Project on Emerging
The Project on
One Woodrow Wilson Plaza
OLD PROBLEMS OR NEW CHALLENGES?
1300 Pennsylvania Ave., N.W.
Washington, DC 20004-3027
Samuel N. Luoma
Project on Emerging Nanotechnologies is supported
by THE PEW CHARITABLE TRUSTS
WOODROW WILSON INTERNATIONAL CENTER FOR SCHOLARS
Lee H. Hamilton, President and Director
BOARD OF TRUSTEES
Joseph B. Gildenhorn, Chair
David A. Metzner, Vice Chair
James H. Billington, The Librarian of Congress; Bruce Cole, Chairman, National Endowment for
TABLE OF CONTENTS
the Humanities; Michael O. Leavitt, The Secretary, U.S. Department of Health and Human
Services; Tami Longabergr, Designated Appointee within the Federal Government;
Condoleezza Rice, The Secretary, U.S. Department of State; G. Wayne Claugh, The Secretary,
Smithsonian Institution; Margaret Spellings, The Secretary, U.S. Department of Education; Allen
4 ABOUT THE AUTHOR
Weinstein, Archivist of the United States
5 EXECUTIVE SUMMARY
PRIVATE CITIZEN MEMBERS
9 I. INTRODUCTION
Robin B. Cook, Donald E. Garcia, Bruce S. Gelb, Sander R. Gerber, Charles L. Glazer,
Susan Hutchison, Ignacio E. Sanchez
14 II. FATE AND EFFECTS OF SILVER
IN THE ENVIRONMENT
14 History of Silver Toxicity
The PROJECT ON EMERGING NANOTECHNOLOGIES was launched in 2005 by the Wilson
Center and The Pew Charitable Trusts. It is dedicated to helping business, governments, and
the public anticipate and manage the possible human and environmental implications of
15 Sources: How Much Silver Is Released
to the Environment by Human Activities?
18 Pathways: What Are the Concentrations
THE PEW CHARITABLE TRUSTS serves the public interest by providing information, advancing
of Silver in the Environment?
policy solutions and supporting civic life. Based in Philadelphia, with an office in
20 Pathways: Forms and Fate
Washington, D.C., the Trusts will invest $248 million in fiscal year 2007 to provide organ-
22 Receptor: In What Forms
izations and citizens with fact-based research and practical solutions for challenging issues.
Is Silver Bioavailable?
25 Impact: Toxicity of Silver
The WOODROW WILSON INTERNATIONAL CENTER FOR SCHOLARS is the living, national memo-
35 III. EMERGING TECHNOLOGIES
rial to President Wilson established by Congress in 1968 and headquartered in
Washington, D.C. The Center establishes and maintains a neutral forum for free, open and
35 Conceptual Framework
informed dialogue. It is a nonpartisan institution, supported by public and private funds and
engaged in the study of national and international affairs.
35 Sources of Nanosilver and
Potential Dispersal to the Environment
39 Mass Discharges to the Environment
from New Technologies
44 Pathways of Nanosilver in the Environment
47 Is Nanosilver Bioavailable?
51 How Does Nanosilver Manifest Its Toxicity?
57 IV. THE WAY FORWARD: CONCLUSIONS
ILLUSTRATIONS BY Jeanne DiLeo
AND THE ENVIRONMENT:
OLD PROBLEMS OR NEW CHALLENGES?
Samuel N. Luoma
PEN 15 SEPTEMBER 2008
The opinions expressed in this report are those of the author and do not necessarily reflect
views of the Woodrow Wilson International Center for Scholars or The Pew Charitable Trusts.
Dr. Samuel Luoma has given us an excellent description and analysis of the science of silver and
nanosilver. His paper raises many questions for policy makers. Its subtitle, “Old Problems or
New Challenges,” is appropriate, because the subject of the paper is both. Metals are among the
oldest of environmental problems. Lead, silver and mercury have posed health hazards for thou-
sands of years, and they are as persistent in the environmental policy world as they are in the
environment. Nanotechnology is a new challenge, but the scope of the policy issues it presents
is as broad and difficult as the technology itself.
As the paper makes clear, there is much we do not know about the environmental pathways
of nanosilver, its environmental effects and its impact on human health. However, as Luoma
notes, ionic silver, a form of nanosilver, when tested in the laboratory, is one of the most toxic
metals to aquatic organisms. Ionic silver is being used now in washing machines and other
products. The need for research is urgent. The major experiment being conducted now is to put
nanosilver products on the market, expose large numbers of people and broad areas of the envi-
ronment and then wait and hope that nothing bad happens. This is a dangerous way to pro-
ceed. The experiments need to come before the marketing so that damage can be avoided rather
Dr. Luoma employs a useful environmental framework, starting with sources of nanosilver,
then dealing with its pathways in the environment and ending with receptors and impact.
Policy makers use the same model, only in reverse. They start with the question of whether
there is an impact, then analyze the environmental pathways and finally deal with whether and
how to control the sources.
The impacts are the policy starting point, so the fact that less than 5 percent of the money
being spent on nanotechnology by the U.S. government is being spent to study health and envi-
ronmental impacts demonstrates a questionable sense of priorities. That is the major policy issue.
However, there is also a need for surveillance and reporting. Workers, consumers, lakes and
streams are being exposed to nanosilver and, while the experimentation is unfortunate, society
should at least learn from it. People working with nano need to be monitored, and key aspects
of the environment exposed to nanosilver should be investigated. Some of this will be done by
scientific institutions, public and private. However, some of it, for example, medical monitoring
of workers, may require government regulation.
There is another connection between regulation and impacts, one that is less well recognized.
As Luoma notes, “the formulation and form of a nanoparticle has great influence on the risks
that it poses.” Silver in different nanoproducts can be in the form of silver ions, silver colloid
solutions or silver nanoparticles. The nanosilver can come in different shapes, have different elec-
trical charges and be combined with other materials and coated in different ways. Each of these
factors, as well as others, affects toxicity and environmental behavior. If we are to discover how
these different factors impact nanosilver’s toxicity and environmental behavior, it will only be by
testing a large number of specific products that have different characteristics. This is not the kind
of testing that will be done by universities or government laboratories. The only way that these
data are likely to be collected is by requiring manufacturers to test their nanosilver products.
Although it would be neater and more efficient to mandate testing of nanoproducts only after
we knew how particular product characteristics influence toxicity, in reality the only way we are
going to gain this knowledge is by first mandating that manufacturers test their nanoproducts
for health and environmental effects.
As Dr. Luoma describes, little is known about the environmental pathways of nanosilver. The
policy challenge that emerges from his description is how to match the antiquated air-water-land
basis of existing laws with the inherently cross-media nature of the problem. Nanosilver can go
from a manufacturing plant to a waste-treatment plant to sludge to crops to the human-food
chain. It is considered primarily a water problem in the environment but primarily an air prob-
lem in the workplace. Like climate change, acid rain and genetically modified crops, nanosilver
is a problem that fits poorly into the old boxes of the existing regulatory system.
One reason a cross-media approach is necessary is that it allows a policy maker to consider
which sources of pollution or exposure are most important and which can be most efficiently
and effectively addressed. Current efforts to address nanosilver are using the few cross-media
tools the United States has—specifically, the Federal Insecticide, Fungicide and Rodenticide
Act (FIFRA) and the Toxic Substances Control Act (TSCA). The two acts are quite different
in several ways. TSCA is broad and potentially could cover most nanomaterials. FIFRA, by
contrast, is limited to pesticides, which are defined to include antimicrobials. However, since
nanosilver is used primarily as an antimicrobial, most nanosilver products may come under
FIFRA. The acts also differ in the degree of public protection and product oversight they offer.
FIFRA is quite stringent and puts the burden of proof for safety on the manufacturer. TSCA
is riddled with loopholes and puts the burden of proof on the U.S. Environmental Protection
Agency (USEPA) to show that a substance is harmful.
The extent to which USEPA will use FIFRA to regulate nanosilver products is uncertain.
The agency has reversed a previous decision and decided that the Samsung Silver Wash wash-
ing machine, which emits silver ions into every wash load, must be registered as a pesticide.
However, that decision was drawn in the narrowest possible terms, making it clear that the
agency has not decided to require registration for the numerous other commercial products that
are using nanosilver as an antimicrobial. Several environmental groups have joined to petition
the agency to require registration for the other products, but the agency has not yet respond-
ed. Meanwhile, USEPA’s San Francisco regional office has imposed a fine on a company sell-
ing computer keyboards and mouses coated with nanosilver on the grounds that the products
should have been registered under FIFRA. However, it is not clear that this represents a gener-
al policy, either in Region IX or for USEPA as a whole. It seems more likely that this is a one-
time case, perhaps intended as a signal to discourage widespread use of nanosilver coatings.
There is no legal or technical reason why FIFRA could not be used to regulate most
nanosilver products. However, an initiative to do so would require dollars and personnel, and
both are in short supply within USEPA. More important, it is not clear that the agency would
want to launch a major regulatory initiative in the waning days of a fervently antiregulatory
administration. The Bush administration has significantly reduced USEPA’s budget, and the
current USEPA administrator seems willing to be guided by White House directives when it
comes to major decisions.
Dr. Luoma, while conceding that little is known about the quantities or concentrations of
nanosilver releases from various sources, states that “industrial releases associated with manu-
facturing the nanosilver that goes into the consumer products or production of the products
themselves is likely to be greater than consumer releases.” If this is so, it will be necessary to
look to the Clean Water Act (CWA) and the Clean Air Act (CAA) to control nanoreleases. This
is unfortunate, because at present there are major technical obstacles to using these acts.
Practical methods for monitoring nanosilver in air and water and methods for controlling
releases to air and water are lacking.
The monitoring problem is especially difficult because it is not clear what should be moni-
tored. Simple measures of quantity, mass or concentration that are used for other pollutants are
probably not adequate for monitoring nanomaterials. As noted above, there are more than a
dozen characteristics of nanosilver that are relevant to its health and environmental impact.
There is no technique for ambient monitoring all these characteristics, nor is it clear how they
can be narrowed to a manageable number for monitoring. Without the ability to monitor, it is
difficult to regulate using the CAA or CWA, although some version of “good management
practices” might be used until monitoring methods are developed.
Silver is an old problem, and nanosilver is a new challenge. The scope of the new challenge
is not yet clear because it is unclear how much nanosilver will be used as an antimicrobial and
because new uses are likely to be discovered. Regardless of the scope of the nanosilver problem,
it underscores the need for new approaches to oversight to deal with the new technologies and
problems of the new century. Laws and institutions shaped in the mid-20th century are not
likely to succeed in addressing 21st-century problems. Developing a new approach to oversight
and regulation may be the biggest challenge of all.
—J. Clarence Davies
Senior Advisor, Project on Emerging Nanotechnologies
Senior Fellow, Resources for the Future
ABOUT THE AUTHOR
Dr. Samuel N. Luoma leads science policy coordination for the John Muir Institute of the
Environment at the University of California, Davis. He is also editor-in-chief of San Francisco
Estuary & Watershed Science and is a scientific associate with The Natural History Museum in
London, United Kingdom (UK). Prior to this, he was a senior research hydrologist with the
U.S. Geological Survey. He served as the first lead scientist for the CALFED Bay-Delta pro-
gram, an innovative program of environmental restoration of over 40 percent of California’s
watershed, and water management issues for 60 percent of California’s water supply. His spe-
cific research interests are studying the bioavailability and effects of pollutants in aquatic envi-
ronments and developing better ways to merge environmental science and policy. He is an
author on more than 200 peer-reviewed publications. He wrote Introduction to Environmental
Issues, published in 1984 by Macmillan Press, and, with coauthor Philip Rainbow, recently fin-
ished Metal Contamination in Aquatic Environments: Science and Lateral Management, which
will be released by Cambridge University Press in October 2008. He is an editorial advisor for
the highly respected Marine Ecology Progress Series, and on the editorial board of Oceanologia.
He was a W. J. Fulbright Distinguished Scholar in the UK in 2004 and is a Fellow of the
American Association for the Advancement of Science. His awards include the President’s Rank
Award for career accomplishments as a senior civil servant, the U.S. Department of Interior’s
Distinguished Service Award and the University of California at Davis Wendell Kilgore Award
for environmental toxicology. He has served nationally and internationally as a scientific expert
or advisor on issues at the interface of science and environmental management, including sed-
iment quality criteria (U.S. Environmental Protection Agency SAB Subcommittee),
Bioavailability of Contaminants in Soils and Sediments (Canadian National Research Council,
1987, U.S. National Research Council subcommittee, 2000–2002), mining issues (United
Nations Educational, Scientific and Cultural Organization; Global Mining Initiative), seleni-
um issues, environmental monitoring and metal effects.
Nanomaterials with silver as an ingredient raise new challenges for environmental managers.
Potentially great benefits are accompanied by a potential for environmental risks, posed both
by the physical and chemical traits of the materials. We need not assume that because nano is
new, we have no scientific basis for managing risks, however. Our existing knowledge of silver
in the environment provides a starting point for some assessments, and points toward some of
the new questions raised by the unique properties of nanoparticles. Starting from what we
know about silver itself, this report identifies 12 lessons for managing environmental risks
from nanosilver. These lessons help set the stage for both the research strategy and the risk
• Silver itself is classified as an environmental hazard because it is toxic, persistent and bioac-
cumulative under at least some circumstances. Aside from releasing silver, the toxicity, bioac-
cumulative potential and persistence of nanosilver materials are just beginning to be known.
But enough is known to be certain that risks must be investigated.
• Nearly one-third of nanosilver products on the market in September 2007 had the potential
to disperse silver or silver nanoparticles into the environment. The silver content of these
materials appears to vary widely. Reports on the form of the silver in these products are gen-
erally inconsistent and do not follow scientific definitions. Guidelines for concentrations and
formulations of reduced toxicity might offer opportunities for regulation.
• The mass of silver dispersed to the environment from new products could be substantial if
use of one product, or a combination of such products, becomes widespread. Traditional
photography established a precedent for how a silver-based technology that was used by mil-
lions of people could constitute an environmental risk. Release of silver to waste streams
when photographs were developed was the primary cause of silver contamination in water
bodies receiving wastes from human activities, and of adverse ecological effects where stud-
ies were conducted.
• Risk assessment(s) will ultimately be necessary for at least some products employing silver
nanomaterials. Risk assessments will require information about mass loadings to the envi-
ronment. Such information is not currently available. Neither government reporting require-
ments nor product information is sufficient to construct reliable estimates of mass discharges
from these new nanosilver technologies, but the potential exists for releases comparable to or
greater than those from consumer usage of traditional photography.
• There are no examples of adverse effects from nanosilver technologies occurring in the envi-
ronment at the present. But environmental surveillance is a critical requirement for a future
risk management strategy, because silver nanoproducts are rapidly proliferating through the
consumer marketplace. Few if any methodologies exist for routine environmental surveil-
lance of nanomaterials, including nanosilver. Monitoring silver itself, in water, sediment or
biomonitors, could be a viable interim approach until methods specific to the nanomaterial
• Silver concentrations in natural waters, even those contaminated by human activities, range
from 0.03 to 500 nanograms/liter (ng/L). Even substantial proliferation of silver nanotech-
nologies is unlikely to produce pollutant concentrations in excess of the ng/L range.
Environmental surveillance methodologies must be capable of detecting changes in concen-
trations within this range.
• Toxicity testing should focus on realistic exposure conditions and exposures in the ng/L
range, and not on short-term acute toxicity. Sensitive toxicity tests and environmental case
studies have shown that silver metal is toxic at concentrations equal to or greater than 50
ng/L. One well-designed study on nanosilver has shown toxicity at even lower concentra-
tions to the development of fish embryos. Even though the potential concentrations in con-
taminated waters may seem low, environmental risks cannot be discounted.
• The environmental risks from silver itself can be mitigated by a tendency of the silver ion to
form strong complexes that are apparently of very low bioavailability and toxicity. In partic-
ular, complexes with sulfides strongly reduce bioavailability under some circumstances. It is
not yet clear to what extent such speciation reactions will affect the toxicity of nanosilver. If
organic/sulfide coatings, or complexation, in natural waters similarly reduce bioavailability
of nanosilver particles, the risks to natural waters will be reduced. But it is also possible that
nanoparticles shield silver ions from such interactions, delivering free silver ions to the mem-
branes of organisms or into cells (a “Trojan horse” mechanism). In that case, an accentua-
tion of environmental risks would be expected beyond that associated with a similar mass of
silver itself. The Trojan horse mechanism is an important area for future research, especially
• The environmental fate of nanosilver will depend upon the nature of the nanoparticle.
Nanoparticles that aggregate and/or associate with dissolved or particulate materials in
nature will likely end up deposited in sediments or soils. The bioavailability of these materi-
als will be determined by their uptake when ingested by organisms. Some types of silver
nanoparticles are engineered to remain dispersed in water, however. The persistence of these
particles, on timescales of environmental relevance (days to years), is not known.
• Silver is highly toxic to bacteria, and that toxicity seems to be accentuated when silver is
delivered by a nanoparticle. Dose response with different delivery systems and in different
delivery environments has not been systematically studied.