
total dose of cadmium administered and by environmental factors such as
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(1977).
6.2.5 Normal Levels
6.2.5.1 In Blood — As mentioned in Section 6.2.2.1, the average "normal"
cadmium level in human whole blood or serum lies below 0.01 ppm. Table 6.5
lists some representative values in whole blood of normal unexposed persons
-------
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and of occupationally exposed workers. Average cadmium levels in whole
blood ranging up to 2 ppm have been reported (Butt et al., 1964); however,
analytical errors are probable because even levels in exposed workers have
been far lower (Table 6.5).
6.2.5.2 In Organs - As mentioned in Section 6.2.2.2, about 50% of the body
burden of cadmium is found in liver and kidneys. A single "normal" concen-
tration cannot be given for these organs because the values increase with
age and vary among individuals, depending on diet, local environment, and
smoking hs.bits. For instance, the cadmium content of liver and kidneys as
a function of age in various parts of the world is shown in Figures 6.4,
6.5, and 6.6. The decline in kidney cadmium levels after age 50 may reflect
such factors as changing dietary and smoking habits, bias in the older groups
with respect to disease and sex, and changes in cadmium content of foods.
It could also result from overt renal damage as high tissue levels of cad-
mium are reached; the damaged organ might then leak cadmium into the urine.
Generally, the average body burden in a "standard man" (70 kg in weight)
lies between 15 and 30 mg in the United States, 15 and 20 mg in the United
Kingdom and Sweden, and 40 and 80 mg in Japan (Figures 6.4, 6.5, and 6.6).
Median levels of cadmium in the pancreas have been reported as 1 ppm wet
1000
ORNL-DWG 77-5291
25
50
AGE (years)
75
100
A WORKERS EXPOSED TO CADMIUM
OXIDE DUST AND FUME
0 ITAI-ITAI PATIENTS
-• NORMALS
• RANGE
I KANAZAWA,JAPAN
IE KOBE,JAPAN
3E UNITED STATES
EZ GREAT BRITAIN
2 SWEDEN ( TWO AREAS)
Figure 6.4. Cadmium content in renal cortex as a function of age,
exposure, and geographical location. Source: Adapted from Friberg et
al., Cadmium in the Environment, 2nd ed., Figure 4:22, p. 62, (c) CRC
Press, Inc., 1974. Used by permission of CRC Press, Inc.
-------
132
ORNL-DWG 77-5292
200 —
A WORKERS EXPOSED TO
CADMIUM OXIDE DUST
AND FUME
D ITAI-ITAI PATIENTS
• • NORMALS
RANGE
I KANAZAWA, JAPAN
H KOBE, JAPAN
HI UNITED STATES
12 GREAT BRITIAN
Z SWEDEN (THREE AREAS)
~3I TOKYO, JAPAN
25
50
AGE (years)
75
100
Figure 6.5. Cadmium content in liver as a. function of age, exposure,
and geographical location. Source: Adapted from Friberg et al. , Cadmium
in the Environment, 2nd ed., Figure 4:24, p. 63, (c) CRC Press, Inc., 1974.
Used by permission of CRC Press, Inc.
weight in the United States (Tipton and Cook, 1963) and 2.8 ppm wet weight
in the Far East (Tipton et al., 1965). A mean cadmium level in the lungs
of San Francisco residents of 0.34 ppm wet weight was found by Tipton and
Shafer (1964); this value compared with a mean level of 0.26 ppm wet weight
found in 21 Scottish persons (40 to 70 years old) (Molokhia and Smith, 1967).
Other lung values reported (Smith eL al., 1960, as cited in Friberg et al.,
1974) ranged up to 0.71 ppm wet weight in three British samples (mean age,
54 years). Lung concentrations of cadmium seem to increase with age. Small
amounts of cadmium are found in other organs (Table 6.1).
-------
133
130
120 —
ORNL-DWG 77-5293
I EAST GERMANY
H UNITED STATES
m EAST GERMANY
IZSWEDEN
UNITED STATES
UNITED STATES
3ZTIKOBE, JAPAN
THE KANAZAWA, JAPAN
IX TOKYO, JAPAN
25
50
AGE (years)
75
Figure 6.6. Cadmium content in renal cortex as a function of age and
geographical location. Source: Adapted from Friberg et al., Cadmium in
the Environment, 2nd ed., Figure 4:25, p. 64, (c) CRC Press, Inc., 1974.
Used by permission of CRC Press, Inc.
-------
134
6.2.6 Blood, Urine, and Feces a!3 Indicators of Body Burden
For practical purposes, blood cadmium levels are not good indicators
of organ cadmium levels, although blood levels may be higher in exposed
workers, especially during exposure, than in unexposed persons. As an
example, two Swedish factory workers (employed 20 years) not exposed
directly to cadmium had blood csdmium levels of 0.021 and 0.031 ppm with
renal damage, whereas two workers directly exposed to cadmium (three to
four years of exposure) had blood cadmium levels of 0.048 and 0.058 ppm
without renal damage (Piscator, 1971, as cited in Friberg et al. , 1974).
The equivocal nature of available data makes meaningful conclusions
impossible.
During long-term, low-level exposure to cadmium, urinary cadmium levels
are related to body burden on a group basis; however, the wide range of
recorded values makes the relationship less meaningful for predicting organ
levels on an individual basis (Nordberg, 1972). A relationship probably
does not exist between urinary cadmium and body burden in occupationally
exposed workers (Section 6.2.3.1). Available data do not permit conclusions
on a relationship between fecal cadmium excretion and body burden.
6.3 EFFECTS
6.3.1 Mechanisms of Action
Before specific systemic effects produced by acute or chronic exposure
to cadmium are discussed, some possible mechanisms of action at the cellu-
lar and molecular levels are mentioned.
6.3.1.1 Metallothionein — Metallothionein (the protein thionein plus a
metal) seems to be intimately involved in cadmium metabolism (Section
2.3.4.2). This low-molecular-weight protein has the ability to bind cad-
mium, zinc, mercury, copper, silver, tin, or iron due to a high cysteine
content and a resultant large number of sulfhydryl groups (Sabbioni and
Marafante, 1975). A good discussion of metallothionein is presented in
Friberg et al. (1974).
Actually, more than one species of metallothionein from different
organs can be distinguished. Various functions have been assigned to the
protein, including roles in cadmium transport in blood, in the organ distri-
bution of cadmium, and in its excretion (Nordberg, 1972). These suggested
functions, while plausible, have not all been critically tested. Quantita-
tive analyses of the renal handling of hepatic cadmium metallothionein, for
instance, have made it appear unlikely that this compound contributes to
cadmium excretion in rabbits (Nomiyama and Foulkes, 1977).
A protective role for metallothionein has also been proposed. Injec-
tion of small doses of cadmium prior to a normally lethal dose of the metal
prevents death, presumably by inducing synthesis of the metal-binding pro-
tein in liver and other organs (Nordberg, 1972; Piscator and Axelsson,
1970; Terhaar et al., 1965). Metallothionein is also less toxic to the
testes than is an equivalent amount of unbound cadmium (Nordberg, 1971).
-------
135
In addition, Suda et al. (1974) observed that, unlike the free metal,
metallothionein-bound cadmium did not inhibit activation of vitamin D by
kidney mitochondria.
On the other hand, metallothionein-bound cadmium is more toxic to the
kidneys than are cadmium salts injected as such (Nordberg, Goyer, and
Nordberg, 1975). High toxicity of cadmium metallothionein was also described
by Webb (1975). The high nephrotoxicity of metallothionein as well as of
other low-molecular-weight complexes of cadmium may be explained by the fact
that such complexes are readily taken up by the kidney (Cherian, Goyer, and
Delaquerriere-Richardson, 1976; Foulkes, 1974; Nordberg, Goyer, and Nordberg,
1975). Inorganic cadmium, in contrast, is neither filtered nor accumulated
by the kidney (Foulkes, 1974). The selective accumulation of cadmium in the
renal cortex may be related to the uptake of circulating metallothionein
(Piscator, 1964, cited in Friberg et al., 1974).
Syversen (1975) isolated a cadmium-binding protein from liver and
kidneys in 19 of 40 human autopsy samples. The mean cadmium level in the
kidneys of the 19 was significantly higher than the mean of all 40 together.
Table 6.6 gives cadmium and zinc levels in kidney and liver as a function
of metallothionein content in these samples.
6.3.1.2 Enzyme Effects — Just as cadmium can combine with the sulfhydryl
groups in metallothionein (thiorein), it also reacts with the sulfhydryl
groups in some mitochondrial and extramitochondrial enzymes. In mitochon-
dria, according to Berry, Osgood , and St. John (1974), the metal is active
in at least three places: (1) it binds to sulfhydryl groups of enzymes
necessary for transfer of electrons from compounds in the citric acid cycle
to compounds in the electron transport chain; (2) cadmium ion binds to and
inactivates one or more enzymes necessary for the synthesis of adenosine
triphosphate (ATP); and (3) cadmium ion also binds to the enzyme adenosine
triphosphatase (ATPase), which is required to convert ATP to ADP (adenosine
diphosphate) + POi,, an important source of energy in cellular reactions.
Jacobs et al. (1956) showed that cadmium at concentrations as low as
5 x 10"6 M completely inhibits the phosphorylation coupled to oxidation of
succinate or citrate in rat liver mitochondria. Similarly, Mustafa, Cross,
and Tyler (1971) and Mustafa et al. (1971) showed that cadmium depresses
respiration of alveolar macrophages. Cadmium completely inhibits uptake of
oxygen by macrophage mitochondria at 5 x 10~5 M and uncouples oxidative
phosphorylation at 5 x 10"6 M. Adenosine triphosphatase activity is also
inhibited. Interference with respiration probably results from Cd2+ bind-
ing to flavoproteins and other dehydrogenases. Cadmium ions bind to cell
membranes and may cause alterations in membrane integrity with resulting
effects on cellular metabolism (Mustafa, Cross, and Tyler, 1971). Cadmium
injected intraperitoneally into rats was subsequently found in purified
liver ribosomes and enzyme preparations, indicating the presence of bound
metal (Norton and Kench, 1977). Incorporation of amino acids into proteins
was depressed, providing a possible explanation for the occurrence of lower-
molecular-weight peptide chains and proteins in cadmium intoxication (Section
6.3.1.1).
-------
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Some cadmium effects may be due to the substitution of cadmium for
zinc in zinc-requiring enzymes (Smith, 1973). Griffin et al. (1973) found
that replacement of zinc by cadmium in aspartate transcarbamylase (from
EsaheF-ich'ia aol'L) altered the ccnformation of the metal-binding site, which
in turn altered the conformation of the active site.
Because cadmium can produce some toxic effects by combining with
sulfhydryl groups in enzymes and by replacing zinc in zinc-requiring enzymes,
it is not surprising that some acute effects of cadmium poisoning can be
prevented or reduced by addition of zinc or sulfhydryl compounds, which act
as competitive inhibitors of the cadmium-enzyme reactions (Gunn, Gould, and
Anderson, 1968; Parizek, 1957; Parizek and Zahor, 1956). Selenium is also
an effective cadmium antagonist (Gunn, Gould, and Anderson, 1968). Chen,
Whanger, and Weswig (1975) suggested that selenium counteracts the toxicity
of metals by altering their tissue concentration and by diverting them to
presumably less critical components. Parizek (1957) found that the testic-
ular damage induced in rats by a subcutaneous injection of 0.04 millimole
cadmium chloride per kilogram body weight could be completely prevented by
injecting 80 to 200 times that amount of zinc acetate divided into three
doses — one given 5 hr before cadmium, one with the cadmium, and one 19 hr
after cadmium. Other effects of cadmium, such as anemia and weight loss,
have been corrected in rats and mice by administration of zinc (Bunn and
Matrone, 1966; Hill et al., 1963). Similar results were obtained in other
studies (Friberg et al., 1974). Rats given a diet with sufficient zinc
suffered typical symptoms of zinc deficiency if an equimolar amount of cad-
mium was also given. The zinc-to-cadmium ratio may be as important as the
absolute amount of either (Voors, Shuman, and Gallagher, 1973). The work
of Webb (1972) suggested that the protective effect of preliminary injec-
tions of zinc can be accounted for by the zinc-induced synthesis of a protein
with a high binding affinity for cadmium (metallothionein).
6.3.2 Toxic Effects
Several good reviews of cadmium toxicity are available (Flick, Kraybill,
and Dimitroff, 1971; Friberg et al., 1974; Fulkerson and Goeller, 1973).
Acute or chronic cadmium poisoning can occur through ingestion, inhalation,
or both. The major problem for human populations is chronic, low-level
exposure through ingestion, although occasional acute poisoning via this
route has occurred. Workers in cadmium-related industries may be chronically
exposed to higher cadmium levels in the air than the general population and
also have a greater chance of acute poisoning through accidents.
6.3.2.1 Effects in Livestock — Miller et al. (1967) gave 3 g of cadmium
daily for two weeks to holstein cows but produced only minimal effects.
Consumption of a food concentrate dropped on the second day of cadmium
administration, remained at less than one-half the pre-cadmium level on the
third and fourth days, and then increased to normal by the eighth day even
though cadmium was still being administered. Effect on total food intake
was not measured; however, the reduced concentrate consumption reflected a
systemic effect on appetite rather than a change in palatability of the food
because cadmium was not mixed with the food. The cows lost an average of
30 kg during cadmium treatment and regained 5 kg during three weeks after
-------
138
cadmium treatment stopped. The depression of milk synthesis was more than
a simple result of decreased concentrate consumption; two weeks after cad-
mium was stopped, milk production was still only 73% of that before cadmium,
as shown in Figure 6.7. The controls had decreased to 82% of initial milk
ORNL-DWG 77-5287
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12 16 20
TIME (days)
24
28
32
Figure 6.7. Effect of oral cadmium administration on milk production
of lactating holstein cows. Source: Adapted from Miller et al., 1967,
Figure 2, p. 1406. Reprinted by permission of the publisher.
production during this time; the small number of experimental animals (three)
makes the significance of the difference questionable. At the time of
greatest depression of milk synthesis, fat content of the milk increased
about 44% and then returned to normal after cadmium administration stopped.
No other cadmium-related effects were found. Other discussions of cadmium
excretion into milk are found in Dorn et al. (1973), Lynch, Cornell, and
Smith (1974), McClanahan et al. (1965), and in Section 6.2.3.4.
Cadmium poisoning of domestic livestock should rarely occur because
most sources of possible contamination are recognized and can be con-
trolled. Unfortunately, this has not been achieved in fact. According
to Aschbacher (1973) , there were no reported toxicities in livestock from
cadmium, but Goodman and Roberts (1971) reported sporadic livestock illness
downwind of Swansea (southeast Wales), an area contaminated by copper, zinc,
lead, and cadmium. A horse which had eaten hay grown in the area developed
lead poisoning; when it died, tissue analysis revealed a renal cadmium level
of 330 ppm wet weight, a level almost certainly associated with renal damage,
regardless of the immediate cause of death.
-------
139
Tissues from nine cattle living about 15 miles from a zinc smelter in
Montana were examined (Munshower, 1972). Cadmium levels in the kidneys and
liver averaged 1.67 and 0.34 ppm (wet weight) respectively. The cadmium
concentration in these organs appeared to increase with age. A similar
situation existed around a smelting operation in East Helena, Montana (U.S.
Environmental Protection Agency, 1972). The hair of mammals in this area
had significantly higher cadmium concentrations than hair from animals in
other areas. Livestock in the area, especially horses, showed signs of
heavy-metal poisoning and had high cadmium and lead concentrations in their
kidneys and livers. Other reports of livestock poisoning are cited by Smith
and Huckabee (1973). Although exposure usually included several metals
which could interact, cadmium levels were high in all cases.
6.3.2.2 Acute Cadmium Poisoning
6.3.2.2.1 Inhalation — Acute cadmium poisoning through inhalation primarily
affects industrial workers (e.g., welders and metal workers) because cad-
mium is present in some silver sclders, brazers, and platings on various
metals. The high temperatures used in welding and other processes can cause
formation of cadmium oxide fumes (Section 2.3.1). Many case histories of
workers poisoned while welding or cutting cadmium-plated metals are reported
in the literature (Friberg et al., 1974; Hise and Fulkerson, 1973). Usually,
no discomfort occurs during acute exposure to cadmium fumes, and symptoms do
not generally appear for 4 to 8 hr; a lethal amount of cadmium can therefore
be absorbed without warning (Beton et al., 1966; Blejer, Caplan, and Alcocer,
1966). Symptoms of acute inhalation of cadmium include: (1) metallic taste
in the mouth; (2) headache; (3) shortness of breath, chest pain, cough with
foamy or bloody sputum, abnormal pulmonary rates, and physical signs which
mimic the flu; (4) weakness and leg pains; (5) pulmonary edema, which may
lead to death or may gradually improve over several days; (6) pneumonic con-
solidation; and (7) late liver damage (Hise and Fulkerson, 1973).
Freshly generated cadmium fume is the most toxic form of cadmium when
inhaled (Princi, 1947). Fume generated from arc welding is twice as toxic
as that thermally generated by oxyacetylene, possibly because of smaller
particle sizes in arc-generated fume (Princi, 1947). The lethal time-dose
of thermally generated fume (air concentration in milligrams multiplied by
the exposure time in minutes) approaches 2900 min-mg/m3 for humans, whereas
the lethal time-dose of arc-generated fume probably does not exceed 1400
min-mg/m3 (Barrett and Card, 1947). Lethal time-doses of thermally gen-
erated fume of 2500 and 2600 min-mg/m3 have also been reported, corresponding
to an 8-hr exposure to about 5 mg/m3 (Beton et al., 1966). A cadmium con-
centration lower than 5 mg/m3 for 8 hr might also be fatal since concentra-
tions as low as one-fourth the LD50 produced acute symptoms and permanent
lung damage in animal experiments (Paterson, 1947).
Data are not available to permit calculation of lethal doses for cad-
mium dusts. In rabbits the lethal concentration of cadmium-iron dust is
three to four times higher than that of cadmium oxide fumes (Friberg, 1950).
6.3.2.2.2 Ingestion — Acute cadmium poisoning due to ingestion by humans
is rare since cadmium use near food or drinks (e.g., cadmium-plated food
-------
140
containers) is prohibited. Organic acids present in many foods and drinks
dissolve cadmium, forming organic cadmium salts which dissolve in gastric
juices (Rise and Fulkerson, 1973). Symptoms following cadmium ingestion are
similar to those of food poisoning (Frant and Kleeman, 1941). Symptoms,
which may begin one-half to one hour after ingestion, include: (1) severe
nausea, vomiting, diarrhea, abdominal cramps, and salivation; (2) headache,
muscular cramps, vertigo, and (rarely) convulsions; (3) exhaustion, collapse,
shock, and death, usually within 24 hr, or gradual appearance of liver and
kidney damage; and (4) death in one to two weeks from acute renal failure
(Hise and Fulkerson, 1973).
Fortunately, cadmium is emetic when ingested, eliminating some cadmium
before absorption can occur. The emetic threshold is probably in the range
of 3 to 15 mg (Hise and Fulkerson, 1973). The same dose of cadmium may be
more toxic in water than in food since some cadmium may bind to components
in the food and be unavailable for absorption (U.S. Department of Health,
Education, and Welfare, 1962). Differences in the amount of ingested cad-
mium bound to food may be responsible for some of the variability in reported
toxic values. The following ranges of acute toxic values in humans have been
reported (Hise and Fulkerson, 1973):
3 to 90 mg Emetic threshold
11 mg Reported nonfatal incidents
10 to 326 mg Severe toxic symptoms (nonfatal)
350 to 3500 mg Estimated lethal dose
8900 mg Reported lethal dose
6.3.2.3 Chronic Cadmium Poisoning — Chronic cadmium poisoning is probably
more important to the general population — and even to workers in cadmium-
related industries — than acute poisoning because safeguards and restric-
tions on cadmium use make it unlikely that cadmium levels high enough to
cause acute effects will be present. Normal background levels of cadmium
in air, water, and food together with regionally higher levels from local
industries and low-level occupational exposure make chronic poisoning more
likely.
6.3.2.3.1 Inhalation — Chronic cadmium poisoning in industry is essentially
an inhalation problem. The most prominent symptoms are chronic bronchitis,
emphysema, and proteinuria (Friberg et al., 1974; Hise and Fulkerson, 1973;
Nordberg, 1974). These effects have been produced by cadmium oxide fumes,
cadmium oxide dust, and cadmium pigment dust; in general, they do not appear
until after a few years of exposure (Friberg et al., 1974). Dose-response
curves are difficult, if not impossible, to determine accurately because
varying exposure conditions permit only estimates of actual doses.
Qualitative evidence of lung damage was obtained 25 years ago from
workers in Sweden (Friberg, 1950). With an average employment time of
20 years, 43 male workers exposed to cadmium oxide dust had impaired lung
function; a group of 15 workers with similar exposure but only one to four
years of employment had normal lung function. Cadmium concentrations in air
were reported as 3 to 15 mg/m3, but measurements were only made once at five
areas of the factory. Similar results were found at a German factory
-------
141
(Baader, 1952). Lauwreys et al. (1974) observed renal damage in men exposed
for over 20 years to a concentration of respirable cadmium of only 21 ug/m
(Section 6.3.2.3.1).
A group of 100 men exposed to cadmium oxide fumes and a group of 104
controls were examined by Bonnell (1955). Eleven of the exposed workers
had emphysema, but no emphysema was mentioned for the controls. There were
significant differences betweer the two groups, on a group basis, in part
of the respiratory function test. The mean flow rates at 30, 50, and 70
respirations per minute were significantly lower in the exposed grouo, but
the vital capacities and maximum ventilatory capacities were similar. No
information on cadmium doses was given. Other studies of occupationally
exposed workers show similar results, with equally poor dose information
(Friberg et al., 1974). It is likely, however, that prolonged exposure to
cadmium oxide fumes at levels below 0.1 mg/m3 could lead to impairment of
lung function.
Suzuki, Suzuki, and Ashizawa (1965) reported a study of workers exposed
to cadmium stearate dust and lead. No differences in lung function tests
between exposed workers and controls were observed. Time of employment was
3.3 years with a standard deviation of 1.9 years. Cadmium concentrations
varied from 0.03 to 0.69 mg/m3 at different operations; particle size varied
from 0.4 to 20 pm. Exposure was for 20 min three or four times a day. The
negative findings may reflect the short employment time.
6.3.2.3.2 Ingestion — The following toxic effects are discussed in this
section because the general population is more likely to be affected by
chronic ingestion of cadmium than by inhalation; however, it should be
understood that chronic cadmium inhalation can also produce these effects.
In addition, ingestion of cadmium also appears capable of producing pul-
monary lesions (Vinegar and Choudhury, 1976).
6.3.2.3.2.1 Proteinuria — The kidney is the critical organ in cases of
prolonged, low-level exposure to cadmium (Friberg et al., 1974; Nordberg,
1974). As mentioned previously (Sections 6.2.2.2 and 6.2.5.2), about one-
third of the body burden of cadmium is found in the kidneys. When the cad-
mium concentration in the renal cortex reaches about 200 ppm wet weight,
morphological changes and/or proteinuria may occur (Friberg et al., 1974;
Nordberg, 1974). The usefulness of this value, which was determined from
autopsy or biopsy samples of renal tissue from cadmium workers and which
agrees with values determined in animal experiments, has been questioned
by Nomiyama et al. (1977). Following onset of proteinuria, the cadmium
level in the kidneys decreases as cadmium is excreted along with the pro-
tein (Friberg et al., 1974). Table 6.7 shows cadmium content in the renal
cortex and morphological change in workers exposed to cadmium oxide dust.
The lower cadmium values associated with the greatest morphological change
probably reflect release of cadmium as mentioned above.
Proteinuria is a common finding in cadmium workers (Bonnell, 1955;
Friberg, 1950; Kazantzis et al., 1963; Smith and Kench, 1957). Other renal
changes, including glucosuria, amino aciduria, decreased concentrating
capacity, and formation of renal stones, are common (Adams, Harrison, and
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142
TABLE 6.7. CONCENTRATIONS OF CADMIUM IN KIDNEY CORTEX OF WORKERS EXPOSED TO CADMIUM OXIDE DUST IN
RELATION TO MORPHOLOGICAL KIDNEY CHANGES SEEN AT AUTOPSY OR BIOPSY
Worker
S.W.H.
K.J.
K.N.
H.B.
A.B.
O.J.
G.J.
G.K.
A.L.
E.Y.
E.H.
J.P.
N.U.
H.N.
K.N.
Age
46
49
57
60
39
62
44
46
36
39
40
43
44
45
50
Years
exposed
28
22
18
26
16
20
11
15
6
7
15
20
12
13
15
Years
since
last
exposure
1
9
6
3
4
1
12
0
0
0
10
6
0
0
2
Year of
autopsy
or biopsy
Autopsy, 1960
Autopsy, 1951
Autopsy, 1952
Autopsy, 1949
Autopsy, 1950
Autopsy, 1967
Biopsy, 1959
Biopsy, 1959
Biopsy, 1959
Biopsy, 1959
Biopsy, 1959
Biopsy, 1959
Biopsy, 1959
Biopsy, 1959
Biopsy, 1959
Morphological „ . .a
, & Proteinuria
changes
Profound +
Profound +
o +
Profound +
Profound +
Profound +
Slight +
Slight +
None (+)
None -
None +
None +
None -
None +
None
Cadmium
in cortex
(ppm wet wt)
83fc
75&
20&
lllb
63
321
152
220
446
320
330
180
21
190
'- — negative results on repeated testing with trichloroacetic acid.
(+) —varying results.
,H positive results on repeated testing.
Figures based on cadmium concentration in whole kidney, assuming that the cadmium concentration
in cortex is 1.5 times the average kidney concentration.
'Results from histological examinations not reported, but in an examination in 1946 this worker
had the lowest kidney function tests of all (inulin clearance, 42 ml/min; maximum specific gravity of
urine, 1016, blood nonprotein in nitrogen, 44 mg %).
Source: Adapted from Friberg et al., Cadmium in the Environment, 2nd ed., Table 6:1, p. 108,
(c) CRC Press, Inc., 1974. Used by permission of CRC Press, Inc.
Scott, 1969; Ahlmark et al., 1961; Friberg, 1950; Kazantzis et al., 1963;
Piscator, 1956). Forty-four percent of a group of workers exposed to cad-
mium dust for more than 15 years had a history of renal stones (Ahlmark
et al., 1961).
Lauwerys et al. (1974) surveyed three groups of workers exposed to
cadmium dusts (Group I: women with less than 20 years of exposure; Group
II: men with less than 20 years; and Group III: men exposed for longer
than 20 years). Group III was exposed to a respirable cadmium concentra-
tion of only 21 yg/m3; these workers showed slight pulmonary but more pro-
nounced renal symptoms (proteinuria). The theoretical calculations of
Friberg et al. (1974) suggest that even lower concentrations of cadmium in
ambient air could lead over a period of 50 years to critical cadmium levels
in the renal cortex.
6.3.2.3.2.2 Anemia — Although kidney damage is usually the limiting factor
in chronic cadmium exposure, the hematopoietic system is also affected
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143
(Friberg et al., 1974; Hise and Fulkerson, 1973; Nordberg, 1974). Moderate
anemia has been found in workers exposed to cadmium oxide dust and fumes
(Friberg, 1950; Tsuchiya, 1967). A significant correlation between high
cedmium levels in blood and low or below normal hemoglobin levels was found
in 16 workers with 5 to 30 years exposure; the mean haptoglobin level was
below normal, indicating hemolysis (Piscator, 1971, as cited in Friberg et
al., 1974). The anemia is apparently reversible since workers with no
exposure for at least ten years had normal or elevated haptoglobin levels
(Piscator, 1971, as cited in Friberg et al., 1974). As in many other epi-
demiological studies, dose-response relationships are impossible to calculat.:
Cadmium-induced anemia has been produced experimentally in animals
including rats, rabbits, and Japanese quail (Decker et al., 1958; Fox and
Fry, 1970; Friberg, 1950; Piscator and Axelsson, 1970). In rats, 31 ppm
cadmium in food for several months produced anemia; 125 ppm cadmium for
seven months also produced an increase in reticulocytes and eosinoohils
and induced h>perplasia of the bone marrow (Wilson, DeEds, and Cox, 1941).
After exposure ended, hemoglobin levels returned towards normal.
Decker et al. (1958) found no pathological changes in the blood of
Sprague-Dawley rats given up to 10.0 ppm cadmium in water for one year;
however, at a level of 50.0 ppm cadmium in water a significant decrease
in hemoglobin was apparent in two weeks. Hemoglobin dropped to 8 g/100 ml
of blood from an average of 15.5 g/100 ml in controls and remained there
for the duration of the study. Anemia may be partly an iron-deficiency
anemia due to decreased uptake of iron from the intestines, partly a result
of increased plasma volume, and partly a hemolytic anemia (Axelsson and
Piscator, 1966; Berlin and Piscator, 1961; Fox and Fry, 1970). Iron supple-
mentation prevented anemia as did ascorbic acid, which probably acted by
increasing iron absorption from the intestines (Fox and Fry, 1970; Pond and
Walker, 1972; Sansi and Pond, 1974). Pond, Walker, and Kirtland (1973)
reported that anemia induced in weanling Yorkshire pigs by 154 ppm cadmium
(as CdCl2) in the diet could be prevented by oral administration of 400 ppm
iron (as FeSOz,*7H20) throughout the experiment or 1000 mg iron (as iron
dextran) in a single intramuscular injection on the first day of the experi-
ment. Chatterjee, Banerjee, and Rudra Pal (1973) showed that anemia induced
in rats by 60 mg/kg body weight daily of CdCl2»H20 could be prevented by the
addition of 1.0 mg/kg body weight daily of L-ascorbic acid along with the
cadmium.
6.3.2.3.2.3 Hypertension — The question whether cadmium can cause hyper-
tension in humans remains unanswered. Hypertension can be induced in some
animals by cadmium treatment, and epidemiological studies have provided
some support for the existence of cadmium-induced hypertension (Friberg et
al. , 1974). The evidence is not conclusive, however. Cadmium-induced
hypertension is reviewed also in Hise and Fulkerson (1973).
In general, some epidemiological data show a correlation between cad-
mium and hypertension in humans; however, these data are ambiguous and
certainly are not proof of a causal relationship. For example, Carroll
(1966) reported a positive correlation between cadmium in air and death
rates from hypertension and arteriosclerotic heart disease in 28 American
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144
cities (coefficient of correlation = 0.76). Several years later Carroll's
data were reanalyzed by other researchers who found an even higher correla-
tion between population density and hypertension than between cadmium and
hypertension (Hunt et al., 1971). In an area with an average urban cadmium
level in ambient air (0.01 yg/m3), the estimated uptake over a 50-year
period would be only 1 mg, a small fraction of the total body burden (Sections
6.2.1.1 and 6.2.5).
Schroeder (1965) reported a correlation between cadmium in the kidneys
and the relative incidence of hypertension in about 400 persons from cities
around the world. Similar studies are reported in Friberg et al. (1974)
and Hise and Fulkerson (1973); however, factors such as population density,
smoking, and disease history, which may also be related to hypertension, are
not discussed. Further, several studies failed to find a relationship
between kidney cadmium levels and hypertension (Hunt et al., 1971; Lewis et
al., 1972a; Morgan, 1969). In addition, there is no evidence that workers
in cadmium-related industries have a higher incidence of hypertension than
does the general population. Patients in Japan with itai-itai disease and
persons living near the endemic area do not have an unusually high incidence
of hypertension (Friberg et al., 1974).
An inverse correlation between hypertension and the hardness of drink-
ing water has been reported (Crawford, Gardner, and Morris, 1968; Morris,
Crawford, and Heady, 1961). Hard water usually contains less cadmium than
soft water (Section 2.3.2.1.1). Soft or acid waters may contain cadmium
levels above the U.S. Public Health Service limits (0.01 ppm) (Schroeder
et al. , 1967) (Table 6.8). In a survey of 969 public water supply systems,
less than 1% exceeded 0.01 ppm (McCabe et al., 1970). Most studies found
this inverse correlation between hypertension and water hardness; however,
one study by Morton (1971) and a controversial study by Bierenbaum (1975)
and Bierenbaum et al. (1975) showed a positive correlation. In the latter
study, Kansas City, Kansas, was reported to have twice the cardiovascular
death rate and a higher average blood pressure than Kansas City, Missouri.
Both cities use the same source of wster, but Kansas City, Missouri, softens
its water to about one-half. While this result seems to contradict most
other studies, the hard water contained three times as much cadmium as the
soft weter, and the serum from hard-water drinkers contained 13 times as much
cadmium as that from soft-water drinkers (16.4 ppb versus 1.2 ppb). The
attribution of a 13-fold higher cadmium concentration in serum to a three-
fold increase in water cadmium, as presented in this study, is highly contro-
versial. In fact, the validity of the measurements in the study has been
questioned (Sharrett and Feinleib, 1975). Also, the possibility of other
sources of cadmium in the populations investigated were not considered in
this study. In addition, zinc is known to reverse cadmium-induced hyper-
tension in animals (Schroeder and Buckman, 1967) and serum zinc levels in
the area of the Kansas City study with lower cadmium and lower blood pres-
sure were three times higher than in the area with high cadmium levels and
elevated blood pressure. The cadmium-zinc ratio may be more important than
the content of cadmium alone (Schroeder et al., 1967). Cadmium could conceiv-
ably affect the kidney at doses too low to produce obvious toxicity and the
resulting increase in sodium retention might raise the blood pressure. The
Kansas City study appears to be consistent with, but does not prove, the
hypothesis that cadmium can induce hypertension in humans.
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145
TABLE 6.8. ZINC AND CADMIUM CONCENTRATIONS IN WATER AND SNOW
Sample type
Natural water
Connecticut River, Vt.
Brook, Vt.
Spring, N.H.
Seawater, Caribbean
Municipal water, Brattleboro, Vt., reservoir
Inlet
Spillway
Main, town
Tap, hospital
Cold, running
Stagnant
Hot, running
Institution, cold, running
Bridgeport, Conn., tap
White Plains, N.Y., tap
Bangor (Roseto), Pa.
Private dwellings
Lake, N.H.
Tap, plastic pipe
Spring, Vt.
Tap, iron pipe
Spring, Vt . , copper pipe
Spring, Vt.
Tap, iron pipe
Well, Vt . , iron pipe
Well, Vt . , artesian, copper and plastic pipe
Spring, S.C., iron pipe
Spring, Ark., bottled
Miscellaneous
Distilled, glass still
Deionized
Snow, melted, 20 m from street, town, moderate traffic
100 m from road, forest, hilltop
50 m from road, hilltop, behind laboratory
Zinc
(ppb)
5
14
3.5
177
24
3.5
3.5
160
1830
3.5
20
770
13
660
100
2160
219
18
<0.3
6
0
1380
45
8
Cadmium
(ppb)
14. 6a
0.5
0.6
2.5
0.3
2.1
2.5
14. 0-21. Oa
8'3
15.0-77.0
n
21.0
1.0
14. Oa
n
14. Oa
0.0
1.1
14. Oa
3.8
3.5
8.3
2.2
3.8
1.1
3.5
12. Oa
8.0
<0.3
0.5
0
1.5
0.35
0.370
Cause for rejection of water supply exceeding allowable limits of 10 ppb.
Two copper pipes, dissolved in acid, contained 57 and 2.76 ppm cadmium.
Galvanized iron pipes contained 140 to 400 ppm cadmium (mean = 300 ppm).
Source: Adapted from Schroeder et al., 1967, Table 10, p.
Reprinted by permission of the publisher.
198.
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146
Probably the main reason why a correlation has been sought between cad-
mium and hypertension in htmans is that cadmium has been reported to induce
hypertension in some experimental animals (Friberg et al., 1974; Hise and
Fulkerson, 1973). Schroeder (1964) induced hyuertension in Long-Evans rats
with 5 ppm cadmium in their drinking water. About 17% of the males were
hypertensive at 17 months; the percentage increased with age until 65% were
hypertensive at 30 months. The incidence of hypertension was more constant
in females, varying from 67% to 83%. The results of this study were possibly
affected by intake of NaCl, although Schroeder concluded that the salt intake
had little or no effect on hypertension in this study. Kidney and liver cad-
mium levels averaged 40 and 6 ppm wet weight, respectively, in another study
by Schroeder, Nason, and Balassa (1967). These levels are comparable to
those in adult North Americans. Animals with a cadmium-to-zinc weight ratio
in the kidney of 0.8 or above were always hypertensive (Schroeder and
Buckman, 1967).
Hypertension has also been produced in rats and rabbits by parenteral
or intraperitoneal injections of cadmium (Schroeder and Buckman, 1967;
Schroeder, Nason, and Mitchener, 1968; Thind et al., 1970). For example,
1 or 2 mg cadmium per kilogram body weight injected intraneritoneally as
cadmium citrate into rats produced hypertension within a month. Blood
pressure of hypertensive rats returned to normal within 300 days following
cessation of cadmium exposure (Schroeder, Nason, and Mitchener, 1968). In
some experiments, hypertension was not induced in rats by ingested (Lener
and Bibr, 1970) or injected cadmium (Castenfors and Piscator, unpublished,
as cited in Friberg et al., 1974). According to Friberg et al. (1974),
strain differences and sodium intake may influence development of hyper-
tension in experimental animals. Porter, Miya, and Bousquet (1974) were
unable to produce hypertension in rats at various dose levels of cadmium
and under various treatment schedules and conditions. Some subtle dietary
or other environmental variables may be of major significance in the pro-
duction of experimental hypertension with cadmium.
It is interesting to note that intraperitoneally injected cadmium in
rats, and to a lesser extent mercury, has been found to increase both appar-
ent renin activity in peripheral blood and blood pressure (Perry and
Erlanger, 1973). For intraperitoneally injected cadmium, the increase in
renin activity following a single dose of about 200 yg Cd+2 was evident
within 1 min and persisted for one month (Perry and Erlanger, 1973). Perry
and Erlanger (1973) also noted that in the case of "fed" cadmium, continuous
exposure to 5 ppm in drinking water increased the renin activity of rats
within a week; the level remained elevated after one month, but not after
three months.
In summary, although cadmium can induce hypertension in animals and
some correlation has been found between cadmium and hypertension in humans,
no clear evidence directly implicates cadmium in human hypertension..
6.3.2.4 Other Effects
6.3.2.4.1 Liver function — An effect of cadmium on liver function has been
seen in several workers with acute cadmium poisoning from cadmium oxide
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147
fumes; however, liver disturbances are not a common finding (Friberg et al.,
1974). As mentioned in Section 6.2.2.2, cadmium concentration in the liver
can be quite high during acute exposure, even higher than in the kidney.
The glutamic oxaloacetic transaminase activity in rabbit serum was increased
following intravenous injection of cadmium (Andreuzzi and Odesalchi, 1958,
cited in Friberg et al. , 1974) (Table 6.9). The authors concluded that a
dose near the LD50 was necessary to produce severe liver lesions; at lower
doses hepatic changes were reversible.
TABLE 6.9. CHANGES IN GLUTAMIC OXALOACETIC TRANSAMINASE ACTIVITY
FOLLOWING INTRAVENOUS INJECTION OF CADMIUM INTO RABBITS
Dose Change in
, ,, , glutamic oxaloacetic Remarks
transaminase activity
3 Considerable increase after 17 hr 60% of animals dead in 24 hr
2.5 Tenfold increase after 24 hr 40% of animals dead in 48 hr
2 Fourfold increase after 24 hr;
back to normal after 72 hr All survived over 72 hr.
1.25 Fourfold increase after 24 hr;
back to normal after 72 hr All survived over 72 hr.
Source: Compiled from Friberg et al., 1974, p. 122.
Gross changes in liver function are rarely found in chronically exposed
workers; however, animal studies have shown that morphological liver changes
can be present when various liver function tests such as activities of glu-
tamic oxaloacetic transaminase, alkaline phosphatase, and lactic dehydro-
genase are within normal limits. These tests therefore may be poor indicators
of cadmium damage to the liver (Stowe, Wilson, and Goyer, 1972). Several
animal experiments, including those of Axelsson and Piscator (1966), Singhal
et al. (1974), and Sporn et al. (1970, cited in Friberg et al., 1974) show
effects of cadmium on liver enzymes.
6.3.2.4.2 Testicular damage — Testicular damage is also seen in animals
following exposure to cadmium. In general, testicular damage occurred in
animals with scrotal testes, but not in animals with abdominal testes.
Strain differences in sensitivity among mice were demonstrated by Gunn,
Gould, and Anderson (1965). Among 19 strains tested, testicular necrosis
was consistently produced in 11 by subcutaneous injection of 3.3 mg/kg cad-
mium chloride. Testes of seven strains were unaffected even when the dose
was raised to the lethal level (value not reported). Strain differences
with respect to dose required to produce minimal testicular damage were also
found in rats. The necrosis is probably due to vascular damage. Data on
testicular effects associated with chronic—&a4aujjm._£jcDipsure,,are_inconclusive;
possibly, induction of metallothionein, which has been shown to protect
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148
animals against acute cadmium-induced testicular damage, prevents testicular
damage during chronic exposure (Nordberg, 1971; Piscator and Axelsson, 1970).
Testicular necrosis has also been prevented by zinc, selenium, cobalt, and
thiol compounds (Gabbiani, Baic, and Deziel, 1967; Gunn, Gould, and Anderson,
1963, 1966, 1968; Parizek, 1957).
On the basis of animal data (Smith et al., 1960, as cited in Friberg et
al. , 1974), testicular necrosis might also be expected in humans, but it has
not been clearly demonstrated following either acute or chronic cadmium
exposure. Some unspecific histological changes in the testes were found at
autopsy in workers exposed to cadmium fume. The authors felt that the changes
resulted from the terminal illnesses rather than from cadmium exposure. Ab-
normally low testosterone levels in the urine and impotence were found in one
of ten workers examined in a 1968 study (Favino et al., 1968).
6.3.2.4.3 Insulin production — Cadmium accumulates in the pancreas, although
to a minor extent compared with the kidneys or liver. Tipton and Cook (1963)
reported a median value of 80 ppm in pancreatic tissue ash (approximately 1.0
ppm wet weight) from adults living in the United States. Tipton et al. (1965)
reported median values of less than 50 ppm of ash in African subjects, 91 ppm
of ash in Near Eastern subjects, and 230 ppm of ash in Far Eastern subjects.
Since cadmium is present in the pancreas, an effect on insulin production is
a possibility, but direct evidence is lacking. Intravenous administration of
cadmium produces hyperglycemia in rabbits (Voinar, 1952) and in dogs (Caujolle
et al., 1964). Blood glucose concentrations rose in mice following a single
intraperitoneal injection of cadmium (2.0 to 6.0 mg/kg), and concentrations
of circulating insulin decreased (Ghafghazi and Mennear, 1975). Ithakissios
et al. (1975) showed that chronic cadmium administration to rats inhibited
pancreatic secretory activity. Also, decreased pancreatic function is asso-
ciated with itai-itai disease in humans (Murata et al., 1970).
Ghafghazi and Mennear (1975) perfused isolated rat pancreata with either
glucose alone (300 mg/100 ml) or glucose in combination with 10"** to 10~3 M
cadmium. Glucose alone produced a rapid release of insulin; the secretion
was significantly depressed by the lowest concentration of cadmium used and
was completely inhibited by the higher concentrations. Inhibition was not
reversed by subsequent perfusion with cadmium-free glucose solution (60 mg/100
ml) but was partially reversed by perfusion with glucose plus theophylline.
On the basis of the work of Brisson, Malaisse-Lagae, and Malaisse (1972) the
theophylline effect was taken to indicate a possible involvement of calcium
ions.
Ithakissios et al. (1975) also found an inhibition of insulin secretion
in perfused pancreata removed from rats that had received 70 intraperitoneal
doses of cadmium (0.50 mg/kg dose every other day). Doses of 0.25 mg/kg did
not cause a significant inhibition. The cadmium level in the pancreas was
about 54 ppm wet weight in the rat receiving the higher dose, a value com-
parable to that reported in human itai-itai patients (45 to 65 ppm) (Ishizaki,
Fukushima, and Sakamoto, 1970). The significance of this value is unclear
since the rats receiving the low dose and showing little or no inhibition of
insulin secretion actually had higher cadmium levels (approximately 76 ppm
wet weight).
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149
6.3.2.4.4 Carcinogenesis — No direct evidence relating cadmium exposure and
cancer in humans has been found. The available epidemiological studies have
examined relatively small numbers of workers and no causal relationship has
been established; the limited data, however, may indicate a possible rela-
tionship between cadmium exposure and cancer of the prostate.
Of eight deaths in a group of 74 workers with at least ten years of
exposure to cadmium oxide, three resulted from cancer of the prostate and
two from other cancers. The actual exposure levels were unknown but were
sufficient to ceuse proteinuria and anosmia (loss of the sense of smell) in
many workers (Potts, 1965). No control group was examined. Four cases of
cancer of the prostate versus an expected number of 0.58 were seen in a group
of 248 workers exposed to cadmium oxide for a minimum of one year (Kipling
and Waterhouse, 1967).
Morgan (1970) found cadmium levels in liver and kidney to be signifi-
cantly higher in persons with bronchogenic carcinoma than in controls (Table
6.10). Later, Morgan (1971) reanalyzed the 1970 data with respect to emphy-
TABLE 6.10. CADMIUM LEVELS IN LIVER AND KIDNEY
WITH RESPECT TO LUNG AND OTHER CANCERS
Condition
Number
of
persons
Cadmium
concentration
(ppm, ash)
Liver Kidney
Lung cancer 47 254 ± 133 3513 ± 1587
Other cancer 50 179 ± 140 2937 ± 2065
Control 55 182 ± 99 2406 ± 1299
Source: Adapted from Morgan, 1970, Table 1,
p. 1395. Reprinted by permission of the publisher.
sema, lung cancer, lung cancer plus emphysema, and controls. Both lung
cancer and emphysema were independently associated with excess cadmium.
Cadmium levels in kidney and liver of persons with carcinoma of the lung,
with or without emphysema, significantly exceeded those in controls. Liver,
but net kidney, tissue contained significantly higher cadmium levels than
controls in cases with pure emphysema (Table 6.11). Although liver and
kidney cadmium levels were significantly higher than normal in persons with
lung cancer, no causal relationship could be proven since trace-metal con-
centrations have been shown to be abnormal in association with many neo-
plastic diseases. In addition, both lung cancer and emphysema have been
linked to cigarette smoking; the body burden of cadmium is higher in smokers
than in nonsmokers (Friberg et al., 1974).
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150
TABLE 6.11. CADMIUM LEVELS IN LIVER AND KIDNEY WITH
RESPECT TO LUNG CANCER AND/OR EMPHYSEMA
Condition
Lung cancer
Emphysema
Number
of
23
26
Cadmium
concentration
(ppm, ash)
Liver Kidney
249 ± 142a 3478 ± 1639a
290 ± 155a 2921 ± 1252
Lung cancer and
emphysema
Control
19
36
268 ± 43
170 ± 95
3660 ± 1602
2512 ± 1427
a.
'P < 0.05.
Source: Adapted from Morgan, Burch, and Watkins,
1971, Table 1, p. 109. Reprinted by permission of the
publisher.
The concern that a causal relationship may exist between cadmium exposure
and cancer in humans stems from the ability of cadmium to induce cancer in
experimental animals. Subcutaneous or intramuscular injections of cadmium in
rats have led to sarcomas at the injection site in several experiments. For
instance, 14 of 20 rats given subcutaneous injections of cadmium sulfate
developed injection site sarcomas; testicular site atrophy and Leydig cell
hyperplasia and neoplasia were also found (Haddow et al., 1964; Roe et al.,
1964). The same treatment did not produce tumors in mice. In another study,
a single subcutaneous or intramuscular injection of 0.17 to 0.34 mg cadmium
chloride induced injection site sarcomas in rats (Gunn, Gould, and Anderson,
1967). No tumors were produced in skin, liver, salivary glands, prostate,
or kidney. Most cancers induced by subcutaneous or intramuscular injection
of cadmium compounds arise in tissues of mesenchymal (intramuscular) origin
and not in tissues of ectodermal (skin), endodermal (e.g., liver and sali-
vary gland), or epithelial (e.g., kidney) origin. Oral cadmium was not
shown to be carcinogenic to mice, although rats given oral cadmium had more
tumors than did controls (Kanisawa and Schroeder, 1969).
6.3.2.4.5 Teratogenesis — Cadmium has been shown to be teratogenic in rats,
hamsters, and mice. Perm and Carpenter (1968) injected pregnant golden ham-
sters intravenously with 2 or 4 mg/kg cadmium sulfate (3CdSOi,»8H20) , 2 mg/kg
zinc sulfate (ZnSO^»7H20), or a mixture of the two (2 mg/kg each) on the
eighth day of gestation (Table 6.12). The cadmium-induced abnormal develop-
ment in the hamster was specific, affecting facial formation. Unilateral
and bilateral cleft lips and palates are usual when cadmium exposure occurs
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151
TABLE 6.12. CADMIUM TERATOGENICITY IN HAMSTERS
Treatment
Cadmium, 2 rag /kg
Cadmium, 4 rag/kg
Zinc, 2 mg/kg
Cadmium and zinc,
2 mg/kg each
simultaneously
Cadmium, 2 mg/kg, plus
zinc, 2 mg/kg 15 min
to 6 hr later
Number of
mothers
treated
20
14
6
10
26
Total
embryos
248
190
70
120
276
Percentage
of embryos
resorbed
13
46
3
5
12
Percentage
of nonabsorbed
embryos
abnormal
66
84
4
2
12
Source: Adapted from Perm and Carpenter, 1968, Table 1, p. 430.
Reprinted by permission of the publisher.
on the eighth day of gestation. Mulvihill, Gaimn, and Ferm (1970) discussed
facial formation in normal and cadmium-treated hamsters. Although closure
of the palatine shelves occurs between 12 and 14 days of gestation (Mulvi-
hill, Gamm, and Ferm, 1970), the critical time for cadmium-induced abnor-
malities of palatal development is the eighth day of gestation (Ferm, 1971).
When cadmium is given early in the eighth day, facial abnormalities pre-
dominate, but when given later or. the eighth day, rib and upper limb abnor-
malities appear and facial defects decrease. When cadmium is given on the
ninth day, most defects are of ribs and limbs (Ferm, 1971).
Doses of 0.8 to 2.0 mg cadmium per kilogram body weight were terato-
genic when given intraperitoneally (but net subcutaneously) to pregnant
Wistar rats on day 9, 10, or 11 of gestation (Barr, 1973). When given on
day 6, 7, 8, or 12, cadmium was not teratogenic. A variety of defects
occured and there were some differences between the two stocks of rats used.
The incidence of the various defects changed with day of cadmium administration.
Daily subcutaneous injections of cadmium chloride into rats (4 to 12
mg/kg body weight) from days 13 through 16 produced a dose-related rise in
fetal death rate, a decrease in fetal weight, and an increase in rate of
fetal anomalies (Chernoff, 1973). Wolkowski (1974) reported that cadmium
crossed the placenta and resulted in increased fetal mortality in mice.
There is no direct evidence for a teratogenic effect of cadmium in
humans, bi.t birth weights of children of women (aged 18 to 48) working in
cadmium industries were significantly lower than weights of children born
to control women (Cvetkova, 1970, as cited in Friberg et al. , 1974). Four
of 27 children born to women working in a zinc smelter in the above study
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152
had signs of rickets and delayed development of teeth. No causal relation-
ship cculd be proved. Friberg et al. (1974) suggested that the teratogenic
effect of cadmium might be due to a secondary zinc deficiency in the fetus
since more zinc is stored in the mother's liver and kidneys during cadmium
exposure. Cadmium does not, however, prevent the placental transfer of
zinc (Perm and Hanlon, 1974).
6.3.2.4.6 Mutagenesis — Cadmium-induced mutagenesis has not been experi-
mentally demonstrated; however, an increased number of chromosomal abnor-
malities were found in peripheral leukocytes from itai-itai patients
(Shiraishi and Yosida, 1972), and chromosomal abnormalities were induced in
cultured human leukocytes by cadmium sulfide at 0.062 yg/ml of culture medium
(Shiraishi, Kurahashi, and Yosida, 1972). Since a sulfide control, however,
was not included in this study, the cytogenetic effects observed cannot be
unequivocally ascribed to cadmium. Deaven and Campbell (1976) have reported
that exposure of cultured hamster ovary cells to 0.224 ppm cadmium as CdCl2
results in multiple chromatid aberrations within 24 to 48 hr and in shatter-
ing of chromsomes after 72 hr.
6.3.2.4.7 Itai-itai (ouch-ouch) disease — Itai-itai disease in Japan is
regarded by many workers as a classic example of chronic cadmium poisoning
resulting from industrial contamination of the environment (Friberg et al.,
1974; Rise and Fulkerson, 1973). Because of the large amount of information
on the various aspects of itai-itai disease, only a summary is presented
here and the reader is referred to Friberg et al. (1974) for further details.
Itai-itai disease has been described as the culmination of many of the
toxic effects and interactions of cadmium with other factors discussed in
this chapter. Primarily, the source of cadmium was contaminated drinking
water and rice grown on land irrigated with contaminated water; the cadmium
contamination came from mining activities. Most of the persons affected
were women who had reached menopause and had given birth to several children.
The disease probably represents renal tubular dysfunction plus osteomalacia
(softening of bones with pain, tenderness, muscular weakness, and loss of
appetite, resulting from a vitamin D or calcium deficiency), and osteoporosis,
There is evidence that cadmium can reduce calcium absorption from the gut and
its uptake into bones (Ando et al., 1977). Standard symptoms of itai-itai
disease are listed in Table 6.13.
Although cadmium is thought to be a causal factor in this disease,
apparently other factors such as calcium and vitamin D deficiency are very
likely also involved. This fact presumably explains the observation that
the patients were multiparous women over 45 years of age. The combination
of mineral loss from bone in connection with pregnancy and lactation, in-
sufficient sunshine resulting in a lack of vitamin D (the women screen
themselves from the sun while working), and generally poor nutrition during
and immediately after World War II possibly produced in those women a cal-
cium and phosphorus balance especially susceptible to disturbance in the
presence of cadmium-induced renal tubular damage.
It should be pointed out that some questions have been raised about
the identification of itai-itai disease with cadmium intoxication (Takeuchi,
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153
TABLE 6.13. SYMPTOMS OF ITAI-ITAI DISEASE
A. Subjective symptoms:
1. Pain (lumbago, back pain, joint pain)
2. Disturbance of gait (duck gait)
B. Physical examination:
1. Pain by pressure
2. "Dwarfism"
3. Kyphosis
4. Restriction of spinal movement
C. X~ray examination:
1. Milkman's pseudofractures
2. Fractures (including callus formation)
3. Thinned bone cortex
4. Decalcification
5. Deformation
6. Fishbone vertebrae
7. Coxa vara
D. Urine analysis:
1. Coinciding positive tests for protein and glucose
2. Protein (+)
3. Glucose (+)
4. Decreased phosphorus to calcium ratio
E. Serum analysis:
1. Increased alkaline phosphatase
2. Decreased serum inorganic phosphate
Source: Adapted from Friberg et al., Cadmium in the
Environment, 2nd ed., p. 146, (c) CRC Press, Inc., 1974.
Used by permission of CRC Press, Inc.
1973); very high therapeutic doses of vitamin D may have contributed to the
renal tubular damage seen in these patients. Murata et al. (1970) consid-
ered itai-itai disease to represent primarily a cadmium enteropathy, which
interferes with normal calcium absorption. Toxic effects of cadmium on the
gastrointestinal tract have also been described by Valberg et al. (1977).
6.3.2.4.8 Effects on the nervous system — Like other heavy metals, cadmium
can also interfere with activity of the nervous system. Friberg, Piscator,
and Nordberg (1971) reported a variety of central effects in workers employed
in a storage battery factory. Such symptoms may of course result indirectly
from vascular effects of the metal. A direct action of cadmium on nerve
cells has, however, also been noted (Gabbiani and Gregory, 1967; Kasuga,
Sugawara, and Okada, 1974).
Several reports have appeared on effects of cadmium on synaptic trans-
mission (Copper et al., 1975; Smirnov, Byzov, and Rampan, 1954). The action
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154
of the metal has been correlated with competitive inhibition of calcium
movement at the presynaptic nerve terminal; this effect prevents normal
release of acetylcholine following stimulation of the presynaptic nerve axon
(Kober, 1977; Kober and Cooper, unpublished).
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155
SECTION 6
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SECTION 7
ENVIRONMENTAL DISTRIBUTION AND TRANSFORMATION
7.1 SUMMARY
Cadmium is a relatively rare metal usually present in small amounts in
zinc ores and commercially obtained as a by-product from the zinc-, copper-,
and lead-producing industries. Its major uses are in electroplating, in
pigment production, in plastic stabilizers, and in batteries. Little cad-
mium is recovered from spent products, and the supply-demand-cost relation-
ships of cadmium production are directly related to the demand-cost of zinc
production.
/ ^/Sources of Ccdmium pollution include smelter fumes and dust, incinera-
' tion of cadmium-bearing materials, burning of fossil fuels, fertilizer
application, industrial waste disposal into water systems, and municipal
wastewater discharge and sludge disposal. Thus, the highest concentrations
of cadmium are most likely to be in the localized regions of smelters or in
industrialized urban areas.
Background levels of atmospheric cadmium are typically quite low and
often are below the limits of detection. Contents in urban areas are varia-
ble; reported cadmium levels range from 0 to as high as 0.150 yg/m3, with
means usually near 0.005 tc 0.015 yg/m3.
Uncontaminated soil contains 0.4 ppm cadmium or less. Soil in the
vicinity of smelters contains high levels of cadmium (about 10 to 100 ppm) ,
which typically decrease with distance from the smelter and with soil depth;
soil in industrialized urban areas contains about 0.1 to 1 ppm cadmium.
Natural waters also contain highly variable amounts of cadmium; waters
near industrial areas have values from 1 to 100 ppb, whereas many open rural
waters contain less than 1 ppb. Sediments also contain highly variable
amounts of cadmium, depending upon proximity to pollution outfalls.
Various processes serve to move cadmium from one medium to another.
Precipitation and fallout deposit airborne cadmium on land or water. Leach-
ing of soil can extract cadmium; the amount removed depends on pH, the chem-
ical form of cadmium, and the type of soil. Runoff can carry particulate
cadmium into surface waters. The fate of cadmium in waters depends on sev-
eral factors; however, much of the cadmium is eventually deposited in
sediments.
Because cadmium is present in a variety of industrial and municipal
wastewaters and sludges, methods of water treatment are needed to reduce the
cadmium content and methods of safe sludge disposal are necessary to reduce
the possible release of toxic heavy metals into the environment.
170
-------
171
7.2 TRENDS IN PRODUCTION AND USAGE
Cadmium is a relatively rare metal in the earth's crust; the most
common geologic form, greenockite (CdS), occurs in a commercially important
zinc ore, sphalerite (ZnS). Table 7.1 gives data on the natural abundance
of zinc and cadmium in the environment (Goeller, Hise, and Flora, 1973).
TABLE 7.1. NATURAL ABUNDANCE OF ZINC AND CADMIUM
Source
Worldwide
Continental
Ultramafic rocks
Basaltic rocks
High-calcium granites
Low-calcium granites
Syenitic rocks
Average for igneous rocks
Shales
Sandstone
Limestone
Soil
Range
Average
Seawater
Abundance
(PPtn)
Zn
80
55
150
112
47
39
26
70
45-95
16
20
10-300
50
10 ppb
Cd
0.18
0.15
0.5
0.03
0.22
0.13
0.13
0.13
0.2
0.3
0.05
0.035
0.01-0.7
0.06
0.1 ppb
Relative
abundance
of Zua
1.46
1.00
2.73
2.04
0.85
0.71
0.47
1.27
0.82-1.72
0.29
0.36
0.2-5.4
0.9
Cd/Zn
(%)
0.23
0.27
0.20
0.28
0.33
0.50
0.27
0.67-0.32
0.31
0.17
0.1-0.23
0.12
1.0
a
Abundance for specific rock type/continental abundance.
Source: Adapted from Goeller, Hise, and Flora, 1973, Table IV-1,
64.
The major commercial supply of cadmium is as a by-product in the pro-
duction of zinc from sphalerite; smaller amounts are supplied as by-products
from the copper- and lead-smelting industries. The processes involved in
the extraction of zinc and cadmium for conversion to usable forms are mining,
ore beneficiation, ore roasting and sintering, zinc smelting, cadmium recov-
ery, and processing. Most of the cadmiuir is recovered from the ore roasting
and sintering flue dusts by cadmium oxide reduction and from cadmium sulfate
solutions (obtained from the purification of zinc) by electrolysis. Figure
7.1 represents a schematic flowsheet for cadmium recovery.
-------
172
dH2S04 AND
NoCl03
ZINC ORE SUL
ROAST l NGL
SINTERING
DUSTS
INSO
TO LE
LEAD AND Z NC
COPPER F
SMELTING U
< 5 % Cd
RE
LEA
SUI
L SOLUTION
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ZINC ORE
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SLAB ZI"NC""~ D
FURIC ACID SOLUTIO
LEACH fiND
1 Zn DUST
PAND H2so4
N CADMIUM Cd ^
PPTN SP
\
\
LUBLE PbS04 ZnS04 AND
AD SMELTERS ZnCI2 TO Zn
ORE SINTERING
ARSINE (AsH,) HAZARD
LAG 1 ,|; N
LUE DUST
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SIDUES TO
D SMELTERS
FURIC AC D
ZINC DUST
Cu AND Cd SPONGE
REMOVAL
ARSENIC As-
Cd REMOVAL CA
ARSEN C TO L
STORAGE
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Co
su
^ni
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RES DUE ELECTROLYSIS
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STILLAT10N VAPORE
CADMIUM-Z NC
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j CARBON
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*ETAL CADM UM CAD
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RESIDUE
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10
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S TO Zn
TERING
MELTERS
H NO?S t
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ZINC
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-Zn CADM UM Cd ME
F&TE PPTN SPON
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TO MAI
AMMONIUM CHLORIDE [NHdci 1
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T * JlFOR AR COVER
MIUM Cd VAPOR Cd REMELT
POR CONDENSATION AND CAST
\ r / .
\ POWDER THALLUM
\ r^WLJtlK CHLQR ^
BYPRODUCT
ND fnn ,_(CHROMATE OR (
ND coo HOICHRQMATE J
Pb-FREE THALLIUM CADM UM
UTION REMOVAL *" PPTN
S THALLIUM CHROMATE 1
BYPRODUCT j C.Q
TAL CADMIUM CdS04 CADMIU
GE RED'SSOLUT ION SOLUTION ELECTRODEP
DLUTION >v
y LEACH \.
SPENT ELECTROLYTE \
Cd CADM UM
fiPOR CONOENSAT ION
ir-jG 1 CADMIUM
ING INGOTS"
CADMIUM METAL
PJRE
I NC DUST
Cd MEL^ UNDER
SPONGE CAUST C SODA
OLN SPENT MOLTEN
CAUSTIC
tl CATHODE
LEAD SMELTER
HIGH PURITY ZINC
Figure 7.1. Schematic flowsheet for recovery of cadmium as a by-
product of zinc and lead recovery. Source: Goeller and Flora, 1973,
Figure V-5, p. 148.
The major uses of cadmium are for electroplating, for pigments used in
plastics, paints, enamels, and inks, for stabilizers in plastics, for alloys,
and for nickel-cadmium batteries. Minor uses include electrical contact pro-
duction, curing of rubber, use in fungicides, and use in solid-state systems
(Heindl, 1970). Figure 7.2 shows a material flow diagram for cadmium in the
United States and gives approximate amounts of cadmium used in each industry
in 1968.
The determination of trends in production and use of cadmium is specu-
lative and depends on many factors, including production and consumption of
zinc, changing technology for recovery of cadmium from ores, development of
substitutes for cadmium, and new uses for cadmium. Table 7.2 gives the per-
centage of total use of cadmium for each industry in 1968 and the projected
use for the year 2000. The greatest projected increases are in electroplat-
ing of parts for motor vehicles, in plastics, and in batteries.
Because production of cadmium depends on zinc production, the output
of cadmium is directly related to the demand for zinc and thus is related
to the price of zinc. The projected world demand for zinc in the year 2000
lies between 6.1 x 109 kg and 11.5 x 109 kg (6,700,000 and 12,720,000 short
tons). This amount would yield a cadmium supply between 2.45 x 107 kg and
4.63 x 107 kg (54,000,000 and 102,000,000 Ib), which approximates the esti-
mated use in the year 2000 - 2.3 x 107 to 3.6 x 107 kg (51,000,000 to
-------
173
Codmiu
ANNUAL DEMAND
ECONOMIC RESERVES
RESERVE/DEMAND RA
CRUSTAL ABUNDANCE
SEA WATER ABUNDANCE
TOTAL ABUNDANCE
Figure 7.2. Societal flow of cadmium in the United States, 1968.
Source: Goeller, Rise, and Flora, 1973, Figure IV-3, p. 86.
79,000,000 Ib). Thus, if the high forecast for zinc demand is correct,
there should be sufficient cadmium to meet projected demands; however, if
the demand for zinc is lower, there will be insufficient cadmium to meet the
estimated high demand. Because production of cadmium is insensitive to cad-
mium demand, some marginal uses of cadmium would become economically infea-
sible (Heindl, 1970).
An important problem arises from the fact that cadmium is used disper-
sively — little is recovered from discarded consumer or industrial products.
With increased demand and improved technology, recovery techniques may be
developed which can alter this supply-demand problem to a small extent.
Presently, the recovery of cadmium from batteries seems the best possibility.
Improvement in mine production technology may yield higher cadmium recovery
from ores; however, this factor would be small since cadmium recovery from
zinc ores is already estimated to be between 70% and 90% (Heindl, 1970).
Goeller and Flora (1973) cited an example in which 98% of the cadmium was
recovered; this value was obtained by adding the 82.5% recovered as market-
able metal to the 15.9% produced as oxide residues.
-------
174
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7.3 DISTRIBUTION OF CADMIUM IN THE ENVIRONMENT
Distribution of cadmium in the environment represents the resultant of
natural occurrence and of cadmium added through natural redistributing pro-
cesses and as a consequence of human activity.
7.3.1 Sources of Pollution
Total emissions of cadmium metal into air, soil, and water from all
sources in the United States were estimated for 1968 to lie between 2.5 x 106
kg and 3.6 x 106 kg (5.5 and 7.9 million Ib) (Goeller, Hise, and Flora, 1973).
Data on amounts released at each stage in the material flow balance sheet are
limited and should be determined to allow identification of crucial stages
for pollution abatement priorities (Figure 7.2 and Table 7.3). The material
balance sheet (Table 7.3) shows that while 2.5 to 3.6 x 106 kg (5 to 8 mil-
lion Ib) of cadmium are listed as emissions for 1968, an additional amount of
almost 5 x 10s kg (11 million Ib) is either delegated for permanent use or
considered as waste with unknown disposition. Thus, total cadmium released
to the environment each year may be considerably greater than the approxi-
mate value of 3.6 x 10s kg (8 million Ib).
Major sources of cadmium pollution are processes involved in the extrac-
tion, refinement, and production of iron, steel, cadmium, zinc, lead, and
copper. Other sources of cadmium pollution include the subsequent conversion
of processed cadmium into various consumer products, emissions from use of
fossil fuels, use of phosphate fertilizers with a high cadmium content, wear-
ing of tires, and combustion of lubrication oil (Tables 7.3 and 7.4). Because
cadmium content in fossil fuels and fertilizers varies with source, emission
amounts can only be approximated (Goeller, Hise, and Flora, 1973). Data com-
piled by the MITRE Corporation (Table 7.4) show the amount of cadmium released
from various industries and the percentage of the total that each source
represents (Goldberg, 1973). Figure 7.3, using data from an independent
study, lists emission amounts and flow of cadmium from various industries.
Differences exist among the estimates of cadmium emission into the
environment. For example, Goldberg (1973) estimated the cadmium released by
fertilizer application in the United States to be less than 907 kg (2000 Ib),
whereas Goeller, Hise, and Flora (1973) estimated it to lie between 2.3 x 10**
and 2.3 x 10s kg (50,000 and 500,000 Ib). This latter value seems more rea-
sonable since the estimate for the amount of cadmium released by fertilizer
application in Sweden was about 10,000 kg (22,050 Ib) (Stenstrom and Vahter,
1974).
Cadmium pollution is associated with production, conversion, and re-
fining industries. Figures 7.4 and 7.5 show major U.S. deposits of zinc
and lead and the locations of major U.S. zinc production mines. Because
cadmium is obtained from zinc ore, cadmium pollution can be expected in
these areas (Goeller, Hise, and Flora, 1973). In addition, large urban and
industrial areas often have a higher cadmium content in the environment due
to various industrial processes involving products containing cadmium (Sec-
tions 7.3.2, 7.3.3, 7.3.4, and 7.3.5). The exact chemical form of cadmium
-------
176
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178
TABLE 7.4. CADMIUM RELEASED FROM VARIOUS SOURCES IN THE UNITED STATES
Cadmium released
Source
Copper mining
Zinc mining
Lead mining
Primary copper
Roasting
Reverberatory furnace
Converters
Material handling
Primary zinc
Roasting
Sintering
Distillation
Material handling
Primary nickel
Primary lead
Sintering
Blast furnace
Reverberatory furnace
Material handling
Secondary copper
Sweating furnace
Blast furnace
Iron and steel, blast furnace
Nonferrous alloys
Furnaces
Material handling
Cadmium paint pigments
Cadmium-barium plastic
stabilizers
Cadmium-nickel batteries
Miscellaneous cadmium products
Use of pesticides, herbicides,
and fungicides
Fertilizer application
Incinerators
Total
(metric
tons)
Negligible
<0.9
Negligible
208
85
245
53
604
258
82
Negligible
Negligible
60
17
2.7
Negligible
64
50
907
2.7
Negligible
10
2.7
<0.9
<0.9
<0.9
<0.9
86
2738
(short
tons)
Negligible
<1
Negligible
229
94
270
59
666
284
90
Negligible
Negligible
66
19
3
Negligible
70
55
1000
3
Negligible
11
3
<1
<1
<1
<1
95
3018
Percentage
of total
Negligible
0.01
Negligible
7.59
3.12
8.95
1.96
22.07
9.41
2.98
Negligible
Negligible
2.19
0.63
0.10
Negligible
2.32
1.82
33.14
0.10
Negligible
0.36
0.10
0.01
0.02
0.01
0.02
3.15
100.06
Source: Adapted from The MITRE Corporation, as cited in Goldberg,
1973, p. 105.
-------
179
ORNL-OWG 77-5255
Roufe
(A Thru air)
[W rhru wot*'!
Figure 7.3. Rates, routes, and reservoirs of cadmium in the environ-
ment. Values are calculated in tons per year for the United States.
Source: Fleischer et al., 1974, Figure 5, p. 282.
released into the environment and the medium to which it is released depend
on the particular industry. Natural and elevated concentrations of cadmium
found in air, land, and water are considered in the next three sections.
7.3.2 Distribution in Air
Because cadmium is a toxic element, there is considerable interest in
air pollution emissions from various industries. Air emissions of cadmium
[estimated to be about 1500 metric tens (1680 short tons) for 1968; see,
however, somewhat higher values in Table 7.3] occur in smelting of various
lead, copper, and zinc ores, in incineration of certain industrial and mu-
nicipal wastes, in combustion of coal and oil, and through electroplating,
pigmerts, and plastic industries (Fleischer et al., 1974). Questions of
concern include the form and concentration of cadmium in the air and the
distribution in rural and urban areas. Presently, little information exists
on the exact chemical form of cadmium in air. Some cadmium is probably re-
leased as dust, most likely as CdS or CdSOj,, during mining and conversion
-------
180
ORNL DWG 71-13240
o LEAD ORE
• LEAD-ZINC ORE
a ZINC-LEAD ORE
Figure 7.4. Location of U.S. deposits of lead, lead-zinc, and zinc-
lead ore. Source: Goeller, Rise, and Flora, Figure IV-5, p. 117.
ORNL- DWG 71- 13243
• MINE AND RANK
( )RANK BY STATE IN ZINC ORE OUTPUT
[ ] APPROXIMATE PRODUCTION, tons/yr OF ZINC, 1968
Figure 7.5. Location and approximate outputs (1968) of major U.S.
zinc production mines. Source: Goeller, Hise, and Flora, 1973, Figure
IV-6, p. 124.
-------
181
processes, and some is probably released as metal vapor during the smelting
process. Such cadmium probably reacts with oxygen to form cadmium oxide
(Section 2.3.1).
The concentration of cadmium in air around point sources can be consid-
erable. Friberg et al. (1974) cited data showing a weekly mean of 0.3 yg/m
at 500 m from a Swedish factory using copper-cadmium alloys and a maximum
24-hr average of 3 yg/m3 near a Japanese smelter. At 500 m from another
Japanese smelter, average values lay between 0.16 and 0.32 yg/m3. The most
common example used for the United States is East Helena, Montana, which
had three-month averages of 0.06 and 0.29 yg/m3 at 1300 and 800 m from the
smelter. Such concentrations usually decrease with distance from the source
due to dispersion and dust fall or precipitation (Friberg et al., 1974).
Although elevated cadmium levels are often found in the vicinity of
zinc smelters, the levels may not be high near lead smelters. De Koning
(1974) found that cadmium levels in air, soil, and plants near a lead smelt-
er were slightly higher than normal, although not arranged geographically to
suggest that the smelter was a point source of cadmium pollution. In con-
trast, Lagerwerff, Brower, and Biersdorf (1973) suggested that elevated cad-
mium levels, especially around smelters which also process zinc ore, indicate
that the smelter is a point source. In addition, high concentrations of cad-
mium in soils and litter were found near the American Metals Climax, Inc.
lead smelter in southeastern Missouri; these concentrations decreased with
increasing distance from the smelter (Andren et al., 1974).
There appears to be little argument that the elevated concentrations
in urban areas are due to industrial.activity (Fleischer et al., 1974).
No data were found on the contribution of various natural processes to the
cadmium content in air. The annual range for airborne particulate cadmium
in New York City was 0.006 to 0.002 yg/m3 in the Bronx, 0.009 to 0.036 yg/m3
in lower Manhattan, and 0.001 to 0.005 yg/m3 in Tuxedo, New York (detection
limit of 0.001 yg/m3) (Kneip et al., 1970). In lower Manhattan the concen-
tration showed a seasonal dependence: November through February had lower
concentrations, perhaps because of higher average wind speed during these
months. In a study of airborne particulates in the Chicago—northwest Indiana
region (50 sampling stations, six times during the summer), the suburban
areas yielded about 0.006 yg/m3 compared to values for the Lake Michigan
shoreline industrial areas of 0.015 to 0.080 yg/m3 (Harrison and Winchester,
1971). These authors suggested that the cadmium in this region comes from
local sources and that, except for one station, it probably arises from
gasoline and coal emissions. This conclusion is based on the fact that com-
bustion of coke, fuel oil, and gasoline produces emissions with ratios of
cadmium to lead, cadmium to copper, and copper to lead similar to those
found in the air samples. The low concentrations in suburban areas indicate
that the emissions are dissipated rather rapidly. A study of trace-element
air pollution in 77 midwestern cities by dust fall analysis showed that in-
dustrial areas had the highest amount of cadmium fallout (0.075 mg/m2-month)
compared to commercial and residential areas, which had 0.063 and 0.040 mg/m2-
month respectively (Hunt et al., 1971). Tables 7.5 and 7.6 present data from
the National Air Surveillance Network for the cadmium content of urban and
-------
182
TABLE 7.5. CADMIUM CONCENTRATIONS
IN U.S. URBAN AIR, 1969
(yg/m3)
Location
Alabama
Gadsden
Huntsville
Mobile
Montgomery
Alaska
Anchorage
Fairbanks
Arizona
Maricopa County
Phoenix
Tucson
Arkansas
Little Rock
Texarkana
West Memphis
California
Anaheim
Burbank
Fresno
Glendale
Long Beach
Los Angeles
Oakland
Ontario
Riverside
Sacramento
San Bernardino
San Diego
San Francisco
San Jose
Santa Ana
Torrance
Colorado
Denver
Montezuma County
Yearly
average
0.003
0.007
0.004
0.003
0.004
0.003
0.006
0.008
0.004
0.003
0.004
0.003
0.006
0.006
0.007
0.007
0.005
0.004
0.013
0.010
0.004
0.005
0.018
Range
0-0.003
0-0.003
0.004-0.010
0-0.005
0-0.004
0.003-0.004
0-0.004
0.005-0.009
0.004-0.012
0-0.006
0-0.004
0-0.008
0-0.005
0.003-0.005
0-0.005
0-0.004
0.004-0.011
0.006
0.005-0.011
0.004-0.010
0.004-0.005
0.004-0.005
0.006-0.020
0.006-0.015
0-0.006
0.003-0.005
0-0.006
0-0.007
0.015-0.027
0
(continued)
-------
183
TABLE 7.5 (continued)
Location
Connecticut
Bridgeport
Hartford
New Haven
Waterbury
Delaware
Wilmington
District of Columbia
Florida
Jacksonville
Miami
St. Petersburg
Tampa
Georgia
Atlanta
Columbus
Savannah
Hawaii
Honolulu
Idaho
Boise City
Illinois
Chicago
East St. Louis
Joliet
North Chicago
Peoria
Rockford
Springfield
Indiana
East Chicago
Evansville
Fort Wayne
Gary
Hammond
Indianapolis
New Albany
South Bend
Terre Haute
Yearly
average
0.012
0.006
0.007
0.020
0.014
0.008
0.005
0.008
0.003
0.006
0.007
0.004
0.015
0.022
0.009
0.007
0.011
0.013
0.005
0.028
0.008
0.008
0.009
0.011
0.015
0.005
0.006
0.005
Range
0.008-0.018
0.005-0.006
0.005-0.009
0.008-0.029
0.006-0.025
0.006-0.010
0.003-0.006
0.005-0.011
0.003-0.004
0.005-0.007
0.006-0.011
0-0.004
0.003-0.004
0
0-0.008
0.014-0.015
0.013-0.045
0.005-0.012
0.004-0.011
0.008-0.015
0.010-0.016
0.004-0.007
0.017-0.046
0.007-0.009
0.007-0.015
0.008-0.012
0.010-0.012
0.005-0.025
0.004-0.006
0.006-0.007
0.005-0.007
(continued)
-------
184
TABLE 7.5 (continued)
Location
Iowa
Davenport
Des Moines
Dubuque
Kansas
Kansas City
Topeka
Wichita
Kentucky
Ashland
Covington
Louisville
Louisiana
Baton Rouge
New Orleans
Shreveport
Maryland
Baltimore
Massachusetts
Boston
Fall River
Springfield
Worchester
Michigan
Dearborn
Detroit
Flint
Grand Rapids
Lansing
Saginaw
Trenton
Minnesota
Duluth
Minneapolis
St. Paul
Missouri
Kansas City
St. Louis
Montana
Helena
Yearly
average
0.010
0.005
0.009
0.010
0.005
0.005
0.023
0.011
0.006
0.003
0.004
0.004
0.011
0.006
0.005
0.006
0.006
0.011
0.012
0.007
0.012
0.004
0.003
0.006
0.007
0.009
0.007
0.036
0.028
Range
0.007-0.016
0.004-0.005
0.004-0.013
0.007-0.012
0.003-0.006
0.004-0.006
0.017-0.026
0.007-0.013
0.006
0.003
0.004-0.005
0.003-0.004
0.008-0.017
0.004-0.008
0.003-0.007
0.004-0.009
0.003-0.008
0.007-0.013
0.010-0.015
0.006-0.009
0.009-0.018
0.003-0.005
0.003-0.005
0.004-0.007
0-0.004
0.006-0.008
0.006-0.015
0.004-0.010
0.013-0.066
0.005-0.077
(continued)
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185
TABLE 7.5 (continued)
Location
Yearly
average
Range
Nebraska
Omaha
Nevada
Las Vegas
Reno
New Hampshire
Concord
New Jersey
Burlington County
Elizabeth
Glassboro
Hamilton
Jersey City
Newark
Paterson
Perth Amboy
Trenton
New Mexico
Albuquerque
New York
Albany
Buffalo
New York City
Niagara Falls
Rochester
Syracuse
Utica
North Carolina
Charlotte
Durham
Greensboro
Winston-Salem
North Dakota
Bismarck
Ohio
Akron
Canton
Cincinnati
Cleveland
Columbus
Dayton
0.004
0.008
0.017
0.010
0.007
0.012
0.038
0.006
0.018
0.010
0.004
0.008
0.008
0.016
0.015
0.013
0.010
0.003-0.005
0-0.004
0-0.005
0.006-
0.009-
0.009-
0.005-
0.010-
0.014-
0.004-
0.011-
0.008-
•0.009
•0.029
0.013
0.009
•0.015
0.097
0.007
0.024
•0.012
0-0.007
0.003
0.007
0.014
0.006
0.008
0.008
0.003
0.004
0.006
0.005
0-0.004
0.006-0.008
0.004-0.023
0.004-0.007
0.004-0.011
0.003-0.010
0-0.005
0-0.005
0-0.003
0.005-0.008
0.004
0.007-0.010
0.006-0.009
0.013-0.019
0.008-0.024
0.008-0.021
0.008-0.011
(continued)
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186
TABLE 7.5 (continued)
Location
Toledo
Youngs town
Oklahoma
Oklahoma City
Tulsa
Oregon
Medford
Portland
Pennsylvania
Allentown
Bethlehem
Erie
Harrisburg
Hazelton
Johnstown
Philadelphia
Pittsburgh
Reading
Scranton
Warminster
West Chester
Wilkes-Barre
York
Puerto Rico
Bayamon
Catano
Guayanilla
Ponce
San Juan
Rhode Island
East Providence
Providence
South Carolina
Columbia
Greenville
Tennessee
Chattanooga
Knoxville
Memphis
Nashville
Yearly
average
0.005
0.012
0.013
0.004
0.020
0.023
0.009
0.005
0,005
0.008
0.015
0.014
0.011
0.008
0.006
0.008
0.008
0.006
0.006
0.003
0.008
0.005
0.007
0.011
0.004
0.004
0.004
Range
0.005
0.009-0.015
0-0.005
0.008-0.025
0-0.004
0.003-0.004
0.011-0.028
0.015-0.029
0.007-0.012
0.004-0.006
0.004-0.008
0.005-0.010
0.010-0.020
0.009-0.020
0.008-0.014
0.007-0.009
0.005-0.008
0.004-0.010
0.006-0.012
0.004-0.008
0.006-0.008
0-0.004
0
0
0-0.003
0.007-0.010
0.004-0.005
0-0.003
0.007-0.008
0.010-0.014
0-0.005
0.003-0.005
0.003-0.004
(continued)
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187
TABLE 7.5 (continued)
Location
Texas
Dallas
El Paso
Fort Worth
Houston
Pasadena
San Antonio
Utah
Ogden
Salt Lake City
Vermont
Burlington
Virginia
Danville
Hampton
Lynchburg
Newport News
Norfolk
Portsmouth
Richmond
Roanoke
Washington
Seattle
Spokane
Tacoma
West Virginia
Charleston
Wisconsin
Eau Claire
Kenosha
Madison
Milwaukee
Racine
Superior
Wyoming
Casper
Cheyenne
Yearly
average
0.005
0.105
0.004
0.004
0.003
0.007
0.009
0.005
0.003
0.003
0.012
0.007
0.004
0.008
0.004
0.012
0.008
0.004
0.010
0.006
0.008
0.004
0.010
0.006
0.003
0.005
Range
0.003-0.008
0.057-0.150
0-0.006
0-0.005
0-0.006
0-0.003
0.005-0.012
0.003-0.016
0.004-0.006
0-0.004
0-0.005
0.008-0.021
0.004-0.009
0.003-0.005
0.007-0.009
0.004-0.005
0.009-0.014
0.003-0.019
0-0.007
0.005-0.016
0.005-0.007
0-0.004
0.004-0.010
0.003-0.004
0.006-0.017
0.005-0.007
0-0.004
0
0.004-0.006
Source: Adapted from U.S. Environmental Protec-
tion Agency, 1973, Table 4-3, pp. 4-9 - 4-12.
-------
188
TABLE 7.6. NONURBAN SITES SHOWING LESS THAN 0.001 pg CADMIUM
PER CUBIC METER OF AIR IN 1969
Arizona
Grand Canyon National Park
Arkansas
Montgomery County
California
Humboldt County
Florida
Hardee County
Idaho
Butte County
Indiana
Monroe County
Parke County
Maine
Acadia National Park
Maryland
Calvert County
Missouri
Shannon County
Montana
Glacier National Park
Nebraska
Thomas County
Nevada
White Pine County
New Hampshire
Coos County
New York
Jefferson County
North Carolina
Cape Hatteras National Park
Oklahoma
Cherokee County
Oregon
Curry County
Pennsylvania
Clarion County
Rhode Island
Washington County
South Carolina
Richland County
South Dakota
Black Hills National Forest
Tennessee
Cumberland County
Texas
Matagorda County
Vermont
Orange County
Virginia
Shenandoah National Park
Wythe County
Wisconsin
Door County
Wyoming
Yellowstone National Park
Source: Adapted from U.S. Environmental Protection Agency,
1973, Table 4-4, p. 4-13.
nonurtan areas in 1969 (U.S. Environmental Protection Agency, 1973). The
significant concentrations of cadmium observed in cities and, more particu-
larly, in industrial areas suggest that the source of cadmium in air is
anthropogenic.
Forms and particle-size distribution of cadmium in air are important in
assessing hazards from eirission sources. Samples of air (taken on different
-------
189
days) from Cincinnati, Ohio, and suburban Fairfax (9 miles away) showed that
cadmium was four times higher in the city (0.08 yg/m3) than in the suburb
(0.02 yg/m3). The mass median diameter was larger for particles in the suburb
(estimated 10 ym) than in the city (3.1 ym). Since about 40% of the parti-
cles in the city had sizes less than 2 ym, significant absorption through the
lung would be expected (Lee, Patterson, and Wagman, 1968).
Particle size and cadmium concentration were examined in fly ash from
the precipitating system and from stack emissions of eight power plants in
the United States. The findings indicate that the highest concentrations
of cadmium occur in the smallest airborne particles (e.g., 35 ppm in ash
from 1.1- to 2.1-ym particles, 22 ppm in ash from 3.3- to 4.7-ym particles,
and 15 ppm in ash from 7.3- to 11.3-ym particles). In precipitated fly ash
tie cadmium concentrations were less than 10 ppm for all particle sizes,
/suggesting that (1) existing particle collection devices allow the emission
/ of small toxic particles and (2) estimates of emission concentrations deter-
mined from precipitated fly ash may "grossly underestimate the actual emis-
sions" (Natusch, Wallace, and Evans, 1974). Why\the highest concentration
of cadmium is associated with the smallest particles is not pre_cisely__known.
A possible explanation may be that cadmium is volatilized at higher
temperatures and is then adsorbed or condensed onto the available surface
area of airborne particles (Natusch, Wallace, and Evans, 1974). Smaller
particles with greater surface-to-mass ratios therefore adsorb more cadmium
than larger particles.
Information on the concentration of different-sized particles in the
air is also needed to assess the potential hazard of an emission source.
Toca, Cheever, and Berry (1973) showed an increasing cadmium concentration
with decreasing particle size in the effluent from a coal-fired boiler and,
in addition, found that the last stages of their sampling train, containing
the smallest trapped particles, yielded the greatest weight per cubic meter
of sample volume.
7.3.3 Distribution in Soils
The distribution of cadmium in soils is a more complex problem than
distribution in air because parent rock may contain cadmium compounds, cad-
mium may be surface deposited by settling from air, and cadmium may become
more or less tightly bound to soil particles. The soil also is a more per-
manent reservoir for cadmium, and concentrations may be expected to increase
with time.
The cadmium content in unpolluted soil is related to the concentration
of cadmium in natural parent materials of the soil. Tables 7.7 and 7.8
illustrate the considerable range in cadmium concentrations in igneous and
sedimentary rocks. Vinogradov (cited in Baes, 1973) reported that zinc and
cadmium contents of soils vary with the nature of the parent rock, being
high in soils on basaltic rock and low in soils on granitic rock. In addi-
tion to natural variations, human activity greatly influences cadmium con-
tent of soils (Table 7.9); for example, uncontaminated soils have average
values of 0.4 ppm or less compared with an average of 72 ppm in soil near a
smelter (Fleischer et al. , 1974). As another example, examination of 5-cm
-------
190
TABLE 7.7. CADMIUM IN SEDIMENTARY ROCKS
Sedimentary
rock
Limestones
Sandstones (composite of
Shales
Organic content <0.5%
Organic content 0.5%-1.
Organic content >1%
Oceanic sediments
Lake sediments
Oceanic manganese oxides
Phosphorites
Number
of
samples
23
14)
103
0%
189
26
34
163
Cadmium
Range
<0. 3-11.0
<0.3-0.8
0.3-1.8
0.5-8.4
0.04-1.88
5-19
<3-21.2
<10-500
TMarowsky and Wedepohl (1971) gave 0.3 ppm.
Aston et al. (1972) reported 0.04-0.58 ppm (av 0.
Atlantic deep-sea sediments.
Source: Adapted from Fleischer et
TABLE
Igneous
rocks
Rhyolitic
Granitic
Intermediate
Basalt, diabase, gabbro
Peridotite
Dunite
Eclogite
Alkalic rock
7.8. CADMIUM
Number of
samples
analyzed
43
43
4
79
3
1
4
7
content
Average
0.10
<0.03
1.4*
0.35
0.8
2.0
0.5*
11.
8
25
226 ppm)
al. , 1974, Table 3, p.
IN IGNEOUS ROCKS
Cadmium content (ppm)
Range
0.03-0.57
0.01-1.6
0.017-0.32
0.01-1.00
<0. 001-0. 029
0.005-0.154
0.03-1.6
0.04-0.90
Average
0.23
0.2
0.13
0.03
0.1
0.25
(ppm)
Median
0.8
0.3
0.7-0.8
1.2
5.3
in 35
260.
Zn/Cd
ratio
480-177
90-7000
80-3600
27-1430
Source: Adapted from Fleischer et al., 1974, Table 2, p. 260.
-------
191
TABLE 7.9. CADMIUM IN SOILS
Locality
and type
of soil
U.S.S.R., tundra, podsols,
forest, red earth
Poland, distant from
industrial areas
Wales, Ystwyth Valley
Maryland, Missouri, Ohio,
32 m from highways
Helena Valley, Montana,
18-60 km from smelter
Annaka City, Japan, 900 m
from refinery
Southwest Wales
Lower Fraser Valley,
British Columbia
Number
of
samples
Normal
40
33
4
17
2
4
33
Cadmium content (ppm)
Depth
^cm^ Range Average
soils
A, B, and C 0.01-0.07 0.06
horizons
0-20 0.04 (max) 0.016
1.0
10-15 0.12-0.52 0.26
b b
6-10 <0.5-2 1.4
40-60 0.3-0.4 0.35
0.3-0.5 0.4
Surface 0.88
Contaminated soils
Poland, industrial areas
Wales, Ystwyth Valley,
contaminated
Maryland, Missouri, Ohio,
8 m from highways
Helena Valley, Montana,
1 km from smelter
Annaka City, Japan
150-250 m from smelter
900 m from smelter
Poland, 600 m from zinc
metallurgical factory
Southwest Wales, Swansea,
1.5 km from contaminated
area
Bartlesville, Oklahoma,
1500 ft from smelter
British Columbia, 15 m
from smelter
Grand Rapids area, Michigan
Residential area
Agricultural area
Industrial area
Airport
67
4
7
1
1
4
70
91
86
7
0-20 0.3-0.8 (max) 0.17-0.28
1.5-3.0
0.5 0.90-1.82 1.28
0.10 26-160 72
Surface 23-88
5 44
0-10 250
15-30 110
26
12.5-27.5 450
Surface 7.9-95.2 49.0
0-5 0.41
0-5 0.57
0-5 0.66
0-5 0.77
Samples collected near U.S. 1, Beltsville, Maryland; Washington-Baltimore
Parkway, Bladensburg, Maryland; Interstate 29, Platte City, Missouri; Seymour Road,
Cincinnati, Ohio.
^"rhese values probably reflect some contamination.
Source: Adapted from Fleischer et al., 1974, Table 6, p. 264. Data collected
from several sources.
-------
192
cores of surface soil about Grand Rapids, Michigan, gave average values of
0.77 ppm for airport locales, 0.66 ppm for industrial locales, 0.57 ppm for
agricultural soils, and 0.41 ppm for residential areas. The same general
trend was found for nine other trace elements (Klein, 1972).
Accumulations of cadmium in the vicinity of lead and zinc smelters
have been reported. Samples from near a lead smelter in Galena, Kansas,
showed that surface soil contamination decreased from 102 ppm at 330 m from
the smelter to 32.6 ppm at 1000 m and 26.8 ppm at 1670 m. At each locale
the cadmium concentration decreased with increasing soil depth. At the 330-m
site, cadmium concentrations were 102 ppm at 0 to 5 cm, 48 ppm at 5 to 10 cm,
and 22 ppm at 10 to 22 cm; the corresponding values at 1000 m were 32.6, 12.2,
and 3.1 ppm respectively (Lagerwerff, Brower, and Biersdorf, 1973). A simi-
lar trend was observed in Annaka City, Japan, site of a large zinc refinery;
surface soil samples contained 31 ppm cadmium (Kobayashi, 1972). Surface
garden soils in Tacoma, Washington, contained 7 to 12 ppm cadmium near a
copper smelter and about 1 tc 2 ppm at distances of 1.6 to 3.2 Ion; "normal"
soils were reported to contain 0.06 ppm cadmium (Ratsch, 1974).
Concentrations of cadmium in the litter horizons of soil near the
American Metals Climax, Inc. lead smelter decreased from about 100 ppm
0.4 km from the smelter to about 20 ppm at 2 km (Andren et al., 1974).
The average nitric acid—soluble cadmium content of 33 agricultural soils
in the Lower Fraser Valley, British Columbia, Canada, was 0.88 ppm; however,
in the vicinity of a battery smelter the surface cadmium concentration was
as high as 95 ppm. Vertical distribution in the soil dropped rapidly from
44 ppm at the surface (15 m from the smelter) to 2.45 ppm at the 5- to 10-cm
depth and to 0.67 ppm at the 10- to 15-cm depth (John, Chuah, and VanLaerhoven,
1972).
In addition to cadmium contamination of soil by fallout of particulate .
cadmium from smelters and from the combustion of coal and oil, portions can
be added during fertilization with superphosphate or any fertilizer contain-
ing phosphate. Cadmium is present in phosphate rock and is concentrated dur-
ing production of phosphate fertilizer (acidulation or electric furnace
processes) (Goeller, Hise, and Flora, 1973). Because plants take up cadmium,
the presence of "excess" cadmium in the soil will lead to higher concentra-
tions in plants (Section 4.2.1). Increased plant uptake of cadmium can be a
potential hazard if it results in increased human uptake. Examination of
cadmium content in several Swedish fertilizers gave values of between 6 and
30 mg/kg fertilizer. With the recommended fertilizer application rate of up
to 600 kg/ha, 4 to 18 g cadmium may be added per hectare. This is comparable
to the amount of cadmium which would be added through the application of the
recommended amount of sewage sludge as fertilizer (Stenstrom and Vahter,
1974). Williams and David (1973) reported the cadmium content of New South
Wales, Australia, fertilizers to lie betv/eer 18 and 91 ppm and to be corre-
lated with the phosphorus content of the fertilizer. The cadmium was available
for plant uptake and tended to accumulate in an exchangeable form in the upper
10 cm of soil.
Sewage sludge can be used for soil improvement programs, but one major
concern is the fate of heavy metals within the sludge. The Swedish Board of
-------
193
Health and Welfare recommended that sludge with greater than 15 mg cadmium
per kilogram (dry weight) not be used for soil improvement and that the
application rate be less than 1 ton/ha (corresponding to about 15 g cadmium
per hectare). Stenstrom and Losjo (1974), in a report of a long-term experi-
ment, suggested that cadmium uptake into wheat grain is proportional to the
total amount of cadmium in the soil. They speculated that if availability
does net decrease with time and if yearly sludge applications are used, cad-
mium concentrations in foods "within a few decades" will be sufficiently
high to cause daily cadmium uptake by humans to reach the limit suggested by
the World Health Organization (60 to 70 yg/day). On the other hand, there
is evidence to suggest that availability of sludge-borne cadmium for assimi-
lation by plants may decrease with time after application (Lue-Hing et al.,
1977) (Sections 4.2.2.1.1 and 7.5).
Studies of metals in soils and plants along roadsides have been used to
determine whether motor vehicles are a source of lead, zinc, nickel, and
cadmium pollution. Lagerwerff and Specht (1970) concluded that contamina-
tion might be related to traffic because the soil concentration of each metal
decreased with distance from the road. Surface soil concentrations of cadmium
were 1.45, 0.40, and 0.22 rag/kg dry weight at distances of 8, 16, and 32 m
from the road. Similar soil concentrations were found in three other road-
side plots. Conversely, in another study Creason et al. (1972) concluded
from analyses of cadmium in dust fall that no concentration gradient exists
near roads and, therefore, that automobiles may not be a major or specific
source of cadmium pollution.
7.3.4 Distribution in Water
As in air and soil, the concentration of cadmium in water varies with
season and with distance from the input source. Tables 7.10 and 7.11
(Fleischer et al., 1974) list concentrations of cadmium in seawater and
fresh water. Since several factors can influence concentrations in partic-
ular locales, different types of water are individually discussed.
There are several reports on the heavy-metal content in water from
mining and smelting areas. The cadmium content of the Biala and Sztola
streams in Poland ranged from 0.8 to 16.7 ppb, with the highest values below
the mouth of industrialized channels of the region. The highest values for
the streams occurred in the autumn-winter period. The mine waters contained
from 1.3 to 3.7 ppb cadmium (Pasternak. 1973). The concentration of cadmium
in water in the lead-zinc mining and industrial area of Springfield, Missouri,
was from 0.11 to 1.22 ppb in surface water, from 0 to 1.66 ppb in shallow
wells, and from 0.35 to 1.06 ppb in deep wells. In the Joplin, Missouri,
area, mean cadmium concentrations were 1.6 ± 3.8 ppb in surface water, 1.7 ±
2.4 ppb in shallow well water, and 0.5 ± 0.7 ppb in deep well water (Proctor
et al., 1974). The Canyon Creek Basin mining area in Idaho had concentra-
tions of cadmium as high as 20 ppb in tailing pond effluents and also had
elevated levels in groundwater (200 to 400 ppb) and surface water (40 ppb)
due to leaching from old tailings buried in the basin area (Mink, Williams,
and Wallace, 1972).
-------
194
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TABLE 7.11. CADMIUM CONCENTRATIONS AND FLOWS IN SELECTED RIVERS
Location
Mississippi-Missouri River
North Dakota
Nebraska
Missouri
Illinois
Missouri
Tennessee
Louisiana
Tributaries to Mississippi-Missouri River
Ohio River, Kentucky
Tennessee River, Alabama
Illinois River, Illinois
Columbia River, Washington
Susquehanna River, Pennsylvania
Alleghenny River, Pennsylvania
Sacramento River, California
Mineral Creek, Arizona
Cadmium
content
(yg/liter)
1
2
4
14
8
25
8
16
12
20
8
6
6
20
90
1
2
5
1
2
30
Cadmium flow
(metric
tons per
year)
23
76
152
603
350
1216
998
3946
3030
5162
1869
1588
1588
809
2794
18
178
46
19
24
0.9
(tons per
year)
25
84
168
665
386
1340
1100
4350
3340
5690
2060
1750
1750
892
3080
20
196
51
21
27
1
Zn/Cd
ratio
20
10
5
0.6
1.6
1.5
16
9.5
30
5
4
60
320
Date
10/9/70
10/9/70
10/9/70
10/14/70
10/14/70
10/5/70
10/13/70
10/13/70
10/14/70
10/15/70
10/14/70
10/20/70
10/20/70
10/23/70
10/21/70
10/6/70
10/6/70
10/14/70
10/12/70
10/7/70
10/8/70
Source: Adapted from Fleischer et al., 1974, Table 24, p. 280.
A regional summary of cadmium in surface water (Table 7.12) shows New
England and the Northeast with the highest frequency of detectable levels
of cadmium; the highest concentration was found in the Southwest (Durum and
Hem, 1972) . There is ample documentation of elevated cadmium levels in
various surface waters near industrial areas. For example, cadmium concen-
trations in the Bristol Channel (industrialized area) ranged from 0.28 to
4.20 ppb (mean of 1.13 ppb) (Abdullah, Royle, and Morris, 1972), and in the
neighboring Severn Estuary the cadmium concentration ranged from 5.8 ppb
near the mouth of the channel to about 0.1 ppb in the adjacent open sea
(Butterworth, Lester, and Nickless, 1972). The decrease in cadmium concen-
tration over a relatively short distance suggests that cadmium is being
deposited in sediments. Fleischer et al. (1974) concluded that "the surface
waters that contain more than a few ppb cadmium near urban areas have almost
certainly been contaminated by industrial wastes from metallurgical plants,
plating works, or plants manufacturing cadmium pigments, cadmium-stabilized
plastics, or nickel-cadmium batteries, or by effluent from sewage treatment."
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196
TABLE 7.12. REGIONAL SUMMARY OF CADMIUM IN U.S. SURFACE WATERS
Region
New England
and Northeast
Southeast
Central
Southwest
Northwest
Cadmium content
(ppb)
Max Min Median
32 <1 2
90 <1 <1
40 <1 <1
130 <1 <1
21 <1 <1
Cadmium
not
detected
(%)
36
55
55
65
78
Cadmium
detected
00
64
45
45
35
22
Source: Adapted from Durum and Hem, 1972, Table 7, p. 30.
Reprinted by permission of the publisher.
Since there is concern over the heavy-metal content of natural waters,
studies have been carried out tc estimate concentrations in surface waters
that serve as drinking water sources in and near urban and industrial areas.
Table 7.13 cites locations in which a U.S. Geological Survey study found
thc-t the Public Health Service mandatory upper limit for cadmium concentra-
tion (10 ppb) was exceeded; the report concluded that there is no widespread
occurrence of cadmium in levels greater than the standard since a large
number (720) of collection sites were examined in both industrial and urban
areas (Anonymous, 1971). The Community Water Supply Survey of 1969 found
that 3 of 969 water supply systems produced finished drinking water with
concentrations of cadmium greater than the Public Health Service mandatory
limit (10 ppb) (McCabe et al., 1970).
Doolan and Smythe (1973) studied the cadmium content of a variety of
waters in New South Wales, Australia. Electrolytic plating wastewater
contained cadmium levels as high as 28,500 ppb; very high levels were also
found in seepage water from mines. Downriver from these sources, the cadmium
content decreased significantly. Tap water contained 0.02 ppb cadmium, but
water from unused galvanized piping showed higher levels (1.2 ppb). Galva-
nized piping (zinc-plated) has been considered as a source for cadmium in
drinking water; rates of dissolution depend on the oxygen concentration, pH,
and carbonate ccncentration (Goeller and Flora, 1973) (Section 2). Schroeder
et al. (1967) presented data (Table 6.8) showing that tap water contains a
higher concentration of cadmium than the water at the inlet, presumably due
to dissolution during passage through galvanized piping (Section 2.3.2.4).
There is a lack of data on the chemical nature of cadmium in waters and
on whether it is present in soluble or particulate form. Joe Mill Creek in
Tennessee flows over carbonate outcroppings which contain sphalerite (ZnS);
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197
TABLE 7.13. LOCATIONS AT WHICH U.S. PUBLIC HEALTH SERVICE MANDATORY UPPER LIMIT
FOR CADMIUM IN DRINKING WATER WAS EXCEEDED
State
Location
Metal concentration
(ppb)
As
Cd
Pb
Hg
Alabama
Arizona
Arkansas
California
Connecticut
Idaho
Illinois
Kentucky
Louisiana
Maine
Mississippi
Missouri
Nebraska
North Carolina
North Dakota
Oklahoma
Cahaba River pump station,
Birmingham 12
Mobile River at Government St.,
Mobile 65
Tennessee River at Whitesburg 90
Mineral Creek near Big Dome, 4.8 km
south of Ray 130
Arkansas River near Lock and Dam 3,
below Pine Bluff 90
Arkansas River at Lock and Dam 6,
below Little Rock 12
Arkansas River at Lock and Dam 13,
below Fort Smith 140
Hot Springs Reservoir on Bull Bayou 20
Hurricane Creek near Sheridan 15
Lake Winona on Alum Fork,
Saline River 18
North Sylamore Creek near Fifty Six 60
Ouachita River near Malvern, below
Hot Springs 18
White River near Goshen, below
Fayetteville 80
Merced River at Happy Isle Bridge
near Yosemite
Naugatuck River at Beacon Falls 22
South Fort Coeur d'Alene River at
Smelterville 21
Mississippi River at Chester 12
Mississippi River at East St. Louis 16
Ohio River at Lock and Dam 53 near
Grand Chain 15
Ohio River at Louisville 70 20
Calcasieu River near Sulphur 30
Cross Lake at Shreveport 16
Red River at Moncla 14
St. Croix River at Baring 22
Escatawpa River at Moss Point 55
Mississippi River at Cape Girardeau 20
Mississippi River at Cottonwood Pt. 15
Missouri River at St. Joseph 14
Missouri River at Lexington 25
Big Blue River at Barneston 40
Cape Fear River at Lock 1 near
Kelly 60
Catawba River near Charlotte 60
Red River of the North, below Fargo 26
Carney River near Ochelata 12
Kiamichi River near Big Cedar
6.0
890
84
(continued)
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198
TABLE 7.13 (continued)
State
Location
Metal concentration
(ppb)
As
Cd
Pb
Pennsylvania Lackawanna River at Old Forge
Spring Brook Reservoir near
Wilkes-Barre
Tulpehocken Creek at Blue Marsh
damsite near Reading
West Branch Susquehanna River at
Renovo
Wolf Creek Reservoir near
Pottsville
32
27
60
55
11
South Carolina
South Dakota
Tennessee
Sugar Creek near Ft. Mill
James River below Huron
James River near Mitchell
Watauga River near Johnson City
1100
60
14
12
Tiany of the locations at which the limit was exceeded are not points where
water is withdrawn for public supplies.
Source: Adapted from Anonymous, 1971, Table 2, p. 175. Reprinted by permis-
sion of the publisher.
85.1% to 95.8% of the cadmium content of the creek water is in soluble form.
Coarse particles (>0.15 ym) accounted for 3.5% to 8.9% of the cadmium, and
colloidal particles between 0.01 and 0.15 ym accounted for 0.5% to 6.0%.
The coarse and colloid particles contained 13 to 24 ppm and 69 to 161 ppm
solid cadmiuir. respectively (Perhac, 1972). Approximately 99% of the cadmium
transported by the Walker Branch Stream in Oak Ridge, Tennessee, is in
soluble form (Table 7.14) (Andren, Lindberg, and Bate, 1975). Tributary
TABLE 7.14. CADMIUM CYCLING BUDGET IN WALKER BRANCH WATERSHED, OAK RIDGE, TENNESSEE, 1974
Month
January
February
March
April
May
June
July
Rainfall
(cm)
24
13
19
9
17
5
2
.47
.47
.74
.01
.66
.10
.74
Cadmium
concentration
(ppb)
9.
9.
4.
3.
4.
12.
6.
6
6
3
6
5
4
3
Wet
input
(g/ha)
23.
12.
8.
3.
7.
6.
4.
7
9
4
3
8
3
5
Estimated
, . a
dry input
(g/ha)
<1
<0
<0
<0
<0
<0
.11
.61
.40
.16
.37
.30
Stream output (g/ha)
Dissolved Suspended
1
0
0
0
0
0
.21
.64 0.004
.69
.53
.27 0.001
.14
Watershed
retention
(%)
95
95
92
85
97
98
Dry deposition input was estimated based on the July aerosol data that the relative contribu-
tion of dry deposition to total atmospheric deposition is constant over the six-month period.
Source: Adapted from Andren, Lindberg, and Bate, 1975, Tables 4, 5, 15, and 16, pp. 14, 15,
32, 33.
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199
streams of Lake Cayuga, New York, in rural areas contained between <0.05 and
0.13 ppb cadmium in particulate form and from 0.07 to 1.10 ppb cadmium in
soluble form. Regions of the streams in urban areas contained from 0.09 to
0.44 ppb in particulate form and from 0.07 to 0.29 ppb in soluble form
(Kubota, Mills, and Oglesby, 1974). The streams contained more cadmium in
April and July than in the other spring and summer months; in April the major
portion of cadmium was present in particulate matter, whereas in July soluble
cadmium made up the greater fraction (Kubota et al., 1974).
Studies of the cadmium concentration in marine environments have usu-
ally been carried out in the vicinity of land masses containing suspected
pollution sources. Table 7.10 illustrates the variation in concentrations
observed in seawater (Fleischer et al., 1974). Recent studies in the trop-
ical northeast Atlantic Ocean between the Canary Islands and the Cape Verde
Islands showed cadmium concentrations ranging from 0.07 to 0.71 ppb (mean of
0.11 ppb), with little change in concentration over depths down to 500 m
(Riley and Taylor, 1972).
Concentrations in estuaries and bays can be expected to show consider-
able variation. Surface waters of Monterey Bay, California, contained 0.24,
0.46, and 0.29 ppb cadmium in March, April, and June; the adjacent open water
concentration was 0.05 ppb (Knauer and Martin, 1973). The high value for
surface waters of the Corpus Christi Bay estuary during September was 78 ppb
near the harbor entrance in contrast to 3 ppb in the bay region. For January,
the concentrations only varied from 2 to 10 ppb (Holmes, Slade, and McLerran,
1974).
7.3.5 Distribution in Sediments
Examination of the metal content of sediments can be used to estimate
levels of the metal in a large regional drainage area (soil and mineral
analyses). In particular, such analyses may be used to assess sources of
specific metal pollution in the area (Lisk, 1971). A direct relationship
need not exist between the sediment concentration of cadmium and the con-
centration in water at any given instant. In the Qishon-Gadura river system
in Israel, the cadmium concentration in sediments varied from 0 to 123 ppm
(with the higher values occurring in the industrial regions of the valley),
although the concentration of cadmium in the water was below the detection
limit (<0.01 ppm) at all times. It is suggested that the high pH of these
waterways (pH 9 to 11 in the contaminated areas) serves to precipitate the
cadmium compounds and that any water pollution controls which would lower
pH values might lead to increasing solubilization of the cadmium compounds
with their subsequent release into Haifa Bay (Kronfeld and Navrot, 1974).
Analyses of sediment cores from lakes and rivers can provide estimates
of mineral composition in precultural times and provide information on rates
of deposition of heavy metals. Cadmium concentration declined somewhat with
depth in the sediments of three of six Wisconsin lakes; the surface concen-
trations of cadmium were essentially the same (2.1 to 4.6 ppm). For example,
in Lake Mendota the 0- to 5-cm sample contained 4.4 ppm cadmium, while below
50 cm, 2.7 ppm cadmium was found (Iskandar and Keeney, 1974). The content
of cadmium was below the limit of detection (1 ppm) in analyses of cores
from the Great March of Lewes, Delaware (Strom and Biggs, 1972).
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200
As would be expected, analyses of sediments in the vicinity of pollu-
tion sources indicate that considerable quantities of cadmium are deposited.
Foundry Cove, New York, which received effluent wastes containing cadmium,
nickel, and zinc from a battery manufacturer, contained 39,000 ppm cadmium
at the pollution outfall and 1930 ppm at 90 m below the outfall. These
findings represent extreme values. Cadmium concentration at the outfall
increased with particle size of the sediment, but only 1.3% of the cadmium
was isotopically exchangeable; at the 90-m site approximately 74% was ex-
changeable. These data suggest that cadmium sediments at the outfall may
be present in biota or in such insoluble forms as CdC03; at the 90-m site
the cadmium was adsorbed to either clay or organic materials (Bondietti et
al., 1974). Studies in the Gulf of Finland gave values for sediments rang-
ing from 0.17 to 1.9 ppm cadmium (dry weight); when expressed per unit non-
ash dry weight, unpolluted areas gave values between 4 and 10 ppm, whereas
polluted areas had between 70 and 130 ppm (Jaakkola, Takahashi, and
Miettinen, 1973). Cadmium levels in San Francisco Bay were 1.22 ± 0.99 ppm
for 1- to 7-cm cores and 0.93 ± 0.75 ppm for core depths of 7 to 10 cm (dry
weight basis) (Moyer and Budinger, 1974). These authors estimated the
"global mean value" for sediments to be about 0.5 ppm cadmium. Santa Barbara
Basin cores contained cadmium in concentrations of about 1 to 2 ppm for all
depths down to 20 cm (Bruland et al., 1974).
7.4 ENVIRONMENTAL FATE
Distribution and levels of cadmium in air, water, and land were dis-
cussed in Section 7.3. A variety of chemical, biological, and physical
processes transport cadmium among environmental media with the residence
time in a particular medium depending on the extent of these processes. In
addition, the biosphere can be considered a medium which can accumulate and
concentrate cadmium. Figure 7.6 illustrates the interrelationships among
these media and the various processes involved. Such a diagram does not
stress sources of cadmium in the environment.
7.4.1 Mobility and Persistence in Air
Little information was found on the residence time of cadmium in air.
The observation that concentrations of cadmium in plants and in soils
decrease with distance from the point source of pollution suggests that
removal does occur either b> direct fallout of the dust (or of the CdO) or
through removal by precipitation. Distance of travel and persistence in
air depend on wind direction and velocity, mixing depth, and stability of
the atmosphere. Buchauer (as cited in Friberg et al., 1974) found increased
cadmium levels in soil at distances up to 20 km from a zinc smelter. A
"dispersion factor" which was determined appears to explain the seasonal
distribution of total suspended particles and trace metals in the air over
New York City. The February to April cadmium concentration in Manhattan is
about 2 to 6 ng/m3, whereas the summer concentration is about 10 to 14 ng/m3;
these figures correlate with a lower dispersion factor, the major component
of which appears to be the decrease in atmospheric mixing in the summer
(Kleinman, Kneip, and Eisenbud, 1974).
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201
ORNL-DWG 77-5294R
a:
a:
tu
i-
I
o
u
LU
z
DC
USES
t 14-
ANTHROPOGENIC
ACTIVITIES
fi
h20-
CONTINENTAL CRUST
(0.2 ppm)
IGNEOUS
(0 1-0.2 ppm)
METAMORPHIC
«0.1 ppm)
SEDIMENTARY
(0.1-04 ppm)
1-2
I
WEATHERING
AND
VULCAN ISM
4-5?
SOILS
(0.01-0.7 ppm)
TERRESTRIAL ORGANISMS
NATURAL WATERS
(002-130 ppb)
RIVERS
SUSPENDED
DISSOLVED
GROUND WATERS
KO 7 ppb)
I TERRESTRIAL SEDIMENTS |
i (0.2-20 ppm) i
SEDIMENTATION
CHEMICAL PRECIPITATION
3.5-5 7
DISSOLVED
ESTUARIES AND OCEANS
MARINE GEOCHEMICALSUBCYCLE
(0.01-0.3 ppb)
TYPICAL RANGE OF CON-
CENTRA TIONS SHOWN IN
PARENTHESES. FLUXES
ARE IN 109 gper year.
WHERE NO DA TA ARE
SHOWN, INADEQUATE
INFORMATION IS
AVAILABLE.
\
07
MARINE SEDIMENTS j
(0 2-3 ppm) i
NEARSHORE
SEDIMENTATION
CHEMICAL
PRECIPITATES
PELAGIC
SEDIMENTATION
CHEMICAL
PRECIPITATES
Figure 7.6. Surface geochemical cycle of cadmium. Source: Adapted
from Eaton, 1974, Figure 1, p. 63. Reprinted by permission of the
publisher.
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202
Cadmium-109 has been used as a high-altitude tracer. During the period
from 1964 to 1968, amounts in precipitation peaked in spring and in late
summer to early fall (Ezemenari and Prescott, 1970). Although this pattern
indicates that rainfall removes cadmium from air, few quantitative estimates
of fallout from low-altitude contamination were found. In the Walker Branch
watershed area, the cadmium budget was determined for the first six months
of 1974 (Table 7.14). The wet fall input was considerably greater than the
dry fall input, and for the six-month period the watershed retained about
95% of atmospheric input (Andren et al., 1974; Andren, Lindberg, and Bate,
1975).
7.4.2 Mobility and Persistence in Soil
The cadmium content of soils varies considerably, depending on soil
type as well as the nature of pollution emanating from nearby sources. For
most soils not associated with landfill uses, cadmium removal from air by
dust fall or precipitation and cadmium added by fertilizer application
(Sections 4 and 7.3.3) or sewage sludge (Section 7.5) are the major sources
of soil cadmium. Although few direct data were found, water from rivers or
lakes could add cadmium to soils on flood plains or in areas of extensive
irrigation. In Japan, paddy soil analyses and distribution studies suggested
that cadmium was transported in the form of suspended particles in irrigation
water obtained from a stream passing through a mining area (Yamagata and
Shiegematsu, 1970).
The mobility and persistence of cadmium in soils depend on chemical
form and the physical and chemical characteristics of the soil. Cadmium
is considered a slowly mobile elemer.t because it readily forms insoluble
compounds under oxidizing conditions. In addition, the form deposited from
the air would probably be either CdO or cadmium in larger particulate form.
The observation that the cadmium concentration is highest in the surface
layer of scil (Section 7.3.3) supports the contention that cadmium is rela-
tively immobile.
An important factor determining the form of cadmium in soils is pH.
At low pH values, cadmium compounds are more soluble and, thus, cadmium is
available for plant uptake. At higher values (pH > 8), cadmium in solution
can undergo hydrolysis to form CdOH+ (Hahne and Kroontje, 1973); however,
if any carbonate is available, the insoluble CdC03 will precipitate. Simi-
larly, CdO and CdS are relatively insoluble compounds that decrease the
availability of cadmium in soil. Thus, liming of the soil results in the
formation of insoluble heavy-metal compounds (Section 2.3.2.1). However,
under favorable soil conditions inorganic sulfur compounds can be oxidized
by microorganisms (Alexander, 1961). Microbiological oxidation is far more
rapid than chemical changes at near-optimum moisture and temperature condi-
tions. Thus, sulfides in soil can be made available for plant uptake when
attacked by microorganisms (Fassett, 1972). No specific data could be found
for cadmium release by sulfide oxidation.
Another mechanism for cadmium retention in soil is through ion exchange
reactions with clay and organic matter. Lagerwerff and Brower (1972) stud-
ied exchange adsorption characteristics of different clays and reported that
-------
203
"tire exchange of Cd2+ in A13+- and Cd2+-treated soils was normal in that the
adsorption was greater in the presence of Ca2+ than of A13+, and decreased
with increasing concentrations of A1C13 and CaCl2." Bondietti et al. (1974)
reported that cadmium adsorption by clays and sesquioxides (iron and aluminum
oxides, common constituents of soils) increases with pH. Humic acids of the
soil were also reported to adsorb or complex cadmium.
Clay and organic fractions thus hold cadmium in an exchangeable state
which ultimately may be removed by plants. Wentink and Etzel (1972) referred
to Grim's list of five factors affecting replaceability of cations: (1)
cation concentration, (2) population of exchange positions, (3) nature of
accompanying anion, (4) nature of cation, and (5) nature of clay material.
The observation that the level of heavy metals in soil decreases in
open habitats after closure of the polluting smelter shows that various
processes act to dissipate contaminants. The time for 50% depletion of
cadmium was 1.98 and 2.38 years for two bare-surface sites and 11 years
for a grass-covered area; vegetation growth in previously bare areas is
expected to increase the time required to reach background levels (Roberts
and Goodman, 1974). Processes causing this depletion were not discussed,
but combinations of wind, erosion, runoff, and leaching through soil are
possibilities.
Cadmium leached from soils by water runoff may be carried to regional
groundwater and eventually to rivers. The seepage of cadmium-containing
plating waste from disposal basins to groundwater has been documented in
Long Island, New York. Perlmutter and Lieber (1970) reviewed the movement
and spread of plating wastes derived from chemical solutions used in anodiz-
ing and other metal-plating processes. Intermittently since 1941, plating
wastes containing cadmium, hexavalent chromium, and other heavy metals have
seeped down from disposal basins through the zone of aeration in the soil
and into the zone of saturation in the upper glacial aquifer directly
beneath the basins. The seepage formed a plume of contaminated water about
13,115 m (4300 ft) long and as much as 3050 m (1000 ft) wide and 213.5 m
(70 ft) thick. The plume extended down gradient to the headwaters of Massa-
pequa Creek, which formed a natural drain for part of the contaminated water,
while the remainder moved slowly down gradient as underflow beneath and paral-
lel to the stream channel. After reviewing the significant geochemical fea-
tures of the plume from 1949 to 1962, Perlmutter and Lieber (1970) concluded
that variations in the quality of the water in the plume down gradient from
the disposal basins may be partly attributable to differences in the age and
history of the contaminated water in different parts of the plume. Cadmium
concentrations were found to vary in different areas of the plume; the authors
suggested that variations in concentrations were probably due to changes in
the chemical character of treated effluent and also to the influence of hydro-
logical and geochemical factors. Concentrations of cadmium were generally
less than 1 ppm at most test wells. However, in 1964, samples from one test
site showed 10 ppm cadmium. This concentration was determined in a zone near
the center of the principal path of flow from the disposal basins. Cadmium
lixiviation from buried mine tailings was demonstrated in the Canyon Creek
Basin near Wallace, Idaho (Mink, Williams, and Wallace, 1972).
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204
7.4.3 Mobility and Persistence in Water and Sediments
Cadmium in the dissolved state in water can be expected to undergo
reactions which depend on other constituents of the water. Solubilities
of cadmium compounds are known and the effects of pH and bicarbonate con-
centration have been reported (Hem, 1972) (Section 2.3.2.1). Gardiner (1974)
stated that concentrations of soluble cadmium in fresh water are lower than
the maximum predicted from the solubility data for cadmium carbonate, the
least soluble cadmium salt. Clearly, adsorption to solids is implicated in
removal of cadmium from waters. From the experimental data, Gardiner (1974)
concluded that adsorption onto mud is rapid and can give concentration fac-
tors of 5000 to 50,000, depending upon type of solid, pH, and water hardness.
Humic material in the water seems to be the major component responsible for
this adsorption. Martin (1970) suggested that abundant molted copepod exo-
skeletons (insoluble chitin) can adsorb considerable amounts of heavy metals
from natural waters. Judging from elemental analysis of stream water, rain,
and soils, the source of cadmium dissolved in the Walker Branch Stream,
Oak Ridge, Tennessee (Table 7.14) appears to be precipitation (Andren,
Lindberg, and Bate, 1975).
The fate of any cadmium precipitate or adsorbed cadmium in water depends
on the ability of the particles to settle. In Corpus Christi Bay, Texas, the
water stagnation in summer — along with the inflow of cadmium pollution —
increases the csdmium concentration until CdS is precipitated in the anaerobic
depths of the harbor. With cold air fronts, water mixing occurs and circula-
tion increases between the bay and harbcr; this circulation oxygenates the
water, which results in desorption from precipitates with transportation of
the metals into the bay (Holmes, Slade, and McLerran, 1974). De Groot and
Allersma (1973) found that metals remain fixed to the suspended matter in
river water as long as the water does net mix with the sea. Mobilization
can occur through decomposition of organic matter releasing organometallic
complexes and yielding less contaminated sediments in the lower regions of
deltas.
Data are limited on the fate of cadmium in sediments of bodies of water.
Certainly, a considerable amount is eventually carried to the sea with river
silt and suspended matter. Deep-sea sediments contain from 40 to 580 ppb
cadmium (average 225 ppb) (Aston et al., 1972). Table 7.11 presents data on
the amount of cadmium flow occurring in several rivers. Ultimately, most of
this cadmium enters the sea; cadmium concentration in the seawater is quite
low (about 0.1 ppb) because most cadmium is deposited in deep-sea sediments
(Fleischer et al. , 1974).
7.5 WASTE MANAGEMENT
Disposal of various domestic wastes is an acute problem due to increas-
ing industrialization and urbanization. This section deals with treatment
of certain waste materials that contain cadmium.
-------
205
Major sources of industrial liquid and solid wastes which contain consid-
erable cadmium are (1) the electroplating industry (liquid slurry and sludge),
(2) nickel-cadmium battery manufacturers (sludge), (3) paint manufacturers
(sludge), and (4) paint in old containers (residues to municipal dumps)
(Cttinger et al., 1973). In addition, cadmium dusts and fumes from extrac-
tion, refining, and processing industries constitute a major source of atmos-
pheric cadmium.
Prevention of cadmium emissions to the air is accomplished through the
use of electrostatic precipitators, bag filters, and cyclones (Goeller and
Flora, 1973). The efficiency for capture of particulate emissions is expect-
ed to increase as technology advances in these areas (Adams, 1974; Frey,
1974).
The usual disposal method for concentrated sludges or wastes involves
coagulation with lime, sedimentation, and then filtration through sand.
These residues are then dried and can be placed in approved chemical land-
fills (Ottinger et al., 1973). Depending on cadmium form and concentration
and on technological developments, wastes could theoretically be used for
cadmium recovery, although at present no cadmium is removed for commercial
use.
Conventional sewage treatmert produces two types of discharge: a
treated wastewater effluent and a concentrated sludge. The wastewater is
discharged into bodies of water, but sludge disposal usually involves either
application to land or incineration (Yost et al., 1973). Application of
sewage sludge to cropland and other lands is based on the concepts that (1)
microorganisms will degrade the organic constituents, (2) soil particles
will retain many of the elements of the sludge, (3) soil will serve as a
filtering system to remove solids from the sludge, and (4) nutrients depos-
ited in soil will be available for plant absorption. One of the drawbacks,
however, is the he^avy-metal concentration in sludge — 600 to 900 ppm dry
weight in industrial areas and 10 to 50 ppm in rural communities (Yost et
al. , 1973). Heavy-metal composition of sludge varies considerably; for
instance, samples of sludge from Michigan ranged from 2 to 1100 ppm with a
median of 12 ppm and an average of 74 ppm (Page, 1974). The ranges of metal
content in digested sewage sludge are presented in Table 7.15; average con-
centrations of metals in raw sludge are shown in Table 7.16. The concentra-
tion of cadmium in several industrial sludges is given in Table 7.17.
Because plants absorb heavy metals (Section 4), increased levels in plants
are a potential hazard to humans (Stenstrom and Lb'nsjo, 1974). It has been
shown that when plants are grown on sewage sludge their cadmium content may
be increased (Sections 4.2.2.1.1 and 4.2.2.1.2; see also, however, Section
7.3.3). Chaney (1973) pointed out that toxic metals added to soils are not
a hazard to the food chain until they have entered an edible part of a plant.
However, some direct ingestion of soil containing large amounts of metals may
become a hazard to animals grazing on sludge- or effluent-treated sites.
In a recent literature review, Page (1974) cited information which sug-
gests that cadmium applied in sludge is not mobile and does not move signif-
icantly beyond the depth of tillage. Practices employing deeper tillage
may allow for greater amounts of sludge to be applied per unit area.
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206
TABLE 7.15. RANGE OF
METAL CONTENTS IN DIGESTED
SEWAGE SLUDGE
Element
Zinc
Copper
Nickel
Cadmium
Observed
range
(ppm)
500-50,000
250-17,000
25-8,000
5-2,000
Boron
Lead
Mercury
0.1-40% of Zn
15-1,000
100-10,000
Source: Adapted from
Chaney, 1973, Table 1,
p. 130.
TABLE 7.16. AVERAGE CONCENTRATIONS OF METALS IN RAW SLUDGE
Metal concentration
(mg/kg dry wt)
Metal
Silver
Boron
Cadmium
Calcium
Chromium
Cobalt
Copper
Mercury
Manganese
Nickel
Lead
Strontium
Zinc
Arithmetic
mean
490
880
30
13,800
1,370
700
860
15
1,310
580
1,380
190
1,960
Standard
deviation
370
410
15
7,830
1,400
770
550
23
2,860
540
775
75
1,000
Geometric
mean
355
775
27
11,700
940
410
740
8.2
460
420
1,150
175
1,740
Standard
deviation
2.51
1.67
1.53
1.82
2.75
2.32
1.67
2.54
3.32
2.12
1.95
1.45
1.66
Median
50%
value
<100
805
20
13,900
750
240
660
5.5
200
335
1,150
<100
1,880
a
Standard deviation of the geometric mean is a ratio and has no units.
Source: Adapted from Salotto, Grossman, and Ferrell, 1974, Table 5,
p. 52.
-------
207
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208
Application of sludge containing low concentrations of cadmium can be ex-
pected to enrich the upper regions of the soil over a relatively short period.
Cadmium removal from water effluents can be considered from the view-
point of industrial waters and municipal wastewaters. Treatment for cadmium
removal from various industrial wastewaters usually involves either chemical
precipitation at high pH with lime or use of ion exchange procedures.
Although chemical precipitation is the more common procedure, the use of ion
exchange may become feasible when the product recovery value of cadmium
increases (Watson, 1973). Aqueous wastes from many electroplating plants
are cyanide solutions [Cd(CN)42~] for which improved methods of removal are
needed. Use of quaternary amines followed by organic solvent extraction is
one possible removal system (Moore, Groenier, and Bayless, 1974).
Treated sewage water effluents are discharged into natural waters or
are filtered through soils. Lehman and Wilson (1971) reported that con-
centrations of cadmium and several other heavy metals were "effectively
reduced during percolation through about 8 feet of calcareous soil material
contained in lysimeters." Cadmium was deposited near the surface of the
lysimeter. Field plot studies indicated that the soil can become saturated
with several elements after three years of intermittent flooding; however,
cadmium was not tested in these experiments.
Urban area studies analyzing patterns of wastewater loading are neces-
sary to identify and estimate the relative importance of each source and to
determine trends in the release of materials. Although heavy metals were
not individually characterized, studies for the San Francisco Bay region
indicated that municipal rather than industrial discharges may be the major
source of heavy-metal pollution (Breslaw, 1974). Necessary improvements to
the components of the wastewater pollution control system depend on the major
polluting source for the locale.
Major inputs of pollutants into municipal discharge have been listed
as (1) wastewater treatment effluents, (2) direct domestic and industrial
wastewaters, (3) combined sewer overflow, and (4) storm runoff from urban,
agricultural, and other rural areas (Warren and Bewtra, 1974). These authors
constructed a computer model to study the effects of time-variable pollutant
loads on stream quality.
The Hyperion Treatment Plant in Los Angeles discharges primary effluents,
secondary effluents, and digested sludge into the Pacific Ocean. Approxi-
mately 80% of the cadmium from the primary effluent (28 ppm) was particulate
(sizes greater than 0.22 ym) , while only about 10% of the secondary effluent
(10 ppm) was particulate (Chen et al., 1974). The settling process in sec-
ondary treatment produced a 64% decrease in total concentration of cadmium,
but the soluble cadmium concentration increased from 2.7 ppb in the primary
effluent to 9.0 ppb in the secondary effluent. The distribution of cadmium
in particulate material of the primary effluent was 34% in the 2- to 8-ym
range, 58% in the 8- to 44-ym range, and 10% in the >44-ym range. For
secondary effluents, the corresponding percentages were 32%, 53%, and 15%.
The 0.2- to 0.8-ym particles contained a higher fraction of cadmium than the
larger particles, perhaps due to the relative surface available for adsorption.
-------
209
The electroplating industry releases about 30 kg (65 Ib) of cadmium
daily into the sewage waters of New York; however, analysis of water influ-
ents at 12 major water treatment plants showed a content of about 73 kg
(160 Ib) cadmium per day (from 0.005 to 0.050 ppm). This analysis indicates
that other sources of cadmium discharge exist besides the electroplating
industry. Residential wastewater contained from 0.001 to 0.007 ppm cadmium;
wastewater from other industries varied from 0.006 (fat rendering) to 0.134
ppm (laundry), and surface runoff contained 0.025 ppm cadmium. Thus, electro-
platers accounted for 33% of the cadmium received in influents at water plants,
runoff accounted for 12%, other industries accounted for 6%, and residential
runoff accounted for 49% of total cadmium. Water released into New York
Harbor comes from treatment plant effluents, storm runoff from sewer overflow
and storm sewers, and untreated wastewaters from areas not served by treat-
ment plants (about 43, 50, and 27 kg/day cadmium respectively). Cadmium
content of sludge dumped at the sludge dumping grounds varied from 0.4 to 9.8
ppm. Concentration of cadmium in harbor waters varied between 0.0008 and
0.0055 ppm, compared with open Atlantic Ocean values of 0.0023 ppm. In New
York City, then, nonindustrial sources of water pollution are significant and
complicate efforts to eliminate all discharges of metal. As a result,
release of hazardous metals into societal flow may have to be severely
restricted (Klein et al., 1974).
The Environmental Protection Agency has proposed guidelines for utiliza-
tion and disposal of sludges (Federal Register, 1976). The Metropolitan
Sanitary District of Greater Chicago (Lue-Hing et al., 1977) succeeded by
ordinance in reducing the cadmium content of sludge at its Calumet treatment
plant by 72% over a period of five years. Clearly, it may become necessary
generally to restrict release of hazardous trace metals into societal flow
(Klein et al., 1974).
Another method used to treat sewage secondary effluent is the use of
stabilization ponds. Sediments from these ponds and the aquatic vegetation
in them represent potential sinks for accumulation of contaminating elements.
In a Michigan study, concentrations of chromium, copper, iron, manganese, and
zinc were reduced in these ponds; however, cadmium, cobalt, and nickel were
not affected (Bulthuis, Craig, and McNabb, 1973).
-------
210
SECTION 7
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69. Perhac, R. M. 1972. Distribution of Cd, Co, Cu, Mn, Ni, Pb and Zn
in Dissolved and Particulate Solids from Two Streams in Tennessee.
J. Hydrol. (Netherlands) 15:177-186.
70. Perlmutter, N. M., and M. Lieber. 1970. Dispersal of Plating Wastes
and Sewage Contaminants in Ground Water and Surface Water, South
Farmingdale-Massapequa Area, Nassau County, New York. Geological
Survey Water-Supply Paper 1879-G, U.S. Department of the Interior,
Washington, D.C. 67 pp.
71. Proctor, P. D., G. Kisvarsanyi, E. Garrison, and A. Williams. 1974.
Heavy Metal Content of Surface and Ground Waters of the Springfield-
Joplin Areas, Missouri. Proc. Univ. Mo. Annu. Conf. Trace Subst.
Environ. Health 7:63-69.
72. Ratsch, H. C. 1974. Heavy-Metal Accumulation in Soil and Vegetation
from Smelter Emissions. EPA-660/3-74-012, U.S. Environmental Pro-
tection Agency, Corvallis, Ore. 23 pp.
73. Riley, J. P., and D. Taylor. 1972. The Concentrations of Cadmium,
Copper, Iron, Manganese, Molybdenum, Nickel, Vanadium, and Zinc in
Part of the Tropical North-east Atlantic Ocean. Deep-Sea Res. (Great
Britain) 19:307-317.
74. Roberts, T. M., and G. T. Goodman. 1974. The Persistence of Heavy
Metals in Soils and Natural Vegetation following Closure of a Smelter.
Proc. Univ. Mo. Annu. Conf. Trace Subst. Environ. Health 7:117-125.
-------
216
75. Salotto, B. V., E. Grossman, and J. B. Farrell. 1974. Elemental
Analysis of Wastewater Sludges from 33 Wastewater Treatment Plants
in the United States. In: Pretreatment and Ultimate Disposal of
Wastewater Solids. EPA-902/9-74-002, U.S. Environmental Protection
Agency, New York. pp. 23-72.
76. Schroeder, H. A., A. P. Nason, I. H. Tip ton, and J. J. Balassa. 1967.
Essential Trace Elements in Man: Zinc; Relation to Environmental
Cadmium. J. Chronic Dis. (Great Britain) 20:179-210.
77. Stenstrb'm, T. , and H. Lonsjo. 1974. Cadmium Availability to Wheat:
A Study with Radioactive Tracers under Field Conditons. Ambio
(Norway) 3:87-9C.
78. Stenstrom, T., and M. Vahter. 1974. Cadmium and Lead in Swedish
Commercial Fertilizers. Ambio ("Norway) 3:91-92.
79. Strom, R. N., and R. B. Biggs. 1972. Trace Metals in Cores from
the Great Marsh, Lewes, Delaware. University of Delaware, Newark,
Del. 35 pp.
80. Toca, F. M., C. L. Cheever, and C. M. Berry. 1973. Lead and Cadmium
Distribution in the Particulate Effluent from a Coal-fired Boiler.
Am. Ind. Hyg. Assoc. J. 34(9) :396-403.
81. U.S. Environmental Protection Agency. 1973. Air Quality Data for
Metals, 1968 and 1969. Research Triangle Park, N.C. pp. 4.9-4.13.
82. Warren, J., and J. K. Bewtra. 1974. A Model to Study the Effects
of Time-Variable Pollutant Loads on Stream Quality. Water. Res.
(Great Britain) 8:1057-1061.
83. Watson, M. R. 1973. Cadmium Removal from Water. In: Pollution
Control in Metal Finishing. Noyes Data Corporation, Park Ridge, N.J.
pp. 87-89.
84. Wentink, G. R., and J. E. Etzel. 1972. Removal of Metal Ions by
Soil. J. Water Pollut. Control Fed. 44(8):1561-1574.
85. Williams, C. H., and D. J. David. 1973. The Effect of Superphosphate
on the Cadmium Content of Soils and Plants. Aust. J. Soil Res.
(Australia) 11:43-56.
86. Yamagata, N., and I. Shigematsu. 1970. Cadmium Pollution in Perspec-
tive. Koshu Eiseiin Kenkyu Hokoku (Japan) 19:1-27.
87. Yost, K. J., W. Burns, J. E. Christian, F. M. Clikeman, R. B. Jacko,
D. R. Masarik, W. W. McFee, A. W. Mclntosh, J. E. Newman, R. I. Pietz,
and A. M. Zimmer. 1973. The Environmental Flow of Cadmium and Other
Trace Metals, Vol. 1. Purdue University, West Lafayette, Ind.
pp. 27-42.
-------
SECTION 8
ENVIRONMENTAL INTERACTIONS AND THEIR CONSEQUENCES
8.1 SUMMARY
Various processes interact to redistribute cadmium among land, water,
and air. Organisms can take up cadmium from these media and, in certain
cases, can concentrate it. Because cadmium is a toxic element, it is im-
portant to identify foods with a high cadmium content and food chains in
which biomagnification of cadmium concentration occurs. A variety of foods
have a low, but measurable, cadmium content. In general, the cadmium con-
tent of vegetables and grains reflects that in the soil but does not repre-
sent the same high magnification found in some neritic organisms (especially
oysters). Little comprehensive work has been done on the movement of cad-
mium in food chains, although concentration and radiocadmium data show that
cadmium does move within the various components of an ecosystem.
8.2 ENVIRONMENTAL CYCLING OF CADMIUM
In Section 7 the sources, distribution, and fate of cadmium in air,
water, and land were described. In addition to background levels of cad-
mium from the processes of weathering and extraction from natural deposits,
elevated levels result from various mining, refining, and processing steps
and from disposal of various municipal wastes. Figure 7.6 illustrates the
environmental cycling of cadmium. Fallout of cadmium-containing dust and
its removal by rain deposit cadmium on land and in water. Although the
residence time in these two media may be longer than in air, the condition
is not static. Cadmium can be retained in the soil through adsorption by
clay and organic matter. Ion exchange can occur, however, depending on the
type and concentration of other ions within any percolating solution. This
reaction releases cadmium to the soil solution where it can be leached into
groundwater. Similarly, cadmium in soil is available for plant uptake
(Section 4.2.1). Wastewater discharges (municipal and industrial), as well
as runoff from urban and rural land masses, add cadmium to surface waters.
The cadmium in these waters can be precipitated and deposited in sediments.
Thus, there is a continuing anthropogenic input of cadmium into the environ-
ment with a subsequent complex cycling of the element among environmental
media.
8.3 FOOD CHAINS
8.3.1 Cadmium in Foods
The effects on the environment, particularly the biota, from increased
levels of cadmium — and ultimately the effects on man — are a major concern.
Human exposure to cadmium occurs through food, air, and water. A reasonable
estimate of the average total daily cadmium intake by humans is about 50 pg,
the major part of which is probably contributed by food (Friberg et al.,
1974). Figure 8.1 identifies cadmium concentrations in surface waters,
217
-------
218
ORNL-DWG 71-7262R5
CONCENTRATIONS
ppm
mg/hter— p.g/g
1000
CHRONIC EFFECTS
SOILS 1
4% OF THE
SURFACE WATER
SAMPLES USGS
U S P H S
MAXIMUM IN POTABLE WATER
42% OF THE
SURFACE WATER •
SAMPl ES USGS
Cj4% OF THE
SURFACE WATF Fv
SAMPLES UV,S
EXTRAPOLATED DAILY INTAKE IN
ppm FOR MAN THOUGHT TO
RESULT IN LISTED SYMPTOM
(BASED ON TOTAL DAILY INTAKE OF
1600 g OF FOOD CONTAINING THE
INDICATED CONCENTRATION OF
CADMIUM IN ppm)
GRANGE FOR
II - -J U S INSTITUTIONAL
DIETS I
JINTSU VALLEY
RICE AND SOYA
EXTREME RANGE
OF U S FOODS
L- CRUSTAL
ABUNDANCE
ITAI ITAI DISEASE
0.08
FRIBERG et al
50 YEAR INTAKE
TO CAUSE KIDNEY
DAMAGE
OOOO^ CARIBBFAN SEA WATER
Figure 8.1. Cadmium concentrations of surface waters, soils, and
foods and estimated dose levels resulting in various symptoms and effects
in humans. Source: Hise and Fulkerson, 1973, Figure VI-1, p. 205.
soils, and foods and gives estimated dose levels resulting in various symp-
toms and effects in humans. The maximum tolerable content of cadmium in
drinking water has been established at 10 ppb by the World Health Organiza-
tion and the U.S. Public Health Service, but no maximum limits have been
agreed on for ambient air or foods (Hise and Fulkerson, 1973).
Apparently, the cadmiuir content of food is the major source of cadmium
for most people. Because the foods ingested are diverse, examination of
cadmium movement in a variety of food chains is necessary. The content of
a particular food may vary because of (1) differences in the soil in which
the food was grown and in the cadmium content of the water supply; (2) the
-------
219
type and amount of fertilizer used; (3) the ability of the plant to absorb,
retain, and concentrate cadmium; and (4) the food processing procedures
(Hise and Fulkerson, 1973).
The cadmium content of several foods as well as the zinc-to-cadmium
ratio is given in Table 8.1. Differences in cadmium content of foods due
to regional influences are shown in Figure 8.2. Food plants from the
vicinity of a smelter in Annaka City, Japan, had much higher cadmium
contents than plants grown in uncontaminated areas (Kobayashi, 1972).
Zook, Greene, and Morris (1970) found significant differences in the cad-
mium content of wheat grains, but they concluded that "no geographical
population of the United States should be expected to differ markedly from
another in its status of mineral nutrition, solely on the basis of consump-
tion of wheat products." Lagerwerff (cited in Sanjour, 1974) suggested
that the principal source of cadmium in vegetables is the natural cadmium
content of the soil. Sanjour (1974) supported this contention with the
following statements:
1. Air levels of cadmium in rural areas are often unmeasurable.
2. Even in urban areas not near smelters, the air concentrations are low
enough not to significantly affect soil concentrations.
3. There are few serious point sources of contamination, and the radius
of effect is about 8 to 24 km.
4. Irrigation water generally has a cadmium concentration too low to
affect soil concentrations.
In a. recent review of cadmium levels in food, Friberg et al. (1975)
cited analyses performed by Kjellstrb'm in which the cadmium content of
Swedish wheat samples, harvested in one geographical area, increased over
the years 1916 to 1972. Friberg et al. (1975) suggested that some mete-
orological, agricultural, or pollution factor, or a combination of such
factors, could explain the observed differences in cadmium concentrations.
Kjellstrom et al. (1975) concluded that the increase in the average cadmium
concentration in fall wheat may be caused by accumulated effects of air
pollution and fertilizers. Statistical analyses performed by Kjellstrom
et al. (1975) did not reveal any correlation between cadmium concentration
and yield, average summer temperature, average summer rain, or type and
amount of fertilizer applied.
A Swedish study on the contribution of land application of sewage
sludge to crop plants suggested that an increased use of sewage sludge will
increase the cadmium content of wheat (Linnman et al., 1973). These authors
estimated that a moderate increase in the cadmium content of wheat flour in
the range of 0.02 to 0.10 ppm would raise average intake of cadmium from
cereal to 17 yg per day (assuming an average individual cereal consumption
of 166 g/day). However, since for various broad food groups ninth decile
figures can exceed the mean consumption by a factor of 3.5, the cadmium
intake from cereals may be as high as 58 yg/day for some people.
-------
220
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50
CADMIUM Ippm)
40 30 20
10
56 .
61 •
ORNL DWG 77 5295
CADMIUM Ippm)
0 10 20
GREENS (USED FOR SALTING)
GREENS (DAMAGED)
OUTER LEAVES OF CABBAGES (1200 m)
INNER LEAVES OF SAME CABBAGES
CHINESE CABBAGES (450 m)
WELSH ONIONS (500 m)
LEAVES OF RADISHES (1200 m)
LEAVES OF TURNIPS (450 m)
ASPARAGUS (500 m)
GRASS FOR COWS (350 m)
POTATOES (850 m)
TARO POTATOES
CARROTS (700 m)
RADISHES (1200 m)
TURNIPS (450 m)
BURDOCK
TOMATOES
FRUIT OF EGGPLANT
PUMPKIN
CORN
AZUKI BEANS
WHEAT FLOUR (1500 m)
BARLEY FLOUR (1500 m)
MOSS
SAMPLES FROM
UNPOLLUTED AREA
Figure 8.2. Cadmium content in various food samples collected in
October 1968 and June 1969 in Annaka City, Japan, compared with unpolluted
samples. Numbers in parentheses indicate distances from the smelter.
Source: Adapted from Kobayashi, 1972, Figure 5, p. 123. Reprinted by
permission of the publisher.
The use of cadmium-containing fungicides has reportedly led to in-
creased levels in plants. After a single application of a cadmium-contain-
ing fungicide to apple trees, cadmium accumulated in fruits and decreased
in foliage during the growing season (Ross and Stewart, 1969). Although
several fungicides contain cadmium, information is lacking on the uptake
of cadmium from these fungicides and on its persistence in plants.
In order to understand and evaluate the effects of cadmium, a descrip-
tion of a food web for man is necessary. To identify stages in which bio-
concentration, bioaccumulation, and/or biomagnification of cadmium occur,
consistent definitions of these terms are necessary (Kneip and Lauer, 1973);
1. Bioconcentration — the ability of the organism to concentrate a sub-
stance from an aquatic system
2. Bioaccumulation — the ability of an organism not only to concentrate
but to continue to concentrate throughout its metabolic lifetime
-------
3.
223
Biomagnification — refers to the substance being found at successively
higher concentrations with increasing trophic levels in the food chain
A simplified food web for man is diagrammed in Figure 8.3. Because
man is basically an omnivore, the cadmium content and concentration factors
for a number of specific food chains should be estimated. For food web
considerations, all ecosystems can arbitrarily be divided into terrestrial
and aquatic ecosystems. Data on cadmium movement through these ecosystems
are presented in Sections 8.3.3 and 8.3.4.
ORNL-DWG 77-5296
AIR AND WATER INGESTIOIN
OF CADMIUM
Figure 8.3.
and movement.
Generalized food web for man showing cadmium introduction
8.3.2 Cadmium in Cigarettes
Because smoking contributes to the body burden of cadmium (Section
6.2.1.1), it is of interest to know whether there have been changes in the
cadmium content of cigarettes with time (Friberg et al., 1975). Such a
study has been conducted by Linnman, Lind, and Kjellstrb'm (1974, cited in
Friberg et al., 1975). Eighteen brands of cigarettes produced in the years
1918 to 1968 were analyzed and, with one exception, the concentrations were
similar to those found today, with no tendency toward an increase
(Figure 8.4).
Friberg et al. (1975) also referred to the work of Elia, Menden, and
Petering (1973) in which lettuce leaf cigarettes were examined. The average
cadmium content was 1.39 yg per cigarette. These cigarettes were smoked in
a smoking apparatus using a standardized procedure. In the mainstream
smoke, only 0.01 to 0.02 yg was found — less than is found in ordinary
cigarettes. On the other hand, these cigarettes emitted more cadmium via
the sidestream than standard cigarettes. In 1972, Menden et al. reported
that 38% to 50% of the cadmium from the smoked portion of ordinary ciga-
rettes is present in the sidestream. Thus, cadmium in the sidestream
smoke of both lettuce leaf and ordinary cigarettes may present a health
hazard to nonsmokers in the vicinity of the smoker, as well as to the
smoker (Menden et al., 1972).
-------
224
ORNL-DWG 77-5297
o
o
••
•:.*
1920 1930 1940 1950
YEAR
1960
1970
T?±guice 8.4. Cadmium concentration in cigarettes of different ages,
Source: Adapted from Linnman, Lind, and Kjellstrom, 1974, as cited in
Friberg et al., 1975, Figure 3:2. p. 3-24. Reprinted by permission of
the publisher.
8.3.3 Terrestrial Ecosystems
Numerous studies have shown that plants take up cadmium; generally,
the concentration in plants grown in high cadmium soils is greater than
in those grown in low cadmium soils. The cadmium content differs in various
parts of the plant; roots often have the highest concentration (Section
4.2.2).
Minerals taken up by plants are distributed throughout the plant and
can be returned to the ground either through leaching of the foliage or
through removal and decay of portions of the plant. Witherspoon (as cited
in Huckabee and Blaylock, 1973) injected 109Cd into tree trunks and two
months later found 36.8% of the activity in the branches, 34.6% in the
trunk, and 28.5% in the foliage; 0.1% of the activity was leached from the
tree by rain. Of this leached activity, 2.7% was in understory vegeta-
tion, 68% was in the litter, and 29.3% was in the soil. A study of cadmium
cycling in an old field ecosystem (109CdCl2 added in water spray) showed
that the initial accumulation was greatest in the soil and litter and that
subsequent loss from the litter resulted from decay. Most of the soil
radiocadmium was in the surface layers and increased with time due to
leaching from the vegetation (Matti, Witherspoon, and Blaylock, 1975).
Thus, cadmium can be leached from vegetation into the soil and litter
layers where it is available for uptake by various plants, microbes, and
soil invertebrates. In addition, biological breakdown of plant materials
introduces cadmium into various decomposer organisms. These soil-dwelling
organisms are components of many complicated food chains and the cadmium
they take up is potentially available for organisms at the next trophic
-------
225
level. For example, data from an invertebrate grassland food chain (Table
8.2) show that although both an omnivore and a predator contained cadmium, .
no biomagnification or concentration occurred (Anderson et al., 1974).
Earthworms may represent an important source of cadmium in terrestrial
food chains. Cadmium levels in six soils were between 0.23 and 0.80 ppm,
whereas in earthworms the concentration ranged from 2.1 to 9.3 ppm — a con-
centration factor of over 10. This reflects bioconcentration of cadmium in
the earthworm; the latter, in turn, may serve as source of cadmium for
higher trophic levels (Van Hook et al., 1974). Soil samples consisted of
only the top 10 cm of soil with vegetation removed. Cadmium is generally
bound to organic matter in the soil and earthworms digest this material;
therefore, it is possible that the concentration factors presented in this
study may be too high to the extent that reported soil values are too low.
In addition to accumulating cadmium, earthworms are responsible for consid-
erable mechanical mixing of soil and thus tend to bring about a uniform
cadmium distribution (Anderson et al., 1974).
Because the amount of cadmium taken up by plants depends on soil con-
centrations, plants growing in the vicinity of smelters often have higher
cadmium concentrations. Animals feeding in these vicinities are therefore
likely to contain higher than normal concentrations of cadmium. For
instance, in the smelter region of East Helena, Montana, mammalian hair
TABLE 8.2. CONCENTRATIONS OF CADMIUM ADDED TO FIELD PLOTS
AS 109Cd(N03)2 IN FOUR GRASSLAND COMMUNITY
FOOD CHAIN COMPONENTS
Cadmium „
_,,.,.. . Concentration
Trophic level concentration . /•,
* . N ratio"
(ppm)
Predator — Lyoosa (spider) 0.030
_^>~ 0.71
Omnivore — Ptevonemob'ius (cricket)
Living and dead vegetation (mean)
Living vegetation
Dead vegetation
Soil
Ratio of cadmium (ppm) in trophic level (n) to that in trophic
level (n — 1).
Source: Adapted from Anderson et al., 1974, Table 5.2.17,
p. 124.
-------
226
contained high concentrations of arsenic, cadmium, and lead; livestock,
especially horses, exhibited symptoms of heavy-metal poisoning and contained
high levels of cadmium in liver and kidney (Smith and Huckabee, 1973).
A study of cadmium, copper, lead, and zinc contamination at a test
farm in the lead-producing region of southeast Missouri showed that the high
lead and cadmium content in dust and air was due to smelter stack emissions,
ore concentrate spillage, and dust from stockpiled ore. Concentrations in
roots were significantly increased at the test farm as were the contents in
the washed tops of the plants. Cattle hair, liver, and kidney contained
higher cadmium and lead concentrations at the test farm (University of
Missouri, 1973). Herbivores may obtain cadmium not only from plant materials,
but also, especially in the case of sheep, from direct ingestion of soil.
In a study of a Montana grassland ecosystem near a smelter that pro-
cessed zinc ore, Munshower (1972) presented data for cadmium concentration
in autotrophs and herbivores. Total soil cadmium concentrations were high
near the smelter; they decreased with depth in the soil. At soil pH 5.8
more cadmium could be leached (0.87% total) by simulated rain than at pH of
6.4 or 7.2 (0.01% to 0.04%). The cadmium content of grass (1 to 2.4 ppm)
was similar in a region near the smelter (1.6 to 6.4 km) and in one farther
removed (19 to 24 km). Shrubs and willows contained higher concentrations
(5.6 and 13.7 ppm respectively) at the closer sites than at the more distant
sites (1.9 and 1.7 ppm). Cadmium was not accumulated to concentrations
greater than that of 1 N HC1 extracts of the soil (50% to 75% to total soil
cadmium concentration). Grasshoppers (herbivores) accumulated cadmium to
levels above that of the plants on which they grazed; thus, grasshoppers
near the smelter contained more cadmium than those farther away. Examina-
tion of three species of grasshoppers and their predominant food plants
shewed cadmium accumulation ratios to be less than 2. For other herbivores
examined, "maximum concentrations recorded in cattle, swine, and ground
squirrel kidneys were evidence of the accumulation of cadmium in this organ
to levels two or more times the cadmium levels found in the food supply of
the animal."
Few other studies were found concerning cadmium movement in ecosystems
with higher herbivores and omnivores. Lichens in Kokkola, Finland, con-
tained 1 ppm cadmium near a zinc refinery and between 0.3 and 0.4 ppm in
other areas (Jaakkola, Takahashi, and Miettinen, 1973). Elk and reindeer
also contained measurable amounts of cadmium in the organs examined, although
no comparisons were made with animals from other areas. Andren et al. (1973)
reported cadmium concentrations in a variety of organisms in different
trophic levels of a forest ecosystem (Figure 8.5). Except for insects
and earthworms, no group of organisms showed a clear concentration increase
in the food chain.
Because grains, seeds, earthworms, and other invertebrates all contain
cadmium, a variety of birds are exposed to a range of cadmium concentrations.
The cadmium content of starlings (Sturnus vulgaris) collected throughout the
United States ranged from levels of less than 0.05 ppm to 0.24 ppm (wet
weight); 72% of the samples contained the lower limit or less. No compara-
tive data are available, so trends in time and space cannot be established
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227
ORNL-DWG 72-14437
SUBSTRATE
PRODUCERS
CONSUMERS
PREDATORS
OMNIVORES
Figure 8.5. Metal cadmium concentrations (ppm dry weight) in selected
trophic levels of a deciduous forest ecosystem in East Tennessee. Source:
Andren et al., 1973, Figure 4.2.15, p. 92.
(Martin and Nickerson, 1973). Information on the cadmium content of each
food and on the proportion of each food in the diet is necessary before
concentration or accumulation can be determined. No data could be found
giving this information for bird food chains.
Studies of the cadmium and other heavy-metal contents of the litter
layer in the Crooked Creek watershed near the American Metal Climax, Inc.
lead smelter suggested that the high concentrations found "may reduce or
eliminate certain bacterial, fungal, and arthropod populations thereby re-
ducing decomposition rates" (Andren et al., 1974).
8.3.4 Aquatic Ecosystems
Several studies of cadmium concentrations in aquatic ecosystems have
been reported. Before citing selected data, it is important to determine
the information required for development of useful models for the environ-
mental cycling of contaminating minerals. Wolfe and Rice (1972) detailed
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228
the following major sets of information necessary for estimating mineral
reservoirs in estuaries:
1. Relative amounts of different physicochemical forms of an element
or radioisotope in natural waters, their relative stabilities, and
the ease of interconversion between the various forms
2. The relative biological availabilities of these different physico-
chemical forms to various types of biota
3. The trophic structure of the entire ecosystem (particularly the
role of microorganisms as sources of metallic elements to consumers
in detritus-based food chains, as producers of organic-metal com-
plexes, and as remineralizers of metals previously incorporated
into plant or animal tissues)
4. Feeding rates and assimilation efficiencies for carbon and metallic
elements at each major trophic interaction
5. Biological retention of metallic elements in the major organisms
consumed by man
6. The interactions of variable environmental parameters on reservoir
size and transfer rates at each step in the overall system
This information is necessary to determine the extent of mineral cycling
for any type of ecosystem. Although some data exist for cadmium on items
1 and 2 for several ecosystems, no studies were found in which all points
of information were determined for the same ecosystem.
Phytoplankton is an integral part of many aquatic food chains. Samples
from Monterey Bay, California, were found to have increased cadmium concen-
trations after periods of peak productivity (Knauer and Martin, 1973). Un-
like copper, lead, manganese, or zinc, sufficient cadmium was apparently
taken up by phytoplankton to decrease the concentration of the metal in the
water. During periods of upwelling, metal concentrations in the plankton
were high and variable. Wissmar (1972) showed that concentrations of cad-
mium, copper, and zinc could synergistically interact to decrease carbon
dioxide fixation. This finding raises the possibility of toxic effects in
rivers or lakes containing such metals. Of course, a variety of other fac-
tors such as presence of other minerals, pH, oxygen, and tension, must also
be considered.
Brooks and Rumsby (1965) found that cadmium was highly enriched in the
scallop (by a factor of 2,260,000) and in the oyster (by a factor of
318,000) as compared with seawater. Actual whole-body levels in the soft
parts of these shellfish taken from the Tasman Bay, north of Nelson, New
Zealand, averaged 249 ppm dry weight in the scallop and 35 ppm dry weight
in the oyster. Cadmium was not detected in the mussel (limit of detection
20 ppm). Essentially all cadmium in the scallop was located in the visceral
mass, which includes the gut content, whereas in the oyster most cadmium was
located in the mantle, heart, kidney, and striated muscle.
Kopfler and Mayer (1973) attempted to relate water concentrations of
various metals in Mobile Bay, Alabama, to their concentrations in oysters.
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229
Bay water contained 0.3 to 0.6 ppb cadmium, while cadmium in oysters from
different locales ranged from 0.46 to 1.04 ppm wet weight (overall average
0.62 ppm). Although bioconcentration occurred, high values in oysters could
not be correlated statistically with high cadmium values in water. Atlantic
Coast oysters contained cadmium concentrations about five times as high
(average 3.10 ppm) as the oysters in Mobile Bay. The poor correlation be-
tween concentration of cadmium in water and its accumulation in oysters may
be due to particulate cadmium ingestion by the Atlantic Coast oyster.
Bender, Huggett, and Slone (1972) reported that Chesapeake Bay oysters con-
tained from <0.6 ppm to >2.5 ppm cadmium. They speculated that heavy-metal
concentrations in sediments and/or salinity of the water may have affected
metal uptake by the oysters.
The experimental addition of sewage sludge and urea fertilizers to
salt marsh plots on the East Coast did not affect growth of oysters (Cras-
sostvea virginiaa) or clams (Meraenaria mevcenaria) but did increase the
cadmium content of each (Valiela, Banus, and Teal, 1974). In the Bristol
Channel, the cadmium content of Patella (clam) was related to physical size;
the cadmium content of samples was highest near the largest population cen-
ters (Nickless, Stenner, and Terrille, 1972).
Uptake of cadmium by the Mediterranean mussel and benthic shrimp was
measured with 109Cd (Fowler and Benayoun, 1974). Radiocadmium concentra-
tions were greatest in the viscera and muscle of both organisms; elimina-
tion of the cadmium was very slow.
In an artificial marine microcosm, oysters (Crassostrea), clams
(MeToenar-ia), sand worms, grass shrimp, and filamentous green algae were
exposed to flowing water containing 50 ppb cadmium (CdCl2) (Kerfoot, 1973).
Results after 67 days of exposure and 14 days of flushing with fresh sea-
water are shown in Table 8.3. The largest percentage of total cadmium was
found in oysters and sediments.
In summary, there is good evidence that oysters concentrate cadmium
above ambient levels. This behavior becomes especially important where the
background cadmium is raised, usually as a result of human activity.
Several studies have been made on the cadmium content of fish. Lovett
et al. (1972) listed the cadmium content of 406 freshwater fish from New
York waters (selected examples in Table 8.4); values were usually below
20 ppb, although values higher than 110 ppb were occasionally found. Fish
from the Adirondack area often contained greater than 20 ppb cadmium; these
higher concentrations may be related to the higher background cadmium level
of this area. Trout of various ages from Cayuga Lake had about the same
cadmium content; thus, accumulation could not be demonstrated. Windom et
al. (1973) reported that inshore and offshore species of chondrichthyes and
osteichthyes had similar cadmium contents. The mean cadmium concentration
in deep-sea fish off Great Britain was 50 ppb, although values up to 150
ppb were found (Portmann, 1972).
In aquarium tests, the cadmium content of bluegills after a two-month
exposure to nonlethal water concentrations of 0.5 ppb and 8.0 ppb cadmium
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230
TABLE 8.3. OBSERVED RETENTION OF CADMIUM IN SEDIMENT, SHELLS, AND
ORGANISMS OF A SYNTHETIC MARINE MICROCOSM
Component
Algae
Shellfish
Oysters
Clams
Shrimp
Sand worms
Shells
Sand
Total
weight
(g)
6.3
236
76
40
12
439
5997
Cadmium content
(yg)
Original
2.5
274.2
7.6
3.2
0.7
174.0
119.9
Final
265
3616
46
340
54
225
6240
„ , . Percent
Cadmium
n . a of
accumulation ..
, , total
8' cadmium
262
3342
38
336
53
51
6120
2.6
32.8
0.4
3.2
0.5
0.5
60.0
a.
Final content minus original content.
Source: Adapted from Kerfoot, 1973, Table 2, p. 6.
was 4 ppb and 30 ppb (ash samples) respectively. No further increase in
concentration was observed over an additional four-month period. Further
accumulation after two months of exposure was not demonstrated even at the
toxic cadmium concentrations of 80 and 850 ppb in water (fish contents
abcut 0.1 ppm and 1 ppm respectively) (Cearley and Coleman, 1974).
A direct relationship between cadmium pollution and cadmium content of
fish is suggested by the studies of Jaakkola et al. (1972). "Unpolluted"
seawater contained 0.1 to 0.2 ppb cadmium as compared to 0.5 ppb in polluted
areas. Corresponding concentrations for cadmium in the sediments were 3 to
10 ppm and 15 to 130 ppm. Pike muscle from unpolluted areas contained 2 to
3 ppb compared to 4 to 13 ppb in polluted areas. Kidney and liver samples
contained about 10 to 50 times these levels. The trend appears to be toward
increased cadmium levels in fish from polluted areas.
In pilot studies, Landner and Jernelbv (1969) could not demonstrate
increased cadmium content in guppies over a five-week period in which their
only food source was Tubifex oligochaetes containing 0, 10, or 20 ppm cad-
mium. Guppies in water with 100 ppb cadmium did accumulate cadmium; how-
ever, when they were transferred to cadmium-free water, the concentration
decreased considerably over a four-week period.
Cadmium was detected by Leatherland and Burton (1974) in a variety of
organisms from the "not grossly polluted" Southampton water and The Solent
(Great Britain); however, no implications regarding specific food chains
were stated (Table 8.5). These workers analyzed the muscle from three
-------
TABLE 8.4,
231
RESIDUES OF TOTAL CADMIUM IN FISH FROM
NEW YORK STATE WATERS, 1969
Location
Blue Mountain Lake
Butterfield Lake
Canadice Lake
Hudson River
Lake Ontario
Lake Placid
Skaneateles Lake
Spring Brook
Species
Bullhead catfish
Rainbow trout
Smallmouth bass
Bowf in
Bullhead catfish
Largemouth bass
Northern pike
Rock bass
Smallmouth bass
Sucker
Walleye pike
Bullhead catfish
Lake trout
Pickerel
Rainbow trout
Rock bass
Smallmouth bass
Atlantic sturgeon
Goldfish
Shortnose sturgeon
Striped bass
Black crappie
Carp
Coho salmon
Rock bass
Smallmouth bass
Splake
Sucker
White bass
Largemouth bass
Brook trout
Lake trout
Rainbow trout
Coho salmon
Number
of
fish
3
2
1
1
3
3
4
2
2
1
3
1
1
2
2
1
5
4
3
1
6
1
1
21
4
10
1
2
1
1
1
2
2
3
Cadmium
residue
(ppb fresh wt)
Mean
27.3
24.0
22.0
16.0
18.7
20.0
44.7
36.0
21.5
20.0
16.3
18.0
<10
11.5
15.5
14.0
13.0
91.5
142.7
12.2
15.0
<10
13.5
17.2
13.6
<10
23.5
<10
13.0
23.0
28.5
16.0
16.3
Std
error
6.1
0.3
1.1
13.6
2.8
1.5
21.7
21.5
1.11
0.8
3.3
1.3
4.9
(continued)
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232
TABLE 8.4 (continued)
Cadmium
Location
St. Lawrence River
Susquehanna River
Trout Lake
Upper Saranac Lake
Utowana Lake
Waneta Lake
West Canada Lake
Species
Brown bullhead
Muskie
Smallmouth bass
Sturgeon
Walleye pike
Walleye pike
Yellow perch
Chain pickerel
Smallmouth bass
Largemouth bass
Smallmouth bass
Rainbow trout
Muskie
Lake trout
Number
of
fish
3
1
6
11
4
1
2
3
1
2
2
2
1
2
residue
(ppb fresh wt)
Mean
23.0
30.0
24.8
26.2
14.5
64.0
51.0
14.3
17.0
14.0
12.5
17.0
14.0
30.0
Std
error
8.7
3.4
1.3
1.4
Source: Adapted from Lovett et al., 1972, Table 2, pp. 1286-
1289. Reprinted by permission of the Journal of the Fisheries
Research Board of Canada.
species of fish and concluded that no apparent bioconcentration of cadmium
occurred in these organisms. The cadmium concentration in the fish muscle
was 0.03 ppm.
Mummichogs (Fundulus heteroclitus) , accumulated 1-15r71Cd from synthetic
seawater solutions, "but the rate of the whole body accumulation decreased
with increasing concentrations of stable cadmium in the medium." The
muscle did not accumulate cadmium, but the viscera, liver, and gills did
(Eisler, 1974).
It is difficult to generalize about the cadmium content of fish. Some
fish seem to concentrate cadmium, but little information is available on
bioaccumulation during the lifetime of the organisms. Concentrations for
whole fish may be misleading because some organs concentrate cadmium more
than others. In addition, the feeding habits of fish may influence the
content of cadmium. For instance, in the Severn Estuary, Great Britain, a
direct relationship was found between the cadmium content of fish and the
proportion of crustaceans in their diet (Hardisty, Kartar, and Sainsbury,
1974).
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233
TABLE 8.5. CADMIUM IN ORGANISMS FROM WATERS OF THE SOUTHAMPTON
AND THE SOLENT AREAS OF ENGLAND
Organism
Location
Cadmium
content
(ppm dry wt)
Algae, Phaeophyceae
Lam-inar*ia digitata
Laminaria saecharina
Halidrys siliquosa
Porif era
panicea
Coelenterata
Tealia felina
Decapoda
Palaemon elegans
Gastropoda
Patella vulgata
Littorina littovea
Crep-idula fornioata
Lamellibranchia
Mytilus edulis
Cephalopoda
Sepia offioinalis
Gills
Mantle
Tunicata
Botryllus sshlosseri
Pisces
Angu-illa angu-illa, muscle
Marone Idbrax, muscle
Platiehthys flesus , muscle
Lee
Lee
Lee
Lee
Hamb1e
Hamble
Netley
Town Quay
Town Quay
Town Quay
Solent
Solent
Town Quay
Marchwood
Gilkicker Point
Marchwood
0.15
0.35
0.43
0.85
0.07
0.31
2.7
0.94
1.4
2.5
0.11
0.03
2.7
0.03
0.03
0.03
Source: Adapted from Leatherland and Burton, 1974,
Table 2, p. 465. Reprinted by permission of the publisher.
A portion of the cadmium released into terrestrial ecosystems eventual-
ly reaches aquatic ecosystems and the effects and extent of this input
should be determined. In a microcosm experiment, 115mCdCl2 was applied to
two terrestrial ecosystems in a simulated rainfall and a total radiocadmium
budget was determined 27 days later (Huckabee and Blaylock, 1973). The
results (Table 8.6) showed that 3.4% and 4.5% of the cadmium entered the
aquatic ecosystem. The fate of radiocadmium in the water was followed by
a stream tag experiment which indicated that cadmium enters all components
of the aquatic ecosystem (Figure 8.6).
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234
TABLE 8.6. DISTRIBUTION OF 284 yd 115mCdCl2
MICROCOSMS 27 DAYS AFTER TAGGING
IN
Microcosm A
Component
Terrestrial
Moss
Higher plants
Litter
Soil
Aquatic
Water
Sediment
Fish
Snails
Watercress
Plastic liner
1 1 5mcd
(yci)
28.90
0.38
43.40
193.50
0.52
8.93
<0.01
0.22
0.02
7.89
Activity
(%)
93.8
10.2
0.1
15.3
68.1
3.4
0.2
3.1
<0.1
0.1
<0.09
2.8
Microcosm B
1 1 5mcd
(yCi)
23.34
0.78
30.20
218.00
0.56
8.63
<0.09
0.14
0.04
3.26
Activity
(%)
95.5
7.9
0.3
10.6
76.8
4.5
0.2
3.3
<0.1
<0.09
<0.09
1.1
Source: Adapted from Huckabee and Blaylock, 1973,
Table 5, p. 137.
ORNL-DWG 73-I86R
10 20 30 40 50 60 70 80
Figure 8.6. Mean activity in stream ecosystem components after labeling
with 109CdCl2. Composite samples for sediments, snails, and periphyton.
Source: Huckabee and Blaylock, 1973, Figure 10, p. 151.
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235
SECTION 8
REFERENCES
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34. Ross, R. G., and D.K.R. Stewart. 1969. Cadmium Residues in Apple
Fruit and Foliage following a Cover Spray of Cadmium Chloride.
Can. J. Plant Sci. (Canada) 49:49-52.
35. Sanjour, W. 1974. Cadmium and Environmental Policy. U.S. Environ-
mental Protection Agency, Washington, D.C. 22 pp.
36. Schroeder, H. A., A. P. Nason, I. H. Tipton, and J. J. Balassa.
1967. Essential Trace Metals in Man: Zinc; Relation to Environ-
mental Cadmium. J. Chronic Dis. (Great Britain) 20:179-210.
37. Smith, R. H., and J. W. Huckabee. 1973. Ecological Studies of
the Movement, Fate, and Consequences of Cadmium. In: Cadmium,
the Dissipated Element, W. Fulkerson and H. E. Goeller, eds.
ORNL/NSF/EP-21, Oak Ridge National Laboratory, Oak Ridge, Tenn.
pp. 278-322.
38. University of Missouri. 1973. Study of Lead, Copper, Zinc and
Cadmium Contamination of Food Chains of Man. EPA-R3-73-034, Environ-
mental Protection Agency, Durham, N.C. 117 pp.
39. Valiela, I., M. D. Banus, and J. M. Teal. 1974. Response of Salt
Marsh Bivalves to Enrichment with Metal-Containing Sewage Sludge
and Retention of Lead, Zinc and Cadmium by Marsh Sediments.
Environ. Pollut. (Great Britain) 7(2) : 149-157.
40. Van Hook, R. I., Jr., B. G. Blaylock, E. A. Bondietti, C. W. Francis,
J. W. Huckabee, D. E. Reichle, F. H. Sweeton, and J. P. Witherspoon.
1974. Radioisotope Techniques to Evaluate the Environmental Behavior
of Cadmium. In: Comparative Studies of Food and Environmental Con-
tamination. International Atomic Energy Agency, Vienna. pp. 23-42.
41. Windom, H., R. Stickney, R. Smith, D. White, and F. Taylor. 1973.
Arsenic, Cadmium, Copper, Mercury, and Zinc in Some Species of
North Atlantic Finfish. J. Fish. Res. Board Can. (Canada)
30(2) -.275-279.
42. Wissmar, R. C. 1972. Some Effects of Mine Drainage on Primary
Production in Coeur D'Alene River and Lake, Idaho. Ph.D. Disser-
tation. University of Idaho, Moscow, Idaho. 61 pp.
43. Wolfe, D. A., and T. R. Rice. 1972. Cycling of Elements in Estu-
aries. Natl. Oceanic Atmos. Adm. (U.S.) Fish. Bull. 70(3):959-972.
44. Zook, E. G., F. E. Greene, and E. R. Morris. 1970. Nutrient Com-
position of Selected Wheats and Wheat Products: VI. Distribution
of Manganese, Copper, Nickel, Zinc, Magnesium, Lead, Tin, Cadmium,
and Selenium as Determined by Atomic Absorption Spectroscopy and
Colorimetry. Cereal Chem. 47(6):720-738.
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SECTION 9
ASSESSMENT OF THE EFFECTS OF CADMIUM IN THE ENVIRONMENT
9.1 INTRODUCTION
Cadmium is a relatively rare element usually present in small amounts
in zinc ores. It is commercially obtained as a by-product of the zinc-,
copper-, and lead-producing industries. Trace amounts of the metal are
also found in fossil fuels, in most soils, and in phosphate rock used for
the production of agricultural fertilizers. Cadmium is introduced into
the environment chiefly during extraction, refining, and production of
metallic cadmium, zinc, lead, and copper; through the wastes generated
during other metallurgical processes such as electrolytic plating; through
the reprocessing of scrap metal such as cadmium-plated steel; and follow-
ing disposal by combustion or as solid waste from many consumer goods
(paints, nickel-cadmium batteries, plastics, etc.). Cadmium also enters
the environment as a result of the agricultural use of cadmium-containing
fungicides, phosphate fertilizers, or municipal sewage sludges.
The metal is relatively volatile, and fumes as well as dusts can be a
significant source of pollution, especially in industrial surroundings;
nevertheless, its major impact on animals and man follows oral ingestion.
Tobacco smoke is a significant additional source of cadmium exposure. The
potential health risks posed by oral exposure relate to the fact that in
spite of the relatively low gastrointestinal absorption of cadmium, its
biological half-life is very long. In effect, the metal acts as a cumula-
tive poison, and its long-range chronic effects should be considered.
This section assesses the significance of the various modes of entry of
cadmium into the environment and the consequent health effects on animals
and man. The assessment is based on information collected and discussed
in Sections 2 through 8 as well as on some additional references cited at
the end of this section.
9.2 NATURE, SOURCES, AND EXTENT OF CADMIUM POLLUTION
9.2.1 Analytical Problems
Analytical methods that require relatively little or no pretreatment
of samples and that permit assay of cadmium at levels as low as 1 ng/g
(1 ppb), a sensitivity adequate for most purposes, are now available. It
must be emphasized that variability of results at such low levels may, to
a significant extent, reflect problems of sampling, sample storage, or
matrix effects. Both sampling and storage techniques, as well as analyt-
ical procedures, therefore require continued careful standardization.
Insufficient attention has been given to the problem of distinguishing
between the various chemical forms in which cadmium may occur in the environ-
ment or in biological specimens. Occurrence of different forms of cadmium
becomes of special importance when, as in many instances, the toxicity or
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toxicological significance for different compounds may greatly differ.
This fact, for instance, makes the choice of a critical total cadmium
concentration in the renal cortex a somewhat arbitrary value.
9.2.2 Domestic Production and Import
In 1968 the U.S. consumption of cadmium was approximately 6000 metric
tons. About 77% of this total (4600 metric tons) was obtained by refining
domestic and imported ores and flue dusts; 9% (540 metric tons) was with-
drawn from industrial and government stockpiles; and roughly 14% (860 metric
tons) was imported as the metal. Because cadmium is generally obtained as
a by-product of zinc-smelting operations, its total production is relatively
independent of direct demand; instead, production will vary with the tonnage
of zinc ores processed in response to the demand for that metal. To project
the entrance of cadmium into the environment over the next 20 or 30 years,
one would therefore have to estimate changes in the demand not only for
cadmium but also for zinc. Although estimates cannot be made with great
accuracy, the use of cadmium is clearly increasing continuously (Section
9.2.3).
,$ .2.3 Uses of Cadmium
Cadmium is used extensively in a variety of industrial processes.
Because little metal is recycled, most of this cadmium ultimately finds
V its way into the environment.
The rates of consumption in 1968 for most categories of use are ex-
pected to double by the year 2000. Some specific processes may consume
four times more cadmium by that date (e.g., batteries and electroplating
of motor vehicle parts). Projected total U.S. consumption of cadmium in
the year 2000 is approximately 14,000 metric tons.
Electroplating thin films on the surface of reactive metals to prevent
corrosion is the most important use of cadmium. More than 2700 metric tons
of the metal was used in the United States for this purpose in 1968. Other
substantial applications include use of cadmium as a pigment in paints,
plastics, inks, and phosphors (about 1000 metric tons) and as a stabilizer
in plastic goods (about 900 metric tons). United States production of
metallurgical alloys, solders, electrical contacts, and solid-state elec-
tronic devices required over 200 metric tons of cadmium in 1968. During
the same year the manufacture of nickel-cadmium batteries consumed 180
metric tons. Minor amounts of cadmium are also used in photography, rubber
processing, nuclear energy, and fungicides. Estimates of these and other
miscellaneous uses in the United States in 1968 varied from 285 to 920
metric tons. In 1975 the total U.S. consumption of cadmium was distributed
as follows: electroplating, 55%; plastic stabilizers, 21%; pigments, 12%;
batteries, 5%; and other uses, 7% (U.S. Environmental Protection Agency,
1976, p. 17).
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9.2.4 Flow into the Environment
Contamination of the environment by cadmium-enriched pollutants occurs
chiefly during the recovery of cadmium, zinc, lead, and copper from their
ores and during the reprocessing of cadmium-plated or galvanized scrap
steel. The volatilitj_of_. the- element encourages its -less to the .atmosphere
during all these operations; fallout and washout return atmospheric cadmium
to soils and water. Estimated losses to the atmosphere during 1968 in the
United States as a result of primary metal production varied from 100 to
950 metric tons (Sargent and Metz, 1975, p. 140). An even larger quantity
of cadmium (about 1000 metric tons) was volatilized that year during repro-
cessing operations, but only about 10% reached the atmosphere; the balance
was collected as dust.
/ An estimated 100 metric tons of cadmium (calculated as the metal) was
// released into the environment during 1968 as a result of industrial uses and
during consumption and disposal of cadmium-containing products. In addition,
between 130 and 1000 metric tons of the metal were contributed by combustion
of fossil fuels and from 20 to 200 metric tons by application of phosphate
fertilizers. To^tal losses of cadmium to the U.S. environment in 1968 were
estimated at 2000 to 3600 metric tons. Not included in this total is approx-
imately 5000 metric tons of the metal designated for permanent use or con-
sidered as waste with unknown disposition.
The association of certain types of cadmium pollution with refining
and manufacturing industries results in localization of exposures. In rural
and suburban locations distant from point sources the concentration of cad-
mium in air is normally below the usual level of detection (about 0.001
yg/m3). However, near smelting operations average concentrations may range
from 0.3 to 3.0 jig/m3. Such concentrations decrease sharply with distance
from the point source due to dust fall or precipitation. Concentrations
of cadmium in urban or industrial air, even in the absence of point sources,
are generally greater than those in rural samples because of combustion of
fossil fuels; in typical urban neighborhoods airborne particulate cadmium
concentrations range from 0.002 to 0.080 yg/m3.
Fallout of cadmium dusts near point sources leads to high concentra-
tions of the metal in soil. For example, uncontaminated soil typically
contains less than 0.4 yg/g, but concentrations as much as 100 times higher
have been reported from within a 1-km radius of a zinc smelter. In such
soils, contaminated mainly by particulate fallout, the vertical concentra-
tion gradient of the pollutant is steep, with most cadmium remaining near
the surface. Typically, at a depth of 5 to 10 cm, the concentration drops
to less than 10% of that at the surface and at 10 to 15 cm to less than 2%.
Soils distant from point sources may be polluted with cadmium from
phosphate fertilizers or sewage sludges. The naturally occurring cadmium
in phosphate rocks, or that added to sewage, is concentrated during prep-
aration of these materials and some forms may contain from 6 to 75 mg/kg.
Such products supply 3 to 45 g of cadmium per hectare when applied at con-
ventional rates. Although uptake of cadmium by plants is controlled by a
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wide variety of variables such as species, soil pH, and others, the con-
centration in plants generally reflects the level of the metal in soil.
Continued deposition of cadmium, especially on agricultural land, may there-
fore represent a potentially important problem; this is further considered
in Section 9.6.
Cadmium concentration in water varies with season and with distance
from polluting sources as well as with the extent of precipitation or
adsorption. The removal of cadmium from water into the sediments depends
in turn on the nature of the sediments, the presence of particulate matter
in suspension, and the chemical composition of the water. Typically, rural
waters contain less than 1 yg cadmium per liter, but the level in waters
near industrial areas may reach as high as 100 yg/liter. The concentration
of cadmium decreases rapidly with distance from polluting source, presumably
because of sedimentation. Chemical forms of cadmium in waters are generally
not well defined.
To the anthropogenic input of cadmium into the environment must be
added input from natural sources such as weathering of rocks and volcanism.
These sources may account for an annual input of as much as 5000 metric tons
and are presumably responsible for the low background concentrations in air,
water, soil, and sediments remote from point sources. The most significant
source of cadmium in the environment, however, is modern technological
society. The precise amount of cadmium contributed by man is difficult to
estimate accurately, but generally about 20% of the amount results from
operations in the primary nonferrous metal industry and about 30% from con-
version, use, and disposal of cadmium products.
An additional 50% of the input into the environment is derived from
activities unrelated to production or use of cadmium metal. Among these,
combustion of fossil fuels and use of cadmium-containing fertilizers and
sewage sludge deserve special mention. Coal from different sources may
contain as much as 2 yg cadmium per gram. In other words, volatilization
of the metal contained in 1 metric ton of coal could add 2 g of cadmium to
the atmosphere. Even though a major fraction of this metal may be trapped
by air pollution controls, this source of environmental contamination is
bound to grow with the increased reliance on coal as an energy source. The
problem posed by the use of cadmium-containing fertilizers is further con-
sidered in Section 9.6.
Automotive transport contributes small amounts of cadmium through the
wear of tires; somewhat larger amounts are contributed through the exhaust.
Although roadside vegetation may contain increased cadmium concentrations,
no strong evidence suggests that the automobile is a major source of cadmium
pollution. In general, however, the concentration of cadmium in emissions
from anthropogenic sources is appreciably higher than background levels, and
the potential for hazardous exposure or adverse ecological consequences is
therefore frequently present.
Airborne cadmium constitutes only a small fraction (about 15%) of the
anthropogenic cadmium flux. The metal is emitted to the atmosphere primar-
ily as oxide, sulfide, or sulfate particles (U.S. Environmental Protection
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Agency, 1975, p. 2-1). Size distribution of the particles varies with
source conditions, but typically one-half have diameters less than 2 i_im and
are therefore readily respirable. The principal sources of airborne emis-
sions are metallurgical processes such as smelting and sintering operations,
the reprocessing of galvanized and cadmium-plated scrap, incineration of
cadmium-containing plastics, and consumptive uses. Most airborne emissions
are deposited on surface soil within 1 km of the point source, but measurable
concentration gradients as far away as 100 km have been reported.
Only perhaps 1% of the anthropogenic cadmium flux in the United States
originates from point sources as water pollution. The most important water
pollution sources are mine and ore beneficiation wastewaters and electro-
plating wastes. Indirect sources include runoff from land contaminated
with cadmium from airborne fallout, fertilizers, and agricultural chemicals.
Dissolved cadmium, however, tends to react readily with other constituents
of the water, and its concentration is reduced by precipitation and adsorp-
tion. Consequently, the metal may accumulate in sediments near its point
of entry into the lake or stream. Cadmium adsorbed on fine silts and on
suspended matter may ultimately reach marine sediments.
The greatest quantities of cadmium wastes from anthropogenic activ-
ities are released into the environment from disposal sites of solid wastes,
slimes, and sludges. A substantial fraction of these wastes are residues
from air and water pollution control. Only a small percentage of these
wastes contains cadmium in concentrations greater than 0.1%. Nevertheless,
the usual concentrations in these deposits greatly exceed those of uncon-
taminated soils so that the deposits represent potentially serious sources
of pollution. In the future, economic and regulatory restrictions may
induce the recycling of cadmium in many such wastes (Sargent and Metz,
1975, p. 169).
9.3 CADMIUM IN THE HUMAN FOOD CHAIN
Cadmium occurs in most American food plants in concentrations well
below 0.1 yg/g; significantly higher values have been found in Japanese rice
samples. The exact cadmium level varies with plant species and form and with
concentration of the metal in the soil. In normal soils cadmium uptake by
plants poses little environmental hazard to man or animals. Crops grown on
soils contaminated by smelter emissions or on soils treated with cadmium-
rich sewage sludges or cadmium-containing fertilizers and fungicides may
contain higher than normal concentrations of cadmium in the edible por-
tions and may thus constitute a direct or indirect source of human ex-
posure. Because use of cadmium is growing and environmental contamination
may increase, this problem deserves continued consideration.
Cadmium is present in milk and tissues of domestic animals raised for
human consumption, but except possibly for liver and kidney, its concentra-
tion falls normally below 0.05 yg/g wet weight and poses little hazard to
humans. Some neritic organisms may contain much higher levels of cadmium,
depending on proximity to and intensity of sources of pollution. Typically,
invertebrate marine animals concentrate the metal from seawater from 1 to
10,000 times. Appreciable consumption of such animals from polluted areas
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could thus result in significant intake of cadmium. Concentrations in fish
are generally lower than in marine invertebrates but may still exceed con-
centrations in ambient water by a factor of several hundred. In spite of
the bioconcentration and bioaccumulation of cadmium in the examples cited,
there is no evidence for biomagnification of the metal in terrestrial or
marine food chains.
9.4 TOXICITY AND HEALTH EFFECTS OF CADMIUM
This section assesses the toxicity and possible health effects of cad-
mium in humans. All evidence suggests that the basic mechanisms of toxicity
are similar in man and higher animals; therefore, information gained from
higher animals may be extrapolated to man.
Acute cadmium poisoning is primarily an occupational problem; the route
of exposure is usually via the lungs. Thus, metal workers can receive toxic
doses of cadmium fumes during welding operations. Cadmium dusts in the res-
pirable size range also represent a definite hazard. About 25% to 50% of
the pulmonary cadmium load may be retained and in acute cases may result in
proliferative interstitial pneumonitis, perivascular and peribronchial fibro-
sis, and possible death from pulmonary edema. The lethal dose of thermally
generated fume lies below 3000 mg-min/m3; arc-generated fume may be twice
as toxic. More chronic, low-level exposure to the metal in the atmosphere
eventually may also lead to pulmonary pathology (bronchitis and emphysema)
as well as to renal damage. Evidence of chronic toxicity has been reported
in workers exposed to levels of cadmium significantly below presently
accepted standards for the industrial environment (Section 9.5).
Pulmonary exposure of the general population is typically very low
except in the case of smokers. The average cigarette may contain 1 to 2 yg
cadmium. If about 10% of this cadmium is inhaled and one-half of this in-
haled load is retained in the body, a smoker may add as much as 2 yg cad-
mium to his body burden with each pack of cigarettes. This represents a
doubling of the average daily increment of body burden for adults in the
United States (Section 9.6). It is worth noting that the side stream of
cigarette smoke contains as much cadmium as the inhaled portion.
The major sources of cadmium to which humans are exposed in the normal
environment are food and water. In the United States the normal intake
from all sources varies from 50 to 75 yg per day (Section 9.6). Fractional
absorption from the gastrointestinal tract varies with diet and other ill-
defined factors but is typically low (around 5%). Given the fact that the
biological half-life of cadmium is very long (tens of years), an average
intake of cadmium over a period of 50 years may thus lead to a total body
burden of approximately 30 mg. A fraction of 50% or more of this body
burden is localized in liver and kidneys, with the renal cortex accounting
for perhaps one-third of this fraction. In average American males aged 50,
levels as high as 50 yg/g fresh weight have been reported for this tissue.
A level of 200 yg/g has been somewhat arbitrarily and provisionally chosen
as the concentration at which renal damage may be expected. Many exceptions
to this value have been noted; at best, it is only an approximation which is
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useful until more is known about the renal effects of cadmium. Clearly,
even normal chronic exposure to cadmium can lead to an accumulation of the
metal in renal cortex; such accumulation represents a significant fraction
of suggested critical levels.
Renal cortical levels of 200 yg/g have resulted also from chronic
exposure by inhalation to low concentrations of cadmium in air. A variety
of renal tubular lesions may result from such concentrations. In extreme
cases, such as those associated with itai-itai disease in Japan, where oral
intake of cadmium may have reached values as high as 600 yg/day, calcium and
vitamin D deficiencies which result in severe bone disease are seen.
Chronic exposure to cadmium does cause lesions in various organ systems,
but the renal effects of the metal are probably the most significant ones.
No causal relationship has been established between cadmium exposure and
human cancer, although a possible link between cadmium and prostate cancer
has been indicated. Cadmium injection induces sarcoma in rats but not in
mice. Similarly, cadmium has been shown to be teratogenic in rats, hamsters
and mice, but no such effects have been proven in humans. Cadmium has also
been reported to increase the frequency of chromosomal aberrations in cul-
tured Chinese hamster ovary cells and in human peripheral leucocytes. More
recent work indicates no statistically significant difference in the fre-
quency of chromosomal aberrations between controls and individuals exposed
to cadmium, including battery workers in Sweden and itai-itai patients in
Japan (Friberg et al., 1975). A suggested role of cadmium in human cardio-
vascular disease remains unproven.
9.5 STANDARDS FOR ENVIRONMENTAL AND OCCUPATIONAL EXPOSURES
Given the appreciable amounts of cadmium introduced into the environ-
ment, it is not surprising that significant amounts of the metal are found
in the biosphere and ultimately in man. A decision on what constitutes
safe levels of cadmium in the environment — levels sufficiently low to
provide a significant safety margin against the risk of any normal individ-
ual attaining critical levels — is therefore of great importance. This
statement of course presupposes agreement on what constitutes a critical
level in man. For the present purpose this can best be defined in terms of
overt histological and/or functional changes in lungs and kidneys (Section
9.7).
Cases of acute poisoning by inhaled or ingested cadmium or its com-
pounds in the general population usually result only from accidents or
suicidal attempts and are relatively rare. Greater danger to the general
public lies in long-term low-level exposures leading to appreciable accumula-
tion of cadmium in the body.
As early as 1962 the U.S. Public Health Service sought to minimize such
exposure by limiting the concentration of cadmium in approved water supplies
to 0.01 rag/liter (U.S. Department of Health, Education, and Welfare, 1962).
In 1975, this standard was incorporated into the National Interim Primary
Drinking Water Regulations by the U.S. Environmental Protection Agency
(Federal Register, 1975), making the standard mandatory for all U.S. public
potable water systems.
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Prior to the 1970s there were no federal standards for cadmium in sur-
face waters other than drinking water. However, the problem was considered
at length by the National Technical Advisory Committee in its 1968 report
to the Secretary of the Interior (Water Quality Criteria, 1968, cited in
National Academy of Sciences and National Academy of Engineering, 1973) and
by a National Academy of Science—National Academy of Engineering committee
on water quality criteria which subsequently revised and augmented the 1968
report (National Academy of Science and National Academy of Engineering,
1973) . The latter group concurred with the previously cited public drink-
ing water limit and recommended that, where aquatic organisms and wildlife
are involved, cadmium in freshwater streams be limited to 30 yg/liter when
the total hardness exceeds 100 mg/liter and to 4 yg/liter for water with
a total hardness of 100 mg/liter or below. Upper limits of 50 and 10
yg/liter were suggested for livestock and irrigation uses respectively. To
protect marine aquatic life, the concentration of cadmium was restricted to
1% of the 96-hr LCso value for the most sensitive organism present in the
water.
No federal standards regulating the cadmium content of industrial water
effluents exist, but implementation of such standards by the. U.S. Environ-
mental Protection Agency is in progress. Meanwhile, laws in several states
restrict the discharge of cadmium in industrial water effluents. The limits
in mg/liter are: Illinois, 0.05; Iowa, 0.05; New York, 0.03; Pennsylvania,
0.4; and Wisconsin, less than 1.0. In addition, Missouri, New Jersey, North
Dakota, and Oklahoma require effluents to be normal or free of toxic mate-
rials (i.e., cadmium must be essentially completely removed). The follow-
ing states require effluents to meet U.S. Public Health Service standards
or to be suitable for various indicated uses: Idaho, Indiana, Kansas,
Kentucky, Maryland, Massachusetts, Michigan, Mississippi, Montana, North
Carolina, North Dakota, Oregon, South Carolina, West Virginia, and Wyoming
(Fulkerson and Goeller, 1973).
At present there are no federal standards for cadmium in ambient air;
however, determination of such standards by the U.S. Environmental Protec-
tion Agency may be expected in compliance with amended provisions of the
Clean Air Act of 1970.
/-* "
• The American Conference of Governmental Industrial Hygienists (ACGIH)
recommends threshold limit values (TLVs) for chemical and physical agents
in the occupational environment. In 1968 the value for an 8-hr work day
was set at 0.2 mg cadmium per cubic meteor. Cadmium fume, a more toxic form,
was limited to a ceiling value of 0.1 mg/m3. Subsequently, in 1976, the
ACGIH reduced the time-weighted average (TWA) and tentative short-term
exposure TLVs for cadmium fume to 0.05 mg/m3 each and the corresponding
values for dust to 0.05 and 0.15 mg/m3 respectively. A recent document on
cadmium (National Institute of Occupational Safety and Health, 1976) pro-
poses a further lowering to 0.04 mg/m3 determined as the TWA for a 40-hr
work week. Chronic toxicity has been observed, however, at even lower ex-
posure levels. In 1971 the Occupational Safety and Health Administration
(OSHA) adopted as federal standards for industrial atmospheres values
numerically equal to the 1968 ACGIH standards for cadmium fumes and dusts
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but defined them as 8-hr TWAs and permitted ceiling concentrations of
3 mg/m3 for dusts and 0.6 mg/m3 for fumes (Federal Register, 1971).
There are no standards for cadmium in foods. It is unlikely, however,
that consumption of food containing an average of no more than 0.1 yg/g
cadmium presents a significant hazard to humans. In addition, it is the
policy of the Food and Drug Administration and the U.S. Department of
Agriculture to reject the use of cadmium-containing materials in food
preparation and packaging (Fulkerson and Goeller, 1973, p. 381).
9.6 ENVIRONMENTAL HAZARDS POSED BY PRESENT AND PROJECTED CONCENTRATIONS
OF CADMIUM IN THE ENVIRONMENT
The total cadmium intake by the average adult human in the United
States presently approaches 50 to 75 yg/day, as discussed in Section 9.4.
For a typical nonsmoker this uptake is made up of less than 1 yg of air-
borne cadmium; 2 to 20 yg may be provided by water and about 50 yg by
food. Because the efficiency of intestinal absorption is low (Section 9.4),
such daily exposure leads to a daily retention of only 1 to 2 ug cadmium.
Nevertheless, in the absence of exposure to polluted air or water, and for
people in the general population who neither smoke nor are closely exposed
to tobacco smoke, food clearly represents the principal source of cadmium.
As pointed out in Section 9.4, this daily dose may be doubled by heavy smoking
The long half-time of cadmium in the body implies that the daily up-
take of the metal approximates the net daily increase in body burden. A high
proportion of the body burden is concentrated in the renal cortex, for which
an approximate critical concentration of 200 yg/g has been suggested (Section
9.4). In order to reach this level it would be necessary to ingest 300 yg
cadmium per day for 50 years, according to the calculation of Sargent and
Metz (1975, p. 131). According to this criterion, typical intake from un-
polluted environments is one-sixth to one-quarter of that required for overt
pathological consequences. Thus, no substantial evidence of hazard to the
general population from current levels of cadmium in air, water, or food
now exists. However, the pronounced tendency of cadmium to accumulate in
the body and the relatively small safety margin noted above are adequate
reasons for concern over possible future increases in background levels.
Indeed, although concentrations of cadmium in samples of water and air
remote from point sources of pollution are low and will probably remain so
because of recently introduced pollution control measures, it is likely that
concentrations of cadmium in food will increase in the future unless ade-
quate safeguards are taken. Several circumstances favor this development.
First, domestic consumption of cadmium is growing at an annual rate of 4%
and is expected to more than double by the end of the century (Section
9.2.3). Improved pollution control measures will probably limit further
direct contamination of air and water, but increased disposal of cadmium-
containing solid waste can result in a general increase of background levels
unless adequate storage techniques are employed. Secondly, use of cadmium-
containing phosphate fertilizers and sewage sludges is increasing (Sargent
and Metz, 1975, p. 8). Application of these materials to crop lands
generally increases the uptake of cadmium by the crops and ultimately,
therefore, by the human consumer.
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There is indeed some suggestion that the cadmium level in certain
crops may have risen over the last 50 years. Whether this increase resulted
from greater use of cadmium-containing fertilizers or whether it was caused
by, for instance, deposition of airborne pollutants originating from indus-
trial sources is not entirely clear. Further uncertainties arise from the
fact that cadmium applied in sludge may not remain in soil in forms readily
available to plants. In addition, there are ways of reducing the avail-
ability of cadmium by, for example, raising soil pH (application of lime).
More work is clearly required before the risks of applying cadmium-containing
fertilizers can be fully assessed.
Removal of the trace levels (from 2 to 20 vig/g) of cadmium normally
present in phosphate fertilizers is technically feasible but not econom-
ically practicable. In the case of sludges, quite significant concentra-
tions of cadmium have been found (Sargent and Metz, 1975, p. 11). These
cannot always be assigned to specific industrial sources. Nevertheless, it
may become advisable to avoid use of sludge as fertilizer except in cases
where restrictions on cadmium pollution have maintained metal concentrations
at relatively low levels. Ordinances to this effect have been successfully
used and may become necessary to forestall leakage of excess cadmium from
sewage sludge disposal sites.
9.7 RESEARCH NEEDS
Although the potential significance of cadmium as an environmental
toxin is evident, the precise nature and risks of its continued and grow-
ing use cannot yet be fully assessed. However, because the metal is a
cumulative poison, possible effects of chronic exposure to even low levels
in the environment cannot be ignored. Full assessment of these potential
risks will require better answers to many questions than we now possess.
This section identifies the most important research needs.
9.7.1 Improvements in Identification and Analysis of Low Concentrations
of Cadmium
There is a continuing need for standardization and interlaboratory
comparisons of rapid and inexpensive methods of analysis of the very low
quantities of cadmium encountered in environmental and especially in bio-
logical samples. Sample collection and storage are critical factors
also requiring standardization. Finally, it: must be remembered that in
many instances it is not only assay of total cadmium content which may be
important, but also identification of the actual cadmium compounds present.
9.7.2 Development of Measures to Minimize and to Adequately Dispose of
Wastes
Increased flow of cadmium into the environment may safely be predicted
from its growing use as well as from increased reliance on cadmium-containing
fossil fuels such as coal. The problem arises not only from direct losses of
cadmium during, for example, combustion, but also from the need to dispose of
the increased amounts of cadmium-containing wastes. Measures to minimize
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such wastes should be an integral part of current coal conversion research
projects. Moreover, because the cited changes will tend to increase back-
ground levels of cadmium and reduce the already relatively small existing
margin of safety, it is essential that adequate background monitoring
facilities be maintained.
Uncertainties about the increased cadmium levels in crops from lands
treated with sewage sludges and other cadmium-containing materials need to
be resolved. This problem becomes especially important as difficulties
increase in finding an adequate means of disposal for cadmium-rich sludges.
9.7.3 Further Information Related to Biological Effects
In general, in toxicological and metabolic studies with cadmium it is
essential to keep in careful focus the extent to which nutrition may alter
the effects of the metal. Factors such as the protein content of food or
the presence of trace nutrients such as zinc or calcium may alter absorp-
tion and/or distribution of cadmium in the body. In addition, however, the
possible interaction of cadmium with other toxic substances must also be
considered. These include lead and arsenic, which are likely to accompany
cadmium in pollution from industrial sources. In the past, most experi-
mental studies with cadmium have dealt with the effects of cadmium alone.
9.7.3.1 Mechanism of Intestinal Absorption — Food and water provide the
major portion of the cadmium to which the general population is exposed;
fortunately, net fractional absorption to the metal from the gastrointes-
tinal tract only amounts to approximately 5%. This value is influenced
by diet and possibly other factors, and more precise information is needed.
It is obviously of major significance to the body burden whether fractional
absorption amounts to 2% or 10%. Before factors controlling the rate and
extent of cadmium absorption can be evaluated, more information is re-
quired. Topics of prime concern here are, for instance, the kinetics of
cadmium absorption and the mechanism whereby dietary constituents alter
this process.
9.7.3.2 Measures of Exposure and Body Burden — Unlike lead, where measure-
ments of delta-aminolevulinic acid excretion in urine or lead in blood
can provide an early estimate of exposure, no such measure is readily
available for cadmium. The fraction of total body cadmium in blood is
small and reflects recent exposure as much as total body burden; the
toxicological significance of blood cadmium levels is not clearly estab-
lished. Usefulness of cadmium levels in hair for monitoring purposes also
remains in question. Variations in urinary solute patterns, for example
of proteins or amino acids, have been investigated but are not informative
in cases of mild or early exposure or have been reported only in isolated
cases. Excretion of 6-2-microglobulins correlates reasonably well with
indices of prolonged exposure (Kjellstrb'm, Evrin, and Rahuster, 1977);
it provides no direct measure of body burden or of only limited exposure.
Assay of tissue biopsies might provide useful information, but it is
obviously inappropriate as a routine procedure. Noninvasive estimation of
cadmium levels by activation analysis has been tested in a few instances
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but requires relatively complex and expensive instrumentation. The same
disadvantage applies to the possible use of isotope dilution techniques -
employing a stable cadmium isotope; an additional problem arises because
the tight binding of cadmium by various tissue constituents may cause
isotopic equilibration of cadmium in the body to be very slow. In summary,
better procedures are clearly required for monitoring body burden of cad-
mium and for quantitating exposure to the metal before screening procedures
for populations at risk can become meaningful.
9.7.3.3 Toxicological Significance of Cadmium Concentrations in Tissues —
At present, not only is the mechanism of cadmium toxicity unclear, but the
toxicological significance of a given tissue level cannot be properly
evaluated. Interaction with other trace metals such as lead and zinc will
alter the normal reactions of cadmium in the body; environmental pollution,
of course, seldom involves cadmium as the only metal. In addition, cadmium
is stored in tissues in a variety of bound forms, such as metallothionein
and other metalloproteins, whose precise nature, function, and toxicity
are unknown. In the absence of this information, a total tissue concen-
tration like the somewhat arbitrarily suggested critical level of 200 ug
cadmium per gram renal cortex can have only limited significance. Even
the function of metallothionein in cadmium metabolism, if indeed it has any,
remains unclear in spite of the extensive work in that area.
In evaluating the toxicological significance of a given body burden,
one must consider not only the general population but also specific sub-
groups which may be at special risk. Thus, the evidence that cadmium may
alter pancreatic function implies that it may pose a special threat to
diabetics or pre-diabetics. Similarly, the transplacental movement of cad-
mium necessitates further study of the possible consequences of fetal accu-
mulation of the metal. In general, genetic, teratogenic, and carcinogenic
effects of different cadmium levels need to be further explored (Fleischer
et al., 1974, p. 300; Hiatt and Huff, 1975).
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SECTION 9
REFERENCES
1. Federal Register. 1971. Occupational Safety and Health Standards.
36:15104.
2. Federal Register. 1975. National Interim Primary Drinking Water
Regulations. 40:59566.
3. Fleischer, M., A. F. Sarofim, D. W. Fassett, P. Hammond, H. T.
Shacklette, I.C.T. Nisbet, and S. Epstein. 1974. Environmental Impact
of Cadmium: A Review by the Panel on Hazardous Trace Substances.
Environ. Health Perspect. 7:253-323.
4. Friberg, L., T. Kjellstrom, G. Nordberg, and M. Piscator. 1975. Cad-
mium in the Environment — III. EPA-650/2-75-049, U.S. Environmental
Protection Agency, Washington, D.C. 218 pp.
5. Fulkerson, W., and H. E. Goeller, eds. 1973. Cadmium, the Dissipated
Element. ORNL/NSF/EP-21, Oak Ridge National Laboratory, Oak Ridge,
Tenn. 473 pp.
6. Hiatt, V., and J. E. Huff. 1975. The Environmental Impact of Cadmium:
An Overview. Intern. J. Environ. Stud. 7:277-285.
7. Kjellstrom, T., P. E. Evrin, and B. Rahuster. 1977. Dose-Response
Analysis of Cadmium-Induced Tubular Proteinuria. Environ. Res. 13:303.
8. National Academy of Sciences and National Academy of Engineering. 1973.
Water Quality Criteria 1972. EPA«R3»73'033, U.S. Environmental Pro-
tection Agency, Washington, D.C. 594 pp.
9. National Institute of Occupational Safety and Health. 1976. Criteria
for a Recommended Standard — Occupational Exposure to Cadmium. HEW
Publication No. (NIOSH) 76-192.
10. Sargent, D. H., and J. R. Metz. 1975. Technical and Microeconomic
Analysis of Cadmium and Its Compounds. EPA-560/3-75-005, U.S. Environ-
mental Protection Agency, Washington, D.C. 209 pp.
11. U.S. Department of Health, Education, and Welfare. 1962. Public Health
Service Drinking Water Standards. Public Health Service Publication No.
956, Washington, D.C. 61 pp.
12. U.S. Environmental Protection Agency. 1975. Scientific and Technical
Assessment Report on Cadmium. EPA-600/6-75-003, Washington, D.C.
13. U.S. Environmental Protection Agency. 1976. Summary Characteristics
of Selected Chemicals of Near-Term Interest. EPA-560/4-76-004, Wash-
ington, D.C.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1 REPORT NO
4 TITLE AND SUBTITLE
Reviews of the Environmental Effects of Pollutants:
IV. Cadmium
6. PERFORMING ORGANIZATION CODE
7 AUTHOR(S) Anna S. Hammons, James Edward Huff, Helen M.
Braunstein, John S. Drury, Carole R. Shriner, Eric B.
Lewis, Bradford L. Whitfield, and Leigh E. Towill
8 PERFORMING ORGANIZATION REPORT NO
3 RECIPIENT'S ACCESSI Qt* NO.
5 REPORT DATE
9 PERFORMING ORGANIZATION NAME AND ADDRESS
Information Center Complex, Information Division
Oak Ridge National Laboratory
Oak Ridge, Tennessee 37830
10 PROGRAM ELEMENT NO.
1HA616
11 CONTRACT/GRANT NO
IAG D-5-0403
12 SPONSORING AGENCY NAME AND ADDRESS
Health Effects Research Laboratory, Cin-OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45219
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/10
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report is a review of the scientific literature on the biological and
environmental effects of cadmium. Included in the review are a general summary
and a comprehensive discussion of the following topics as related to cadmium and
specific cadmium compounds: physical and chemical properties; occurrence;
synthesis and use; analytical methodology; biological aspects in microorganisms,
plants, wild and domestic animals, and humans; distribution, mobility, and
persistence in the environment; assessment of present and potential health and
environmental hazards; and review of standards and governmental regulations.
More than 500 references are cited.
^Pollutants
' Toxicology
. Cadmium
i
Health Effects
06F
06T
13 DISTRIBUTION STATEMENT
Release to public
19 SECURITY CLASS (Tina Report)
Unclassified
21 NO OF PAGES
274
20 SECURITY CLASS (This page)
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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