United States
Environmental Protection
Agency
Ofh.. . tfater
Regulations and Standards (WH-553)
Washington DC 20460
June 1981
EPA-440/4-81-017
&EPA
Water
An Exposure
and Risk Assessment
for Silver
-------
DISCLAIMER
This is a contractor's final report, which has been reviewed by the Monitoring and Data Support
Division, U.S. EPA. The contents do not necessarily reflect the views and policies of the U.S.
Environmental Protection Agency, nor does mention of trade names or commercial products
constitute endorsement or recommendation for use.
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REPORT DOCUMENTATION »• «PORT NO. 2.
PAGE EPA-440/4-81-017
4. TIM* and Subtitle
An Exposure and Risk Assessment for Silver
7. Autnartt) Scow> K. . coyer, M. ; Nelken, L.; Payne, E.; Saterson, K.;
Walker, P.; Wood, M. (ADL) Cruse. P.: Moss. K. (Acurex)
9. Performing Organliation Name and Addresa
Arthur D. Little, Inc. Acurex Corporation
20 Acorn Park 485 Clyde Avenue
Cambridge, MA 02140 Mt. View, CA 94042
12. Sponsoring Organisation Nam* and Addraaa
Monitoring and Data Support Division
Office of Water Regulations and Standards
U.S. Environmental Protection Agency
Washington, D.C. 20460
3. Recipient's AectMlon No,
& Report Data
June 1981
&
& Performing Organization Rapt. No.
10. Project/ToO/Work Unit No.
11. CaittracKC) or Grant(G) No.
(0 C-68-01-3857
,„ C-68-01-5949
» C-68-01-6017
13. Typa of Rapoit A Period Covered
Final
14.
IS. Supplementary Notas
Extensive Bibliographies
10, Abstract (limit 200 words)
This report assesses the risk of exposure to silver. This study is part of a program
to Identify the sources of and evaluate exposure to 129 priority pollutants. The
analysis is based on available information from government, industry, and technical
publications assembled in June of 1981.
The assessment includes an identification of releases to the environment during
production, use, or disposal of the substance. In addition, the fate of silver in the
environment is considered; ambient levels to which various populations of humans and
aquatic life are exposed are reported. Exposure levels are estimated and available
data on toxicity are presented and interpreted. Information concerning all of these
topics is combined in an assessment of the risks of exposure to silver for various
subpopulations.
17. Oocumant Amlyaia a. Daacifpton
Exposure
Risk
Water Pollution
Air Pollution
b. IdantMais/Opan-endad Tarmi
Pollutant Pathways
. Risk Assessment
e. COSATI Ftald/Qroup Q6F Q6T
Effluents
Waste Disposal
Food Contamination
Toxic Diseases
Silver
IS, Availability Statamant
Release to Public
19. Sacwtty Claaa (Thla Report)
Unclassified
20. Security Claaa (Thla Paga)
Unclassified
21. No. of Pagaa
232
22. Price
$20.50
'.S«*ANSt-Z39.18)
> imtnictlafii
OPTIONAL FORM 272 (4-77)
(Formerly NTIS-3S)
-------
EPA-440/4-81-017
June 1981
AN EXPOSURE AND RISK ASSESSMENT
FOR SILVER
by
Kate Scow
Muriel Goyer, Leslie Nelken, Edmund Payne,
Katherine Saterson, Pamela Walker, Melba Wood
Arthur D. "Little, '
U.S. EPA Contract 68-01-3857
68-01-5949
Patricia Cruse. Kenneth Moss
Acurex, Inc.
U.S. EPA Contract 68-01-6017
Gregory Kew
Project Manager
U.S. Environmental Protection Agency
Monitoring and Data Support Division (WH-553)
Office of Water Regulations and Standards
Washington, D.C. 20460
OFFICE OF WATER REGULATIONS AND STANDARDS
OFFICE OF WATER AND WASTE MANAGEMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
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FOREWORD
Effective regulatory action for toxic chemicals requires an
understanding of the human and environmental risks associated with the
manufacture, use, and disposal of the chemical. Assessment of risk
requires a scientific judgment about the probability of harm to the
environment resulting from known or potential environmental concentra-
tions. The risk assessment process Integrates health effects data
(e.g., carcinogenicity, teratogenicity) with information on exposure.
The components of exposure include an evaluation of the sources of the
chemical, exposure pathways, ambient levels, and an identiflr.ation of
exposed populations including humans and aquatic life.
This assessment was performed as part of a program to determine
the environmental risks associated with current use and disposal
patterns for 65 chemicals and classes of chemicals (expanded to 129
"priority pollutants") named in the 1977 Clean Water Act. It Includes
an assessment of risk for humans and aquatic life and is intended to
serve as a technical basis for developing the most appropriate and
effective strategy for mitigating these risks.
This document is a contractors' final report. It has been
extensively reviewed by the individual contractors ?nd by the EPA at
several stages of completion. Each chapter of the draft was reviewed
by members of the authoring contractor's senior technical staff (e.g.,
toxlcologists, environmental scientists) who had not previously been
directly involved in the work. These Individuals were selected by
management to be the technical peers of the chapter authors. The
chapters were comprehensively checked for uniformity in quality and
content by the contractor's editorial team, which also was responsible
for the production of the final report. The contractor's senior
project management subsequently reviewed the final report In Its
entirety.
At EPA a senior staff member was responsible for guiding the
contractors, reviewing the manuscripts, and soliciting comments, where
appropriate, from related programs within EPA (e.g., Office of Toxic
Substances, Research and Development, Air Programs, Solid and
Hazardous Waste, etc.). A complete draft was summarized by the
assigned EPA staff member and reviewed for technical and policy
implications with the Office Director (formerly the Deputy Assistant
Administrator) of Water Regulations and Standards. Subsequent revi-
sions were included in the final report.
Michael W. Sllmak, Chief
Exposure Assessment Section
Monitoring & Data Support Division (WH-553)
Office of Water Regulations and Standards
ii
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TABLE OF CONTENTS
I. TECHNICAL SUMMARY
II. INTRODUCTION
III. MATERIALS BALANCE
A. Introduction and Methodology III-l
B. Overview III-l
C. Metals Production " III-3
1. Mine Production ' III-3
2. Milling of Silver-Containing Ores 111-10
3. Smelting and Refining of Ores
Containing Silver 111-12
a. Overview 111-12
b. Copper Recovery 111-12
c. Lead Recovery 111-12
d. Zinc Recovery 111-16
e. Silver Recovery 111-17
i. Primary Silver Refining 111-17
ii. Secondary Silver Refining 111-17
D. Production in Which Silver is a Byproduct 111-18
1. Overview 111-18
2. Cement Manufacture 111-18
3. Combustion of Coal and Petroleum
Products 111-18
4. Iron and Steel Manufacture 111-20
E. End Uses 111-21
1. Overview 111-21
2. Photography 111-21
a. Overview IHi-21
b. Production IH-27
c. Professional Photoprocessing 111-27
d. Amateur Photoprocessing 111-33
e. Atmospheric and Land Releases
by the Photographic Industry 111-33
f. Total Discharges by the Photographic
Industry 111-33
3. Other Uses 111-33
a. Contacts and Conductors IIIr-33
b. Batteries 111-36
c. Jewelry, Sterling Ware, Collector
Pieces, Government Coinage 111-36
iii
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TABLE OF CONTENTS (continued)
IV.
d. Brazing Alloys and Solders
e. Catalysts and Olefin Separation
f. Electroplating
g. Dental, Medical, and Non-medicinal
Antimicrobial Uses
h. Mirrors
i. Bearings
j. Cloud Seeding
k. Miscellaneous Uses
F. Municipal Disposal
1. Publicly Owned Treatment Works
2. Urban Refuse
G. Natural Sources
1. Overview
2. Silver-producing Ores
3. Silver Releases in Aquatic Systems
4. Silver Releases in the Atmosphere
H. Areas for Future Investigation
I. Summary
1. Anthropogenic Sources
a. Metals Production
b. Other Production in Which Silver
is a Byproduct
c. End Uses
d. Municipal Disposal
2. Natural Sources
3. Conclusions
References
ENVIRONMENTAL FATE AND DISTRIBUTION
111-37
111-37
111-38
111-39
111-40
111-40
111-40
111-41
111-41
111-41
111-44
111-46
111-46
111-46
111-49
111-51
111-51
111-51
111-51
111-51
111-53
111-53
111-54
111-54
111-54
111-55
IV-1
A. Introduction IV-1
B. Physical and Chemical Properties iv-1
1. Physical Properties IV-1
2. Chemical Properties IV-1
C. Environmental Fate XV-9
1. Methodology IV-9
2. Major Environmental Pathways . IV-9
3. Important Fate Processes IV-13
a. Overview IV-13
b. Pathway 1 - Atmospheric Transport IV-13
c. Pathway 2 - Land Disposal IV-16
d. Pathway 3 - Industrial Aqueous Discharges IV-20
iv
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TABLE OF CONTENTS (continued)
e. Pathway 4 - POTW's
D. Biological Fate IV-28
1. Aquatic Organisms IV-28
a. Animals IV-29
b. Monitoring Data IV-31
c. Plants IV-36
2. Terrestrial Organisms IV-36
a. Animals and Plants IV-36
b. Biomagnification in the Food IV-41
Chain IV-41
c. Microorganisms IV-41
E. Concentrations Detected in the
Environment IV-41
1. Surface Water IV-41
2. Well Water IV-44
3. Sediment IV-49
4. Dissolved and Suspended Matter IV-49
5. Effluent Waters IV-52
6. Air IV-55
7. Soil IV-57
F. Summary 17-59
1. Physical and Chemical Properties IV-59
2. Fate and Distribution in the Environment IV-59
a. Atmosphere . IV-60
b. Land IVr60
c. Water IV-61
d. POTW's IV-62
References IV*-63
V. EXPOSURE AND EFFECTS — BIOTA V-l
A. Exposure of Biota V-l
1. Introduction V-l
2. Aquatic Systems Exposed to Surface Water V-2
a. Exposure Levels - Monitoring Data V-2
b. Sources of Silver Releases to Surface
Waters . v-2
i. Photography V-4
ii. Electroplating V-4
iii. Mining and Milling v-4
3. Weather Modification V-5
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TABLE OF CONTENTS (continued)
4. Land Disposal of Silver Waste
5. Sources of Silver to Wastewater
Treatment Systems V-7
B. Effects on Biota V-8
1. Introduction V-8
2. Freshwater Organisms V-9
a. Acute Toxicity v~9
b. Chronic and Sublethal
Toxicity V-9
3. Marine Organisms V-14
a. Acute Toxicity , V-14
b. Chronic and Sublethal
Effedts V-14
4. Factors Affecting Toxicity to Aquatic
Species V-19
5. Terrestrial Organisms V-19
a. Animals • V-19
b. Plants V-19
6. Microorganisms V-21
C. Summary , V-22
References V-24
VI. EXPOSURE AND EFFECTS — HUMANS VI-1
A. Human Exposure VI-1
1. Introduction VI-1
2. Ingestion VI-1
a. Food VI-1
b. Water VI-4
c. Products Containing Silver VI-6
3. Dermal Contact VI-6
a. Medicinal Applications VI-6
b. Photography VI-7
c. Industry VI-7
d. Jewelry and Sterling Silver VI-7
e. Swimming Pools VI-8
4. Inhalation VI-8
B. Human Toxicity VI-10
1. Introduction VI-10
2. Metabolism and Bioaccumulation • VI-10
a. Absorption VI-10
b. Excretion VI-11
c. Tissue Accumulation VI-12
vi
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TABLE OF CONTENTS (continued)
Page
3. Human and Animal Studies VI-13
a. Carcinogenesis VI-13
b. Mutagenesis VI-13
c. Adverse Reproduction Effects VI-14
d. Other Toxic Effects VI-14
i. Animal Studies ' VI-15
ii. Observations in Man VI-16
e. Interactions With Selenium, Vitamin E,
Copper VI-17
C. Summary VI-18
References VI-20
VII. RISK CONSIDERATIONS VII-1
A. Risk Statement VII-1
B. Biotic Risk Considerations VII-1
1. Aquatic Life in Natural Systems VII-1
2. Microorganisms VII-6
a. Cloud Seeding VII-6
b. Sludge VII-7
c. Wastewater Treatment VII-7
3. Biota of Significance to Human Exposure VII-8
C. Human Risk Considerations . 'VI1-9
References VII-15
APPENDIX A: PRELIMINARY DATA FOR SILVER
CONSUMPTION - 1979 A-l
APPENDIX B: MAPS SHOWING RATIO OF Ag CONCENTRATION
IN WHOLE WATER TO CRITERIA AGGREGATED
BY COUNTY B-l
vii
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LIST OF TABLES
Table
No. Page
1 Summary of U.S. Silver Supply and Demand, 1978 III-2
2 Summary of Estimated Environmental Releases of Silver,
1978 HI-4
3 Mine Production of Recoverable Silver by State, 1978 III-7
4 Mine Production of Silver by Ore Type and Mine, 1978 III-8
5 Estimated Releases of Silver During Mining and Milling III-ll
6 Smelting and Refining of Ores Containing Silver in the
U.S., 1978 111-13
7 Estimated Environmental Releases of Silver From Primary
and Secondary Smelting/Refining in the U.S., 1978 111-15
8 — Estimated Environmental Releases From Production Pro-
cesses in Which Silver is a Byproduct, 1978 111-19
9 Materials Balance for End Uses of Silver, 1978 111-23
10 Silver Levels in the Wastewater of Photographic
Material and Equipment Producers 111-30
11 Releases of Silver to Water by Different Photographic
Industry Subcategories 111-31
12 Total Annual Production and Silver Aquatic Discharges
of Photoprocessing Establishments by Processing
Capacity 111-32
13 Estimated Annual Aquatic Discharges of Silver From
Home Darkrooms 111-34
14 Overall Environmental Releases of Silver by the
Photographic Industry, 1978 111-35
15 Silver Materials Balance for POTWs and Refuse, 1978 111-42
16 Silver Distribution in POTW Sludge: Selected U.S.
Cities 111-43
viii
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LIST OF TABLES (continued)
Table
No. Page
17 Silver Content of Silver Ores 111-47
18 Estimated U.S. Silver Releases to Surface Water From
Natural Sources 111-50
19 Estimated Global Silver Releases to the Atmosphere -
From Natural Sources 111-52
20 Physical Properties of Silver IV-2
21 Solubility Products of Various Silver Salts IV-5
22 Dissociation of Homogeneous Silver Complexes in Water
At Room Temperature IV-6
23 Dissociation Constants of Mixed Silver Complexes in
Water at Room Temperature IV-8
24 Accumulation of Silver in Aquatic Animals IV-30
25 Silver Concentrations Detected in Aquatic Biota IV-32
26 STORET Data on Silver Concentrations in Fish Tissue IV-35
27 Background Concentrations of Silver in Terrestrial
Animals ' IV-37
28 Silver Content of Terrestrial Plants IV-38
29 Distribution of Silver Concentrations in U.S. Ambient
Waters, STORET, 1970-1979 IV-43
30 Major U.S. River Easins in Which Annual Mean Concentra-
tions of Silver in Surface Water Exceeded SO ug/1,
STORET, 1970-1979 IV-46
31 Silver Concentrations Detected in Well Waters, STORET,
1977-1979 IV-48
32 Silver Concentrations Detected in Sediment, STORET,
1977-1979 IV-50
ix
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LIST OF TABLES (continued)
Table
No. Page
33 Mean Silver Concentrations of Ten U.S.
Rivers IV-51
34 Silver Concentrations in Suspended Matter in U.S.
Rivers IV-53
35 Silver Concentrations in Dissolved Form and Absorbed
Onto Matter in Major U.S. River Basins, 1977-S-1979 IV-54
36 Silver Concentrations Detected in Air and Precipitation IV^-56
37 Silver Concentrations Detected in Soil IV-58
38 Distribution of Unremarked Observations For Silver
Concentrations in Major River Basins, 1975-1979 V-3
39 Acute Effects of Silver on Freshwater Vertebrates V-10
40 Acute Effects of Silver on Freshwater Invertebrates V-ll
41 Chronic and Sublethal Effects of Silver on Freshwater
Fish V-12
42 Chronic and Sublethal Effects of Silver on Freshwater
Species V-15
43 Effects of Silver on Freshwater Microflora V-16
44 Acute Effects of Silver on Marine Invertebrates V-17
45 Chronic and Sublethal Effects of Silver on Marine
Invertebrates V-18
46 Effects of Silver on Terrestrial Plants V-20
47 Effects of Silver on Microorganisms V-20
48 Estimated Silver Ingestion in Foods VI-2
49 Estimates of Daily Silver Intake in Human Diet VI-3
50 Concentrations of Silver Detected in Drinking
Waters VI-5
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LIST OF TABLES (continued)
Table
No. Page
51 Estimated Silver Intake by Inhalation VI-9
52 General Ranges of Silver Concentrations Resulting in
Effects on Aquatic Biota VII-3
53 Estimated Exposure Levels of Silver for Humans VII-10
54 Silver Exposure Scenarios for Humans Exposed to
Multiple Sources VII-11
55 Adverse Effects of Silver on Mammals VII-13
xi
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LIST OF FIGURES
Figure
No. Page
I Potential Exposure Routes to Silver Affecting
Human and Non-Human Biota 1-3
II Anthropogenic Flow of Silver Through the
Environment 1-7
1 Materials Balance of Anthropogenic Silver III-5
2 U.S. Silver Material Balance III-6
3 Locations of and Particulate Silver Emissions
From Primary Copper, Lead and Zinc Smelters
in the U.S., 1974 111-14
4 Distribution of Industrial End Uses of Silver 111-22
5 Flow Diagram for Silver from Photographic Wastes 111-29
6 Flow Diagram of Silver in a Municipal
Incinerator III-4S
7 Geographic Distribution of Silver-Producing
Ores in the U.S. 111-47
8 Major Environmental Pathways of Silver
Releases IV-10
9 Major Pathways of Anthropogenic Silver
Released to the Environment IV-12
10 Soil Profile of Silver Concentrations on~Site Receiv-
ing Secondary Treatment Plant Effluent by Surface
Flooding IV-19
11 Eh-pH Diagram for the System Ag-S-O-H IV-22
12 Sediment Profile of Silver in the St. Croix
River Downstream from a Paper and Pulp Plant IV-25
13 Distribution of Silver in Coastal Sediments
of the North Sea IV-25
14 Trends in Mean and Maximum Silver -Concentrations
In Surface Waters of the United States, STORET,
1970-1979 TV-42
15 Distribution of Silver Concentrations in Surface
Waters (85th Percentiles); STORET, 1973rl975 IV-45
xii
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LIST OF FIGURES (continued)
Figure
No. Page
16 Percentage Change in Silver Concentrations in
Ambient Waters of Major River Basins, STORE!,
1970-1974 versus 1975-1979 Period IV-47
17 Summary of Silver Exposure Effects Levels
for Freshwater Organisms VII-5
18 Summary of Chronic Human Exposure Due to
Ingestion or Inhalation of Silver VII-14
xiii
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ACKNOWLEDGMENTS
The Arthur D. Little, Inc., Task Manager for this study was
Kate Scow. Other major contributors were Muriel Goyer (human effects),
Jane Metzger (editor), Leslie Nelken (environmental fate), Edmund Payne
(monitoring data), Katharine Saterson (biological fate and effects),
Pamela Walker (human exposure), Melba Wood (monitoring data), and
Alfred Wechsler (technical reviewer). Other reviewers and contributors
included John Ennis, Joseph Fiksel, Bruce Goodwin, Warren Lyman, and
Joanne Perwak. Pearl Hughes was responsible for the typing and prepara-
tion of the final draft report.
The materials balance for silver (Chapter III) was provided by
Acurex Corportion, under Contract 68-01-6017 to the Monitoring and Data
Support Division (MDSD), Office of Water Regulations and Standards (OWRS),
U.S. EPA. Patricia Cruse was the task manager and Kenneth Moss was the
other major contributor.
Gregory Kew, MDSD, was the project manager at the U.S. EPA.
-xiv
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CHAPTER I.
TECHNICAL SUMMARY
GENERAL STATEMENT OF RISK
Due to the low ambient concentrations of silver to which humans are
exposed and the high concentrations required to elicit adverse effects,
the likelihood of nonoccupational exposure to humans to harmful levels
is low. In addition, metabolic factors such as the low efficiency of
absorption through skin, lungs and gastro-intestinal tract, reduce the
probability of adverse exposure.
The most likely adverse effect to-occur from environmental exposure
of humans is argyr-ia, a localized non-lethal skin discoloration.
However, the chronic accumulative exposure required to elicit the effect
is unlikely to occur from ingestion and/or inhalation of typical
environmental concentrations of silver.
Animal data indicate that chronic exposure to higher concentrations
of silver may result in kidney hemorrhaging, this may not be applicable
to humans. Based on extrapolation of results from one experiment on
laboratory rats, the subpopulations likely to be exposed to con-
centrations high enough to elicit this effect are users of silver-
containing medicinal products and people living in the vicinity of a
government mint. The sizes of these subpopulations are expected to be
very small. The subpopulation of amateur photographers who develop film
in home darkrooms is not expected to be adversely exposed to silver based
on a low dermal absorption efficiency and localization of any accumu-
lated silver in the area of skin exposed.
There is some potential for environmental exposure of fish and
aquatic invertebrates to harmful levels of silver in surface water.
However, the actual likelihood of adverse effects is difficult to
determine due to several factors. While silver in ionic form is one of
the most toxic of the metals to fish and many aquatic organisms, fish and
other aquatic organisms are physiologically more sensitive to silver
than mammals due to a higher absorption efficiency through gill uptake
and due to exposure to higher concentrations in water. Although surface
water concentrations (as total Ag) are often reported at levels
\ comparable to concentrations found toxic to biota (as measured in
bioassays), only a fraction of the total silver concentration reported
is biologically available. Therefore, the actual "effective" con-
centration may be significantly lower. Determination of this fraction
requires knowledge of pH, concentration of complexing agents, water
hardness and other variables. Without this knowledge and the requisite
focus on a localized level, the conservative assumption must be made that
a potential for adverse exposure of sensitive aquatic organisms exists
and the likelihood of harm increases with conditions conducive to
ionization of available silver.
1-1
-------
Microbial populations, both in natural systems and wastewater
treatment plants, do not appear to be sensitive to silver at typical
environmental concentrations. Certain highly specialized locations such
as in the immediate vicinity of cloud-seeding machinery or an activated
sludge treatment plant which receives unusually high concentrations of
silver may experience reductions in microbial activity. Due to the
immobility of silver in soil -and its propensity for adsorption onto
sludge, any localized adverse effects would probably be long-term unless
a silver resistant microbial population adapted to replace the more
sensitive one.
HUMAN EXPOSURE AND EFFECTS
Human exposure to silver can occur through ingestion, dermal
absorption or inhalation, but all. three routes prove to result in low
exposures. Figure I illustrates the potential exposure pathways to
silver for humans as well as for fish and wildlife populations and shows
their relationship to silver in various environmental media. The figure
does not quantify the levels of exposure associated with each pathway.
Humans ingest silver in their diet and drinking water. Typical
daily dietary exposure ranges from 35-88 ug, although higher levels are
likely for certain subpopulations ingesting large quantities of silver-
contaminated bran, mushrooms, fish or shellfish. The maximum daily
exposure resulting from ingestion of drinking water is 0.06 mg, but the
average is much lower. A small fraction of the U.S. population who
customarily drink untreated surface water may be exposed to levels of
silver exceeding EPA's Water Quality Criterion for protection of human
health.
Dermal absorption is a significant exposure route only for patients
suffering from major burns. In these cases, as much as 100 mg of silver
may be involved per application although not all of this amount would be
absorbed. Home processing of photographic film does not appear to be
associated with a high level of silver uptake.
Inhalation of silver will expose large subpopulations in urban
areas to exposure levels of approximately 45 ng to 185 ng per day. Very
small subpopulations may be exposed to significantly higher exposure
levels in the vicinity of smelters (approximately 450 ng/day but as high
as 1576 ng), steel mills (up to 216 ng/day) and government mints
(0.86 mg/day as a worst case, more likely 0.29 mg/day).
In conclusion, the highest human exposure levels are due to
localized atmospheric concentrations of silver affecting small sub-
populations and to medicinal use of silver-containing products. Exposure
levels from ingesting untreated surface water may exceed the EPA
drinking water standard; however, typical concentrations in drinking
water are usually lower than the standard.
1-2
-------
I
LJ
Human inhalation exposure
in vicinity of coal-combustion
and other fuel-using plants
Human dermal or ingestion
exposure to jewelry.
silverplated ware,
photographic material
SILVER
SUPPLY
Exposure of
soil microbial
populations
Human exposure
through ingestion of
contaminated plants grown
on sludge-applied soil
Exposure of
aerobic and non-aerobic
microorganisms
WASTEWATER
TREATMENT PLANTS
Human exposure
due to ingestion of
contaminated finished water
DRINKING WATER .
Human exposure
through ingestion of
contaminated fish
Exposure of
aquatic organisms
GROUNDWATER
Human exposure
due to ingestion of
contaminated well water
FIGURE I POTENTIAL EXPOSURE ROUTES TO SILVER AFFECTING HUMAN AND NON-HUMAN BIOTA
-------
Few data are available for adverse effects resulting from exposure
to silver at different concentrations and exposure routes. Systemic
toxicity is rare due to the poor absorption of silver by all routes of
exposure (e.g., less than 10% by the oral route). The only known
consequence of human exposure to silver is argyria. Considered a
cosmetic defect with no significant physiological effects, argyria is
believed to occur after retention of Ig or more of silver.
There is no evidence suggesting that silver is carcinogenic to
humans. Silver has not been found to be carcinogenic to laboratory
animals exposed through subcutaneous implantation of silver foil or
colloidal suspensions. No chronic feeding or inhalation studies have
been conducted on laboratory animals. The data now available on
mutagenic effects appear to conflict so further investigation is
required. Little information is available regarding the reproductive
and teratogenic effects of silver.
NONHUMAN BIOTA EXPOSURE AND EFFECTS
The environmental medium of primary interest for fish and wildlife
exposure is water. Soil is of more direct interest to human exposure due
to the potential for bioaccumulation in edible plants grown in silver-
contaminated soil. Air does not appear to provide a significant exposure
route to nonhumans due to the small amount of silver released to air from
any source and the short half-life of silver in air. Small subpopulations
in the immediate vicinity of sources (smelters, mints) may be affected
but it was not possible to quantify this route due to lack of appropriate
toxicity information and lack of source-specific monitoring data.
The most significant cultural sources of silver to water are
discharges from the photographic industry (totaling 109 kkg) and from
mining, milling, smelting and refining of silver and other metallic ores
(totaling 5 kkg annually). Publicly Owned Treatment Works (POTWs) also
discharge a significant amount of silver to water following treatment,
an estimated 70 kkg annually.
Typical fresh surface water concentrations range from 0.1 ug/1 to
10 ug/1 of total silver. Higher concentrations, however, are observed
with 10% of all positive observations between 10.1 ug/1 and 100 ug/1.
Observations reported in marine water are fewer and tend to be lower than
those reported in freshwater.
As stated previously, silver is toxic at low concentrations to
aquatic life. Acute effects levels vary by species and experimental
procedure but generally range from 4.3 ug/1 to 100 ug/1 for freshwater
fish and 1.5 to greater than 1000 ug/1 for freshwater invertebrates. A
"no effects" level between 0.09 and 0.17 ug/1 was established for chronic
exposure of rainbow trout.
Toxicity of silver has been attributed to the metal's induction of
mucous secretion in the gills leading to suffocation. Other hypotheses
1-4
-------
suggested are blocking of essential enzymes and destruction of gill
epithelial tissue.
Environmental parameters influencing aquatic toxicity of silver
include: 1) water hardness—toxicity decreases with increasing hard-
ness, and 2) size of fish—smaller animals are more susceptible. Other
variables determining toxic levels of metals as a group such as pH,
presence of complexing agents, salinity, etc., will also affect silver
availability and toxicity.
MATERIALS BALANCE
Releases Due to Human Activities: Approximately 4640 metric tons
of silver were used in the United States in 1978. Over 40% of this total
was used in the manufacture of photographic materials. Manufacture of
electrical and electronic components consumed an additional 25% of the
total. These and other uses are illustrated in Table 1 on page 16.
While domestic ores are a significant source of silver (1225
kkg/yr), approximately twice as much (2354 kkg) is imported in a variety
of forms. Recycling of silver (from a variety of sources) is widely
practiced, accounting for 1150 kkg of U.S. refined silver production in
1978.
Consumer use and disposal of products containing silver eventually
releases more silver to the environment than ore mining, processing,
smelting and subsequent reprocessing combined. A large proportion (77%)
of the silver discharged goes to landfills and approximately 10% goes
directly to surface water. Around 7% goes to POTWs, and 6% to air.
Further details may be found in Table 2,. page 18.
The most significant manmade sources of silver air emissions are
the silver smelting and refining industry (30%), municipal waste
incineration (13%) and inadvertant sources such as from fossil fuel
combustion, cement manufacture and iron and steel production/manu-
facturing (23% total).
Photographic manufacture and processing are the only manmade
sources of silver going to POTWs or discharged directly to surface waters
(although POTW pass-through of silver accounts for a tonnage equal to 33%
of the total going to surface waters due to human activity).
The largest contributions to the landfilled or land-applied silver
burden are from photographic manufacturers and processors (62%), silver
mining, processing, and refining (16%), and from POTW sludge whose
contribution is equivalent to 22% of all manmade sources.
Natural Releases: Natural releases of silver to the U.S. environ-
ment are mostly attributable to the weathering of minerals. These
mechanisms result in release of around 440 kkg/yr to freshwater streams
and rivers and deposition of approximately 40 kkg of silver in sediments,
largely in the form of very insoluble oxides and sulfides.
1-5
-------
Very small quantities of silver also are released to the U.S.
environment as dust carried in sea salt spray, but these are negligible
in comparison to the quantity due to weathering of minerals which is
released to the water and sediment. The global burden of silver in the
atmosphere due to all types of dust has been estimated as SO kkg/yr. Sea
salt spray contributes only around 2 kkg/yr to the global burden.
ENVIRONMENTAL PATHWAYS OF SILVER
Figure II roughly illustrates the flow of silver throughout the
different environmental media based on materials balance and fate
pathway information. Interaction between environmental compartments is
low due to the immobility of silver in most soils, its tendency to
associate tightly with sediment in aquatic systems, and its very low
release rates to the potentially more dynamic air compartment.
The fate and distribution of silver following release to the
environment can be characterized by one of four source-dependent
pathways: atmospheric emissions (accounting for 67, of total manmade
releases), land disposal of solid waste including mine tailings (77%),
aquatic discharges to surface water (10%) and aquatic discharges to
POTWs (7%).
Atmosphere; Atmospheric emissions originate from smelting activi-
ties, inadvertent releases (fuel combustion, steel manufacturing, etc.),
and certain silver-consuming industries. Particles of less than 20 urn
diameter (from smelting and combustion) will be widely dispersed in the
atmosphere in the form of oxides, sulphides, sulphates and chlorides,
eventually reaching land and water via rainout and dry deposition.
Particulates larger than 20 urn in diameter (from smelters) are likely to
settle out within 1 km of the source of emission. The form of silver in
these particulates is expected to be the same as in the ore undergoing
smelting.
Levels of silver present in air in both urban and rural regions
generally are less than 5 ng/m^. Levels in the vicinity of some
inadvertant sources such as coal-fired steam plants or steel mills are
not notably higher. However, levels in the vicinity of some metal
smelters may be depending on the silver concentration in the ore. For
example, levels of up to 36.5 ng/m were detected near a lead smelter
processing ores known to contain high silver concentrations. Cloud
seeding activities only result in increased air levels in the immediate
vicinity of the land-based equipment used.
Land: The largest contributions to the landfilled or land-applied
silver burden are from photographic manufacturers and processors (62%),
silver mining, processing, and refining (16%), discard of electrical
equipment having silver contacts and conductors (15%), and from POTW
sludge whose contribution is equivalent to 22% of all manmade sources.
1-6
-------
AIR
t
6%
SILVER
SUPPLY
WATER
Variable SEDIMENT
SOIL
Anthropogenic Pathways
Natural Pathways
FIGURE II ANTHROPOGENIC FLOW OF SILVER THROUGH THE ENVIRONMENT
-------
Acid mine drainage does not appear Co be an important contributor of
silver releases. Once in the soil, the element is relatively immobile,
with little potential for leaching into groundwater. Because silver
accumulates in the upper soil layer following soil surface application
or disposal, it may be transported to water through runoff.
Silver concentrations in soil are more commonly derived from parent
rock rather than cultural sources. Typical ambient levels reflect the
substrate concentration and thus are variable, ranging from 0.02 mg/kg
to as high as 1000 mg/kg. An average natural background level is
approximately 0.1 mg/kg to 0.2 mg/kg. Silver in sludge or other wastes
being disposed of on land is at concentrations as high as 900 mg/kg,
although 100 mg/kg is more typical. No information was available on
levels at landfill sites following incorporation of the waste.
Background concentrations of silver in terrestrial plants ranged
from 0.02 mg/kg in alfalfa tops to 5.5 mg/kg in mushroom caps.
Experimental data indicate that silver may be accumulated from solution
at concentrations as high as 1760 mg/kg in bush beans. In most cases,
however, accumulation is not so extreme. Specific food crops with
reported silver residues included whole wheat (0.4 mg/kg), wheat germ
(0.8 mg/kg), tea (2 mg/kg), and fruits and nuts (up to 1 mg/kg).
Although data on accumulation of silver in terrestrial organisms
are limited, silver does not appear to have a strong potential for
biomagnification in terrestrial food chains.
Water; Effluents containing silver are discharged by the photo-
graphic industry, both in production and development, by electroplaters
and by smelters. Most companies practice in-house recovery techniques
using precipitation, ion exchange, electrolytic recovery, and/or re-
ductive exchange. Fifty percent of the photographic producers discharge
to POTWs. Amateur photographers discharge untreated wastes, primarily
to POTWs, however, the total amount is small. In surface water, the fate
of the silver is dependent on the form discharges. Thiosulfate silver
complexes, which are the primary form released by the photographic
industry, are degraded slowly and then precipitated as a halide or
sulfide. The distribution of silver ions between the freeform and
complexes is dependent upon pH, redox potential, and the presence of
complexing agents. According to the results of a chemical speciation
model, AgCl2 is the most prominent form in maring waters, with only
negligible amounts of the ionic form; in freshwater in the presence of
sulfur, AgHS predominates, especially in areas of low salt concen-
trations. In freshwater streams, approximately 10% of the total load of
silver is found in suspended sediment. Silver accumulates in bottom
sediments in the vicinity of sources, especially in the surface layer.
Monitoring data for total silver levels in U.S. surface water
indicate typical annual mean concentrations of less than 10 ug/1.
Regions with higher than average concentrations include the North
Atlantic, South Atlantic, and North Mississippi River basins. Samples
1-8
-------
from groundwater in mining areas revealed concentrations even lower than
Che national average.
Sediment levels of silver in surface water usually range from
1 mg/kg to 10 rag/kg, with a high a 95 mg/kg; sediment concentrations are
usually two to three orders of magnitude above water levels. In dissolved
and suspended matter in rivers, silver concentrations ranged usually
from 0.1 ug/1 to 7 ug/1 in 1968. More recent data indicate that levels
were usually less than 0.06 mg/1. Levels to surface waters in effluent
industrial wastewater, and sewage treatment discharges are generally
less than 20 ug/1 (mean values), with a maximum of 730 ug/1.
The mean concentration of silver in fish from U.S. river basins
according to STORE! is 0.235 mg/kg, with a range of 0.004 to 1.9 mg/lg.
Other studies report levels up to 9 mg/kg (in shellfish) and 4.4 mg/kg in
bone tissue of cut-throat trout. In general, however, most con-
centrations rarely exceed 1.0 mg/kg in marine and freshwater fish and
invertebrates. Reported bioconcentration factors (tissue levels/water
levels) range from 2.4 to 333 for various freshwater fish species.
Marine species, according to the available data, have a greater tendency
to accumulate silver up to levels that are 3300 times the concentration
in surrounding seawater. Both marine and freshwater plants are reported
to concentrate silver by a factor of 200; typical measured concen-
trations are less than 1.0 mg/kg.
POTWs; Wastewater treatment techniques such as lime and settling,
activated carbon, and cation-exchange are over 90% effective in removing
silver from influents. However, these techniques are not used in most
POTWs. In facilities utilizing more conventional technology, 75% of the
silver is partitioned into the sludge leading to concentrations of
100 mg/kg or greater.
1-9
-------
CHAPTER II.
INTRODUCTION
The Office of Water Planning and Standards, Monitoring and Data
Support Division, of the U.S. Environmental Protection Agency is con-
ducting a program to evaluate the exposure to and risk of 129 priority
pollutants in the nation's environment. The risks to be evaluated
include potential harm to human beings and deleterious effects on fish
and other biota. The goal of the task under which this report has been
prepared is to integrate information on cultural and environmental flows
of specific priority pollutants and estimate the risk of receptor
exposure to these substances. The results are intended to serve as a
basis for evaluating the magnitude of the risk and developing suitable
regulatory strategy for reducing any such risk when action is warranted.
This report provides a brief, but comprehensive, summary of the
manufacture, use, distribution, fate, effects and potential risk of
silver ot humans and nonhumans. Making effective use of the information
given requires an understanding of uncertainties regarding the data and
qualifications regarding conclusions presented herein.
Silver is found naturally at low levels in the earth's crust and
various environmental media. The amount released annually from these
sources to air and water is an important factor in the assessment of
the environmental impacts due to human activity. However, natural load-
ing rates are difficult to estimate and are not known with great certainty.
As is characteristic of inorganics in general, silver is commonly
found in association with other metals. Although silver is relatively
toxic to aquatic life, its concentration is usually significantly lower
than those of other metals, thus reducing its contribution to the overall
effect of the mixture. In some cases, synergistic effects may result
from associations with different metals.
Silver's market value encourages intensive recovery practices for
industries which produce and consume the metal. Wherever possible,
knowledge on current recovery practices for specific industries were
used to try to make realistic estimates of their emissions. Estimates
of silver loading from industrial sources are based on treated effluent
concentrations whenever possible. Otherwise, raw wastewater concentra-
tions are used which may result in an overestimate of that particular
release.
II-l
-------
The report is organized as follows:
Chapter III presents a materials balance for silver
that considers quantities of the chemical consumed
in various applications, the form and amount of
pollutant released to the environment, the environ-
mental compartment initially receiving it, and, to
the degree possible, the locations and timing of
releases.
Chapter IV describes the distribution of silver in
the environment by considering the critical environ-
mental pathways for silver that determine its fate in
the environment and describing the distribution of the
element in the environment reported in monitoring data.
Chapter V considers toxicological effects and exposure
to non-human biota, predominantly aquatic biota and
microorganisms.
Chapter VI describes the available data concerning
the toxicity of silver for humans and laboratory
animals and quantifies the likely level of human
exposure via major known pathways.
Chapter VII presents likely exposure conditions
for nonhuman biota and presents various exposure
scenarios for humans; the exposure levels are
correlated with reported effects levels from
Chapters V and VI, in order to assess the risk
presented by environmental exposures to silver.
II-2
-------
CHAPTER III.
MATERIALS BALANCE
A. INTRODUCTION AND METHODOLOGY
An environmental materials balance for silver presented in this
chapter considers man-made releases of the metal to the first point
of entry into the environment. Natural releases are also briefly con-
sidered. Potential sources of silver releases were identified by a
review of industrial activities involving the metal, including extrac-
tion, refining, use, and disposal. The amount of silver used by man
was followed as best as possible from the original sources through its
life cycle of production and uses to final disposal. At each stage in
the life cycle, potential releases to the environment were identified.
For each source of pollutant release, the amount of material emitted,
the process point at which the emission occurred, and the environmental
compartments (water, air, and soil) initially receiving and transporting
the metal were identified. In addition, the locations for sources of
releases were distinguished when sufficient information was available.
There are many uncertainties inherent in this type of analysis: not
all current releases have been identified and past and future patterns
of production, use, and disposal are difficult to determine. However,
sufficient information is available to provide a general picture of the
anthropogenic environmental loading of silver in terms of nature, magni-
tude, and location.
The scope of the materials balance has been limited to a review of
published and unpublished data concerning sources of silver releases to
the environment. The available literature has been critically reviewed
and compiled in order to present an overview of major sources of silver
emissions, annotated tables containing assumptions and estimations used
in deriving numbers, and an indication of data gaps. Data collection
was significantly aided by Smith and Carson's (1977) comprehensive
review concerning silver in the environment.
B. OVERVIEW
The 1978 U.S. industrial demand for silver was approximately 4640
kkg; an additional 700 kkg was exported in unprocessed form and silver-
containing products. The sources of silver in the U.S. are both domestic
and foreign. Table 1 summarizes the industrial supply of and demand for
silver in 1978.
Silver occurs commonly and is widely distributed at low concen-
trations in crustal deposits; therefore water, soil, and air contain
low background levels of the element. Silver is produced
III-l
-------
TABLE 1. SUMMARY OF U.S. SILVER SUPPLY AND DEMAND, 1978
Source/Consumer Supply Consumption
(kkg) (kkg)
U.S. Mine Production (1.230)1
Primary Smelting and Refining (of ores) 1,690
Secondary Smelting and Refining (of
(of scrap) 1,150
Imports (ore, dore, scrap) 450
Imports (refined metal) 1,910
U.S. Stocks 5,990
Photographic Material 2,000
Contacts/Conductors 960
Sterling Ware 560
Brazing Alloys/Solders 340
Other 920
Exports 700
U.S. Stocks 5.850
11,190 11,190
lThis number is not included in the total in order to prevent double-
counting of amounts for primary smelting.
Note: The above figures are estimations for the year 1978. Due to
considerable yearly statistical variation, these values do not
necessarily represent typical annual levels of production and
use.
III-2
-------
from mining and milling of various ores containing the -metal at con-
centrations from 1 mg/kg to almost 1000 mg/kg. Additionally, since a
large amount of silver is contained in discarded products, the recycling
of this scrap is also an important source of silver. Unintentional
production of silver occurs both through cultural activities and natural
processes.
Environmental releases of silver during production processes and
consumptive uses are presented in Table 2 and Figure 1 and 2. The
largest single discharger of silver to water and soil is the photographic
industry during manufacture of products and film development. This is
not surprising since the photographic industry consumes 43% (including
the products exported) of the annual U.S. total consumption of silver.
Other major releas.es are generated by milling activities, primary
smelting, and from production, use, and disposal of contact/conductors
and brazing alloys/solders, which are significant silver consumers. Less
important releases come from secondary smelting and inadvertent sources
such as cement manufacturing, fuel combustion, and iron and steel pro-
duction.
A special category of releases to the environment are those'from
Publicly Owned Treatment Works (POTWs) and urban refuse landfills.
Some portion of the releases to water and land are made directly to
POTWs and landfills for subsequent release to various environmental
media. These releases are shown separately from those of other anthro-
pogenic sources in order to avoid possible double counting.
C. METALS PRODUCTION
1. Mine Production
Underground and open-pit mining of silver, copper, lead, gold, and
zinc ores produced 1225 kkg of recoverable silver in 1978 (Drake and
Butterman 1979). Underground mining involves drilling and blasting
tunnels and shafts and raising the ore to the surface for transport.
Open-pit mining requires the removal of overburden, thereby exposing
the ore to the surface, where it is drilled, blasted and transported
for further processing. Table 3 lists 1978 mine production of recover-
able silver by state. Major silver-producing mines (accounting for
about 50% of annual production), ore type, and location are shown in
Table 4.
Silver ores are the most important source of silver, accounting
for nearly one-half of total mine production. Much of this ore is found
in the Coeur d'Alene district of Idaho, which is one of the major silver-
lead-zinc producing areas in the world. In 1978, the Sunshine Mine,
located in this area, produced 154 kkg of silver from ore with a silver
concentration of approximately 860 mg/kg (Lindstrom 1979).
III-3
-------
TABLE 2. SUMMARY OF ESTIMATED ENVIRONMENTAL
RELEASES OF SILVER, 1978
Release (kkg/year)
Source
Metals Production
Mining and Milling
Smelting and Refining (primary)
Smelting and Refining (secondary)
Other Production in Which
Silver is a Byproduct
Cement Manufacture
Coal and Petroleum Combustion
Iron and Steel Production
End Uses
Photographic Industry
• manufacture
• developing
Contact/Conductors
Sterling Ware
Brazing alloys/Solders
Catalysts
Electroplated Ware
Jewelry
Batteries
Commemorative Coins, Medallions
Dental/Medical
Mirrors
Bearings
Cloud Seeding
Coinage
Total from anthropogenic sources
POTWs
Urban Refuse4
Natural Emissions
Urban Runoff
Direct
Aquatic POTW
1
2
2
-
^ ^
34 88
65
-
- -
-
-
1
- -
0.03
0.003 -
-
0.06
-
125 88
(10%) (7%)
70
_
438
72 96
Air
3
19
8
2
9
7
}•
22
1
2
0.01
-
0.4
-
_
0.05
-
-
77.7
(6%)
10
2
_
Land
62
103
™ *
2
-
^
\ 630
150
60
-
-
—
-
_
—
—
21
1009 - 1300
(77%)= (100%)
220
370-520
NEJ
_
1Actually discharged to both surface water and land.
2Global estimate of 52 kkg per year. (See Table 19.)
3Not estimated
**Includes land disposal of products listed above.
III-4
-------
IMPORTS AND DOMESTIC PRODUCTS
(11.190 kkg)
Exports
700 kkg
Import:
Secondary
450. kkg
Secondary Production
1,150 kkg
INADVERTANT SOURCES
Coal and Petroleum
Primary Production
1,690 kkg
CONSUMED
Total Shook*-1*Total.— Exports
Batteries/Conductors
1.150 kkg
Other
1,070 kkg
Photography
2,000 kkg
POTWs
1 Sffftkg
•Air
78 kkg
FIGURE 1 MATERIALS BALANCE OF ANTHROPOGENIC SILVER, 1978
III-5
-------
A» Watar ?OTW band
3 nagc I6S
2000 kkg
9«nriH
190 kkg
GonuctConaucran
960 meg
Staring Ware
860 kkg
Snzmg
AllowSoldtn
Cunvm
260 kkg
gtaaraoliMWira
230 kkg
210 kkg
Coin*. Maoallbm.
OMObitcQ
90 km
80kkg
«0kk«
Sanngi
IQkkg
Cain*ga
Ikkg
CkHidS
-------
TABLE 3. MINE PRODUCTION OF RECOVERABLE SILVER BY STATE, 1978
State
Alaska
Arizona
California
Colorado
Idaho
Michigan
Missouri
Montana
Nevada
New Mexico
New York
Oregon
South Dakota
Utah
OTHER
1
TOTAL
Production
(kkg)
0.064
206.4
1.80
131.2
571.6
10.99
63.9
90.8
25.0
27.8
0.650
0.053
1.65
89.7 .
3.22
1224.8
Includes Illinois, Tennessee, Texas, Washington.
Source: Drake and Butterman (1979).
III-7
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TABLE 4. MINE PRODUCTION OF SILVER BY ORE TYPE AND MINE, 1978
I
GO
Ore Type 'and Mine
Silver Ores
Sunshine
Galena
Coeur
Bulldog Mt.
Crescent
Sherman Tunnel
DeLamar
Copper Ores
Berkley Pit
Mission
Utah Copper
Lead Ores
Location (State) Method of Mining
Idaho Underground
Idaho
Idaho
Colorado
Idaho
Colorado
Idaho Open Pit
Montana Open Pit
Arizona
Utah Copper Open Pit
Production
(kkg)
154
124
75
65
N/A
N/A
61
73
15
N/A
Lucky Friday
Gold Ores
Homestake2
I0re types from Drake (1
-------
Copper ore, containing 1-3 mg/kg silver, accounted for 31.6% of
the mine production of recoverable silver in 1978 (Drake 1979). Open-
pit mining of copper ore is practiced more frequently than underground
mining. Silver as a byproduct from copper ore in the U.S. comes mainly
from Utah, Arizona, New Mexico, and the Keweenaw district of Michigan
(Smith and Carson 1977).
Lead, gold, sine, and complex copper-lead-zinc ores yield the "
remaining 13.2% of the total silver mined. Underground mining of silver-
containing lead ore, mainly in Idaho and Michigan, provided 5.2% of the
U.S. silver production in 1978 (Drake 1979). Silver produced from gold
ore, recovered in South Dakota and Nevada by underground, open-pit, or
placer methods, produced 17 kkg silver in 1978 (Drake 1979). Zinc and
complex copper-lead-zinc ore provided 8% of the recoverable silver in
1978. Zinc ore bearing 34 mg/kg silver is found in Colorado and New
York. Complex ores occur as veins in fracture zones and are mined
chiefly in Idaho and Colorado, generally by underground mining tech-
niques .
Losses of silver from mining of various ore types do not appear to
be significant. Particulate emissions of silver are assumed to occur
during drilling and blasting operations, but no specific data were found.
Mine drainage from precipitation, groundwater, and runoff from water
sprayed for dust control apparently discharge little silver to the
environment. Smith and Carson (1977), for example, report silver con-
centrations ranging from 1 mg/1 to 8 mg/1 in drainage of abandoned mines.
Larsen et al. (1973), in a study concerning treatment of metal-contain-
ing mine drainage, stated that "very little silver" was found in mine
drainage of the Red Mountain mining district in Colorado, even though
silver, lead, and gold were "extensively mined" In the area.
2. Milling of Silver-Containing Ores
Milling is the beneficiation of mined ore to yield a mineral con-
centrate. Silver-containing ores are milled most frequently by flota-
tion processes based upon the hydrophobic or hydrophilic character of
minerals such as silver sulfide. Other methods such as gravity concen-
tration, and amalgamation-cyanidation are less common.
Flotation of all ore types involves crushing, grinding, and classi-
fication of the ore; the actual flotation processes and cleaning and
conditioning of mill pulp are dependent upon the specific ore type and
the metal content, but generally involve the following steps: A slurry
of finely ground particles is agitated in a tank (flotation cell) and,
as air is forced through the tank, air bubbles attach to non-wettable
minerals. Frothing agents and conditioning agents are added to "float"
or separate the minerals by species. Separation is effected by skimming
the stabilized froth and withdrawing wettable mineral from the tank
bottom.
III-9
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Gravity concentration is used in milling of silver-bearing lead-
zinc-ore in the Coeur d'Alene district in Idaho, the Tri-State district
(Missouri, Kansasi and Oklahoma), and the Old Dick copper-zinc mill in
Arizona (Smith and Carson 1977). The method used today is a fluid
medium, in which minerals sink or float depending upon their densities
relative to that of the medium (Smith and Carson 1977).
Amalgamation and cyanidation, involves grinding the ore to a coarse
size, gravity separation of the metal containing black sands, and con-
centration of the metal by batch amalgamation of the sands (addition of
mercury), to form an alloy (Schack and Clemmons 1963). Metal is recov-
ered by grinding the amalgam to eliminate solid impurities; squeezing
the amalgam through heavy canvas to remove excess mercury; retorting;
and distilling to give a molten gold-silver bullion, which is transported
to a smelter (Smith and Carson 1977). Amalgamation is used by the Home-
stake Mine in South Dakota and for recovery of placer gold from Alaska
and western states.
In cyanidation, the ore is ground and classified into slime and
sand fractions; precious metals from each fraction are first extracted
with cyanide solution and subsequently precipitated using zinc shavings
or dust. The precipitate is then melted, usually in a reverberatory
type furnace to yield dore metal, a gold-silver concentrate (Schack and
Clemmons 1963).
The total loss of silver to all environmental media during milling
in 1978 is estimated to be 66 kkg (Table 5). Silver emissions to the
air occur during crushing and grinding of the ore. The particles are
relatively large and settle quickly (Smith and Carson 1977).
The wastewater from milling operations—flotation, cyanidation,
and amalgamation—is sent to tailing ponds for settling, and in some
cases a final clarification pond (U.S. EPA 1975c). Because floation
process water is normally alkaline (pH 8), heavy metals, including
silver, are precipitated in tailing ponds. Wastewater discharge from
silver milling is further reduced by recycling of the settling pond
decant. Negligible amounts of silver are reported to be discharged
(U.S. EPA 1975c).
Tailing ponds are, however, responsible for relatively large
discharges of silver to land. Mill residue consisting of process water
and waste rock is pumped to these ponds, where the solids are settled
and the water is either recycled to the mill or discharged directly.
The amount of silver discharged from tailing ponds depends upon the
specific milling practices and metal recovery processes for different
ore types. Reports prior to 1977 indicate that 32% of the available
silver in Missouri lead ore was lost to tailings during milling opera-
tions (Smith and Carson 1977). The total amount of silver lost in such
ores is not extensive, however, because the silver concentration of the
ore is low. Loss of silver to tailings during milling of silver ore in
Idaho is approximately 2% (Schack and Clemmons 1963).
111-10
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TABLE 5. ESTIMATED RELEASES OF SILVER DURING MILLING
Ore % of Total
Type Production
Ag
Cu
Cu-Pb-Zn
Au/Ag
Pb
Au
Old Tailings
Zn
TOTAL8
46.9
31.6
7.4
6.6
5.2
1.4
0.6
0.2
99.9
Ore Mined
(kke)
999,670
223,147,740
3,262,630
669,010
7,961,820
3,173,700
110,270
1,257,230
240,469,800
Recoverable Ag
(kke)
574
387
91
81
647
17
8
2
1225
% Ag Total Estimate
Recovery1 Milling Loss
(kkg)
98
91
90
90
68 MO
98 Others
98
98
81
11
35
9
8
1
1
0.4
0.2
0.4
66
id Estimated Releases (kkg)2
Air Land Water
I3 13 I"
<1 46 -6
<1 3 -6
_
- - -
- - -
- - -
3 62 1
'Smith and Carson (1977).
2Data not otherwise noted based on emission and recovery figures of Schack and Clemmons (1963). Due to the different
data source for these numbers, these columns do not add up to number in Total Estimated Milling Loss column.
3Based on amount of ore crushed, 0.75 kg dust/ton ore for Cu, Pb, and Zn processing, and amount of silver in ore.
Smith and Carson (1977).
'IBased on "average" mill water data extrapolated to 1978 production levels (U.S EPA 1975c).
^Included in tailing pond discharge listed under land.
fMissouri Pb ore accounts for 5.2% of total, fyrake (1978 and 1979).
'Totals may not add due to rounding.
Source: Drake (1980) unless otherwise noted.
-------
3. Smelting and Refining Containing Silver
a. Overview
Primary smelting separates metals of value from waste minerals
present in the ore concentrate (gangue), a step necessary prior to
refining. The process used for different ores involves basically the
same "operations, though the amount of silver discharged varies. Silver
recovered as a byproduct from the smelting and refining of copper, lead,
and zinc ore concentrate totaled 1180 kkg in 1978. Approximately 510
kkg silver were produced from smelting and refining of silver ore con-
centrates (Drake 1979). Additionally, 300 kkg of silver ore and con-
centrates were imported in 1978 (Drake 1979). Processing of these
imported materials is included in the amounts for domestic smelting and
refining, shown in Table 6.
Secondary smelting is the recovery and refining of silver contained
in scrap material and discarded products. Approximately 1150 kkg of
silver were produced by this process in 1978. The locations of U.S.
smelting and refining facilities are shown in Figure 3.
b. Copper Recovery •
Primary copper smelting and refining require roasting of the ore
concentrate, reverberatory furnace smelting of the concentrate to form
copper matte, oxidation of the matte in converters to yield blister
copper, furna.ce purification of the blister copper and casting of anodes,
electrolysis to produce pure copper, and processing of slime residue by
hydro- pyro- or electrometallurgic means to recover precious metals
(Schack and Clemmons 1963).
•
Smelters recover an estimated 95% of the copper, silver, and gold
initially present in the ore concentrate (Schack and Clemmons 1963).
Most silver emitted from smelting and refining operations is lost to
the atmosphere as dusts and fumes from roasting and converting processes.
Although dusts and fumes are collected and recycled, approximately 8 kkg
of silver were emitted to the atmosphere in 1978 (Smith and Carson 1977).
Slag from the reverberatory furnace, which contains 1-2% of the silver
originally present in the ore concentrate, is discharged to land.
An estimated 1 kkg of silver is lost annually to water, mainly through
disposal of spent electrolyte solutions used in the refining process
(U.S. EPA 1975a). Silver releases from copper smelting and refining
are summarized in Table 7.
c. Lead Recovery
Lead smelting and refining involve sintering to agglomerate feed
material, smelting to produce lead bullion, dressing the impure bullion
to remove copper, and refining by electrolytic or kettle methods (Smith
and Carson 1977). Silver is removed at many points during these pro-
cesses (largely as slags or mattes), but most is recovered in the lead
111-12
-------
TABLE 6. SMELTING AND REFINING OF ORES CONTAINING
SILVER IN THE U.S., 1978
Source Amount of Silver
(kke)
Primary Refining (Concentrates & Ores)
Domestic 1370
Foreign 320
Total 1690
Ore Type1
Cu)
Pb I
Zn j 1180
Ag " 510
Total 1690
Secondary Refining
Old Scrap2 1110
Coins 40
Total 1150
New Scrap3 1280
TOTAL NET PRODUCTION 2840
TOTAL PRODUCTION (including new scrap) 4120
Refinery production by ore type is approximate; Drake (1979) states
that 70& of primary refining is attributed to Cu, Pb, and Zn ore.
201d scrap is silver containing material that has moved into commerce
as a silver containing product
w scrap is metallic material (bullion) held in stockpiles and even-
tually recycled at refineries, and is thus not included in this total
net production
Source: Drake (1979).
111-13
-------
H
Legend:
KAsarco (Taco I ;
(7.1) \] Kennecott (Hur|ey) 3.55
Phelps Dodge (Douglas) 48 -*\ itv (36.2) (
(Glover) 1.76
"TCItiej Seryice (CopporHjH) ~ 0
Copper
Lead
Zinc
.
f
o) of* *\ i
(7.1) \J
ge (Douglas) 48 -* \
tt?01 i> i -11
Magma (San Manual £33
( A«l .0 }
'Asarco (El Paso) 3.5
\\ (36)
' Asarco (El Paso) 0.2
I . • .M , '
Note: Values in parentheses are estimates of silver emissions in
troy oz/day based on data for one smelter: 10.2 troy oz
silver/ton particulate emissions.
Source: U.S. EPA. 1974.
*>
V'.i
;
Asarco (Corpus Christ!)
~O
V
V
FIGURE 3 LOCATIONS OF AND PARTICULATE SILVER EMISSIONS FROM PRIMARY COPPER.
ID. Zlft ELI N1 .S.. <
-------
Process
Primary Smelting/
Refining
TABLE 7. ESTIMATED ENVIRONMENTAL RELEASES OF SILVER FROM
PRIMARY AND SECONDARY SMELTING/REFINING IN THE
U.S., 1978
Estimated Silver Input (kkg) Silver Production (kkg)
1180
510
Copper ore \
Lead ore (
Zinc ore J
Silver ore
1300
510
Total 1810
1690
Secondary Smelting/
Refining
Silver scrap
Copper scrap } 1160
Lead scrap
Total 1160
Estimated Silver Releases (kkg)
Air Land Water Total
83
25
48
511
<1** 8
256 <1? 27
787 I10
83
5
19
8
103
213
123
10
1 Inputs based solely on addition of emission and production values.
2Production data from Drake (personal communication 1980).
dBased on 45 mg/kg Ag in particulate emitted (Smith and Carson 1977).
11 Based on waste effluent concentration of 0.02 mg/1 Ag, plant effluent flow rate (U.S. EPA 1979b) and 1978 copper
production figures (II. J. Drake, personal communication, 1980).
5Assume 45% of silver production is via Pb smelter; 1165 kkg particulates emitted per year containing 0.175%
silver (Smith and Carson 1977).
6Based on 5% smelting loss, minus estimated air and water emissions (Schack and Clemmons 1963)
7Based on an average waste effluent of 0.064 kkg of silver and an approximate flow rate of 1.8 mgd (U.S. EPA 1975a).
uBased on 1714 mg/kg Ag in particulate, 7.56 tons particulate/day (Smith and Carson 1977).
9Based on 473 mg/kg Ag in retort residue (Smith and Carson 1977). See text.
10Based on 1979 EPA Effluent Guidelines data and 1978 production figures (H. J. Drake personal communication 1980).
11
12
Assume 1% loss during furnace operations (Smith and Carson 1977).
Assume 1% smelting loss, minus estimated water loss (Smith, and Carson 1977).
13Based on EPA Effluent Guidelines Data (U.S. EPA 1976).
'Based on emission estimates (Smith and Carson 1977).
-------
bullion desilverizing step or as anode slime. Silver contained in
mattes or slags may be recycled to a copper smelter. Retorting of the
dross from the desilverizing step and oxidation of the remaining lead
yields dore metal (94% to "97% silver). Anode slimes are recovered in
a similar manner (see Section e.i., Primary Silver Refining).
As in other nonferrous smelting and refining processes, wastes
are extensively recycled; the major sources of silver release are from
stack gases and slag. On the basis of measurements at lead smelters,
an estimated 2 kkg of silver were lost to the atmosphere in 1973 (U.S.
EPA 1974). For an average concentration in waste effluent of 0.064 mg/
kg silver and an approximate flow rate of 1.8 million gallons per day,
an estimated 1 kkg of silver was lost to water (U.S. EPA 1975a). Dis-
charges to land (as slag) are more difficult to quantify. If the over-
all loss of silver is assumed to be 5%, approximately 25 kkg are 'lost
to land (Schack and Clemmons 1963). Such an assumption seems at least
reasonable; in 1974 8.8% of the silver present in Missouri lead concen-
trates was reported to be lost as slag during smelting and refining
operations (Smith and Carson 1977).
d. Zinc Recovery
Primary smelting and refining of zinc ore is by the retort process,
or the electrolytic process. Both are efficient for zinc recovery, but
since the electrolytic process recovers more precious metals, all new
plants use this process (Schack and Clemmons 1963). In either process,
zinc concentrates are first roasted in multiple hearth or fluidized bed
furnaces to remove sulfur and most of the lead, fluorine, chlorine, and
mercury. Particulate emissions are collected and recycled to a lead
smelter.
Wastes are in the form of flue dusts (containing approximately
1700 rag/kg silver), lead sulfate residue (—2600 ng/kg silver), and the
distillate trom zinc reduction. Most of the 'wastes are presumably
recycled within the same process (Phillips 1962; Nauert 1962; Smith and
Carson 1977) or, if the quantity of any of the other metals in the waste
is high enough, to a processing facility for that metal.
On the basis of a silver concentration of 1700 mg/kg in flue dusts
and an emission rate of 6.9 kkg of particulates per day from all zinc
operations in the U.S., an estimated 4.3 kkg silver is emitted to the
atmosphere annually from primary zinc smelting and refining (U.S. EPA
1974). This estimate is conservative, since approximately 26% of zinc
production involved horizontal retorts with uncontrolled emissions
(Smith and Carson 1977). The large amounts of silver lost to land are
a result of stockpiling of retort residue, which contains as much as
470 mg/kg silver (Smith and Carson 1977). The residue is shipped to a
lead smelter when metal concentrations are high enough to warrant
recovery (Schack and Clemmons 1963). Silver losses to water from zinc
processing are estimated to be 1.2 kkg per year (see Table 7). A sur-
vey by the U.S. EPA demonstrated that five out of the six U.S. zinc
111-16
-------
smelting and refining planes in operation today discharge process-water—
directly; the highest silver concentration, 200 ug/1, was found in
leachate effluent (U.S. EPA 1979b).
e. Silver Recovery
i. Primary Silver Refining
In primary refining, silver is recovered from copper refinery
slimes (^1 to 2% silver) and silicate slags (up to 2000 mg/kg silver),
in a process involving leaching and roasting to form a matte. This
substance is further refined (with sodium carbonate or potassium nitrate)
and oxidized to yield dofe metal containing 94-97% silver (Johnson 1967).
Then, by use of either the Balbach-Thum or Moebies electrolysis process,
the dofe metal is broken down into an anode slime from which silver is
collected through leaching or dissolution.
No specific data were found concerning losses to the environment
from primary silver smelting and refining. If the silver loss is assumed
to be 1%, 5 kkg of silver were emitted to the atmosphere during furnace
operations in 1978 (Smith and Carson 1977).
ii. Secondary Silver Refining
Secondary smelting and refining—the processing of silver, copper,
'and lead scrap—yielded 1150 kkg of silver in 1978 (Drake 1979).
Initially, this scrap is segregated into low- and high-grade scrap.
Low-grade scrap is mixed with lead scrap and pyrite (an iron-lead ore)
and smelted to yield lead bullion. High-grade silver scrap is added to
the lead bullion; this mixture is refined to dofe metal.
Few specific data were found concerning releases to the environment
from these processes. If 1% of the silver is lost from secondary silver
smelters, 6 kkg of silver were emitted to the air in 1978 (Smith and
Carson 1977). In 1978, approximately 2 kkg of silver were discharged
to water from secondary silver smelting and refining (Table 7), U.S.
EPA data concerning wastewater from 24 plants indicated that most of
the silver was discharged from disposal of electrolyte solutions (U.S.
EPA 1979b).
f
Other sources of silver discharges to the environment are secondary
lead and copper smelters. An estimated 1 kkg of silver was emitted to
the atmosphere from secondary lead smelting, on the basis emission data
from Smith and Carson (1977) and 1978 production figures. According to
U.S. EPA wastewater data concerning the secondary lead smelting indus-
try, disposal of battery electrolyte solutions was responsible for the
majority of the estimated 1 kkg silver lost to water. Furnace scrubber
effluent and waste electrolyte solutions accounted for most of the
estimated 1 kkg silver lost to water from secondary copper smelting
and refining (U.S. EPA 1979b). No data are available from which to
estimate air emissions from secondary copper smelting.
111-17
-------
D. PRODUCTION IN WHICH SILVER IS A BYPRODUCT
1. Overview
Cement manufacturing, combustion of coal and petroleum, and pro-
duction of iron and steel are all sources of silver emissions. Silver
losses from these processes (Table 8), however, do not appear to be
significant in comparison with those from milling, smelting, and refin-
ing of silver containing ore, concentrates, and scrap.
2. Cement Manufacture
In 1978, 68.6 x 10^ kkg of cement clinker was produced from approx-
imately 116.8 x 10** kkg of raw materials, the majority of which were
limestone, clay, shale, and gypsum (see Table 8). The silver content
of these materials is 0.07 mg/kg, 0.1 mg/kg, 0.1 mg/kg and .1 mg/kg,
respectively. If limestone, clay, shale, and gypsum are assumed to be
approximately 70% of all raw materials used in cement manufacture, the
silver content in cement is estimated to be 0.3 mg/kg. Table 7 deline-
ates silver discharges to the environment from the cement industry. The
major releases are from the kiln, where raw materials are heated, and
the dry piling of dust collected from the kiln.
Cement is produced by either a wet method, in which materials are
fed to the kiln as a slurry, or a dry method, in which materials are
fed in a dry solid form. In 1976, 58% of the cement was manufactured
by the wet method, 42% by the dry method (Wingard 1976). If these same
proportions are assumed for 1978, 40 to 105 kkg cement was produced via
wet method and 29 x 106 kkg via dry method.
The major source of releases to the environment from cement manu-
facturing is the kiln. If the silver content of the emissions is the
same as that of the charge (0.3 mg/kg) for each kkg of cement produced
by the wet method 12 kg particulates are emitted; 40 x 106 kkg cement
clinker was produced in 1978, If the silver content of the emissions
is the same as that of the charge (0.3 mg/kg) less than 1 kkg silver
was emitted to the air from cement manufacturing via the wet method.
Similarly, for each kkg of cement produced by the dry method, 34 kg
particulates are emitted, and 29 x 106 kkg cement containing 0.3 mg/kg
were produced. Thus less than 1 kkg of silver was emitted to the atmos-
phere from cement production via the dry method (U.S. EFA 1976b).
3. Combustion of Coal and Petroleum Products
Coal and petroleum contain trace amounts of silver; combustion of
these materials necessarily results in environmental silver discharge.
Petroleum supplied for use in the U.S. in 1978 total 9.6 x 10n(U.S. DOE
1980). If the silver concentration is assumed to be 0.001 mg/1 approxi-
mately 1 kkg of silver was emitted to the atmosphere from petroleum com-
bustion (Smith and Carson 1977).
111-18
-------
TABLE 8. ESTIMATED ENVIRONMENTAL RELEASES FtflM PRODUCTION
PROCESSES IN WHICH SILVER IS A BYPRODUCT , 1978
Source
Estimated Silver
Input (kkg)
Estimated Silver
in Produce (kkg)
Estimated Releases (kkg)
Air Land Water Total
Cement Manufacture
wet process
dry process
Petroleum Combustion
Coal Combustion
bituminous
sub-bituminous
anthracite
lignite
Iron and Steel Manufacturing
iron production:
I2
1*
176
2
1
1
5"'
1
1
1
5
1
1
1
sintering
blast furnace
steel production:
open hearth furnace
basic oxygen furnace
electric arc furnace
Iron Foundries
TOTAL
4
9
3
9
4
3
8
2
3
8
I8
I9
1
1
1
210
18
1
1
1
2
1
1
1
1
1
neg 2
neg 20
1Assume 39.7 x 10s kkg produced, 12 kg particulate/kkg cement produced, and 0.3 mg/kg Ag in particulate
(Portland Cement Association, personal communication, 1980, U.S. EPA 1976b; Wingard,1978).
2Assume 39.7 x 106 kkg prodcued, 97 kg particulate/kkg produced, and 0.3 mg/kg Ag (Wingard 1978; U.S. EPA
f1976b; Portland Cement Association personal communication, iVtfU;.
'Assume 2B.H x 10" kkg produced, tl kg particuiated/kkg cement produced, and 0.3 mg/kg Ag in particulate,
(Wingard 1978; U.S. EPA 1976b; Porland Cement Association personal communication, 1980).
'•Assume 28.8 x 106 kkg produced, 87 kg particulate collected/kkg produced, and 0.3 mg/kg (Wingard 1978;
U.S. EPA 1976b; Portland Cement Association,personal communication 1980).
5Assume .001 mg/kg Ag concentration and 9.6 x 10lll product supplied for use (Smith and Carson 1977 and U.S.
DOE 1980).
Assume 0.04 mg/kg Ag in bituminous coal, 0.02 mg/kg Ag for Che remainder (P. Zubovik personal communication,
1980; Assume 74Z of coal bituminous, 19Z sub-bituminous, 6Z lignite, and 1% anthracite (U.S. DOE 1980).
7Assume emission factor to air of 0.3 (Slater and Hall 1973).
"Assume 32.7 x 10s kkg iron production by sintering in 1978, 0.02 kkg particulate emitcad/kkg produced,
and maximum silver content of 0.1 mg/kg (Desy 1978, J. Copeland, personal cownunication, 1980). See text.
^Assume 79.5 x 10s kkg iron production by blast furnace in 1973, 0.42 kg particulate/kkg produced/ and a
maximum Ag content of 0.1 mg/kg (U.S. EPA 1978a).
l°Assume 27200 kkg particulate nationally from cupola ( C. Mann personal communication, 1980; 0.08Z Ag in
emissions (U.S. EPA 1973b). Does not include 112 x 106 kkg emissions from non-melting operations.
1 Negligible. Silver concentration of 0.01 mg/1 found In three of 44 waste streams ( J. Williams,
personal communication 1980).
111-19
-------
Coal production in 1978 totaled 5.67 x 108 kkg, 76% of which was
used to generate electricity. The remainder was used in coke plants,
steel mills, and sold to retail dealers. The silver concentration is
assumed to be 0.04 mg/kg in bituminous coal, and 0.02 mg/kg in sub-
bituminous coal, anthracite, and lignite. Silver emissions to the
atmosphere, as noted in Table 8, are estimated to be 5 kkg for bitumi-
nous coal and approximately 1 kkg each for anthracite, lignite, and sub-
bituminous coals. Though silver might also be discharged to ground water
supplies as a result of flyash and bottom ash leaching, silver migration
is expected to be minimal because of the basic nature of ash.
4. Iron and Steel Manufacture
Manufacture of iron and steel is apparently responsible for small
discharges of silver to the environment. Iron is produced by sintering,
a process that fuses small ore particles before they are fed to the
blast furnace, or by direct reduction in a blast furnace. Steel is
produced from open hearth, basic oxygen, or electric arc furnaces.
Emission to the atmosphere is apparently the major pathway for silver
loss from iron and steel manufacture. Silver, however, is also probably
lost in the discarded slag in the same proportion as it is found in the
charge.
In 1978,-32.7 x 105 kkg iron was produced by sintering (S. H. Desy,
personal communication, 1980). On the basis of EPA estimates that 0.02
kkg particulates were emitted per kkg iron produced (U.S. EPA 1978a) and
that particulates contain 0.1 mg/kg silver (J. Copeland, personal com-
munication, 1980), less than 1 kkg silver was lost to the atmosphere
from sintering. Blast furnace iron production for 1978 totaled 79.5 x
10s kkg. An estimated 0.42 kg of particulates were emitted per kkg iron
produced (U.S. EPA 1978a). If the silver concentration is assumed to
be 0.1 mg/kg, less than 1 kkg silver was emitted to the atmosphere from
blast furnace operation.
Steel production via open hearth, basic oxygen, and electric arc
furnaces resulted in releases of 27500 kkg, 19500 kkg, and 21800 kkg of
particulates, respectively, in 1978 (R. Sevaydarian, Effluent Guidelines
Division, U.S EPA, personal communication, 1980). Silver levels in
these emissions were less than the 0.1-nig/kg lower detection limit of
the analytical technique used. For purposes of estimating the silver
content of the particulate emissions, 0.1 mg/kg was used as the maximum
silver concentration. Thus, each of the three furnace types emitted
less than 1 kkg of silver to the atmosphere.
In 1978, U.S. iron foundries produced approximately 15 kkg of gray,
malleable, and ductile iron and steel using pig iron, iron scrap, coke,
limestone and silica sand (National Foundry Association, personal com-
munication, 1980). Particulate emissions from the cupola furnace in
which iron is melted, were estimated by U.S. EPA to be 27200 kkg
(C. Mann, personal communication, 1980). This figure does not,
111-20
-------
however, include fugitive emissions from non-melting operations such as
grinding, operation of cooler ovens, and sand handling estimated to be
112 x 10° kkg.(C. Mann, personal communication, 1980). Since the
ratio of charge materials to the kiln varies widely, as do their silver
concentrations, no specific value for the silver concentrations of
foundry emissions is available. The U.S. EFA estimated the silver con-
tent of cupola emissions to be 80 mg/kg (U.S. EPA 1973b). If these
data are used, 2 kkg of silver is estimated to be emitted as particulate
matter form cupola furnaces.
Aqueous discharges of silver from iron foundries are negligible.
An EPA survey detected silver in only 3 of 44 waste streams sampled;
the highest silver concentration was 0.01 mg/1 (J. Williams, personal
communication, 1980).
E. END USES
1. Overview
The uses of silver are diverse, ranging from photography to cloud
seeding. Approximately 5,340 kkg of silver were consumed for end uses
in 1978. Statistics for silver consumption by end use are presented
in Figure 4; estimated environmental releases resulting from the varipus
uses or operations are summarized in Table 9.
2. Photography
a. Overview
The photographic industry consumed 2000 kkg silver in 1978, or 40%
of the total industrial consumption (Drake and Butterman 1979); this
sector is the largest single end user of silver.
The principal uses of silver by the photography industry are the
manufacture of photographic paper, cloth, film, and plates, X-ray film,
and office copying systems. Some substitution of silver will occur in
photography and X-ray systems as progress continues with silverless
image reproduction, but no significant reduction in the use of silver
by such systems is foreseen (Drake 1978).
The use of silver results from the reduction (i.e., development)
of exposed silver salts under mild conditions. When exposed to radiation
of suitable energy (X<400 nm) silver halides are photolyzed to yield
silver and halogen. After development of sensitized crystals, the
photographic image is "fixed" by removal of any remaining silver salt
with a complexing agent, generally sodium thiosulfate, which forms an
extremely stable complex with Ag+ (log K = 13.23). Photographic emul-
sions are prepared from silver nitrate and sodium or potassium chloride
or bromide, in the presence of a colloidial substance, which prevents
their coalescence.
111-21
-------
Jewelry 4.2%
Electroplated
Ware 4.5%
Catalysts 5.1%
Photographic
Materials
40.1%
19.2%
Contact and
Conductors
6.9%
Brazing Alloys
Solders
Coins
Medallions
Commemorative
Objects 1.7%
Bearings
Coinage
Cloud Seeding
Miscellaneous
0.8%
Dental,
Medical
Supplies
1.3%
Batteries 3.8%
Electrical/Electronic
Products 23%
FIGURE 4 DISTRIBUTION OF INDUSTRIAL END USES OF SILVER
111-22
-------
TABLE 9. MATERIALS BALANCE FOR END USES OF SILVER, 1978
Environmental Release (kke)
M
ISJ
End Use
Photographic Industries
Electrical/Electronic Products
Batteries6
Contacts/Conductors
Sterling Ware10
Brazing Alloys/Solders
Catalysts13
Electro-plated Ware15
Jewelry16
Coins, Medallions & Commemorative
Dental/Medical Supplies17
Mirrors18
Bearings19
Coinage16
Cloud Seeding17
Miscellaneous Uses20
TOTAL
Consumption1
(kke)
2000 2
(1860)
190
960
560
340
260
230
210
Objects16 90
60
60
10
1
2
30
5000
(4860)
Air Land Water
43 6301* 207 *
21. 68 1509
1.2 neg
211 6012
0.011"
- - 1
0.4 neg
_
_
0.05
_ _ _
neg
2
neg
27 842 208 = 1077
-------
I.
TABLE 9. MATERIALS BALANCE FOR END USES OF SILVER, 1978 (continued)
figures for 1978 (Drake and Butterman 1979). See Appendix A for 1979 preliminary totals.
2Seven percent of the silver-containing photography products are not consumed in the U.S. (Census
Bureau, 1976). Therefore, 1860 kkg is actually consumed domestically, contributing to environmental
releases. J
i
3AgNO3 production emissions are assumed to be negligible because an enclosed reaction vessel is used,
fumes are scrubbed, and all byproduct streams are reused (Guccione 1963). Smith and Carson (1977) {use
a 1928 figure of 0.2% silver loss in manufacturing of photographic products (Addicks 1940). The 4 kkg
shown is a CCA (U.S. EPA 1973b) unsubstantiated estimate, extrapolated to 1978, for emissions from,
silver recovery. i
i
'•Smith and Carson (1977), U.S. EPA (1973b) and Schack and Clemmons (1963) estimates, extrapolated tot
1978; assume 50% silver recovery (35% by precipitation, 15% by incineration) from amount used in photo-
graphic materials and 90% of silver going into fixing baths: 840 kkg with 75% estimated to end up in
sewage sludge, 25% remaining in water (U.S. EPA 1980). Of the 840 kkg, 540 kkg come from larger,
£ professional photoprocessors (see Table 10), with silver recovery practiced on at least some processes,
w and the rest from amateurs and hobby 1st4 (Smith and Carson 1977).
Ni
5Based on calculations in following section. At least 88 kkg of this amount goes to POTW's (from producers)
and up to 119 kkg to surface water and POTW's.
Unsubstantiated discharge estimate from GCA (U.S. EPA 1973b), for sintering, electrolytic processes,
and chemical losses: 0.03 kkg.
7Virtually no silver oxide or sulfide should escape enclosed contacts or make-and-break switches.
BBased on GCA (1973) and estimate of atmospheric emission during spray painting of conductors adapted
for 1978 consumption (ADL estimate 1980) is M).3 kkg. 'A GCA-derived estimate for atmospheric release
of contacts eroding over time (average lifetime = 20 years); estimate applies to 5% of all contracts
in use) is 21.3 kkg.
9Land: discarded home appliances (Smith and Carson 1977). Attrition rate of contacts depends on number
and severity of duty cycles.
-------
TABLE 9. MATERIALS BALANCE FOR END USES OF SILVER, 1978 (continued)
10GCA (U.S. EPA 1973b), unsubstantiated discharge estimate, primarily aerosols from buffing and
polishing operations, 0.006 kkg. Based on estimate by Smith and Carson (1977), 0.2% loss of
consumption during manufacture of sterling ware and assuming all releases are to air.
nCCA (U.S. EPA 1973b) estimate: 1% of the silver emitted as fume, 50% of this 1% is controlled during
use. GCA (U.S. EPA 1973b), estimate for loss during, production of alloys and solders: 0.005 kkg.
Smith and Carson (1977) conclude little uncontrolled silver emissions, strictly an occupational
hazard as an aerosol.
12Land: in discarded home appliances (Smith and Carson 1977).
1 Principal uses: formaldehyde and ethylene oxide production.
'''Based on estimate by Smith and Carson (1977) for aerosol emission, adapted for 1978 consumption
(ADL estimate 1980).
M ^Electroplating Point Source Category: 9400 firms, 3000 of which are independent job shops (metal
i finishing as their primary line of business, as opposed to "captive"). Based on a sampling of the
ui industry (13.4% of total) by Hamilton-Standard (1980), then approximately 700 plants, total, conduct
silver-plating. This can be broken down into 269 job shops and 433 captive operations. Based on
Versar estimates (1980), the flow rates for job and captive shops are 32,300 gal/day and 277,000 gal/day,
respectively. Hamilton-Standard (1980) estimates mean raw wastewater concentrations of 0.38 mg/1 and
0.83 mg/1, respectively. Discharges are assumed to occur 250 days/year. Total annual discharges of silver
are 0.003 kkg by'job shops and 0.009 kkg by captives. In addition to these numbers, a chemical and liquid
spill estimate of 0.008 kkg (U.S. EPA 1973b) 'is added to give a total of 0.10 kkg of silver released.
More than 50 % of this amount is released to POTW's (Hamilton-Standard 1978) but because the total
number is so small, all is assumed discharged directly to water.
16Based on estimate by Smith and Carson (1977) of 0.2% loss of consumption during manufacture of jewelry
and coins and assuming all releases are to air.
-------
TABLE 9. MATERIALS BALANCE FOR END USES OF SILVER, 1978 (continued)
17Dental/Medical and Cloud Seeding considered "dispersive" uses; that is, exposure to silver is a
normal consequence of use. Dental/Medical includes non-medical antimicrobial uses in food, drinking
water and swimming pools. GCA (U.S. EPA 1973b) discharge estimate for preparation of materials:
0.003 kkg. In cloud seedings, a large majority of the silver should end up in water or land.
Release have been all allocated to land. Measured mean rainwater [Agl during seeding - surface:
6 x 10"11 g/ml, cloud base: 4 x 10~9 g/ml (Wisniewski et al. 1976).
18In solar applications. 3 Quads (1015 Btu, 2.5 x 101** Cal)/yr is the national goal for the year 2000.
3 Quads = 8.4 x 108 m surface area; 10~6m - silver thickness of mirrors; 10.5 x 106 g/m3 = silver
density. Thus, by 2000 9000 kkg of silver could be used annually for solar mirrors. GCA (EPA 1973b)
unsubstantiated discharge estimate for spraying of mirroring solutions: 0.05 kkg. Electroless silver
solutions must be neutralized before disposal as the sllver-amine complex is explosive.
19GCA (U.S. EPA 1973n) unsubstantiated discharge estimate: "0.06 kkg for bearings and lubricants, loss
of flake silver lubricant in use"; the amounts of metals in jet engine lubricating oils are criteria
M for changing the oils.
n
M
N 20lncludes Ag-bearing copper, Ag-bearing lead anodes, ceramic paints, etc. Discharge estimate is
unsubstantiated.
-------
The major photographic supply manufacturers number approximately
134 (U.S. EPA 1980) and are located in the northeast corridor, particu-
larly in New York and New Jersey. These include Kodak, GAF, Englehard,
and 3M, along with DuPont in Wilmington, Delaware. Silver nitrate is
also manufactured in Illinois by-D.F. Goldsmith Chemical and Metal,
Apache Chemicals and NL Industries, Goldsmith Division. Photoprocessing,
in contrast to manufacturing, is widespread throughout urban centers in
the U.S. ,
As shown in Table 9, the photographic industry releases an esti-
mated 4 kkg to air, 630 kkg to land, and 207 kkg to water each year.
The silver-bearing wastes generated by the photographic industry result
from consumption as well as manufacture of the photosensitive products.
Liquid wastes are chiefly spent fixing, bleaching, and post-fix washing
solutions released during manufacturing and photoprocessing operations.
Solid wastes include spoiled, out-dated, developed and undeveloped nega-
tives and print paper, as well as contaminated emulsions and scrap trim-
mings. During the manufacture of emulsions, silver discharge is probably
negligible, due to the fact that an enclosed reaction vessel is used,
fumes are scrubbed, and all byproduct streams are reused (Guccione 1963).
The following discussion summarizes environmental releases of silver
by photographic equipment and supply manufacturers, commercial photo-
processors, and amateur photoprocessors. The available data concerning
environmental releases by the photographic industry are not consistently
disaggregated into the three industry categories mentioned above. There-
fore, aqueous discharges by the three subcategories are first discussed
and then releases to air and land are summarized for the photography
Industry'as a whole.
b. Production
Silver is discharged to both surface waters and POTW's by producers
of photographic products. Photographic aqueous point sources have been
categorized by the Effluent Guidelines Division (U.S. EPA 1980) into
the following groupings:
(1) Silver Halide Subcategory
(2) Dlazo Aqueous Subcategory
(3) Photographic Chemical Formulation Subcategory
(4) Thermal Product Subcategory Process
For each Subcategory, Table 10 summarizes plant flow rates and typical
Ag concentrations in effluent from data collected in the Effluent Guide-
lines Division sampling program.
111-27
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Major producers of photography products are expected, due to
economic incentives, to recover a large fraction of the silver contained
•.in solid and liau-M wastes (U.S. EPA 1973b, Schack and Clemmons 1963).
However, quantifying the percentage recovery and the.amount of silver
actually released to the environment is difficult due to lack of Infor-
mation for all plants. The usual system for in-house treatement and
recovery is chemical precipitation and sedimentation, which results in
a large fraction of silver ending up in sludge. At least 20 photo-
graphic producer plants currently use this technique and 18 additional
plants use settling or clarification (U.S. EPA 1980). The effectiveness
of the treatment in removing silver from raw wastewater is variable.
Due to a lack of information on current silver recovery practices by
the remaining producers, and efficiencies of treatment for silver by the
photographic industry, the estimates of total discharges are based on levels
in raw wastes. Figure 5 illustrates silver recovery from photographic wastes.
In order to estimate annual releases to aquatic systems the follow-
ing assumptions were made:
• The mean raw wastewater concentration (usually greater
than median or flow-adjusted concentration) was represen-
tative of all plants and provided a reasonable worst-
case estimate (Table 10);
r
• Discharge occurred 365 days per year;
• Discharges from sources for each subcategory contained
silver originating only from the subcategory for that
process. In other words, each plant and/or discharge
of wastewater is discrete and uses only one process.
Table 11 shows the magnitude and distribution of the estimated aqueous
discharges of silver to surface water and POTW's by each photographic
industry subcategory.
c. Professional Photoprocessing
The larger photoprocessors of film are estimated to recover, by
in-house refining or shipment to commercial refiners, approximately 50%
of silver in liquid and solid wastes (U.S. EPA 1973b, Schack and
Clemmons 1963). The usual system for in-house silver recovery of liquid
wastes (fixer and bleach) is an electrolytic primary unit, followed by
a metallic replacement tailing unit. Silver removal efficiencies of
over 95% are possible when the two methods are used in series (U.S. EPA
1979c).
i
The approximately 10,620 professional photoprocessing establishments
in the U.S. range in processing capacity from less than 23 m2 to greater
than 47,000 m2 of film annually. Table 12 presents estimated annual
discharges to water by size of establishment. The total annual release
is approximately 50 kkg on the basis of Effluent Guidelines (U.S. EPA 1979c)
111-28
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Waste Film
To Landfill
Silver-Free
Water
Silver-Free
Water
Photographic Film Scrap
I
Granulation
Oust
Stripping
I
Sedimentation
& Filtration
Precipitation
I
Silver Sludge
Filtration
I
Roasting
Casting
I
Electrolysis
Melting
& Casting
Baghouse
Nitric Acid
• Precipitation Reagents
Recovered Oust
Waste Photographic Solutions
Silver-Bearing Photographic
Film Ash
Electrolysis Slimes
To Au & Pt Recovery
Silver Ingots
Source: U.S. EPA, 1979b.
FIGURE 5 FLOW DIAGRAM FOR SILVER REFINING FROM PHOTOGRAPHIC WASTES
111-29
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TABLE 10. SILVER LEVELS IN THE MASTEWATER OF PHOTOGRAPHIC MATERIAL AND EQUIPMENT PRODUCERS
Silver Concentration
t-t
M
M
1
CO
o
Subcategory
Silver llallde
Olozo Aqueous
Photographic
Chemical
Formulation
Thermal Product
in Uastewater (ng/ 1 ) Flow-
No. Average Dally Proportioned
of Plants Flow (I/day) Minimum Maximum Mean Mud tan Concentration
22 804013 0.39 36.88 14.11 12.85 9.
32 4459 0.00124 0.00271 O. 00298 0.00198 0.00191
(+5 that do not
discharge)
59
(+8 that do not 66207 0.00444 0.063 0.02845 0.02900 0.01195
discharge)
10 7986 0.04191 0.61906 0.28074 0.18126 0.25543
No. Observations
I Released To
Surface
(Positive/Negative POTW Water
14/0
2/14
9/8
3/6
64 33
71 5
39 60
99 O
Source: U.S. EPA (1980).
-------
TABLE 11. RELEASES OF SILVER TO WATER BY DIFFERENT PHOTOGRAPHIC INDUSTRY SUBCATEGORIES
Subcategory
Silver llalide
Diazo Aqueous
Photographic Chemical
Formulation
Thermal Product
TOTAL
Total Annual Load
For All Plants (kke)1
91
8
40
8
147
Load To
POTW'S
58
6
16
8
88
Load To
Surface Water
30
0.4
24
0
54
Other
3
1.6
1
1
5
Estimated by multiplication of mean silver concentration in raw wastewater x daily flow x 365 days/year x
number of known discharging plants.
-------
TABLE 12. TOTAL ANNUAL PRODUCTION AND SILVER AQUATIC DISCHARGES OF
PHOTOPROCESSING ESTABLISHMENTS BY PROCESSING CAPACITY
Processing Capacity
(loV/vr)
<23
23 - 35
35 - 47
<47
TOTAL
No
Est ablishmen t s
9,900
150
50
520
10,620
Total Production1
(106m2/yr)
19
3
4
138
Silver Discharges2
To Water (kkg/yr)
13
1
1
35
50
M
I
Is)
*(T. Dufficy, personal communication, 1980).
Estimates are based on (1) 0.68 kg/103m2 and 0.26 kg/103m2 Ag discharge from plants with Ag recovery on
some or all processes, respectively (U.S EPA 1979c), and (2) the assumption that smaller processing
establishments (i.e., 23 x 10 m /yr) are more likely to use Ag recovery on only some of the processes.
-------
data and the assumption that waste recovery at smaller establishments
is less efficient than at larger plants.
d. Amateur Photoprocessing
Amateur photographers with home darkrooms are most likely to dis-
charge their spent fixing solutions and other aqueous waste directly
down the drain without treatment. If one assumes that most home
developers live in urban areas, most of this amount most probably goes
to POTW's and not directly to surface water. Table 13 estimates the
annual discharges of silver to water from this source. The amount dis-
charged is relatively minor, 15 kkg, compared with larger operations,
primarily because of the relatively small amount of film developed by
amateurs.
e. Atmospheric and Land Releases by the Photographic Industry
The photogrphic industry, both producers and processors, also
release silver to the atmosphere and land in waste material. Air
emissions from silver recovery of solid waste by incineration of film
scrap are estimated to be 4 kkg per year (U.S. EPA 1973b). Releases
to land are in the form of sludge from in-house wastewater treatment
processes and film scraps and are estimated to contain 630 kkg of silver
each year. Both estimates are described in greater detail in Table 9.
f. Total Discharges by the Photographic Industry
Table 14 summarizes the estimated total discharges to the environ-
ment by the photographic supplies producers, by small and large photo-
processors, and by amateur photographers. The total is approximately
840 kkg per year and comprises 40% of the total annual consumption of
silver by the photographic industry in the U.S.
It should be re-emphasized that the estimated aqueous discharge
for photographic producers is based on raw waste concentrations.
Assuming treatment of the waste stream by precipitation/sedimentation
techniques at 100% efficiency, and practice of this technique by 15%
of the industry (20 out of a total of 134 plants), then the direct
aqueous discharge would be reduced to 46 kkg annually. However, there
is not enough complete information on the total industry to provide an
understanding of the effectiveness of recovery practices . As a con-
servative estimate, raw wastewater levels were used and the silver con-
tribution of the photographic industry is perhaps somewhat overestimated.
3. Other Uses
a. Contacts and Conductors
Manufacturers of electrical contacts and conductors consumed
960 kkg of silver in 1978 (Drake and Butterman 1979). Silver is the
most common material in make-and-break contacts, the primary uses of
111-33
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TABLE 13. ESTIMATED ANNUAL AQUATIC DISCHARGES OF SILVER
FROM HOME DARKROOMS
i
u>
(1)
Category
B & W. print paper
sq. ft.
Color print paper
Sq. ft.
Color reversal paper
sq. ft.
B & W film rolls
Color film rolls
(2)
No. of Units
x 106
1201
8l "
I1
5-10 » 2
I2
(3)
No. of sq. ft.
x 106
120
8
1 '
0.75 (.5-1)
0.075 (.05-1)3
(4)
Anit. of Ag
Recoverable per
10 3 units
(Troy oz)(4)
3.2 - 4.3
2.3 - 2.6
2.5 - 2.8
3.3 -13.2
12 - 23
(5)
Average Arat .
Ag per
10 3 units
(Troy oz)
3.75
i
2.45
2.7
6
15
1Arthur D. Little, Inc., estimate.
2Arthur D. Little, Inc., estimate.
Calculated - 28 rolls of 36 Exp. 35 mm filra/sq. meter or 2.8 rolls/sq. ft. •= 0.36 sq. ft./roll. A
rolls more than offset by large format film, then 0.5 sq. ft./roll.
''Eastman Kodak (1977).
-------
TABLE 14. OVERALL ENVIRONMENTAL RELEASES OF SILVER
BY THE PHOTOGRAPHIC INDUSTRY, 1978
Discharges (kkg)
Source
Production
Professional Processors
Amateurs
.TOTAL
Surface
Water POTW's
542 882
503
Air1 Land1
4 630
119
88
630
lAir and land emissions are combined for all industry categories;
see preceeding section e.
2See Table 11.
3See Table 12; these releases may also include discharges to POTW's,
4See Table 13; these releases may also include discharges to POTW's.
111-35
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which are in automotive parts, appliances, motor controls, communications
and electronic components such as relays, resistors, switches, etc.
There are three classes of silver contacts, depending upon the form of
silver used: pure silver or alloys (75-99.9% Ag), silver with semi-
refractory elements (40-99.3% Ag, most commonly AgCd)), and silver with
refractory constituents (Ag-WC, 40-65% Ag or Ag-W, 27.5-90% Ag). •
Electrical contacts in discarded home appliances account for a
large fraction of silver disposal onto land. Schack and Clemmons (1963)
estimated that about 40% of the total silver used in production of alloys
and electrical products is returned to refineries for processing and
reuse (Schack and Clemmons 1963). The remainder (60%) is too widespread
among various end uses to be recovered economically. On the basis of
1978 silver consumption by this industry, an estimated 150 kkg of silver
in appliances, demolished buildings, etc. is deposited in landfills.
In that contacts and make-and-break switches are enclosed systems,
attrition is assumed to contribute a.'negligible amount of aerosol silver
to the environment.
b. Batteries
The amount of silver used for batteries in 1978 was 190 kkg
(Drake and Butterman 1977). The major use of silver batteries is in
defense and aerospace applications where space is at a premium (e.g.,
submarine propulsion, missiles, satellites, space vehicles, and in
military portable communications equipment). Silver-containing batteries
are also used commercially in hearing aids, electronic watches, photo-
electric exposure devices, portable equipment, and small appliances.
Approximately 0.03 kkg of silver are estimated to be lost each
year, through sintering, electrolytic forming processes, and chemical
losses in washing and rinsing steps of storage and primary battery
production (U.S. EPA 1973b). Most of the silver (mainly silver oxide)
is reported to be recovered from wastewater treatment sludge, rejected
cells, and scrap cells and then recycled (U.S. EPA 1975d). Thus infor-
mation concerning this industry indicates that discharges are negligible.
c. Jewelry. Sterling Ware. Collector Pieces, Government Coinage
As the manufacture of jewelry, sterling ware, collector items and
coins utilizes similar production processes, such processes are con-
sidered as a single category of sources. Total silver consumption for
this group in 1978 was 860 kkg: 210 kkg for jewelry; 560 kkg for sterling
ware; 90 kkg (1.8%) for coins, medallions and commemorative objects;
1 kkg (0.02%) for coinage. Shavings and dust that settle from grinding,
buffing, and polishing operations are recycled by sweeping. Therefore
air emissions are probably only an occupational hazard. The jewelry
industry utilizes silver in electroplating of base metals or plastic,
fabrication from refinery forms, or incorporation into pieces as solder,
alloys and inlays. Sterling flatware and hollowware are the primary
111-36
-------
uses of sterling silver. GCA (U.S. EPA 1973b) estimates that 0.006 kkg
silver is lost annually from buffing and polishing of sterling and
jewelry.
Other uses include collector arts such as commemorative medals and
medallions, souvenir plates and bars, etc. Consumption of silver in
metal currency dropped sharply when the Coinage Act of 1965 eliminated
silver from dimes and quarters and reduced the amount in half-dollars
to 40%. .Since that time, the trend has been to substitute alloys and
less costly metals for silver, with the exception of special memorial
coins, such as the Eisenhower dollar.
d. Brazing Alloys and Solders
Production of silver brazing alloys and solder used 340 kkg of
silver in 1978 (Drake and Butterman 1979). Brazing is distinguished
from normal soldering in that relatively infusible alloys are used,
brazing temperatures (315-815°C) are higher than soldering temperatures
(175-315°C), and brazing alloys contain up to 93% silver, while solders
contain 35% silver or less.
The brazing and soldering processes have similar applications (in
approximate order of importance): air conditioning and refrigeration
(copper tubing seals), plumbing and heating (industrial and commercial
piping), automotive parts, aircraft and aircraft engines, and electrical
appliances. Other applications of brazing alloys are shipbuilding,
motors and generators, electronic components, and silverware and Jewelry.
Solders are also used in food service and processing utensils.
GCA (U.S. EPA 1973b) estimated that 1% of the silver used for the
alloys and solders is emitted to the air as fumes during soldering
operations, and that one-half of this 1% is controlled, most likely
through the uses of fluxes and controlled atmospheric furnaces. On the
basis of these assumptions, approximately 2 kkg were released to the
atmosphere in 1978. Silver lost from production of alloys and solders
has been estimated to amount to 0.005 kkg annually (U.S. EPA 1973b).
Most of the brazing alloys and solders, however, are lost in land dis-
posal of home appliances and scraped, non-recycled automobiles. On
the basis of amount of silver in household appliances, the number of
appliances sold each year, and the number of discarded appliances in
1978 (Smith and Carson 1977), an estimated 60 kkg of silver were dis-
charged and disposed of in landfills; an additional 10 kkg was recycled
in steel scrap.
e. Catalysts and Olefin Separation
The production of silver catalysts accounted for 260 kkg silver in
1978 (Drake and Butterman 1979). Of the many silver-catalyzed reactions,
only oxidation of ethene to ethylene oxide and methanol to formaldehyde
use significant amounts of silver as catalysts. Silver is reported to
111-37
-------
be used for a third process, oxidation of ethylene glycol to glyoxal,
but specific data are unavailable.
Ethylene oxide production for 1978- was approximately 2.3 x 106 kkg
(U.S. ITC 1979). Ethylene oxide plants are located primarily on the
Gulf Coast or in Puerto Rico, near supplies of ethene. Ehtylene oxide
is produced in the United States exclusively by oxidation of ethene in
the vapor phase at 250°C. There are two variations to this process
based upon whether air or oxygen itself is used as the oxygen source.
In the air oxidation process, the catalyst charge (10-15% silver) is
1.7 kg (0.2 kg silver) per kkg of ethylene oxide capacity. This cata-
lyst is generally removed and regenerated after 18 months of use. In
oxygen plants, the catalyst charge is two to three times larger, but
its life is prolonged. Most ethylene oxide producers manufacture their
own catalysts; two exceptions however, are those plants that use either
the Scientific Design process (supplied by Scientific Design's Catalyst
Development Corporation) or the Shell process (supplied by Harshaw
Chemical Company).
A second important use of silver is production of formaldehyde via
oxidation of methanol at approximately 450° to 600°C. The. silver cata-
lyst is comprised of high-purity (>99.95) silver in the form of silver
needles or gauze. The catalyst charge is regenerated, by heating to
temperatures sufficient to remove carbonaceous deposits, treating with
concentrated hydrochloric acid, removal of the resultant silver chloride
with ammonium hydroxide, and electrolizing twice. Catalyst life is
reported to be on the order of 6 months to 1 year (Smith and Carson 1977)
A second general application of silver as a catalyst is the separa-
tion of olefin mixtures, based upon the formation of complexes of hydro-
carbons and silver salts such as nitrates, perchlorates, and fluoro-
borates. Both liquid and solid phase systems are known (Smith and
Carson 1977). The extent to which such systems are used, however, is
unclear in that no specific data are available.
No specific data regarding silver loss from catalyst attrition,
preparation, or regeneration, are available. On the basis of U.S. EPA
estimates (1973b), and the quantity of silver used for catalyst prepara-
tion in 1978, 7 kg of silver are estimated to be discharged annually.
f. Electroplating
Silver electroplating is used in a wide variety of products:
silverware, bearings, chemical and food processing equipment, electrical
machinery, Jewelry and decorative art. The Bureau of Mines (Drake 1978)
data are given for one major use category, electroplated ware. In 1978,
the industrial consumption of silver for electroplated ware was 230 kkg
(Drake and Butterman 1979).
111-38
-------
The silver plating process is basically performed in three steps:
pre-treatment, plating, and post-treatment. First, strike solutions
low in silver (1.5-5g concentration AgCN/1) are used to prevent an
immersion deposit of silver precipitates. This is followed by plating
in a more concentrated bath (30-50g AgCN/1) until the desired thickness
is'obtained (Lowenheim 1980 and F.A. Lowenheim, personal communication,
1980). Post-treatment with chrornate coatings is sometimes employed, to
reduce silver tarnishing.
Coatings other than those electroplated include paints (containing
50% to 60% silver) which are used for solder bonding to nonconducting
and hdrunetallic surfaces, decoration of porcelain and glass, and forma-
tion of conductive surfaces on nonconductors. Upon firing of the paints,
silver loss is approximately 33% (based upon limited data)(Smith and
Carson 1977).
The silver wastes generated in the production of silver-plated
tableware are spills of silver-rich electrolyte, dilute wash solutions,
and spent electrolyte. Waste plating solutions generally contain
250 mg/1 Ag+ and the rinse water may contain 50-250 mg/1 (Smith and
Carson 1977). Silver-bearing solutions are usually brought together as
mill waste and processed to precipitate (or otherwise recover) the
silver and oxidize the CN before discharge as a plant waste.
Approximately 36 independent electroplating job shops and 57 cap-
tive shops conduct silverplating (Hamilton-Standard 1980), In a small
survey of electroplating shops, the median raw wastewater concentration
of silver was 0.83 mg/1 in captive and 0.38 mg/1 in independent job
shops (Hamilton-Standard 1980). Based on average flow data (Versar,
Inc. 1980) and assuming discharge of 250 days/year, a total of approxi- '.
mately 0.09 kkg silver is annually discharged to water. In addition,
GCA (U. S. EFA 1973b) estimates that 0.008 kkg of silver is lost annually
from chemical and liquid electroplating spills. The estimates are
described in greater detail in Table 9. Releases to land and air are
assumed to be negligible because of the nature of electroplating opera-
tions.
g. Dental. Medical, and Non-medicinal Antimicrobial Uses
Silver consumed in dental, medical and antimicrobial products in
1978 amounts to 60 kkg, or 1.2% of the total (Drake and Buttermore
1979). These uses, in contrast to uses previously described, represent
"dispersive" applications; that is, exposure to silver results as a
normal consequence of use. Emissions from preparation of these supplies
(e.g., melting, casting and cleaning in the manufacture of amalgam
alloys) are estimated to be 0.003 kkg/yr (U.S. EFA 1973b).
Amalgam alloys for dental fillings contain 67-70% silver; however,
after the alloys have been mixed with mercury for actual application of
the filling, the concentration is closer to 33% silver (Smith and
Carson 1977). Other dental uses include solders, wires, and local
application of ammoniacal silver nitrate to arrest dental decay.
111-39
-------
Silver nitrate also has medical applications. Aqueous solutions
of 0.01-0.1% silver nitrate are effective antiseptics; compresses soaked
with 0.05-0.1% solutions can be applied to severe burns; and highly
corrosive 10-20% solutions are applied locally to remove warts
(Tischer 1969). Metallic silver is used for prosthetic devices
and/or splints, and in electrodes to record brain or heart function.
Silver may also be used in water disinfection systems because of
germicidal activity. Although silver has been widely used in Europe as
a disinfectant, the extent of such use in the U.S. is unknown. Current
applications may include swimming pool disinfection.
h. Mirrors
In 1978, 60 kkg of silver were consumed in electroless plating of
mirrors (Drake and Buttermore 1979). The primary difference between
electroless plating and electroplating is that in the former, the
electrons for reduction are supplied by a chemical reducing agent in
solution, rather than as applied potential. Silver mirrors are used
for decorative purposes and optical Instruments, and their use could
become significant as solar energy is developed (see Table 9).
GCA (1973) estimated an annual emission to the atmosphere of less than
0.05 kkg of silver from "spraying of mirroring solutions."
i. Bearings
Ten kkg of silver were used in the manufacture of bearings in 1978
(Drake and Buttermore 1979). The principal method of bearing manufac-
ture is to electroplate silver onto steel and machine to size, then to
plate a lead-tin overlay. Representative applications of silver-plated
bearings are rotor bearings, high-temperature bearings, and self-lubri-
cated bearings. GCA (U.S. EPA 1973b) estimate that approximately
0.06 kkg silver is lost from bearings as flake silver in lubricants
annually. Smith and Carson (1977) point out that silver is often
measured in used jet engine lubricating oils, as the concentration
of metals present is a criterion for changing the oils.
j. Cloud Seeding
Silver iodide has long been 'favored as a seeding agent for ice
nucleation in supercooled clouds, the goal being enhanced cloud growth
and increased precipitation; however its use is decreasing. Operational
and research cloud seeding operations accounted for 2 kkg silver in 1978
or approximately 0.03% of the total industrial consumption (National
Oceanic and Atmospheric Administration 1978). The largest national
weather modification project is devoted to augmenting the Colorado River
Basin snowpack.
III-AO
Arthur D Little Ir.,
-------
The fate of silver iodide used as a seeding agent is relatively
well defined; virtually all of the 2 kkg of silver dispersed is con-
tained in rainwater or snowfall to surface water and land. Wisniewski
et al. (1976), in a review of a 1973 Florida seeding experiment, reported
that silver concentrations on the order of 10-u ug/ml and 10~9 ug/ml
were found in surface and cloud base rainwater, respectively.
k. Miscellaneous Uses
In 1978, approximately 30 kkg of silver (0.6% of the total) were
consumed in a myriad of minor uses (Drake and Buttermore 1979). The
Bureau of Mines (Drake 1978) lists these as "silver-bearing copper,
silver-bearing lead anodes, ceramic paints, etc." Smith and Carson(1977)
include additional applications, such as rocket propellants (AgC10t»),
hair colorings (AgNOs) solutions, and nuclear reactor rods (Ag-Cd-In
alloy). Most silver compounds are prepared from silver nitrate. Unlike
other industrial chemicals, the numerous silver compounds are offered
on the market in small quantities, generally of high purity. No esti-
mates of emissions from these sources are available, except that approxi-
mately 0.3 kkg is lost, probably to the atmosphere, from spray painting
of electrical conductors (e.g., ceramic paints) (U.S. EPA 1973b).
F. MUNICIPAL DISPOSAL
This section deals with the ultimate disposition of silver discharged
to municipal waste facilities: publicly-owned treatment- works (POTVS)
and urban refuse landfills or incinerators. For some sources, the esti-
mated amounts of silver involved overlap the estimates of releases by
silver consumers and/or producers. For many industry categories, it
was not possible to determine what portion of aqueous discharges were
to POTWs and what portion of land disposal was to urban refuse land-
fills. Therefore releases from POTWs and urban refuse landfills have
not been combined with other releases from anthropogenic sources shown
previously in Table 2 in order to avoid double counting. A summary
material balance for POTWs and refuse is given in Table 15.
1. Publicly-Owned Treatment Works
Silver loading to POTWs is largely dependent upon the type of
industry in a particular municipal area. A framework for calculating
the total silver flow through the nation's POTWs (see Table 15) is
provided by data from a recent U.S. EPA study. A materials balance of
silver at the treatment plants can be constructed by use of a total
POTW flow of approximately 1011I/day (U.S. EPA 1978b) and median values
of 0.008 mg Ag/1 (influent), and 0.002 mg Ag/1 (effluent) (see Table 16).
For purposes of these calculations, influent and effluent flow rates
are assumed to be equal, i.e., water loss from sludge removal and evapo-
ration are assumed to be minimal. The amount of silver in sludge is
assumed to be the difference between the silver in the influent and in
the effluent since losses of silver to the air are assumed to be negligigle.
111-41
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TABLE 15. SILVER MATERIALS BALANCE FOR POTWs AND REFUSE, 1978
Environmental Releases (kkg/yr)
Source
POTW
Urban Refuse
Incineration
Lamlfill
2902
143'»
705
3109
Air
neg1
106
Land
2202 (40)3
1071*
607
3109
Water
702
361*
neg
*•
Engineering judgment, Acurex Corp.
2Flgures calculated from U.S. EPA data (see Table 12) based on 1011 I/day total POTW flow and median
values for; influent Ag concentration = .008 mg/1; Affluent Ag concentration = .002 mg/1. For land
value, sludge is difference between influent and effluent loads and, therefore, includes recycled
sludge. Effluent flow equals influent flow. Air emission assumed to be negligible.
3A second method of calculation based on 6 x 106 dry kkg sludge produced/yr (U.S. EPA 1979a) , wet sludge
"95% water by weight, 0.368 mg/1 Ag in wet sludge (see Table 12), and assume 1 liter wet sludge has same
density as 1 liter of water (1 kg). Wet sludge flow rate = ( 6 x 10s) (11/kg) (1 kg/103 kkg) = 1.1 x 10nl/yr.
.05
''Non-air discharge for photography (see Table 9) . Assumes that up to 143 kkg from all categories goes
to POTWs and 75% of this ends up in sewage sludge on land (U.S. EPA 1980),
5Law and Gordon (1979) give values for silver flow through a municipal incinerator processing 920
dry kkg solid waste per week. Total municipal solid waste (MSW) incinerated 10 kkg yr (U.S. EPA 1976).
Smith and Carson (1977) suggest that combustible refuse may contain as much as 400 kkg silver annually.
6Assume 1 kg Ag atmospheric emission/920 kkg MSW and 10 7 kkg MSW/yr; yields 10 kkg Ag/yr.
7Assume 5 kg Ag in ash/920 kkg MSW and 10' kkg MSW/yr; yields 60 kkg Ag/ yr.
8Assume <0.3 kkg Ag/yr.
9Estimate for discarded household appliances, appliances recycled into steel scrap and other non-
combustible refuse (Smith and Carson 1977).
10The concentration of silver in the combustible fraction of MSW has been estimated at 3 mg/kg
(Haynes et al. 1977). If this concentration is similar to that in the non-combustible fraction,
and if 95% of MSW is not incinerated (107 out of 1.60 x 108 kkg MSW is incinerated), approximately
460 kkg of silver could go to landfills from non-combustible refuse. However, the 3 mg/kg assumption
appears to be an unverified estimate. If instead, this is taken as a minimum concentration, since
the non-combustible portion includes appliances, contacts, etc., which have a much higher silver
content than combustibles, then 460 kkg also represents a minimum.
-------
TABLE 16. SILVER DISTRIBUTION IN POTU SLUDGE:
SELECTED U.S. CITIES
H
I
Ag Concentration (ug/1)
City City
(Plant Location)
Indianapolis, IN
Cincinnati, OH
Lewis ton, ME
Atlanta, GA
St. Louis, MO
Potts town, PA
Grand Rapids, MI
Average Flow Influent
(10 I/day)
400
30
38
340
95
23
190
8
1
1
18
23
15
5
Effluent
<2
ND
<4
3
2
3
1
Sludge
(1°& 2°
combined)
107
78
368
1966
1903
1625
117
Range
(ug/1)
2
2
4
7
4
8
2
- 18
- 6
- 7
- 30
- 40
- 23
- 11
No.,
Samples
With
Ag
18
2
2
6
6
6
5
Total
Sampl
23
7
10
6
6
6
6
Source: Unpublished data - U.S. EPA Effluent Guidelines Division; figures shown represent data fr<
The study is ongoing and will be expanded to other urban centers.
-------
It is further assumed that though silver is recycled within the
activated sludge process, all of the metal will eventually be released.
Although greater trace metal removal can be achieved with advanced treat-
ment processes, less than 2% of the nation's POTWs use these advanced
methods (Linstedt et al. 1971). On the basis of these assumptions, the
discharges by POTWs are estimated to contain 220 kkg of silver in 1978.
An alternative method for estimating the annual silver discharge
to sludge is to calculate silver release from the silver concentration
in sludge and the quantity of dry sludge produced annually (5.5 x 105 kkg).
If the silver concentration in FOTW wet sludge is assumed to be 0.368 mg/1
and wet sludge is assumed to be 95% water by weight, approximately 40 kkg
are discharged to land.
The U.S. EPA (U.S. EPA 1979a) has estimated the disposition of POTW
sludge as follows:
landfill 24%
incineration 21%
ocean dumping 18%
food chain 15%
non-food chain 3%
giveaway/sale 11%
other (including stockpiling and
storage in lagoons) 6%
unknown 2%
For this materials balance, silver releases to the environment in sludge
are assumed to be releases to land because ocean dumping of sludge has
been mandated to cease by 1981 and more stringent air quality standards
may curb incineration of sludge (U.S. EPA 1979a).
2. Urban Refuse
The three options for handling of urban refuse are energy recovery
(primarily by incineration), material recovery, and disposal through
incineration or landfill. Urban refuse consists of two major components:
the combustible fraction (paper, cardboard, plastics, fabrics, etc.) and
the noncombustible fraction (ferrous and non-ferrous metals, glass,
ceramics, etc.). Figure 6 depicts the flow of silver through a munici-
pal incinerator processing 920 kkg of dry refuse per week (Law and
Gordon 1979). From this material balance and an assumed annual volume
of municipal solid waste totalling 107 kkg (U.S. EPA 1976a), silver
loading to air and land is estimated to be 10 kkg and 60 kkg, respec-
tively (Table 18). Water discharges from incineration processes are
negligible. Law and Gordon (1979) postulate that non-combustibles are
significant contributors to the total incinerator silver emissions,
perhaps accounting for as much as two-thirds of the total, because not
111-44
-------
.*— ^ — - — — .
114.00OV al
SPRAT
WATCH
uNoiuoivu sauos
4PBAT CHAM8KA
WAfEA
oi«oiv«o sauos
0
.0004
I
<0.
002
I
MUlMCIPAh
0.
SgWgH STSTgM
01
i
1,
_J
0
.01
1
Note: Based on input of 920 kkg of solid waste (combustibles and noncombustibles).
Numbers represent relative proportions.
Source: Law and Gordon (1979).
FIGURE 6 FLOW DIAGRAM OF SILVER IN A MUNICIPAL INCINERATOR
111-45
-------
all of the incinerator output can be accounted for the silver content
of the combustibles fraction.
Statistics concerning silver in landfill are difficult to obtain
because of the myriad of possible contributors. Smith and Carson (1977)
estimate that over 300 kkg of silver is disposed of on land in discarded
home appliances, appliances recycled in steel scrap,and other non-com-
bustibles, such as junked automobiles, lost jewelry, etc. Ten percent
(by weight) of the approximately 1.6 x 103 kkg of municipal solid waste
generated annually consists of metals, with 1% being non-ferrous metals
(Gordon 1978). No information was available on what percentage of this
amount of metal non-ferrous group is silver. (The behavior of silver
in soil is discussed in Chapter IV, Pathway 2.)
G. NATURAL SOURCES
1. Overview
Natural background levels of silver are present in soil, water and
air at very low concentrations. The original natural source
is bedrock, both exposed and underlying soil, from which silver is
released through the process of weathering. The following section
discusses the natural distribution of silver in physical media and
estimates the rate of deposition or release to surface water and air.
All estimations should be used with caution due to the large degree
of error associated with each number because of the use of average
concentrations.
2. Silver-producing Ores
Silver occurs In rocks and soils, usually as~ a small component of
sulfide minerals, as native silver, or in humus complexes* In. natural
waters, silver exists as Ag*1", colloidal complexes, or as a trace element
in living organisms. Though widely distributed, elemental silver is
typically present only in small amounts. Other sources of silver are
silver-bearing minerals such as argentian tetrahedrite and tennantite,
pyroustite, argentite, acanthite, pyragyrite, chloroargyrite, and
argentojarosice (Smith and Carson 1977). The silver content of these
and other common mineral forms is summarized in Table 17.
Silver deposits in the U.S. have been found mainly in Idaho,
Nevada, Colorado, Arizona, Utah, New Mexico, and Michigan as shown
in Figure 7. The silver content of individual deposits varies widely
with geographic location. Argentian tetrahedrite in the Coeur d'Alene
district of Idaho, for example, averages from 65 mg/kg to 335 mg/kg of
silver but may contain 0.1 or more percent of silver; shale deposits in
Michigan contain up to 150 mg/kg of silver; the silver content of sand-
stone is generally of the same range, but concentrations greater than
1000 mg/kg of silver (Silver Reef, Utah and in Michigan) are known
(Smith and Carson 1977). Further discussion of natural levels in soil,
air, water and biota and their comparison to anthropogenic levels can
be found in Chapter IV-E.
£11-46
-------
TABLE 17. SILVER CONTENT OF SILVER ORES
Mineral Form
Chemical Formula
% Silver
M
Native Silver
Mineral Forms
Argentiferous galena
Argentite
Acanthite
Argentian tetrahedrite
Argentian tenanite
Pyroustite
Pyrargyrite
Clilorargyrite
Argentoj arosite
Stephanite
Naumannite
llessite
Polybasite
Ag
AgPbs
aAg2S
BAg2S
(Cu(Fe,Zn,Ag)12SbilSi3
3Ag2S.As2S3
3Ag2S.Sb2S3
AgCl
Ag5SbS|,
Ag2Se or (Ag2Pb)Se
Ag2Te
Ag16Sb2Sn
100
87
2.6 - 4.5
64.5 - 65.4
59.5 - 60.8
75.3
68.3
43.0
63
75.6
Smith and Carson (1977)
Source: Smithells (1976) unless otherwise noted.
-------
I
00
i i-- r- -i-*"»
. / | . \
] / \
—1-—-— \
Source: Smith and Carson (1977).
FIGURE 7 GEOGRAPHIC DISTRIBUTION OF SILVER-PRODUCING ORES IN THE U.S.
-------
3. Silver Releases in Aquatic Systems-
Weathering of silver containing mineral deposits is reported to be
responsible for the bulk of silver present in freshwater, 0.24 ug/1
(boyle 1968), with anthropogenic sources contributing only a small por-
tion of the total load. Waters that leach silver-bearing natural
deposits sometimes carry up to 100 times more silver than other fresh
waters. Silver present in the suspended material in rivers and streams
varies greatly; eastern rivers tend to carry higher silver concentrations
than rivers west of the Mississippi, even though their suspended loads
are lower (Smith and Carson 1977). Seawater, the ultimate reservoir for
much of the continental sediment, has a silver concentration approxi-
mately the same as freshwater', "0.2 ug/1.
Table 18 lists several pathways of silver to surface water and the
estimated magnitude of each. Included are total U.S. runoff, urban
runoff specifically, sediment release and precipitation. The numbers
are based on average media concentrations and do not reflect the regional
variability discussed in the previous section.
As mentioned earlier, silver enters surface water in runoff that
picks up natural deposits of silver from soil and bedrock. In many cir-
cumstances, some releases from human activities will also be trans-
ported in runoff, e.g., from mine tailings, so that this contribution is
not strictly of natural origin. The U.S. runoff number also includes
urban runoff; however, the contribution from this pathway can be estimated
separately.
Urban runoff receives silver from both natural and anthropogenic
sources including background soil levels, contacts and conductors,
brazing alloys and solders, and solid wastes disposed of in landfills.
In eleven out of twelve samples of urban runoff water, silver was
detected at concentrations of 3 to 8 ug/1 (U.S. EPA 1977). Assuming
an annual urban runoff volume of 2.1 x 10l3 1 (U.S. EPA 1977) then a
release of 63 to 168 kkg of silver can be estimated. Combined sewers
and separate storm sewers receive 57% of the total runoff, with the
remaining 43% going to unsewered areas. Therefore up to 96 kkg and
72 kkg of silver go to sewers and surface water, respectively, accord-
ing to the previous estimates.
The estimate of sediment loading assumes that sediment formed from
weathering of stream beds, decay of organic material, and other sources
contributes the silver present in the parent material to total concen-
trations in the water column.
Precipitation is a pathway leading to land, as well as surface
water. A large fraction of silver in rain falls on land and is probably
retained in the soil (Chapter IV) unless carried to water in runoff.
The estimate has been included in Table 18 to give an idea of how it
compares in magnitude to other pathways.
111-49
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TABLE 18. ESTIMATED U.S. SILVER RELEASES TO SURFACE WATER
FROM NATURAL SOURCES
Source
Freshwater Scream
Supply
Silver
Discharge (kkg/vr)
408
Sediments
30
Urban Runoff
63 - 168
a
Precipitation
400
CotnmentS
Based upon an overage U.S.
annual runoff of 1.7 x 10151
(US6S 1978) and a silver con-
centration of 0.24 ug/1
(Boyle 1968).
Estimate of mobilization
of silver by weathering
to sediment by Bertine
and Goldberg (1971).
Based on annual U.S. urban
runoff of 2.1 x 1013 1 and
silver concentration of
3 ug/1 to 8 ug/1
(U.S. EPA 1977).
Based upon average U.S. annual
precipitation of 2 x 10151
and silver concentration
of 0.02 ug/1 (Rattonetti 1974),
a
Note this number may include contribution from sources outside
the U.S., e.g., ocean spray. See text.
111-50
-------
4. Silver Releases in the Atmosphere
Silver is released to the atmosphere from a number of natural
sources. Table 19 lists these sources, and when possible, their
estimated annual contribution to the atmosphere. Due to the global rather
than national pattern of atmospheric transport processes and the importance
of the oceans as a source of aerosol, the atmospheric sources must be
examined globally and not only within U.S. boundaries. The actual amount
of silver entering the atmosphere over the United States annually cannot
be estimated with the data available; therefore rates of atmospheric
loading cannot be compared directly to those for runoff and sediment
loadings by natural sources.
H. AREAS FOR FUTURE INVESTIGATION
All of the numbers derived for the silver materials balance are
based on several assumptions, some of which have a great deal of
uncertainty associated with them due to lack of data. Therefore, fur-
ther study of these areas would improve the accuracy of the environ-
mental materials balance for silver.
Recommendations for further study' include a general survey of
silver recovery techniques practiced by industries in light of recent
increases in the market price of the metal, especially those of major
aqueous dischargers such as the photography Industry. Other information
needs include: (1) a better estimate of the contribution of silver to
the environment from natural sources, expecially in runoff; (2) identifi-
cation of the sources of silver to POTWs (currently only 30% from indus-
trial releases and an additional 33% from urban runoff can be accounted
for); (3) integration of data concerning land disposal of used silver
products and wastes with urban land disposal information (including
product lifetimes or replacement rates) in order to prevent double
counting; (4) quantification of discharges of silver from non-silver
using electroplaters; and (5) information regarding the recovery
practices of small professional photoprocessors, which do not have in-
house facilities for treatment, in order to determine whether any
discharge effluents directly to surface water.
I. SUMMARY N
1. Anthropogenic Sources
a. Metals Production
Mining, milling and smelting of silver-containing ores and the
smelting of new (bullion) and old scrap material containing silver, all
release silver to the environment. It is not possible to keep a mass
balance on the silver flow through mining, smelting and subsequent
releases.
111-51
-------
TABLE 19. ESTIMATED GLOBAL SILVER RELEASES TO THE ATMOSPHERE
FROM NATURAL SOURCES
Source
Windblown dust
(all sources)
Silver
Discharge
(kkg/yr)
50
Sea Salt Sprays
Volcanogenic particles
neg
Forest fires
neg
Meteoric debris
Comments
Largest continental source from
grinding and dispersion of soils
and rocks. Estimate assumes a
global dust production of
500 x 106 kkg/yr and silver con-
centration of 0.1 rag/kg (Boyle 1968).
Not expected to be as important as
for other metals (Mulvey 1979).
Estimated based on global pro-
duction of aerosols from se salt
spray of 1000 x 10s kkg/yr
(Elsaesser 1975) and silver con-
centration of 0.2 ug/1 (Boyle 1968).
No specific data available for
silver; based on global aerosol
production of 10 x 106 kkg/yr
(Elsaesser 1975) and silver con-
centration of 0.1 mg/kg (Boyle 1968).
Young and Jan (197?) estimate aerial
fallouts of silver to a 10,000 km
area to be 0.6 kkg/day and 0.15 kkg/day
during and following a fire, respectively.
No specific data available for silver.
111-52
-------
Approximately 1230 kkg of silver were mined in 1978, primarily in
the form of silver ore and copper ore, with lesser quantities obtained
from lead, gold, zinc and other ores. Primary and secondary smelting
of ores and additional recycled scrap material extract a total 2840 kkg
of silver annually.
An estimated 66 kkg silver are released to the environment from the
processes of mining and milling, primarily during milling* 94% is released
in solid form (tailings) to land, with less than 6% going to water and
air. The locations of mines and mills processing silver are concentrated
in Idaho, Colorado, Montana, Arizona, Utah and South Dakota.
From all smelting processes combined, a total of 134 kkg of silver
is released to the environment, of which 77% goes to land in the form
of slag, 3%( to air in dust and fumes (from roasting and converting),
and 20% to water, primarily in spent electrolyte solutions. The 27
smelters that process silver are scattered throughout the U. S.
b. Other Production Processes In Which Silver Is a Byproduct
Unintentional releases of silver occur during the processes of
cement manufacturing, iron and steel production and coal and petroleum
combustion. Of the 20 kkg of silver released by the three categories, 90%
is released to water, 10% to soil, and a negligible amount to air. These
releases are expected to be evenly distributed across the U.S., with
generally higher rates of release in urban areas.
c. End Uses
The greatest consumer of silver is the photographic industry (40%
of total production), followed by the manufacturers of contacts and
conductors (~20%). Other consumers include electroplaters, jewelry-
makers, producers of sterling ware, catalyst, brazing alloys and solders,
batteries, coins, dental supplies, mirrors, bearings and cloud-seeding
material.
Releases to the environment from consumers totalled approximately
1080 kkg in 1978 and reflected consumption patterns. The compartment
receiving the largest amount of releases from consumers of silver was
land (78%), followed by water (19% including POTW's). Air received
only a minor fraction of the total releases (<3%). The biggest dis-
chargers were the photographic industry and the contact/conductor indus-
try, which together contributed 94% of consumer discharges, primarily
to land. The brazing alloy/solder industry released 60 kkg of silver
(7% of total releases to land). Most other industries had negligible
silver discharges from both manufacture and use of silver-containing
products.
111-53
-------
The discharges from the photoprocessing industry included releases
by producers of photographic equipment (films, solutions) and developers
of film, both amateurs and professionals. Producers were responsible
for approximately 50% of all photographic discharges to water. Thirty-
eight percent of the total 142 kkg aqueous discharge was directed to
surface water; the remainder to POTWs. Amateur photographers were
estimated to discharge only 15 kkg to surface water or POTWs; profes-
sional developers were collectively estimated to discharge 50 kkg.
d. Municipal Disposal
Silver is released to POTWs and urban refuse landfills or incinera-
tors during the ultimate disposal of silver in used products, sludge and
effluents from wastewater treatment. An estimated 290 kkg of silver is
discharged to POTWs of which 75% goes to land the remainder to surface
water. An estimated 70 kkg of silver is incinerated, with approximately
86% going to solid waste and the remainder to air. Up to 460 kgg of
silver is disposed of in landfills.
2. Natural Sources
Natural background levels of silver, as indicated by the location
of silver-producing ores, are greatest in the western United States.
The most significant natural pathways into the environment are in runoff
to water (including urban runoff), in sediment formation, and in dust
production. Transfer of silver from .the atmosphere to soil and water
takes place via precipitation. The total annual natural release of
silver to U.S. surface water is estimated to be 438 kkg, of which up to
38% is urban runoff. The total amount of silver released to soil through
surface and subsurface weathering of bedrock cannot be determined.
There is a large amount of uncertainty associated with these estimates.
3. Conclusions
In conclusion, the greatest source of releases of sAver to the
environment from all sources (with a total of 710 kkg annually), appears
to be release through natural weathering processes and transfer to other
media ( ^69% of total). However, relative to natural sources, industrial
production activities produce a significant mass of silver (^28%), some
of which would be in a more mobile form (e.g., small participates from
smelters, vapors). Inadvertent releases of silver from certain cultural
activities (e.g., fuel combustion) contribute a relatively minor fraction
(i3%) of the total releases.
111-54
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•
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U.S. Environmental Portection Agency (U.S. EPA). Controlled and uncon-
trolled emission rates and applicable limitations for eighty processes.
Report EPA 450/3-77-016; U.S. EPA; 1976b.
111-57
-------
U.S. Environmental Protection Agency (U.S. EPA). Comprehensive sludge
study relevant to Section 8002(g) of Resource Conservation and Recovery
Act of 1976. Report SW 802. Washington, DC: U.S EPA; 1976c.
U.S. Environmental Protection Agency (U.S. EPA). Heavy metal pollution
from spillage at ore smelters and mills. Washington, DC: U.S EPA; 1977.
U.S. Environmental Protection Agency (U.S EPA). Assessment of fugitive
emission factors for industrial processes. Report EPA 450/3-78-107.
Washington, DC: U.S. EPA; 1978a.
U.S. Environmental Protection Agency (U.S. EPA). Needs survey, Office
of Water Planning and Standards. Washington DC: U.S. EPA; 1978b.
U.S. Environmental Protection Agency (U.S. EPA). Environmental impact
statement: Criteria for classification of solid waste disposal facili-
ties and practices. Report SW-821. Washington, DC: Office of Solid
Waste, U.S. EPA; 1979a.
U.S. Environmental Protection Agency (U.S. EPA). Development document
for effluent limitations guidelines nad standards for the non-ferrous
metals manufacturing point source category. Report EPA 440/l-79-019a..
Washington, DC: U.S EPA; 1979b.
U.S. Environmental Protection Agency (U.S. EPA). Draft development
document for effluent limitations guidelines (BATEA), new source per-
formance standards, and pretreatment standards for the photographic
processing point source category. Contract 68-01-3273. Washington, DC:
U.S. EPA; 1979c.
U.S. Environmental Protection Agency (U.S. EPA). Effluent guidelines and
standards; electroplating point source category; pretreatment standards
for existing sources. Federal Register 44(175):52590-52629; 1979d.
U.S. Environmental Protection Agency (U.S. EPA). Development document
for effluent limitations guidelines and standards for the photographic
equipment and supplies segment of the photographic point source category.
Report EPA 440/1-80/0-77-3. Washington, DC: Effluent Guidelines Divi-
sion, U.S. EPA; May 1980.
United States International Trade Commission (USITC). Synthetic organic
chemicals, United States sales and production, 1978. Report 1001.
Washington, DC: USTIC; 1979.
Versar, Inc. Calculations of discharges of copper, silver and zinc for
36 industrial categories. Preliminary draft. Washington, DC: Monitor-
ing and Data Support Division, U.S. Environmental Agency; 1980.
111-58
-------
Wingard, N.E. Minerals yearbook, 1976, Metals, Minerals, and Fuels,
Vol 1. Washington, DC: Bureau of Mines, U.S. Department of Interior;
1978.
Wisniewski, J.; Cotton, W.R.; Sax, R.I. Silver content of precipitation
from seeded and nonseeded Florida cumuli. Appl. Meteorol. 15:9; 1976.
Young, D.R; Jan, T. Fire fallout of metals off California. Marine
Poll. Bull. 8:5; 1977.
111-59
-------
CHAPTER IV.
ENVIRONMENTAL FATE AND DISTRIBUTION
A. INTRODUCTION
The purpose of this chapter is to ascertain the distribution and
concentration of silver in different environmental compartments follow-
ing release to the environment. Silver is not subject to many transfor-
mation processes under environmental conditions. It is subject primarily
to transport processes, both in individual media and in intermedia move-
ment between certain media. In addition, silver is released to the
environment at low concentrations from a few, well-defined sources.
Because there is an adequate data base describing both environmental
levels and fate processes, the pathways approach was used to charac-
terize the important processes determining the environmental fate of
silver.
The following chapter is organized as follows:
B) Physical and Chemical Properties
C) Environmental Fate
D) Biological Fate
E) Concentrations Detected in the Environment
F) Summary and Conclusions
•
B. PHYSICAL AND CHEMICAL PROPERTIES
1. Physical Properties
107 109
Of the 27 known isotopes of silver, only Ag and Ag are found in
nature and are not radioactive. They are present in roughly equal
amounts, 51.82% and 48.18% of the total, respectively. Table 20 lists
selected physical properties of silver.
In many respects, the physical properties of silver are different
from other IB metals, copper, and gold. .Metallic silver has the highest
electrical and thermal conductivities of all the elements; silver has
the lowest melting and boiling point of IB metals. The reflectivity of
polished silver is also very high, although dependent on wave length;
in the infrared region reflectivity approachs 98%, but falls to 10%
at 3200°A.
2. Chemical Properties
Silver is a white, lustrous metal found in nature both in its
elemental state and in association with various minerals, usually
sulfides of copper, lead, and arsenic. It is the most reactive of the
IV-1
-------
TABLE 20. PHYSICAL PROPERTIES OF SILVER
log P,
nmHs **
log P
atm
Atomic weight
Melting point
Heat of fusion
Boiling point
Heat of vaporization
Entropy of pure annealed silver at 298.15°K
Entropy of transition, solid-liquid
Entropy of transition, liquid-gas
Heat of sublimation
Vapour pressure of. liquid silver, mm Hg
10-1
1
10
100
760
Vapour pressure of solid silver, 735-9608C
-1.4580xlO'H-9.22
T(BAbs)
Vapour pressure of liquid silver .965-2152°C
-1.3680xl0lf+5.615
T('Abs)
Critical temperature
Critical pressure
Critical volume
Density of solid silver (depends on sample and
sample history)
Density of liquid silver (over whole normal
liquid range)
Coefficient of expansion (0-100°C)
Coefficient of expansion 90°A
Specific heat (0-800°OC,=
0.055401+0.14414xlO"4T-0.16216x10-3T2
Specific heat of liquid silver up to 1300°C
Specific heat of silver 'vapour
vjr" Thermal conductivity (a*0°C)
f Electrical c^vduc-t-i-v-ity (20°C)
\*\ ^Temperature" coefficient of conductivity (20°C)
'*' \i<* lonization potentials:
,>'* c 1st: 7.574 cV
'
-------
TABLE 20. PHYSICAL PROPERTIES OF SILVER (continued)
o
Crystal ionic radius Ag** •= 1.26 A
AgH" = 0.89 A
Viscosity 1000°C 3.89 cp
1100'C ' 3.89 cp
Surface tension (1268°K) 920 dynes/cm
Magnetic susceptibility -0.181xl(f6cgs units/g
Source: Thompson (1973).
IV-3
-------
noble metals and dissolves in oxidizing acid and in cyanide solutions
in the presence of oxygen or peroxide; although silver is not oxidized
at room temperature by oxygen, a thin oxide film forms at 200°C. The
most common oxidation state is +1, and although Ag(II) and Ag(III) are
known, they are unstable in the aqueous environment. A descriptive
review of the chemistry of silver has been given by Thompson (1973).
The chemistry of silver also bears few resemblances to copper and
gold. Comparisons between silver and alkali metals, which also have
a single s electron, are not useful. A better analogy, in terms of
chemical behavior and reactivity, would be to palladium, from which
silver differs electronically only by its possession of a 5s electron.
Although the Ag(I) is the most common oxidation state, Ag(II) and
Ag(III) are known and may be of importance in catalytic oxidation pro-
cesses (Cotton and Wilkinson 1973). The importance of Ag(II) and
Ag(III) in the environment is unknown.
t
Numerous silver compounds are photosensitive, the most important
of which are (in order of sensitivity) silver, bromide, and chloride.
Other photosensitive compounds are silver(I) fluoride, iodide, oxide,
imide, phosphate, sulphite, and dithionate. This phenomenon is, in
fact, the basis of the photographic industry (silver salts are not,
however, used solely because of their photsensitivity). Upon irradia-
tion at wavelengths less than 400 nm, silver halides are reduced to
elemental silver and halogen.
Ag X » Ag° + X°
Once a silver atom has been formed, according to the Gurney-Mott mecha-
nism, a silver atomic center can trap an electron and then a second
mobile silver ion, thus forming a more stable silver center, Ag2
(Pouradier et al. 1977). This aggregation can continue as long as
light is supplied. This effect is not restricted to halides, but is
general for other photosensitive silver compounds.
A wide variety of silver(I) compounds are known, including organo-
silver compounds as well as the more typical inorganic compounds and
complexes. Compounds commonly found in nature or which are often
released to the environment include: bromide, chloride, fluoride,
iodide, cyanide, thiocyanate, oxide, hydroxide, sulphide, carbonate,
nitrate, sulphate, as well as Ag(I) complexes with ferrocyanide and
thiosulfate. The majority of these compounds are relatively insoluble
(see Table 21). Silver nitrate is the most notable exception.
With regard to environmental transport, silver complexes involving
halides, cyanides, amines, and thiosulfates are particularly important.
Stability constants for various complexes are shown in Table 22. In
natural systems where more than one ligand type is present, mixed
complexes exist in equilibrium with homogeneous complexes. A variety
of mixed silver complexes are listed in Table 23. Pol/nuclear silver
complexes may also be important. For example, argentothiosulfate
complexes are formed in exhausted photographic fixing booths.
IV-4
-------
TABLE 21. SOLUBILITY PRODUCTS OF VARIOUS SILVER SALTS
Salt
A OH
8
Ag2Cr04
Ag2Cr207
Ag2Mo04
Ag2W04
Ag4[Fe(CN)6]
Ag[Ag(CN).2]
AgCNO
AgSCN
Ag2C03
AgN3
Ag3P04
Ag3As04
Ag2S
Ag2SO
AgCl
AgBr
AgBr03
Agl
AgI03
A82C2°4
A CH.COOH
g 3
U=0 (-log S)1
7.71
11.95
6.7, dil.2
11.55
11.26
2
40.8,diL.
6.64
11.97
11.09
8.54
15.84
19.95
49.2
4.80
9.752
12.305
4.28
16.08
7.51
11.0
2.7
U-.l
"7.6
11.3
10.9
10.6
11.3, var.3
6.5
11.7
10.4
8.3
14.7
18.9
48.2
4.1
9.50
12.06
4.0
15.83
7.3
10.4
2.1
1. Most values refer to a temperature of 20 or 25°C.
2. Dilute solution, below 0.01M
3. Ionic strength was not specified.
Source: Ringbom (1963).
IV-5
-------
TABLE 22. DISSOCIATION OP HOMOGENEOUS SILVER COMPLEXES IN WATER
AT ROOM TEMPERATURE
Stability Constant
T.igand
Cl
Br
I
CN
SCN
SeCN
SO
SO
S 0
Thiourea
S
IIS
Se
OH
Nil
Aliphatic primary amines
Aliphatic secondary amines
Aliphatic tertiary amines
Diethylenetriamine
1-Ethylened iamine
1,2,3-Triaminopropane
TriaminotriethyIamine
Triethylenetetramine
Ethylenediaminetetraacetate (EDTA)
Piperidine
Pyridine
Imidazole
Ethanolamlne
Tr i e t h a noIamine
sp 1 2 3 4
9.75
12.31
16.09
15.8
11.97
15.4
13.8
4.9
49.1
63.7
7.71
3.3
4.5
7.5
9
4-5
—
5.5
9
7.3
13.2
2.0
3.3
3.0-3.5
3
2.6
6.1
5.0
5.6
7.8
7.7
7.0
3.0
2.0
3.5
3.2
2.3
5.25 5.7
7.4 8.5
11.6 14
20.7 21.9
8 10.3
11.0 13.8
8.7 8.9
13.3 13.9
10.6 12.8
17.2
4.0
7.2
6.8-7.5
5.3-6.4
3.6-4.6
7.8
6.5
4.2
6.9
6.8
4
5.4
9.0
15
21
10.9
13.7
-------
•vl
TABLE 22. DISSOCIATION OF HOMOGENEOUS SILVER COMPLEXES IN WATER
AT ROOM TEMPERATURE (Continued)
Stability Constant
pK
Ligarid • v sp
Source: Pouvradier etal. (1977).
a-Amino acids without complexing
residue on the side chain 3.5-3.7 7.0-7.2
Arginine 3.5 8
Cysteine 5.2 18.2
Histidine (neutral medium) — 7.5
(high pH) 7.3 8.9
Methionine (low pH) 3.2 5.7
w-1-3 to 1-6-n-Amino acids 3.4-3.7 7.5-7.8
Monothioglycol 19.6 13.2 17.8
Thiosemicarbazide 12.8
li l-Phenyl-5-mercaptotetrazole 16.2 10.9 . 13.6 15.3
-------
TABLE 23. DISSOCIATION CONSTANTS OF MIXED SILVER
COMPLEXES IN WATER AT ROOM TEMPERATURE
f
oo
Ligands ' 2
L1
Cl
Cl
Br
I
1
SCN
Cl
CN
Cl
£
CN
Cl
Br
1
CN
Cl
Br
Cl
Br
I
CN
L11 pk
Br
I
I
SCN 12.1
SeCN
SeCN
OH 4.7
Oil 13 . 2
SO
SO 9.2
SO
S 0
S 0
S 0
S 0
Nil 6.3
Nil
thiourea
thiourea
thiourea
thiourea
pk
13.5
15.4
>
7.8
10.2
11.1
10.8
12.0
13.2
15.7
7.1
7.6
13.9
Total No. Tied Ligands
3
. pk pk
9.5
7.6
12.3 13.8
14.7
13.8 13.4
7.1
12.5
•
11.3
13.6
12.6
13.1
15.5
4
pk pk
7.9
14.7
,
14.4
10.0
13.5
18.1 21.3
7.8
14.5 14.2
18.8
Source: Pouvradier et al. (1977),
-------
C. ENVIRONMENTAL FATE
1. Methodology
This section characterizes the physiochemical and bulk
transport processes that determine the fate of silver released to air,
water, and soil. Pathways are described for the major sources of
environmental releases. A general overview of the environmental chemis-
try of silver conducted by Versar, Inc. (1979) has been used as the
basis for judgments concerning the directions and rate of transport
silver in an ecosystem. Additional studies available in the literature
are cited as necessary. Biological pathways are treated separately in
Section D. of this chapter.
2. Major Environmental Pathways
The major pathways of physical transport and the qualitative rates
at which they occur are designated in Figure 8. Atmospheric emissions
(Pathway 1) have been separated into point source and dispersive emis-
sions. Combustion processes—such as incineration and smelting/refining-
and the processes of brazing alloys, soldering and photoprecessing con-
tribute to localized pollution. Releases from cloud seeding, mining
and milling are more widely dispersed and contribute to the concentra-
tions of silver found in urban runoff.
Pathway 2 in Figure 8 follows the flow of silver that originates
from solid waste disposal sites and mine tailings. The industrial
processes that contribute the largest amounts of solid waste (in the
form of sludge or solid material) include photoprocessing, contacts/
conductors production, smelting and refining, and brazing alloys and
solders production. As environmental controls restrain further dis-
charges to air and water, the quantity of silver disposed upon land
surfaces can be expected to increase. The fate of silver discharged
with process effluents by industries such as electroplating and pho-
tography" into local surface waters or publicly-owned treatment works
(POTW) is reviewed in Pathway 3. The fate of silver in influent to
POTW's is described in Pathway 4.
Figure 9 gives an overview of all of the major pathways of anthro-
pogenic silver in the environment. The land compartment receives a sub-
stantial portion of all silver releases. The migration of ground waters
containing silver to nearby surface waters has not been shown in this
figure since (1) the process is very slow, and (2) the current magnitude
of this transport pathway has not been well documented. Also the 3lives
in sediments is not represented, nor is the silver in soils resulting
from atmospheric fallout.
IV-9
-------
Pathway No.
1.
f
Atmospheric Emissions
(paniculate)
Ag Production
Smelting
Iron and Steel Production
Coal Combustion
Incineration
Atmospheric Emissions
(paniculate)
Crushing and Grinding
Dusts
Cloud Seeding
Mostly Local
Soil Surfaces
Pavement and Local
Road Soils
Groundwater
Slow
Surface Waters
Sediments '
Pathway #4
Oceans
Uptake by
Aquatic Organisms
2.
Solid Waste and
Tailings. Coal
Piles and Open Pit Mines
Primary Ag Production
Coal Mining
Ore Mining and Beneficiation
Landfill
Sludges
Uptake by
Aquatic Organisms
i
Source: Arthur D. Little. Inc.
Surf ace Waters
Sediment
Slow
Dissolved Solids
Susp. Sediment
Groundwater
Uptake by
Aquatic Organisms
FIGURE 8 MAJOR ENVIRONMENTAL PATHWAYS OF SILVER RELEASES
-------
Pathway No.
3.
I
Aqueous Discharges
Photography
Electroplating
POTW
Pathway #4
Treatment
System
Effluent 1 /
Hazardous/
Solid Waste
Dump
Surf ace Water j
1 Sediments
Slow —+~
Groundwater
Oceans
^
f
POTW
Influent
i
Primary
Treatment
^
\.
Biological
Treatment
»
«-*
Effluent
Ocean Dumping
Incin-
1 Landfill J
Air
Soil
Uptake by
Aquatic
Organisms
\
f 1
Surface Waters
Sediments '
A j(
S ^^
Groundwater
/s
Slow*" ' *
Source: Arthur D. Little. Inc.
FIGURE 8 MAJOR ENVIRONMENTAL PATHWAYS OF SILVER RELEASES (continued)
-------
f
M
NJ
Primary and
Secondary
Smelting
Air Emissions (6%)
Silver Use and
Inadvertent
Emissions
Aqueous Discharges
(17%)
Land Disposal (65%)
Photography Materials
Metal Ores
Discarded Appliances
Sludges
FIGURE 9 MAJOR PATHWAYS OF ANTHROPOGENIC SILVER RELEASED TO THE ENVIRONMENT
-------
3. Important Fate Processes
a. Overview
Silver is released into Che atmosphere from stacks and flues both
from industrial processes and from inadvertent sources such as coal
combustion. Particle size, height or release, and chemical speciation
determine the residence time of silver in the atmosphere although little
is known about.the specific influence of these parameters. Generally
large participates generated from mining operations, such as grinding,
settle in the vicinity of the source; smaller particulates from smelters
are airborne for a longer period and eventually deposited with rainfall.
Silver deposited onto soils by atmospheric fallout, agricultural
use, and solid waste disposal is largely in the form of insoluble compounds
or is quickly sorbed onto clays or organic matter and thus becomes in-
soluble. Silver is so strongly adsorbed in soils that leaching of silver
is not a probable transport route. High concentrations of silver on soil
surfaces will be reduced by erosion and soil runoff. In waters, silver will
be concentrated in the sediments, associated with clays and organic matter,
or as a precipitated species, such as AgCl or Ag2S.
b. Pathway 1 - Atmospheric Transport
Atmospheric
Emissions
Groundwacer
Ocean
POTU
> Pathway ,'M
Air
Physical and Chemical Characteristics; The fate of silver in the
atmosphere is expected to depend upon particle size, the chemical form,
and the height at which the release occurs. Unfortunately, very little
is known regarding the distribution of particle sizes of airborne silver
or its chemical forms. Consequently, most of the literature describing
the environmental fate of atmospheric silver relies on inference from
the observed distribution of other metals that are also likely to be
present concurrently with silver emissions.
IV-13
-------
Silver may be released as a fume or an aerosol. The metal's low
melting point and vapor pressure insure that fumes are rapdily converted
to fine participates, much less than 20 urn in aerodynamic diameter.
Particles of this size will typically remain airborne for large dis-
tances from the source, and are more likely to be rained out than to
settle out. Particles released by mechanical abrasion, as in ore crush-
ing and grinding, are likely to be much larger >20 urn) and will tend to
be deposited by settling within a kilometer or so of the source.
The chemical forms of atmospheric silver are essentially unknown.
Though most thermodynamically plausible species are relatively insoluble
in water, Smith and Carson (1977) speculate that mining and milling
operations will release silver to the atmosphere in the same chemical
forms as are present in the ores—predominantly sulfides, chlorides,
or sulfates. Releases from smelting, coal combustion, and iron and
steel making are from combustion zones; since these have a high sulfur
concentration, silver releases are likely to consist of sulfides, sul-
fates, and oxides. Silver oxides may be readily converted to carbonates
in the atmosphere. Other combustion sources that emit silver, such as
cement kilns and solder usage, are likely to release silver or silver
oxides.
Crushing, grinding, sorting* etc. of ores containing silver and coal
generate relatively course participates. Since these processes seldom
lead to emissions from an elevated stack, the impacts of such sources
are likely to be localized (within about a kilometer of the source).
Most of the total emissions from such sources will be deposited locally
by gravitational settling. During precipitation, these large particles
will be effectively scavenged by rainfall and deposited on land.
Fine particulates that pass particulate control devices (such as
cyclones, electrostatic precipitators, and baghouses) at ore smelters,
fossil-fuel fired power plants, and solid waste incinerators are gener-
ally smaller than 5 urn in aerodynamic diameter. When released from tall
stacks, these particulates will be dispersed widely, as indicated in
the study by Klein and Russell (1973) of a coal-fired power plant on
Lake Michigan. Silver contamination was observed over an area of 115
square miles and accounted for 80% of the silver emitted by the plant
over its lifetime. The degree of silver contamination observed in this
study was not severe: contaminated soils averaging only 0.272 mg/kg,
compared with a background level of 0.247 mg/kg.
At a smelter in Idaho, Ragaini et al. (1977) found much higher con-
centrations of silver, averaging 20.0 ± 10.2 mg/kg compared with a back-
ground of 3.3 mg/kg. Rugged topography at that site constrained wind
patterns such that Ag contamination was confined to the river valley.
Nonetheless, elevated levels of silver were observed about 4 miles from
the smelter complex. In the soil profile, levels of silver in con-
taminated soils fell rapidly with depth from the surface to a 20-cm
depth,indicating the metal's immobilization in soil.
IV-14
-------
The data of Ananth et al. (1976) show that several metals with
relatively high vapor pressures (Cd, Mn,'Pb, and Cr) all occur at sig-
nificant concentrations in the finer size particulate fractions of coal
fly ash (1.5 urn) as compared with coarse fractions (up to 25 urn). Con-
centrations of these metals In the fine partiuclates range from a factor
of 1.7 to 20 times greater than in the coarse fractions (median ratio is
2.4). Metals having lower vapor pressures (Al, B, Be, Cu, Fe, Ni, and
V) did not exhibit this preference for the finer particulate size frac-
tions, with a median ratio of concentrations between fine (1.5 urn) and
coarse (25 um) fractions of 1, and a range of 0.8 to 1.7. The high
vapor pressure of Ag places it in the former group, and it is inferred
that Ag will be concentrated preferentially in the finer fly ash particu-
lates, which are more likely to pass through particulate control devices
and are dispersed over wide areas.
Major Point Sources; The association between silver contamination
of the atmosphere or soil and a major point source has been demonstrated
clearly only for the above-mentioned power plants and smelter complex.
Although some investigators have identified iron and steel mills as a
major source of airborne silver, ambient monitoring data reviewed by
Smith and Carson (1977) for the vicinity of three steel mills did not
indicate a significant variation in ambient levels associated with the
mills. The monitoring data were for a highly industrialized area, in
which background levels of silver were comparatively high.
Galloway and Likens (1977) analyzed sediment core samples from a
remote Adirondack lake for silver and found much higher concentrations
in near-surface sediments than in deeper sediments. They conclude that
the profiles reflect recent increases in the rate of silver deposition
from the atmosphere.
The use of silver iodide in weather modification, particularly for
enhancement of winter precipitation in the Colorado River Basin, has
been shown to have relatively little ecological effect by Cooper and
Jolly (1970). Freeman (1977) presents extensive multi-media data for
a Colorado alpine lake/watershed showing relatively little enrichment
of silver in this watershed within the target area for silver iodide
cloud-seeding experiments.
Summary Statement; Silver released during smelting and from inad-
vertent sources such as incinerators and coal combustion plants is likely
to be associated with the particulates less than 20 um in diameter.
This will permit wide dispersal of silver, with rainout as the primary
mechanism leading to silver deposition onto land or surface waters.
Of the silver released during smelting, coal combustion, photoprocess-
ing and other industrial processing, roughly one-half of the silver will
be dispersed more than 100 km from its source and eventually deposited
by rain. The speciation of silver is not really known, but it is sus-
pected that silver will exist predominantly as sulfides, chlorides,
and sulfates in the ore.
IV-15
-------
Mechanical operations, such as grinding and crushing lead,to emis-
sions of silver in larger participates. These are expected to be short
lived in the atmosphere and to be deposited within a kilometer of the
source.
No enrichment of otherwise virgin lakes has been noted from use of
silver iodide for cloud-seeding purposes. The amount of silver used
in this capacity is expected to decrease due to increasing costs of
the precious metal and replacement by other substances in cloud-seeding
applications.
c. Pathway 2 - Land Disoosal
Air
Solid Wastes,
Coal Piles and
Open Mines
Surface
Macer
Sedlrcon
Ocean
Forms of Silver in Soil; Lindsay and Sadiq (1979) have recently
reviewed the theoretical relationships of silver in soils. Oxides,
sulfates, carbonates, and phosphates of silver are too soluble to per-
sist in soils. Silver bromide, chloride, and iodide are the likely
forms of silver in soil; under reduced conditions Ag° is formed. Com-
plexes with halides (and possibly NHa) may be important in soil systems.
Under reducing conditions, AgHS becomes a significant silver complex.
Under typical soil conditions, therefore, only a minor fraction of
silver is expected to be present as free ionic silver.
Sources; The land is the major recipient of silver releases to
the environment. Sources to land include tailing piles from metal ore
and coal mining; landfills of municipal solid wastes, photographic
wastes, incinerator fly ash, and sludges; and incorporation of waste-
water effluents and sludges for agricultural purposes. These three
categories are discussed individually.
IV-16
-------
Tailings and Mining Wastes; Silver is refined directly from silver
ores or as a byproduct of copper, zinc, gold, and lead ores. Approxi-
mately 50% of silver is a product of base-metal ores. The remaining 50%
is obtained from "silver ores" (Chapter III). Silver concentrations in
coal range from 0.02-0.04 mg/kg up to 300 mg/kg and from approximately
0.001 mg/kg up to 100 mg/kg in crude oil (Chapter II, Smith and Carson
1977). The form of silver in these energy sources is a metal-organic
complex. Some also occurs in the pyrite found in coal (Smith and Carson, 1977).
The major loss of silver due to milling and refining occurs in the
flotation effluent (Smith and Carson 1977). This effluent is discharged
to tailing ponds when recommended disposal practices are observed. In the
past (as late as 1968) direct discharge to surface waters was practiced.
Leonard (1977) found that negligible solid waste disposal results from
silver production at smelters designed for lead, zinc, and copper refin-
ing. Any solid residue generated from silver refining is recycled in
order to ensure the maximum recovery of silver.
Tailing ponds are made either by depositing tailings behind earth
dams or by building the dams from tailings (Smith and Carson 1977).
Some tailing leachate is trapped in order to recover any precious metals.
Silver is recovered as Ag2S by a precipitation technique. Activated
carbon and electro-oxidation are other methods used to recover silver
from tailings leachate.
Metal concentrations in leachate resulting from abandoned mine
tailings has been studied extensively in the Coeur d'Alene mining area
of Idaho. Until 1968, concentrator tailings were discharged directly
into the Coeur d'Alene River, although leaching of the tailings waste has
not been demonstrated to increase silver levels in the river (Smith and
Carson 1977).
Galbraith et al. (1972) analyzed the trace metal concentrations in
ground water underneath abandoned mine tailings in Cataldo Mission Flats
of the Coeur d'Alene mining district. The concentration of silver in
the tailings was 12.5 mg/kg at a depth of 3 feet, and about 0.5 mg/kg at 6
feet. The concentration of silver dissolved from the tailings was "too
low to measure accurately" but ranged between 0.01 mg/kg andO.02 mg/kg.
For metals in general, the authors hypothesized that sulfur-oxidizing
bacteria cause formation of H2SOl+ from sulfide, resulting in pH reduction
and dissolution of the metals. At a pH of 6.6, sulfur-reducing bacteria
precipitate the metals as sulfides. Since the pH decreases with depth
in the tailings (killing off the sulfur-reducing bacteria), more dis-
solution occurs deeper in the tailings. The applicability of this theory
to silver is borderline, since silver solubility, unlike that of most
metals, increases as pH increases.
IV-17
-------
Trace metal distribution in ground water of a mineralized region in
Colorado was analyzed in order to determine if the mineralized area con-
tributed to drinking water contamination (Klusman and Edwards, 1976).
Silver was found in concentrations ranging from 0.5 ug/1 to 5 ug/1 in
samples collected from wells. The results obtained do not illustrate
any clear trend with regard to silver concentrations resulting from
mineralization.
Wachter (1977) analyzed heavy metal concentrations in leachate
originating from coal piles stocked for production and use purposes.
Eight samples were subjected to a simulated rain equivalent to an
average yearly rainfall.. Silver concentrations were below the
detection limit for all samples. (The detection limit was not speci-
fied. )
Acid Mine Drainage; Silver is apparently not a problem metal in
acid mine drainage. Smith and Carson (1977) reported that the concen-
tration of silver in acid mine drainage ranges from 1 ug/1 to 8 ug/1,
which is significantly lower than the concentrations of other metals.
Landfills: Little information was available concerning silver
leaching from municipal or hazardous waste landfills to the ground water.
Smith and Carson report that silver is quite inert as a constituent of
solid waste, and, although its form in sludge is not well known, it is con-
sidered fairly resistant to mobilization. Law (1978) studied the metal
constituents in municipal and coal fly ash. Silver in municipal ashes
was about three times more concentrated than average levels in coal and
other feedstocks, and in coal ashes, about two times more concentrated.
No indication was given as to the tendency of silver to leach from the
fly ash.'
-Agricultural Purposes: Olsen et al. (undated) used the wastewaters
from two different secondary treatment plants for spray irrigation and
surface flooding. The effluents contained about 0.002-0.006 ug/1 Ag.
No surface accumulation was noted for the site receiving spray irriga-
tion, but was noted for silver in the top of 0-15 cm of the plot that
was flooded. Figure 10 illustrates the silver concentration with
respect to the soil profile. Smith and Carson (1977) stated that since
silver concentrated in sludge may approach 900 mg/1, the concentration
of silver in agricultural soils may be enhanced significantly when
sludge is applied.
Transport; Silver In soils may be adsorbed or complexed to organic
matter, clays, and iron, and manganese oxides. Mobilization in soils
may be favored by good drainage, and formation of soluble organic com-
plexes. If surface erosion occurs in areas where high silver concen-
trations have accumulated in the upper soil layers, then silver may be
transported to adjacent soil or surface water.
IV-18
-------
Control
0-15
16-30
•g 31-45
- 46-60
f 61-75
O 76-90
91-105
106-120
0-15
16-30
•§ 31-45
3 46-60
f 61-75
% 76-90
91-105
106-120
0.2 0.6 1.0 1.4
Disposal
i i i i i I i
0.2 0.6 1.0 1.4 1.8 2.2 2.6 3.0 3.4
Source: Olson et at. (undated) Units are in tag/kg
FIGURE 10 SOIL PROFILE OF SILVER CONCENTRATIONS ON SITE
RECEIVING SECONDARY TREATMENT PLANT EFFLUENT
BY SURFACE FLOODING
IV-19
-------
Statement; Silver in tailing ponds, abandoned mine tail-
ings, coal pile stocks, landfills for solid and municipal waste (includ-
ing photographic solid waste) , and acid mine drainage has not been shown
to enrich the surface and ground waters in proximity to the researched
areas. In most cases, silver concentration was near or below the detec-
tion limit of the apparatus used to measure aqueous concentrations in
the leachates. Therefore, the transport of silver from land to water
is not expected to be significant due to leaching except under condi-
tions favoring mobilization or under conditions of severe surface erosion.
No incidents of these conditions were reported. Agricultural irrigation
by surface flooding did cause surface accumulation of silver in the top
few centimeters of soil. Sludge application for agricultural soil amend-
ment might result in a similar accumulation of silver.
d. Pathway 3 - Industrial Aqueous Discharges
Effluenc
Aqueous
Discharge
sludge
Hazardous U
Solid tfasce Dump r
Sources: Silver is used industrially in the soluble form (Ag
in ceramic paint production, photography, electroplating, ink manufac-
ture, and for medicinal purposes. The metal is also used for production
of batteries, jewelry, coinage, mirrors,, contacts, and conductors. Only
the photography and electroplating industries have significantly high
effluent levels of silver, and so release significant aqueous discharges
at least locally.
Silver recovery processes, such as smelting and refining, also release
some silver to the water. The probable form of silver in photography pro-
cessing effluents is the silver thiosulfate complex, Ag
IV-20
-------
About one-half of the silver recovered from photoflnishing solution
originates from hypo solutions, processing emulsions, and spent
film and X-rays. Two-thirds of the liquid waste containing silver
results from spent fixing and bleach solutions (Smith and Carson 1977).
Electroplating wastes consist of "mill wastes" (spilled and spent
electrolyte) and rinse solutions. Mill wastes usually contain silver
as silver cyanide and concentrations of silver average about 250 mg/1
Ag+ in the mill wastes, and range from 50 mg/1 to 250 mg/1 Ag+ in the
rinse (Smith and Carson 1977).
Forms of Silver in Surface Water; In natural waters, silver exists
as Ag+, colloidal complexes, or as a trace element in living organisms.
The equilibrium of silver between water and solid phases (e.g., soils
and minerals) is influenced by the pH, the redox environment, and the
presence of complexing ligands. Figure 11 illustrates the relationship
between these factors for the Ag-S-O-H system. At silver ion concen-
trations of 10-8 and 10~10, predominant species are AgO and AgS; silver
(I) oxide is found only under conditions of high pH and redox potential
and therefore is probably not an important species in terms of environ-
mental transport.
Two recent studies offer important insight into the distribution
and speciation of silver in natural waters. Jenne and co-workers (1979)
have recently modeled speciation in fresh and marine waters. At silver
and total sulfur (^S + HS-) concentrations of ~10-10M and 10-9M respec-
tively, AgHS is an important species. In river environments where salt
concentration is generally low, the concentration of AgHS is predicted
to exceed that of Ag+ and AgCl by as much as tenfold. In marine environ-
ments, only AgCl~2 concentration is predicted to exceed that of AgHS,
and "free" Ag is negligible. Kharkar et al. (1968) have estimated the
flux of silver (dissolved and suspended) from freshwater streams to the
ocean. Of the total stream load of approximately 0.32 ug/1, silver is
supplied largely as dissolved species ("0.3 ug/1); suspended components
account for approximately 10% of the total stream load (~0.02 ug/1).
Treatment Techniques: Treatment techniques to recover silver are
precipitation, ion=exchange, electrolytic recovery, and reduction ex-
change. The efficiency of each method depends upon the initial silver
concentration, the presence of other metals, and the pH.
Precipitation removes silver as silver chloride, which is soluble
to the extent of 1.9 mg Ag+/l at 25°Cin distilled water. A slight
excess of chlorine reduces this value, but a large excess results in
formation of a soluble silver chloride complex. Precipitation as AgCl
allows selective recovery of silver from a waste containing other metal
ions. Reduction of silver concentrations to 0.1 mg/1 is possible by
making the solution alkaline. AgCl is precipitated along with metal
hydroxides. Washing the precipitate with dilute acid dissolves the
metal hydroxides and leaves pure AgCl. For electroplating wastes
containing cyanide, the cyanide must be oxidized in order to achieve
effective silver recovery. Patterson et al. (1971) found that a
ratio of 3.5 mg Cl to 1 mg CN would achieve 90-99% removal of
IV-21
-------
1.5
1.0
0.5
Eh 0
-OJ5
-1.0
-1.5
Ag
1 3
Source: Brookins (1978)
pAg*" 8
pAg+= 10
7
PH
Ag
Ag20
11 13
FIGURE 11 Eh - pH DIAGRAM FOR THE SYSTEM Ag-S-O-H
IV-22
-------
silver as AgCl. At an electroplating plant (Oneida Ltd.)fchlorination-
oxidation was found to result in a supernatant containing 0-8.2 mg/1 Ag
from a raw water containing 130-585 mg/1 Ag (Eichenlaub and Cox 1954).
The photography industry has long used sulfide precipitation to
recover silver. This method is no longer used to a great extent because
of energy and financial costs and the fact that it does not distinguish
between metals. Kodak precipitates silver from solutions containing organic
acids by adding magnesium sulfate and lime, producing a silver sulfate
oxide complex in the sludge (Patterson et al. 1971).
Ion exchange in a resin column is an effective process for dilute
aqueous solutions. The silver is recovered by elution of silver salts
or incineration of the resin. Silver in extremely dilute solutions have
been removed at efficiencies up to 85.8% by cation exchange, and 91.7% by
cation-anion exchange (Patterson et al. 1971). For the photography industry,
this method may be uneconomical in its own right, but in combination with
electrolytic recovery, silver is efficiently recovered from thiosulfate
developer baths (Patterson et al. 1971). The Sperry Rand Corporation
used ion exchange coupled with oxidation precipitation to recover silver
from their electroplating waste (Eidness and Bergman 1956). Cation
exchange columns were used for metals, while anion columns were used
for CN. Column regeneration formed an acid and alkaline waste respec-
tively. The alkaline waste was oxidized in order to eliminate the
CN and when it was subsequently combined with the acid metallic waste,
silver was precipitated as AgCl.
•
Electrolytic recovery is a treatment method for high concentrations
of metal ions in the waste. It cannot operate for silver at concentra-
tions lower than 100-500 mg/kg (Patterson et al. 1971). Generally large
photofinishing industries use this method. The supernatant allows reuse
of the fixer and gives a high purity silver (Smith and Carson 1977).
Reductive exchange is a treatment in which one metal is precipitated
onto another metal. Usually zinc or iron are used, and the result is
zinc or iron ions in solution. If enough surface area is present, such
as in zinc or steel wool, about 95% removal of silver is achieved.
Aqueous Discharges; The most obvious releases of silver to the
aqueous environment (most likely to POTWs) are from small amateur photo-
finishers, small electroplating companies, and certain photographic product
manufacturers. From photofinishing, the most likely form of silver would
be a thiosulfate complex. Gradual chemical degradation causes silver
to be precipitated as a silver halide or sulfide.
Very little silver (as AgCN)is discharged from electroplaters.
Aqueous discharge from small-to medium-sized plating shops are either
placed in a lagoon from which the precipitated metals are recovered,
or evaporated with the water recycled to the plating bath after treat-
ment with CaOH2 (Smith and Carson 1977). Because cyanide is also present
IV-23
-------
in electroplating wastes, the restrictions on cyanide disposal also
prevent much silver from being discharged. More than 50% of all plants
in the silver halide, diazo aqueous, photographic chemical formulation
and thermal product subcategories of the photographic products category
discharge wastes directly to POTWs. Some, usually treated, wastes are
discharged directly to surface water by <50% of the plants.
Some researchers have investigated the concentration of metals in
sediments of water receiving industrial discharges. Eisler et al. (1977)
studied the sediments of Narragansett Bay, which is a depository for
electroplating wastes. Silver was found concentrated in the upper 5 cm
of sediment. The silver concentration was lower than the concentrations
of cobalt, chromium, copper, iron, manganese, nickel, lead, and zinc, but
was higher than that of cadmium. The authors compared the average
sediment surface concentration of silver (1.4 mg/kg dry weight) with that
for other contaminated bays and estuaries (where 0.05-1.0 mg/kg dry
weight were reported).
Fink et al. (1976) determined the contamination in the St. Croix
River and estuary, which receives paper mill effluent, untreated sewage,
and mine runoff. Mo silver was detected (detection limit =0.3 mg/kg) in
the suspended solids of the St. Croix River. As revealed in Figure 12,
analyses of sediment core samples also revealed low silver levels,
except for the core directly downstream of the paper mill (Sta. K in
the figure). The authors speculate that the silver in paper mill
effluent results from the trace metal content of the trees.
Finally, sediment analysis of a highly industrialized estuary in
Scotland revealed that silver levels fluctuate very little at the points
of industrial inputs (Tyne, Hear Tees, and Humbar) (Talor 1979).
Figure 13 indicates that the sediment silver concentration was consis-
tently near 1 mg/kg.
Sludges: Sludges resulting from treatment of aqueous effluents for
silver recovery are often treated further to recover any residual silver.
The silver that is not recovered would likely be placed in a landfill or
lagoon or be incinerated. The fate of silver as a result of these dis-
posal routes is addressed in Pathway 2.
Summary Statement; Silver is discharged as an industrial waste
effluent primarily by photographic product manufacturers Q.42 kkg),
electroplaters (1 kkg), and professional and amateur photoprocessors
(65 kkg). The remainder of aqueous discharges are made by smelting and
refining processes ("15 kkg). Companies large enough to treat their
waste effluents for silver recovery employ precipitation with chloride
or sulfide, ion exhange, electrolytic recovery,, and/or reductive exchange
as effective treatment techniques, which are a function of the initial
Ag+ concentration. Smaller companies may use waste-holding lagoons,
from which AgCl is precipitated. Amateur photographers are the most
IV-24
-------
PPM
2 4 a a
Note: Core 50 is directly downstream from a paper and pulp plant.
Source: (Fink et aL 1976).
FIGURE 12 SEDIMENT PROFILE OF SILVER IN THE ST. CROIX RIVER
DOWNSTREAM FROM A PAPER AND PULP PLANT
1000
c
j
100 •:
ICi
01-=
001-
•Ag
Cd
• Mg
itr°~
- r
200 250
Distance ftcm area 14 (km) '
Tyn« Wear Tee* Humb«f
Note: Area 14 is beginning point of sampling analysis.
Source: (Taylor 1979).
FIGURE 13 DISTRIBUTION OF SILVER IN COASTAL SEDIMENTS
OF THE NORTH SEA
IV-2 5
-------
probable dischargers of silver who do not practice recovery; the releases
from this source, are estimated to total 15 kkg each year. The silver
thiosulfate complex in these discharges undergoes chemical and biological
degradation to form AgCl or
e. Pathway 4 - POTW's
Effluent
I PRIMARY . ^
iNT | ~ J TREATMENT |-» [_ HLUl. TREAT. ~
JPOTW INFLUENT |~ J TREATMENT |-H HIOL. TREAT. ~ta WATERS — | OCEAN |
INCINERATION, LAND
DISPOSAL, OCEAN DISPOSAL
Influent! Pathway 4 describes the fate of silver entering a
Publicly Owned Treatment Work. The influent to a POTW may consist of
combinations of industrial effluents, domestic wastes, and surface
runoff. The nature of the influent is quite varied, but Smith and Carson
(1977) report most influents contain less than 0.05 mg/1 Ag. Domestic
wastes probably account for a small percentage of the silver entering
POTWs because of discharges by amateur photographers of spent solutions
down the sink. Industrial contributions would be accounted for by electro-
plating industries and photographic material producers.
Treatment; The degree to which silver is removed from the raw
wastewater, and thus the silver concentration in the discharged waste-
water, depends on the type of treatment involved. Mytelka et al. (1973)
reported that for all municipal treatment plants in New York, New Jersey,
and Connecticut, the incoming, as well as the outgoing waters, from
primary treatment and biological treatment contained less than 0.5 mg/1
Ag. Linstedt et al. (1971) investigated the effectiveness of coagulation,
sedimentation, sand filters, activated carbon, and ion exchange, upon an
effluent obtained from a trickling filter (Ag concentration » £ 4.6 ug/1).
Fifty ug/1 AgNO was added for the experiment. The percentage removed by
each is as follows:
IV-26
-------
Unit Process % Ag Removal
Cumulative Removal After Given Process
Sand Filter 11.6
Lime Coagulation and Settling 97
Activated Carbon 97.1
Cation Exchange 98.8
Anion Exchange 99.4
Linstedt et al. (1971) concluded that activated carbon is a promising
technique for removal of silver. Cation exchange, alone, removed 85.8%
Ag, and coupled with anion exhchange, removed 91.7% As.
Supporting the results obtained by these researchers for activated
carbon is the research conducted by Netzer et_al. (1974) using discarded
tires for metal removal from wastewaters. The tires serve as carbon
surfaces (and perhaps provide sulfur to precipitate the silver) , which
remove the metals from the water. This researcher found that lime
removed only 3% of the silver added; this is much lower than the per-
centage removal reported above. Subsequent introduction of tires removed
more than 99.9% of the silver ion over the pH range 6-10.0.
Free silver ion is among the most toxic elements to microorganisms.
Poon and Bhayani (1971) researched how organisms in activated sludge respond
to slug doses of silver introduced as AgN03. Twenty-five mg/1 Ag+ (as AgNOs)
produced total inhibition of microorganism growth. Obviously, this con-
centration is far above what would be encountered in a treatment plant.
Concentrations of 5 mg/1 and 1 mg/1 did not totally inhibit growth. However,
no attempt was made to determine the amounts of silver ion adsorbed on
sludge or complexed after addition. Therefore, the threshold for inhibition
by free silver ion is still not well defined.
Sludge ; Silver is partitioned into the sludge portion of the waste
during treatment. Smith and Carson (1977) report silver concentrations
ranging from 0.005 mg/kg to 900 mg/kg in sludge. This would represent
up to 50% of the soluble silver, and up to 70% of the total silver, if
suspended solids are included. Anaerobic digestion would retain 90% of
the silver, mostly as
Fortescue et al. (1975) analyzed sludge from six wastewater plants
in Ontario. Three of the plants accepted principally residential wastes,
and the other three were more industrial in nature. The silver concen-
tration in the sludge ranged from 8 mg/kg to 37 mg/kg, with no clear
trend developing according to the nature -of the wastewater or treatment
scheme. As illustrated in the pathway flow diagram, sludge may be incin-
erated, used for agricultural purposes, disposed of in a landfill or in
the ocean. The land disposal fate of silver is covered in Pathway 2.
IV-27
-------
Effluent: Silver that is eventually discharged after treatment
is in the form of silver thiosulfates, colloidal silver chloride and
sulfide, and soluble organic complexes (Smith and Carson, 1977). Morel
et al. (1975) used Los Angeles County sewage to study the effects of
ocean disposal upon the mobility of trace metals. The sewage contained
20 ug/1 of silver after primary treatment, compared with the seawater
concentrations of 0.3 ug/1. The speciation and mobility of the metals
were studied by use of an aqueous chemical equilibrium model, REDEQL,
which has the capability of modelling inorganic and organic complexation,
and surface adsorption. For all three model options, it was predicted
that 100% of the silver would be present as Ag2S. The authors generalized
for all metals that dilution and oxidation of the sewage at the outfall
would permit only about 1% of the metals to be deposited in that area.
Summary Statement: According to one study, the concentration of
silver entering a POTW is quite low C<0.05 mg/1). The average influent
level reported in Chapter III was 0.008 mg/1. Treatment techniques that
appear to be particularly effective in removing silver from wastewater
are lime and settling (97% removal), activated carbon (>97% removal)
and cation-anion exchange resins (91.7% removal). The average treated
effluent level from the same study reported in Chapter III was 0.002
mg/1.
Silver is partitioned into sludge for which maximum concentrations
of 900 mg/kg and more typical levels of 100 mg/kg have been reported.
In anaerobic sludges, approximately 90% of the silver will be partitioned
with the sludge. Although silver is toxic to microorganisms, it is unlikely
that concentrations will approach those inhibiting growth. One study
found that the organisms in activated sludge were only slightly inhibited
at nominal concentrations of 1-5 mg/1 AgNOs.
D. BIOLOGICAL FATE
1. Aquatic Organisms
Fish, aquatic invertebrates, and plants may accumulate silver from
either water or sediment. According to the preceding section, water
concentrations are usually low, while sediments serve as a reservoir of
silver, especially in the vicinity of sources. Most laboratory studies
are concerned with uptake from filtered water, with no consideration of
the role of.the sediment burden in regard to bioaccumulation, even though
certain bottom dwellers, such as shellfish and scavenger fish, would have
considerable contact with these silver sources. However, due to the limita-
tions of available data, the following discussion is of bioaccumulation by
aquatic organisms, usually involving only dissolved or suspended forms
of silver.
The biological action of silver may involve reversible chemical
bonding with enzymes and other active molecules at cell surfaces. The
lipid phase of the cell membrane appears to play an important role in
the absorption of silver ions by living cells (Cooper and Jolly 1970).
IV-28
-------
a. Animals
Table 24 presents Che levels of silver chat have been reported to
accumulate in a number of aquatic animals. The ratio of accumulated
concentration to exposure concentration from experimental work by
Coleman and Cearley (1974) ranges from 2.4 to 333 for bass and bluegil'ls.
Internal organs and gills concentrated greater levels of silver
than did the remainder of the body. Davies et al. (1978) feel that
Coleman*s results are understated due to Che use of relatively hard
water with an atypically high chloride concentration (Davies et al.
1978). Higher levels of silver (up to 4,400 mg/kg in bone) were accumu-
lated by cut-throat trout, while marine organisms such as oysters
accumulated 189 mg/kg. No correlation was observed between size and
weight of red abalone and accumulated silver concentration (Anderlini
1974).
Enrichment factors as high as 22,000 have been calculated for
marine animals. Marine animals (containing 1.0 mg/kg dry matter)
accumulated 3,300 times the silver content of seawater, while freshwater
animals (containing 0.40 mg/kg dry matter) have been reoorted to con-
centrate silver by a factor of 3,080 (Smith and Carson 1977).
Shellfish, particularly oysters, passively accumulate many metals
much more readily than fish (Phillips and Russo 1978). Silver is
not likely to be bioaccumulated in freshwater fish muscle and marine
fish muscle, but it is considered likely Co be bioaccumulated in marine
shellfish or crustaceans (Phillips and Russo 1978). A study of fish
and silver concentrations in German rivers concluded that the bioaccumu- .
lation factor (BCF) for fish flesh is inversely proportional to the
silver concentration in water. The BCF was approximately 9 at a con-
centration of 0.1 ug/1 silver, while at 10 ug/1 silver, the BCF was
reduced to approximately 0.20 (Feldt and Melzer 1978).
Coleman and Cearley (1974) found that the main site of silver
intake in bluegill is the gills. Silver accumulation was greatest in
the internal organs of large-mouth bass. After 2 months of exposure
to silver, equilibrium developed between the concentration in the water
and in the fish tissue. These authors have hypothesized that the
absence of significant additional accumulation after 2 months could be
related to the mechanisms affecting uptake and elimination. They postulated
that the mechanisms affecting elimination may have been stimulated so
that uptake rate approximated elimination. The study cited an investiga-
tion in which Ag20^was found to accumulate in large amounts in the kidney
and liver tissues of goldfish. The authors found that juvenile large-
mouth bass and bluegills exposed to 0.01 mg/1 or 0.001 mg/1 for 6 months
continued to accumulate silver for 2 months and then leveled off. The
internal organs contained more silver than the muscle tissue. The 1974
study by Coleman and Cearley found gills and internal organs from bass
reaching much higher silver levels than the remaining tissue.
IV-29
-------
TABLE 24. ACCUMULATION OF SILVER IN AQUATIC ANIMALS
Accumulated
f
Species Orcan' Conditions
FRESHWATER
Largemouth Body Remainder Moderately Hard
Bass Water (180 rag
Micropterus CaC03/l) 4 months
salmoldes
Internal Organs
Gills
Bluegill Total Body
Lepomis
Machrochirus
Exposure
Concen-
(ug/1)
0.3
(control)
0.9
7.0
0.3
0.9
7.0
0.3
0.9
7.0
0.3
0.9
7.0
70
Accumu-
Concen-
(ug/1 dry)
0.0012
(Ash Ut.)
0.009
0.017
0.050
0.300
0.600
0
0.220
0.370
0.003
0.008
0.040
0.250
Exposure
("BCF")
•4
10
2.42
166
333
85.7
0
244
52.86
8.33
8.33
5.71
3.57
1
i
Reference
Coleman and
Cearley (1974)
Coleman and
Cearley (1974)
28 days
.03
0
U.S. EPA (1979)
-------
Tables 24 and 25 also Indicate the organs where bioaccumulated
levels were high. Cut-throat trout from an Alpine lake located in a
region undergoing extensive eloud seeding with silver iodide was
found to contain the greatest concentrations of silver in liver and
bone tissue. The marine fish species, dover sole, exposed to silver-
contaminated wastewater in an outfall off the coast of California was
also observed co contain higher concentrations of silver in the liver
as compared with the flesh (McDermott et al. 1976).
Silver is accumulated by the hepatopancreas and nephridial organs
of brachiopods, moHusks, and arthropods (particularly Crustacea)
(Smith and Carson 1977). Silver is concentrated in the glandular
tissue of the liver of fish and most vertebrates (Smith and Carson 1977).
The rate of silver uptake by Japanese eel (Anguilla j aponica)
and goldfish (Carassium auratus) was determined to be 1.2-4.2 x 10~7
mg/hour from a 0.74 mg/1 solution of radiosilver sulfate (Ag110) (Smith
and Carson 1977).
The bioaccumulation of silver is affected by those parameters that
affect the biological action of silver compounds. Behavior of silver
compounds in water is strongly affected by temperature, oxygen concen-
tration, the presence or absence of other cations, and pH. Also, since in-
formation on antagonistic and synergistic effects is lacking in much of
the published work, it is difficult to evaluate the influence of such
effects on the results of many experiments reported in the literature
(Cooper and Jolly 1970).
b. Monitoring Data
Surveys of the tissue concentrations of metals in fish from both
marine and freshwater environments show that silver is usually present
in low concentrations, usually less than 100 mg/kg (Phillips and Russo
1978).
Trout in unpolluted environments have been shown to contain con-
centrations of silver comparable to those In fish in more polluted areas
(see Table 25). Tong et al. (1974) studied trout in Cayuga Lake (NY) at
ages between 1 year and 12 years. They reported levels ranging from
0.68 ug/kg to 0.48 ug/kg, with steadily decreasing levels with age.
Somewhat higher levels, with an average concentration of 0.57 mg/kg for
all body parts, were reported by Freeman (1977) for trout in an alpine
lake in Colorado. Although the lake was in an isolated area, there was
the possibility of some contamination from cloud seeding with Agl.
Greig and Wenzloff (1977) collected several species of finfish from
marine waters in Long Island Sound and the New York Bight in the vicinity
of dredge spoil and sewage sludge disposal sites. Levels in fish muscle
and liver were similar among the different species sampled, ranging from
IV-31
-------
TABLE 25. SILVER CONCENTRATIONS DETECTED IN AQUATIC BIOTA
Concentration (me/kg)
OJ
10
Description of Species
Colorado Alpine Region - Trout
muscle
fat
liver
Cayuga Lake, N.Y. - trout
1-6 years of age
7-8 years of age
9-31 years of age
12 years
Long Island Sound/N.Y. Bight - finfish
- windowpane
flounder
- rock crab
Southern California outfall - Dover sole
control
outfall
Alpine Lake contaminated - cutthroat trout
by Cloud Seeding (various organs)
Mean
0.29
0.01
1.81
0.00068
0.00048
0.00058
0.00048
0.19
0.1
0.39
0.3
0.2
(wet)
(wet)
(wet)
(wet)
Range
ND- .99
ND-0.04
0.94-3.65
0.1 - .8 (wet)
0.24-0.79 (wet)
Reference
Freeman (1977)
Tong et al. (1974)
Greig and Wenzloff (1977)
Greig et al. (1977)
Greig et al. (1977)
McDermott et al. (1976)
0.09-4.4
Goettl et al. (1974)
North Atlantic scallops - muscle 0.12 (wet)
- total mass 0.51 (wet)
North Atlantic - surf clam 0.8
North Atlantic marine clam - Rhode Island 2.34 (dry)
Mid-Atlantic scallops 1.80 (dry)
England clams - contaminated estuary 0.57 (dry)
- non-contaminated estuary 0.4
0.97-0.24
0.22-1.9
0.39-1
1.16-4.64
0.39-9.08
0.23-1.2
0.37-0.6
Greig et al. (1978)
Greig et al. (1978)
Creit (1975)
Eisler (1978)
Pesch et al. (1977)
Bryan and Hamraerstone (1978
Bryan and Hammerstone (1978
-------
TABLE 25. SILVER CONCENTRATIONS DETECTED IN AQUATIC BIOTA (continued)
Concentration (me/kg)
f
OJ
Description of Species
\
California - mussels (whole body)
polluted area
unpolluted area
- oysters (gills)
polluted area
unpolluted area
California Coast - Red abalone
gill, mantle, foot
and digestive gland
Philadelphia near acid water - sea scallop
and sewage sludge disposal area
whole body
Los Angeles - rock scallop (digestive gland)
outfall area
control area
Mean
0.6
0.18
189
3.7
1.8
2.0
0.02
Range
0.130-129
0.43-9.08
Reference
Martin (1979)
Martin (1979)
Anderlini
Pesch et al. (1977)
Young and Tsu-Kai
(1979)
-------
less than 0.1 mg/kg to 0.8 ing/kg, and averaging 0.19 mg/kg. In a study
of the same area, Greig et al. (1977) reported silver levels of less
than 0.1 mg/kg in flounder and an average of 0.39 mg/kg in rock crab.
In a study of Dover sole in southern California, McDermott et al.
(1976) reported an average silver concentration of 0.2 mg/kg in the
vicinity of a municipal waste outfall; samples taken in a control area
had levels higher than those at the outfall, 0.3 mg/kg. It appears
that there is very little difference between silver concentrations in
fish living in enriched and unpolluted environments.
Background silver levels have been published for a number of marine
animals. The jellyfish has been observed to contain 2.8 mg/kg (dry
weight) while sea anemones are reported to have 6.0 mg/kg (dry weight).
The soft parts of an oyster have been observed to contain 4.5-73 mg/kg.
Detectable amounts of silver have been found in the ash of crabs and
fish (Cooper and Jolly 1977). Silver burdens of 2.6-7.1 mg/kg (dry
weight) have been reported for the saltwater worm, Neris diversicolor.
from sediments with almost the same concentrations (Lockwood 1976).
Silver residues in the liver of the Greater Scaup seaduck (Aythya
marila) were found to be .04-.032 mg/kg (wet weight) near Vancouver,
B.C.; this concentration is one order of magnitude greater than the
level in the food of these birds (Vermeer and Peakall 1979).
Silver concentrations in scallops, crabs, and other marine biota
consistently are reported at values similar to those for fish. Greig
et al. (1978) collected sea scallops along the North Atlantic Coast and
reported an average concentration of 0.12 mg/kg silver in muscle tissue.
In a similar, earlier study Greig (1975) reported silver levels in
North Atlantic clams and crabs of 0.8 mg/kg and 1.8 mg/kg respectively.
Clams were collected in the vicinity of an electroplating firm
during the fall of 1973 in Narragansett Bay, Rhode Island, by Eisler
et al. (1977). They reported a mean concentration of 2.34 mg/kg, with
a range of 1.16 to 4.64 mg/kg. Pesch et al. (1977) reported levels
averaging 1.8 mg/kg in scallops inhabiting the area in and around a
mid-Atlantic disposal site, and Bryan and Hummerstone (1978), in an
examination of burrowing clams in a contaminated and an uncontaminated
estuary, recorded only slightly higher levels in the contaminated
sample area; 0.57 mg/kg and .4 mg/kg respectively.
In conclusion, it appears that silver content in aquatic animals
is negligibly -affected by high pollutant concentrations in their habi-
tat. Silver levels range from less than 1 ug/kg up to 9.08 mg/kg with
most reported concentrations falling between 0.1 mg/kg and 0.9 mg/kg.
Table 26 summarizes the silver concentrations found in fish tissue
in different basins of the U.S., with maximum concentrations ranging
from 0.02 mg/kg to 1.9 mg/kg.
IV-34
-------
TABLE 26. STORET DATA ON SILVER CONCENTRATIONS IN FISH TISSUE
Concentrations
01
1.
2.
3.
5.
7.
9.
10.
12.
13.
16.
1975 1976
Basin Max. Mln. (No.) Max. Mln. (No.)
Northeast 690 90 (72) 120 120 (1)
•
North Atlantic 1900 70 (51) 230 110 (2)
Southeast 820 80 (8)
Ohio River 500 500 (7)
Upper Mississippi
Missouri River
Lower Mississippi
Western Gulf
Pacific Northwest
Max.
Gross 1900
1977 1978 1979
Max. Min. (No.) Max. Min. (No.) Max. Mln. (No.)
60 50 (9)
50 50 (11) 70 50 (10)
104 104 (1) 650 50 (4)
210 210 (1) 400 400 (1)
200 200 (1) 1000 4 (27) 30 20 (9)
20 20 (6)
Min. (No.) Mean
4 221 235
Source: U.S. Environmental Protection Agency, STORET (1980).
-------
c. Planes
The reported background silver concentrations in aquatic planes
vary widely (Cooper and Jolly 1970): 0.2 mg/kg silver (dry weight; for
diatoms, 0.2-0.8 mg/kg for algal species.
Marine plants (from water with an unspecified silver content) have
been reported to contain up to .060 mg/kg silver (dry weight) and most
freshwater plants up to 0.026 mg/kg; both concentrate silver by a factor
of 200 (Smith and Carson 1977). Silver residues in vascular marine plants
near British Columbia contained 0.01-0.48 mg/kg silver (wet weight)
(Vermeer and Peakall 1977).
The freshwater water hyacinth (Eichnomia crassioies) and alligator
weeds (Altemanthera philoxeroides) have been observed to absorb 650 mg/kg
and 440 mg/kg (dry weight) silver per day, respectively (Wblverton
et al..'undated). Concentrations of silver in water were not reported.
2. Terrestrial Organisms
a. Animals and Plants
In general, mammals do not accumulate much silver because of the low
solubility of most silver compounds and because of a generally low rate
of absorption through body membranes (Phillips and Russo 1978). Table 27
presents the background concentrations of silver in tissue of terrestrial
animals. One study concluded that the chronic accumulation of silver in
the rumen of ruminant species is unlikely because most of the administered
silver passed to the rumen is in insoluble form (U.S. EPA 1979).
Table 28 presents the background concentrations of silver in
terrestrial plants. The background silver content of plants ranges
from 0 mg/kg to 2.4 mg/kg, although silver is not an essential consti-
tuent of plants (Smith and Carson 1977).
Plants appear to contain silver in concentrations similar to those
found in aquatic biota, levels falling primarily between 0.03 mg/kg
and 4.3 mg/kg (Young et al. 1973), There is a large seasonal variation
in silver concentration of common juniper and club moss; from 5 to 50
times larger amounts are found in the spring compared with those in the
fall, most likely due to seasonal changes in the plants' chemical compo-
sition (Horovitz et al. 1974). Young et al. (1973) reported the widest
range in concentrations, 5.5 mg/kg. In food crops, Vanselow (1966)
reported levels ranging from less than 0.2 mg/kg to 2 mg/kg in tea and
Cooper and Jolly (1970) resorted concentrations of "up to several hundred
mg/kg (dry weight)." Among other edible plants that concentrate silver
are Mentha and Dioscorea (Smith and Carson 1977).
IV-36
-------
TABLE 27. BACKGROUND CONCENTRATIONS OF SILVER
IN TERRESTRIAL ANIMALS
Species
Mollusc
Land Snail
(Unio mancus)
Organ
Shell
Flesh
Accumulated
Silver
(mg/kg)-(Drv)
0.16-0.8
0.05-0.7
Reference
Bowen(1966)
Bowen(l966)
Mammals
Bones (Apatite) 0.01
Soft Tissue 0.005-0.04
Bowen(1966)
Bowen(1966)
Ducks
Tissue
Vermeer and Peakall
(1979) and Bagley
and Locke (1967)
1Wet weight.-
IV-3 7
-------
TABLE 28.
SILVER CONTENT OF TERRESTRIAL PLANTS
f
to
00
Species
BACKGROUND CONCENTRATIONS
Common juniper
(Junlperus communis)
Club moss
(Lycopodium circinatum)
Gymnosperros
Alfalfa
(Medicago aativa)
Wheat
(Triticum sp.)
Mushroom
(13 species)
Accumulated Ag
(me/kg Dry Weight)
May; 1.5
Sept: 0.02
May: 1.0
Sept: 0.02
0-1.4
(0-3.0 in ash)
0.02-1.3
in tops
0.5
1.0 in bran
average: 1.4
range: 0.03-5.5
Ag in Soil
frag/kg)
0.09
(Exposed land of
a botanical garden)
0.03
(Greenhouse of a
botanical garden)
Field grown
average 1.0
(unpolluted area in
Norway)
Reference
Horovitz et al (1974)
Horovitz et al (1974)
Cooper and Jolly (1970)
Smith and Carson (1977)
Smith and Carson (1977)
Allen and Stelnnes (1978)
-------
TABLE 28. (continued)
SILVER CONTENT OF TERRESTRIAL PLANTS
Species
EXPERIMENTAL
Grass
2-1/2 years after
application of:
100,000 ing/kg NO3
1,000 mg/kg N03
100,000 mg/kg Agl
1,000 mg/kg Agl
Cactus
100,000 mg/kg N03
1,000 mg/kg NO3
100,000 mg/kg Agl
1,000 mg/kg Agl
Bush Beans
(Phaseolus vulgaris)
13 days in 10~5 M AgNOa
Accumulated Ag
(me/kg dry weight)
Ag In Soil
(mg/kg)
Reference
46,500
1,800
3,580
10
1,740
100
840
30
16,610.
483
20,530
285
16,610
483
20,530
285
1,760.0 roots
5,1 stems
5.8 leaves
Klein and Molise (1975)
Klein and Molise (1975)
Klein and Molise (1975)
Klein and Molise (1975)
Klein and Molise (1975)
Klein and Molise (1975)
Klein and Molise (1975)
Klein and Molise (1975)
Klein and Molise (1975)
Wallace and Romney (1977)
* Wallace (1979) reports 760,000 for roots.
-------
Experimental data show that grasses have higher relative silver
concentrations than cactus, but that both species accumulate approxi-
mately one-tenth of the soil concentrations resulting from Ag treatments.
Grasses had higher silver concentrations than soils following AgNOa treat-
ment. Klein (1975) concluded that silver from AgNOs will be taken up by
plants to a greater extent than from Agl, but that with increasing con-
centration of silver in soil, more silver is localized in roots than in
above-ground plant parts.
The ash of terrestrial plants usually contains 0.2 mg/kg of silver,
with the highest concentration in seeds, nuts, and fruit (Smifh and
Carson 1977), 0.400 mg/kg has been detected in whole wheat, and 0.800
mg/kg have been detected in wheat germ (Smith and Carson 1977).
The availability of silver .in soil for plant uptake depends on the
pH of the soil solution. At about pH 7, silver ion concentration in
soil solution is less than 0.05 mg/kg. At pH 5 to 6, the concentration
increases, and at pH 7.5 to 8.5, the concentration decreases. In a
study in Colorado, soils with a high silver concentration exhibited
lower pH, higher water content, respiration rate, and concentration of
organic matter with increasing silver iodide content up to 50 mg/kg,
and greater numbers of microorganisms. Adsorption and complexing of
silver by soil humates would tend to inhibit their decomposition and
lessen the toxic effect of silver on soil microorganisms (Smith and
Carson 1977).
Bioaccumulation of silver by plants may be influenced by the
presence of other heavy metals. Preferential uptake of copper over
silver has been observed in white oak trees (Quercus alba): Cu/Ag
ratios were greater in the twigs than in the surrounding soil (Leavitt
et al. 1979).
IV-40
-------
b. Biomagnification in the Food Chain
There seems to be little likelihood that silver will be increased
through terrestrial food chains to a level that is dangerous to higher
organisms (Cooper and Jolly 1970). Aquatic organisms seem to have a
greater ability to bioconcentrate silver than terrestrial mammals.
This may be due to uptake through a greater number of and more efficient
exposure routes (e.g., gill absorption, better gut absorption efficiency).
c. Microorganisms
Bacterial populations may accumulate high levels of silver, especially
groups acclimated to silver concentrations. Up to 300 mg/g (dry weight)
of silver was measured in a 3-species bacterial population growing in a
chemostat (Charley and Bull 1979). An uptake race of 21 mg silver h"1
(g biomass)-1 was measured; the extent of removal of silver from water
was concentration-dependent. Pseudomonas maltophilia comprised 50% by
numbers of the community and was particularly resistant to the toxic
effects of silver. The authors suggested that exposure of multispecies
communities of bacteria could be used in the wastewater treatment of
silver as a removal process.
The more commonly observed effect of silver on microorganisms,
however, is toxicity; investigations of this subject are discussed in
Section V-B. Not enough information is available to assess the likeli-
hood that natural populations of microorganisms would accumulate silver
rather than be inhibited by typical environmental levels of silver. If the
propensity for microbial bioaccumulation is common in the environment,
then there are situations where-microorganisms may serve as a signifi-
cant reservoir of silver (e.g., in systems with high biomass such as
eutrophic lakes, estuaries, etc.).
E. CONCENTRATIONS DETECTED IN THE ENVIRONMENT
1. Surface Water
Annual mean concentrations of silver in surface water in the U.S.
have ranged from 1 ug/1 to 9 ug/1 during the period 1970 to 1979. Maximum
concentrations of silver over the same time period ranged from 94 ug/1 to
790 ug/1. Figure 14 exhibits the trends in maximum and mean silver con-
centrations in the United States from 1970 to 1979.
The distribution of silver concentrations in surface water is
given in Table 29. The majority of "unremarked^'observations between
1970 and 1979 were for concentrations of 0-1 ug/1. From 78% to 98%
of all observations in a given year for this period were for concentra-
tions of less than 10 ug/1.
Unremarked data are observations above detection limits.
IV-41
-------
1000
900
800
700
600
500
-. 40°
j 300
S
.2 200
2
I 100
I
10
8
6
4
2
0
Maximum
Mean
1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 (Years)
Source: U.S. Environmental Protection Agency. STORET, 1980.
FIGURE 14 TRENDS IN MEAN AND MAXIMUM SILVER CONCENTRATIONS
IN SURFACE WATERS OF THE UNITED STATES, STORET, 1970-1979
IV-42
-------
TABLE 29. DISTRIBUTION OF SILVER CONCENTRATIONS
IN U.S. AMBIENT WATERS, STORET, 1970-1979
Percent of Observations
Number of at Concentration (ug/1)
Year Unremarked Observations
1970 167
1971 518
1972 1,048
1973 879
1974 960
1975 1,436
1976 2,468
1977 2,033
1978 3,054
1979 3,047
Average - 72.8 17.1 9.7 0.6
Source: U.S. Environmental Protection Agency, STORET (1980)
0-1.
92
78
74
81
65
69
56
49
75
89
1.1-10
2
9
17
12
22
• 24
29
29
18
9
10.1-100
5
13
8
6
12
8
15
21
7
2
100.1-1000
1
1
1
1
1
0
0
1
0
0
IV-43
-------
The ratio of silver concentrations (total Ag) to the EPA Water
Quality Criterion for protection of freshwater aquatic life is presented
in Figure 15, aggregated by U.S. county. Remarked data are set to 0 and
85th percentiles are reported. Appendix B includes maps of the distribu-
tion using remarked data, and for the 50th percentile. States in which
concentrations exceed the water quality criterion include Washington,
Idaho, Colorado, Wisconsin, Oklahoma, California, Ohio, West Virginia,
North Carolina, Pennsylvania, Maine, Louisiana, Mississippi, and at
scattered locations throughout the remaining states.
Monitoring data were disaggregated for the major river basins in
order to discern regional variations in silver concentrations. When the
data were grouped in this manner, five of the 18 continental basins had
annual mean surface water concentrations of silver exceeding the 1975
EPA National Interim Water Standard of 50 ug/1. However, the standard
was not actually in effect until June 1977, while most instances of
annual means exceeding 50 ug/1 occurred between 1971 and 1973 as shown
in Table 30. While four basins exceeded this level once during the ten
years, the Northeast basin did so from 1971 to 1973 and again in 1976.
Recently, very few basins have had annual mean concentrations exceeding
the standard (in fact, none during 1977 to 1979).
A more realistic picture of regional variations in silver concen-
trations may be gathered from Figure 16. For the ten-year period,
1970-1979, the percentage change in annual mean concentrations of silver
in major river basins was calculated using the difference between the
combined mean for the first 5 years (1970 to 1974) and that for the
second 5-year period (1975 to 1979). Too few data were available to allow
this comparison for five basins—Lake Erie, Colorado River and Great Basin,
Lake Huron, and Hudson Bay. Figure 16 indicates that levels of silver
in 10 of the 13 basins shown, or 77%, have decreased over the past 5 years.
Considering individual basins, silver concentrations decreased by 23%
to 98% and for the United States as a whole, by 55% during the 1975-1979
interval. The concentrations in the North Atlantic, Southeast, and
Lower Mississippi basins have increased by 420%, 300%, and 300%, respec-
tively. Still, even with these increases annual mean concentrations of
silver in these basins do not exceed the EPA Interim Drinking Water
Standard.
2. Well Water
Silver concentrations in well waters are fairly uniform across
the country, as reflected in observations in STORET. Of the 2,232
observations recorded from 1977 to 1979, the maximum concentration was
30 ug/1, with the mean around 14 ug/1. Table 31 exhibits silver con-
centrations in well waters in the major river basins from 1977 to 1979.
In no case, however, was the Interim Drinking Water Standard (50 ug/1)
violated.
Bradford (1971) investigated trace elements in the water resources
of California. Silver concentrations in well waters at the San Joaquin
Valley and in the area surrounding the Salton Sea ranged from less than
0.1 ug/1 to 0.4 ug/1.
IV-44
-------
£~
Ol
f«IKUHnfNIflL PRJIICIIOH HQltf.l
STORE! SYSTtM
ft i OOCC TO
a 2-oocc TO
:«IE-1 *?.
r,.co&c
5 COOP
01? 220-'J:j JIUEG/lNfH
n: t r. G «»o'
:2.IO 4,.20 6f> 30
_i 1 1
30-40
FIGURE 15. RATIO OF AG CONCENTRATION IN WHOLE WATER TO CRITERIA AGGREGATED BY
COUNTY 85 %TILE USING REMARK CODES 85TH PERCENTILES
-------
TABLE 30. MAJOR U.S. RIVER BASINS IN WHICH ANNUAL MEAN CONCENTRATION
OF SILVER IN SURFACE WATER EXCEEDED 50 ug/1, STORET, 1970-1979
Year
Basin 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979
1 Northeast XXX X '
2 North Atlantic
3 Southeast
4 Tennessee River X
5 Ohio River X
M 6 Lake Erie
-------
500
400
300
200
100
-10
-20
-30
-40
-50
-60
-70
-80
-90
100
1
*
^mm
^^m
2
•M
3
"
4
•••
S
•«
7
MM
8
MM
9
^MM
•MB
10
12
13
14
••Mi
22
—
US
MAJOR BASIN CODES
1 -Northeast
2-North Atlantic
3—Southeast
4—Tennessee River
5-Ohio River
7-Upper Mississippi
8-Lake Michigan
9—Missouri River
10-Lower Mississippi
12-Western Gulf
13-Pacific Northwest
14-California
22-Lake Superior
US-UNITED STATES
Source: Arthur 0. Little. Inc., based on U.S. EPA STORET.
FIGURE 16 PERCENTAGE CHANGE IN SILVER CONCENTRATIONS IN AMBIENT
WATERS OF MAJOR U.S. RIVER BASINS. STORET,
1970-1974 PERIOD VERSUS 1975-1979 PERIOD
TTT_A7
-------
TABLE 31. SILVER CONCENTRATIONS'DETECTED
IN WELL WATERS, STORET, 1977-1979
Major River Basins
1 Northeast
2 North Atlantic
5 Ohio River
6 Lake Erie
7 Upper Mississippi
8 Lake Michigan
10 Lower Mississippi
13 Pacific Northwest
14 California
21 Lake Huron
22 Lake Superior
23 Hudson Bay
UNITED STATES
Number of
Observations
27
27
1,448
632
69
5
1
14
1
1
2
5
2,232
Concentrations (ug/1)
Maximum
8
10
30
30
30
30
10
2
0
30
25
5
30
Mean
5
9
16
13
10
16
10
2
0
30
15
5
14
Monitoring stations reporting -2,206. Includes remarked and unremarked
data.
Source: U.S. Environmental Protection Agency, STORET, 1980.
The STORET data file for 1977 through 1979 contains information on silver
in sediments from one-half of the major river basins in the U.S.
IV-48
-------
In a study of metal levels in ground water In the Colorado Front
Range mineral belt, a total of 149 samples were collected over an area
of approximately 2,070 square kilometers (800 square miles), both within
and outside the mining area (Klusman and Edwards 1976). Average silver
concentrations in samples from the mineral belt and outside were measured
at 0.55 ug/1 and 0.77 ug/1, respectively. The higher silver concentra-
tion for the non-mineral belt is labeled as suspect because of a single
high value, which may be invalid. In both cases, however, silver con-
centrations were lower than the Water Quality Standard of 50 ug/1.
3. Sediment
The STORET data file for 1977 through 1979 contains information
on silver in sediments from % of the major river basins in the U.S.
These basins were selected to be representative of all regions of the-coun
try. During this 3-year period, maximum concentrations of silver in
ranged from 1 mg/kg to 95 mg/kg and mean concentrations from 1 rag/kg to
10 mg/kg. Silver concentrations in sediment are disolaved in Table 12 for
the reporting basins and the United States. In general, silver con-
centrations in sediment are two to three orders of magnitude higher
than silver concentrations in ambient waters.
Heavy metal pollution in the sediments of the Coeur d'Alene River
delta in Northern Idaho was investigated by Maxfield et al. (1974).
Mining and smelting operations have discharged large quantities of
wastes containing high levels of heavy metals in the river for several
decades. Silver concentrations in the top layer of the dry sediments
ranged from 6 mg/kg to 15 mg/kg, with a mean value of + 2 mg/kg.
In the Southern California Coastal Zone, sediment samples were
collected in four inner basins: San Pedro, Santa Monica, Santa Barbara
and Soledad (Bruland et al. 1974). Silver appeared to have accumulated
at higher rates in the San Pedro and Santa Monica basins and less dis-
tinctly in deposits at the Santa Barbara basin. This difference was
attributed to human activities. In the Soledad basin, an area
not measurably affected by human activities, concentrations did not
change as a function of depth. Over 3 years, silver concentrations
in sediment for both the San Pedro and Santa Monica basin increased
from 1 mg/kg to 3.5 mg/kg and from 1 mg/kg to 3 mg/kg respectively.
In the Santa Barbara basin, silver concentrations increased from 1 mg/kg
to 2 mg/kg in sediment, and at the Soledad basin remained constant at
a level of 2 mg/kg.
4. Dissolved and Suspended Matter
Water samples for 10 rivers across the United States were analyzed
by Kharkar et al. (1968) to determine stream supply of several dissolved
metals to the oceans. The concentration of silver was found to have a
relatively narrow range among the rivers studied. Table 33 shows mean
values of silver concentrations for the 10 rivers, ranging from 0.10
ug/1 to 0.55 ug/1. These results are consistent with reports of
IV-49
-------
TABLE 32. SILVER CONCENTRATIONS DETECTED IN SEDIMENT, STORET
1977-1979
Concentrations (me/kg)
Major River Basins
1.
2.
5.
7.
9.
10.
11.
12.
13.
Northeast
North Atlantic
Ohio River
Upper Mississippi
Missouri River
Lower Mississippi
Colorado River
Western Gulf
Pacific Northwest
UNITED STATES
wo.
Observations
14
4
7
3
10
5
13
92
37
185
Maximum
10
10
10
1
2
3
15
22
95
95
Mean
10
3
10
1
1
1
3
2
5
3
Source: U.S. Environmental Protection Agency, STORET, 1980.
IV-50
-------
TABLE 33. MEAN SILVER CONCENTRATIONS OF TEN U.S. RIVERS
River and State
Mississippi, Minnesota
Susquehanna, Pennsylvania
Mad, California
Klamath, California
Russian, California
Eel, California
Brazos, Texas
Housatonic, Connecticut
Connecticut, Connecticut
Neuse, North Carolina
1 In dissolved form
Source: Kharkar et al.(1968)
Mean Silver Concentrations (ug/1)
0.24
0.37
0.26
0.55
0.10
0.17
0.38
0.39
0.17
0.37
IV-51
-------
silver concentrations in dissolved form from the STORE! system as shown
previously in Table 29. For the nation as a whole, a mean value of 0.87
ug/1 depicts silver concentrations in dissolved form for 1977 to 1979.
Turekian and Scott (1967) studied concentrations of silver in
suspended material in 18 rivers in the eastern and southern portions
of the country. They concluded that regional differences in concentra-
tions were due to the presence of a greater quantity of a trace-element
rich soil component and to industrial contamination in the eastern rivers.
The Susquehanna River in Pennsylvania, in particular, was highlighted as
the waterway stressing the regional variation due to the two factors
mentioned. Results from the study indicate a range of 0.4 mg/1 to
15 mg/1 for silver concentrations in suspended matter; concentrations
for each river are displayed in Table 34.
Silver concentrations in suspended matter recorded in the STORET
system (0.002 mg/1 to 0.06 mg/1; Table 35) are lower than those found
by Turekian and Scott. Over the 10-year span between the Turekian and
Scott (1967) study and the 1977 to 1979 values in STORET, the decreases
in concentrations were parallel to those noted in the STORET ambient
water concentrations.
5. Effluent Waters
The Interstate Sanitation Commission, which oversees the estuarine
tidal waters of New York, New Jersey and Connecticut, examined heavy
metals in wastewater and treatment plant effluents. Of 192 samples
collected, less than 2% of the influent and less than 1% of the effluents
contained silver concentrations above the detection limit of 50 ug/1
(Mytelka et al. 1973).
In upstate New York, the Genesse River has received photoprocessing
effluents for roughly seven decades. Sampling from May 31 to October 17,
1973, revealed an average silver concentration of 20 ug/3, although con-
centrations as high as 260 ug/1 were recorded during the study period.
The raw water intake at the main photoprocessing company in the area was
documented as containing 1 ug/1 of silver (Bard et al., 1976).
Page (1974) reported silver concentrations treated wastewater
effluent in California averaging 7.1 ug/1, approximately 60% lower
than the influent concentrations. In another study of California
sewage treatment plant (Young et al. 1973), effluent silver concentra-
tions were recorded as ranging from 2 to 20 ug/1.
Effluent silver concentrations in the STORET system are documented
for three basins since 1977—Northeast, North Atlantic and Southeast.
Summary maximum and mean effluents concentrations are:
IV-52
-------
TABLE 34. SILVER CONCENTRATIONS IN SUSPENDED
MATTER IN U.S. RIVERS
River and State
Brazos, Texas
Colorado, Texas
Red, Louisiana
Mississippi, Arkansas
Tombigbee, .Alabama
Alabama, Alabama
Chattahoochie, Georgia
Flint, Georgia
Savannah, South Carolina
Klateree, South Carolina
Pee Dee, South Carolina
Cape Fear, North Carolina
Neuse, North Carolina
Roanoke, North Carolina
James, Virginia
Rappahannock, Virginia
Potomac, Virginia
Susquehanna, Pennsylvania
Silver Concentrations (mg/1)
0.4
0.6
0.3
0.7
1.0
4.0
7.0
1.0
2.0
1.5
0.4
0.7
• 4.0
4.9
7.0
1.0
1.5
15.0
Source: Turekian and Scott (1967) .
IV-53
-------
TABLE 35. SILVER CONCENTRATIONS IN DISSOLVED FORM AND ADSORBED ONTO
MATTER IN MAJOR U.S. RIVER BASINS, 1977-1979
Diaaolved Form (uR/1)
On Suspended Matter (ug/1)
?
Ul
Major River Basins
1. Northeast
2. North Atlantic
3. Southeast
4. Tennessee River
5. Ohio River
6. Lake Erie
7. Upper Mississippi
8. Lake Michigan
9. Missouri River
10. Lower Mississippi
11. Colorado River
12. Western Gulf
13. Pacific Northwest
14. California
15. Great Basin
21. Lake Huron
22. Lake Superior
UNITED STATES
No. Obs.
253
107
462
43
235
67
306
69
440
528
234
378
683
209
397
25
39
4475
Max
2
3
3
2
16
1
5
1
50
10
5
15
4
4
85
1
4
85
Mean
.02
.05
.06
.14
.14
.03
.20
.03
.45
.10
.13
.06
.41
.03
5.70
.04
.19
.87
No. Obs.
245
85
446
41
224
66
268
67
396
468
208
290
340
143
143
24
39
3493
Max
3
2
10
2
3
5
10
1
10
60
30
30
20
10
10
1
10
60
Mean
.14
.05
.14
.10
.18
.12
1.39
.09
.72
.60
.98
.66
.93
1.22
.79
.28
.57
.60
Source: U.S. Environmental Protection Agency, STORET (1980)
-------
Concentration (ug/1)
Basin Observations Maximum Mean
Northeast 229 120 4.8
North Atlantic 62 730 18.7
Southeast 12 27 10.3
All Basins 303 .730 7.8
6. Air
Silver is generally found at very low concentration in the atmos-
phere (Table 36). The differences in levels between urban and rural
areas also appear to be relatively insignificant: in a sparsely inhabi-
ted region of Nebraska, Struempler (1975) reported a silver concentra-
tion of .15 ng/m3; in the non-industrial city of Washington, D.C., Trout
(1975) reported a concentration of 1.1 ng/m3, and Brar et al. (1970),
in a study of heavily industrial Chicago, Illinois, reported an ambient
level of only 4.3 ng/m3. In a study of urban areas including Chicago, •
Bogen (1974) reported levels ranging from 1 mg/m3 to 2.4 ng/m3. Even
lower levels, 0.05-0.2 ng/m3, were reported for San Francisco by John
et al. (1973). Andren et al. (1974) reported a level of 0.17 ng/m3 in
the vicinity of three coal-fired steam plants at Oak Ridge, Tennessee.
Almost all of the reported data are in general agreement with these
levels. Thus the effect of human activity on atmospheric silver
levels is limited.
Monitoring data for Europe reveal silver concentrations within
this same range. In Glasgow, a heavily and diversely industrialized
city, McDonald and Duncan (1979) reported levels ranging from 0.3 mg/m3
to 12.9 ng/m3, with a mean of 2.7 ng/m3. Bogen (1974) reported a
level of 4.2 ng/m3 in Heidelberg, Germany.
In an examination of the contribution by steel mills to atmospheric
levels of silver, Harrison et al. (1971) collected samples in the East
Chicago area, located near three major steel mills, as well as other
large manufacturing facilities. Silver concentrations ranged from less
than 0.5 ng/m3 to 5 ng/m3.
When compared with iron levels at the same station, Dams et al.
(1971) reported that since maximum levels of iron were not correlated
with high silver levels, the steel plants were unlikely to be the source
of the silver. The highest levels reported in the literature were
measurements taken at the Kellog, Idaho, city hall; Ragaini et al.
(1977) reported an average silver level of 10.5 ng/m3, with a range of
0.94 ng/m3 to 36.5 ng/m3. The site is in close proximity to a smelting
operation that processes lead with a high concentration of silver.
High levels may occur in areas of occupational exposure. Anania
and Seta (1973) reported levels ranging from 0.01 mg/m3 to 0.04 mg/m
(averaging 0.02mg/m3) at the San Francisco mint during melting and
IV-55
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TABLE 36. SILVER CONCENTRATIONS DETECTED IN AIR AND PRECIPITATION
Description
Nebraska
Washington, D.C.
Chicago, IL
East Chicago, IL
San Francisco, CA
Oak Ridge, TN
Glasgow, UK
Heidelberg, Germany
E. Chicago (steel mills)
Kellog, Idaho (smelter)
San Francisco Mint
Cloud seeding
Concentration (ng/m )
Mean Range
0.15
1.1
4.3
1-2.4
.05-.2
0.17
2.7
4.2
10.5
.02mg/m3
0.1
0.3 -12.9
0.5 -5
0.94-36.5
Reference
Struempler (1975)
Trout (1975)
Brar et al. (1970)
Bogen (1974)
John £t al. (1973)
Andren eit al. (1974)
McDonald and Duncan (1979)
Bogen (1974)
Harrison et. al. (1971)
Ragaini £t al. (1977)
Anania and Seta (1973)
Standler and Vonnegut (1972)
Nebraska - snow
- rain
St. Louis, Mo. - rain
Ag I - seeded precipitation
(ug/1)
'0.05
0.09
0.002-.216
0.001-.45
Struempler (1975)
Struempler (1975)
Rat tone tti (1974)
Cooper and Jolly (1970)
-------
casting operations. Similar levels may be present during production
of medallions and other cast silver objects. Atmospheric levels during
cloud seeding operations may also be significant. Standler and Vonnegut
(1972) reported levels of approximately 0.1 ng/m3 downwind of cloud-
seeding operations.
Precipitation due to rain and snowfall is often a good indicator
for levels of silver in the atmosphere and also aids in understanding
the transfer of silver from air to water and the soil. In the previously
mentioned study of uninhabited sections of Nebraska (Struempler 1975),
a level of .08 ug/1 was reported for silver in overall precipitation
(0.05 ug/1 for snow and 0.09 ug/1 for rain). Rattonetti (1974) reported
levels of 0.002-0.216 ug/1 in St. Louis, Missouri in unseede'd rainfall
and Cooper and Jolly (1970) reported levels of O.'0'Olug/l to 0.45 ug/1 in
AGI-seeded precipitation.
Mulvey (1979) examined precipitation, both snow and rain, in urban
and uninhabited areas of the U.S. Uninhabited areas included Yellowstone
National Park, the Sierra Nevada, and the Rocky Mountains in Colorado.
For urban areas, he reported an average concentration of 36.9 ug/1 and
for uninhabited regions an average level of 27.3 ug/1.
7. Soil
The terrestrial concentration of silver has been estimated, on the
basis of average concentrations in various rock formations, as between
0.02 mg/kg (Goldschmidt 1954) and 0.2 mg/kg (Green 1959) (Table 37).
Taylor (1964) reported a concentration of silver in the continental
crust of 0.07mg/kg, based on 0.1 mg/kg in basalt and 0.04 mg/kg in
granite. In comparison with these levels, concentrations of up to
7.0 mg/kg (Mitchell 1955) have been reported in mineral soils. High
levels have also been found in forest humus, which appears to concen-
trate silver.
Boyle (1968) reported a similar range of from less than 0.01 mg/kg
to 5 mg/kg in unpolluted soils, with an average value of .1 mg/kg.
These average values are in close agreemtnt with concentrations found
in various rock types, ranging from .04 mg/kg in granite to 0.12 mg/kg
in gabbro (Boyle 1968). Though these are typical levels, silver-rich
deposits can have concentrations reaching over 1000 mg/kg (Smith and
Carson 1977).
In the humus of a birch forest, Vinogradov's (1959) soil samples
indicated that humus can accumulate concentrations of silver much higher
than levels in the underlying rock formation. He reported a level of
5.0 mg/kg. Mitchell (1955) reported generally lower levels than these
in mineral soils, 0.1-1 mg/kg, but also reported a maximum of 7.0 mg/kg.
IV-57
-------
TABLE 37. SILVER CONCENTRATIONS DETECTED IN SOIL
1000
5.0
0.1-1
0.37
0.19
0.-13
0.'29
0.247
0.272
30
25
130
190
100
0.01-5
max 7.0
Reference
Smith and Carson (1977)
Smith and Carson (1977)
Taylor (1964)
Boyle (1968)
Boyle (1968)
Smith and Carson (J.977)
Boyle (1968)
Vinogrado (1959)
Mitchell (1955)
Klein (1972)
Klein (1972)
Klein (1972)
Klein (1972)
Klein and Russell (1973)
Klein and Russell (1973)
Smith and Carson (1977)
max 1000 Smith and Carson (1977)
16-44 (dry weight) Fortescue £t al. (1975)
Law (1978)
Ruttermore et, al. (1972)
Wilson and Akers (1970)
-------
Klein (1972) did a detailed study of silver in different urban
land use areas of Grand Rapid, Michigan. The industrial classification
included all land up to 1 mile beyond the land actually devoted to
industrial use, agricultural land was soil used exclusively for agri-
culture, and residential land was primarily unimproved woodlands and
low-density residential areas. Samples were taken from the top 2 in. of
.of the soil and at least 30 ft from any road. Industrial soils (0.37mg/kg
contained levels twice those of the agricultural areas (0.19 mg/kg)
and three times the levels found in residential areas (0.13 mg/kg).
Airport levels (0.29 mg/kg) fell between the industrial and agricultural
levels. Elevated levels in the agricultural soils may in part be the
result of the silver content in fertilizers, which typically ranges from
a trace amount (30 mg/kg in super phosphate) to as hish as 1000 out/kg in
phosphate rock (Smith and Carson 1977).
Sludge from waste treatment plants is often used for landfill or
soil amendment. The silver content of sludge collected from the Niagara
Peninsula of Ontario sewage treatment plants-ranged from 16 mg/kg to
44 mg/kg, with an average value of 25 mg/kg (dry weight) (Fortescue e£
al. 1975). Law (1978) examined silver content in municipal incinerator
fly ash destined for a landfill in Alexandria, Virginia. He reported a
level of 130 mg/kg, comparable to levels in Washington, D.C. fly ash of
190 mg/kg (Buttermore =et al.1972) and 100 mg/kg (Wilson and Akers
1970).
i
F. SUMMARY
1. Physical and Chemical Properties
Silver is characterized by the low aqueous solubility of most of its
compounds, a low elemental vapor pressure, and few physico-chemical
resemblances to other metals commonly found in the environment. The most
prevalent oxidation state is Ag(I). Silver can serve as a catalyst for
oxidation reactions involving other substances. Numerous silver com-
pounds exist including halides, cyanides, hydroxide, carbonate, and sulfur-
containing compounds. Most are relatively insoluble, with the exception of
silver nitrate, chlorate and perchlorate. Environmental mobility of
silver may be increased, however, by its propensity to form complexes,
primarily halides, cyanides, amines, and thiosulfate. Organo-silver
compounds derived from unsaturated hydrocarbons are also found in the
environment.
2. Fate and Distribution in the Environment
The typical fate and distribution of silver following release to
the environment can be characterized by one of four source-dependent
pathways: atmospheric emissions (accounting for 6% of total man-made
releases), land disposal of solid waste including mine tailings
(77%), aquatic discharges to surface water (10%) and aquatic discharges
to Publicly Owned Treatment Works (POTWs) (7%).
IV-59
-------
a. Atmosphere
Atmospheric emissions originate from smelting activities, inad-
vertent releases (fuel combustion, steel manufacturing, etc.), and
certain silver-consuming industries. Particles of less than 20 ur..
diameter (from smelting and combustion) will be widely dispersed in the
atmosphere in the form of oxides, sulphides, sulphates and chlorides,
eventually reaching land and water via rainout and dry deposition.
Particulates larger than 20 urn in diameter (from smelters) are likely
to settle out within 1 km of the source of emission. The form of silver
in these particulates is expected to be the same as in the ore under-
going smelting.
Low levels of silver are commonly present in air in both urban and
rural regions, generally at less than*5 ng/m3. Levels are not notably
higher than ambient levels in the vicinity of potential silver sources
such as coal-fired steam plants or mills and smelters. Relatively
high levels of up to 36.5 ng/m were detected near a smelter processing
lead known to contain high silver concentrations. Weather modification
activities do not appear to increase air silver levels much above levels
in unseeded air.
b. Land
Land disposal of silver occurs in the form of spent tailings, coal
pile stocks and municipal waste including solid waste from certain
silver-consuming industries. Acid mine drainage does not appear to be
an important contributor of silver releases. Once in the soil, the
element is relatively immobile, with little potential for leaching into
ground water. Because silver accumulates in the upper soil layer follow-
ing soil surface application or disposal, it may be transported to water
through runoff erosion.
Silver concentrations in soil are most commonly derived from parent
rock rather than cultural sources. Typical ambient levels reflect the
substrate concentration and thus are variable, ranging from 0.02 mg/kg
to as high as 1000 mg/kg. An average natural background level is
approximately 0.1 mg/kg to 0.2 mg/kg. Silver in sludge or other wastes
being disposed of on land is at concentrations as high as 900 mg/kg,
although a more typical level is 100 mg/kg; no information was available
on levels at landfill sites following incorporation of the waste.
Little information was available on tissue levels of silver in
terrestrial animals; the highest level reported was 2.0 mg/kg in ducks.
In higher organisms concentrations are expected to be low due to the low
efficiency of gastrointestinal absorption.
IV-60
-------
Background concentrations of silver in terrestrial plants ranged
from 0.02 mg/kg in alfalfa tops to 5.5 ing/kg in mushroom caps. Experi-
mental data indicate that silver may be accumulated at concentrations
as high as 1,760 mg/kg' in bush beans exposed to 10-5 M AgN03 for 13
days. In most cases, however, accumulation is not so extreme. Specific
food crops with reported silver residues include whole wheat (0.4 mg/kg),
wheat germ (0.8 mg/kg), tea (2 mg/kg), and fruits and nuts (up to 1 mg/kg)
Although data on accumulation of silver in terrestrial organisms
are limited, silver does not appear to have a strong potential for bio-
magnification in terrestrial food chains.
c. Water
Aquatic discharge of silver is practiced by the photographic indus-
try, both in production and development, by smelters and by electroplaters
at low levels. Most companies practice in-house recovery techniques, using
precipitation, ion exchange, electrolytic recovery, and/or reductive
exchange. Fifty percent of the photographic producers discharge
to POTWs. Amateur photographers discharge untreated wastes, primarily
to POTWs; however, the total amount is small. In surface water, the
fate of the discharged silver is dependent on its form. Thiosulfate
silver complexes, which are the primary form released by the photo-
graphic industry, are degraded slowly and then precipitated as a
halide or sulfide. The distribution of silver ions between the ionic
form and complexes is dependent upon pH, redox potential, and the concen-
tration of complexing agents present. According to the results of a chemical
speciation model, AgClj is the most prominent form in marine waters,
with only negligible amounts of the ionic form. In freshwater in the
presence of sulfur, AgHS predominates, especially in areas of low salt
concentrations. In freshwater streams, approximately 10% of the total
load of silver is found in suspended sediment. In the vicinity of
sources, silver is accumulated in the bottom sediment, expecially in
the surface layer.
Monitoring data for total silver levels in surface water indicate
typical annual mean concentrations of less than 10 ug/1 for individual
river basins and nationally. Regions with higher than average concen-
trations include the North Atlantic, South Atlantic, and North Missis-
sippi River basins. Silver concentrations in well water averaged
14 ug/1, with a high of 30 ug/1. Samples from mining areas revealed
concentrations even lower than the national average.
Sediment levels of silver in surface water usually range from 1 mg/
kg to 10 mg/kg, with a high of 95 mg/kg; sediment concentrations are
usually two to three orders of magnitude above water levels. In
suspended matter in rivers, silver concentrations ranged usually from
0.4 ug/1 to 15 mg/1 in 1967; more recent data indicate that levels
were usually less than 0.06 mg/1. Levels to surface waters in
IV-61
-------
effluent industrial wastewater, and sewage treatment discharges are
generally less than 20 tig/I (mean values), with a maximum of 730 ug/1.
Most 'laboratory studies of the accumulation of silver by aquatic
biota are for freshwater fish. However, some data are available on
the levels of silver present in samples of marine species as'well as
the levels detected in the same species, from polluted versus unpolluted
sites.
The internal organs of largemouth bass are reported to accumulate
0.6 mg/kg silver, whereas the bone of cut-throat trout contained up to
4.4 mg/kg silver. The mean concentration of silver in fish from U.S.
river basins according to STORE! is 0.235 mg/kg, with a range of 0.004
to 1.9 mg/kg. Other studies report levels up to 9 mg/kg (in shellfish).
In general, however, concentrations rarely exceed 1.0 mg/kg in
marine and freshwa'ter fish and invertebrates. Reported bioconcentration
factors (tissue levels/water levels) range from 2.4 to 333 for various
freshwater fish species. Marine species have a greater tendency to
accumulate silver, and have been reported to accumulate silver to levels
that are 3300 times the concentration in surrounding seawater. (Oyster
gills from a polluted site contained 189 mg/kg silver.)
Silver residues of 0.01-0.48 mg/kg have been reported for vascular
marine plants, while 0.2-0.8 mg/kg has been reported for algae species.
Freshwater plants have been reported to contain up to 0.026 mg/kg silver.
Both marine and freshwater plants have been reported to concentrate silver
by factors of up to 200.
Bacteria were reported to accumulate 182,000 mg/kg silver from
solution. The environmental parameters affecting the bioaccumulation
of silver include temperature, oxygen concentration, pH, water hardness,
the presence or absence of other cations, and soil organic matter content.
Aquatic organisms have a greater potential for bioaccumulation of
silver than terrestrial organisms due to a greater potential for exposure.
However, due to the generally low rates of absorption in most species,
bioaccumulation is not expected to be significant. Seaducks, a species
at a high level in the aquatic food chain, were observed to accumulate
silver to levels one order of magnitude greater than the level in their
food.
d. POTWs
In POTWs treatment techniques such as lime and settling, activated
carbon, and cation-exchange are over 90% effective in removing silver
from influents. In most POTWs, however, the latter two techniques are not
used. In facilities utilizing more conventional technology, 75% of the
silver is partitioned into the sludge at concentrations on the order of
100 mg/kg or greater. These levels are not expected to affect microbial
activity in activated sludge.
IV-62
-------
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*
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IV-67
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IV-68
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IV-70
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CHAPTER V.
EXPOSURE AND EFFECTS—BIOTA
A. EXPOSURE OF BIOTA
1. Introduction
Fish and wildlife are exposed to low-level natural background con-
centrations of silver present in environmental media, as well as to
higher concentrations near anthropogenic sources of silver. A major
portion of the total silver discharge is to land (79%) (Chapter III).
Although the amount released to water and POTW's is low (17%), there is
always potential for transfer of silver between soil and water through
sediment transport, in addition to accidental discharges to water due
to spills or leaks. The following section discusses the potential for
exposure of aquatic organisms, terrestrial plants, and microbial systems
to silver, both in general and in the vicinity of specific sources of
silver releases.
To understand the contribution of human activity to silver exposure
levels in soil and water, it is important to account for the natural
background levels of the metal in these media. Silver is present in
different types of parent material at low concentrations, approximately
0.05 mg/kg to 0.7 mg/kg (Lisk 1972). Typical soil levels vary between
0.1 mg/kg and 100 mg/kg, depending on local site characteristics (e.g.
composition of parent material, source of organic matter, degree of
weakening). In freshwater, silver levels vary from non-detectable to
38 ug/1 with an estimated average of 0.24 ug/1 (Boyle 1968). Background
levels are discussed in greater detail in Section IV-B. Although a
considerable degree of variability exists in soil and water background
levels, few studies of anthropogenic silver contamination make a point
of estimating and subtracting the background levels from the total
measured level. As a result, an overestimation of industrial or other
anthropogenic contributions of silver to a specific location may occur.
The following discussion is divided into exposure categories relat-
ing to mode of exposure and specific silver sources:
(1) Surface water - exposure of aquatic systems;
(2) Exposure due to weather modification activity;
(3) Exposure due to land disposal of solid waste containing
silver; and
(4) Exposure of waste water treatment populations.
Since releases of silver to the atmosphere are less than 5% of total dis-
charges, the exposure of biota to silver in air is expected to be minimal
and has not been considered.
V-l
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2. Aquatic Systems Exposed to Surface Water
a. Exposure Levels - Monitoring Data
Between 1970 and 1979, the mean concentration of silver in 15,610
observations regarding surface water in all major river basins ranged
from 1.0 ug/1 to 9.0 ug/1 (Chapter IV.E). The variation in mean con-
centrations among river basins is low; the major river basins with the
highest levels were the Northeast, California, Western Gulf, and the
Ohio River and Tennessee River. Only for 'the Northeast basin were high
concentrations (>0.05 mg/1) reported for more than 1 year. Concentra-
tions decreased between 1970 and 1979 in most river basins; the excep-
tions were the North Atlantic, Southeast, and Lower Mississippi basins.
Even with increases in levels of silver, the annual mean concentrations
in these basins did not exceed 0.05 mg/1.
•
Another method of interpreting the STORE! data considers what per-
centage of the total number of observations fall within the various seg-
ments of the entire range in measured concentrations. Tables 29-30
(in Chapter IV-e) present these data for the years 1970-1979 for the
entire U.S. and for each major river basin. For the years 1975-1979 and
all river basins, 59% of all concentrations observed were < 0.10 ug/1,
10% ranged from 0.11 ug/1 to 1.0 us/1, 20% were between 1.1 ug/1 and
10 ug/1, and 11% were greater than 10.1 ug/1 (Table 38). Individual
river basins in which the distribution of observations was weighted
toward the high end of the concentration range were the Southeast, Ohio
River, Lake Erie, California and the Western Gulf Basins.
b. Sources of Silver Releases to Surface Waters
According to the materials balance data (Chapter III), the photo-
graphic industry (photo equipment producers, professional photoprocessors
and amateur photographers) is responsible for the majority of the known
annual aquatic discharge of silver. Each subcategory has its own charac-
teristic discharge practices. For example, producers discharge comparable
amounts of silver to both POTW's and surface water; photoprocessors and
amateurs are expected to discharge primarily to POTW's.
Although other industries are responsible for minor releases in
terms of the national mass balance of silver, small discharges can
nevertheless be responsible for significant exposure levels on a local
scale. For this reason, the contribution of selected industries to
aquatic exposure is discussed in the following section. The relative
importance of these sources can be better understood by examination of
materials balance/effluent guidelines data, qualitative information on
industrial processes, and field studies of local impact. Industries
that discharge directly to POTW's are considered in a later section on
exposure of wastewater treatment populations (V.A.5).
V-2
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TABLE 38. DISTRIBUTION OF UNREMARKED OBSERVATIONS
FOR SILVER CONCENTRATIONS IN MAJOR RIVER
BASINS, 1975-1979 (ug/1)
Major River Basin
Northeast
North Atlantic
Southeast
Tennessee River
Ohio River
Lake Erie
Upper Mississippi
River
Lake Michigan
Missouri River
S. Central Lower
Mississippi River
Colorado River
Western Gulf
Pacific Northwest
California
Great Basin
Lake Huron
Lake Superior
TOTAL
Percentage of Total
-
321
594
492
' 70
491
135
633
137
1308
767
983
360
371
137
228
27
37
7091
59
0.10
(88)
(65)
(78)
(42)
(35)
(36)
(89)
(71)
(68)
(34)
(84)
(68)
(73)
(46)
(60)
(45)
(76)
0.11-1
29
102
54
61
70
6
38
34
331
278
64
44
70
21
26
6
6
1240
10
(8)
(11)
(9)
(37)
(5)
(2)
(5)
(18)
(17)
(12)
(5)
(8)
(14)
(7)
(7)
(10)
(12)
1.1-10
8
125
12
22
447
29
34
19
245
1081
94
63
57
92
89
27
5
2449
20
(2)
(14)
(2)
(13)
(32)
(8)
(5)
(10)
(13)
(48)
(8)
(12)
(11)
(31)
(23)
C45)
(10)
10.1-100
7
96
76
14
404
206
6
2
38
133
28
64
7
46
25
1
1153
10
(2)
(10)
(12)
(8)
(29)
(55)
(1)
(1)
(2)
(6)
(2)
(12)
(1)
(15)
(7)
(2)
>100 Total
365
2 919
634
167
4 1416
376
3 714
192
1922
6 2265
2 1171
2 533
505
3 (1) 299
12 (3) 380
60
49
34 11967
1
Source: STORET Water Quality Control Information System.
V-3
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i. Photography
According Co the Materials Balance (Chapter III), approximately SO kkg
of silver is discharged directly to surface water by producers of photo-
graphic equipment. Other categories are assumed to discharge primarily
to POTW's. The discharge estimate is based on raw wastewater concentra-
tions assuming no treatment. The highest concentration was for the silver
halide subcategory with a mean of 14 mg/1 and a maximum of 37 mg/1. The
forms of silver released for all subcategories are either silver halide
complexes or thiosulfates.
No field studies were available which concerned the impact of photo-
graphic discharge on aquatic systems. Therefore, the relationship between
aquatic exposure and this industry is not well understood. Certain factors,
however, are likely to reduce potential exposure levels. Since the re-
covery of silver is cost-effective for the photographic industry and effec-
tive recovery techniques are available (U.S. EPA 1980), it is expected
that the raw wastewater levels would be reduced significantly before dis-
charge in the plant effluent. Additionally, the forms discharged are
relatively insoluble. The compounds, therefore, would either form complexes
and/or end up in the sediment, reducing the biological availability of
the silver (Chapter IV-C).
ii. Electroplating
Although electroplaters consume a relatively small amount of the
silver produced each year (4,5%) and are responsible for minor aquatic
discharged on a national level, the industry may have local impacts on
aquatic systems, at least in terms of accumulation. No information was
available on electroplaters who use silver; however, elevated concentra-
tions of silver (up to 15.3 mg/kg dry weight) were reported in the surficial
sediment in the vicinity of an electroplating facility located on a bay
in Rhode Island (Eisler et al. 1977). Other metals such as chromium,
copper, lead, and zinc were present at concentrations one or two orders
of magnitude higher than silver levels. At the same site, following the
plant's closure, samples of clam tissue were found to contain 1.16-4.64
mg/kg silver (dry weight), as well as other metals; all levels were
significantly higher than those in control samples (Eisler et al. 1977)
and indicated the presence of silver even after the discharge has ceased.
If the availability of the form of silver is negligible at high salinity
levels as indicated in the model of Jenne et al. (1980) , then much of the
silver release from electroplating operations would also not be available
for uptake by aquatic species.
iii. Mining and Milling
In mining wastes, silver is found at concentrations one to two orders
of magnitude below the concentrations of zinc, copper, cadmium, and other
metals. This is at least partially explained by the fact that more effort
is spent in recovering silver from these wastes due to economic incentives.
Therefore, although silver is generally more toxic than most other metals,
it is found in mining wastes in conjunction with relatively larger concentra-
tions of other metals and thus is probably a minor contributor to the
-------
toxicologic characteristics of the wastes. Total discharges of silver to
water from mining operations are expected to be negligible (<1 kkg) due to
recovery practices and the low initial silver concentrations (Chapter III).
Most of the silver mining activity is concentrated in the Coeur
D'Alene river basin in Idaho (River Basin No. 13). Unlike the data for
copper, the STORE! data base does not report higher than average silver
concentrations for surface water in this river basin. In addition, the
mean concentration of silver in this basin has decreased by nearly 100%
between the 5-year periods 1970-1974 and 1975-1979 (Figure 16). This may
be the result of averaging levels for areas of the basin in which no min-
ing occurs or the low discharge rates associated with mining and milling.
Aggregate data for a major river basin reveal only the most obvious overall
trends in the distribution of pollutant concentrations.
In a risk assessment for copper (Perwak et al. 1980), more in-depth
investigation of the Coeur D'Alene area revealed that the surface waters
were relatively soft (<50 mg/1 CaCO-), the pH was between 5.0 and 7.0,
and the concentration of complexing agents was expected to be low. The
combined effect of these factors would favor the soluble form of all
metals, including silver. Some areas of the basin, notably the South
Fork,* were obviously very toxic to aquatic life; however, the presence
of extremely high concentrations of other metals (zinc at up to 5000 ug/1,
cadmium at 25 ug/1, silver was not reported) would implicate these metals
or the combined effects of all of the metals present as the cause of
toxicity rather than the probably low levels of silver. Unfortunately,
minor river basin data were not available to determine the silver con-
centrations at individual sampling stations.
In conclusion, an area of high mining activity with environmental
characteristics conducive to metal toxicity was found to have localized
areas with potentially toxic concentrations. Either seasonally (during
periods of dilution) or for short-term exposures,these concentrations
did not elicit toxic effects in aquatic basins. The concentrations of
other metals, in the Coeur D'Alene basin and in all mining areas, are so
great that the contribution of silver to the overall toxicity is expected
to be overshadowed by and indistinguishable from the effects of other
metals.
3. Weather Modification
Cloud seeding activity has decreased on a nationwide basis largely
because of mixed results of early experiences. Issues associated with
the practice include liability for "stealing" someone else's rain;
liability for producing rain in areas that do not want it; and reduced
availability of federal funding. Small applications by Independent
operators are continuing, but the scale is reduced from that of the
Federal programs several years ago.
The recent sharp increases in the price of silver has made the use
of silver in cloud-seeding operations less cost-effective than the
available substitutes. Compared with other agents, the principal ad-
vantage of silver iodide is its ability to induce ice crystal formation
at high temperatures. Because of its chemical properties, Agl can be
finely subdivided; this enhances- its ability to disperse, which increases
V-5
-------
potential for initiating crystallization. Several organic compounds
(phioroglucinol, 1,5-dihydroxynaphthalene and metaldehyde) have been
suggested as alternative cloud-seeding agents. They induce crystal-
lization at higher temperatures than Agl but are not as efficiently dis-
persed from ground generators (Cooper and Jolly 1970). Several factors
point to a decline in the use of silver iodide. Advances in weather
modification indicate a greater reliance on pyrotechnic devices, air-
craft, and other aerial delivery systems that do not require Agl, and
less reliance on ground generators.
Thus, weather modification activity has decreased and the applica-
tion of silver iodide is also declining. The danger of silver in this
application is not expected to be sufficient to warrant significant
concern for exposure of most natural populations. Microorganisms,
however, are more likely to be affected than other species so that exposure
levels resulting from weather modification warrant further consideration.
A three-year study of a large area in the San Juan Mountains undergoing
weather modification reported no significant increases in silver levels in
different media (Teller et al. 1976). It is often not possible to dis-
tinguish the silver resulting from modification from natural background
levels (Klein 1978). The possibility of greater Ag accumulation in
another habitat, however, cannot be discounted due to the number of
variables which determine silver concentrations in soil.
A worst case example of silver effects resulting from weather modi-
fication activity is illustrated in a field study investigating the re-
lationship between silver concentrations in the soil surrounding a cloud-
seeding generator and its effects on microbial activity (Sokol and Klein
1975). Concentrations as. high as 1400 ug/g soil (ash) were detected
within 50 m of the generator, primarily in the top 2 cm of soil. An
apparent decrease in organic matter turnover rate was associated with
the high silver levels as well as a higher soil water content, lower pH,
higher respiration rates (six times greater than the control), and
slightly higher microbial populations.
In conclusion, weather modification activities probably do not
result in significant exposure levels for natural populations or micro-
organisms. Areas exposed to such high silver concentrations, such as
near generators, are very few and, due to the immobility of silver in
soil, are contained and have little likely impact on surrounding areas.
4. Land Disposal of Silver Waste
A major portion of all silver releases to the environment are made
directly to land. Waste is applied in the form of industrial sludges
from wastewater treatment, solid waste (in junked steel scrap, home
appliances) and in sludges from POTW's. An estimated 370-520 kkg silver is
applied to landfill in solid form each year, with up to 220 kkg in POTW
sludge. Other sources of silver to land include leaching of tailings
ponds, spills from tailings ponds, and industrial waste holding lagoons
(Smith and Carson 1977); however, the amounts released from these sources
are expected to be small.
V-6
-------
The type of silver product or the chemical form released to the
environment will determine its mobility. Silver in solid wastes is
inert and virtually immobile. The behavior of silver in sludge applied
to a disposal site depends on sludge and site characteristics. Most
forms of silver are insoluble salts (chlorides, hydrous oxides, halides),
which would be immobilized by precipitation. In the presence of organic
matter, complexation and/or adsorption will occur. In addition, the
inorganic fraction of the soil will also readily adsorb silver. Certain
site characteristics (e.g., sandy, low organic soils, low pH, immediate
proximity of water table) may support movement of silver out of a con-
tainment area, but these opportunities are expected to be few. 'In
general, silver remains on the top 2 cm of soil. Certain disposal
practices (e.g., in a liquid form into a holding lagoon) have a higher
potential for releasing silver from the disposal site, especially if
the metal is suspended or dissolved in liquid. Again, however,
following a spill, the surrounding soil would be expected to retain the
metal and it is unlikely it would move into ground water or nearby
surface water.
Several activities may lead to high silver exposure levels in soil.
Weather modification activities, as described previously, are a potential
source of higher than background levels of silver in soil although the
induced concentrations appear to be low. Land application of sludge
from wastewater treatment facilities may expose microbial populations
to high silver levels in soil. Sludge contains silver at levels as
high as 900 mg/kg, although more commonly at 100 mg/kg (Smith and
Carson 1977); however, these levels are approximately an order of magni-
tude below the soil concentrations surrounding the cloud-seeding appara-
tus and would be further diluted by incorporation into soil before
exposure of microbial populations. Much of the silver present in sludge
is apparently recovered and recycled before the material is disposed of
on land. In addition, disposal is usually limited to controlled waste
disposal sites where there would be little potential for interference
with natural microbial processes. Other reported soil concentrations,
either background levels or those near indirect sources (Chapter IV-E),
are significantly lower than the levels reported previously, averaging
0.37 mg/kg in industrial areas and 0.19 mg/kg in agricultural areas.
No information was available on silver levels in mining areas.
In conclusion, it appears unlikely that silver in soil will reach
significant levels except in the immediate vicinity of a silver source.
Under conditions of continual release, significant levels may accumulate
due to silver's immobility (Chapter IV-C). At this time, however,
no such situation is known.
5. Sources of Silver to Wastewater Treatment Systems
There has been speculation that silver may interfere with micro-
bial processes in wastewater treatment due to its known microbiocidal
effects at low concentrations. Typical ambient concentrations of silver
in surface waters are lower than those triggering effects (Chapter IV-C);
V-7
-------
however, In Che vicinity of certain sources, discharges of silver at
high concentrations and/or on a continuous basis could affect sewage
treatment processes.
Amost all amateur photographers, photoprocessors, and certain
photographic equipment producers discharge their effluents directly to
POTW's. Silver is usually released in the form of halide complexes or
thiosulfate which would partition into the sludge (Chapter IV-C). Concentra-
tions of up to 5 mg/1 in photoprocessing water were followed through waste-
water treatment and found to have no adverse effect on biological activity
(Bard et al. 1976). Typical concentrations of silver in photoprocessing
effluents are expected to be lower; for example, 0.28 mg Agl was detected
in a sewage influent originating from a process plant (Bard et al. 1976).
Home photographers for the most part do not practice silver recovery for
their wastewater. Ag concentrations are on the order of 12g/l in raw
waste, but the waste is diluted when poured down the sink (see Section III).
Home photographers are widely distributed and discharge intermittently a
total annual release of approximately 15 kkg. They are thus expected to
have a minimal impact on microbial processes on a national scale. No
information was available on POTW influent concentrations from other
dischargers.
B. EFFECTS ON BIOTA
1. Introduction
•Before low doses of silver can be toxic to biota, the ionic form of
the metal must come into direct contact with metabolically active sites,
such as cell membranes of microorganisms or the gas exchange surfaces
of fish gills. The solubility of many silver salts is low making these
compounds less accessible for biological uptake. AgNOs is quite soluble
and therefore is commonly used in laboratory studies. Silver is general-
ly considered to be more toxic to aquatic life than mercury (Phillips
and Russo 1978).
In studies of the pollutants to aquatic organisms, a certain amount
of inconsistency in bioassay results may be expected, owing to several
factors. Static toxicity tests are designed to simulate the aquatic
environment of a standing or slowly flowing body of water that has re-
ceived a single discharge of toxicant. In a continuous-flow bioassay,
toxicant concentrations are maintained by repeated addition of the toxic
substance, thus simulating a constant, chronic exposure such as might
be found near an industrial site. In both types of experiments, the
toxicant concentrations are often determined nominally (i.e., by diluting
a measured amount of the substance), and may not be directly monitored
during the test. Nominal determination of silver concentrations does
not account for absorption and metabolism by test organisms, absorp-
tion onto particles and test tank walls, or for complex formation when
complexing agents are present, and so nay result in less accurate
estimations of lethal and sublethal levels. Consequently, a
V-8
-------
wide discrepancies may appear between the results of a static nominal
bioassay and those of a continuous-flow test in which the toxicant con-
centrations were measured during the exposure period.
2. Freshwater Organisms
a. Acute Toxicity
Table 39 summarizes selected data on the acute effects of various
concentrations of silver on freshwater vertebrate species. The values
lethal to 50% of the test population (LC^'s) depend upon the species
and the particular conditions of the laboratory experiment (e.g., water
hardness and temperature). The mean 96-hour LC-Q of silver for rainbow
trout was 6.5 ug/1 and 13.0 ug/1 in soft and hard water, respectively
(Davies et al. 1978). Rainbow trout are considered to be one of the
species of fish most sensitive to heavy metals (Davies 1975). The range
of silver concentrations observed to cause mortality was from 4.3 ug/1
(guppies) to 100 ug/1 (sticklebacks).
Silver is believed to interfere with gas exchange in the gills of
fish, but the mechanism is not understood. Some investigators suggest
that silver in a dilute- solution causes secretions of mucus in
the gill, filling the interlamellar spaces to the point that normal
movement of the gill filaments becomes impossible. Since this prevents
the contact between water and gill tissues that is necessary for oxygen
uptake, the fish die of suffocation. Other investigators believe that
the mode of action involves the swelling and breakdown of gill epithelium,
perhaps through the blocking of enzymes. Because low Ag concentrations
often are lethal to fish, the second hypothesis is thought to be more
likely.
Table 40 summarizes data concerning the acute effects of silver
on other freshwater species. Concentrations as low as 1.5 ug/1 have
acute effects on Daphnia magna. A concentration of 6.0 ug/1 was reported
to kill Escherichia coli in 2-24 hours (Cooper and Jolly 1970).
b. Chronic and Sublethal Toxicity
Table 41 summarizes the chronic and sublethal effects of silver
on freshwater vertebrates. The chronic "no effects" concentration for
silver was determined to be between 0.09 ug/1 and 0.17 ug/1 based on 18
months' exposure in soft water. This concentration defines the level
exerting no obvious effect, but does not account for possible reductions
in spawning behavior or reproduction because the study was terminated
before the female rainbow trout reached sexual maturity of 3 years.
Silver concentrations of 0.17 ug/1 or greater reduced egg hatching
success and the growth rate in fry (Davies et al. 1978).
Coleman and Cearley (1974) found that the rate of weight gain of
blue gill and large-mouth bass exposed to silver decreased slightly (not
significantly) as the concentration increased. These authors mentioned
V-9
-------
TABLE 39. ACUTE EFFECTS OF SILVER ON FRESHWATER VERTEBRATES
Silver
Concentration
70
100
Species
Effect
Water Hardness
(me/1 CaCO,)
Reference
4.3
6.5
10
13
28.8
25
64
Guppy
(Puecilia retlculata)
Rainbow trout
(Salmo gairdneri)
Stickleback
(Casterosteua aculeatus)
Rainbow trout
(Salmo gairdneri)
Rainbow trout
2 months old
Chinook salmon fry
(Oncorhynchus tshawytscha)
Fathead minnow
(Pimephales
promelaa)
LC50
LC50
(96 hours)
Death in 96 hours
LC50
(96 hours)
LC50
(96 hours)
Majority killed
in 48 hours
60% mortality
in 96 hours
J
Flow through,
soft water (26)
pH 6-6.81 very
soft water (1)
Flow through,
hard water (350)
Flow through,
tested 5-80 ug/1
Tap water
Soft water (49)
Smith and Carson (1977)
Davies (1978)
Jones (1964)
Davies (1978)
Hale (1977)
Marsh and Robinson (1980)
Terharr et^ al.
(1972)
Bass
(no species given)
Stickleback
(Gasterosteus aculeatus)
Death in 24 hours
Death in 24 hours
Moderately hard
(180)
15-18°C,soft
water (1)
Coleman and Cearley (1974)
Doudoroff and Katz (1953)
-------
TABLE 40. ACUTE EFFECTS OF SILVER ON FRESHWATER INVERTEBRATES
Ag
Concentration
(ug/1)
Species
Conditions
Effects
Reference
.001-500
1.5
15.0
30.
30.
1000
1400
Bacteria
Daphnia magna
Cladoceran
Polycelis nigra
flatworm
Daphnia magna
Microregma
Water-snail
Australorbis
Glabratus
Philodina
•
Static soft
water (40 mg
. CaC03/l)
4 days at 23-
27"C
4 days a5 23-
27°C
4 days at 23-
27°C
In distilled
water
Static
Bacteria killed
(water sterilized)
LC . (48 hours)
Death
Death threshold
toxicity concen-
tration
Death
Fatal in 24 hours
96-hour LC
U.S. EPA (1979)
U.S. EPA (1979)
McKee (1963)
McKee and Wolf (1963)
McKee and Wolf (1963)
Harry and Aid rich (1958
Buikema et al. (1974)
acuticornis
Rotifer
-------
TABLE 41. CHRONIC AND SUBI.ETHAL EFFECTS OF SILVER ON FRESHWATER FISH
t-*
10
Ag
Concen-
tration
(ufi/1)
0.09
0.07-.13
0.17
0.2-0.8
0.6
0.88
Species
Compound
Conditions
Effects
Reference
Rainbow trout
(Salmo gairdneri) AgNO-
Silver nitrate 18 months: soft water No mortality due to silver Davies elt al. (1978)
Rainbow trout
Agl
Rainbow trout Silver nitrate
(Salmo gairdneri) AgNO
Rainbow trout Silver nitrate
(Salmo gairdneri) AgNO-
Rainbow trout
(embryo-larval)
'3
Silver
Goldfish Silver
(embryo-larval)
(Carassius auratus)
Rainbow trout Agl
(Salmo gairdneri)
1 year
18 months: soft water
18 months: soft water
28 mg CaC03/l
Static: 28 days (ferti-
lization to posthatch-
ing). Hard water (195
mg CaC03/l)
7 days (fertilization
to posthatching. Hard
water (195 mg CaCO /I)
6 weeks: soft water.
15 mg CaC03/l pll 6.5-6.8
Stickleback
(Gasterosteus
aculeatus)
Stickleback
Silver nitrate large fish, soft water
Silver nitrate
7 days: soft water
(1 mg Ca)
No effects
17.2% more mortality than
control
Premature hatching of eggs;
Reduced growth rate in try
Threshold value (LC )
Threshold value (LC )
94% of fish died.
delayed fry swim-up by 2
weeks, retarded growth
Lethal concentration limit:
survival time equals that
of control (10 days)
Death of fish
Davies (1975)
Davies e£ al_. (1978)
Davies et al.. (1977)
Birge et. al. (1979)
Birge e£ al,. (1979)
Davies (1975)
Davies et_ al. (1978)
Duodoroff and Katz
(1953)
-------
TABLE 41. CHRONIC AND SUBLETHAL EFFECTS OF SILVER ON FRESHWATER FISH (Continued)
AS
Concen-
tration
(UR/1)
10
30
70
Species
Rainbow trout
(embryo-larval
stages)
Goldfish
(embryo-larval
stages)
Compound
Conditions
Silver
Silver
Blueglll Silver nitrate
(Lepomia macrochirus)
Effects
28 days, hard water LC
7 days, hard water LC
SO
6 months, hard water No lethal effect
Re f erence
Birge et_ al. (1979)
Blrge e^ al^. (1979)
Coleman and Cearley
-------
that metal concentrations having little or no effect on growth
could be deleterious to other physiological functions later in the
life cycle. Bass were reportedly more sensitive to silver than bluegill
(Coleman and Cearley 1974). Adult oysters and-fish are more resistant
than other age classes; e.g., gametes, embryos, and fry (Smith and
Carson 1977).
Table 42 summarizes chronic and sublethal effects of silver on
freshwater invertebrates and other species. A concentration of less than
1 ug/1 silver represents a 14-day LC5(jfor mayflies. Daphnla exposed to
5.1 ug/1 silver in Lake Erie Water at 25°C were immobilized (Cooper and
Jolly 1980). Other species were more resistant to silver.
Table 43 presents the effects of silver on freshwater algae.
These species are generally not as sensitive as bacterial species.
Concentrations of 10-140 ug/1 retarded growth and 2000 ug/1 was toxic
in the species studied.
3. Marine Organisms
a. Acute Toxicity
No information was available on the acute effects of silver for
marine vertebrates. Table 44 summarizes data on the acute effects of
silver for marine invertebrates. The observed LCgg's ranged from
3.7 ug/1 for American oyster to 262 ug/1 for mysld shrimp.
b. Chronic and Sublethal Effects
^^^^^^^^•^^^^^^•^^^•^^^^•"•^•M""^^""^^™^^^^"^^""*^"^^^"^^^"^""""^^™ *
No information was available on the chronic and sublethal effects
of silver on marine vertebrates. Table 45 summarizes data concerning
the chronic and sublethal effects of silver on marine invertebrates.
Observations of abnormal egg development and spawning delays were re-
ported for concentrations of 2-103 ug/1 for echinoderms and shrimp.
Data on the effects of silver on marine algae were limited. A
96-hour ECgg (concentration at which effects are observed in 50% of
test organisms) was reported for the algae Skeletonema costatun at
130 ug/1. The effect was growth inhibition, as reflected by a reduction
in cell number (U.S. EPA 1979).
V-14
-------
TABLE 42. CHRONIC AND SUBLETHAL EFFECTS OF SILVER ON OTHER FRESHWATER SPECIES
Ag
Concen-
tration
Species
Conditions
Effects
Reference
Ui
<1 Mayfly
Emphemerella grandis
10 Narrowraouth-toad
embryo-larval
50-100 Snail
Australorbis glabratus
5.1 Daphnia magna
30
Daphnia magna
14 days, CaCO.
30-70 mg/1
LC
50
7days, hard water LC
24 hours, distilled
water
Lake Erie HO
at 25°C
River Haval in
Germany
50
Distress syndrome.
Snail unable to
attach itself to
substrate .
Immobilized
Threshold toxicity
level
Nehrlng (1976)
Birge et al. .(1979)
Harry and Aldrich (1958)
McK.ee and Wolf (1963)
Bringmann and Kuhn (1959)
-------
TABLE 43. EFFECTS OF SILVER ON FRESHWATER MICROFLORA
Ag
Concentration
(ug/1)
10-60
20
80
UO
Organism
Chlorella vulgaris
Algae (no species given)
Phormidium inundatum
Phormidium inundatum
(blue-green algae found in
swimming pools)
Conditions
Silver nitrate
Silver sulfate
Silver nitrate
Effect
Growth retardation
Average survival
time is 2 days
Prevented growth
Prevented growth
Reference
Hutchinson and Stokes
(1975)
Doudoroff and Katz
(1953)
Smith and Carson (1977)
Fitzgerald (1967)
2,000
6 Algae species
Toxic
Gratteau (1970)
-------
TABLE 44. ACUTE EFFECTS OF SILVER ON MARINE INVERTEBRATES
Ag
Concen-
tration
(ug/1)
0.5
3.0
3.7
6.4
21
33
40
Organism
Conditions
Effects
262
Sea urchin
Arbacia lixula
American oyster
Grassestrea virginica
American oyster
Crassostrea virginica
American oyster
Crassostrea virginica
Hardshell clam
Mercenaria mercenaria
Bay scallop (juvenile)
Argopecten irradians
Killifish (mummichog)
Fundulus heteroclitus
My aid shrimp
Mysidopsls bahla
52-hour exposure
Embryo: (this is
background cone.
In seawater)
Embryo 48-hour static
test (5.8 ppb AgNO3)
Embryo 48-hour static
test (10 ppb AgNO-j)
Embryo 48-hour static
Static
Reduced egg develop-
ment significantly
LC0 Failure to
develop
LC50
100% mortality
100% mortality
LC
50
Reference
U.S. EPA (1979)
Calabrese et al. (1973)
Calabrese et al. (1973)
Calabrese et al. (1973)
Calabrese et al. (1973)
Nelson (1976)
Ag (Salt), 96 hours Inhibition of 3 liver Jackim and llamlin (1970)
in 20-25°C. deawater enzymes (first step of
toxicity or metabolic
Impairment)
Flow through 96 hours LC,
50
Sosnowski and Gentile
(und.)
-------
TABLE 45. CHRONIC AND SUBLETHAL EFFECTS OF SILVER ON MARINE INVERTEBRATES
i-1
CD
Ag
Concen-
tration
(ug/1)
2
10
10.2
3.3
103
Species • Compound
Echinoderra AgNO
(Paracentrotua)
Echinoderm AgNO_
(Paracentrotua)
Mysid shrimp AgNO
(Mysidopsia bahia)
Mysid shrimp AgNO
(Mysidopsia bahia)
Mysid shrimp AgNO
(Mysidopsia bahia)
Conditions
-
-
58 days
20°C
58 days
20 °C
58 days
20°C
Effects
Delay in 'development and
deformation of plutei
Inhibited and abnormal
development of eggs
No effect on growth,
reproduction, or survival
Delay in spawing time,
smaller brood size
No spawning
Reference
Davies et al. (1978)
Soyer (1963)
U.S. EPA (1979)
U.S. EPA (1979)
U.S. EPA (1979)
-------
~47 Factors~Affecting Toxicity to Aquatic Species
Some of Che parameters that affect aquatic toxicity include water
hardness, temperature, concentration of dissolved oxygen, pH, form
of the silver, other solids present, and fish size and species.
Silver toxicity has been observed to decrease with increases in
water hardness. This is probably the result of increased anion complexa-
tion and precipitation of silver, which reduces the amount available
for uptake (Davies et al. 1978). The effects of silver are also likely
to be greater in pure water than in water that contains appreciable concentra-
tions of other metal ions (Cooper and Jolly 1970). Silver is less toxic
in hard, alkaline waters with pH from 7.5 to 9.5 than at lower pH's
(Smith and Carson 1977).
Smaller fish may be more susceptible to Injury from silver than
are larger fish. This is most likely a consequence of greater respira-
tory and metabolic rates in smaller fish. Long-term exposure may in-
crease the resistance of an aquatic organism to silver (Davies et al.
1978).
5. Terrestrial Organisms
a. Animals
Chronic exposure studies of birds and mammals have revealed effects
of silver including lowered immunological activity, altered membrane
permeability, vascular hypertension, enzyme inhibition, and shortening
of life spans (Smith and Carson 1977).
•
Continued Intake of silver or silver compounds by mammals may cause
an irremediable discoloration of the skin and mucous membranes called
argyria which does not in itself involve other serious effects (Cooper and
Jolly 1970). Silver administered orally to mice has caused ovarian cyto-
pathic effects (Hadek 1966) and in mammals, in general, may cause ventricular
hypertrophy (Olcott 1948).
b. Plants
Table 46 summarizes the effects of silver on terrestrial plants.
Silver is not considered likely to be concentrated to harmful levels
through terrestrial food chains (Cooper and Jolly 1970). Many investi-
gators consider silver to be one of the most toxic heavy metals to fungi,
slime .molds, and bacteria (Cooper and Jolly 1970).
Dilute solutions of silver nitrate have been toxic to wheat and
pea seeds, while 20 mg/1 has seriously injured tomato and snapdragon
seedlings (Smith and Carson 1977). Metallic silver has been noted to
stimulate root growth of watercress, onion and other plants while it
inhibits root growth of tobacco (Smith and Carson 1977). Silver is more
phytotoxic in soils low in organic matter than in soils with high levels
(Romney et al. 1977). Exposure of germinated Pisum seeds to a
V-19
-------
TABLE 46. EFFECTS OF SILVER ON TERRESTRIAL PLANTS
Ag Concentration
•Ln solution fug/I)
4900
9800
20,000
Lupine
Maize
Wheat and Pea
uj-.Lci.ka
Fatal
Fatal
Toxic
Reference
Clark (1899)
Clark (1899)
Smith and Cars
(seeds)
(1977)
TABLE 47. EFFECTS OF SILVER ON MICROORGANISMS
Ag Concentration
(ug/1)
1-1200
6 (AgN03)
35 (Agl)
10
100
Species
Effects
Reference
Bacteria, yeast Death (in 2-24
and fungi (in hours)
water substrate)
Escherichia coli Death (in 2-24
hours)
Escherichia coli Death (in 2-24
hours)
Mycobacterium Completely in-
hibited growth
Arthrobacter Inhibited growth
soil tnicroorgan- (and, therefore,
ism retarded cellu-
lose decomposi-
tion of mud by
10%)
Goetz et al. (1940)
Smith and Carson
(1977)
Smith and Carson
(1977)
Golubovich (1974)
Smith and Carson
(1977)
Unit is ug/g of mud.
V-20
-------
solution with a 0.001 M concentration of silver ions caused chromo-
somal damage in the form of swollen prophase cells (U.S. EPA 1979,
Von Rosen 1954).
Growth for 13 days in a 10~ M solution of AgNOj reduced the yield
of bush beans by 85% (from 1.4 g/plant to 0.21 g/plant) and decreased
the calcium in the leaves by 67%. The result of decreased Ca uptake
may be impaired membrane permeability, resulting in leakiness and in-
creased phytotoxicity (Wallace and Romney 1977, Wallace 1979). Davis
and Beckett (1978) determined a tentative toxicity threshold for ac-
cumulation of silver in young barley tissue. These authors suggested
that accumulation of more than 4.0 ppm silver causes adverse effects on
growth (Davis and Beckett 1978). (Table 28 in Chapter IV identifies
background levels in terrestrial plants).
6. Microorganisms
Silver ion is highly toxic to microorganisms and has been used,
especially in the past, as a microbiocide to sterilize water at con-
centrations of 0.001-500 ug/1 (usually 0.5 ug/1) (Smith and Carson
1977, Cooper and Jolly 1970). In plate culture studies for more acute
exposure, silver ion added as AgN03 inhibited microbial growth at
6 ug/1 and when added as Agl did so at 35 ug/1 (Sokol and Klein 1975).
An anaerobic study of cellulose degradation in mud indicated a 10%
decrease in rate from the control at 100 ug Agl/g (Sokol and Klein
1975). Table 47 summarizes these results of laboratory studies on
silver toxicity to microorganisms.
Under more natural conditions in soil, silver iodide was found
to reduce microbial activity while AgN03 did not under equivalent
conditions. In a field study of silver accumulation and effects
resulting from Agl applied to a grassland system (Klein and Molise
1975), threshold concentrations for decreased breakdown (of glucose)
were measured at 1.0 to 2.0 ug silver/g ash (in soil) with a significant
decrease at greater than 60 ug/g. No effects were observed below
0.6 ug/g. Equivalent tests on silver nitrate showed no effects at
even the higher concentrations though it is a more water soluble
compound than Agl. The authors attributed the greater toxicity of
Agl to its interaction with ammonia, amines, and other compounds
present in soil, substances which would Increase its solubility.
Effects of silver iodide and silver phosphate on the usually more
sensitive anaerobic and aerobic processes of wastewater treatment
microbial populations were Investigated (Castignetti and Klein 1979).
Silver present at concentrations up to 236 ug/1 in culture media had no
significant effect on methanogenesis; in fact, stimulation was observed
at lower concentrations (32-64 ug/1) of silver phosphate. Concentrations
of 500 ug/g of silver in sewage sludge (as Agl-NH, and Ag-Nal) signifi-
V-21
-------
candy reduced methanogenesis. A less common form of silver,
AgI-Ti02, was considerably more toxic, significantly reducing the pro-
cess at 1.0 ug/g (Klein and Giangiordano 1976).
C. SUMMARY
Fish and wildlife are exposed to natural background levels of silver
and also concentrations of cultural origin. The majority of surface
water levels are less than 0.10 ug/1 with approximately 30% between
0.11 ug/1 and 100 ug/1 and less than 1% greater than 100 ug/1. Major
river basins with consistently higher concentrations include the
Southeast, Ohio River, Lake Erie and Western Gulf. The Northeast also
registered occasional individual incident-« Of high concentrations.
Intensive recovery practices are in effect in all large silver-con-
suming industries, due to economic incentives, and usually remove a large
fraction of silver from raw wastewater before discharge. Most of the silver
discharged is believed to either form complexes or to precipitate and
settle into the sediment layer. Silver is present in mining and milling
wastes in conjunction with other metals which occur at higher concentra-
tions and thus tends to exhibit a greater toxicity than for silver alone.
Use of silver as a cloud-seeding agent does not appear to signi-
ficantly increase silver concentrations in treated areas except in the '
immediate vicinity of generators. Soil microorganisms may be exposed to
high silver levels in such locations.
Silver releases to land in most cases do not appear to be associated
with high exposure levels for terrestrial organisms. Silver applied in
sludge is expected to be immobilized in soil and contained at the site
of disposal. Silver released in solid waste form (e.g. old appliances)
is also not expected to be mobile in soil. Under conditions of continual
release high silver levels may accumulate in soil because of the metal's
immobility and inability to be degraded.
The primary known cultural source of silver to POTWs is the photographic
industry. Typical levels in effluents are below concentrations thought
to inhibit activated sludge processes. Amateur photographers may discharge
significant quantities of silver to POTWs in discarded solutions. The
impact of these releases is reduced by dilution in sewers before reaching
the POTW. On a national scale, these releases do not constitute a very
large amount of silver discharge. •
Silver is acutely toxic to aquatic organisms at concentrations
as low as 0.5 ug/1, while chronic and sublethal effects have been
observed upon exposure to 0.2 ug/1.
V-22
-------
The lowest LCeQ reported for freshwater vertebrates, is 4.3 ug/1
(for guppies), while acute effects in freshwater invertebrates have been
recorded at concentrations as low as 1.5 ug/1 for Daphnia magna
(LCso). The threshold level for chronic damage to rainbow trout
gairdneri) is 0.2-0.8 ug/1, while the chronic LCso value for the
embryos of this species is 10 ug/1. Similar concentrations of silver
produce chronic effects in freshwater invertebrates.
No data were available on the acute or chronic effects of silver on
marine vertebrates. Among marine invertebrates, concentration of 0.5 ug/1
produced acute effects in the sea urchin and 2 ug/1 produced chronic
effects in an echinoderm.
Water hardness is an important variable influencing the concentrations
of silver producing acute and chronic effects in aquatic biota. In fact,
the EPA Ambient Water Quality Criterion for protection of freshwater aquatic
life from silver is expressed as a function of water hardness at a par-
ticular location. At hardness of 50, 100 and 200 mg/1 as CaC03 the con-
centration of silver (total) should not exceed 1.2, 4.1 and 13 ug/1,
respectively, at any time. Figure 15 and Appendix B include maps of
locations in the U.S. where violations of the hardness-related water
quality criterion for protection of aquatic life were found.
Data on the effects of silver on terrestrial animals were limited.
Chronic exposure studies for birds and mammals indicate effects that
include ventricular hypertrophy, skin discoloration, lowered immuno-
logical activity, and altered membrane permeability.
Silver concentrations of 4900 ug/1 have been fatal to terrestrial
plants (lupines). Soil organic matter affects the phytotoxicity of
silver.
Microorganisms (bacteria, yeast, and fungi) have been killed in
2-24 hours by silver concentrations as low as 1 ug/1. Silver may be added
to water at levels of 0.5 ug/1 or higher to act as a general bactericide.
The form of silver is an important variable in toxicity. A mixed
population of microorganisms in soil showed a significant reduction in
activity at 60 ug/g of Agl but not at an equivalent concentration of
AgNOs- In sludge populations, microbial activity was reduced following
exposure to silver at levels ranging from 1.0 ug/g up to 500 ug/g,
deoendine on the cnmnnunri. -
V-23
-------
REFERENCES
Anderlini, V. The distribution of heavy metals in the red abalone,
Haliotis rufescens, on the California coast. Arch. Environ. Contain.
ToxLcol. 2(3):253-265, 1974. (As cited by Phillips and Russo 1978)
Bard, C.C.> Murphy, J.J., Stone, D.L., Terhaar, C.J. Silver in photo
processing effluents. J. Water Poll. Control Fed. 48(2), 1976.
Birge, W.J.; Black, J.A.; Westerman, A.G.. Evaluation of aquatic pollu-
tants using fish and amphibian eggs as bioassay organisms. Animals as
Monitors of Environmental Pollutants. Washington, DC: National
Academy of Sciences; 1979; p. 108-117.
Boyle, R.W. Geochemistry of silver and its deposits with notes on geo-
chemical prospecting for the element. Geolog. Survey Can. Bull. 160; 1968<
Bringmann, G., Kuhn, R. Comparative water-toxicology investigations
on bacteria, algae, and daphrids. Ges. Ind. 80:115; 1959. (As cited
in EPA 1979)
Buikema, A.L.,Jr., Cains, J.,Jr.; Sullivan, G.W. Evaluation of Philo-
dina acuticornis (rotifera) as a bioassay organism for heavy metals.
Water Resources Bull. 10:648- ; 1974. (As cited in EPA 1979)
Calabrese, A.; Collier, R.S.; Nelson, D.A.; Maclnnes, J.R. The toxicity
of heavy metals to embryos of the American Oyster, Craaaostrea virginica.
Marine Biology 18:162-166; 1973.
Castignetti, D; Klein, D.A. Silver iodide burn complex and silver
phosphate effects on methanogenesis. J. Environ. Sci. Health
A14(6); 529-546; 1979.
Clark, J.F. On the toxic effect of deleterious agents on the germina-
tion and development of certain filamentous fungi. Bot. Gaz. 28:289-327,
378-404; 1899. (As cited by Cooper and Jolly 1970)
Coleman, R.L.; Cearley, J.E. Silver toxicity and accumulation in large-
mouth bass and bluegill. Bull, of Environ. Contarn, and Toxicol. 12(1):
53-61; 1974.
Cooper, C.F.; Jolly, W.C. Ecological effects of silver iodide and other
weather modification agents: A review. Water Res. 6(l):88-98; 1970.
Davies, P. A method for determining the long-term toxicity of insoluble
metal compounds demonstrated by silver iodide in natural water. Andrew,
R.W.; Hodson, P.V.; Konasewich, D.E.; editors: Toxicity to biota of
metal forms in natural water. Proceedings of Workshop in Duluth, MN.
October 7-8, 1975. April 1976; p. 118-120.
V-24
-------
Davles, P.H.; Goettl, J.P.; Sinley, J.R. Toxicity of silver to rainbow
trout (Salmo gairdneri). Water Research 12: 113-117; 1978.
Davis, R.D.; Beckett, F.H.T. The use of young plants to detect metal
accumulations in soils. Water Poll. Control. 77(2):193-210; 1978.
Doudoroff, P.; Katz, M. Industrial wastes. Critical review of litera-
ture on the toxicity of industrial wastes and their components to fish.
Toxicity of wastes to fish. II. 25(7): 802-839; 1953.
Eisler, R.; Lapan, R.L.; Telek, G.; Davey, E.W.; Soper, A.E.; Barry, M.
Survey of metals in sediments near Quonset Point, RI. EPA Report No.
600/J-77-147. Narragansett, RI: Environmental Research Laboratory;
1977. 6 p. Available from: NTIS, Springfield, VA; PB 295 374.
i
Fitzgerald, G.P. The algistatic properties of silver. Water Works
114:185; 1967. (As cited by U.S. EPA 1979)
Goetz, A.; Tracy, R.L.; Harris, F.S.,Jr. The oligodynamic effect of
silver. L. Addicks, Ed., in Silver in industry, New York, NY:
Reinhold Publishing; 1940. (As cited by Smith and Carson 1977)
Golubovich, V.N. "Toksicheskoe Deistvie lonnogo Serebra na Pazlichnye
Gruppy Mikroorganizmov" [Toxic effect of ionic silver on various groups
of microorganisms]. Mikrobiologiva, 43_,922-924; 1974. (As cited by
Smith and Carrson 1977)
Gratteau, J.C. Potential algicides for the control of algae. Water
Sewage Works R-24; 1970. (As cited by U.S. EPA 1979)
Hadek, R. Preliminary report on the cellular effect of intravital
"silver on the mouse ovary. Jour. Ultrastruct. 15:66; 1966. (As cited
in U.S. EPA 1979)
Hale, J.G. Toxicity of metal mining wastes. Bull. Env. Cont. Toxicol.
17(l):66-73; 1977.
Harry, H.W.; Aldrich, D.V. The ecology of Australorbis Glabratus in
Puerto Rico. Bull Wld. Hlth. Orgn. 18:819-832; 1958.
Hutchinson, T.C.; Stokes, P.M. Heavy metal toxicity and algal bioassays.
Water Quality Parameters. ASTN SPT 573:320; 1975. (as cited by U.S.
EPA 1979)
Jackim, E.; Hamlin, J.M.; Sonis, S. Effects of metal poisoning on five
liver enzymes in the killifish (Fundulus heteroclitus). J. Fisheries
Res. Board of Canada. 27(2):383-390; 1970.
Jen tie, E.A. ; e_t al. Inorganic speciation of silver in natural waters-
fresh to marine. Trans. Am. Geophys. Union 58:1168; (as cited in U.S. EPA
1979)
V-25
-------
Jones, J.R.E. Fish and river pollution. London: Butterworth; 1964.
(As cited by Davies et al. (1978).
Klein, D.A. ed. Environmental impacts of artificial ice nucleating
agents. Strandsburg, PA: Dawden, Hutchinson & Ross, Inc.; 1978.
Klein, D.A.; Giangiordano, R.A. Evaluation of potential impacts of silver
iodide nucleating agents on aerobic and anaerobic aquatic microbial
processes. Froc. 2nd WHO Sci. Conf. Weather Modification, Boulder, Colo.;
1976, p 569-575. (As cited in Klein 1978)
Klein, D.A., Molise, E.M. Ecological ramification of silver iodide
nucleating agent accumulation in soil and aquatic environments. J. Appl.
Meteorol. 14(5):673-680; 1975. (As cited in Klein 1978)
Lisk, D.J. Trace metals in soils, plants, and animals. Advances Agron.
24:267, 365; 1972.
Marsh, M.C.; Robinson, R.K. The treatment of fish-cultural waters for
the removal of algae. Bull. Bur. Fisheries; 28(Part 2): 871-890; 1980.
(As cited by Duodoroff and Katz 1953)
McKee, J.E.; Wolf, H.W. Water quality criteria. 2nd ed. California
State Water Quality Control Board Publ. 3A; 548p. (As cited in Klein 1978)
Retiring, R.B. 1976. Aquatic insects as biological monitors of heavy
metal pollution. Bull. Environ. Contarn. Toxicol. 15:147. (As cited by
U.S. EPA 1979)
Nelson, D.A. Biological effects of heavy metals on juvenile bay
scallops, Argopecten irradians. in short-term exposures. Bull. Environ.
Contain. Toxicol. 16:275; 1976. (As cited by U.S. EPA 1979)
Olcott, C.T. Experimental argyrosis IV. Morphologic changes in the
experimental animal. Am. J. Pathol. 24:813; 1948. (As cited by U.S.
EPA 1979)
Perwak, J.; Bysshe, S.; Delos, C.; Goyer, M.; Nelken, L.; Schimke, G.;
Scow, K.; Walker, P.; Wallace, D. An exposure and risk assessment for
Copper. Draft. Contract EPA"68-01-3857. Washington DC: Monitoring
and Data Support Division- Office of Water Planning and Standards, U.S.
Environmental Protection Agency; 1980.
Phillips, G.R. ; Russo, R.C. Metal bioaccumulation in fishes and aquatic
invertebrates: A literature review. Report No. EPA-60073-78-103.
Bozeman: Montana Fisheries Bioassay Laboratory, Montana State; 1978;
115 p.
Romney, E.M. ; Wallace, A.; Wood, R.; El-Gazzar, A.M.; Childress, J.D. ;
Alexander, G.V. Role of soil organic matter in a desert soil on plant
response to silver, tungsten, cobalt, and lead. Commun. Soil Science
Plant Analysis 8(1):719-725; 1977.
V-26
-------
Smith, I.C.; Carson, B.L. Trace metals In the environment. Volume 2 -
Silver. Ann Arbor, MI: Ann Arbor Science Publishers Inc.; 1977.
Sokol, R.A.; Klein, D.A. The response of soils and soil microorganisms
to siver iodide weather modification agents. J. Environ.'Qual. 4:211-214;
1975.
Sosnowski, S.L; Gentile, J.H. Chronic toxicity of copper and silver
to the mysid shrimp Mysidopsis bahia. Manuscript. Narragansett,, RI:
EPA Environmental Research Laboratory. (As cited in U.S. EPA 1979)
Soyer, J. Contribution to the study of the biological effects of mer-
cury and silver on sea water. Vie et Milieu 14: 1-36; 1963. (As cited
by Davies et al. 1978)
Teller, H.L.; Cameron, D.R.; Klein, D.A. Disposition of silver iodide
used as a seeding agent in ecological impacts of snowpack augmentation
in the San Juan Mountains of Colorado. Final report of the San Juan
Ecology Project. Fort Collins, CO: Colorado State University; 1976;
p. 105-139. Available from: NTIS, Springfield, VA; PB-255-012. (As
cited in Klein 1978)
•
Terhaar, G.J., et. al. Toxicity of photographic processing chemicals
to fish. Photographic Sci. Engr. 16:370; 1972. (As cited by U.S., EPA
1979)
US Environmental Protection Agency (U.S.EPA). AmBlent Water Quality
Criteria. Criterion Document—silver. Washington, DC: Criteria and
Standards Division. Office of Water Planning and Standards. 1979.
Available from: NTIS, Springfield, VA: PB 292 441.
U.S. Environmental Protection Agency (U.S. EPA). Development document
for effluent limitations guidelines and standards for the photographic
equipment and supplies segment of the photographic point source category.
Report EPA 440/l-80/0-77-a. Washington, DC: Effluent Guidelines Division,
U.S. EPA; May 1980.
Von Rosen, G. Mutations induced by the action of metal ions in Pisum.
Hereditas 43:644; 1957.
Wallace, A. Excess trace metal effects on calcium distribution in
plants. Common. Soil Science Plant Analysis 10(1&2): 473-479; 1979.
Wallace, A; Romney, F.M. Roots of higher plants as a barrier to
translocation of some metals to shoots of plants. In Drucker, H. et al.
Ed: biological implications of metals in the environment; 1977.
V-27
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CHAPTER VI.
EXPOSURE AND EFFECTS—HUMANS
A. HUMAN EXPOSURE
1. Introduction
The most commonly reported effect of human exposure to silver is
the occurrence of argyria, a bluish-gray pigmentation of the skin.
Cases have been documented that associate the condition with dermal
contact, ingestion,and inhalation. Thus, all three major routes by
which humans can be exposed to silver can be important. This section
considers human exposures via ingestion, dermal contact, and inhalation.
The major sources of ingested silver are foods and accidental
ingestion of silver-bearing products (e.g., silver beads, bearings, and
jewelry by children). Since concentrations of silver in surface, well,
and tap waters are typically below detection limits, drinking water does
not represent a major exposure route for humans. Dermal absorption of
silver occurs as a result of medicinal applications, occupational expo-
sure, handling of jewelry and other silver objects (e.g., silver flat-
ware, trophies, bowls, etc.), and contact with photographic developing
and fixing solutions. Inhalation of silver is an exposure route in
urban areas, and in the vicinity of silver mines, steel mills, and ore
smelters.
2. Inges tion
a. Food
Silver exists as a normal trace constituent in many foods in varying con-
centrations presented in Table 48. Silver has been detected in food
items in concentrations ranging from 2.0 ug/g in crustaceans to 0.007
ug/g in legume and root vegetables (Table 48). When these concentra-
tions are combined with average daily consumption levels for each food
group (U.S. FDA 1974), the average daily intakes shown in Table 48 can
be calculated for each group. As can be seen in Table 48 , individuals
who consume 'large amounts of mushrooms, mollusks, crustaceans, and bran
will ingest more silver than those who consume less silver-intensive
foods.
The Water Quality Criterion Document (.U.S. EPA, 1979) indicates that
daily dietary intake of silver in the United States ranges from 35 ug/day
to 88 ug/day (see Table 49). There is a small difference in intake levels
for men and women. These estimates are calculated based on typical rather
than maximum silver concentrations in food and assume average dietary pat-
terns and thus are expected to better represent the general U.S. population
VI-1
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TABLE 48. ESTIMATED SILVER INGESTION IN FOODS
Food Croup
Average
Consumption
(g/day)
Average
Concentration
Silver (ug/g)
Dairy 763"1
Meat, Fish and .
Poultry, Total 267a
Beef
Beef Liver
Fork
Mutton & Lamb
Crustaceans
Trout
Mollusks j
Grains, Cereals, Brans 422.
Potatoes 183}
Leafy Vegetables 55:
Legume Vegetables 69.
Root Vegetables 33.
Garden Fruits 92..
Fruits . 221:
Mushrooms 55
Oils &Fats 72*
Sugars 82:
Beverages 712
Water
Coffee
Tea
0.027-0.054'
345
6 7
0.004-2.00
0.004-0.024"
0.005-0.194*
0.007-0.012-
0.006-0.OilJ
2.05
0.48-0.99
0.1-10.0;
0.4-1.00° 0
0.005-0.012*
N.D.-0.008* o
0.0029-0.0073!
0.0062-0.0075*
N.D.9
N.D.9
5.510 "several
hundred ppm"11
N.I. .,
0.001-0.030
0.03
0.02
13
14
Average Silver
Intake
(ug/day)
20.60-41.20
1.07-534.00
**
**
**
**
**
**
**
168.80-422.00
0.92-2.20
0-0.44
0.20-0.50
0.20-0.25
300-5,500
0.08-2.46
60.00
0.20-2.00
14
Total - Based on Dietary Analysis
of Husband and Wife
Range 18-103
15
Mean: 35 male, 44 female
15
1. U.S. FDA (1974)
2. Murthey and Rhea (1966)
3. Armour Research Foundation (1952)
4. Masironi (1974)
5. Boyle (1968)
6. Tong et al. (1974)
7. Freeman (1977)
8. Kent-Jones and Amos (1957)
9. Oakes et al (1977)
10. Allen and Steinnes (1978)
11. Ramage (1930)
12. Hamilton and Minski (1973)
13. U.S. DHEW (],970)
14. Vanselow (1966)
15. Tipton et al. (1966)
Only available data concern the concentration of silver in milk.
Because milk is a constituent of cheese, butter, etc., this was
used for an extreme case determination of total silver consumption.
However, this neglects eggs and other "dairy" products that may
have varying silver concentrations.
**Since Food Group consumption was presented for the group as a whole and
nor. bv food tvpe. associated silver consumption for the meats are
comoined into one number on meat, fish and poultry.
VI-2
-------
Chan a compilation of estimates from Table 48. Therefore, the total diet
levels are used to estimate human risk in Chapter VII.
TABLE 49 . ESTIMATES OF DAILY SILVER INTAKE
IN HUMAN DIET
Amount of Silver
Ingested Daily (ug/day) Population Reference
0.4 3 Italian populations Clements et al. (1977)
27 Population in U.K. Hamilton and Minski
(1973)
35 Man (U.S.) Tipton et al. (1966)
44 Woman (U.S.) Tipton et al. (1966)
70 Reference man (U.S.) Snyder et al. (1975)
(average intake)
Not given- Kehoe et al. (1940)
Reasonable estimate U.S. EPA (1979)
based on proceeding
results
Source: U.S. EPA (1979).
Tipton et al. (1966) conducted a 30-day diet study on two human
subjects, monitoring trace element concentrations in food and excreta,
ingestion rates of food and liquids, and excretion rates. Estimated
daily intake rates for silver (30-day average) were 35 ug and 44 ug of
silver for the male and female subjects, respectively. The average
daily excretion rate (in urine and feces) was 89 ug and 37 ug, respec-
tively. This resulted in a balanee (+7 ug) for the female but a sig-
nificant negative balance (-54 ug) for the male subject. The results
indicate an .efficient removal mechanism for ingested silver from the
body. In the case of the male subject the negative balance evidently
resulted from uptake of silver from other unaccounted sources (e.g., in-
halation of air, amateur photography) or metabolism of silver deposits
already contained in the body. The intake rates from food and water
were on the same order of magnitude as the other ingestion estimations
reported in Table 48.
Sludge-amended soil used to grow agricultural produce contains
silver in concentrations as much- as 10 times greater than normal soils
(U.S. EPA 1979). Sewage sludge has been reported to contain as much as
VI-3
-------
900 mg/kg although typical concentrations are much lower, around 100
nig/kg (Smith and Carson 1977). Plants have been observed to cake up
silver from solution under experimental conditions (see Chapter IV-D).
Also uptake has been reported to be related to soil concentration (Smith
"and Carson 1977). However, no laboratory studies were available on up-
take from sludge-amended soil nor reports of concentrations in crops
grown on sludge-amended fields. Therefore, it is not possible to ascer-
tain how significant this exposure route is to humans.
Weather modification techniques utilize silver iodide as a nuclea*-
ting agent. Precipitation associated with this process deposits some
portion of the seeded silver iodide on plants and soils, which may then
enter the food chain (Jones and Bailey 1974). However, monitoring
studies show that media silver concentrations resulting from cloud
seeding are not significantly greater than normal background levels
with extreme levels 200 times as great (Teller et al. 1974). Therefore,
this activity is not expected to contribute to increased human exposure
in areas subject to weather modification. Additionally, the use of silver
in weather modification activities has declined recently.
b. Water
The U.S. Public Health Service Standard and EPA Water Quality Criterion
for human health are 0.05 mg/1 (U.S. EPA 1980b). The Food and Drug
Administration also has a 0.05 mg/1 criterion for bottled waters (U.S.
EPA 1979). A consumption of 2 liters ner day of water containing this
level of silver would result in a daily intake of 0.10 mg.
Silver has been used as a bacterlcide to purify potable waters
carried by tankers, drilling rigs, and airlines. Some water bottlers
also use it for this purpose. In 1978, 19 companies were registered by
the U.S. EPA to manufacture filters containing silver to purify waters;
this represented almost a doubling from the number registered in 1976
and suggests that the use of silver for this purpose may be increasing
(U.S. EPA 1979).
Water supplies (surface waters, wells, and tap waters) that have
been monitored for existence of trace elements consistently contain
silver at concentrations below the EPA Water Quality Criterion for human
health of 0.05 mg/1. The silver concentrations found in various waters
are presented in Table 50 and discussed in Chapter IV-E.
The U.S. Department of Health, Education and Welfare (1970) reported
that the maximum concentration of silver found in community water supplies
was 0.03 mg/1 (in 2595 samples taken at the tap). The maximum human
ingestion based on consumption of ?, 1 water containing this concentra-
tion would be 0.06 mg of silver per day. In STORET, the maximum silver
concentrations reported for major river basins ranged from 0.095 mg/1 to
0.790 mg/1 (STORET 1980). The ingestion of these waters without further
treatment would provide an individual with 0.188-1.580 rag/day of silver.
VI-4
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TABLE 50. CONCENTRATIONS OF SILVER DETECTED IN DRINKING WATERS
i
in
Sample '
Tap Water
Tap Water
Bottled Water
Water-(Gen. U.S.
moni tored-maximuras)
Well Water
WelJ Waters (Gen. U.S.
monitored)
Concentration (mg/1)
Range Mean
0.0940-0.790
0.0001-0.0004
0-0.0300
0.0260
0.0300 (max.)
0.0500 (FDA
recommended)
0.0002
0.0140
Reference
Smith and Carson (1977)
U.S. DHEW (1970)
44 FR 12169 - U.S. FDA (1979)
STORET (1980)
Bradford (1971)
STORET (1980)
-------
• For well waters, the 2,232 observations In STORE! over a two-year
period indicated a mean concentration of 0.014 mg/1 and a maximum of
0.030 mg/1. The-exposure associated with ingestion of these waters
would be 0.028 mg/day and 0.060 mg/day, respectively.
C. Products Containing Silver
There is a potential, especially for small children, to ingest
silver objects. However, due to the probable inert form of silver in
the ingested object (ball bearings, small Jewelry) and the inefficiency
of uptake from the gastrointestinal tract, this route of exposure is
not expected to be significant.
3. Dermal Contact
a. Medicinal Applications
Through the end of the 19th century, silver nitrate was widely used
medicinally. With the increased development of more advanced drugs in
the 20th century, the application of silver nitrate for medicinal pur-
poses decreased. More recently, the medical community has begun to
reevaluate silver nitrate for local applications such as the treatment
of bums (U.S. EPA 1979).
Argyrol solution, which consists of a colloidal preparation of silver
oxide In a casein, alkaline gelatin or serum albumin solution, was in-
vented in 1902, but Crannel (1975) reports that it is still widely used
as a local disinfectant. Argyrol solution contains 19-23% silver and
recommended applications are 5-50% Argyrol concentration. The maximum
amount of silver in a 1-ml application of Argyrol would be 100 mg. Other
silver-containing solutions include Protargol and Neo-Silvol; their
prescribed application would result in about the same dermal exposure
used to the same amounts as the compounds described previously (Crannel 1975)
Silver is a constituent of dental amalgan along with tin, copper,
and zinc. Although amalgam is as much as 67 to 70% silver, it is mixed
with mercury for application, reducing the silver concentration in dental
fillings to 33% (Crannell 1975). Lierskar (1974) found in vitro release
of some silver from amalgam dental fillings into a human monolayer
epithelial cell culture (up to 0.02 ug Ag/ml at 3 days). Hals (1976),
however, reports that in real situations because of the nature of teeth
restorations and the composition of amalgam, little silver is released
to the surrounding tissues in the mouth. One case study documented
effects of absorption of dental silver resulting in localized argyria.
A crown with one-third silver alloy filling was placed on a primary
tooth. The site of the tooth exhibited grey stained tissue. Pigmenta-
tion was attributed to the impregnation of adjacent tissues with silver
particles (Burton 1972). Due to the small total amount of silver avail-
able for uptake and the low translocation rate of silver in mammals
following silver uptake (U.S. EPA 1979), this exposure route is not
expected to be significant in terms of more than local effects.
VI-6
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b. Photography
One of Che more prominent human exposures to silver, in terms of
total silver mass involved, is through film development and printing;
however, in terms of the amount actually absorbed into the body, the
exposure does not appear to be very significant.
A home developer works with developing and fixing solutions which
may accumulate 16g of silver or more in the course of a single developing
session. This assumes l.Sg silver per m of film, 2 m per roll, and that
six rolls are developed in one session.. Exposure to silver could occur
through dermal contact or, more remotely, through inhalation.
Two factors suggest that dermal absorption is not a significant
exposure route beyond potential development of localized argyria. First,
most home developers wear, gloves or use implements to avoid direct con-
tact with the solution. Second, observation of individuals with argyria
indicate that the primary concentration of silver remains in the surface
layer of the skin (Buckley 1963). A woman exposed to fixing solution
(no concentration given) over a period of several months developed
discoloration on the skin actually in contact with the solution; no
other effects were reported. The author noted that occurrences such as
this one were unusual due to low silver concentrations in fixing solu-
tion and the common practice of wearing gloves when using fixer.
Due to the low volatility of silver, inhalation is not expected to
expose amateur photographers to significant levels of silver. No spe-
cific information on this subject was available.
c. Industry
Few reports of industrial releases and associated occupational
exposures to silver are found in the literature. One case related to
the silver mining industry concerns of an individual who worked in the
mines for 20 years during the last part of the 19th century. Within
5 years after he had stopped working there, his entire body was a
"deep blue, and from a distance appeared almost black." He was diagnosed
as having generalized argyria as a result of dust accumulation on the
skin and/or inhalation (U.S. EPA 1979). Further discussion of industrial
exposure can be found in Carson and Smith (1977) and NAS (1977).
d. Jewelry'and Sterling Silver
Silver jewelry such as rings, bracelets, necklaces, and earrings
obviously are in frequent contact with the skin. No work has been done
to estimate quantities of silver released as a result of skin contact
nor have there been any indications of adverse health or cosmetic
effects. The uptake rate of silver by intact skin has. been reported as
low (U.S. EPA 1979).
VI-7
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e. Swimming Pools
Silver chloride (at concentrations as high as 150 ug/1) has been
used as a bactericide in swimming pool applications. Also some U.S.
swimming pools use activated carbon filters coated with metallic silver,
effecting water concentrations of 20-40 ug/1 (U.S. EPA 1979). However,
these uses are believed to have decreased significantly due to cost
(HAS 1977). Two factors contribute to this circumstance: regulations
have restricted the use of silver compounds in potential skin-contact
applications to prevent outbreak of argyria; and advances in chlorina-
tion techniques have decreased the use of silver. Also there is very
little evidence for uptake of silver by intact skin (U.S. EPA 1979).
Therefore, the exposure of humans to silver in swimming pools is assumed
to be negligible.
4. Inhalation
Silver is inhaled by many individuals at ambient concentrations and
by much small subpopulations in special situations at higher levels.
Ambient atmospheric concentrations are presented in Table 51 with rates
of daily inhalation. The available data indicates that the most signi-
ficant atmospheric exposure is in locations adjacent to or in close
proximity to smelters (Ragaini 1977) and steel mills (Harrison et al.
1971). The typical respective intakes of silver in these locations
would be 453.6 ng/day and 21.6-216.0 ng/day, respectively, and might
be as high as 1576.8 ng/day near smelters. High air concentrations
of silver were found near the San Francisco Mint, in which daily expo-
sure is 0.86 mg/day (note shift in units). Presumably, this is an
occupational exposure and would not be continual over a 24-hour period;
therefore, the intake by inhalation would be 0.29 mg/day (U.S. EPA
1979).
The urban atmosphere will provide its residents with fairly consis-
tent amounts of silver ranging from 47.5' ng/day in non-industrial
Washington D.C. to 185.8 ng/day in heavily industrial Chicago. San
Francisco had relatively lower exposures to silver, only 2.2-8.6 ng/day
Non-urban and rural locations senerallv have lower atmosoheric
loads of silver.
The literature indicates that dust particles from mines producing
silver and ores in which silver is a byproduct could provide a potential
occupational exposure, as can metal working shops. No data were avail-
able to quantify exposure by this route.
Soldering, especially at high temperatures, releases silver
to the atmosphere during the stage in which the solder is heated and
applied. The magnitude of this release depends upon the scale of the
operation and the concentration of silver in the solder. Inhalation
exposure of both industrial workers and jewelry soldering hobbyists may
result from this activity. Large-scale industrial soldering shops would
provide a larger and more consistent release than domestic use. Daily
intake of silver through inhalation in the workplace is restricted by
VI-8
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TABLE 51. ESTIMATED SILVER INTAKE BY INHALATION
s
Atmospheric Silver Concentration
(np./day)
Source
Range
0.05-0.2
0.3-12.9
Urban Areas
Washington, D.C.
Chicago, IL
San Francisco, CA
Glasgow, UK
Heidelberg, Germany -
Steel Mills - East
Chicago 0.5-5.0
Smelter - Kellog, Idaho 0.94-36.50
San Francisco Mint
Other Areas
Nebraska
Chicago, IL
Oak Ridge, TN
1.0-2.4
Mean
1.1
4.3
2.7
4.2
10.5
3
0.02 rag/m
0.15
0.17
Silver Inhaled
(ng/day)
Range Mean
2.16-8.64
1.30-557.28
21.60-216.0
40.61-1576.80
43.2-103.68
47.52
185.76
116.64
181.44
453.60
9.86 mg
6.48
7.34
Reference
Trout (1975)
Brar £t al. (1970)
John et al. (1973)
McDonald and Duncan (1979)
Bogen (1974)
Harrison e_t al. (1971)
Ragainl et al. (1977)
Anania and Seta 1973
Strueropler (1975)
Bogen (1974)
Andren et_ al. (1974)
1 3
Assuming an inhalation rate of 1.8 m /hr and 24 hours per day.
-------
OSHA to 100 ug/day (0.01 mg/m3 x 10 m3 per workday) (U.S. EPA 1979).
The significance of domestic exposure of hobbyists could not be determined,
but due to the small amounts of silver used in soldering, the resulting
silver concentration in air is expected to be very small and less than the
OSHA limit.
B. HUMAN TOXICITY
1. Introduction
The ingestion of silver, even in trace quantities, has no known
beneficial effects as an essential micro-nutrient (NAS 1977). Silver,
however, has been used since antiquity for various medicinal purposes.
Various silver compounds have been utilized as preservatives, astringents,
nose drops, mouthwashes and as remedies for gastrointestinal disorders.
Instillation of 1% silver nitrate solution into the eyes of newborn
infants is still legally required in many states for prophylaxis of
gonorrhea and silver nitrate and silver sulfadiazine are used in the
topical treatment of severe burns as protection against infections with
gram-negative bacteria (Grier 1977). Because of its bactericidal activity,
the silver ion has also been added to drinking water for disinfection
purposes (NAS 1977).
2. Metabolism and Bioaccumulation
a. Absorption
The metabolism of silver in man and animals has not been extensively
studied due to poor absorption by all routes of administration. A maxi-
mum of 10% of ingested silver salts is absorbed in mice, rats, monkeys
and dogs (Furchner et al. 1968); there are no precise data available
for man. Poor gastrointestinal absorption is attributed to the sparing-
ly soluble nature of most silver salts; the soluble sulfate and nitrate
salts are converted to insoluble chlorides in the stomach (Venugopal and
Luckey 1978). Absorption via inhalation is also believed to be low, although
there are no quantitative data concerning the extent of absorption via
inhalation (Fowler and Nordberg 1979).
Some absorption has been demonstrated via mucous membranes or non-
intact skin, but absorption through intact skin is poor, presumably due
to the binding of the silver ion to skin proteins (Petering 1976).
Wahlberg (1965) reported less than 1% absorption of a silver nitrate
solution (25.8 mg Ag/ml) applied to intact skin of guinea pigs. Several
similar studies indicating poor absorption through intact skin were
reviewed by Hill and Pillsbury (1939). With respect to broken skin,
Harrison (1979) reported that peak attachments of Ag110- labeled sulfa-
diazine silver to the burn wounds of humans and rates were 1% and 8% of
the dose, respectively, within 24 hours. Dissection of the wounds showed
81-98.7% of the attached silver was present in the most superficial
layers of cells. Similarly, Constable and co-workers (1967) found that
VI-10
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the majority of 0.5% silver nitrate solution applied to open wounds
(3.5 x 3.5 cm2) on the .backs of guinea pigs for 5 days remained in the
general area of the wound but with some absorption evident in liver and
kidney. Daily skin application of a saturated solution of colloidal
silver and silver oxide to the depilitated backs of rats for 3 months
resulted in findings of 1.54 mg/kg silver in kidney, 1.50 mg/kg in
spleen, 0.16 mg/kg in liver plus traces in heart and lungs (Desquldt et_
al. 1974). Additional data on the dermal absorption of silver, par-
ticularly with respect to burn therapy, can be found in the U.S. EPA
Criterion Document for Silver (1979).
Parenterally injected silver salts remain at the site of injection
bound to tissue proteins; only a fraction of the dose is actually absorbed
(Venugopal and Luckey 1978). Large doses of intravenously administered
silver compounds produce hemolysis and agglutination of erythrocytes;
at lower doses, silver complexes with serum albumin and is transported
to the tissues (Venugopal and Luckey 1978).
b. Excretion
In mammals, excretion of silver is almost entirely fecal (reflecting
poor absorption), with a trace in urine. For example, 70% of an intra-
venous dose (0.1 mg 110Ag/kg) of silver was eliminated in rat feces
within 4 days (45 % in the first 24 hours) with less than 0.5% of the
dose found in urine during this time period (Klaassen 1979). Of the
abosrbed silver, over 90% is excreted via the feces in mice, rats,
monkeys, and dogs given radioactive 110Ag (as the nitrate by the oral,
intravenous or intraperitoneal routes (Furchner et al. 1968). The fecal
elimination of absorbed silver is mainly explained by biliary excretion.
Furchner et al. (1968) reported an increased renal excretion and a
concomitant reduction In fecal excretion of silver in laboratory animals
following bile duct ligation. Klaassen (1979) measured the disappear-
ance from plasma and excretion into bile of 110Ag following intravenous
injection of rats with 0.01, 0.03, 0.1 or 0.3 mgll°Ag/kg. Biliary con-
centrations peaked within 30 minutes of administration, then slowly
decreased with time. Over a 2-hour interval, 25-45% of the administered
silver was excreted into the bile. The ratio of bile to plasma 110Ag
concentrations was 16-20 to one.
A similar comparison between the disappearance of silver from plasma
and its excretion into bile following Intravenous injection of 0.1 mg
110Ag/kg into rats, rabbits, and dogs revealed marked species variation
in the biliary excretion of silver. The rat excreted silver into bile
at a rate about 10 times that of the rabbit and about 100 times that of
dogs. This difference is due to the concentration of silver in bile
rather than the rate of bile production and appears to be associated
with species differences in the rate of transfer of silver from liver
to bile; i.e., at 2 hours, silver concentrations in liver were 1.24,
2.13 and 2.90 ug Ag/g tissue for the rat, rabbit and dog, respectively
(Klaassen 1979).
VI-11
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The biological half-time for silver in the lungs was on the order
of 1 day for a man who accidently inhaled 110mAg dust; the half-time
for the liver was 52 days (Newton and Holmes 1966). No silver was detected
in urine during the first 50 days, but it was present in fecal samples
up to about day 300. Similarly, an apparent biological half-life of
approximately 1 day was found by whole-body scintillation counting in
mice, rats, dogs and monkeya after oral administration of 110Ag, which
is partially attributable to fecal elimination of unabsorbed silver
(Furchner et al. 1968). Somewhat longer half-lives were observed after
intravenous administration in monkeys (1.8 days) and dogs (2.4 days)
(Habighorst and Buchwald 1971).
c. Tissue Accumulation
Based on the data of Tipton and Cook (1963), the average silver
content in tissue of normal Americans is about 0.005 ug/g wet weight.
The highest concentrations of silver are usually found in the liver,
spleen and to some extent in brain, muscle and skin (NAS 1977).
Hamilton et al. (1973) reported concentrations of 0.008, 0.006, 0.004,
0.002 and 0.002 ug/g wet weight for blood, liver, brain, kidney-and lung
tissue, respectively. Indrapraist et al. (1974) found 0.4, 0.7 and
2.7 ug/g on a dry weight basis in kidneys, liver and spleen of normal
people. Creason et al. (1976) reported silver concentrations of 0.5 ug/
lOOg in placental tissue and 0.4 and 0.5 ug/100 ml in maternal and cord
blood, respectively.
Newton and Holmes (1966) reported more than 50% of the body burden
of silver was found in the liver of an individual 16 days after acciden-
tal exposure to radioactive silver.
Silver apparently accumulates in the body with age (Venugopal and
Luckey 1978, Smith and Carson 1977) but the nature, site and extent of
accumulation are not definitely known. Based on an average human
dietary intake of 88 ug/day (Kehoe et al. 1940), and assuming 100%
absorption of ingested silver, Smith and Carson (1977) estimated that
it would require 31 years to accumulate Ig of silver. However, if the
average tissue content of silver in normal Americans is .005 ug/g wet
weight (Tipton and Cook 1963), then the tissue content of the average
individual (68 Kg) at this concentration would only be 32 mg of silver
or 3.2% of a 31-year ingestion total (Smith and Carson 1977).
VI-12
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3. Human and Animal Studies
a. Carcinogenesis
Oppenheimer and co-workers (1956) subcutaneously injected two 1.5-cm
silver foil circles or squares into the abdominal wall of 25 male
rats; there were no control animals. Fourteen of the treated rats (32%)
developed fibrosarcomas at the injection site between 275 and 625 days.
Similarly, subcutaneous implantation of 17-cm diameter silver disks
into rats (8 disks/rat) resulted in sarcomas in 65 of 84 rats by 23
months (Nothdurft 1956). No sarcomas were seen, however, in a lifetime
study in which 35 rats were subcutaneously implanted with silver foil
fragments (1x1x0.02 mm). There were 24 survivors at 18 months (Noth-
durft 1958).
Schmaahl and Steinhoff (1960) found 8 of 26 (31?) surviving rats
injected subcutaneously or intravenously with divided doses of a colloi-
dal silver suspension over an 8-month period (total dose 65 mg Ag/rat)
developed malignant tumors. Tumors included six sarcomas at the injec-
tion site, one leukemia and one laminar epithelial carcinoma; the aver-
age latency period was 695 days. The physical state of the compound
probably played a role in the development of tumors.
In contrast, Furst and Schlauder (1977) found no tumors in rats
at 2 years following repeated monthly intramuscular injections with
300-mesh silver powder suspended in trioactanoin. The total dose was
75 mg Ag/rat.
In a skin tumor promotion study with the carcinogen 7, 12-dimethyl-
benz(a)anthracene (DMBA) (1.5%) mice were treated dermally with aqueous
silver nitrate twice a week for 44 weeks following initial treatment
with DMBA. Three of 13 survivors at 20 weeks developed eight pipillomas
(but no carcinomas) with an average latent period of 19 weeks. Silver
nitrate was judged to cause marked epidermal hyperplasia (Saffiotti
and Shubik 1963).
Thus, there are no indications that exposure to silver by the
normal intake routes is carcinogenic. Although several studies have
demonstrated tumor induction by implantation of silver foils or disks,
carcinogenesls resulting from injections or implantation in which the
tumors are induced only at the site of application are generally regarded
as irrelevant to human exposure.
b. Mutagenesis
Several bacterial mutagenicity assays with various silver salts
have proved negative. Demerec et al. (1951) reported negative findings
in Escherichia coll with 0.000005 to 0.0001% silver nitrate solution.
Similarly, Clark (1953) reported negative effects in Micrococcus pyogenes
VI-13
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1
var. aureus exposed to 0.000001% AgNOj-. In a rec-assay with Bacillus
subtills. Nishloka (1975) also noted negative results with 0.72% AgCl
solution.
Sirover and Loeb (1976), however, reported that 0.0005% AgNC>3
altered fidelity of DNA synthesis in vitro (i.e., increased the error
frequency by greater than 30%). They, therefore, designated silver
as a suspect carcinogen.
Recently, Casto et al. (1979) also reported that AgNC>3 enhanced
transformation of Syrian hamster embryo cells by a simian adenovirus,
SA7. An enhancement ratio of 2.7 above control was recorded for a
0.001% concentration of AgNOj after 18 hours exposure.
Thus, the data concerning mutageniclty are conflicting. Bacterial
assays with relatively low concentrations of silver salts are negative,
while a test with mammalian cells at somewhat higher concentration indi-
cated some enhancement of cell transformation. Additional work is
needed to clarify this issue.
c. Adverse Reproductive Effects
Little is known concerning the effects of silver on reproduction
and/or embryonic development. Barrie (1976) reported the absence of
'the left fibula and right ulna and related limb-reduction defects in
an infant born to a mother who conceived and maintained a pregnancy
with a Grafenberg ring intrauterine device in situ. The intrauterine'
device was stated to be composed mainly of German silver. Thrush et al.
(1968), however, report that German silver is composed of nickel, copper,
and zinc but no silver.
Freeman and Coffey (1973) injected 10% silver nitrate solution
directly into the vas deferns of eight mature Sprague-Dawley rats.
Subsequent mating with female rats beginning 2 weeks after treatment
for a period of 8 months indicated complete sterility in males. His-
tological studies of the vas deferens showed the lumen completely
replaced by scar tissue and the complete absence of sperm. Similar
treatment of a dog produced the same pathologic lesions. The pathology
associated with direct injections of a caustic solution of silver
nitrate into the testes of rats and dogs, however, has little signifi-
cance to human risk from ingestion of silver salts.
d. Other Toxic Effects
The toxicity of the silver ion is attributed to its ability to form
stable complexes with structural and functional proteins, and thereby
disrupt life processes. The data available on the toxic effects of
silver to humans are meager. The limited systemic effects of silver are
due, at least in part, to the poor absorption of silver from the intestinal
tract (Furchner et al. 1968), through intact skin (Petering 1976), and
presumably, via inhalation (Fowler and Nordberg 1979).
"*" A method for screening chemical mutagens which observes differencial
growth sensitivities to chemicals in wild and recombination-deficient
strains of bacteria.
VI-14
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i. Animal Studies
Intravenous injections of colloidal silver or silver salts have
routinely been used to induce acute pulmonary edema in dogs for study
purposes (NAS 1977, U.S. EPA 1979). Intravenous injections of labora-
tory animals with silver compounds are principally associated with
effects on the central nervous system: weakness, rigidity, contractures
of the legs, loss of voluntary movements and interference with cardiac
hemodynamics (Hill and Pillsbury 1939). Fifty percent lethal dose
(LDso) values of 100 mg/kg and 420 mg/kg, respectively, have been
recorded for colloidal silver following oral exposure in the mouse
(Venugopal and Luckey 1978) and intraperitoneal injection in the rat
(Desquidt et al. 1974). Pretreatment of ICR Swiss mice with the silver
ion (4/10 LDsoip) 48 hours prior to an LDso study afforded protection
by significantly increasing the LDso value by intraperitoneal injection
to 18 (16.6-19.4) mg Ag/kg in contrast to a value of 12.5 (10.4-15.1)
mg Ag/kg for mice without prior exposure. Pretreatment is believed to
induce the synthesis of metallothionein, a metal-binding protein (Jones
et al. 1979). Additional studies on the acute effects resulting from
injection of silver salts into laboratory animals can be found in Smith
and Carson (1977) and U.S. EPA (.1979).
The primary toxic effects of chronic silver exposure in animals
are seen in the cardiovascular, hepatic and, hematopoietic systems
(Fowler and Nordberg 1979). Olcott (1950) reported hypertrophy of the
right ventricle and thickening of the glomerular membrane, presumably
due to vascular hypertension, in rats given 635 mg Ag/L (as AgN03) or
660 mg Ag/L (as Ag£ S203) in their drinking water for up to 30 months.
Deposits of silver granules in the glomeruli and tubules of the
kidney, as well as pathological changes in renal tubules, were reported
by Fuchs and Franz (1971) in rats given 0.2% silver nitrate in their
drinking water from 10 to 50 weeks. Similar findings were reported by
Day et al. (1976) and Brozman et al. (1976) in rats administered 0.1%
or 0.2% silver nitrate, respectively, in drinking water for 3 months.
Albino rats given 0.05 mg Ag/1 in drinking water showed no changes
in gastric secretions, blood serum enzymes, or liver and kidney mor-
phology at 5 months nor in conditioned-reflex activity at 11 months
(Barkov and El'piner 1968). Savluk and Moroz (1973) noted no changes
in hematogical parameters or liver function in rats ingesting 0.2 mg
Ag/1 in drinking water for 3 months and exposure to this concentration
for 6 months reportedly produced no effect on conditioned-reflex activity
in rats (Kharchenko and Stepaneko 1972).
Additon of 0.4 mg Ag/1 to the drinking water of rats for an in-
determinant time period was stated to have produced small hemorrhages
in rat kidneys (Just and Szniolis 1936). At a drinking water concen-
tration of 0.5 mg Ag/1, lowered nucleic acid content was seen in rat
brain tissue at 6 months (Kharchenko et el. 1973), reduced conditioned-
VI-15
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reflex.activity in rats at 11 months (Barkov and El'piner 1968), lowered
immunological resistance in rabbits at 11 months (Barkov and El'piner
1968) and increased brain weight in rats at 12 months (Kharchenko et al.
1973). Pathologic changes in vascular, nerve, brain, and spinal cord
tissues were also observed in animals at the 11-month mark (Barkov and
El'piner 1968). Additional details on a variety of studies, conducted
predominantly in the USSR, in which silver ion was added to the drink-
ing water of laboratory animals can be found in U.S. EPA (1979). In
essence, adverse effects associated with the ingestion of silver In
drinking water are generally evident in laboratory animals at concen-
trations greater than 0.2 mg Ag/1. , '
11. Observations in Man
Acute toxic effects from silver in humans generally occur only
from accidental or suicidal overdoses (Smith and Carson 1977). Inges-
tion of 10 g of silver nitrate is usually fatal in humans but 30 g have
been survived (Hill and Pillsbury 1939). Acute toxic symptoms following
Ingestion of caustic silver nitrate include severe gastroenteritis,
diarrhea, fall in blood pressure, decreased respiration, spasms,
paralysis and eventual death depending on the level of exposure
(Venugopal and Luckey 1978).
Hill and Pillsbury (1939) reported lethal responses to therapeutic
intravenous injections of 50 mg or more of Collargol (^0.7 mg Ag/kg).
Pulmonary edema, hemorrhage and necrosis of bone marrow, liver and
kidney were observed upon post-mortem examination. Intrauterine admini-
stration of approximately 25 g of silver nitrate also was reported to
be rapidly fatal (Reinhart et al. 1971).
Dressings soaked with 0.5% AgN03 have been extensively used in the
treatment of burns without any evident local or systemic silver toxlcity
(Hartford and Ziffren 1972). Electrolyte imbalances (due to a tendency
of precipitate AgCl) have been reported in burn patients treated with
silver sulfadiazine (Burke 1973). Leukopenia was also once indirectly
associated with treatment of burn patients with silver sulfadiazine but
is now known to result from thermal injury and not the treatment (Kiker
et al.1977).
There is also a report in the literature of an allergic reaction
to silver amalgams, which manifested itself as peridontal disease in a
52-year-old'woman (Catsakis and Sulica 1978).
Prolonged intake of low doses of soluble silver salts can produce
a variety of toxic effects in man including fatty degeneration of liver
and kidney, changes in blood cells, irritation of the skin, eyes and
intestinal tract and both localized and generalized argyria (NAS 1977).
Argyria is an unsightly, permanent blue-gray pigmentation of the skin,
hair, fingernails, mucous membranes, and eyes resulting from the
deposition of microscopically detectable silver-containing granules in
VI-16
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the dermis, hair follicles and/or sebaceous and sweat glands and is most
pronounced in areas exposed to light (Venugopal and Luckey 1978). Depo-
sition also occurs in the cornea (often seen as a blue halo) and anterior
capsule of the lens but not in the optic nerve (Fowler and Nordberg 1979).
In localized argyria, only limited areas are pigmented. Although gener-
ally considered a cosmetic defect with no significant physiologic effect,
some investigators maintain that deposition of silver in the kidney is
associated with arteriosclerotic changes and deposition in the eye, with
impairment of vision, particularly night vision (NAS 1977). Zech et al.
(1973) attributed a nephrotic syndrome with associated proteinuria in
a 73-year-old argyric man to the use of a silver-containing mouthwash
for 10 years. There is no recognized effective treatment for argyria;
chelation therapy is ineffective (Lehnert 1973).
In an examination of 30 employees of an industrial plant involved
in the manufacture of silver nitrate and silver oxide, Bosenman et al.
(1979) noted that the majority of workers complained of eye and both
upper (nose and throat) and lower (cough, wheezing and chest tightness)
respiratory tract irritation, usually on a daily basis. Other complaints
included nausea (23% of the workers), headaches (30%), nervousness (33%),
tiredness (30%) and abdominal pain (33%). Abdominal pain was found to
be significantly associated with detectable levels of Ag in blood:
median 1.95 ug/100 ml, range 1.1-84. ug/100 ml.
In a follow-up of these workers, Moss et al. (1979) examined them
for the frequency and extent of ocular argyria. Pigmentation of the
conjunctiva was present in 20 workers and cornea! pigmentation in 15.
A direct relationship was found between the level of pigmentation and
duration of employment. Ten workers noted decreased night vision but
no structural deficits could be found in seven workers.
Although never common, generalized argyria is rarely seen today
due to Improved work conditions. The exposure conditions -giving rise to
argyria have not been well defined. Estimates from industrial exposures
indicate gradual accumulation of between Ig and 8g Ag by inhalation
(Bill and Pillsbury 1939) or ingestion of 1 to 30g soluble silver salts
(Lehnert 1973) will lead to generalized argyria. Instillation of 0.25%
AgN03 into the eyes for 3 weeks has been reported to result in localized
argyria (Hill and Pillsbury 1979). The National Academy of Sciences
(1977) calculated that consumption of 2 1 of drinking water containing
50 ug Ag/1, a concentration several fold higher than that normally found
in U.S. drinking water, and an assumption of 50% retention of intake,
would result in the retention of 50 ug Ag per day or Ig Ag in 55 years
(borderline argyria).
e. Interactions With Selenium. Vitamin E, Copper
Coverage of all the potential interactions of silver with other
compounds are beyond the scope of this report. However, the accentuation
or mitigation of a toxic response with .silver or its salts, in the presence
of selenium, Vitamin E and copper should be noted.
VI-17
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Silver has been shown Co accentuate copper deficiency in chicken
and cattle, presumably by interfering with copper metabolism (Underwood
1979, Smith and Carson 1977).
Silver is also antagonistic to selenium and will reduce the toxic
effects associated with elevated levels of selenium in the diet (Jensen
et al. 1974). Conversely, silver (100 mg/1 in drinking water) promotes
liver necrosis characteristic of vitamin E and selenium deficiency in
chicks (Ganther et al. 1973). Silver is believed to exert its antagonis-
tic effect on selenium, either through an inhibitory effect on the
activity of liver glutathione peroxidase or via decreased biosynthesis
of this enzyme due to interference with selenium metabolism (Wagner e_t
al. 1975). Addition of ionic silver to the diet of vitamin-E-deficient
rats also causes rapidly fatal hepatocellular necrosis, muscular dystro-
phy, and brain necrosis (Grasso et al. 1969).
C. SUMMARY
«
Human exposure to silver can occur through a number of exposure path
ways—through ingestion, dermal absorption and inhalation—however all
routes are associated with low exposure levels of silver. Typically
daily dietary exposure levels range from 35-88 ug; higher levels are
likely for certain subpopulations ingesting large quantities of silver-
contaminated bran, mushrooms, fish and shellfish. The maximum daily
exposure level resulting from ingestion of drinking water is 0.06 mg,
which is below the exposure level of 0.1 tag/day which would result from
ingestion of water with a silver concentration equivalent to EPA'3
Drinking Water Standard of 0.05 mg/1.
Exposure to higher levels can be found in subpopulations drinking
untreated surface water with concentrations exceeding 10 mg/1 (approxi-
mately 11% of the samples in STORZT). This subpopulation, however, is
expected to be extremely small.
The route of dermal absorption appears to be significant only for
subpopulations using medicinal products containing silver primarily
during treatment of burns. Exposure levels associated with dermal appli-
cation may be as high as 100 mg per application although not all of this
amount would be absorbed. Other potentially significant exposure
routes are home developing of photographic film and use of silver
solders; however, these do not appear to be associated with a high
level of silver uptake.
Inhalation of silver will expose large subpopulations in urban
areas to exposure levels of approximately 45 to 185 ng per day;
although certain cities have significantly lower air-borne silver levels.
VI-18
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Very small subpopulations may be exposed to significantly higher
exposure levels in the vicinity of smelters (approximately 450 mg/day
but as high as 1576 og), steel mills (up to 216 ng/day) and government
mints (0.86 mg/day as a worst case, more likely 0.29 mg/day).
In conclusion, the highest exposure levels are associated with very
localized atmospheric concentrations of silver affecting a very small
subpopulation and with medicinal use of silver-containing products.
A small fraction of the U.S. surface water supply, if consumed untreated,
would exceed the drinking water criterion. Typical concentrations in
drinking water are much lower than the Public Health Service Standard
and EPA Water Quality Criterion for human health.
The ingestion of silver, even in trace quantities, has no known
beneficial effects as a micronutrlent. System human toxicity, however,
is rare due to the poor absorption of silver by all routes of exposure
(e.g., < 10% by the oral route). The only known consequence of chronic
human exposure to silver is argyria, which does not involve significant
physiological effects. Argyria is believe to occur at a total body
burden of approximately Ig Ag'and above.
The possibility of silver acting as a carcinogen in mammals due to
ingestion or inhalation has not been studied directly. However, long-term
toxicity tests examining other adverse effects in laboratory animals
exposed through ingestion have found no increased incidences of
tumors. Long-term human occupational exposures, which involve all
three routes, have not been linked to carcinogenic effects. Solid
silver implants and suspensions of colloidal silver have resulted in
tumors in laboratory animals at the site of implantation, but these are
considered examples of silver acting as a nonspecific irritant rather than
as a specific carcinogen and, therefore, are not of particular relevance
to human risk from ingestion of silver. Conflicting mutagenicity data
require additional studies for clarification of the mutagenicity of
silver. In addition, little is known about the effects of silver on
reproduction and/or embryonic development.
In animals, the primary toxic effects of silver are associated with
the cardiovascular, hepatic and hematopoietic systems. A broad spectrum
of shorter-than-lifetime studies suggest 0.2 mg Ag/1 to be a no-effect
concentration of silver in drinking water of laboratory animals. In
that this concentration is several fold higher than the maximum reported
silver concentration in surface waters of the United States, there
appears to be little or no likelihood of acute human poisoning with
silver from the environment.
VI-19
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REFERENCES
Allen, R.O.; Steinnes, E. Concentrations-of some potentially toxic
metals and other trace elements in wild mushrooms from Norway. Chemo-
sphere 4:371-378; 1978.
Anania, T.L.; Seta, J.A. Industrial hygiene survey report. United
States Mint. San Francisco, CA: Natl. lust. Occup. Safety and Health
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VI-20
-------
Buckley, W.R. Localized argyria. I. Chemical nature of the silver
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VI-21
-------
e-a
Q
x
^owler^B.A.; No<^
"fl
fe
o
o
eeman,
PJ
w gichs , E.I. ; Minski, S.J. Abundance
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VI-22
-------
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•
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VI-23
-------
T-S
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VI-24
-------
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VI-25
-------
T-V
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silver iodide in ±hfi National Hail Research Experiment. Opera^^a^ Rep.
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nr o
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AT S8U7JB9S
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1974. (As cited £yzU.S. EPA 1979) 9JBfl
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ft4*ftT
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„ /TT O 1?TJ_A\ A«»V m ^••^ .^^^^^
locument— Silver. Washington, D.C. : Criteria^!
Standards Division, Office of Water Planning and Standards; 1979. 161 p.
Available from: NTIS, Springfield, VA; PB 2
IVO
.
6L6I - NOUfflSROD SAlIS HOI VIVO XWNIiClIHa 'V
VI-26
-------
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Monitoring and Data Support Division, U.S. EPA; 1980.
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Regulations and Standards; 1980b. 204 pages. Available from NTIS,
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pp. 32-36; 1978.
Wagner, P.A.; Hoekstra, W.6.; Ganther, H.E. Alleviation of silver
toxicity by selenite in the rat in relation to tissue gluthathione
peroxidase. Proc. Soc. Exp. Biol. Med. 148(4):1106-1110; 1975.
Wahlberg, J.E. Percutaneous toxicity of metal compounds. A comparative
investigation in guinea pigs. Arch. Environ. Health 11:201; 1965.
(As cited by U.S. EPA 1979)
Zech, P.; et al. Syndrome nephrotique avec depot d'argent dans les
membranes basales glomerulaires au cours d'une argyrle (Nephrotic
syndrome with silver deposits in the glomerular basement membranes
during argyria). Nouv. Presse. Med. 2:161; 1973. (As cited by U.S.
EPA 1979)
VI-27
-------
REFERENCES
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weather modification agents: A review. Water Resource Res. 6(1):88-98;
1970.
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362-376; 197?
Perwak, J.; Bysshe, S.; Delos, C.; Coyer, M.; Nelken, L.; Schimke, G.;
Scow, K.; Walker, P.; Wallace, D. An exposure and risk assessment for
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and Data Support Division, Office of Water and Planning Standards, U.S.
Environmental Protection Agency, 1980.
Perwak, J.; Goyer, M.; Nelken, L.; Schimke, G.; Scow, K.; Walker, P.;
Wallace, D. An exposure and risk assessment for Zinc. Draft. Contract
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Office of Water Planning and Standards, U.S. Environmental Protection
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exposure and risk assessment for mercury. Draft. Contract EPA 68-01-3857.
Washington, D.C.: Monitoring and Data Support Division, Office of Water
Planning and Standards, U.S. Environmental Protection Agency, 1980.
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Silver. Ann Arbor, MI: Ann Arbor Science; 1977.
U.S. Department of Commerce. Statistical abstract of the United States.
Washington, DC: Bureau of the Census, U.S. Department of Commerce; 1980,
U.S. Environmental Protection Agency (U.S. EPA). Ambient Water Quality
Criteria. Criterion Document—Silver. Washington, D.C,: Criteria,
and Standards Division, Office of Water Planning and Standards; 1979.
Available from STIS, Springfield, VA: PB 292 441.
VII-15
-------
CHAPTER VII.
RISK CONSIDERATIONS
A. RISK STATEMENT
There is some potential for occurrence of adverse effects in
aquatic organisms in certain areas of the U.S. due to exposure to
silver. Typical total silver concentrations in surface water sometimes
exceed non-lethal effects concentrations (based on laboratory bioassays
on ionized silver). An important factor in determining whether potentially
toxic levels will cause harm at a specific location is the set of
environmental variables at the site. Since, at this time, these factors
must be considered on a site-specific basis, the actual environmental
significance of silver on a national scale cannot be ascertained.
Silver does not appear to be interfering with microbial processes,
in the environment or in wastewater treatment with any great frequency.
Adverse effects are not likely among humans because the silver con-
centrations in drinking water, food, and air are low relative to the
concentrations required to cause effects—sublethal as well as lethal—in
humans and laboratory animals. In addition, the rates of absorption by
the gastrointestinal tract, skin, and lungs are low, as is the rate of
accumulation in tissue.
•
Discussion of the assumptions and supporting evidence for these
conclusions is presented in this chapter.
B. BIOTIC RISK CONSIDERATIONS '
Risks to non-human biota are discussed separately for (1) aquatic
life in natural waters, excluding microorganisms, (2) microorganisms in
natural waters and wastewater treatment systems, and (3) food crops and
fish consumable by humans.
1. Aquatic Life in Natural Waters
The risk to aquatic biota of exposure to silver varies considerably
by location. Few industry categories regularly practice direct aquatic
discharge of high levels of silver because of the economic incentives to
recover silver. Approximately 10% of all environmental releases from
human activities are made directly to surface water. Inadvertent dis-
charges due to leakage, spills and overflows of holding reservoirs appear
more likely to be responsible for any adverse effects in water; however,
no specific information is available concerning such discharges.
VII-1
-------
'IA
The Impact of any silver release on a local aquatic population
. . , ? i'Doiiad aiDsodxa
depends, upon the .preexisting background concentrations or silver; tne
a
complexing agents, the pH and hardness of the water, species present,
and other factors. In natural waters, silver is found u*flu*r'e1euI3BigaHseaI
form, as soluble AgHS (in the presence of H2S and HS ) and in other
slightly soluble silver su£tff$e*c£fiplexes. A fraction of the total
concentration may* W 3£V&Sl1K95Frform or assBESated with othe^
material such as organic matter, metal hydroxides and iron manganese
oxides. The silver held in this reservoir may reenter the water column
under certain conditi6iSIf2s>uch*&r¥n the presence of ammonia (Smith
and-Tarson 197?FPT05o3gv!?,OffidIl<%pical c8S82*ions, most «*HIP*
silver present remains in insoluble form. The equilibrium between
and solid phases of silver is dependent upon pH. the presence
fffeing asenfS?u£ffd*fhe JM&& potential, as describidHS331c*lU
t/8v 8m g-Q i«i pauoTaipuoo
a
_Silver is toxic at low concentrations when its ionic form is avail-
e'8m 9iota. Therefore, th«u?6^rm of silver to which organisms are
very *£fff?&£?£& In^&eWning the threshold concentration
. W3BW2K^rA>r example^ relatf^!^s°5!3btlnpra
with'a low potential for dissociation and, therefore, is not very bio-
logically active. In almost all toxicity studies, silver is used
form of AgN03 (Section V.B;? wnJcfi^Ls presumably
due to its complete ioInffatioiF'a?a?est concentrations
T/av am ceo ael
with reported concentrations of silver
Comparison
injhe envirotifi
concentrations are reported rassutffi£ng nearly lODi? lonizaczon. Monitoring
data, on the other hand, reflect concents?ipj5flpnsbf total silver, summing
all forms of silva*r including sUi^TixBS, complexes,
fraction in fine suspended material, and so forth.
The percentage available to biota cannot be generalized since the
chemical constitution o£Jotih>e/j^t:.atrUTsample in each monitoring observation is
^liVlfi6^/60 ^B^^jiHT^iSoflWl"11"*61011' Jenne et al. (1978)
^|h^im^tlshe^aSn^aH€iTIB94elT^idlcting ^S inorganic gres&U?Bm?f •
silver u natural waters over a range of salinity. Due to the large
effort required to estimate fHPe£%vailab^l±ey in natural waters Tfi?°a •
representative number of locations, such an analysis has not
taken for this risk assessment.
-
the reSfilWTaPnpSPoftW^ studies concerning the toxicity of
aqS«t?!'V5*ffi»iffsJTffti3PSl ranges'^1 concentrations can
distinguished and associated with types of effects and soeeies groups
52). These 3fis35?i% no mH^OTfeictly defini3aaHi
due to sv&9M9°3$LdG?GR5es or environmental parameters do
exist. As mentioned previously, most of the test solutions were pre-
pared using AgN03 as the source of silver.
STVWWVK NO H3A1IS 10 S131U3 3SH3AOV 'SS I1SV1
VII-2
-------
TABLE 52. GENERAL RANGES OF SILVER CONCENTRATIONS
RESULTING IN EFFECTS ON AQUATIC BIOTA
Concentration
Effect
<0.1 ug/1
0.1-1.0 ug/1
1.2 ug/1
1
2.3 ug/1 (maximum at
any time)
1-10 ug/1
1
13 ug/1
10-100 ug/1
100-1000 ug/1
>1000 ug/1
No effects reported for any species
Chronic effects on most sensitive freshwater
fish (mortality of trout in soft water) and
invertebrates (mayfly LCso). Acute effects on
most sensitive marine invertebrates. (Sea
urchin egg development.)
EPA criterion to protect freshwater aquatic
life at water hardness of 50 mg/1 as CaC03.
EPA criterion to protect saltwater aquatic
life from acute toxicity.
Acute effects on most sensitive freshwater
vertebrates (guppy) and Invertebrates (daphnia).
The typical concentration range for chronic
effects on freshwater vertebrates and inver-
tebrates. Chronic effects on most sensitive
and typical marine invertebrates.
EfA criterion to protect freshwater aquatic
life at water hardness of 200 mg/1 as CaC03.
Most reported effects levels for freshwater •
vertebrates and invertebrates fell within this
range. Chronic effects (growth retardation)
on freshwater algae. Typical range for acute
effects on marine Invertebrates.
Includes the highest concentration reported to
cause acute and chronic effects on marine
invertebrates. (Shrimp LCso at 262 ug/1 and
no spawning at 103 ug/1). Sublethal effects
noted for marine algae in 4 days.
Includes the maximum reported concentration
causing acute effects on freshwater invertebrates.
(1400 ug/1) reported for rotifer LCso) and
chronic effects on algae (freshwater) (toxic
at 2000 ug/1).
^TJ.S. EPA (1980).
Source: Chapter V, except as note'*
VII-3
-------
IT-IIA
. us paauasaac sasp ai^TT iaddn ooiJ
In considering Che concentration ranges causing deleterious effects
to aquatic biota reported in Chapter V, several points can be made about
the potential exposure of aquatic organisms:
• Concentrations of total silver in surface water, while
usually less than 10 ug/1, frequently exceed or over-
lap the lowest observed range in effects levels for
aquatic organisms (see Figure 17) at various locations
in the U.S.
• Surface water concentrations are fairly uniformly dis-
tributed nationally, with slightly higher than average
levels appearing consistently in the Southeast, Ohio
River, Lake Erie and Western Gulf major river basins,
• The only river basins that have exhibited increases in
mean concentrations recently are the North Atlantic,
Southeast and Lower Mississippi while most of the other
basins have experienced decreases.
\_
• Although only water hardness has been tasted for its
influence on silver toxicity, based on observations
on metals in general, other environmental* ^iHSSlil
commonly encountered in natural systems are i8Be€te8A
to mitigate the toxic effects of measurBa^SH&iu3if9e
concentrations, so that they are not equivalent0Jo?° u°T3saSui
TT*n>So&&trations of the &§£!? available cMipaHS8 ul&l?s ?° asn
in bioassays.
• Examples of environmental conditions conducive t8AOCl* Paaon SB
greater biological availability of sS£*a?WIu?JiciA
(1) his*^ 7 0)
processes approach the same ra
(Klein 1978): (2) oresence of ammonia whic
silver held in suspended sediment (?SitV
(3) high saline levels typical of marine, Xft61t§TAwti?rSo punoaS
the concentration of Ag ion is great
of AgCl2~, whereas in fresh water Ag+
tions are roughly equivalent although at
(Jenne <
go MI ajnsooxa . ofa^uaas aansodxa
1 These examples are meant to be illustrative of specific conditions and
do not account for other variaffiES9Ul£t!a3'U^'l£iifce¥fere with these
all
conditions favorable to ion availability.
VII-4
-------
Frequency
of Observation
Usual
Frequent
Occasional
Rare
0.001
t
Lethal to
Bacteria
(1 Study)
0.01
Ambient Surface
Waters
Chronic Effects
Region of
Potential Risk
10
t
t
No-effect
Level for
Trout
Mean
Ambient
Levels
(1970-79)
100
1000
Aqueous
concentration
FIGURE 17. SUMMARY OF SILVER EXPOSURE AND EFFECTS FOR FRESHWATER ORGANISMS
-------
9-IIA
for two species of fish. In invertebrates such as the red abalone and
the rock scallop, concentrations equivalent to those measured in fish
are reported (Section IV. D). Tissue levels higher than control levels
(three to ten times) have been related to certain silver sources i
sewage e^£«ll»? ladustniai-paptas^wtste. dispoaaidsitMaeOgdpeifQfiretp
-paAaasqo uaaq SBU. aa33Fm STUBS ao go tooap au.3 UT
B ajau« *sio3Baaua8 SuTpaas-pno-p 30
pasn aaATTB jo 8>pi
• SS8S3€QHSIBiBAESQK8n pue
T3i
silver
is its medicinal use in topical preparations. However , the^ dur« ion^o f
this form of exposure and the size of the exposed sugg^i^Gptyj^s ara^ll.
In addition, the relative benefits of using these compounds may make
them the preferred treatment. Almost all other ind^ti^fH^jtf&J&tJi1'1* L'j?uCes
occur at levels at least three orders of magnitude lover compared to
long-term daily medicinal exposure l$Bg&5o£{&£9 9$J
-------
b. Sludge
The disposal of industrial and municipal sludge onto land (approxi-
mately 220 kkg annually) may also result in the adverse exposure of
soil microbial populations. Sludge levels range from 100 mg/kg up to
900 mg/kg. When the sludge is mixed with the soil, the sludge levels
would be decreased even further. This does not mean to imply, however,
that microbial processes are unaffected by sludge-derived levels; effects
will be dependent upon the environmental characteristics of the treated
site.
Lower effects levels for microbial processes in soil, on the order
of 60 mg/kg, have been reported in laboratory studies. The 15% of muni-
cipal sludge used for amending agricultural soil may interfere with
processes essential to the cycling of nitrogen, sulfur and organic
matter. No toxicity or exposure data directly relating to the species
responsible for these processes were available to indicate threshold
effects concentrations. In addition no data were available reporting
soil levels of silver resulting from sludge application.
Other non-waste disposal related, soil concentrations (see
Section IV.E) are usually reported to be significantly lower than the
effects levels cited earlier, averaging 0.37 mg/kg in industrial areas
and 0.19 mg/kg in agricultural areas.
Silver appears to be quite immobile in soil (Section IV.C). It is
likely to accumulate in the vicinity of a continual release and to
remain in the surface layer. The problem of availability appears again
in interpreting the potential bioaccumulation and toxicity of soil
concentrations to terrestrial organisms. A large fraction of the total
amount detected is unavailable for plant uptake due to complexation and
adsorbtion by organic matter, clay and oxides. A smaller fraction may
be in the form of insoluble silver sulfide in anaerobic soils (Smith and
Carson 1977).
c. Wastewater Treatment
There has been speculation that silver may interfere with microbial
processes in wastewater treatment due to its microbiocidal effects at
low concentrations. Typical ambient concentrations of silver in surface
waters are usually lower than those triggering effects in sewage treat-
ment plants (10-25 mg/kg as reported in Section IV.B).
Although effects concentrations as low as 0.001 ug/1 have been
determined in laboratory studies, much lower than typical silver con-
centrations in wastewater influent (usually ^50 ug/1 - Section IV.B), it
is unlikely that the influent levels have the same effects on sewage
treatment microbial populations as those observed in the laboratory.
VII-7
-------
L-11&
Much of the silver entering a treatment facility, 50-70%, is removed
by sedimentation before reaching the activated sludge process (Smith
and Carson 1977). Therefore, both reduction in silver concentrations
in the waste stream due to nonbiological processes prior to reaching
h3HVoitaiida»AaTfte8«Vl3
uesq seq
Theoretically'significant bioaccumulatiafiaBfBH4vil3ia^ Slieur in
food crops grown on sludge-amended soil. Although no studies directly
addressing this subject were available—silver is_generaii^65tu?ncldded
Section 3.C.3). Smith and Carson (1977) r
sludge of up to 900 mg/kg whic
(see
oncentrations in
to uptake and accumulation in the edible fraction of the plant
- eSpnfs mozg aursinsaa aaA^js j
thatffc &^affl&^T^TS3m*^^&&SBW&?. P3ft.v$Pnfl£ SfgJgLvely
•Tmi!^^!iWn¥War& in
a
significant' problem in terms of crop uptake from sludge-amended soil.
•arps
re$ABfe^
gH' 9®Sial
data
^Concentration' in tissue divided by concentration in water
VII-8
-------
for two species of fish. In invertebrates such as the red abalone and
the rock scallop, concentrations equivalent to those measured in fish
are reported (Section IV.D). Tissue levels higher than control levels
(three to ten times) have been related to certain silver sources:
sewage outfalls, industrial areas, waste disposal sites, and electro*-
plating facilities.
The implications of accumulated silver in biota to human exposure
and risk are discussed in the following section.
C. HUMAN RISK CONSIDERATIONS
The most significant human exposure, in terms of amount, to silver
is its medicinal use in topical preparations. However, the duration of
this form of exposure and the size of the exposed subpopulation is small.
In addition, the relative benefits of using these compounds may make
them the preferred treatment. Almost all other individual exposure routes
occur at levels at least three orders of magnitude lower compared to
long-term daily medicinal exposure levels of 50 mg/day which may occur
during treatment of severe, widespread burns.
Table 53 summarizes exposure level ranges derived previously in
Section VI.A. Only inhalation exposure in the vicinity of a government
mint (^10 mg/day) approached that of medicinal application; however, the
degree of absorption may not be equivalent for these two routes- Inhala-
tion in the vicinity of other silver sources was associated with very low
exposures, on the order of 10-500 ng/day. °
In Table 54 three exposure scenarios are presented in order to
estimate the magnitude of maximum levels of silver to which humans are
likely to be exposed. One scenario results in a maximum exposure of
0.13 mg/day for a large fraction of the U.S. population, and is
attributable to ingestion of food and treated drinking water for the
most part. Also included is the amount of silver added by exposure
to urban air, in the absence of a specific source, which is nearly
identical to that for rural populations near a smelter or mining
operation (less than 0.001 mg/day difference). A second scenario
combines ingestion of contaminated food, unfinished drinking water and
inhalation near a source. This results in an exposure of 1.35 mg/day.
The size of this subpopulation (ingesting unfinished drinking water
with high silver concentration) is expected to be quite small. Thus
the likelihood of this exposure level being achieved is remote.
VII-9
-------
SMSINV9UO uaiVMHsatu uoj SJ.D3jda aw aunsodxa HBAiis jo AUvwiAins vi aunou
TABLE 53. ESTIMATED EXPOSURE LEVELS OF SILVER FOR HUMANS
i
M
O
Exposure Pathway
Medicinal Applications
Developing Film
s|aA8-| Silver
Exposure
001
snoanbv
^50 mg .in one application
Usually low; see VI.A.3.b.
% - 103 ug/day .l °
Ingestion of Drln
• Unfinished drin
• Tap water
• Well water
Inhalation of Silver in Air
• Urban areas
• Non-Urban areas
• In vicinity of sources
• In vicinity of mint
f dietary Intake (see
$53 (1980)
of
Exposed
01
Very Small
Very Small
6
100*0
,6 X 10 (general population)
Very Smal
Large (50
Large (50
165.5 X 1
55 X 106
Small
Extremely
Based on an extrapolation of 1970 data on urban a
Source: Chapter VI
population distribution to 1980 < ensus data.
IIJQJW^
1°
i of U.S. population)
of U.S. population)*?
M
6 |BUOISK»O
Small
luanbajj
-------
TABLE 54. SILVER EXPOSURE SCENARIOS FOR HUMANS EXPOSED
TO MULTIPLE SOURCES
Exposure Scenario
Exposure Level1
Estimated Size
of Subpopulation
Ingestion of food,
ingestion of tap or
drinking water,
inhalation of urban back-
ground or in vicinity of
rural source such as a
smelter or mining operation.
Ingestion of food,
ingestion of unfinished
drinking water, inhalation
as noted above.
0.13 mg/day
Large
1.35 mg/day
Small
Use of silver ointment,
ingestion of food,
ingestion of unfinished
drinking water and
inhalation as noted above.
58 mg/day
Very Small
1
From upper limit data presented in Table 53.
VII-11
-------
C-IIA
The third exposure scenarip.^^^^ ,AaJ#j$ugh rWflft^ding the
extrapolated effects level, is even more unlikely to occur than the
second one because it assumes both medicinal ugeOflSiftiftg Bfitfcjtreatment
and ingestion of unfinished drinking water. The chances for this
combination of circumstances are believed to be very sum.
is very high—10 g orally
be directly compared with
because #8» BggigLcity of
silver nitrate is partially attributed to its caustic properties.
No.jAtha^JLefll?jyai!^Ila3!?48Jo¥»t^?fon itself. The threshold for
be approached after around
daily.
03 pauodai uoTaeasaaonoa ssaqSTq aq3 sapn-pux i/8n OOOI-OOI
Comparison of effects and exposure levels reveals that none of the
Tables S3 and 54 or any reason-
serious human effects for the
18 shows the relationship between
f>or Ch£nro0i&»$s of inhalation
and ingestion. The most likely potential effect, based on exposure levels,
wo
a 50% absorption efficiency (ex-
the gut and SSgyeaxs of exposure,
the lowest exposure level to result in argyria would be less than one
found in drinking water.
estimate to 25Z means that
2%f rftift fia^yfifbdseuMTa letftuired to produce argyria.
from exposure to
of adverse efVlSdTresulting
1ulte low-
3B
OS
03
88a
uo S3oajj» B3TOV '
PUB (J83BA 3JOS
3HOJ3 JO £3TJ*32Oa)
ason uo
sajaads XOB aoj pasaodaa ssaajja OK
(8BT3
I/8n
i/8n :-T
I
T/8n O'T-T'O
T/8n vo>
339JJ3
vioia onvnov NO sums ra
SNOIIVS1N3DNOO H3A1ZS 10 S30KVH TVH31QO '25 379VX
VII-12
-------
TABLE 55. ADVERSE EFFECTS OF SILVER ON MAMMALS
Adverse Effect
Argyria
Species
man
Lowest Reported
Effect Level
No Detected
Effect Level
not well defined ^Ig Ag
-------
CHAPTER!vii.
RISK CONSIDERATIONS
g
B)
§
o
c
a
m
H>
00
v>
a
i
o
X
m
X
m
O
m
o
m
v>
O
a
z
O
•n
m
a
A. RISK STA'
There is some p
aquatic organisms in
silver. Typical tot
exceed non-lethal .•£
on ionized silver)?
toxic levels will ca
environmental variab
must be considered oh a site-specific basis, the
>tential for occurrence of adverse effects in
certain areas of the U.S. due to exposure to
il silver concentrations in surface water sometimes
[ects concentrations (based on laboratory bioassays
"An important factor in determining whether/pojtentially
ise harm at a specific location is the sjft of»
es at the site. Since, at this t
significance of silv
p
Silver does net
in the environment o
.r on a national scale
•appear to be interi
in wastewater
effects
in drink
. „ _>ns requi
humans8ai;d:slaborator r
the gastrointestinal
accumulation in tiss
Discussion of t
conclusions is prese
B. BIOTIC RISK CON
life in natural wate
be
'these factors
environmental
ascertained.
'ing with microbial processes,
.tment with any great frequency.
are not lijie'ly among humans because the silver con-
Lng water/f food, and air are low relative to the
ed toy»use effects—sublethal as well as lethal—in
animals. In addition, the rates of absorption by
trac£, skin, and lungs are low, as is the rate
le.
assumptions and supporting evidence for jfcCse
ited in this chapter.
IDERATIONS
natural waters and w istewater trea
fish consumable bySh mans.
= •? o s o °
Life in
Natural Waters
Risks to non-huaan biota are discussed.separately for (1)
tic
rs, excluding microorganisms, (2) microorgai^LSms in
systems, and (3) food crops and
3 Thee risk to aquatic biota of exposure to silver varies considerably
by location. Few industry/tategories regularly practice direct aquatic
discharge of high 4.e irelsyof silver because of the economic Incentives to
recover silver, ^ppoximately 10% of all environmental releases from
human activities are mafie directly to surface water. Inadvertent dis-
charges due to leakage; spills and overflows of holding reservoirs appear
more likely to be responsible for any adverse effects in water; however,
no specific informatjion is available concerning such discharges.
• 2 3"
£ yS
5S8
5 I" §
fi.
D) ^*
fa
= >
ill
VII-1
BI
-------
REFERENCES
Cooper, C.F.; Jolly, W.C. Ecological effects of silver iodide and other
weather modification agents: A review. Water Resource Res. 6(1):88-98;
1970.
Jenne, E.A.; Girvin, B.C.; Ball, J.W.; Burchard, J.M. Inorganic specia-
tion of silver In natural waters—fresh to marine; D.A. Klein, ed., in:
Environmental impacts of artificial ice nucleating agents; Dowden,
Hutchinson, and Ross, Inc.; 1979.
Klein, D.A. Potential impacts on aquatic systems; D.A. Klein, ed., in:
Environmental impacts of artificial ice nucleating agents; Dowden,
Hutchinson,and Ross, Inc.; 1979.
Olson, B.H.; Guinn, V.F.; Hill, D.C.; Nassiri, M. Effects of land dis-
posal of secondary effluent on the accumulation of trace elements in
terrestrial ecosystems. Trace substances in Environmental Health. XII.
362-376; 197?
Perwak, J.; Bysshe, S.; Delos, C.; Goyer, M.; Nelken, L.; Schimke, G.;
Scow, K.; Walker, P.; Wallace, D. An exposure and risk assessment for
copper. Draft. Contract EPA 68-01-3857. Washington, D.C.: Monitoring
and Data Support Division, Office of Water and Planning Standards, U.S.
Environmental Protection Agency, 1980.
Perwak, J.; Goyer, M.; Nelken, L.; Schimke, G.; Scow, K.; Walker, P.;
Wallace, D. An exposure and risk assessment for Zinc. Draft. Contract
68-01-3857. Washington, D.C.: Monitoring and Data Support-Division,
Office of Water Planning and Standards, U.S. Environmental Protection
Agency, 1980.
Perwak, J.; Goyer, M.; Nelken, L.; Scow, K.; Wald, M.; Wallace, D. An
exposure and risk assessment for mercury. Draft. Contract EPA 68-01-3857.
Washington, D.C.: Monitoring and Data Support Division, Office of Water
Planning and Standards, U.S. Environmental Protection Agency, 1980.
Smith, I.C.; Carson, B.L. Trace metals in the environment, Vol. 2—
Silver. Ann Arbor, MI: Ann Arbor Science; 1977.
U.S. Department of Commerce. Statistical abstract of the United States.
Washington, DC: Bureau of the Census, U.S. Department of Commerce; 1980.
U.S. Environmental Protection Agency (U.S. EPA). Ambient Water Quality
Criteria. Criterion Document—Silver. Washington, D.C,: Criteria,
and Standards Division, Office of Water Planning and Standards; 1979.
Available from NTIS, Springfield, VA: PB 292 441.
VII-15
-------
U.S. Environmental Protection Agency (U.S. EPA). STORE!. Washington, DC:
Monitoring and Data Support Division, U.S. EPA; 1980.
U.S. Environmental Protection Agency (U.S. EPA). Ambient water quality
criteria for silver. EPA 440/5-80-071. Washington, DC: Office of Water
Regulations and Standards; 1980b. 204 pages. Available from NTIS,
Springfield, VA.; PB-81-117822.
U.S. Food and Drug Administration (U.S. FDA). Total diet studies.
Compliance program evaluation. Washington, D.C.: U.S. Food and Drug
Administration, 1974.
U.S. Food and Drug Administration (U.S. FDA). Food and Drug Adminis-
tration: Quality standards for foods with no Identity standards.
Federal Register 44:12169; 1979.
Vanselow, A.P. Silver; Chapter 26. Diagnostic criteria for plants and
soils; Chapman, H.D. ed. Riverside, CA: Univ. of California, Div.
Agric. Sci. 405:1966. (As cited in U.S. EPA 1979)
Venugopal, B.; Luckey, T.D. Metal toxicity in mammals-2. Plenum Press;
pp. 32-36; 1978.
Wagner, P.A.; Hoekstra, W.6.; Ganther, B.E. Alleviation of silver
toxicity by selenite in the rat in relation to tissue gluthathione
peroxidase. Proc. Soc. Exp. Biol. tied. 148(4):1106-1110; 1975.
Wahlberg, J.E. Percutaneous toxicity of metal compounds. A comparative
investigation in guinea pigs. Arch. Environ. Health 11:201; 1965.
(As cited by U.S. EPA 1979)
Zech, P.; et al. Syndrome nephrotique avec depot d1argent dans les
membranes basales glomerulaires au cours d'une argyrie (Nephrotic
syndrome with silver deposits in the glomerular basement membranes
during argyria). Nouv. Presse. tied. 2:161; 1973. (As cited by U.S.
EPA 1979)
71-27
-------
APPENDIX A. PRELIMINARY DATA FOR SILVER CONSUMPTION - 1979
End Use Consumption (kkg)
Photography 2030
Electrical/Electronic Products
Contacts/Conductors 1040
Batteries 140
Sterling Ware . 410
Brazing Alloys/Solders 340
Catalysts 240
Electroplated Ware 250
Jewelry 170
Coins, Medallions & Commemorative Objects 90
Dental/Medical 70
Mirrors 60
Bearings 10
Coinage 5
Miscellaneous 30
TOTAL 4905
Source: Drake (1980).
A-l
-------
Nishioka, H. Mutagenic activities of metal compounds in bacteria.
Mutat. Res. 31:185-189; 1975.
Northdurft, H. 1956. (As cited by U.S. EPA 19791
Nothdurft, H. Uber die Nichtexistenz von 'Metallkrebs' 1m Falle der
Edelmetalle (The non-existence of metal cancers in the case of noble
metals). Naturviss. 45:549; 1958. (As cited by U.S. EPA 1979)
Oakes, T.W.; Shank, K.E. Concentration of radionuclides and selected
stable elements in fruits and vegetables. Trace Substances in Environ-
mental Health. 11:123-132; 1977.
Olcott, C.T. Experimental argyrosis. V. Hypertrophy of the left
ventricle of the heart in rats ingesting silver salts. Arch. Pathol.
49:138; 1950. (As cited by U.S. EPA 1979; NAS 1977)
Oppenheimer, B.S.; et al. Carcinogenic effect of metals in rodents.
Cancer Res. 16:439; 1956. (As cited by U.S. EPA 1979).
Petering, H.G. Pharmacology and toxicology of heavy metals: silver.
Pharmacol. Ther., Fart A; 1(2):127-130; 1976.
Ragalni, R.C., et al. Environmental trace metal contamination in
Kellogg, Idaho, near a lead smelting complex. Environ. Sci. Technol.
11:773; 1977. (As cited by U.S. EPA)
Ramage, H. Mushrooms - Mineral Content. Nature 126:279; 1930.
Reinhart, G.; Geldmacher-Mallinckrodt, M; Kittel,. HI; Opitz, 0. Arch.
Kriminol. 148:69-78; 1971. (As cited by Fowler and Nordberg 1979)
Rosenman, K.D.; Moss, A.; Ron, S. Argyria: clinical implications of
exposure of silver nitrate and silver oxide. J.O.M. 21(6):430-435;
June, 1975.
Saffiotti, U.; Shubik, P. Studies on promoting action in skin carcino-
genesis. Natl. Cancer Inst. Monogr. 10:489; 1963. (As cited by U.S. •
EPA 1979)
Savluk, O.S.; Moroz, O.G. Reaktsiya organizma belykh krys na dlitel'
noe wedenie serebra s pit'evoi vodoi (Reaction of albino rats to long-
term intake of silver with the drinking water). Vodopodgot. Ochistka
Prom. Stokov 10:99; 1973. (As cited by U.S. EPA 1979)
Schmaahl, D.; D.; Steinhoff, D. Versuch zur Krebserzeugung mit kolloidal
Silberund Goldlosungen an Ratten (Experimental carcinogenesis in rats
with colloidal silver and gold solutions). Z. Krebstorsch. 63:586;
1960. (As cited by U.S. EPA 1979).
VI-25
-------
APPENDIX B. MAPS SHOWING RATIO OF Ag CONCENTRATION IN
WHOLE WATER TO CRITERIA AGGREGATED BY COUNTY
B-l
-------
C0
N>
Ififi
FIGUTTE B-
oi-OOOtt
g
•O • OT -O X
lainTi) MOttCOio
*J -H M tJ
•rl M M H 13
0 Q.
^
a vo at a
OF 5G^C6NCENTRATION IN WHOLE WATER
USING REMARK CODES=0 85TH
i
M
>
CRITERIA AGGREGATED
PERCENTILES
BY COUNTY 85 %TILE
-------
LU
I
f NVIRUWIENIBI PHUTtrilON RUNCT
STORET SYSTEM
RflTIO OF flG CONCENTRflTION
TO CRITERIfl flCGRECflTED BY COUNT
50 XTILE USING REMflRK CODES-0
50TH PERCENTILES
^ -. i.ooco
1.0000 TO
2.0000 TO
2-0000
5-0000
• > 5-0000
?.CfltE-l TO MOOOOOO OR 220.99 HUES/INCH
0.00
MILES »10'
22.10 44.20
66.30
00-40
FIGURE B-2. RATIO OF AG CONCENTRATION IN WHOLE WATER TO CRITERIA AGGREGATED BY COUNTY 50 %TILE
USING REMARK CODES=0 50TH PERCENTILES
-------
03
•IN
flTIO
T£D GbY.COUNT
cflqfis
o P.O
o
" (X,
M?lEi>/INCH 2
U
" W C
• o o Td
to
IN Mug
USING REMARK CODES 50TH PERCENTILES
------- |