STAR Series
ASSESSMENT REPORT
ON CADMIUM
nvironmental Proteelion Agency
lice of Research and Development
Washington, D.C. 20460
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EPA-600/6-75-003
March 1975
SCIENTIFIC AND TECHNICAL
ASSESSMENT REPORT
ON CADMIUM
(Program Element 1AA001)
Assembled by
National Environmental Research Center
Research Triangle Park, North Carolina
for
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Research and Development
Office of Program Integration
Washington, D.C. 20460
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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 series. These broad categories were established to facilitate further development and
application of environmental technology. Elimination of traditional grouping was consciously planned to
foster technology transfer and a maximum interface in related fields. These 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)
9. Miscellaneous Reports
This report has been assigned to the SCIENTIFIC AND TECHNICAL ASSESSMENT REPORTS (STAR)
series. This series assesses the available scientific and technical knowledge on major pollutants that would be
helpful in possible EPA regulatory decision-making regarding the pollutant or assesses the state of
knowledge of a major area of completed study. The series endeavors to present an objective assessment of
existing knowledge, pointing out the extent to which it is definitive, the validity of the data on which it is
based, and uncertainties and gaps that may exist. Most of the reports will be multi-media in scope, focusing
on a single mecKum only to the extent warranted by the distribution of environmental insult.
EPA REVIEW NOTICE
This report has been reviewed by the Office of Research and Development, EPA, and approved for
publication. Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
DISTRIBUTION STATEMENT
This report is available to the public from Superintendent of Documents, U.S. Government Printing Office,
Washington, D.C. 20402.
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PREFACE
Although this report is issued in the Scientific and Technical Assessment Report Series, it differs in
several respects from the comprehensive multi-media format that the Series will usually have because it was
nearly completed prior to the creation of the STAR series in August 1974.
This document was prepared by a task force convened at the direction of Dr. John F. Finklea,
Director, U.S. Environmental Protection Agency (EPA), National Environmental Research Center (NERC)
at Research Triangle Park (RTF), N. C. Assembly, integration, and production of the report were directed
by the Special Studies Staff, NERC-RTP. The objective of the task force was to review and evaluate the
current knowledge of cadmium in the environment, especially in the atmosphere, as related to possible
deleterious effects upon human health and welfare. Information from the literature and other sources has
been considered generally through January 1973.
The primary reference for this report was Cadmium in the Environment (Publication Number
EPA-R2-73-190), a review on cadmium performed under a contract agreement between the U. S.
Environmental Protection Agency and the Department of Environmental Hygiene of the Karolinska
Institute, Stockholm, Sweden.
The following members served on the NERC Task Force:
James R. Smith, Chairman Robert E. Lee
Roy L. Bennett Magnus Piscator
Robert P. Botts John E. Sigsby
Dennis C. Drehmel E. C. Tabor
J. H. B. Garner Richard Thompson
Jay D. Gile Darryl Von Lehmden
Bruce Henschel Anthony Zavadil
The substance of the document was reviewed by the National Air Quality Criteria Advisory
Committee (NAQCAC) in public session on March 15, 1973. Members of the NAQCAC were:
Mary O. Amdur Harvard University
David M. Anderson - Bethlehem Steel Corporation
Anna M. Baetjer Johns Hopkins University
Samuel S. Epstein - Case Western Reserve University
Arie D. Haagen-Smit - California Institute of Technology
John V. Krutilla Resources for the Future, Inc.
Frank J. Massey, Jr. - University of California
James McCarrol - University of Washington
Eugene P. Odum University of Georgia
Elmer P. Robinson - Washington State University
Morton Sterling - Wayne County (Michigan) Health Department
Arthur C. Stern - University of North Carolina
Raymond R. Suskind - University of Cincinnati
Elmer P. Wheeler Monsanto Company
John T. Wilson Howard University
Ernst Linde, Executive Secretary
iii
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A final formal review of the report was conducted by a Task Force convened under the direction of
Dr. J. Wesley Clayton, Jr., of the Office of Research and Development, EPA, Washington, D. C., on October
9, 1973. Members of the Task Force were:
Dr. Kenneth Cantor, Division Coordinator
J. H. B. Garner
T. Gleason
A. J. Goldberg
Irene Kiefer
Robert E. McGaughey
Robert B.Medz
Jeannie L. Parrish
Lawrence Plumlee
Review copies of this document also have been provided to other governmental agencies and to
industrial and public interest groups.
All comments and criticisms have been reviewed and incorporated in the document where deemed
appropriate.
IV
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CONTENTS
Page
LIST OF FIGURES ... vi
LIST OF TABLES '.'.'."".'"'.... vii
LIST OF ABBREVIATIONS vii
LIST OF CHEMICAL ELEMENTS AND COMPOUNDS viii
1. INTRODUCTION 1-1
1.1 REFERENCE FOR SECTION 1 1-1
2. SUMMARY AND CONCLUSIONS 2-1
2.1 SUMMARY . 2-1
2.2 CONCLUSIONS 2-3
3. CHEMICAL AND PHYSICAL PROPERTIES 3-1
3.1 REFERENCES FOR SECTION 3 . . 3-1
4. SAMPLING, PREPARATION, AND ANALYSIS 4-1
4.1 SAMPLING PROCEDURES 4-1
4.1.1 Air . . . 4-1
4.1.2 Water . . . 4-1
4.1.3 Soil 4-1
4.1.4 Food .... 4-2
4.2 ANALYTICAL METHODS .... . . ... ... 4-2
4.2.1 Air . . . 4-3
4.2.2 Water ... .... 4-3
4.2.3 Soil . 4-3
4.3 REFERENCES FOR SECTION 4 . . . 4-3
5. ENVIRONMENTAL APPRAISAL 5-1
5.1 ORIGIN AND ABUNDANCE .. 5-1
5.1.1 Natural Sources . . . . . 5-1
5.1.2 Man-made Sources . ... ... . 5-2
5.2 CONCENTRATIONS . . . 5-8
5.2.1 Air . . 5-8
5.2.2 Water . . - ... - - .5-16
5.2.3 Soil • • 5-18
5.2.4 Food • • 5-18
5.2.5 Tobacco • 5-21
5.3 REFERENCES FOR SECTION 5 . 5-22
6. ENVIRONMENTAL EXPOSURE . . . . 6-1
6.1 HUMAN EXPOSURE AND INTAKE RATES 6-1
6.1.1 Food • • • • 6-1
6.1.2 Air • • • 6-3
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Page
6.1.3 Smoking 6'3
6.1.4 Water 6'3
6.1.5 Soil 6-4
6.2 REFERENCES FOR SECTION 6 6-4
7. MECHANISMS OF EXPOSURE AND RESPONSE 7-1
7.1 RESPIRATORY ABSORPTION 7-1
7.2 GASTROINTESTINAL ABSORPTION 7-1
7.3 TRANSPORT AND DISTRIBUTION 7-1
7.4 EXCRETION 7-3
7.4.1 Urine 7-3
7.4.2 Feces 7-3
7.4.3 Hair 74
7.5 BODY BURDEN 74
7.6 BIOLOGICAL HALF-TIME 7-4
7.7 CONCLUSIONS 7-4
7.8 REFERENCES FOR SECTION 7 7-5
8. EFFECTS 8-1
8.1 HUMAN IMPACT 8-1
8.1.1 Respiratory Effects of Cadmium Exposure 8-1
8.1.2 Systemic Effects of Cadmium Exposure 8-1
8.1.3 Clinical Studies 84
8.2 ECOLOGICAL IMPACT 8-6
8.3 REFERENCES FOR SECTION 8 8-9
9. CONTROL TECHNOLOGY 9-1
9.1 AIRBORNE EMISSIONS 9-1
9.2 WATERBORNE EMISSIONS 9-1
9.3 CONTROL METHODS 9-1
9.3.1 Control of Airborne Cadmium Emissions 9-1
9.3.2 Control of Waterborne Cadmium Emissions 94
9.4 REFERENCES FOR SECTION 9 9-5
TECHNICAL DATA SHEET AND ABSTRACT 10-1
LIST OF FIGURES
Figure Page
5.1 Flowsheet of societal flow of cadmium in U.S., 1968 5-6
5.2 Cadmium concentrations (ng/m3) and isopleths for May 21-22, 1968 5-12
5.3 Helena Valley Environmental Pollution Study: settleable particulate cadmium distribution . 5-15
6.1 Cadmium concentrations of surface waters, soils, and foods and estimated dose levels resulting in
various symptoms and effects in humans ... 6-2
8.1 Environmental transport of cadmium . .... . . .8-7
VI
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LIST OF TABLES
Table page
5.1 Data on Natural Abundance of Zinc and Cadmium . 5-1
5.2 Total and Recoverable Reserves and Resources of Zinc and Cadmium in the U.S. and the World 5-2
5.3 U.S. and World Production of Cadmium, 1964 to 1970 . 5-2
5.4 Summary of U.S. Zinc and Cadmium Producers ... . ... 5-3
5.5 Operating Temperatures of Activities in which Zinc and Cadmium can be Released as Airborne
Pollution . .5.4
5.6 Estimated Cadmium Emissions to the Atmosphere in the U.S., 1968 . . .5-5
5.7 Estimated U.S. Emission Inventory for Cadmium, 1971 . . 5-7
5.8 Anticipated Growth, by use, in Demand for Cadmium in the U.S., 1968-2000 .... 5-8
5.9 Quarterly and Annual Average Cadmium Concentrations in Air of the 20 Most Populated U.S.
Cities, 1969 . . . .... ... 5-9
5.10 Quarterly and Annual Average Cadmium Concentrations at NASN Sites with Annual Average
Concentrations Greater than 0.015 Mg/m3, 1969 5-10
5.11 Number of Stations within Selected Cadmium Concentration Intervals, 1966 Through 1969 5-11
5.12 Cadmium Concentrations in Ambient Air for Selected Locations and Averaging Times . 5-13
5.13 Particle Size Distribution of Cadmium in Airborne Particulate Matter 5-14
5.14 Cadmium in Settleable Particulates in the Helena Valley . . .. . 5-14
5.15 Cadmium in Settled Particulates - Roadside Study . ... 5-16
5.16 Deposition of Cadmium around an Emitting Factory, 1968 to 1970 5-17
5.17 Zinc and Cadmium in Municipal Water, Brattleboro, VT 5-17
5.18 Uptake of Cadmium by Rice and Wheat . . . 5-19
5.19 Cadmium Content in Different Food Categories in U.S.A. . ... 5-19
5.20 Cadmium in Selected Foods in Various Countries 5-20
5.21 Metal Content of Tobacco Products . . .. 5-20
5.22 Trace-Metal Content of Cigarette Fractions 5-21
6.1 Daily Intake of Cadmium VIA Food in Different Countries . 6-1
7.1 -Average Cadmium Concentration in Renal Cortex by Age Groups in the United States . 7-2
7.2 Mean Cadmium Concentrations in Renal Cortex at Age 50 . . . 7-3
8.1 Estimated Minimum Cadmium Levels Via Inhalation or Ingestion Necessary for Reaching 200
ppm (Wet Weight) of Cadmium in Renal Cortex (Total Body Burden: 120 mg Cadmium)
8.2 Concentration of Cadmium in Various Substances
LIST OF ABBREVIATIONS
AAS Atomic absorption spectrophotometry
acfm Actual cubic feet per minute
AFS Atomic fluorescence spectroscopy
ASV Anodic stripping voltametry
°C Degrees Celsius
CD Colorimetric dithizone
EPA United States Environmental
Protection Agency
°F Degrees Fahrenheit
km Kilometer
Vll
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1 Liter
Ib/ton Pounds per ton
M_ Molar concentration
m Meter
m3 Cubic meters
mg Milligrams
mg/m3 Milligrams per cubic meter
min Minutes
min-mg/m3 Time-concentration exposure or
or Exposure time in minutes times
mg/m3 -min concentration in mg/m3
MX Metric tons
Hg Micrograms
Mg/m3 Micrograms per cubic meter
jug/ml Micrograms per milliliter
/um Micrometer
NAA Neutron activation analysis
NASN National Air Surveillance
Network
ng/m3 Nanograms per cubic meter
OES Optical emission spectroscopy
ppb Parts per billion
ppm Parts per million
LIST OF CHEMICAL ELEMENTS AND COMPOUNDS
B2042-
Cd
115Cd
CdC03
CdS
co32-
CdO
CdSe
CdS04
CuFeS2
HC03
H20
PbS
Si032-
S02
S03
ZnC03
ZnO
ZnS
Zn2 Si04
Zn4Si207(OH)2
ZnS04
Metaborate
Cadmium
Cadmium isotope having
atomic weight of 115
Cadmium carbonate
Cadmium sulfide
Carbonate
Cadmium oxide
Cadmium selenide
Cadmium sulfate
Copper-iron sulfide
(chalcopyrite)
Bicarbonate radical
Water
Lead sulfide
Silicate
Sulfur dioxide
Sulfur trioxide
Zinc carbonate
Zinc oxide
Zinc sulfide
Zinc silicate (willemite)
Basic zinc silicate (hemimorphite)
Zinc sulfate
Vlll
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SCIENTIFIC AND TECHNICAL
ASSESSMENT REPORT ON CADMIUM
1. INTRODUCTION
The purpose of this document is to summarize the current knowledge on cadmium in relation to its effect
upon human health and welfare. Cadmium in the Environment1 served as a basic reference for the review;
however, the results of later studies and contributions from EPA staff members have been incorporated.
The references cited do not constitute a comprehensive bibliography on the subject.
Our knowledge concerning the cycling of cadmium in the environment is incomplete. Because the principal
human intake routes include food, water, and air, and because the half-time of cadmium in the human body
is very long, any assessment of effects should consider the environmental cycle. The atmosphere may serve
as a medium through which cadmium enters the soil and water, and hence the food chain. This document
makes no attempt to treat this aspect of the subject in detail, but it recognizes the possible impact upon
decisions concerning control strategies.
Each of the major human intake routes for cadmium is reviewed. Where justified by available evidence,
estimates have been made of normal and "critical" intake levels.
1.1 REFERENCE FOR SECTION 1
1. Friberg, L., M. Piscator, G. Nordberg, and T. Kjellstrom. Cadmium in the Environment, II. The
Karolinska Institute, Stockholm, Sweden. Prepared for U. S. Environmental Protection Agency,
Research Triangle Park, N. C., under Contract No. 68-02-0342. Publication No. EPA-R2-73-190.
February 1973. 169 p.
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2. SUMMARY AND CONCLUSIONS
2.1 SUMMARY
Cadmium is widely distributed in the environment in trace amounts. Concentrations exceeding fractions of
a part per million occur only in areas of rich ore deposits or in areas contaminated by man's activities.
Cadmium emitted into the atmosphere will generally be in the form of particles — usually as the oxide, but
also as sulfide or sulfate. The primary man-made sources of cadmium released to the environment are
metallurgical processing, reprocessing of materials, incineration or other disposal processes, and consump-
tive uses.
Because the boiling point of cadmium is quite low (767°C), the metal may be vaporized in
high-temperature processes and condensed into particles as the process off-gases are cooled. This
condensation would result in fine particulate matter, primarily in the micrometer and submicrometer range.
The exact size distribution of cadmium-containing particles from these sources has not been clearly defined.
Available data indicate that approximately 40 percent of the mass is in particles smaller than 2 micrometers
in diameter; hence, a large portion of the particles would be in the respirable range.
Evidence indicates that a considerable mass of cadmium-containing particles is deposited on the surface of
the earth at relatively short distances from the emission source — the maximum gradient is from 0 to 1
kilometer (0 to 0.6 mile), suggesting that large particles are also emitted. The submicrometer particles,
however, would be transported greater distances - detectable gradients up to 100 kilometers (60 miles)
have been reported.
In 1969, atmospheric concentrations of cadmium at 29 nonurban stations in the U. S. were below the
minimum detectable level of 0.003 microgram per cubic meter (^g/m3). Cadmium is present in small but
measurable amounts in the air over almost all urban areas sampled by the National Air Surveillance
Network of EPA. Higher annual average concentrations of cadmium are found in the small-to-medium size
cities with heavy industry than in the most populous areas. The highest 24-hour, quarterly, and annual
values — 0.73, 0.15, and 0.12 jUg/m3 > respectively — were found in El Paso, Texas, where a known cadmium
source is located. Average 24-hour concentrations of cadmium in urban areas are generally less than 0.1
Mg/m3. In the immediate vicinity of major emission sources, average 24-hour concentrations may reach 5 to
6 /ug/m3. Annual averages of 0.3 /ug/m3 have been reported in Sweden.
The cadmium content of surface water is normally less than 1 part per billion (ppb). However, a
concentration of 77 ppb has been found in hot, running tap water, which was attributed to cadmium in the
water pipe.
Cadmium values reported in foods vary widely; however, the accuracy of many of the values are
questionable because of the analytical methods used. Values range from below detectable levels to several
parts per million (ppm), depending upon the type of food and the degree of contamination. The varying
ability of different species of plants to concentrate cadmium has not been explained. Tobacco, for example,
has been found to contain a high concentration of cadmium. The uptake of cadmium by wheat has been
related to the mount of cadmium added to the soil; however, the rate of uptake may be influenced by the
presence of other elements or compounds. Fertilization and harvest practices are suspected of contributing
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to the cadmium content in food; however, the relationship has not been conclusively demonstrated. The
role of the atmosphere in the transport of cadmium, with subsequent deposition on the soil, is not
understood. The majority of food consumed in the United States is grown in areas remote from primary
cadmium emission sources.
Large doses of cadmium are known to be toxic. Some deaths have been reported as a result of exposure to
high concentrations of cadmium oxide fumes. Acute pulmonary edema or proliferative interstitial
pneumonitis may result from an acute exposure; the dose of cadmium necessary to produce such reactions
has been calculated to be approximately 2,500 minutes-milligrams per cubic meter (min-mg/m3). (This
could, for example, represent an exposure to 100 mg/m3 for 25 minutes, or to 50 mg/m3 for 50 minutes).
Friberg found emphysema of the lung among male workers chronically exposed to cadmium oxide dusts in
an alkaline accumulator factory in Sweden. Quantitative data concerning the exposure levels were
incomplete; however, a range of 3 to 15 mg/m3 was reported. Several other incidents of lung damage
caused by cadmium exposure have been reported. Little information is available, however, concerning the
possible association between respiratory diseases and exposure to cadmium via ambient air. Dose-response
relationships cannot be established at the present time because time-weighted average exposures are
available for only short periods of time.
In fatal cases of acute cadmium poisoning via inhalation, pathological changes have been found in the
kidneys. The relationship between the dose of cadmium and the degree of kidney damage is poorly defined,
however.
Microscopic changes have been reported in the livers of workers suffering from acute cadmium poisoning as
a result of exposure to cadmium oxide fumes. Whether these changes represent a direct toxic effect of
cadmium on the liver or whether they are merely secondary to cadmium-induced pulmonary edema is not
known.
Long-term exposure to cadmium may cause renal tubular damage; "tubular proteinuria" is a major sign of
this damage. The critical concentration of cadmium that may cause renal tubular dysfunction has been
estimated to be 200 ppm in the renal cortex.
Evidence from animal experiments suggests a relationship between cadmium exposure and anemia,
hypertension, testicular necrosis, and carcinogenesis; however, the evidence is not conclusive, and
dose-response relationships have not been established in humans. Studies have shown that the addition of
zinc, selenium, and sulfhydryl compounds may influence the effects of cadmium.
The body burden of cadmium is cumulative. The biological half-time is very long—over 10 years. Absorbed
cadmium is stored mainly in the liver and kidney. The total body burden at age 50 varies considerably — 15
to 30 mg for people in some European countries and the United States; 50 to 60 mg in nonpolluted areas of
Japan. The mean cadmium concentrations in renal cortex at age 50 is reported as 25 to 50 ppm in some
European countries and the United States and 125 ppm in Tokyo. A critical level for the renal cortex is
estimated at 200 ppm.
Minimum detectable health effects have been theoretically associated with long-term (25 to 30 years)
exposure to air concentrations of 2.5 Mg/m3, or long-term daily dietary intake of 300 Mg for the average
man. The primary sources of cadmium intake for humans are food, tobacco smoke, water, and ambient air.
The intake from breathing ambient air is small (about 1 percent) in comparison with food and tobacco,
except in the immediate vicinity of point sources. Present estimates for some European countries, the
United States, and Japan indicate that populations in areas not polluted by cadmium have a daily intake of
cadmium from food of 25 to 75 Mg. It has been calculated that, with an absorption of 5 percent of ingested
cadmium, the daily intake would have to be 88 Mg to reach the 50 ppm level in renal cortex in 50 years. To
reach the 200 ppm level, approximately 300 Mg would be required. Considerably less intake via food would
be required for smokers and those living in the immediate vicinity of primary emission sources. Higher
absorption rates may be found for individuals with calcium deficiency.
2-2 CADMIUM
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2.2 CONCLUSIONS
Many uncertainties remain regarding the cycling of cadmium, the contribution of man's activities to the
redistribution of cadmium in the environment, and the effects upon human health and welfare. However, a
number of conclusions can be made, albeit some of these may best be classified as tentative.
• Cadmium has a long biological half-time, and its toxicity is high. Chronic effects may result from
long-term exposures to lower concentrations. The evidence suggests that cadmium may act as a
carcinogen in man, but it is not conclusive.
• Of the three most important exposure routes for cadmium, exposure via breathing ambient air is the
least significant, except in the vicinity of point sources. The major route is via food intake. Smoking
may be an additional means of exposure.
• Transfer mechanisms whereby cadmium enters food chains are not adequately described.
• Detailed information on absorption factors, biological half-time, renal concentrations, and total body
burden as related to acute and chronic health effects is lacking.
• Atmospheric concentrations approaching a "critical exposure" level may occur in the immediate
vicinity of point sources.
• In general, current ambient atmospheric concentrations of cadmium do not pose a direct threat to the
health and welfare of the general population; however, certain practices such as disposal of plastics
and other materials containing significant amounts of cadmium by incineration may tend to make the
pollutant more ubiquitous.
• Any action in pollution control that reduces particulate matter emissions will reduce the potential
exposure to airborne cadmium; however, the degree of control with current technology is not known.
Current technology is inadequate for capturing very fine particles.
• Not enough is known regarding the cycling of cadmium and dose-response relationships to specify the
degree of control required.
• The atmospheric transport of cadmium from primary emission sources, with subsequent deposition,
will contribute to cadmium contamination of soil; however, the degree to which this mechanism
contributes to cadmium in the general food supply of the United States is unknown. Evidence
suggests that fertilizing and harvesting practices may be more important factors than atmospheric
transport.
Summary and Conclusions 2-3
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3. CHEMICAL AND PHYSICAL PROPERTIES
Cadmium is chemical element number 48 and has an atomic weight of,l 12.40. It melts at 320.9°C and boils
at 767°C. Two and zero are its only stable valences.
The saturation vapor pressure of cadmium is so low that at room temperature less than 1 nanogram of
cadmium per cubic meter of air (1 ng/m3) is in the vapor phase when the metal and the atmosphere are in
equilibrium.1
Cadmium is a bluish-silver metal which retains its metallic luster even after tarnishing in the air. It is ductile
and easily worked.1'2
Cadmium is more chemically reactive than mercury, which is below it on the atomic table, and less reactive
than zinc, which is above it. It is, therefore, intermediate in its behavior between mercury and zinc.3 It
readily forms alloys with a majority of the heavy metals. It also forms a number of salts, the most common
of which is cadmium sulfate. Cadmium sulfate is soluble in both cold and hot water.1
3.1 REFERENCES FOR SECTION 3
1. Handbook of Chemistry and Physics, 53rd Ed. Cleveland, Chemical Rubber Co., 1972. p. D-56;
2. Mineral Facts and Problems, 1970 Ed. U. S. Department of Interior, Bureau of Mines, Washington, D. C.
Bulletin No. 650. 1970.
3. Cadmium: The Dissipated Element. Fulkerson, W. and H. E. Goeller (Ed.). Oak Ridge National
Laboratory, Oak Ridge, Tenn. 1973.
3-1
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4. SAMPLING, PREPARATION, AND ANALYSIS
The two major factors essential to obtaining reliable emission data are sampling procedures that provide
quantitatively representative samples of the pollutant emissions and analytical methods that meet the
requirements for sensitivity, accuracy, and precision. By contract, EPA has reviewed sampling and
analytical procedures for cadmium and developed a tentative procedure for sampling cadmium from
stationary sources. The methods discussed below are based on an evaluation of available technical literature
but should be subjected to laboratory and field testing, with modification where necessary.
4.1 SAMPLING PROCEDURES
The problem of collecting representative samples is complicated by the multitude of source configurations
that exist. Cadmium is emitted from both stack and diffuse sources. Because stacks constitute a relatively
well-defined source configuration, the possibility of obtaining reliable stack emission data is much better
than in the case of diffuse sources. For stack sources, EPA recommends a sampling train consisting of
probe, filter holder, impingers, and associated metering system for isokinetic sampling. The volume flow
rate of stack effluents also must be obtained in order to derive pollutant mass emission rates. For diffuse
sources, accurate emission data are virtually impossible to obtain by methods currently employed. The
usual practice is to do sampling and analysis for ambient concentrations in the vicinity of such sources and
to use such data in conjunction with estimated rates of thermal diffusion, turbulent diffusion, deposition,
etc. to derive approximate emission rates.
Except in the case of continuous monitors, it is most convenient to consider environmental sampling and
analysis separately. Generally, the method of analysis is independent of the origin of the sample, with
procedural differences consisting of variations in methods of sample preparation.
4.1.1 Air
Samples are taken from ambient air by filtration through porous media of low, known cadmium content
such as glass-fiber filters or membrane filters. The filter is held by a flexible gasket in a holder that is a part
of a device made to exclude debris, facilitate maintenance, regulate the time of sampling, and permit
estimation of the air volume. The sample of particulate matter so collected is prepared for subsequent
analysis by combustion (use of a low-temperature asher will eliminate loss of cadmium by volatilization)
and dissolution of cadmium in the residue by use of acids.2'3 Wet digestion with acids is also a reliable
technique.
4.1.2 Water
Water may be sampled by continuous withdrawal of a sample from a pipe or stream, but the more common
method is batch sampling. Clean, acid-washed borosilicate containers should be used, and the samples
analyzed as soon as possible. When only one set of samples is to be taken from a stream or lake, it is best to
sample at the middle depth. Cadmium can be lost from solution in trace quantities by absorption on
container walls, even those made of resistant glass.
4.1.3 Soil
Soil samples for cadmium are taken using a systematic method such as sampling at points on a grid plotted
to cover the area of interest. In general, a soil sample obtained from the top 12 inches is thoroughly mixed
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and reduced to a size suitable for analysis by using a riffle or the cone and quarter method; both reduce the
sample by discarding a portion in each operation. The sample is then ashed (preferably at low temperature),
and the cadmium is extracted with mineral acids of low cadmium content.
4.1.4 Food
Food samples may be taken as "market basket" samples, which are obtained" from normal supply channels
in the proportions representative of an average diet. Market basket survey samples are probably the best
index of average human ingestion. When the intake of individuals is surveyed, a fixed proportion of each
dish to be consumed by an individual is placed in a sample container for subsequent analysis-. Food samples
are ashed at low temperature, and the residue is extracted with acid to yield a solution suitable for analysis.
4.2 ANALYTICAL METHODS
Methods available for analysis of collected cadmium emission samples include atomic absorption, atomic
fluorescence, anodic stripping voltametry, ultraviolet and visible spectroscopy, polarographic procedures,
and titrimetric analysis. Multielemental techniques sometimes used are spark-source mass spectrography and
optical emission spectrography. X-ray fluorescence appears promising as a rapid, accurate, nondestructive,
multielemental technique.
In general, the analytical methodology employed is determined by resource considerations and how the
data are to be used. Potentially, any method of analysis capable of determining cadmium in the
concentrations to be found in environmental samples should be acceptable, but in practice the number of
methods in extensive use has been restricted to the classical procedures of colorimetric dithizone (CD),
optical emission spectroscopy (OES), neutron activation analysis (NAA), atomic absorption spectro-
photometry (AAS), and anodic stripping voltametry (ASV). The dithizone method consists of the
formation of a colored dithizone cadmium complex, separation of interferents by closely controlled
multiple extractions with various reagents, spectrophotometric determination of the colored complex, and
estimation by reference to known responses. The CD method is slow, tedious, and requires excellent
technique, but gives reliable results.
The OES procedure uses expensive instrumentation and consists of exciting the cadmium atoms in a sample
by electric arc or spark, separation of the emitted light that is characteristic of cadmium by means of a
prism or grating, elimination of other lines by means of selective slits, and measuring the light intensity on
film or by phototube. The line intensity is compared with the response from standards, and the cadmium
content is estimated. The film approach is semiquantitative, whereas the photometric procedure is more
quantitative.
The NAA approach involves irradiation of a sample with neutrons. Cadmium is detected by identification
of the radiation emitted by activated cadmium atoms; chemical separation may be necessary to remove
interferents. NAA costs, comparatively, are very high, but the sensitivity is good, and the accuracy
compares favorably with that of OES.
The AAS procedure consists of exciting vaporized sample atoms in a flame positioned in the path of light
from a lamp that has a cathode made of the metal of interest - cadmium in this case. The cadmium atoms
in the ground state in the beam will absorb this characteristic radiation. The attenuation of light by the
sample is compared with that caused by known cadmium standards, and the cadmium content of the
sample is estimated. Using a deuterium background corrector, atomic absorption spectroscopy meets the
requirements for sensitivity, accuracy, precision, ease of handling, speed, and relatively low-cost equipment.
AAS is the most frequently used analytical method and is rapidly becoming the accepted method to
determine cadmium at trace levels. The sensitivity of AAS can be increased by using dithizone as a chelating
agent1 or by using a heated graphite atomizer.
4-2 CADMIUM
-------
Interferences in the analysis of cadmium by AAS have been reported3 to be caused by anions such as
B204~2, SjCV2, C03"2, and HCO3 . Phosphate in concentrations above 0.1 molar (M) could decrease the
absorption, and sodium chloride above 0.01M could increase absorption. These interferences can be
removed, if necessary, by extraction of the cadmium into an organic solvent before analysis.
The ASV method consists of measuring the current flow per unit time at varying voltages, which are
characteristic of the deposition of metals. Most of the cadmium experience with ASV has been with blood
samples for which rapid, cheap, accurate results are claimed.
Atomic fluorescence spectroscopy has high sensitivity, but this method should be held in reserve until it is
more widely accepted.
4.2.1 Air
Cadmium in air can be estimated continuously by using an excitation source consisting of graphite rods
energized by induction with a radio-frequency coil. At present, the sensitivity of the procedure does not
permit ambient air analysis, and the equipment is too bulky and complex to be portable. The method in
general use consists of examination of a solution obtained by processing a particulate matter sample on a
filter of glass fiber or organic membrane. The detection is by OES when a multi-element survey is required:
AAS is used when cadmium values alone or data of high accuracy are desired.
In the National Air Surveillance Network, particulate matter samples are sectioned, and composites are
ashed in a low-temperature asher using 50 to 100 milliliters (ml) of oxygen per minute at 1 torr2 with an
induction coil energized with 250 watts. At this combustion temperature (about 150°C) cadmium is
retained essentially quantitatively, whereas half of the cadmium in samples oxidized in a muffle furnace is
lost at between 500 and 550°C.1 The residue is extracted using a mixture (4:1 by volume) of redistilled
nitric and hydrochloric acid and concentrated. The solution is then freed of silica by centrifugation and
brought up to volume with redistilled nitric acid. The solution is analyzed directly by OES, which has a
detection limit of 0.3 microgram per miHiliter (jug/ml) of sample and a relative standard deviation of 8
percent at 0.8 Mg/ml- For special studies, this solution is diluted 10:1 with water prior to analysis by AAS.
The minimum level detectable by AAS is 0.04 jug/ml, and the standard relative deviation is 2 percent at or
above 0.5 yug/ml.
4.2.2 Water
Water samples are best analyzed directly by AAS, using the graphite furnace technique. If interferents are
expected, the samples may be taken to dryness, and the residue digested with nitric acid. If the cadmium
concentration is not detectable, evaporation or extraction with a chelating agent and organic solvent will
serve to concentrate the cadmium in the solution analyzed. Friberg et al.4 describe measurement of
cadmium in water very well.
4.2.3 Soil
Soil samples, prepared for analysis by oxidation and acid extraction, can be analyzed for cadmium by
suitable techniques; AAS is the usual method of choice.
4.3 REFERENCES FOR SECTION 4
1. Martin, R. M. Construction Details of Isokinetic Source Sampling Equipment. U. S. Environmental
Protection Agency, Research Triangle Park, N. C. Report No. APTD-0581, April 1971.
2. Thompson, R.J., G. B. Morgan, and L. J. Purdue. Analysis of Selected Elements in Atmospheric
Particulate Matter by Atomic Absorption. Air Quality Instrum. 7:178, 1972.
Chemical and Physical Properties 4-3
-------
3. Kneip, T. J., M. Eisenbud, C. D. Strehlow, and P. C. Freudenthal. Airborne Particulates in New York
City. J. Air Pollut. Contr. Assoc. 20:144-149, March 1970.
4. Friberg, L., M. Piscator, and G. Nordberg. Cadmium in the Environment. Cleveland, Chemical Rubber
Co. Press, 1971.
4-4 CADMIUM
-------
5. ENVIRONMENTAL APPRAISAL
5.1 ORIGIN AND ABUNDANCE
5.1.1 Natural Sources
Cadmium, a relatively rare metal with an estimated abundance in the earth's crust of 0.55 gram per metric
ton, is always found in nature in association with zinc. It varies from 0.1 to 5 percent of the amount of zinc
present in zinc and polymetallic ores.1 Table 5.1 shows both the average terrestrial abundance and the
amounts in different types of rocks, soils, and sea water. The ratio of cadmium to zinc is based on 55 ppm
for the continental abundance of zinc and 0.15 ppm for cadmium. The continental abundance is based on
rocks that are predominantly granitic and contain larger amounts of cadmium.2
Table 5.1. DATA ON NATURAL ABUNDANCE OF ZINC AND CADMIUM2
Type source
Worldwide
Continental
Ultramatic rocks
Basaltic rocks
High-calcium granites
Low-calcium granites
Syenitic rocks
Avg. igneous rocks
Shales
Sandstone
Limestone
Soil
Range
Average
Seawater5
Abundance, ppm
Zinc
80
55
150
112
47
39
26
70
45-95
16
20
10-300
50
0.01
Cadmium
0.18
0.15
0.53'4
0.0
0.22
0.13
0.13
0.13
0.2
0.3
0.05
0.035
0.01-0.7
0.06
0.0001
Specific zinc/
average zinc3
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
Abundance for specific rock type/continental abundance.
Assuming these two abundance values, the topmost 2 kilometers of the continental lithosphere contain on
the order of 40 trillion tons of zinc and 100 to 200 billion tons of cadmium. Ah1 of the oceans contain!
roughly 15 billion tons of zinc and 150 million tons of cadmium.2 Economically, it is possible to recover
only small amounts of these reserves. Known U. S. and world reserves and potential resources of zinc and
cadmium are given in Table 5.2.
5-1
-------
Table 5.2. TOTAL AND RECOVERABLE RESERVES AND RESOURCES OF
ZINC AND CADMIUM IN THE U.S. AND THE WORLD2
(103MT)
Zinc
Reserves, measured and indicated
Reserves, inferred
Total reserves
Potential resources
Total reserves and resources
Cadmium
Reserves, measured and indicated
Reserves, inferred
Total reserves
Potential resources
Total reserves and resources
Total in resources
U.S.
15,500
15,100
30,600
56,400
87,000
95
91
186
•v195
^381
World
112,000
-^97,000
^209,000
-v 336,000
'^545,000
712
-v730
•v/ 1,442
M,800
-v3,242
Recoverable3
U.S.
12,000
11,600
23,600
43,400
67,000
54
51
105
M05
'V210
World
86,000
•W5,000
^161,000
'V259,000
-^420,000
400
'WHO
-V810
M,020
-v 1,830
Based on Bureau of Mines estimates of 77 percent of zinc and 56 percent of cadmium in ore; higher percentages,
especially for zinc recovery in the U. S. CV86 percent), are thought to be currently more appropriate.
Cadmium and zinc occur in ore deposits principally as sulfides. Ores in the eastern United States are purer
zinc ores; those west of the Mississippi River are chiefly mixed sphalerite—galena-chalcopyrite (ZnS-
PbS-CuFeS2)ores.2
5.1.2 Man-made Sources
5.1.2.1 Stationary Sources—The principal industrial sources that release cadmium into the environment are
the primary metals industry, including mining and processing; waste disposal by incineration; fertilizer
processing; and the burning of fossil fuels. Metallic cadmium is prepared commercially as a by-product of
primary metal industries, principally the zinc industry. Cadmium is found not only in zinc ore, but in lead,
copper, and other ores that contain zinc minerals. During ore separation, cadmium remains with the zinc.
Because the separation processes are not complete, lead concentrates will contain small amounts of zinc and
smaller amounts of cadmium. The U. S. and world production of cadmium for the period 1964 to 1970 is
shown in Table 5.3. The producers of zinc and cadmium in the United States are listed in Table 5.4.
Table 5.3. U. S. AND WORLD PRODUCTION OF CADMIUM, 1964 TO 19704
(103 kg)
Year
1964
1965
1966
1967
1968
1969
1970
United States
4,743
4,387
4,745
3,946
4,831
5,736
4,445
World
12,704
11,907
13,002
12,827
14,076
17,049
15,600
5-2
CADMIUM
-------
Table 5.4. SUMMARY OF U. S. ZINC AND CADMIUM PRODUCERS4'5
Rank in
primary
zinc
output
1
2
3
4
5
6
7
8
9
10
11
Producer
St. Joseph Lead Co.a
New Jersey Zinc Co.a
American Smelting & Refining Co.
The Anaconda Co.
American Smelting & Refining Co.
The Bunker Hill Co.
Blackwell Zinc Co.
The Eagle Pitcher Co.a
National Zinc Co.
Athletic Smelting & Refining Co.
International Smelting & Refining Co.
Sherwin Williams Co.
Apex Smelting Co.
Arco Die Cast Metals Co.
W. J. Bullock, Inc.
General Smelting Co.
Gulf Reduction Co.
H. Kramer Co.
Pacific Smelting Co.
Sandoval Zinc Co.
Superior Zinc Co.
Wheeling Steel Corp.
Arkansas Metals Co.
United Refining & Smelting Co.
Location
Josephtown, PA
Herculaneum, MO
Palmerton, PA
Depue, IL
Amarillo, T X
Corpus Christi, TX
Selby, CA
El Paso, TX
Denver, CO
Beckenmeyer, IL
San Springs, OK
Trenton, NJ
Anaconda, MT
Hillsboro, IL
Kellog, ID
Blackwell, OK
Henryetta, OK
Galena, KS
Bartlesville, OK
Fort Smith, AR
Tooele, UT
Coffeyville, KS
Chicago, IL
Detroit, Ml
Fairfield, AL
Bristol, PA
Houston, T X
El Segundo, CA
Torrance, CA
Sandoval, IL
Bristol, PA
Martins Ferry, OH
Jonesboro, AR
Chicago, IL
Primary
cadmium
producer
X
X
X
X
X
X
X
X
aThese companies also produce major quantities of zinc pigments and compounds directly from ore at eight plants.
Cadmium and zinc are released into the environment either through volatilization or through washing and
solubilization. Volatilization occurs at quite low temperatures (cadmium 767°C and zinc 907°C) so that
they are readily released by such thermal processes as ore roasting, pyrosmelting, steel scrap melting,
incineration of wastes, and burning of fossil fuels.2 Activities through which cadmium can be released to
the air because of volatilization are listed in Table 5.5.
Environmental Appraisal
5-3
-------
Table 5.5. OPERATING TEMPERATURES OF ACTIVITIES IN WHICH ZINC AND CADMIUM
CAN.BE RELEASED AS AIRBORNE POLLUTION2
Activity
Galvanizing
Rolled zinc, melting
Diecasting (2500 psi)
Silver solders
Refuse incinerators
Zinc ore roasting
Brass ingot making
Lead slag fuming
Zinc ore sintering
Zinc ore smelting
Lead blast furnace
Copper converting
Steel scrap melting
Temperature
"C
425-460
445-510
500
650
810
920
1,000-1,100
1,100-1,150
1,200
1,300
1,400
1,200
1,670-1,700
°F
790-850
840-950
930
1,200
1,500
1,600
1,830-2,000
2,000-2,090
2,190
2,360
2,550
2,200
3,000-3,200
Approximate quantities, 1968,
MT
Zinc
435,000
45,000
508,000
1,000,000
295,000
73,000
530,000
530,000
-v73,000
<45,000
145,000
Cadmium
(204}a
(11)
(16)
5,900
(140)
45
3,200
450
-v45
<180
1,000
"Values in parentheses indicate approximate amounts of cadmium as impurities in zinc.
Release of cadmium from washing and solubilization occurs from overburden, tailing piles, and ponds at
mines, slag heaps at smelters, residue piles at electrosmelters and refuse dumps, and from accidental releases
from chemical and electroplating plants.2 Estimates made by Davis and Associates6 of the total annual
emissions of cadmium to the atmosphere in the United States from major known source groups are shown
in Table 5.6. Cadmium emissions to the atmosphere as the result of electroplating operations were
estimated to be negligible. Another tabulation of cadmium emissions, prepared by the Standards
Development and Implementation Division of EPA, is presented in Table 5.7. It should be clearly
understood that these emission data are estimates and that efforts to obtain better information should
continue.
Losses of cadmium to the environment at various stages in the societal flow of cadmium are poorly known.
For this reason, the estimates given in Figure 5.1 are very crude.
Output of cadmium from incinerator sources may increase considerably because of rapid growth in the use
of plastics. Cadmium compounds are used as stabilizers as well as pigments in plastics. It is difficult to
estimate how much of a given compound is used industry-wide because of rapid changes in types and
amount used. Although the cadmium concentration of phosphate rock processed into fertilizer varies from
one source to another, it is usually greater than the natural abundance of the element.
More data are needed on the cadmium content in coal and other fuels to obtain a better assessment of
cadmium release from the burning of fossil fuels. Coal combustion processes are potentially a significant
source of cadmium emissions, but the magnitude of the emissions is not yet clearly defined. If the 454
million metric tons (MT) (500 million tons)4 of bituminous coal burned in the United States during 1970
are assumed to have had a cadmium content of about 0.5 ppm, then the maximum possible cadmium
emissions from combustion of this coal - assuming no controls - would be 245 MT (270 tons). This figure
is over 10 percent of the total emissions from other sources listed in Table 5.6. The actual emissions of
cadmium from coal combustion processes will depend upon the efficiency of cadmium removal by control
5-4
CADMIUM
-------
devices treating the off-gases from the processes. Device efficiency varies from source to source. Moreover,
the stated efficiencies of devices in use apply to their efficiency in collecting total particulate matter;
because a significant fraction of cadmium may be present in very fine particles that a're difficult to collect,
it is quite possible that the efficiency of these devices in removing cadmium may be well below the total
design efficiency. It is clear, men, that total combustion may be a significant source of cadmium, but that
additional investigation is required before a meaningful estimate can be made.
The principal uses of cadmium are as protective coatings (mainly by electroplating), as a paint pigment, as a
plastic stabilizer, and in electrical storage batteries. Cadmium plating protects steel, iron, copper, and brass
from corrosion. The estimated growth in demand projected by the Bureau of Mines1 (Table 5.8) suggests
that a large increase in the use of cadmium as a plastic additive will occur. Smaller quantities of cadmium
are used as alloying agents, in fungicides, pesticides, nuclear control elements, photography, and cathode
ray screens.
Table 5.6. ESTIMATED CADMIUM EMISSIONS TO THE ATMOSPHERE
IN THE UNITED STATES, 19686
(kilograms)
Source category
Mining
Metallurgical processing
Cd separation
from ores
Reprocessing
Pigments
Plastics
Alloys
Batteries
Miscellaneous
Consumptive uses
Rubber tires
Motor oil
Fungicides
Fertilizers
Incineration or other
disposal processes
Plated metal
Radiators
Other
Total emissions
Estimated
emissions
240
950,000
9,500
3,000
2,000
200
500
15,200
5,200
830
200
410
6,640
900,000
110,000
86,000
1,096,000
2,068,080
Environmental Appraisal
5-5
-------
CONVERSION
CONSUMPTION-FATE
EMISSIONS TO
DISSOLVED AND SUSPENDED
CADMIUM FROM ORE FLOTATION
PROCESS AND TAILINGS RUNOFF
SOIL
WATER
TOTAL EMISSIONS < 3,600,000
< 100 000
ELECTROSTATIC
PRECIPITATOR
o
>
o
2
MH
C
s
950,000
WORLD ABUNDANCE
ANNUAL DEMAND
ECONOMIC RESERVE
RESERVE DEMAND RATIO
CRUSTAL ABUNDANCE
SEA WATER ABUNDANCE
TOTAL ABUNDANCE
\
REMELTING
Cd PLATED AND GALVANIZED
SCRAP STEEL
^890,000
BURIED AS DUST
INCINERATION OF
PIGMENTS AND PLASTICS
,230
PERMANENT USE
UNACCOUNTED AND DISCARD
< 4,940,000
NATURAL OCCURRENCE AND
UNINTENDED DISPERSIONS
FOSSIL FUELS
450,000,000 MT COAL AT 0.25 TO 2.0 ppm
230,000 kg Cd
180,000,000 MT DIESEL AND
FUEL OIL AT 0.1 TO 0.5 ppm
< 90,0001(g Cd
130,000
1,000,000
5,200
14,300 MT
650,000 MT
45
0.15 ppm
0.1 ppb
91 x 10'0 MT
FERTILIZER
2-20 ppm Cd IN SUPERPHOSPHATE
AT ll.OOO.OOOMT/yr
,830
MOTOR OIL
CONSUMPTION
0.48 ppm NATURAL Cd
23.000
230.000
Figure 5.1. Flowsheet of societal flow of cadmium in U.S.
indicated otherwise.)
1968.2 (Quantities in kilograms of metal unless
-------
Table 5.7. ESTIMATED U.S. EMISSION INVENTORY FOR CADMIUM, 1971
Source category/source
Estimated
emissions, kg
Estimated
emission factor
Number of
emitting
facilities
Mining
Mining
Primary metallurgical processing
Zinc operations
Lead smelting
Copper smelting
Cadmium units
Metallurgical reprocessing
Reclaiming of steel scrap
Secondary copper operations
Secondary zinc operations
Reprocessing
Plastic stabilizers
Pigments
Alloying
Other
Disposal
Municipal incineration
Sewage sludge incineration
Other sources
Consumption of coal"
Coal-fired power plants
Coke ovens
Industrial and commercial
boilers
Consumption of diesel and
heating oils
Consumption of rubber tires
Limited information sources
Processing of phosphate rock
Secondary cadmium recovery
operations
Consumption of gasoline
320
584,200
148,000
212,000
54,400
70,800
59,000
19,000
3,000
6,400
1,100
450
44,000
125,000
73,000
34,000
18,000
54,000
5,170
0.01 kgCd/MTCd mined
155 kg Cd/MT Cd input
490 kg Cd/MT Cd input
900 kg Cd/MT Cd input
15 kg Cd/MT Cd input
0.001 kg Cd/MT scrap
2 kg Cd/MT auto radiators
0.007 kg Cd/MT Zn produced
3 kg Cd/MT Cd charged
8 kg Cd/MT Cd charged
5 kg Cd/MT Cd charged
1 kg Cd/MT Cd charged
500 kg Cd/MT Cd incinerated
500 kg Cd/MT Cd incinerated
500 kg Cd/MT Cd burned
750 kg Cd/MT Cd burned
500 kg Cd/MT Cd burned
1000 kg Cd/MT Cd input
100 kg Cd/MT Cd impurity
100
9
6
15
8
160
<50
12
3
8
Unknown
Unknown
197
190
750
65
Unknown
Vlobile and unknown
stationary
Mobile
Total estimated kg/year: stationary 1,479,840; mobile - 32,000; combined - 1,511,840
Derived from emission factors in Ib/ton by multiplying by 0.5 to convert to kilograms per metric ton.
Based on 0.5 ppm cadmium content in coal and no control of emissions.
Environmental Appraisal
5-7
-------
Table 5.8. ANTICIPATED GROWTH, BY USE, IN DEMAND
FOR CADMIUM IN THE UNITED STATES, 1968-20001
Application
Electroplating:
Motor vehicles
Aircraft and
boats
Other
Subtotal
Plastics
Pigments
Batteries
Other
Total
1968
103MT
0.59
0.36
2.68
3.63
1.13
0.68
0.18
0.42
6.04
%of
total
9.8
6.0
44.4
60.2
18.7
11.3
3.0
6.9
100
2000
103MT
2.04
0.59
4.50
7.13
4.10
1.13
0.68
0.68
13.72
%of
total
14.9
4.3
32.8
52.0
29.9
8.2
5.0
5.0
100
% increase
1968-2000
245
64
68
96
263
66
277
62
127
5.1.2.2 Mobile Sources-The available data concerning the emissions of cadmium directly from motor
vehicles are limited. lungers et al.7 reported that the levels of cadmium in 22 samples of premium gasoline
ranged from < 0.001 to 0.03 Mg/mL In 22 samples of regular gasoline, the cadmium concentration was less
than 0.08 /ug/ml; in six samples of low-lead gasoline, it was less than 0.04 jug/ml.7 These values were
obtained by the isotope dilution spark source mass spectrometry, an analytical technique that provides
great precision and accuracy.
5.2 CONCENTRATIONS
5.2.1 Air
Cadmium emitted into the air from numerous and varied sources is associated with particles ranging from
submicrometer to possibly 100 micrometers or greater in diameter. The retention time of these particles in
the air depends on particle size, wind factors, and other physical and meteorological parameters. The
smaller particles may remain suspended indefinitely, whereas the larger ones settle out immediately and are
deposited on various surfaces. The greatest research effort has been expended on studies of suspended
cadmium, although a number of investigations directed at cadmium deposition have been carried out.
5.2.1.1 Cadmium in Suspended Paniculate Matter
5.2.1.1.1 National Air Surveillance Network Studies-Sines 1957, ambient air concentrations of cadmium
collected in suspended particulate matter samples at some 300 urban and 30 nonurban NASN sites
distributed over the United States have been determined. Because of relatively low sensitivity, the
spectrographic method of analysis was unable to determine the low ambient cadmium concentrations
prevailing in the majority of cities. Thus, the data base is not adequate for determining the long-term trend
for cadmium. In recent years, analytical methodology has been improved to the extent that data for a large
number of sites are now available. The 1969 data representing the maximum number of NASN sites provide
the most comprehensive base for demonstrating the distribution of cadmium in the atmosphere. The
quarterly and annual average concentrations in the air of the 20 most populous cities are shown in Table
5.9. Table 5.10 provides the same kind of information, plus the percentage of cadmium in the particulate
5-8
CADMIUM
-------
Table 5.9. QUARTERLY AND ANNUAL AVERAGE CADMIUM CONCENTRATIONS3
IN AIR OF THE 20 MOST POPULATED U.S. CITIES, 1969
3)
City
New York City, NY
Chicago, IL
Los Angeles, CA
Philadelphia, PA
Detroit, Ml
Houston, TX
Baltimore, MD
Dallas, TX
Washington, DC
Indianapolis, IN
Cleveland, OH
Milwaukee, Wl
San Francisco, CA
San Diego, CA
San Antonio, TX
Boston, MA
Memphis, TN
St. Louis, MO
New Orleans, LA
Phoenix, AZ
Quarterly average
1
0.017
0.015
0.006
0.010
0.011
<0.003b
0.011
0.005
0.010
0.005
0.012
0.006
0.005
0.007
0.003
0.007
0.003
0.013
0.004
0.005
2
0.023
0.014
0.006
0.014
0.015
0.005
0.010
0.003
0.006
0.020
0.024
0.017
<0.003
0.012
<0.003b
0.008
0.004
0.060
0.004
0.005
3
0.004
0.015
0.006
0.020
0.014
0.005
0.008
0.004
0.007
0.025
0.015
0.010
<0.003
0.015
0.003
0.005
0.003
0.041
0.005
0.005
4
0.011
0.015
0.006
0.015
0.010
0.005
0.017
0.008
0.008
0.011
0.008
0.008
0.006
0.006
0.003
0.004
0.005
0.031
0.004
0.009
Annual
average
0.014
0.015
0.006
0.015
0.012
0.004
0.011
0.005
0.008
0.015
0.015
0.010
c
0.010
0.003
0.006
0.004
0.036
0.004
0.006
aMinimum detectable concentration (MDC) = 0.003 ng/
bMDC/2 used for computation of annual averages.
clnsufficient data to permit computation.
Environmental Appraisal
5-9
-------
matter for those cities with annual average concentrations greater than 0.015 Mg/m3. The quarterly values
could reflect any seasonal differences that might be attributed to fuel used for domestic heating. The
annual average concentrations are of use in evaluating long-range exposures. All cities in the first table
(except St. Louis, which appears in both) have annual averages of 0.015 Mg/m3 or less. This indicates that
some of the highly industrialized smaller cities can have high levels of some pollutants. A review of all
available cadmium data uncovered the fact that El Paso, Tex., had the highest 24-hour average recorded,
0.73 Mg/m3 in 1964; the highest quarterly average, 0.150 Mg/m3 in 1969; the highest annual average, 0.120
Mg/m3 in 1964; and the highest percentage of cadmium in the particulate sample, 0.07 percent in 1969.
These high values are probably attributable to emissions from a large lead smelter located in the area. In
contrast, cadmium levels in 1969 at the 29 active nonurban stations were below the minimum detectable
concentration (0.003 Mg/m3).
Table 5.10. QUARTERLY AND ANNUAL AVERAGE CADMIUM CONCENTRATIONS AT
NASN SITES WITH ANNUAL AVERAGE CONCENTRATIONS GREATER
THAN 0.015 Mg/m3, 19698
City
Denver, CO
Waterbury, CT
E. St. Louis, IL
E. Chicago, IN
Ashland, KY
St. Louis, MO
Helena, MT
Elizabeth, NJ
Newark, NJ
Perth Amboy, NJ
Cincinnati, OH
Allentown, PA
Bethlehem, PA
El Paso, TX
Quarterly average, Mg/m3
1
0.022
0.008
0.045
0.017
0.022
0.013
0.077
0.009
0.015
0.024
0.016
0.011
0.022
0.083
2
0.015
0.029
0.013
0.046
0.017
0.060
0.004
0.029
0.014
0.020
0.017
0.023
0.029
0.150
3
0.018
0.020
0.016
0.027
0.026
0.041
0.005
0.018
0.024
0.017
0.019
0.028
0.015
0.057
4
0.019
0.023
0.015
0.024
0.026
0.031
0.026
0.013
0.099
0.011
0.013
0.017
0.027
0.130
Annual
average,
M9/m3
0.018
0.020
0.022
0.028
0.023
0.036
0.028
0.017
0.038
0.018
0.016
0.020
0.023
0.105
Cadmium
in particulate
matter, %
1.3
2.4
1.8
1.5
1.3
1.7
4.8
2.3
5.1
2.3
1.4
1.9
2.6
7.0
NASN sites listed alphabetically by state.
5-10
CADMIUM
-------
Table 5.11 presents a summary of cadmium data from both urban and nonurban NASN stations collected
after 1965 when the low-temperature sample ashing procedure that prevents loss of cadmium by
volatilization was adopted. For each of the years (1966 through 1969), the annual cadmium averages from
all the sites are categorized into four concentration intervals. The table illustrates that even though the
number of sites has increased over the time period, the cumulative percentage (percentage of sites in that
interval or below) within an interval by year has remained essentially the same. The table, however, does
not indicate the number of stations (estimated to be at least 50 percent) with cadmium below the minimum
detectable concentration. No strong evidence indicates a long-term trend in the cadmium data.
Table 5.11. NUMBER OF STATIONS WITHIN SELECTED CADMIUM
CONCENTRATION INTERVALS, 1966 THROUGH 19698
Number and per-
cent of sites
1969
Number
Percent
1968
Number
Percent
1967
Number
Percent
1966
Number
Percent
Concentration interval, jLig/m3
<0.010
169
81
175
98
119
90
116
91
0.011-0.020
31
15
2
1
7
6
7
5.5
0.021-0.030
5
2.5
2
1
2
1.5
3
2.5
>0.030
3
1.5
0
0
5
2.5
1
1
Total
208
100
179
100
133
100
127
100
5.2.1.1.2 Chicago and northwest Indiana study-During the period May through August 1968, Winchester
and Harrison9 conducted a special study of the areawide distribution of heavy metals in Chicago and
northwest Indiana. Six sets of 24-hour suspended particulate samples collected at 22 sites in Chicago and at
15 industrial and 11 other sites in northwest Indiana were analyzed for lead, copper, and cadmium. Figure
5.2 shows the concentration for each Chicago site on May 21 and for Indiana sites on May 22, and the
corresponding isopleths. Although this represents only one day, it may provide a clue to the distribution of
trace metals in the air over a densely populated, highly industrialized area and the influence of concentrated
sources on pollutant levels over a large urban area.
5.2.1.1.3 Miscellaneous studies-Many special studies have been directed at the definition of the
atmospheric burden of cadmium.10"12 Some were designed to detect the influence of specific sources on
the cadmium levels in the immediate area. The results (Table 5.12) clearly show the contributions of
cadmium-emitting industries in East Helena, Mont., Sweden, and Japan.
5.2.1.2 Size Distribution of Particulate Cadmium13'14-Knowledge of the particle size distribution of
cadmium-containing suspended particulate matter is essential to an evaluation of the human intake by the
respiratory route. Research on the subject has been limited primarily because of the problems associated
with analysis for the very minute amount of cadmium present in each particle size fraction collected by
available equipment. A summary of results obtained by Lee and coworkers in Cincinnati and St. Louis is
presented in Table 5.13.
Environmental Appraisal
5-11
-------
21 MAY 1968 22 MAY 1968
(TUESDAY) \ j (WEDNESDAY)
^-'"+ND"9J \
-> ' 30 1
'30 + >
40 (
|ND 5p V
~1 if"
CHICAGO j 80 \
' / ' ' \
30- + 2f 3^l
LAKE MICHIGAN
iW 10 yo-
|+ . E(lV
?-l , ••h-vi°A
11 ""'-t 3-° ? llO 115 •?°+^o'^>——
» -t-—"-i 70+ An '7
ILLINOIS
•|7.0+ -30 _j
L-, • r-
--»! ••—i '
10 H
GARY
ND
INDIANA
10km
10
MICHIGAN CITY
MICHIGAN CITY
ILLINOIS INDIANA
Figure 5.2. Cadmium concentrations (ng7m3) and isopleths for May 21-22, 1968.
5-12 CADMIUM
-------
Table 5.12. CADMIUM CONCENTRATIONS IN AMBIENT AIR FOR
SELECTED LOCATIONS AND AVERAGING TIMES
Location
Tuxedo, NY10
Sweden11
Stockholm, Sweden11
Manhattan, NY10
Bronx, NY10
Helena, MT12
East Helena, MT12
Sweden11
Japan, City 111
Japan, City 211
Site
Rural
Rural
Center City
Urban
Urban
Urban
Industrial
(Pb smelter)
Industrial
(Cd alloy)
Near zinc
smelter
Near zinc
smelter
Concentration,
,ug/m3
0.003
0.0009
0.005
0.023
0.014
0.03
0.06-0.29
0.7
0.6
0.3
5.4
0.5
0.2
0.16-0.32
Averaging
time
Annual
Month
Week
Annual
Annual
"Several weeks "
24-hr (max)
"Several weeks "
24-hr (max)
Month
Week
24-hr (max)
Week (of 8-hr
values)
Week (of 8-hr
values)
Week (of 8-hr
values)
Source
distance, meters
7,000
800-1,300
800
100
500
100
400
500
The limited available data indicate that a substantial portion of urban particulate cadmium occurs in the
respirable size range (< 3.5 /urn aerodynamic diameter).
5.2.1.3 Cadmium in Settled Particulate (Dustfallj—Most of the particles emitted into the atmosphere
eventually settle out and are deposited on soil, water, roadways, building roofs, and other surfaces. The
fallout rate is dependent on particle size, density, and wind conditions. Thus, when particles containing
cadmium settle out of the air, they contribute either directly or indirectly to the cadmium content of soil
and surface waters. Consequently, data on deposition of cadmium should be of value in any study relating
to the environmental aspects of that element.
5.2.1.3.1 Helena Valley, Montana, Area Environmental Pollution Study12 —A study was conducted in the
Helena Valley during the summer and fall of 1968 to define the extent of pollution in a valley with a large
lead smelter and a zinc recovery plant. As part of the study, settled particulate samples were collected
monthly at six sites and subsequently analyzed for cadmium. The results, summarized in Table 5.14 and
illustrated in Figure 5.3, show that sites 3 and 6, situated nearest the smelter stack, had consistently higher
cadmium fallout.
Environmental Appraisal
5-13
-------
Table 5.13. PARTICLE SIZE DISTRIBUTION OF CADMIUM IN
AIRBORNE PARTICULATE MATTER13'14
Ambient concentration,
M9/rn3
MMDa, jum
Percent <3.5 /im
Percent <2 ,um
Percent <1 jinn
Cincinnati
Business
1966
0.08
3.1
45
40
25
Suburban
1967
0.02
10
45
40
20
St. Louis
Business
1970
0,01
1.5
65
28
MMD—Mass median diameter (the median diameter of suspended particles aerodynamically determined with reference to
spheres of unit density). Fifty percent of the mass is represented by particles with diameters > MMD, and 50 percent of
the mass is composed of particles < MMD.
Table 5.14. CADMIUM IN SETTLEABLE PARTICULATES IN
THE HELENA VALLEY12
(mg/m2-mo)
Station and location
Month
June
July
August
September
October
ib
1.3 km; 34°
0.0
0.5
0.2
0.5
0.5
2
4.0 km; 105°
0.0
0.1
0.1
0.3
0.4
3
0.6 km; 11 2°
2.0
3.0
1.6
1.2
1.5
4
7.2 km; 274°
0.1
0.1
0.1
0.2
0.2
6b
0.8 km; 2°
2.2
3.2
Distance and direction from lead smelter stack immediately south of East Helent,; degrees are computed from north side
of stack in clockwise direction.
Sites 1 and 6 located in East Helena (Figure 5.3).
5-14
CADMIUM
-------
> 1 to<4
SAMPLING STATION LOCATION
N
.
012345
I 1 ' ' • 1
km
Figure 5.3. Helena Valley Environmental Pollution Study: settleable particulate
12
cadmium distribution.
In the final report of the study, it was concluded that 1 to 4 mg Cd/m2-mo was deposited within a 1.6-km
radius of the smelter and 0.1 to 1 mg/m2-mo over an area of 150 km2. No data relative to wind direction
during the study are included in the report. For a S-year period (1949 to 1954) the prevailing wind was
from the west (W-18 percent, WNW-14 percent, WSW-13 percent). Consequently, it is not possible to
explain the data on the basis of meteorological conditions prevailing during the study.
5.2.1.3.2. Roadside study-Creason and coworkers,15 in an attempt to determine if motor vehicles are
sources of trace metal pollutants, determined the cadmium, lead, and zinc content of settled particulate
samples collected monthly at four sites in Cincinnati, Ohio, in July, August, and September 1968 (Table
5.15). Samples were collected at distances of 7.6 and 30.5 meters (m) (25 and 100 feet) from the roadway
at each site.
In this study, the cadmium fallout did not prove to be substantial, and the amount deposited at 30.5 m was
only slightly less than that at 7.6 m, a distribution which could possibly indicate fairly uniform and small
particle size and wind turbulence. Although it has been established that some cadmium is injected into the
air as a result of wear of automobile tires, which contain small amounts of this element, the data obtained
in this study were not suitable for use as a measure of the contribution from this source.
Environmental Appraisal
5-15
-------
Table 5.15. CADMIUM IN SETTLED PARTICULATES - ROADSIDE STUDY15
(mg/m2-mo)
Site
Industrial
Residential
Suburban
Suburban /
commercial
Distance
from
road, meters
7.6
30.5
7.6
30.5
7.6
30.5
7.6
30.5
Month
July
0.084
0.073
0.080
0.067
0.085
0.067
0.061
August
0.054
0.046
0.023
0.023
0.061
0.046
0.252
September
0.076
0.118
0.077
0.077
0.061
0.046
0.069
0.026
5.2.1.3.3 The 77-city study-^ Hunt and coworkers,16 in September through December 1968, conducted a
study of the trace-metal content of settled particulates collected at residential, commercial, and industrial
sites in each of 77 midwestern cities. Standard Metropolitan Statistical Areas with more than 1 million or
less than 100 thousand people were excluded. The investigators reported geometric mean cadmium
deposition (mg/m2-mo) for all cities as a group: residential 0.040, commercial 0.063, and industrial 0.075.
The purpose of this study was to examine a possible relationship between cadmium, lead, and zinc
pollution and cardiovascular disease; however, careful analysis of the cadmium fallout data failed to
uncover any significant relationship.
5.2.1.3.4 Swedish study—Olofson, cited in Friberg et al.11 measured deposition of cadmium emitted from
a Swedish factory (Finspong Plant) at the rate of 460 kg/month. Samples were collected at different times
at seven sites located around the plant during one or more years in the period 1968 to 1970.
The results of this study (Table 5.16) dramatically illustrate the impact of a single major source on the
quality of the surrounding environment. The cadmium fallout from this source contributed substantially to
the pollutant burden of the surrounding area.
5.2.2 Water
The soluble cadmium content of natural waters is low. The major portion will be found in suspended
particles and in the bottom sediments. In water considered not to be polluted by cadmium, concentrations
of less than 1 Mg/liter (ppb) have been reported. In samples from a site 500 meters downstream from a
cadmium-emitting factory, the cadmium content of the water was found to be 4 ppm, while the bottom
sediments contained 80 ppm (dry weight).11
The proposed U. S. interim drinking water standard (1975) for cadmium is 10 jug/liter (0.01 ppm). The
average cadmium concentration in main streams and lakes draining 16 major U. S. watersheds was 9.5
;ug/liter as measured from 1962 to 1967.17
A number of studies have shown mat the cadmium concentration of municipal water systems varies from
the inlet valves to the outlet taps with the latter being the higher. The increase has been attributed to the
cadmium content in the pipes. The cadmium content in galvanized iron pipe has been reported as 360 ppm;
5-16
CADMIUM
-------
polyvinyl chloride (PVC) pipe contains from 0.2 to 2.0 ppm cadmium. The variation in the cadmium
content of the water is apparently dependent upon the pH and temperature of the water and the residence
time in the pipe. Increases in the pH and/or carbonate concentration resulted in lower levels of cadmium.
Results of a study by Schroeder18 are shown in Table 5.17.
Table 5.16. DEPOSITION OF CADMIUM AROUND AN EMITTING FACTORY,
1968 TO 197011
Direction
Number of years
Number of measure-
ments
Deposition, mg/m2-mo
Minimum
Maximum
Average
Distance from factory, km
0.1
S
3
10
4.0
40.0
16.7
0.3
NE
1
2
0.7
1.8
1.3
0.3
N
1
5
1.2
5.3
3.4
0.5
NNW
2
8
0.5
3.0
1.7
0.7
NE
3
10
0.4
4.0
1.3
1.0
sw
2
6
1.0
3.5
1.8
10.4
ENE
1
5
<0.03
0.7
0.3
In 2,595 community water samples analyzed by the Bureau of Water Hygiene in 1969,19 the cadmium
content was found to exceed the mandatory limit in 0.2 percent of the samples.
A study by the U. S. Geological Survey (cited by Fulkerson2), in which 720 water samples were collected
from lakes and rivers throughout the United States and analyzed for the presence of various elements,
showed cadmium present in 42 percent of the samples. The range was from 0.001 to 0.01 mg/liter. The
general conclusion was that higher concentrations of cadmium in water are usually found in areas of high
population density.
Table 5.17. ZINC AND CADMIUM IN MUNICIPAL WATER,
BRATTLEBORO, VT18
(ppb)
Inlet
Spillway
Town water main
Cold running tap water
Stagnant - in pipes
Hot running tap water
Zinc
3.5
3.5
160
1830
Cadmium
2.1
2.5
14.0 to 21.0
8.3
15.0 to 77.0
21
Environmental Appraisal
5-17
-------
5.2.3 Soil
The amount of cadmium in soils, unless contaminated by human activities, is highly dependent upon the
underlying parent rock. Organic matter usually has a higher cadmium content than other soils.2 In soils not
known to be polluted by cadmium, concentrations of less than 1 ppm were reported.11 Bowen20 lists the
cadmium concentration of soil as being 0.06 ppm.
Analysis of the soil at the Virgin Islands Agricultural Station18 revealed 3.38 ppm cadmium in soil
fertilized with phosphatic fertilizer but only 0.15 ppm in untilled and 0.8 ppm in tilled, unfertilized soil.
In the Helena, Montana, study,12 soil concentrations decreased with distance from the smelter complex:
68 ppm at 1.6 km (1 mile)
17 ppm at 3.2 km (2 miles)
4 ppm at 6.4 km (4 miles)
Similar results have been found in Japan in the vicinity of emission sources.
Phosphate fertilizers contain cadmium. Because of the wide usage of phosphate fertilizers, cadmium could
be added to soil in this manner; however, because phosphates tend to precipitate cadmium, it would not be
available to plant or animal life unless converted to a soluble form.2
Cadmium can be added to the soil in sewage sludge. Studies in Sweden and England have reported the
addition of metals to soil in this form. In Sweden, the median concentration of cadmium in sludge was 12
ppm dry weight; the range was from 2 to 61 ppm.21
Deposition of atmospheric particulates in the vicinity of emission sources, water runoff from polluted
sources (factories and mines), use of polluted water in irrigation, and fertilization with cadmium-containing
sewage sludge may all add to the cadmium content of soil.
5.2.4 Food
The cadmium concentrations in food, despite many studies and analyses, are still subject to debate. The
mechanisms involved in the transport of cadmium from its primary sources into the physical environment
and then through the various pathways into the food chain are still not clear. In addition, the results of the
various studies are influenced by the following factors:
• Varying ability of different species of plants and animals to concentrate cadmium.
• Accuracy of the data produced by the analytical methods used.
• Possibility of sample contamination.
• Interpretation of the data.
• Regional differences in soils in which the food plants are grown and water sources when plants are
irrigated.
• Processing through which the food has passed.2 >n
Friberg et al.21 indicate that foodstuffs generally contain less than 0.05 ppm cadmium (wet weight).
Marine organisms, such as shellfish, and the liver and kidney of calves or swine, however, may contain much
higher quantities of cadmium, even in unpolluted areas. Rice and wheat also tend to accumulate cadmium
to concentrations of more than 1 ppm in polluted areas (see Table 5.18).
5-18 CADMIUM
-------
Table 5.18. UPTAKE OF CADMIUM BY RICE AND WHEAT2
Addition
of Cd
to soil.
% CdO
0
0.001
0.003
0.01
0.03
0.1
0.3
0.6
1.0
Rice
Cd, ppm
Yield,
%
100
100
92
92
93
69
32
19
1
Polished
(10%)
0.16
0.28
0.40
0.78
1.37
1.62
1.94
1.37
4.98a
Bran
0.59
0.79
0.84
1.60
2.68
2.94
3.19
3.94
Whole grain
wheat
Yield,
%
100
106
72
16
13
3
3
2
r
Cd,
ppm
0.44
8.27
15.5
29.9
41.4
60.7
48.6
90.8
139.0
Factors of increase in plant concen-
tration for each 10-fold increase
in soil
Rice
Polished
2.8
2.1
...
Bran
2.0
1.8
Whole grain
wheat
3.6
2.0
2.3
Unpolished.
Cadmium levels in food samples collected from 1968 to 1970 from 30 markets in 24 different cities in the
United States are shown in Table 5.19. Table 5.20 shows the cadmium content of selected foods from
several different countries.
Table 5.19. CADMIUM CONTENT IN DIFFERENT FOOD CATEGORIES IN U.S.21
Type of food3
Dairy products
Meat, fish, and
poultry
Grain and cereal
products
Leafy vegetables
Legume vegetables
Root vegetables
Garden fruits
Fruits
Oils, fats, and
shortening
Sugar and adjuncts
Beverages
Potatoes
Cadmium, ppm wet weight
1968-1969
No. ^0.01
10
21
27
27
16
24
25
15
27
18
8
Maximum
0.09
0.06
0.08
0.08
0.03
0.08
0.07
0.38
0.13
0.07
0.04
1969-1970
No.>0.01
9
22
27
28
10
27
27
10
28
27
9
29
Maximum
0.01
0.03
0.06
0.14
0.04
0.08
0.07
0.07
0.04
0.04
0.04
0.08
aTotal number of samples: 30.
Analyzed by atomic absorption and/or polarography at sensitivity of 0.01 ppm.
Environmental Appraisal
5-19
-------
Table 5.20. CADMIUM IN SELECTED FOODS IN VARIOUS COUNTRIES11
(ppm wet weight)
Country
U.S.A.
Western
Germany
Czechoslovakia
Rumania
Japan (non-
polluted areas)
Potato
0.001
0.039
0.09
0.017
0.038
Tomato
0
0.015
0.013
0.032
Wheat flour
0.07
0.047
0.02
0.025
Milk
0.0015-0.004
0.009
0.01
0.003
In the comparison of concentration data from different countries, consideration should be given to the
location of the agricultural area in relation to the cadmium emission sources and the contamination
processes. The majority of the food consumed in the United States is grown in areas remote from primary
emission sources. Similar conditions do not exist in Japan.
Cadmium concentrations in U. S. oysters have been reported to range from 0.1 to 7.8 (jig/
the east coast and 0.2 to 2.1 jug/g on the west coast.22
wet weight on
In general, it may be concluded that most foods, not from cadmium polluted areas, contain less than 0.05
jug/g of cadmium, wet weight.
5.2.5 Tobacco
Analyses of cigars, cigarettes, pipe tobacco, and snuff reveal that tobacco in these forms contains
appreciable amounts of cadmium and nickel. When tobacco is smoked, cadmium is released into the
mainstream and may be inhaled. Menden et al.23 found that American cigarettes have amounts ranging
from 1.56 to 1.96 jug per cigarette. Through the use of a smoking machine, which puffed 35-ml puffs for 2
seconds every minute, the investigators found that the particulate phase of the mainstream contained 0.10
to 0.12 /ig per cigarette. A person who smokes a pack of cigarettes (20 cigarettes) a day inhales about 2 jUg
of cadmium per day (see Table 5.21, and 5.22). The data presented in Table 5.22 suggest that 38 to 50
percent of the cadmium in smoked cigarettes is present in the sidestream. Cadmium, therefore, not only is
inhaled by the smoker but enters the air in the smoke from the sidestream (smoke from cigarette not drawn
in by smoker) and may be inhaled from there also.
5-20
CADMIUM
-------
Table 5.21. METAL CONTENT OF TOBACCO PRODUCTS
23
Kentucky reference
cigarettes (KR)
Commercial brand
cigarettes (CB)
Batch 1
Batch 2
Metal content,3
;itg/cigarette
Cadmium
1.56±0.19
(6)c
1.90±0.14
(4)
1.96±0.11
(4)
Nickel
4.25±0.18
(2)
7.55±0.15
(4)
Zinc
33.4± 2.4
(7)
38.9± 9.0
(4)
20.0± 0.8
(4)
Values are mean ± standard deviation.
KR cigarettes weighed 1.12 ± 0.04 grams and CB cigarettes weighed 1.12 + 0.10 grams.
Value in parentheses denotes number of samples.
Environmental Appraisal
5-21
-------
Table 5.22. TRACE-METAL CONTENT OF CIGARETTE FRACTIONS
23
Fraction
KRC cigarettes
Smoked portion
(73% of total)
Smoked butt
TSCC (mainstream
particulate phase)
Ash
Sidestream
CBC cigarettes
Smoked portion
(73%)
Smoked butt
TSCC (mainstream
particulate phase)
Ash
Sidestream
Metal contenta'b
Cadmium
1.14
0.56 ± 0.03(6)
0.1210.03(5)
10.1%
0.45± 0.03 (4)
39.4%
0.43
38%
1.43
0.67± 0.02 (4)
0.10±0.01 (2)
7%
0.48± 0.02 (4)
33.5%
0.72
50%
Nickel
3.10
1.3310.07(2)
'0.08
2.6%
1.81±0.16(2)
58.4%
1.03
33%
5.51
2.6410.17 (4)
0.021 0.01 (2)
0.4%
4.271 0.20 (4)
77.5%
0.62
11%
Zinc
24.3
12.411.9(6)
0.36
1.5%
21.314.7(5)
87.6%
-0.66
3%
14.6
7.61 0.8 (4)
0.061 0.01 (2)
0.4%
11.910.5(4)
81.5%
0.40
3%
Concentrations are in Mg per fraction listed. Values are means ± standard deviation or calculated values. Parentheses
indicate the number of samples.
Percentages were calculated on basis of smoked portion.
CKR = Kentucky reference; TSC = tobacco smoke condensate; CB = commercial brand.
Sidestream was calculated by subtracting the values of smoked butt, TSC, and ash from the total cigarette value given in
Table 5.22. (Enrichment can be estimated by subtracting the calculated value for unsmoked butt from the experimental
value given.)
5-22
CADMIUM
-------
5.3 REFERENCES FOR SECTION 5
1. Mineral Facts and Problems, 1970 Ed. U. S. Department of Interior, Bureau of Mines, Washington,
D.C. Bulletin No. 650. 1970.
2. Cadmium: The Dissipated Element. Fulkerson, W., and H. E. Goeller (Ed.). Oak Ridge National
Laboratory, Oak Ridge, Tenn. 1973.
3. Lange's Handbook of Chemistry. Lange, N. A. (Ed.). 8th Ed. New York, McGraw-Hill Book Co., 1952.
4. 1971 Minerals Yearbook, Vol. HI. U. S. Department of Interior, Bureau of Mines, Washington, D. C.,
1973.
5. Handbook of Chemistry and Physics, 53rd Ed. Cleveland, Chemical Rubber Co., p. D-172.
6. National Inventory of Sources and Emissions: Cadmium, Nickel and Asbestos. W. E. Davis and
Associates. Prepared for U. S. Department of Health, Education, and Welfare, National Air Pollution
Control Administration, Washington, D. C., under Contract No. CPA-22-69-131. February 1970.
7. lungers, R. H., R. E. Lee, Jr., and D. J. von Lehmden. The EPA Fuel Surveillance Network. 1. Trace
Constituents in Gasoline and Commercial Gasoline Fuel Additives. Environ. Sci. Technol. (in press)
8. Unpublished NASN cadmium data stored in the National Aerometric Data Bank, U. S. Environmental
Protection Agency, Research Triangle Park, N. C.
9. Winchester, J. W., and P. R. Harrison. Area-wide Distribution of Lead, Copper, Cadmium and Bismuth
in Atmospheric Particles in Chicago and Northwest Indiana. University of Michigan, Department of
Meteorology and Oceanography, Ann Arbor, Mich. Report No. 01173-4-T. 1970.
10. Kneip, T. J., M. Eisenbud, C. D. Strehlow, and P. C. Freudenthal. Airborne Particulates in New York
City. J. Air Pollut. Contr. Assoc. 20:144-149, March 1970.
11. Friberg, L., M. Piscatof, and G. Nordberg. Cadmium in the Environment. Cleveland, Chemical Rubber
Co. Press, 1971.
12. Helena Valley, Montana, Area Environmental Pollution Study. U. S. Environmental Protection Agency,
Office of Air Programs, Research Triangle Park, N. C. Publication No. AP-91. January 1972.
13. Lee, R. E., R. K. Peterson, and J. Wagman. Particle Size Distribution of Metal Components in Urban
Air. Environ. Sci. Technol. 2:288-290, 1968.
14. Lee, R. E., S. S. Goranson, R. E. Enrione, and G. B. Morgan. National Air Surveillance Cascade
Impactor Network, II. Size Distribution Measurements of Trace Metal Components. Environ. Sci.
Technol. 6:1025-1030, 1972.
15. Creason, J. P., 0. McNulty, L. T. Heiderscheit, D. H. Swanson, and R. W. Buechley. Roadside
Gradients in Atmospheric Concentrations of Cadmium, Lead, and Zinc. In: Trace Substances in
Environmental Health, V. Columbia, University of Missouri Press, 1972.
16. Hunt, W. F., C. Pinkerton, 0. McNulty, and J. Creason. A Study of Trace Element Pollution of Air in
77 Midwestern Cities. (Presented at 4th Annual Conference on Trace Substances in Environmental
Health, University of Missouri. Columbia.1970.)
Environmental Exposure 5-23
-------
17. Lagerwerff, J. V. Trace Elements and the Quality of Our Environment. Prepared for presentation at the
Symposium on Micronutrients in Agriculture. Muscle Shoals. Ala., April 20-22, 1971.
18. Schroeder, H. A., A. P. Nason, I. H. Tipton, and I. I. Balassa. Essential Trace Metals in Man: Zinc.'
Relation to Environmental Cadmium. J. Chron. Dis. 20:179-210,1967.
19. Community Water Supply Study. Environmental Health Service, Bureau of Water Hygiene, Cincinnati,
Ohio.1970.
20. Bowen, H. J. M. Trace Elements in Biochemistry. London, Academic Press, 1969.
21. Friberg, L., M. Piscator, G. Nordberg, and T. Kjellstrom. Cadmium in the Environment, II. The
Karolinska Institute, Stockholm, Sweden. Prepared for U. S. Environmental Protection Agency,
Research Triangle Park, N. C., under Contract No. 68-02-0342. Publication No. EPA-R2-73-190.
February 1973. 169 p.
22. Pringle, B. H., D. E. Hissong, E. L. Katz, and S. T. Mulawka. Trace Metal Accumulation by Estuarine
Mollusks. J. Sanit. Eng. Div. 94:455-475, 1968.
23. Menden, E. E., F. J. Elia, L. W. Michael, and H. W. Petering. Distribution of Cadmium and Nickel of
Tobacco During Cigarette Smoking. Environ. Sci. Technol. 6:830-832, 1972.
5-24 CADMIUM
-------
6. ENVIRONMENTAL EXPOSURE
6.1 HUMAN EXPOSURE AND INTAKE RATES
Cadmium enters the body mainly through ingestion or inhalation. Skin penetration by soluble cadmium
compounds can take place, but this exposure route is of minor importance to the general population. The
estimated cadmium concentrations and the media through which human exposure may occur are listed in
Figure 6.1.
6.1.1 Food
Whereas the estimates of exposure via air or water are relatively accurate, reliable estimates of exposure via
food are difficult to obtain. There are several reasons for this lack of data. One is the difficulty of analyzing
cadmium in food; another, the fact that, whereas cadmium often is determined in the raw food material,
the actual exposure takes place through mixed diets, which have been processed in different ways. This
processing may result either in the loss of cadmium during cooking or result in further contamination from
the utensils used.
Because of ambient cadmium concentrations, consumption of foods, even from uncontaminated areas, will
result in a daily intake of approximately 50 ,ug. Estimates of daily intakes in selected countries are given in
Table 6.1. These estimates are based on cadmium concentrations in raw agricultural products and available
data on consumption of different foodstuffs.
Table 6.1. DAILY INTAKE OF CADMIUM VIA FOOD IN DIFFERENT COUNTRIES2
Country
Cadmium,
jug/day
Measurement
method
United States
West Germany
Rumania
Czechoslovakia
Japan (nonpolluted
area)
4 to 60
48
38 to 64
60
59
Dithizone
Atomic absorption after
extraction
Dithizone
Dithizone or isotope dilution
or atomic absorption
Dithizone or atomic absorption
after extraction
6-1
-------
CONCENTRATIONS
ppm
mg/liter y g/g
1000
CHRONIC EFFECTS
500-
100
13-15-
•50
-10
9.0-
U.S. SUPERPHOSPHATE
5.0 —
SOILS <
2.45-
EXTRAPOLATED DAILY INTAKE IN
ppm FOR MAN THOUGHT TO
RESULT IN LISTED SYMPTOM
(BASED ON TOTAL DAILY INTAKE OF
1600g OF FOOD CONTAINING THE
INDICATED CONCENTRATION OF
CADMIUM IN ppm)
•3.0-
-3.4-
1.0
0.26-
,-0.13-
•0.5
-0.35-
-1.6-
4% OF THE
SURFACE WATER/
0.1
I
VALLEY
RICE AND SOYA
CRUSTAL
•0.15-ABUNDANCE
0.064-
0.05—
USPHS
MAXIMUM IN
POTABLE WATER
LES USGS
I OF THE
HCE WATER <
-ESUSGS
— 0.027-
{
.C
1
>EXTREME RANGE
OF U.S. FOODS
:ANGE FOR
U. S. INSTITU-
TIONAL DIETS
ITAI ITAI
-0.08—^r-
50 YEAR INTAKE
TO CAUSE KIDNEY
DAMAGE
0.001
54%OF THE
SURFACE WATER
SAMPLES USGS ]
0.0003 CARIBBEAN SEA WATER
Figure 6.1. Cadmium concentrations of surface waters, soils, and foods and estimated
dose levels resulting in various symptoms and effects in humans.1
6-2
CADMIUM
-------
As can be seen, there if fairly good agreement between estimates obtained in different countries. It should
be pointed out, however, mat because of the method used, U.S. values are higher. The method using
extraction of the element is more accurate.
Generally, there is agreement that fruit has the lowest cadmium levels and that shellfish and the kidney and
liver of animals have the highest concentrations.
Polluted areas present a different picture. Rice in the Jintsu Valley of Japan was found to have a cadmium
content 30 times greater than in nonpolluted areas.3 The rice fields were polluted by industrial activities.
A study by EPA in East Helena, Mont, indicates that up to 83 /ag/day of cadmium could be added to an
ordinary diet by the consumption of fruits and vegetables grown in soil contaminated by cadmium.
Eating shellfish can also add to the amount of cadmium ingested. The Eastern oyster was found to contain
an average of 3.1 ppm; the soft shell clam and Northern Quahaug clam contained 0.27 and 0.19 ppm,
respectively.5 Seawater has an average cadmium concentration of 0.0001 ppm, and the biological
accumulation of cadmium by shellfish ranges from 100 to more than 3,000 ppm.
6.1.2 Air
In ambient air, mean yearly cadmium concentrations may range from less than 0.001 to 0.05 ,ug/m3. Higher
values have been reported in areas near cadmium-emitting industries, such as in Sweden where monthly
means of up to 0.3 Mg/m3 have been measured.2
Few data dealing with the deposition, retention, and elimination of cadmium aerosol exist.2 If the
assumption is made, however, that the deposition of inhaled cadmium aerosols in the respiratory system is
similar to the behavior of other particulate matter, then the deposition depends not only on the air
concentration but also on particle size. It can be said, then, that the amount of cadmium inhaled depends
on the volume of air (average inhalation is 20 m3/day) and the ambient concentration of cadmium. The
fraction of the inhaled portion that is deposited in the lung depends on the particle size—the smaller the
particle, the greater the rate of deposition.
6.1.3 Smoking
Cadmium has been found in cigarettes in amounts of about 1 to 2 jug per cigarette.6"8 Using smoking
machines and standardized methods, it has been shown that 0.1 to 0.2 /ug of cadmium per cigarette will be
found in the mainstream.
The smoking of 20 cigarettes per day, then, could cause the inhalation of 2 to 4 /ug of cadmium depending
on the amount of smoke inhaled. Autopsies made of smokers and nonsmokers substantiate this statement.9
It was found that there was a significant correlation between the number of years of cigarette smoking and
the amount of cadmium in kidney, liver, and lungs.
The smoker is not the only person exposed to cadmium, however. Studies indicate that more cadmium is
emitted from cigarettes in the sidestream than from the mainstream. Sidestream smoke has been shown to
contain from 0.43 to 0.72 ug of cadmium per cigarette.8
6.1.4 Water
The cadmium concentration of waters, in areas unpolluted by cadmium, has been reported as being 1
/ug/liter (1 ppb) or less.2 The proposed EPA drinking water standard is 10 /ug/liter (0.01 ppm). Although
higher concentrations for drinking water have been reported in certain areas of the United States, drinking
water generally contains less than 1 /ug/liter. At this level, consumption of up to 4 liters of water per day
Environmental Exposure 6-3
-------
would result in the ingestion of only a few micrograms. At a concentration of 10 ;ug, a daily intake of 20 to
40 pig of cadmium would result if 2 to 4 liters of water were consumed.
6.1.5 Soil
Comprehensive studies of cadmium exposure from soils have not been made. Cadmium in the soil may be
taken up by plants and thus become available to man through food.
6.2 REFERENCES FOR SECTION 6
1. Cadmium: The Dissipated Element. Fulkerson, W., and H. E. Goeller (Ed). Oak Ridge National
Laboratory, Oak Ridge, Tenn. 1973.
2. Friberg, L., M. Piscator, and G. Nordberg. Cadmium in the Environment. Cleveland, Chemical Rubber
Co. Press, 1971.
3. Yamagata, N. and I. Shigematsu. Cadmium Pollution in Perspective. Bull. Inst. Public Health. 79:1-27,
1970.
4. Helena Valley, Montana, Area Environmental Pollution Study. U. S. Environmental Protection Agency,
Office of Air Programs, Research Triangle Park, N.C. Publication No. AP-91. January 1972.
5. Pringle, B. H., D. E. Hissong, E. L. Katz, and S. T. Mulawka. Trace Metal Accumulation by Estuarine
Mollusks. J. Sanit. Eng. Div. 94:455-475, 1968.
6. Szadkowski, D., H. Schultze, K. H. Schaller, and G. Lehnert. Zur Okologischen Bedeutung des
Schwermetallgehalts von Zigarettes. (Consideration of the Oncologies Significance of the Heavy Metals
in Cigarettes.) Arch. Hyg. Bakteriol. 153:\, 1969.
7. Nandi, M., H. Jick, D. Slone, S. Shapiro, and G. P. Lewis. Cadmium Content of Cigarettes. Lancet.
11:1329, 1969.
8. Menden, E. E., F. J. Elia, L. W. Michael, and H. G. Petering. Distribution of Cadmium and Nickel of
Tobacco During Cigarette Smoking. Environ. Sci. Technol. (5:830-832, 1972.
9. Lewis, G. P., L. Coughlin, W. J. Jusko, and S. Hartz. Contribution of Cigarette Smoking to Cadmium
Accumulation in Man. Lancet. 7:291-293, 1972.
6-4 CADMIUM
-------
7. MECHANISMS OF EXPOSURE AND RESPONSE
7.1 RESPIRATORY ABSORPTION
Respiratory absorption is one of the chief avenues of entrance of pollutants into the human body. There
are, however, very few data dealing with the deposition, retention, and elimination of cadmium aerosols
entering the lungs.1 The rate of deposition of particles in the lungs is dependent on particle size as well as
the concentration in the air.1
Cadmium is absorbed to a large extent after inhalation. Absorption occurs primarily in the lungs, but occurs
also in the gastrointestinal tract after mucociliary clearance. Data dealing with human absorption are not
available, but animal experiments suggest an absorption of between 10 to 40 percent of the cadmium
inhaled.2 For instance, calculations based on experiments by Friberg3 in which rabbits were exposed to
cadmium iron oxide dust for several months showed that about 30 percent of the inhaled cadmium was
absorbed into the body.
7.2 GASTROINTESTINAL ABSORPTION
The absorption and excretion of radioactive cadmium in five human volunteers was studied by Rahola et
al.4 They found that during the 3 to 5 days following the administration of labeled cadmium (' : s Cd) in
calf-kidney suspension, about 70 percent of the activity was eliminated. The total ingestion of cadmium
was about 100 /ug. Most of the excreted activity was in the feces. Rapid elimination of the tracer continued
until about 6 percent of the dose remained in the body, indicating an average absorption of at least 6
percent.
Experiments in adult animals have shown that between 1 and 3 percent of the oral dose of cadmium is
retained in the body several days after exposure. These results suggest that a considerable amount of
unabsorbed cadmium will be excreted in feces as late as between the 5th and 10th day.2 The decrease in
whole-body retention of radioactive cadmium was very slow from 20 days to 2 months after exposure.2
The influence of calcium deficiency on absorption and retention of cadmium after oral intake has been
studied. The studies indicated that rats on low-calcium diets accumulate more cadmium in their livers and
kidneys than rats on high-calcium diets.1'2 Vitamin D and the protein level of the diet appear to affect
cadmium retention in animals since (1) rachitic chickens absorb more cadmium when vitamin D is
administered along with cadmium1 and (2) mice on a low-protein diet for 24 hours preceding and following
an oral dose of cadmium chloride absorbed about twice as much cadmium as mice on a high-protein diet for
the same period.1
The available data, therefore, indicate that the absorption rate of cadmium is about 6 percent in male adult
human beings. Absorption may be higher for individuals with a calcium deficiency or a greater calcium
demand.2
7.3 TRANSPORT AND DISTRIBUTION
Most of the work on the transport and distribution aspects of cadmium metabolism has been done in
animals. Because such a small proportion of orally administered cadmium is absorbed, it has not been
7-1
-------
possible to study the distribution of radioactive cadmium in the blood after ingestion of the materials.
After interperitoneal administration, most of the cadmium initially found in the blood is associated with
the plasma. It is then rapidly cleared from the plasma and, after about 12 to 24 hours, the concentrations in
the whole blood begins to rise again. This is caused by an increase in the cadmium content of the red blood
cells, which, at mat time, also contain metallothionein.1 When animals are given repeated injections of
cadmium, the concentrations of the metal in the erythrocytes becomes many times greater than the
concentration in the plasma. Further distribution of cadmium throughout the body is dependent on the
elapsed time since the absorption of the material. The largest concentrations of the metal are found in the
liver and the kidneys. The concentrations of the metal in these organs are roughly proportional to the
intake of cadmium; but as the dose of cadmium is increased, the proportion in the liver becomes greater.1
In individuals without known "over" exposure to cadmium, the mean level in whole blood is less than 1
jug/100 ml. In workers exposed to cadmium, concentrations of up to 30 jug/100 ml of whole blood have
been found. In workers exposed to cadmium, the blood cadmium concentration will decrease when
exposure stops.1
Cadmium concentrations have been determined in the organs of various populations. In the United States,
the average concentration of cadmium in the liver of "normal" individuals varies with age. The values
usually do not exceed 2 jug/g of tissue (wet weight). "Normal" values from two Japanese studies are
higher.1
The placenta is an effective barrier for cadmium, and the concentration in the liver of the newborn is less
than 0.002 jug/g.
Data on the concentration of cadmium in the livers of workers who have been exposed to cadmium oxide
dust in the past have shown that there is no tendency for the concentration to decrease substantially with
time following the cessation of exposure to cadmium.1 Data from the United States, Japan, Sweden, and
East Germany show that there is a progressive increase in the concentration of cadmium in the renal cortex
with increasing age. The average concentration of cadmium in the renal cortex by age groups in the United
States is shown in Table 7.1
Table 7.1. AVERAGE CADMIUM CONCENTRATION IN RENAL
CORTEX BY AGE GROUPS IN THE UNITED STATES
Age group
1 to 9
" 10 to 19
20 to 29
30 to 39
40 to 49
Cadmium content,
jug/g wet weight
7
25
30
46
53
After age 50 to 60, there is a decline in the concentration of cadmium in the renal cortex. Why this occurs
is not known. Recent investigations by Hammer et al.s have shown that in North Carolina the average
cadmium concentration at age 50 is about 25 /ug/g of tissue (wet weight). This result is similar to values
reported from Sweden and East Germany, but lower than in areas in Japan regarded as not being polluted
by cadmium (Table 7.2).
7-2 CADMIUM
-------
Table 7.2. MEAN CADMIUM CONCENTRATIONS IN RENAL CORTEX AT AGE 501'2
Country
East Germany
East Germany
Sweden
(Stockholm)
United States
(large cities)
United States
(North Carolina)
Japan
(Kobe)
Japan
(Kanazawa)
Japan
(Tokyo)
Sex
M
F
M and F
Mand F
M and F
M and F
Mand F
Mand F
Cadmium content,
M9/g wet weight
30
15
30
50
25
60
85
125
7.4 EXCRETION
7.4.1 Urine
The average normal excretion of cadmium in urine is less than 5 Mg/day. Most of the studies done in the
past years have found the excretion to be 1 to 2 Mg/day in adults. Recent investigations in Japan have
shown that the urinary excretion will increase with age, being about 0.5 /ug/liter in children and about 2
Mg/liter at age 40.6' 7
Various studies have found cadmium excretion varying from less than 1 Mg/day to 100 Mg/day. It has
recently been shown that in workers with long-term exposure to relatively low concentrations of cadmium
oxide dust, urinary excretion of cadmium generally did not exceed 10 Mg/g creatinine in workers with
normal urine protein electrophoretic patterns, whereas workers with tubular proteinuria excreted
considerably larger amounts. Renal tubular dysfunction may thus cause increased excretion of cadmium. In
workers with short-term, high-level exposure to cadmium oxide dust or fumes, the urinary excretion of
cadmium may sometimes be high without any changes in renal function. In these cases the increased
urinary excretion probably reflects the more recent exposure than the body burden.1
The increased urinary excretion when there is renal damage explains why renal concentrations of cadmium
often have been quite low in autopsied workers with severe morphological kidney changes.1
7.4.2 Feces
Animal experiments have shown that a small percent of injected cadmium will be excreted via the
alimentary tract. This excretion is mainly dependent on recent exposure.1 The data do not indicate the role
this excretion route plays in human beings.1
Mechanisms of Exposure and Response
7-3
-------
7.4.3'Hair t
A small amount of cadmium is excreted in the hair. Although this excretion is not important as a means of
ridding the body of cadmium, it has been explored as a possible indicator of cadmium exposure. The
method is complicated by the fact that hair can be contaminated by metals in the atmosphere as well as
metals in hair lotions and hair spray.
7.5 BODY BURDEN
Schroeder and Balassa8 estimated the total body burden of cadmium to be about 30 mg in the "standard
American man." In a study in North Carolina, Hammer et al.5 found the corresponding figure to be about
15 mg, which is similar to what has been found in some European countries.
According to Friberg et al.1 the total body burden at age 50 in noncontaminated areas in Europe is 15 to
20 mg and in Japan 40 to 80 mg. Recent studies of Tsuchiya et al.7 support the conclusions that even in
so-called nonpolluted areas of Japan, body burdens of cadmium are much higher than in other
industrialized areas of the world.
Earlier assumptions that smokers will have higher body burdens than nonsmokers have been verified by the
results of Lewis et al.9 They determined the cadmium content in the kidney, liver, and lungs of 45 male
smokers (mean age 60 years) and in 22 male nonsmokers (mean age 60 years). It was possible to calculate
the number of "cigarette pack years" for each smoker. Cadmium in kidney, liver, and lungs of nonsmokers
averaged 6.6 mg; in smokers, the corresponding figure was 15.8 mg. There was a significant association
between the number of pack years and cadmium accumulation.
About half of the total cadmium will be found in liver and kidneys together—about a third in the kidneys
alone. In exposed workers, the percentage in the liver increases in relation to the kidney.
7.6 BIOLOGICAL HALF-TIME
The biological half-time of cadmium in humans is extremely long. This conclusion is based on a model for
cadmium accumulation in the body based on the concept that one-third of the body burden was in the
kidneys.1 Kjellstrom10 and Tsuchiya et al.11 used autopsy data and calorie consumption in these
calculations. Biological half-times of from 18 to 33 years were thus obtained. Tsuchiya et al.12 calculated
the biological half-time to be about 17 years in the kidney and 6 years in the liver, based on renal and liver
burdens of cadmium obtained by autopsies on inhabitants of Tokyo.
In these reports, it was noted that many parameters must be taken into account when calculating biological
half-time, such as changes in food intake and changes in kidney weight with age. Changes in exposure over
the years must also be taken into account.13 All data continue to favor a very long biological half-time,
although the question of the exact biological half-time of cadmium in the human body is still under
discussion.2
7.7 CONCLUSIONS
Current knowledge of the mechanisms of exposure and response lead to the following conclusions:
• Uncertainties with regard to absorption rates after inhalation in humans and other animals still exist
and demand extensive investigation.
• Calcium deficiency will cause a considerable increase in cadmium absorption whether exposure occurs
through food or drinking water.
7-4 CADMIUM
-------
• The initial accumulation of cadmium in red blood cells is followed by a decrease and later by a new
accumulation. This distribution is associated with a buildup of metallothionein in the cells. After
exposure to cadmium ceases, blood levels gradually drop.
• Repeated exposure to small amounts of cadmium results in its continuous buildup in liver, kidneys,
and other organs.
• In human beings, an absorption of ingested cadmium of up to 10 percent must be considered possible
when conditions such as a calcium or protein deficiency exist.
• Total body burden of cadmium at age 50 is approximately 15 to 20 mg in Europe; 15 to 30 mg in the
U.S.; and 40 to 80 mg in Japan.
• In normal human beings, daily excretion of cadmium via urine is very low, 2 /ag/liter or less.
• Estimates based on mathematical models show that the half-time for cadmium in the total body may
be between 10 and 30 years. Many uncertainties still exist with regard to biological half-time in total
body and in different organs. It is obvious, however, that the biological half-time of cadmium is
extremely long.
7.8 REFERENCES FOR SECTION 7.
1. Friberg, L., M. Piscator, and G. Nordberg. Cadmium in the Environment. Cleveland, Chemical Rubber
Co. Press, 1971.
2. Friberg, L., M. Piscator, G. Nordberg, and T. Kjellstrom. Cadmium in the Environment, II. The
Karolinska Institute, Stockholm, Sweden. Prepared for the U. S. Environmental Protection Agency,
Research Triangle Park, N.C., under Contract No. 65-02-0342. Publication No. EPA-R2-73-190.
February 1973. 169 p.
3. Friberg, L. Health Hazards in the Manufacture of Akaline Accumulators with Special Reference to
Chronic Cadmium Poisoning. Acta. Med. Scand. Suppl. 138:240, 1950.
4. Rahola, T. R., R. R. Aaren, and J. K. Miettinen. Half-time Studies of Mercury and Cadmium by Whole
Body Counting. (Presented at IAEA/WHO. Symposium on the Assessment of Radioactive Organ and
Body Burdens, Stockholm. Nov. 22-26, 1971.)
5. Hammer, D. I., A. V. Colucci, V. Hasselblad, M. E. Williams, and C. Pinkerton. Cadmium and Lead in
Autopsy Tissues. J. Occup. Med. 75:956-963, 1973.
6. Katagiri, Y., M. Tati, H. Iwata, and M. Kawai. Concentration of Cadmium in Urine by Age. Med. Biol.
52:239, 1971 (in Japanese).
7. Tsuchiya, K., Y. Seki, and M. Sugita. Organ and Tissue Cadmium Concentrations of Cadavers from
Accidental Deaths. (Presented at 17th International Congress on Occupational Health, Buenos Aires.
1972.)
8. Schroeder, H. A., and J. J. Balassa. Abnormal Trace Metals in Man: Cadmium. J. Chron. Dis. 14:236,
1961.
9. Lewis, G. P., W. J. Jusko, L. Coughlin, and S. Hartz. Contribution of Cigarette Smoking to Cadmium
Accumulation in Man. Lancet. 7:291-293, 1972.
Mechanisms of Exposure and Response 7-5
-------
10. Kjellstrom, T. A Mathematical Model for the Accumulation of Cadmium in Human Kidney Cortex.
Nord.Hyg. J. 55:111, 1971.
11. Tsuchiya, R., M. Sugita, and Y. Seki. A Mathematical Model for Deriving the Biological Half-life of a
Chemical. Nord. Hyg. J. 5J:105, 1971.
12. Tsuchiya, K., M. Sugita, and Y. Seki. A Mathematical Approach to Deriving Biological Half-time of
Cadmium in Some Organs, Calculation from Observed Accumulation in Organs. (Presented at 17th
International Congress on Occupational Health, Buenos Aires. 1972.)
13. Kjellstrom, T., and L. Friberg. Interpretation of Empirically Documented Body Burdens by Age of
Metals with Long Biological Half-Times with Special Reference to Past Changes in the Exposure.
(Presented at 17th International Congress on Occupational Health, Buenos Aires. 1972.)
7-6 CADMIUM
-------
8. EFFECTS
8.1 HUMAN IMPACT
8.1.1 Respiratory Effects of Cadmium Exposure
8.1.1.1 Acute Effects~Anima[ studies indicate that effects from the inhalation of cadmium oxide or
cadmium chloride aerosols occur in three clearly demarcated stages:
• Acute pulmonary edema, developing within 24 hours of exposure.
• Proliferative interstitial pneumonitis, observed from the third to the tenth day after exposure.
• Permanent lung damage in the form of perivascular and peribronchial fibrosis.1
The first two stages have been confirmed clinically or through autopsy for humans.1
The cadmium dose that resulted in two human deaths was calculated to be approximately 2,500
mg/m3-min. This represents an exposure to 100 mg/m3 for 25 minutes or 50 mg/m3 for 50 minutes.1
8.1.1.2 Chronic Effects—Friberg2 found emphysema of the lung among male workers chronically exposed
to cadmium oxide dust in an alkaline battery factory in Sweden. Quantitative data concerning the exposure
levels were incomplete; however, a range of 3 to 15 mg/m3 was reported. Several other instances of lung
damage, including pulmonary sclerosis, bronchitis, and emphysema have been reported.1 Little information
is available, however, concerning the possible association between respiratory disease and exposure to
cadmium via ambient air. The establishment of dose-response relationships is hindered at present because
time-weighted average exposures are available only for short time spans.1
8.1.2 Systemic Effects of Cadmium Exposure
8.1.2.1 Kidney Effects—In fatal cases of acute cadmium poisoning via inhalation, pathological changes have
been found in the kidneys.1 Transient proteinuria has been detected in individuals with nonlethal cadmium
exposure.1
Prolonged exposure to cadmium oxide dust has given rise to renal damage in factory workers. Proteinuria is
the most common clinical manifestation of this type of renal damage.1 Piscator and Lind3 have shown that
the magnitude of proteinuria is related to the length of exposure. Glycosuria, amino-aciduria, diminished
concentrating capacity, and renal stones have also been reported in cadmium-exposed workers. Although
proteinuria occurs frequently in cadmium workers, its magnitude tends not to progress once the exposure
to the metal ceases.
The relationship between the dose of cadmium and the degree of kidney damage is poorly defined. Present
data are inadequate to accurately quantitate the magnitude of the cadmium exposure of industrial workers.
Furthermore, because there is no constant relationship between the concentration of cadmium in the blood
and the cadmium content of the kidney, the former cannot be used to estimate the dose of cadmium in the
kidneys.
8-1
-------
On the basis of data from workers exposed to cadmium and from animals manifesting functional and
morphological changes in the renal cortex following exposure to cadmium, the authors of Cadmium in the
Environment1 have concluded that a cadmium concentration of about 200 ppm (wet weight) in the renal
cortex is a "critical concentration." When a level of 200 ppm is reached, the first sign of tubular
dysfunction (tubular proteinuria) may appear in sensitive persons. Estimates of the long-term exposure
necessary to achieve a concentration of 200 ppm of cadmium in the renal cortex have been made (Table
8.1).
Table 8.1. ESTIMATED MINIMUM CADMIUM LEVELS VIA INHALATION
OR INGESTION NECESSARY FOR REACHING 200 ppm (WET WEIGHT) OF
CADMIUM IN RENAL CORTEX (TOTAL BODY BURDEN: 120 mg CADMIUM)
(jugCd/m3)
Exposure,
years
10
25
50
Total daily
ingestion
Retention rate, %
2.5
1324
530
265
5
662
265
132
10
331
132
66
Ambient aira
Retention rate, %
10
16.2
6.5
3.2
25
6.5
2.6
1.3
40
4.1
1.6
0.8
Industrial aira
Retention rate, %
10
52.5
21.0
10.5
25
21.0
8.4
4.2
40
13.1
5.2
2.6
A lung ventilation of 20 m3 per day has been used for evaluation of ambient air exposure. A lung ventilation of 10 m3 per
8 hours for 225 days per year has been used for evaluation of industrial air exposure. No corrections have been made for
cumulative effects of different types of exposure, including tobacco smoking. A linear approximation of the accumulation
of cadmium has been used.
Using Table 8.1, it can be noted that a daily oral intake over 50 years of 100 to 150 Mg cadmium with a 5
percent retention may give rise to renal dysfunction. Long-term exposure to low levels of cadmium usually
result in about one-third of the cadmium remaining in the kidneys.1
Calcium deficiency has been shown to increase the absorption of cadmium.1 Exposure via water and
smoking should also be taken into account.
8.1.2.2 Liver Effects—In workers suffering from acute cadmium poisoning as a result of a toxic exposure to
cadmium oxide fumes, microscopic changes were evident in the liver. Increases in serum gamma globulin
have also been reported in several victims. Whether these changes represent a direct toxic effect of cadmium
on the liver or whether they are merely secondary to cadmium-induced pulmonary edema is not known.
Changes in liver function in humans after long-term exposures have not been extensively examined.1
Changes in the activity of certain hepatic enzymes were noted in rats receiving 1 ppm cadmium in drinking
water for 335 days; however, cadmium concentrations were not determined in the organs. In a similar
experiment where rats received 0.5 ppm cadmium in drinking water for 1 year, the mean cadmium
concentration in the liver was found to be 1.1 ppm, which is of the same magnitude as the cadmium
concentration found in the liver of normal human adults.1
8.1.2.3 Bone Effects—Cadmium is not known to be concentrated in bone tissue; thus, any direct action
upon bone is unlikely.1 Some instances of pseudo-fractures have been reported among cadmium workers;
however, the effects on bone are probably secondary to the effects on calcium-phosphorous metabolism. It
8-2
CADMIUM
-------
is thought that chronic cadmium poisoning in conjunction with a calcium and vitamin D deficiency causes
the Itai-itai disease, a bone malady occurring in Japan.1 This disease is a form of osteomalacia afflicting
mainly post-menopausal Japanese women living in Toyama Prefecture. The disease is characterized
symptomatically by lower back and leg pains. Chronic cadmium poisoning is thought to be one of the
causative agents because a cadmium mine is located upriver from the endemic area. Analysis of food and
water in the area, in combination with data on the average daily intake of different foods, led to an
estimated daily ingested dose in recent years of 600 ,ug. Estimates for earlier years are not available.1
Animal studies have shown that exposure to cadmium in calcium-deficient rats will cause a rapid
demineralization.4 Further studies5 revealed that rats exposed to 10 ppm of cadmium in drinking water
and a low-calcium diet showed renal tubular damage as well as a significant reduction in the mineral content
of bone. It is not known whether the bone changes were caused by changes in renal function or by an effect
of cadmium on the intestinal absorption of calcium.
8.1.2.4 Anemia— Anemia has been observed in cadmium workers exposed to cadmium oxide dust or fumes.
A significant correlation was found between high cadmium levels in blood and low hemoglobin levels.1
Although the number of eosinophile cells increases, white cells are generally normal in exposed workers.1
Anemia has been frequently evident in experimental animals that were either orally or systematically
exposed to cadmium.1
8.1.2.5 Cardiovascular Disease and Hypertension-Cadmium has been shown to cause hypertension in
animals; furthermore, human beings with hypertension excreted more cadmium via urine and had a higher
cadmium-to-zinc ratio in their kidneys than normotensive subjects. Carroll6 found a correlation between
the concentration of cadmium in the air of 28 American cities and death rates from hypertension and
arteriosclerotic heart disease. Rickey et al.7 made a similar study and found that cadmium together with
vanadium was correlated with mortality from heart disease.
Hunt et al.8 reanalyzed Carroll's data and found that there was a higher correlation between population
density and death rates than between cadmium concentrations in air and death rates.
In Cadmium in the Environment1 this question was discussed in detail and it was stated: "The results from
epidemiological studies are hitherto ambiguous. They have been obtained by associating cardiovascular
disease with dustfall data or cadmium concentrations in air. Other more important sources of cadmium
exposure have not been considered." In addition to the earlier mentioned effect of population density, it
was pointed out that smoking had not been considered as a variable in Carroll's analysis. Furthermore, a
higher prevalence of hypertension has not been found among workers exposed to cadmium or in
populations in Japan exposed to cadmium via food.
Hammer et al.9 studied groups of workers with low, intermediate, and high exposure to cadmium. They
could not find a consistent relationship between cadmium and blood pressure. Evidence is still lacking for
associating hypertension with cadmium exposure.
8.1.2.6 Gonadal Effects—Systemic administration of cadmium has caused acute testicular necrosis in a
number of animal species. Although high concentrations of cadmium have been found in testicular tissue
from occupationally exposed men, acute testicular necrosis from exposure to cadmium has not been
reported in humans. The effects of cadmium on testes and ovaries of humans have not been studied
extensively. The repeated, demonstrated effects of cadmium on animal gonads emphasize the need for
further study.1
8.1.2.7 Carcinogenesis—Studies in rats have shown that cadmium injected subcutaneously or intramuscu-
larly has resulted in sarcomas (solid tumors) at the injection site.1
The evidence that cadmium may act as a carcinogen in man is not conclusive.1 One report on the
prevalence of cancer among workers exposed to cadmium oxide dust in the production of alkaline batteries
Effects 8-3
-------
showed that 8 of 74 men with at least 10 years exposure had died. Of the eight, three had died of cancer of
the prostate.1 Another report on 248 workers exposed for a minimum of 1 year to cadmium oxide showed
that four had developed cancer of the prostate.1 According to annual incidence rates supplied by the
regional cancer registry, the expected number of cases of prostatic cancer was 0.58.' Further studies are
needed to obtain conclusive evidence of carcinogenesis associated with cadmium in humans.
The possible association between cadmium and cancer of the gastrointestinal tract has not been studied
extensively.
8.1.2.8 Teratology—Data dealing with the teratogenic effects of cadmium in humans are lacking. One study
indicates a significant decrease in weight in newborn children of cadmium-exposed women.1
8.1.2.9 Mutagenesis-Very little information is available concerning possible genetic effects of cadmium
and cadmium compounds.
8.1.2.10 Summary-
• Based on animal experiments, three clearly demarcated stages result from the inhalation of cadmium
oxide or cadmium chloride aerosols. Only the first two of these have been found in man.
• Emphysema of the lung was found among male workers chronically exposed to cadmium oxide dust.
Exposure levels were in the 3- to 15-mg/m3 range.
• Determination of dose-response relationship is not possible at the present time because of the absence
of data.
• In fatal cases of acute cadmium poisoning by inhalation, pathological changes have been found in the
kidneys.
• Proteinuria is the most common clinical manifestation of renal damage.
• A concentration of approximately 200 ppm (wet weight) in the renal cortex may cause the
appearance of tubular dysfunction in sensitive individuals.
• Microscopic changes may appear in the liver as a result of acute exposure to cadmium oxide fumes.
• Cadmium effects on bone do not appear to be direct but are probably secondary, reflecting defects
upon calcium metabolism.
• A significant correlation seems to exist between high cadmium levels in the blood and low levels of
hemoglobin.
• Further evidence is necessary before hypertension in humans can be linked with cadmium in the
body.
• To definitively associate cadmium with carcinogenesis, further studies are necessary.
• Data dealing with teratogenic and mutagenic effects of cadmium are lacking.
8.1.3 Clinical Studies
8.1.3.4 Itai-itai Disease, Proteinuria, and Cadmium Exposure - The Japanese Experience -The so-called
Itai-itai disease was first seen in villages along the Jintsu River in Toyama Prefecture, Japan. This is a bone
disease, osteomalacia, that mainly affects women above 40 years of age who have had multiple pregnancies.
8-4 CADMIUM
-------
The cause of this disease is thought to be long-term ingestion of rice contaminated by cadmium from river
water used in irrigating rice fields.
In Cadmium in the Environment? this disease is discussed in detail. The authors concluded that "The
Itai-itai disease is a manifestation of chronic cadmium poisoning. It might well be, however, that cadmium
has acted upon a population particularly sensitive because of deficient consumption of certain essential
food ingredients and vitamins. A low intake of calcium and vitamin D may have been of particular
importance."
Epidemiological studies in the Toyama area showed that in the endemic district about 50 percent or more
of the inhabitants older than 60 had proteinuria. A high prevalence of proteinuria also occurred in males;
however, males generally did not show signs of Itai-itai disease. The proteinuria was of the tubular type seen
in chronic cadmium poisoning. A higher prevalence of glycosuria was also found in the endemic area.1
The findings in Toyama initiated studies in other areas of Japan where high concentrations of cadmium had
been found in rice—such as in a polluted area on Tsushima Island.1 Itai-itai disease was not found, but a
higher prevalence of proteinuria was discovered among both males and females living in the most polluted
area compared with a control area. It was concluded that the data from Tsushima Island strongly supported
the hypothesis that cadmium intoxication might have occurred in parts of Japan other than Toyama.
During the past few years several areas have been under study for the effects of cadmium pollution. The
main aim has been to find cases of Itai-itai disease, but as the screening methods for detection of this
disease include tests for proteinuria, some data can be used for epidemiological evaluations. A
comprehensive review of the recent experience includes descriptions of the methods used, the areas under
study, the exposure conditions, etc.10
At present, data are available from Fuchu (Toyama Prefecture), Tsushima (Nagasaki Prefecture), Bandai
(Fukushima Prefecture), Annaka (Gumma Prefecture), Ikuno (Hyogo Prefecture), Kakehashi (Ishikawa
Prefecture), and Omuta (Fukuoka Prefecture) and from areas in Akita, Miyagi, and Oita Prefectures.10
In most areas, several thousands of women above 30 or 40 years of age living in both polluted and control
areas have been examined for proteinuria. Testing has usually been by using trichJorouric acid or
sulfosalicylic acid. Although the standard screening method set criteria for evaluating proteinuria, very few
of the published studies give detailed ratings. A careful examination of the procedures has shown that in
many instances only ± has been used and that in some areas a ± outfall of the test has been recorded as
positive, whereas in other investigations a ± result has been recorded as negative.10 This inconsistency
makes it difficult to compare different areas. Moreover, the investigations have not been performed on a
blind basis. It has not always been possible to obtain age-related prevalences of proteinuria in both exposed
and control areas. Furthermore, at least one control area (in Annaka) is not a true control area because the
concentrations of cadmium in rice were about the same as in the polluted area. In other control areas, it has
not always been possible to estimate the exposure because cadmium has not been estimated in the rice.10
Despite many difficulties in interpreting the results from the recent investigations in Japan, the following
findings are worth mentioning. In Ikuno, 1700 women over 30 years of age were examined in 1971 in the
polluted area where average cadmium concentrations in rice were 0.56 ppm in 1970 and 0.39 ppm in 1971.
The prevalence of proteinuria was 58 percent, compared with 33 percent in a control area. In two other
control areas investigated in 1972, the prevalence of proteinuria was 4 and 9 percent. In Kanahira,
Kakehashi, where the average cadmium concentration in rice was 0.8 ppm, the prevalence of proteinuria
was 39 percent, as compared with 22 to 30 percent in three villages with average rice concentration? of 0.23
to 0.34 ppm.10
In Gumma, age-related prevalences could be calculated, but since the exposure in the "control area" was
probably about the same as in the polluted area, the results from this study can thus not be used. In both
areas there was a sharp increase in proteinuria with age.
Effects 8-5
-------
Earlier findings in Fuchu (Itai-itai area) have been confirmed, whereas recent investigations on Tsushima
Island in 1971 and 1972 have not confirmed the earlier mentioned findings in the polluted area. In these
later studies, however, one control area was omitted in 1971, and in 1972 no control area was included,
which makes it difficult to compare the studies.10
There are many inconsistencies and errors in the epidemiological methods. A great need exists for more
carefully designed epidemiological studies in Japan. The present data, however, indicate that in areas with
excessive exposure to cadmium, the prevalence of proteinuria seems to be higher than in the areas with
lower exposures. Although the evidence is not conclusive, it points to cadmium toxicity as the cause of
Itai-itai disease.
8.2 ECOLOGICAL IMPACT
Studies that deal with the concentrations of cadmium in aquatic and terrestrial ecosystems and the effects
of the concentrations upon these ecosystems are limited in number.
The chief concerns regarding cadmium in these ecosystems are the possibility of its movement through food
chains to humans and its possible detrimental effects upon plants and animals within the ecosystems.
Cadmium is usually present in the environment in small amounts and is usually associated with zinc.11 Zinc
is considered to be an essential element for both plants and animals12 and is translocated from the soil
through various food chains. Under normal circumstances, the level of cadmium in the environment is
determined by the geochemical composition of the region and is not high enough to adversely affect the
health of the indigenous plant or animal populations. Ecological dangers from cadmium exposure,
therefore, arise from activities associated with the production and use of the metal.
The large variety of sources from which cadmium may enter the environment are discussed in Section 5 of
this report. Concentrations of cadmium in various substances and plants or animals are listed in Table 8.2.
Table 8.2. CONCENTRATION OF CADMIUM IN VARIOUS SUBSTANCES11
(ppm of dry plant and animal tissue)
Abiotic components
Substance
Igneous rock
Shales
Sandstones
Limestones
Soils
Fresh water
Sea water
Concentration
0.2
0.3
0.05
0.035
0.06
0.08
0.00011
Marine and land plants
Substance
Plankton
Brown algae
Bryophytes
Ferns
Gymnosperms
Angiosperms
Bacteria
Fungi
Concentration
0.4
0.4
0.1
0.5
0.24
0.64
--
4.0
Animals
Substance
Coelenterata
Annelida
Mollusca
Enchinodermata
Crustacea
Insecta
Pisces
Mammalia
Concentration
1
-
3
1
0.15
-
3
-
The possible avenues of environmental transport of cadmium are shown in Figure 8.1. The term "biota"
refers to all living organisms, including humans. Biological organisms may be affected by cadmium intake at
any of the points listed.
8-6
CADMIUM
-------
MINING, PROCESSING,
AND INCINERATION'
FALLOUT
DUMPING
AIR
MICROBIAL POPULATIONS
AND AGRICULTURAL PRACTICES
TERRESTRIAL SYSTEM
f
LEACHING
IRRIGATION
BIOTA
i
FRESH
WATER
RIVER
FLOW
7
BIOTA
ESTUARIES
MIXING
BIOTA
OCEANS
EVAPORATION
Figure 8.1. Environmental transport of cadmium.
Effects
J-7
-------
Studies and surveys in areas surrounding smelters have shown decreasing concentrations of zinc and
cadmium in the soil, as well as in plants and animals, with increasing distances from the source.13'14 Leafy
crops show higher levels of cadmium than root crops, probably because of direct deposition.
A study conducted by Dorn et al13 on lead mining in Missouri points out the levels of cadmium, copper,
lead, and zinc that may be added to naturally occurring levels of these elements in soil and vegetation by
mining processes. Two farm sites were selected for study: one approximately 0.8 km and the other 26 km
from the smelter stack. Soil and vegetation and hair, blood, and milk from cows were collected from each
farm at three time periods during 1 year. Statistically significant differences in cadmium levels were
observed between farm sites for the following variables: soil, roots of vegetation, leaves of vegetation, and
hair collected from cows. The levels of cadmium in milk never exceeded 0.5 jug per 100 ml. There was no
significant difference in cadmium concentrations in milk between the farm sites, which would seem to
indicate that cadmium is not readily assimilated and/or secreted in milk of cows. Vegetation levels were
reported to be between 3 and 10 jug/g of dry weight. Exposure longer than 1 year to the same levels of
cadmium in vegetation as these would probably result in higher levels in milk than reported here, however.
Smith and Huckabee14 report that Munshower in his studies in Deer Lodge Valley in Southern Montana, an
area near a smelter, found soil concentration factors were: 1 for grasses, 2 for forbs, and 1.5 to 3.0 for
insects; however, concentration factors varied considerably with species. The same study noted an increase
in the concentration of cadmium in the kidney and liver with increasing age in the cattle in the area.
Cadmium is added to the soil through deposition from the air and through addition of fertilizers and
pesticides. The airborne forms of cadmium also fall on growing vegetation through precipitation and
dustfall.
The uptake of cadmium by oats was studied by John et al.ls The cadmium content of the soil was shown
to markedly affect the cadmium content of the roots. Cadmium was translocated to the tops to a lesser
extent. The type of soil appeared to affect the movement of cadmium into the shoots. Oat shoots grown in
Richmond soil with 46.4 ppm of cadmium contained 16.1 ppm as compared with 0.51 ppm in shoots
grown in soil with cadmium levels of 1.3 ppm. Cadmium levels were measured using nitric acid extraction.
In another study, John et al.16 noted that the cadmium content of the plants appeared to be related to the
amounts of exchangeable cadmium in the soil rather than to the total cadmium present in the soil. The
higher levels of cadmium were associated with increased soil acidity.
Lagerwerff17 observed that large changes in the cadmium content of the soil caused only small increases in
the cadmium content of radish tops; a five-fold increase in the soil resulted in a two-fold increase in the
tops. The cadmium uptake in radishes was greater in soil with a pH of 5.9 than in soil with a pH of 7.2.
Also, when plants were grown near a cadmium source, the aerial deposition accounted for more than 40
percent of the contents of the tops.
Schroeder and Balassa18 reported cadmium uptake by 10 garden vegetables-in some, uptake was only by
the roots and in others by the entire plant.
The availability of cadmium to plants is undoubtedly associated with microbial metabolism. Although the
microbial metabolism of zinc has been rather thoroughly studied,12 that of cadmium has not.
Sulfate-reducing microorganisms are known to have produced sphalerite from zinc metal and zinc
carbonate.12 Sphalerite ores are a common source of both zinc and cadmium. Zinc carbonate (smithsonite)
occurs naturally, although zinc metal does not. Sulfate-reducing microorganisms are also capable of
reducing cadmium carbonate to cadmium sulfate.19
Cadmium behaves differently when in the presence of zinc than when alone. Zinc is a cofactor for many
enzymes and without it the enzymes do not function. Cadmium can replace zinc as a cofactor and thereby
cause many of the enzymes to cease functioning.14 The presence of zinc in the soil changes cadmium
8-8 CADMIUM
-------
uptake in plants. At low concentrations of cadmium, zinc suppresses its uptake, but at high concentrations
of cadmium the zinc increases uptake.14
Lichens, mosses, leaf litter, and humus tend to accumulate metals deposited on their surfaces.20 The metals
do not appear to penetrate the plant as long as a cuticle is present. In mosses they tend to accumulate
because of ion exchange.
Accumulations of metals in leaf litter may be the most serious effect of metal deposition. The effect of
cadmium and other metals on the organisms that decompose leaf litter is not known; however, the blocking
of negatively charged organic groups by metal ions would decrease the probability of litter decomposition.
Extremely high levels of metals would be required to prevent litter decomposition. The effect of the metals
on the microorganisms that bring about litter decay is not known, but the decomposition of litter is an
integral part of mineral turnover and biogeochemical cycling. Any interference with this cycling will
produce a profound effect upon terrestrial ecosystems.
The discharge of cadmium into oceans and fresh water streams results in an increase in the cadmium levels
in the organisms living in these waters.14'21 Both marine and fresh water animals are capable of
concentrating cadmium;14'21 however, the effects of cadmium at sublethel levels on the organisms
themselves are not known.
Present knowledge concerning the ecological effects of cadmium can be summarized as follows:
• Data dealing with the effects of cadmium in terrestrial and aquatic ecosystems are limited.
• Under normal circumstances the level of cadmium in the environment is insufficient to adversely
affect the health of the indigenous plant and animal populations.
• Organisms living in the proximity of cadmium sources have higher levels of cadmium within their
bodies than those in non-contaminated areas.
• Leafy crops show higher levels of cadmium than root crops, probably because of direct deposition.
• The amount of uptake of cadmium from the soil is determined by soil type, pH, amount of
exchangeable cadmium, and microorganismal activity. The amount of zinc in the soil also influences
cadmium uptake.
• Lichens and mosses tend to accumulate metals deposited on their surfaces. The accumulation results
from ion exchange. The metals do not appear to penetrate the plant as long as an intact cuticle is
present.
• The accumulation of cadmium and other metals in the leaf litter and humus may be the most serious
aspect of metal deposition. The effect of metal deposition on litter decomposition and biogeo-
chemical cycling is not known.
8.3 REFERENCES FOR SECTION 8
1. Friberg, L., M. Piscator, and G. Nordberg. Cadmium in the Environment. Cleveland, Chemical Rubber
Co. Press, 1971.
2. Friberg, L. Health Hazards in the Manufacture of Akaline Accumulators with Special Reference to
Chronic Cadmium Poisoning. Acta. Med. Scand., Suppl. 138:240, 1950.
3. Piscator, M., and B. Lind. Cadmium, Zinc, Copper and Lead in Human Renal Cortex. Arch. Environ.
Health. 24:426, 1972.
Effects 8-9
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4. Larsson, S.E., and M. Piscator. Effect of Cadmium on Skeletal Tissue in Normal and Calcium-deficient
Rats. Israel J. Med'. Sci. 7:495, 1971.
5. Piscator, M., and S. E. Larsson. Retention and Toxicity of Cadmium in Calcium-deficient Rats.
(Presented at 17th International Congress an Occupational Health, Buenos Aires. 1972.)
6. Carroll, R. E. The Relationship of Cadmium in the Air to Cardiovascular Disease Death Rates. J.
Amer. Med. Assoc. 198:261, 1966.
7. Hickey, R. J., E. P. Schoff, and R. L. Clelland. Relationship Between Air Pollution and Certain Chronic
Disease Death Rates. Arch. Environ. Health. 75:728, 1967.
8. Hunt, W. F., C. Pinkerton, O. McNulty, and J. Creason. A Study in Trace Element Pollution of Air in
77 Midwestern Cities. In: Trace Substances in Environmental Health. Hemphill, D. D. (Ed.) Columbia,
University of Missouri Press, 1971. p. 56-61.
9. Hammer, D. L, J. F. Finklea, J. P. Creason, S. H. Sandifer, J. E. Keil, L. E. Priester, and J. F. Stara.
Cadmium Exposure and Human Health Effects. In: Trace Substances in Environmental Health.
Columbia, University of Missouri Press, 1972. p. 269-283.
10. Friberg, L., M. Piscator, G. Nordberg, and T. Kjellstrom. Cadmium in the Environment, II. The
Karolinska Institute, Stockholm, Sweden. Prepared for the U. S. Environmental Protection Agency,
Research Triangle Park, N.C., under Contract No. 68-02-0342. Publication No. EPA-R2-73-190.
February 1973. 169 p.
11. Bowen, J. J. M. Trace Elements in Biochemistry. London, Academic Press, 1966. 241 p.
12. Zaijic, J. E. Microbial Biogeochemistry. New York, Academic Press, 1969. 345 p.
13. Dorn, C. R., J. 0. Pierce, G. R. Chase, and P. E. Phillips. Study of Lead, Copper, Zinc and Cadmium
Contamination of Food Chains of Man. University of Missouri, Columbia, Mo. Prepared for U. S.
Environmental Protection Agency, Research Triangle Park, N. C. under Contract No. 68-02-0092.
1972.
14. Cadmium: The Dissipated Element. Fulkerson, W., and H. E. Goeller, (Ed.). Oak Ridge National
Laboratory, Oak Ridge, Tenn. 1973.
15. John, M. K., H. H. Chuah, and C. J. Van Laerhoven. Cadmium Contamination of Soil and Its Uptake
by Oats. Environ. Sci. and Tech. 6:555-557, 1972.
16. John, M. K., C. J. Van Laerhoven, and H. H. Chuah. Factors Affecting Plant Uptake and Phytotoxicity
of Cadmium Added to Soils. Environ. Sci. and Technol. 6:1005-1009, 1972.
17. Lagerwerff, J.V. Uptake of Cadmium, Lead and Zinc by Radish from Soil and Air. Soil Sci.
777:129-133, 1971.
18. Schroeder, H. A., and J. J. Balassa. Cadmium: Uptake by Vegetables from Superphosphate in Soil.
Science. 740:819-820, 1963.
19. Silverman, M.P., and W. L. Shrlich. Microbial Formation and Degradation of Minerals. Advan. in
Appl. Microbiol. 6:153-205, 1964.
20. Pringle, B. H., D. E. Hissong, E. L. Katz, and S. T. Mulawka. Trace Metal Accumulation by Estuarine
Mollusks. J. Sanit. Eng. Div. 94:455475, 1968.
21. Tyler, G. Heavy Metals Pollute Nature, May Reduce Productivity. Ambio. 7:52-59, 1972.
8-10 , CADMIUM
-------
9. CONTROL TECHNOLOGY
9.1 AIRBORNE EMISSIONS
Cadmium emitted into the atmosphere will generally be in the form of particulate matter-usually as the
oxide, but also as the sulfide or sulfate. Because the boiling point of cadmium is fairly low, 767°C
(1410°F), the metal may be vaporized in high-temperature processes and condensed into particles as the
process off-gases are cooled. This method of formation would result in very fine particles in the micrometer
and submicrometer range.
The exact size distribution of cadmium-containing particles from these various processes has, unfortunately,
not been clearly defined. The limited information available indicates that 40 percent of the particulate mass
may be smaller than 2 micrometers in diameter. In processes where a large fraction of the
cadmium-containing particulate is formed by the vaporization/condensation method, it is possible that a
significant amount of cadmium may be contained in particulate matter even smaller than 0.1 micrometer.
The shape of the condensed particles is not known, either, although there are indications that the particles
might not always be spherical. There is evidence that the percentage concentration of cadmium in fly ash is
higher in the finer particles than in the coarser particles.
It is evident, therefore, that the control of atmospheric cadmium emissions requires the ability to capture
fine particles.
9.2 WATERBORNE EMISSIONS
Waterborne cadmium emissions are generally in the form of suspended particulates, although cadmium may
sometimes be present in a soluble form such as cadmium sulfate. These aqueous emissions may result
directly from various processing steps involving cadmium (such as the aqueous beneficiation of zinc ores or
the spills, washdowns, and rinsings from cadmium electroplating operations) or they may result from
leaching and washing of smelter slag heaps by rainwater.
9.3 CONTROL METHODS
9.3.1 Control of Airborne Cadmium Emissions
The technology currently employed to control cadmium emissions is directed toward control of particulate
matter in the micrometer range. The devices most frequently used are fabric filters and electrostatic
precipitators. Scrubbers are also utilized, but less often, possibly because many sources of cadmium
emissions must keep the particles dry for purposes of recycle to the process. Cyclones, which are not
efficient in collecting fine material, can be employed only to remove the coarser particulate matter
upstream of one of the other devices.
Reasonably high removal efficiencies for fine particulate matter in the range of 0.2 to 1.0 micrometer are
possible using existing devices, either alone or in combination, but only if these devices are large enough,
installed in sufficient number, supplied with adequate energy, and operated correctly. The economics of
installing the equipment required to provide removals higher than those currently achieved by cadmium
emitters, will thus be unfavorable at best, and possibly prohibitive, depending upon what degree of
9-1
-------
additional removal is desired. Research programs currently underway within EPA are intended to make
greater control of fine particles feasible by improving the efficiency of control techniques in the
submicrometer range at a limited increase, or possibly even at a decrease, in system cost.
Capital costs of completely installed, high-efficiency particulate collection systems vary from about $4 to
$12 per actual cubic foot per minute (acfm) of gas treated and are highly dependent on the nature of the
source, the efficiency required, and the size of the unit. Complete operating costs, including amortization,
depreciation, and maintenance can vary from about $0.50 to $5.00/acfm-year. The selection of the most
economical device in any one particular case depends on many factors. '
If, indeed, a significant fraction of cadmium emissions consists of particles smaller than 0.1 micrometer,
then the technology for controlling this fraction of the emissions may not exist at the present time.
9.3.1.1 Fabric Filters1—Fabric filters, or baghouses, are currently employed to control many cadmium
emission sources. This technique involves passage of the particle-containing gas stream through a porous
filter medium consisting of woven or fibrous fabric. The fabric may be wood or cotton, or—for higher
temperature and more corrosive environments—may be Dacron, Teflon, glass, or any of a number of other
materials. The collected particles form a cake on the filter, which must be removed periodically.
Particles are collected via several mechanisms in bag filters. The most important are:
• Direct interception of a particle by the filter (or, more accurately, by the cake of collected particles
built up on the filter) as the particle is carried by the gas stream.
• Inertia! impaction, in which the momentum of entrained particles causes them to leave the gas stream
and to collide with the filter.
• Brownion diffusion of fine particles, causing diffusion of these particles to the surface of the filter.
Fabric filters are efficient for removing fine particles in the micrometer range. There are indications that—if
the appropriate fabric is selected, if the air/cloth ratio (i.e., the gas velocity) is held sufficiently low, and if
the entire baghouse system is correctly built and maintained leak-free—the fraction collection efficiency of
particles 1.0 micrometer in size may be as high as 99 percent. Filters employed by some of the emitters of
cadmium do not appear to be designed or operated to achieve such high efficiencies. Although a correctly
operated baghouse without imperfections in the filters can be efficient, in practice a large number of filters
are often not in correct working order throughout the entire operating period. Thus collection efficiencies
below the design efficiency are quite possible during operation.
Most fabric filter bags cannot be operated above 284°C (550°F); for this temperature, a glass fabric is
required. This temperature limitation does not appear to be a severe problem in many of the high-
temperature processes emitting cadmium; the process off-gases must be cooled before entering the filter
anyway because the filter is frequently followed by a scrubber for S02 removal. The concentrations of S02
expected (e.g., in off-gases from smelter operations) are not believed to pose a serious problem for filters, so
long as an appropriate fabric is selected.
In summary, the advantages of fabric filtration as a technique for controlling cadmium emissions are:
• Filters can be very efficient in removing fine particles on the order of 1.0 micrometer, and possibly
smaller.
• Disturbances in the process operation would not affect filter performance.
The disadvantages of filters are:
9-2 CADMIUM
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• Low air/cloth ratios are required in order to reduce the pressure drop and to maintain high
efficiencies (i.e., the baghouse must be large).
• Pressure drop across the filter is high relative to electrostatic precipitators, although low in
comparison with high-energy scrubbers.
• Maintenance requirements are high for correct operation.
• Temperature limitation of fabric filters may limit application in some cases and could result in filter
damage in the event of a temperature excursion.
• Fabric filters would be. blinded if the particles were sticky (although this should not be a problem for
most cadmium emission sources).
• The efficiency of fabric filters on particles below 0.1 micrometer is not clear.
9.3.1.2 Electrostatic Precipitators'1 -Precipitators, along with fabric filters, are perhaps the most commonly
employed devices for removing cadmium-containing particles from process off-gases. This technique
involves: (1) production of an electric charge on the particles in the gas stream, (2) attraction of the
charged particles toward oppositely charged plates placed in the gas stream and precipitation of the
particles onto the plates; and (3) removal of the collected material from the plates.
Precipitators can be fairly efficient in removing fine particles, but not as efficient as fabric filters. Fine
particles are more difficult to charge than coarser ones; moreover, the fine material migrates more slowly to
the collection plates, thus necessitating a large plate area. For these reasons, the capital cost of a
precipitator increases exponentially with increasing collection efficiencies. Some precipitators have been
reported to be 98 percent efficient in collecting particles of 1.0 micrometer in diameter. It is not apparent,
however, that such high efficiencies on fine particulate matter are frequently attained with precipitators
employed by cadmium emission sources.
A problem encountered in precipitation of cadmium-containing particles is the high resistivity of the
particles. Moisture conditioning of the inlet gas to the precipitator may be required for efficient removals.
Like filters, precipitators are limited by a maximum operating temperature. For precipitators, this limit is
currently about 425°C (800°F). Although it is sometimes advantageous to operate a precipitator near the
maximum temperature, most sources of cadmium emissions should find little difficulty in operating at
temperatures well below the maximum.
The concentration of S02 (and S03) expected (for example, in the off-gases from smelter operations)
should, if anything, aid precipitator performance.
The advantages of precipitators for controlling cadmium emissions are:
• Precipitators can be relatively efficient in removing fine particles in the micrometer range.
• Precipitators give very little pressure drop, with the result that power consumption is low compared
to other control devices offering the same removal efficiencies.
The disadvantages are:
• Precipitators must be large, because of the low gas velocities required to maintain high collection
efficiencies and to prevent reentrainment of collected particles.
• The efficiency of precipitators on particles smaller than 0.1 micrometer is not known.
Control Technology 9-3
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• The small size and high resistivity of cadmium-containing particles make them difficult to charge.
9.3.1.3 Scrubbers3— Scrubbers are not used as widely for the control of cadmium emissions as are filters
and precipitators. One reason for their more limited application may be that in smelters—the most
significant sources of cadmium emissions—the collected particulates must be dry so that they can be
recycled to the process. With the advent of high-energy, high-efficiency scrubbers, however, these devices
may find increased application in situations where simultaneous removal of particulates and of SO2 is
desired.
Scrubbers are available in a number of different designs, but are generally based upon the principle of
impaction of water droplets against the entrained particles. Scrubbers operating with a very high energy
input to the water or the gas streams—i.e., scrubbers operating with a pressure drop on the order of 40 to
100 inches of water-provide significant removal efficiencies in the submicrometer range. For example,
some experience indicates that such high-energy scrubbers may be approximately 99 percent efficient in
removing particles of 1.0 micrometer.
Scrubber efficiency can be improved in general by increasing the energy input to the devices. Currently
available high-energy scrubbers supply this energy to the water and gas streams in such a manner that
particle collection by the impaction mechanism is increased. It appears, however, that high efficiency in
control of fine particulate matter may be achieved more effectively and more economically if the scrubbers
are designed so that mechanisms in addition to impaction are brought into play-such as diffusiophoresis,
thermophoresis, and condensation effects. Scrubbers incorporating these effects—including condensation
scrubbers and charged droplet scrubbers—are still in the development stage.
The advantages of scrubbers are:
• Small size relative to competing devices.
• High efficiency in removing particles in the micrometer range.
• Potential for simultaneous removal of particulate matter and gaseous pollutants.
The disadvantages of scrubbers are:
• They give a slurry by-product. Consequently, they would complicate recycling the solids to the
process if the scrubber system were used as the primary control technique, and they would
necessitate a settling pond or equivalent means for removing the suspended particulate matter. A
contaminated water disposal problem may result.
• The efficiency of scrubbers on particles smaller than 0.1 micrometer is not known.
9.3.2 Control of Waterborne Cadmium Emissions
If the cadmium is present in the form of suspended particulate, the aqueous emissions that result directly
from process operations involving cadmium may be controlled by employing settling ponds or thickeners.
Filtering or centrifuging the aqueous wastes might also be considered.
If the cadmium is present as a soluble compound, it might be removed by precipitation, followed by
removal of the resulting solids. Alternatively, the techniques of ion exchange, solvent extraction, or
electrolytic deposition might be employed.
9-4 CADMIUM
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9.4 REFERENCES FOR SECTION 9.
1. Handbook of Fabric Filter Technology. GCA Corporation, Bedford, Mass. Prepared for U.S.
Environmental Protection Agency, Research Triangle Park, N.C. under Contract Number CPA-22-69-38
(2 vols.). Publication Number APTD-0690 and APTD-0691. 1970.
2. Manual of Electrostatic Precipitator Technology. Southern Research Institute, Birmingham, Alabama.
Prepared for U. S. Environmental Protection Agency, Research Triangle Park, N.C. under Contract
Number CPA-22-69-73 (3 vols). 1970.
3. Scrubber Handbook. Ambient Purification Technology, Riverside, Calif. Prepared for U. S. Environ-
mental Protection Agency, Research Triangle Park, N.C. under Contract Number CPA-70-95 (2 vols).
Publication Number EPA-R2-118a and b. 1972.
4. Air Pollution Control Technology and Cost in Nine Selected Areas. Industrial Gas Cleaning Institute,
Stamford, Conn. Prepared for U.S. Environmental Protection Agency, Research Triangle Park, N.C.
under Contract Number 68-02-0301. Publication Number APTD-1555. 1972.
Control Technology 9-5
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing}
. REPORT NO.
EPA-600/6-75-003
I. RECIPIENT'S ACCESSIOWNO.
4. TITLE AND SUBTITLE
Scientific and Technical Assessment Report
on Cadmium
5. REPORT DATE
July 1975
6. PERFORMING ORGANIZATION CODE
. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORG A_N I ZATI ON NAME AND ADDRESS
National Environmental Research Center
Office of Research and Development
Environmental Protection Agency
Research Triangle Park, North Carolina 27711
10. PROGRAM ELEMENT NO.
1AA001
ROAP No. 26AAA
11 CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
13. TYPE OF RE PORT AND PERIOD COVERED
Final Report
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This report is a review and evaluation of the current knowledge of cadmium in
the environment as related to possible deleterious effects on human health and
welfare. Sources, distribution, measurement, and control technology are also con-
sidered. Cadmium is widely distributed in the environment. The air over urban
areas has contained generally less than 0.1 microgram per cubic meter (yg/rn^), 24-
hour average, but a 24-hour average as high as 0.73 yg/rrr has been measured in the
air of a community with a known cadmium source. The cadmium content of water
generally is less than 1 part per billion although much higher values have been
found. The cadmium content in foods varies widely. The estimated intake from foods
is 25 to 75 micrograms per day. The human body burden of cadmium is cumulative.
The half-time of cadmium in man is estimated at over 10 years, ^an's primary
exposure is from food, tobacco smoke, water, and ambient air. Food and tobacco
smoke are the major sources except in the immediate vicinity of major sources of
atmospheric emissions of cadmium. Emphysema and other lung diseases have been
related to industrial exposure to airborne cadmium, compounds. Kidney damage has
also resulted from long-term exposure to cadmium. Animal experiments link anemia,
hypertension, testicular necrosis, and carcinogenesis with cadmium exposure. Cur-
rent knowledge of the dose-response relationship does not provide criteria on which
to base standards.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
:. COSATI Field/Group
Cadmium
Pollution
Environmental biology
Toxicity
Cardiovascular disease
Urological disease
Respiratory disease
Chemical analysis
Abatement
Air
Water
Environmental
Envi ronmental
Food
pollution
distribu
ion
07B 07B
13B 13BJ4D
06F 13B
06T 08H
06E
06E
3. DISTRIBUTION STATEMENT
Release unlimited
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
72
20 SECURITY CLASS (This page)
Unclassified
EPA Form 2220-1 (9-73)
10-1
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