A Chronology of 

Middle Missouri Plains 

Village Sites

By Craig M. Johnson

with contributions by

Stanley A. Ahler, Herbert Haas, and Georges Bonani

Smithsonian Institution

Scholarly Press

Smithsonian Institution

Scholarly Press

s m i t h s o n i a n c o n t r i b u t i o n s t o m u s e u m c o n s e r va t i o n • n u m b e r 1

Pesticide Mitigation in 

Museum Collections:

Science in Conservation

Proceedings from the MCI Workshop Series

Edited by

A. Elena Charola and

Robert J. Koestler
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s m i t h s o n i a n c o n t r i b u t i o n s t o m u s e u m c o n s e r v a t i o n • n u m b e r 1

washington d.c.

2010

Pesticide Mitigation in 

Museum Collections: 

Science in Conservation

Proceedings from the MCI Workshop Series

Edited by

A. Elena Charola and

Robert J. Koestler
ABSTRACT

Charola, A. Elena, and Robert J. Koestler, editors. Pesticide Mitigation in Museum Collections: Science in Conservation. Proceedings from the MCI Workshop Series. Smithsonian Contributions to Museum Conservation, number 

1, vi + 72 pages, 51 figures, 15 tables, 2010. — The Smithsonian Museum Conservation Institute Workshop on 

Pesticide Mitigation was one of the first professional meetings dedicated to current research on removing pesticide 

residues from museum objects. Seven papers were presented at the workshop, and two more were added to introduce topics not focused on during the meeting but of significant importance when considering actual application of 

any of these methods.

The aim of the workshop was to bring together conservators, scientists, and even industry representatives to 

discuss the complex issues associated with pesticide removal from artifacts and to provide representative examples 

of the research and work being carried out at different institutions in the United States and abroad. Among the issues explored were possible methods and techniques that might become useful in the museum conservation field to 

reduce, mitigate, clean, or remediate undesirable pesticides on objects. The meeting also served to inform conservators and scientists in the Smithsonian Institution of the wide range of approaches that are currently being tested and 

that might prove useful in the future.

Topics covered in the presented papers included removal of mercury and arsenic contamination with α-lipoic 

acid; the treatment of Haudenosaunee medicine masks with surface active displacement solutions; the possibility of 

using mercury-resistant bacterial communities to remediate contamination; solvent extraction through the use of 

special solvents such as hydrofluoroethers; carbon dioxide as a cleaning fluid either in liquid or in supercritical state; 

and novel cleaning techniques either through the use of additives to improve the efficiency of liquid or supercritical CO2 cleaning, other gases in a supercritical state, or other techniques such as fluidized beds. The introduction 

of novel techniques at the workshop was encouraged in order to broaden the range of promising methods that 

might improve the technology of pesticide mitigation or remediation. The two supplemental papers discuss pesticide 

analysis on objects and safety measures that should be implemented by institutions with contaminated collections.

Cover images, from left to right: Figures 11, 2, and 9 (detail) by Tello and Unger.

Published by Smithsonian Institution Scholarly Press

P.O. Box 37012

MRC 957

Washington, D.C. 20013-7012

www.scholarlypress.si.edu

Library of Congress Cataloging-in-Publication Data

Smithsonian Museum Conservation Institute Workshop on Pesticide Mitigation (2007 : Washington, D.C.)

Pesticide mitigation in museum collections : science in conservation : proceedings from the MCI workshop 

series / edited by A. Elena Charola and Robert J. Koestler.

 p. cm. — (Smithsonian contributions to museum conservation, ISSN 1949-2359 ; no. 1)

Papers from a workshop held April 23–24, 2007.

Includes bibliographical references.

1. Museum conservation methods—Congresses. 2. Decontamination (from gases, chemicals, etc.)—Congresses.

3. Cleaning—Congresses. 4. Museum buildings—Pest control—Congresses. 5. Museums—Collections management—Congresses. 6. Pesticides—Risk mitigation—Congresses. I. Charola, A. Elena. II. Koestler, Robert J. 

(Robert John), 1950– III. Museum Conservation Institute. IV. Title. 

AM145.S65 2010

069’.53—dc22

2009048678

ISSN: (print) 1949-2359; (online) 1949-2367

The paper used in this publication meets the minimum requirements of the American National Standard 

for Permanence of Paper for Printed Library Materials Z39.48–1992.
Contents

INTRODUCTION by Robert J. Koestler and A. Elena Charola v

Pesticide Remediation in Context: Toward Standardization of 

Detection and Risk Assessment 1

Odile Madden, Smithsonian Institution, Museum Conservation 

Institute

Jessica Johnson, Smithsonian Institution, National Museum of 

the American Indian 

Jae R. Anderson, Tuba City, Arizona

Aqueous α-Lipoic Acid Solutions for Removal of Arsenic and 

Mercury from Materials Used for Museum Artifacts 7

Peggi S. Cross, Arizona State Museum, University of Arizona, Tucson

Nancy Odegaard, Arizona State Museum, University of Arizona, 

Tucson 

Mark R. Riley, University of Arizona, Tucson

Solvent Cleaning of Fragile Artifacts without Mechanical Agitation 13

Robert Kaiser, Entropic Systems, Inc.

Mitigation of Surface Contaminants on Haudenosaunee Medicine Masks 25

Peter A. Reuben, Seneca Nation of Indians, Tribal Historical 

Preservation Office

Bacterial Removal of Mercury from Museum Materials: A New 

Remediation Technology? 29

Timberley M. Roane, University of Colorado, Denver

Lisa J. Snelling, University of Colorado, Denver

Liquid and Supercritical Carbon Dioxide as a Cleaning and 

Decontamination Agent for Ethnographic Materials and Objects 35

Helene Tello, Ethnological Museum - National Museums in Berlin

Achim Unger, Rathgen Research Laboratory, National Museums 

in Berlin
i v • S mithsonian C ontributions to museum conservation

Pesticide Extraction Studies Using Supercritical Carbon Dioxide 51

Werner S. Zimmt, Arizona State Museum, University of Arizona, 

Tucson 

Nancy Odegaard, Arizona State Museum, University of Arizona, 

Tucson

Teresa K. Moreno, Arizona State Museum, University of Arizona, 

Tucson 

Rachael A. Turner, University of Arizona, Tucson 

Mark R. Riley, University of Arizona, Tucson 

Bo Xie, University of Arizona, Tucson 

Anthony J. Muscat, University of Arizona, Tucson

The Potential for Adapting Some Cleaning Methodologies to Pesticide 

Removal from Museum Objects 59

Werner S. Zimmt, University of Arizona, Tucson 

Nancy Odegaard, University of Arizona, Tucson

David R. Smith, University of Arizona, Tucson

Discussion: Mitigation of Contaminated Collections 65

R. Eric Hollinger, National Museum of Natural History, Smithsonian 

Institution

Greta Hansen, National Museum of Natural History, Smithsonian 

Institution

APPENDIX: COMMON MUSEUM PESTICIDES 71
The conservation of objects of cultural, historic, and artistic value is 

an interdisciplinary endeavor that draws from many fields—from the 

pure to the applied sciences, from the history of classical art to folk 

traditions, and from industry to arts and crafts. Problem solving in 

this field is complex. An example is the past use of pesticides for the protection 

of natural history and ethnographic objects. This action was well intentioned; 

however, at the time no one knew the extent of the health hazard that was being created for anyone who would have to handle these objects in the future. 

With today’s increased knowledge about health risks, it is evident that we must 

“undo” previous conservation interventions. The challenge is to figure out how.

It is a difficult challenge, as complex as the objects that have been treated 

in the past and as vast as the list of chemicals that have been used and, in some 

cases, are still being used. The complexity is compounded by the variable retention rates of different materials for specific chemicals and by the fact that documentation is rarely sufficient to determine exactly how an object was treated. 

Questions abound: Can we determine the amount of pesticide(s) present on any 

given object? What is the risk for those who have to handle the object? Are there 

cultural sensibilities that must be considered regarding the object or the removal 

of the pesticide present from that object? What methods can be used to mitigate 

this risk? And, as we “undo” yesterday’s problems, are we perhaps inadvertently 

creating new problems for tomorrow’s museumgoers and personnel? 

These were some of the considerations that prompted the Pesticide Mitigation in Museum Collections Workshop held at the Smithsonian Institution’s 

Museum Conservation Institute on 23–24 April 2007. The papers in this volume 

resulted from the workshop. During the mornings of those two days, seven presentations were made, with the afternoons devoted to discussion of each day’s 

presentations. A final discussion panel served to close the workshop. 

It was the aim of the workshop to provide representative examples of the 

research and work being conducted at different institutions in the United States 

and abroad. The objective was to alert conservators and scientists in the Smithsonian Institution of the wide range of approaches that are currently being 

tested and that might prove useful in the future. As pointed out by Hollinger and 

Introduction
v i • S m i t h s o n i a n C o n t r i b u t i o n s t o m u s e u m c o n s e rvat i o n

information together and presenting it to members of the 

conservation field in one volume should help stimulate 

progress. We hope that further research will result from 

this workshop and that promising methodologies will be 

developed to safely and appropriately mitigate or remediate pesticides on museum objects.

Acknowledgments

This publication would not have been possible without the enthusiasm and support provided by Dr. Paula T. 

DePriest. Many others contributed to this work also, and 

among them we thank, in particular, Jeff Speakman, Ann 

N’Gadi, Mary Ballard, and Carol Grissom from the Museum Conservation Institute (MCI), and Ginger Strader 

from the Smithsonian Institution Scholarly Press. Last, but 

not least, Beverley Smith, Francine Lewis, and Vernetta 

Williams from the MCI are thanked for their behind-thescenes assistance. 

Robert J. Koestler 

Director, Museum Conservation Institute

Smithsonian Institution

A. Elena Charola

Scientific Consultant in Conservation

Hansen (this volume, p. 69), “it is unlikely that there will 

ever be a single method for cleaning all types of objects 

or materials.” Therefore, understanding the potential and 

the problems presented by each method will allow further 

development of the most promising application(s) on such 

sensitive materials as those found in ethnographic and natural history collections. This is the long-term objective of 

the workshop and the reason for this publication.

Workshop presenters were asked to submit papers reviewing the information given during their presentations; 

these papers constitute the bulk of those included herein. 

Two supplemental papers are included: (1) an introduction to the problems presented by the analysis of pesticides 

on objects by Odile Madden, Jessica Johnson, and Jae Anderson, and (2) a summary of the conclusions that resulted 

from the workshop by R. Eric Hollinger and Greta Hansen. These two overviews provide valuable perspectives 

on the state of the art of pesticide mitigation in museum 

collections. 

The workshop succeeded in defining topics that need 

to be addressed to improve mitigation and remediation 

of pesticide-contaminated collections. While no endorsements for the application of any one technique were made, 

as much more testing needs to be performed, the workshop was a good forum for discussing advantages and 

disadvantages of different approaches. Bringing all this 
Paper presented at the Pesticide Mitigation in 

Museum Collections Workshop held at the Smithsonian’s Museum Conservation Institute in April 

2007 exploring possible methods and techniques 

that may become useful for the museum conservation field to reduce, mitigate, clean, or remediate 

undesirable pesticides on objects.

Odile Madden, Smithsonian Institution, Museum Conservation Institute, 4210 Silver Hill 

Road, Suitland, Maryland 20746, USA. Jessica 

Johnson, Smithsonian Institution, National Museum of the American Indian, Cultural Resources 

Center, 4220 Silver Hill Road, Suitland, Maryland 

20746, USA. Jae R. Anderson, P.O. Box 1868, 

Tuba City, Arizona 86045, USA. Corresponding 

author: O. Madden (maddeno@si.edu). Manuscript received 12 June 2008; accepted 26 June 

2009.

Pesticide Remediation in Context:

Toward Standardization of Detection and 

Risk Assessment

Odile Madden, Jessica Johnson, and

Jae R. Anderson

ABSTRACT. The Smithsonian Museum Conservation Institute workshop on pesticide 

mitigation is likely the first professional meeting dedicated entirely to current research 

efforts to remove pesticide residues from museum objects. However, the question of remediation is but one part of a broader field of research into pesticide residues on cultural 

property. Challenges of consultation and collaboration, identification and detection, risk 

assessment, and mitigation with regard to residues are inextricably related, and responsible and comprehensive solutions are being researched simultaneously around the world 

in response to these challenges. This paper attempts to contextualize the topic of remediation within the field of analytical research into pesticide residues on museum objects.

Keywords: pesticide residues, arsenic, mercury, lead, detection, analysis, remediation, mitigation, cleaning, removal, risk assessment, museum objects.

INTRODUCTION

When discussing the removal of pesticide residues from museum objects, 

often the instinctive assumption is that the pesticides present are known and 

that their concentrations present a hazard to human health. In fact, this is not 

so. Detection and quantification of pesticide residues is an ongoing topic of 

research, and deciding what levels of contamination present a human health 

risk remains under discussion. Remediation is but one part of a broader field of 

research into pesticide residues on cultural property. Challenges of consultation 

and collaboration, identification and detection, risk assessment, and mitigation 

are inextricably related, and responsible and comprehensive solutions are being 

researched simultaneously around the world in response to these challenges.

The Museum Conservation Institute (MCI) workshop on pesticide mitigation provided a forum for sharing novel methods to reduce pesticide concentrations on artifacts. As such, the tone of the presentations was more technical than 

cultural and focused on remediation experiments rather than detection methods 

or risk characterization. Group discussions between the presentations, which 

are not recorded in this volume, highlighted some gaps in consensus about the 

appropriateness of treatments and standards for detection. They also articulated 
2 • S miths o n ia n C o n tri b u ti o n s t o m u s e u m c o n s e rvati o n

common practice in North American museums to address 

pesticide questions collaboratively, with conservators, scientists, health and safety professionals, and, in the case 

of ethnographic collections, consultants from indigenous 

communities. All of them contributed expertise on this 

topic and brought to the table diverse priorities (Johnson 

and Henry, 2002), which were reflected in two issues of 

Collection Forum in 2001. Particularly for Native American material, the cultural appropriateness of testing and 

treatment protocols is an overriding concern, predominantly for those objects that are considered to possess 

a life force of their own (Sadongei, 2001; Johnson and 

Henry, 2002). Stakeholders now meet regularly in conferences and smaller meetings to discuss cultural ramifications as well as advances in detection and quantification of 

residues, risk assessment, and mitigation strategies. Some 

of these meetings have broad scopes, such as educational 

outreach to indigenous communities and conservation 

professionals, while others focus more narrowly on specific issues such as X-ray fluorescence spectrometry (XRF) 

or computerized options for health risk assessment.

Mitigation, Remediation, and

Risk Assessment

What exactly is meant by “pesticide mitigation”? The 

term mitigation generally is used to describe the reduction 

of the risk posed by a pesticide. The risk may be to human 

health, the health of another species, or the environment. 

Mitigation can be accomplished in several ways. The pesticide can be removed from an object, which is known 

as remediation, or the potential for exposure can be reduced, for example by modifying the way artifacts are 

handled or by the use of protective clothing (Odegaard, 

2001). The papers presented at MCI’s workshop on pesticide mitigation were studies in remediation. Each presentation discussed an experimental treatment designed 

to remove one or more pesticides from an artifact material. Most of the work was performed on experimental 

samples, though Reuben’s work was carried out directly 

on repatriated Haudenosaunee medicine masks (Reuben, 

this volume). As the treatments are still experimental, 

they might be termed more appropriately as studies in 

potential remediation treatments rather than mitigation. 

The ultimate goal of remediation experiments and of the 

wider field of mitigation is to reduce the risk posed by the 

pesticide(s).

The risk posed by a toxic substance can be described 

by the following equation:

the need to consider any remediation effort within 

the context of mitigating risk to human health and the 

environment.

BACKGROUND

In the past, museum artifacts have been treated with 

a range of pesticides to eradicate and prevent infestation 

by insects, rodents, and mold. Because many of these 

chemicals are hazardous to human health, it is incumbent on museums to identify those potentially hazardous 

items in collections and determine whether the risk posed 

is significant. The National Museum of Natural History 

(NMNH) was among the first museums in the United 

States to research and publish the history of pesticide use 

in its collections (Hawks and Williams, 1986). The results, 

published in “A History of Pest Control Measures in the 

Anthropology Collections, National Museum of Natural 

History, Smithsonian Institution” sounded a wake-up call 

to museums across the country (Goldberg, 1996). Though 

concern over the health risks associated with poisons used 

in museums has long been present, only recently did the 

issue of pesticide residues on cultural material and natural 

history specimens become a hot topic of discussion in conservation. Solutions to this problem are being sought by 

many museums as well as tribal groups.

A major impetus for the current wave of pesticide 

research in the United States is the National Museum of 

the American Indian Act of 1989 and the Native American Graves Protection and Repatriation Act (NAGPRA) 

of 1990.1 According to these, museums that receive funds 

from the U.S. government are required to return certain 

Native American artifacts and human remains to the tribe 

of origin and inform the recipients of any known treatments that have been applied. The need to comply with 

this legislation, concern over potential liability, and ethical 

considerations have spurred research programs focused on 

pesticide detection and quantification as well as management of the potential health risks (Nason, 2001; Tsosie, 

2001; Johnson and Henry, 2002). Concurrently, the importance of evaluating these same issues for the protection of museum workers and visitors was also recognized 

(Makos, 2001; Odegaard and Sadongei, 2005).

The bulk of early research focused on formulating 

the problem and identifying those groups with a stake in 

the issue. Seminal meetings were held at the Arizona State 

Museum in 2000, San Francisco State University in 2000, 

and Shepherdstown, West Virginia, in 2001. As is evident 

from the lists of participants in those meetings, it is now 
n u m b e r 1 • 3

It follows that to mitigate risk one can reduce or remove the hazard or lower one’s exposure to that hazard. 

The remediation studies presented in this volume address 

the hazard term of the equation.

Detection and Quantification

of Residues

Each remediation study included in this volume employs an analytical method to identify and quantify pesticide residues. X-ray fluorescence spectrometers were used 

to measure arsenic and mercury at parts per million concentration directly on samples (Cross et al., this volume; 

Roane and Snelling, this volume). More sensitive atomic 

absorption methods were used on both wipes (Reuben, this 

volume) and digested samples (Roane and Snelling, this 

volume), presumably with a limit of detection on the order 

of parts per billion. Zimmt and Odegaard took a different 

approach by using a toxicological screening of rat lung 

epithelial cells to detect Diazinon residues (Zimmt et al., 

this volume). Whether analysis of artifacts or preparations 

of experimental samples in the laboratory are discussed, 

an agreed method to accurately identify and measure the 

amount of pesticide present is required.

The importance of detection is obvious. Although it 

may be known through personal recollection or archival 

research that a collection was treated with a pesticide, 

the full pesticide treatment history of specific objects is 

rarely known. Certain analytical methods, such as XRF 

spectrometry, serve to identify the presence of heavy metals on objects and their contamination levels. Detection is 

equally important in the laboratory when testing remediation treatments. In order to judge the degree of pesticide 

removal, the amount present before and after treatment 

must be measured.

What analytical detection methods cannot do is determine whether the contamination detected poses a human 

health risk. This assessment requires knowledge of the contaminant, its toxicological profile, and human judgment.

The MCI workshop on pesticide mitigation revealed 

two things. First, there is no standard methodology for 

measuring pesticide residues on artifacts or on samples 

prepared in the laboratory. Every study approached this 

problem differently, and though each showed a reduction 

in the amount of pesticide present after treatment, it is difficult to compare results between studies. Second, there 

was no consensus as to what degree of removal is sufficient 

or ideal. Most of the studies reported results as the amount 

of pesticide removed with no discussion of an appropriate 

Hazard × Exposure = Risk.

The hazard is the pesticide. What is it? How much is 

on the artifact? How labile or mobile is it? Museums and 

tribal groups continue to invest heavily in sophisticated 

methods to answer these questions.

Exposure is more complicated to assess. One aspect 

has to do with the way in which pesticides are transferred 

from object to person or environment. How does the person interact with the contaminated artifact? What is the 

route of entry (ingestion, skin contact, or inhalation)? At 

what rate is the pesticide transferred to a person or the 

environment? How long will he or she be exposed and 

how frequently? These questions are complicated given 

the wide range of artifact types and ways in which museum staff, visitors, and people outside the museum interact with them.

Specific details about the person who handles the artifact are also a factor. For example, is it a 40-year-old 

man or a pregnant woman in her twenties? The toxicological profiles of these two populations can be very 

different (C. Chaisson, The LifeLine Group, personal 

communication).

All of these factors should be taken into consideration 

when assessing the risk posed by a contaminated artifact. 

The matrix of potential hazards, types of exposure, and 

diverse populations is extremely complex.

Different research groups approach risk assessment in 

a range of ways. Working with Health Canada, the Canadian Conservation Institute has developed a red-yellowgreen warning system that correlates concentration ranges 

for inorganic and organic pesticides with high, moderate 

and low toxicity (J. Sirois, unpublished). The Arizona 

State Museum has collaborated with medical toxicologists at the Arizona Poison and Drug Information Center 

to determine total potential dose per object ranges that 

constitute high, moderate, and low risk (also using a redyellow-green warning system) as well as to draft toxicological assessments of individual artifacts (Odegaard et al., 

2005, 2006). More recently, the Smithsonian Institution’s 

MCI, NMAI, and NMNH and the Canadian Conservation Institute have been exploring the potential of computer modeled risk assessment in conjunction with the 

U.S. Environmental Protection Agency (EPA) and The 

LifeLine Group, a nonprofit organization that specializes 

in software tools for unique public health issues related 

to exposure assessment and risk. For all institutions, the 

ultimate goal is a risk management solution that distinguishes between hazardous situations and those of little or 

no consequence.
4 • S miths o n ia n C o n tri b u ti o n s t o m u s e u m c o n s e rvati o n

adverse health effect. For example, the fact that an instrument has a lower detection limit of 1 ppm does not mean 

that concentrations below 1 ppm are safe or that concentrations above 1 ppm are hazardous. At the same time, we 

do not need to go overboard by using the most sensitive 

technique available if the lowest detectable amount would 

not be expected to have any adverse health (or environmental) effect. In general, lower detection limits and higher 

precision often translate into larger price tags for analysis 

and usually require far longer sample preparation time.

The analytical constraints for experimentally prepared 

samples differ from those for actual artifacts. Experimental samples are prepared under controlled conditions such 

that the composition of the substrate and all applied treatments are known (and limited). It is likely that the sample 

can be analyzed destructively, and, for that reason, it can 

be analyzed directly and completely.

This is not the case for cultural artifacts. The exact 

composition and history of artifacts are rarely known. Artifacts are often assembled from diverse materials and may 

have been treated with pesticides (and other substances) 

an unknown number of times throughout their histories. 

These treatments are seldom documented. Analytical techniques for artifact analysis must be minimally destructive 

or nondestructive. Typically, the techniques used analyze 

discrete spots on the artifact (or small samples removed 

from the artifact) rather than the entire object. Consequently, data quality relies on testing multiple spots in 

order to obtain a statistically valid result. The tests should 

be relatively straightforward for conservators or trained 

and experienced technicians to execute. Finally, techniques 

using portable equipment have the added potential for onsite analysis and the ability to survey multiple artifacts in 

a relatively short amount of time.

Each technique has its own set of variables. It is imperative that researchers publish detailed, acceptable parameters so that everyone can use them. The Smithsonian 

Institution is making strides in this direction with respect 

to handheld XRF spectrometry. Researchers at NMAI, 

MCI, and NMNH spent 2006 and 2007 examining the 

variables of this analytical technique, figuring out how 

each variable influenced data accuracy and analytical precision, and setting up protocols that controlled for each 

variable as much as possible. The ultimate goal has been 

to standardize XRF testing protocols for pesticides across 

the Smithsonian Institution and make these protocols 

available to interested outside groups (O. Madden and 

J. Anderson, unpublished). It has become clear that standardization methodology depends on constraints of the 

analytical technique, calibration of data to standards of 

endpoint or goal. The exception was the Zimmt study that 

evaluated the degree of removal of the pesticide Diazinon 

using a biological toxicity screen of living rat lung epithelial 

cells (Zimmt et al., this volume). The target level of cleaning was reached when fewer than 50% of the cultured cells 

died from exposure to the treated samples. Toxicity bioassay tests are unique in that they indicate directly whether a 

substance is present in sufficient quantity to be toxic to living things. This type of testing removes the need to identify 

a specific pesticide (any toxic substance is measured) and 

avoids the risk that an instrument may not be sufficiently 

sensitive to detect toxins at threshold levels.

Though relative terms like percent removal demonstrate whether cleaning was efficient, they do not address 

the fundamental question: Is an object safe to handle? It 

became clear during the informal discussions at the workshop that we need to come to some consensus about target levels of pesticide residues on treated artifacts. This 

does not mean that we necessarily would assert that an 

artifact is “safe” when these levels are reached. For example, an appropriate target concentration might be tied to 

some accepted threshold value such as the No-­ObservedAdverse-­Effect level or a reference value for a given pesticide.2 Nevertheless, it would provide researchers involved 

in remediation with a goal, so that treated artifacts are 

not reported unwittingly to be nontoxic and, at the other 

end of the spectrum, so that we do not put artifacts at risk 

(and waste our time and effort) in “cleaning” beyond the 

accepted reference levels. This is not an easy topic to reach 

a consensus on as there are many factors to consider, but it 

is an issue that needs to be addressed in the coming years.

Choice of Appropriate Analytical 

Methods

It is not the goal here to assert which analytical methods are most appropriate but rather to highlight some of 

the factors to be considered when choosing an analytical 

framework for pesticide analysis in the museum context. 

The question of which detection method is to be used depends on several factors. The first is the anticipated contaminant of interest. More than 90 different pesticide 

formulations are known to have been applied to museum 

artifacts (Pool et al., 2005), and no single technique can 

identify all of them.

The next distinction is the detection limit of the technique. We need to aim for methods that are appropriate 

to our problem. Namely, the technique should detect the 

highest amount of a contaminant that would not cause any 
n u m b e r 1 • 5

useful. The numbers from one research group or museum 

must be consistent with those from another group if we 

are ever going to arrive at a universal framework for assessing the risk posed by pesticide residues on artifacts. 

Without consistent data, one remediation study cannot be 

compared to data from other studies or peer-reviewed effectively. We might benefit from the EPA Office of Pesticide Programs’ approach to this problem. Under the Food 

Quality Protection Act of 1996, “All pesticides distributed 

and sold in the United States must be registered by EPA, 

based on scientific data showing that they will not cause 

unreasonable risks to human health, workers, or the environment . . ..”3 Any company that distributes or sells 

pesticide products in the United States must provide a detailed analytical method for detecting and quantifying that 

pesticide in target commodities. For example, a company 

that sells a pesticide for spray application onto cabbage 

crops must provide a written analytical method to the 

EPA that details how the company measures the amount 

of pesticide in cabbages that have been sprayed with this 

product. These analytical methods are listed with the EPA 

as part of its Residual Analytical Methods program. The 

premise of the program is that “reliable residual analytical 

methods are necessary to measure the magnitude of a residue in a commodity . . .” (U.S. EPA, 2007). This situation 

can be compared to that of pesticides on artifacts.

In cases where experimentally prepared samples are 

required, it also may be beneficial to use standard substrate materials, such as those used at the Arizona State 

Museum for remediation tests (Reuben, this volume) and 

instrument calibration studies (J. Anderson, unpublished). 

By standardizing these points and making them available 

to colleagues in the field, uniform methods for detecting 

and quantifying pesticides can be achieved. The measured 

pesticide levels on artifacts will then be comparable between institutions allowing peer review of remediation 

studies and the ultimate goal of developing improved remediation treatments attained.

The MCI workshop on pesticide mitigation highlighted several experimental methods for pesticide removal 

that show promise in pesticide remediation of museum 

collections and repatriated objects. These remediation experiments are part of a larger body of pesticide research 

and should be viewed within that context. The workshop 

made clear some deficiencies in the current state of pesticide mitigation research. For example, in order to compare 

remediation strategies, standard methodologies for detection and quantification of residues are needed. Of prime 

importance is the definition of the target levels that treated 

objects should attain so as not to pose hazards to people 

known composition, and the steps by which the technique 

is carried out.

The factors that affect XRF data can be divided into 

three categories: instrumental factors, working practice, 

and statistical considerations. Some of these factors can 

be standardized in order to make XRF data more consistent across time, users, and instruments. Examples of 

instrumental factors include the voltage and current of the 

X-ray tube, duration of the measurement, and the selection of appropriate primary and secondary filters. Instrumental performance can be regulated to some extent by 

calibrating the instrument to standards of known composition that resemble artifact materials in terms of density, elemental composition, and thickness. For example, 

calibration standards for arsenic in an organic matrix that 

mimics cellulosic materials were prepared in collaboration 

with the National Institute for Standards and Technology.

Guidelines for working practices also have been proposed to limit data variability that results from multiple 

XRF operators. These guidelines include recommendations for setting a consistent working distance between 

instrument and artifact, eliminating background signal, 

holding the instrument still, and avoiding contamination 

of the instrument head. A computerized database was developed to facilitate analysis and improve the quality and 

statistical accuracy of data collected.

Finally, as XRF analyzes discrete spots on an artifact, 

statistical factors ought to be taken into consideration. 

All objects analyzed for pesticide residues must undergo 

a given number of analyses. The number of analyses is 

chosen to be representative of the object as a whole and be 

consistent with the time constraints of a typical workday. 

However, because artifacts often are composed of multiple 

materials that may have different concentrations of pesticides, artifacts are divided conceptually into one or more 

“zones.” A zone might be a material type such as wood, 

bone, or red paint. It might also be a part of the object 

that presents more of a handling or contact risk, such as 

the mouthpiece of a musical instrument and interior of a 

mask. For each zone within an artifact, a preset minimum 

number of analyses is defined. Therefore, the averaged 

XRF data for the artifact are presented by zone as well as 

for the artifact as a whole.

Toward Standard Analytical 

Methods

For reasons discussed above, pesticide concentration 

data must be accurate, reliable, and reproducible to be 
6 • S miths o n ia n C o n tri b u ti o n s t o m u s e u m c o n s e rvati o n

Goldberg, L. 1996. A History of Pest Control Measures in the Anthropology Collections, National Museum of Natural History, Smithsonian Institution. Journal of the American Institute for Conservation, 35(1):23–43.

Hawks, C. A., and S. L. Williams. 1986. Arsenic in Natural History Collections. Leather Conservation News, 2(2):1–4.

Johnson, J. S., and J. P. Henry. 2002. “Repatriation and Pesticides at 

the National Museum of the American Indian.” In Preprints of the 

ICOM-CC 13th Triennial Meeting, pp. 673–678. London: James 

& James.

Makos, K. A., 2001. Hazard Identification and Exposure Assessment Related to Handling and Use of Contaminated Collection Materials 

and Sacred Objects. Collection Forum, 17(12):93–112.

Nason, J. D. 2001. A New Challenge, A New Opportunity. Collection 

Forum, 17(1–2):9–13.

Odegaard, N. 2001. Methods to mitigate risks from use of contaminated 

objects, including methods to decontaminate affected objects. Collection Forum, 17:117–121.

Odegaard, N., and A. Sadongei, eds. 2005. Old Poisons, New Problems. 

Walnut Creek, Calif.: AltaMira Press.

Odegaard, N., A. Sadongei, and M. Pool. 2005. “Addressing the Problem: The Team Approach.” In Old Poisons, New Problems, ed. 

N. Odegaard, and A. Sadongei, pp. 33–52. Walnut Creek, Calif.: 

AltaMira Press.

Odegaard, N., D. R. Smith, L. V. Boyer, and J. Anderson. 2006. Use of 

a Handheld XRF for the Study of Pesticide Residues on Museum 

Objects. Collection Forum, 20(1–2):42–48.

Pool, M., N. Odegaard, and M. J. Huber. 2005. “Identifying the Pesticides: Pesticide Names, Classification, and History of Use.” In Old 

Poisons, New Problems, ed. N. Odegaard, and A. Sadongei, pp. 

5–31. Walnut Creek, Calif.: AltaMira Press.

Reuben, P. A. 2010. “Mitigation of Surface Contaminants on Haudenosaunee Medicine Masks.” In Pesticide Mitigation in Museum 

Collections: Science in Conservation, ed. A. E. Charola and R. J. 

Koestler, pp. 25–28. Smithsonian Contributions to Museum Conservation, no. 1. Washington, D.C.: Smithsonian Institution Scholarly Press.

Roane, T. M., and L. J. Snelling. 2010. “Bacterial Removal of Mercury 

from Museum Materials: A New Remediation Technology?” In 

Pesticide Mitigation in Museum Collections: Science in Conservation, ed. A. E. Charola and R. J. Koestler, pp. 29–34. Smithsonian 

Contributions to Museum Conservation, no. 1. Washington, D.C.: 

Smithsonian Institution Scholarly Press.

Sadongei, A., 2001. American Indian Concepts of Object Use. Collection 

Forum, 17(1–2):113–116.

Tsosie, R. 2001. Contaminated Collections: An Overview of the Legal, 

Ethical and Regulatory Issues. Collection Forum, 17(1–2):14–29.

U.S. Environmental Protection Agency (U.S. EPA). 2007. Residual Analytical Methods. http://www.epa.gov/oppbead1/methods/ramindex.

htm. (Website last updated 24 July 2007; accessed 28 September 

2009.)

Zimmt, W. S., N. Odegaard, T. K. Moreno, R. A. Turner, M. R. Riley, 

B. Xie, and A. J. Muscat. 2010. “Pesticide Extraction Studies Using 

Supercritical Carbon Dioxide.” In Pesticide Mitigation in Museum 

Collections: Science in Conservation, ed. A. E. Charola and R. J. 

Koestler, pp. 51–57. Washington, D.C.: Smithsonian Institution 

Scholarly Press.

handling them. This could be accomplished by working 

with the Environmental Protection Agency, medical toxicologists, and risk assessment professionals to establish a 

set of risk thresholds or by linking pesticide target levels 

to a toxicological marker, like rat epithelial cells. It is important to remember that the aim of pesticide mitigation 

treatments is to make contaminated objects less hazardous 

to human health.

Acknowledgments

We thank our collaborators at NMAI, MCI, and 

NMNH as well as collaborators at numerous other institutions: Nancy Odegaard and the conservation department 

of the Arizona State Museum; Jane Sirois and the Canadian Conservation Institute; Christine Chaisson, Claire 

Franklin and Elizabeth Dederick of The LifeLine GroupTM; 

Liz Resick of the Environmental Protection Agency; Aaron 

Shugar of Buffalo State College; Eric Hollinger and Greta 

Hansen of the National Museum of Natural History; 

Kathy Makos of the Smithsonian Office of Safety Health 

and Environmental Management; and John Sieber of the 

National Institute of Standards and Technology.

NOTES

1 NMAI Act of 1989 (Public Law 101-185) and NMAI Act Amendment of 1996 (Public Law 104-278). 2 The EPA defines NOAEL as “The highest exposure level at which 

there are no biologically significant increases in the frequency or severity 

of adverse effect between the exposed population and its appropriate 

control; some effects may be produced at this level, but they are not 

considered adverse or precursors of adverse effects.” The reference value, 

an estimate of exposure that would not cause deleterious effects during 

one’s lifetime, may be many times lower than the NOAEL (http://www

.epa.gov/iris/gloss8.htm, accessed 20 September 2007). 3 P.L. 104-170, formerly known as H.R. 1627.

REFERENCES

Cross, P. S., N. Odegaard, and M. R. Riley. 2010. “Aqueous α-Lipoic 

Acid Solutions for Removal of Arsenic and Mercury from Materials Used for Museum Artifacts.” In Pesticide Mitigation in Museum 

Collections: Science in Conservation, ed. A. E. Charola and R. J. 

Koestler, pp. 7–11. Smithsonian Contributions to Museum Conservation, no. 1. Washington, D.C.: Smithsonian Institution Scholarly 

Press.
Paper presented at the Pesticide Mitigation in 

Museum Collections Workshop held at the Smithsonian’s Museum Conservation Institute in April 

2007 exploring possible methods and techniques 

that may become useful for the museum conservation field to reduce, mitigate, clean, or remediate 

undesirable pesticides on objects.

Peggi S. Cross, Arizona State Museum, University of Arizona, 6193 N Yellow Wood Trail, Tucson, Arizona 85704. Nancy Odegaard, Arizona 

State Museum and Departments of Anthropology 

and Materials Science & Engineering, 1013 E. 

University Blvd., Bldg. 26, University of Arizona, 

Tucson, Arizona 85721, USA. Mark R. Riley, 

Agricultural and Biosystems Engineering, Shantz 

Bldg. Room 403, 1177 E. Fourth Street, University of Arizona, Tucson, Arizona 85721, USA. 

Corresponding author: P. Cross (peggicross@

yahoo.com). Manuscript received 12 June 2008; 

accepted 26 June 2009.

Aqueous α-Lipoic Acid Solutions for 

Removal of Arsenic and Mercury from 

Materials Used for Museum Artifacts

Peggi S. Cross, Nancy Odegaard, and

Mark R. Riley

ABSTRACT.  The viability of α-lipoic acid to act as a chelating agent in the removal 

of arsenic- and mercury-based pesticides from artifacts and museum surfaces was examined. High concentrations (50–1000+ μg/cm2) of arsenic and mercury were removed 

from test materials such as Whatman No.1 filter paper, untreated cotton, wool, and 

feathers. Alpha-lipoic acid was chosen because it is a natural chemical that is ubiquitous 

in mammals and plants and that is deemed environmentally benign. These attributes 

make α-lipoic acid attractive for use in removing toxic elements from sacred objects. 

Culturally, these objects may be considered to house sacred living beings that must be 

treated with the same level of care as a human being. This also applies for the safety of 

persons performing the treatment.

Keywords:  alpha-lipoic acid, arsenic, mercury, pesticide removal, museum objects, 

cleaning.

INTRODUCTION

Lipoic acid has been shown to be effective as an agent to prevent morbidity 

from arsenic and mercury poisoning (Grunert, 1960). The chemical contains a 

carboxyl group on one end and a five-member disulfide ring that can be reduced 

by homolytic scission using ultraviolet light as shown in Figure 1.

Arsenic and mercury in the form of sodium arsenite, arsenous acid, and 

mercuric chloride were among the many pesticides that museums used. The 

study focused on arsenic and mercury salts for several reasons:

• They are highly persistent and toxic.

• Arsenic-based chemicals are carcinogens.

• Mercury-based chemicals are neurotoxins.

• The contamination of collections has been validated.

The level of arsenic and mercury contamination on various materials found 

in museum collections varies, particularly because some materials may contain 

these elements inherently. Table 1 presents a list of the most used materials in 
8 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

The sorption mechanism of arsenic and mercury salts 

to materials involves weak forces that can be overcome in 

part by immersion in distilled water and more efficiently 

in aqueous reduced lipoic acid solution. Both arsenic (III) 

and mercury will bind to the sulfur or sulfhydryl moieties 

of reduced lipoic acid at a kinetic rate that allows minimal 

exposure of the chemical to the materials being treated. 

The reduced lipoic acid will not leave residues on the 

treated materials or alter them in any way.

METHODS

Alpha-lipoic acid (Sigma Aldrich) was dissolved in 2 

M ammonium hydroxide and diluted to concentrations of 

0.05–0.015 M lipoic acid in 0.04–0.2 M ammonium hydroxide. The lipoic acid was then reduced by exposing it 

to natural sunlight or 8 W 302 nm laboratory ultraviolet 

lamps in closed borosilicate test tubes. Optimum conditions were found to be 0.01 M lipoic acid in 0.07 M ammonium hydroxide with a pH range of 8.4–9.0. At this 

pH range, no toxic hydrogen sulfide gas was evolved during reduction, while at lower pH solutions it was evolved. 

Higher pH values approached the pKa of the thiol end 

groups decreasing the extent of reduction.

To carry out the contamination removal studies test 

materials were treated with arsenic or mercury in deionized water at a 1000 ppm concentration for both solutions of sodium arsenite (Na3AsO3) and mercuric chloride 

(HgCl2) and allowing the materials to dry prior to removal 

treatment. Test materials included Whatman No. 1 filter 

paper; Style 532 wool jersey knit fabric and Style 46001 

ethnographic artifacts and their range of concentrations of 

arsenic and mercury.

Previous research on removal of arsenic and mercury 

has been limited. For example, compressed air cleaning 

removed 40% of arsenic residues from objects (Glastrup, 

2001); soap and water washing and vacuuming techniques 

were used by Seneca tribal members to reduce unspecified 

amounts of arsenic on masks (Jemison, 2001); and vacuuming techniques were unsuccessfully used by Arizona 

State Museum researchers to remove arsenic from feathers 

(Odegaard et al., 2003).

FIGURE 1. The structure of lipoic acid and reduced lipoic acid (dihydrolipoic acid).

TABLE 1. Summary of the inherent levels of arsenic and mercury 

found in natural materials used to make artifacts.

Average level Average level

of As of Hg

Material (ppm) (ppm)

Hair (human)a 0.04–1.04 <0.06–6.1

Hair or fur (animals)b 20 or less 20 or less

Skinc 3.5 or less No data

Feathersd 0.05–9.16 0.01–22.3

Wood and other plant objectse <1.0 <0.5

Soilsf 0.2–40 0.01–20

a Gibson and Gage, 1982; Foo et al., 1988; Oskarsson et al., 1994; Saad and Hassanien, 2001; Pesch et al., 2002; Ali and Tarafdar, 2003.

b Cumbie, 1975; Sheffy and St. Amat, 1982; Stevens et al., 1997; Evans et al., 1998; 

Ben-David et al., 2001; Kocar et al., 2004; Duffy et al., 2005. c

 Kocar et al., 2004.

d Burger and Gochfeld, 1997; Monteiro et al., 1998; Becker et al., 2002; Veerle et 

al., 2004; Palma et al., 2005.

e

 Shacklette and Connor, 1973.

f Cadigan, 1971; Shacklette and Connor, 1973; Carey et al., 1980; Tack et al., 

1997.
num b e r 1 • 9

sulfur, were obtained by using a sequence of steps, which 

included (1) prewetting the contaminated material with 

deionized water; (2) soaking the material in lipoic acid 

without stirring for 10 seconds; and (3) rinsing the material with deionized water using a serpentine pattern rinse 

from top to bottom. The treatment was then compared to 

the same sequence without the reduced lipoic acid soaking.

Tables 3 and 4 report the percentage of arsenic and 

mercury removed from the different materials tested in 

this study using the above steps in one sequence with 

and without the reduced lipoic acid soak step and two 

sequences without the reduced lipoic acid soak step. To 

be taken into account is that feathers are hydrophobic so 

that the metal salts dispersed on them from an aqueous 

solution do not adhere the way they do with wool, as can 

be seen in the amount of arsenic that remained on the feathers after treatment.

The sequence with reduced lipoic acid soak removed 

statistically significantly more arsenic from filter paper (p

= 0.0005) and wool (p < 0.0001) but not from the thicker 

unbleached, cotton interlock knit fabric from Test Fabrics 

Pittston, Pennsylvania; and wild quail feathers.

The contamination levels were measured using a 700 

series Niton handheld X-ray fluorescence spectrometer 

(XRF) before and after treatment. The treatment sequence 

was developed by running a series of designed experiments 

using replicate samples and the statistical significance of 

the variables was determined until a sequence was obtained 

that resulted in removal to a level below the lower detection limit of the XRF (1 μg/cm2, valid for both As and Hg).

RESULTS

The test results show that the α-lipoic acid must be 

reduced in order to react with arsenic (III) from sodium 

arsenite in solution. However, reaction with mercury from 

mercuric chloride does not require reduction for instantaneous reaction because α-lipoic acid reacts directly with 

mercury (Brown and Edwards, 1969).

Kinetic studies were carried out in order to ascertain 

the rate of reaction of arsenic (III) with reduced lipoic acid 

and the factors that influenced that rate. It was determined 

that the reaction was chemically rate limited and was predominately complete in eight seconds. The presence of 

ambient air significantly decreased the overall extent of 

the reaction, particularly during rapid stirring, suggesting 

that oxidation of the acid was the cause. The use of a nitrogen atmosphere verified this assumption as the extent 

of the reaction was not affected.

Other experiments showed that reduced lipoic acid 

also binds to other cations such as iron, copper, nickel, 

cadmium, zinc, and calcium to form precipitates so that 

the presence of those cations on an object must be considered. Appreciable interference of the binding of arsenic 

(III) by the anions fluoride, chloride, sulfate, and nitrate 

were not evident.

Solutions of α-lipoic acid were tested with and without alcohol in order to determine if an aqueous solution 

was as effective as an alcohol solution. The preliminary 

results obtained for the removal of arsenic (III) from filter 

paper with reduced lipoic acid, with or without alcohol, 

are presented in Table 2.

Further experiments were carried out to optimize the 

technique for the removal of arsenic from materials using 

a series of experimental designs. The best results, where 

reduced lipoic acid was capable of removing up to 1000 

μg/cm2 of arsenic or mercury from materials that contain 

sulfur, and mercury from materials that do not contain 

TABLE 2. Removal of 48.8 μg/cm2 arsenic (III) from filter paper 

using reduced lipoic acid. Control = two rinses with deionized 

water.

Number Average    Percent

of residual As Standard As

Treatment samples (μg/cm2) deviation removed

Control 5 14.04 5.40 71%

Lipoic acid + alcohol 15 11.13 3.32 77%

Lipoic acid 15 5.32 1.39 89%

TABLE 3. Percent removal of arsenic from various materials 

contaminated with sodium arsenite after one cleaning sequence 

with and without lipoic acid and two cleaning sequences without 

lipoic acid. The amount removed in the second cleaning is calculated with respect to the original concentration.

Initial As Percent As removed by treatment

Contaminated concentration 1 cleaning 1 cleaning 2 cleanings

material (μg/cm2) (lipoic acid) (water) (water)

Filter paper 1484 99.4 96.5 99.8

Cotton 1224 98.9 90.8 98.0

Wool 1354 99.3 95.6 99.7

Feathers 565 Not tested 92.5 92.5
1 0 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

represent the official position or policies of the National 

Park Service or the National Center for Preservation Technology and Training.

The work was carried out by the first author in partial 

fulfillment of the requirements for a Ph.D. degree in Materials Science and Engineering at the University of Arizona. 

The first author acknowledges Drs. Wendell Ela, David 

Lynch, and Werner Zimmt of the University of Arizona for 

their guidance throughout the experimental work.

REFERENCES

Ali, M., and S. A. Tarafdar. 2003. Arsenic in Drinking Water and in Scalp 

Hair by EDXRF: A Major Recent Health Hazard in Bangladesh. 

Journal of Radioanalytical and Nuclear Chemistry, 256(2):297–305.

Becker, P. H., J. Gonzalez-Solis, B. Behrends, and J. Croxall. 2002. 

Feather Mercury Levels in Seabirds at South Georgia: Influence of 

Trophic Position, Sex and Age. Marine Ecology Progress Series, 

243:261–269.

Ben-David, M., L. K. Duffy, G. M. Blundell, and R. T. Bowyer. 2001. 

Natural Exposure of Coastal River Otters to Mercury: Relation to 

Age, Diet, and Survival. Environmental Toxicology and Chemistry, 

20(9):1986–1992.

Brown, P. R., and J. O. Edwards. 1969. Reaction of Disulfides with Mercuric Ions. Biochemistry, 8(3):1200–1202.

Burger, J., and M. Gochfeld. 1997. Metal Levels in Feathers of 12 Species of Seabirds from Midway Atoll in the Northern Pacific Ocean. 

Science of the Total Environment, 257(1):37–52.

Cadigan, R. A., 1971. Geochemical Distribution of Some Metals in the 

Moenkopi Formation and Related Strata of the Colorado Plate. 

U.S. Geological Survey Bulletin 1344.

Carey, A. E., J. A. Gowne, T. J. Forehand, H. Tai, and G. B. Wiersma. 

1980. Soils. Pesticides Monitoring Journal, 13(4):150–154.

Cross, P. S. 2007. Aqueous Alpha-Lipoic Acid Solutions for Removal of 

Arsenic and Mercury from Materials Used for Museum Artifacts. 

Doctoral dissertation. Tucson: University of Arizona.

Cumbie, P. M. 1975. Mercury Levels in Georgia Otter, Mink and Freshwater Fish. Bulletin of Environmental Contamination & Toxicology, 14(2):193–196.

Duffy, L. K., R. S. Duffy, G. Finstad, and C. A. Gerlach. 2005. A Note 

on Mercury Levels in the Hair of Alaskan Reindeer. Science of the 

Total Environment, 339(1–3):273–276.

Evans, R. D., E. M. Addison, J. Y. Villeneuve, K. S. MacDonald, and D. 

G. Joachim. 1998. An Examination of the Spatial Variation in Mercury Concentrations in Otter (Lutra canadensis) in South-Central 

Ontario. Science of the Total Environment, 213:239–245.

Foo, S. C., C. H. Ngim, W. O. Phoon, and J. Lee. 1988. Mercury in Scalp 

Hair of Healthy Singapore Residents. Science of the Total Environment, 72:113–122.

Gibson, R. S., and L. A. Gage. 1982. Changes in Hair Arsenic Levels in 

Breast- and Bottle-Fed Infants during the First Year of Infancy. Science of the Total Environment, 26(1):33–40.

Glastrup, J., 2001. The Effectiveness of Compressed Air in the Removal 

of Pesticides from Ethnographic Objects. Collection Forum, 16(1–

2):19–22.

Grunert, R., 1960. Effect of DL-alpha-Lipoic Acid on the Heavy Metal 

Intoxication in Mice and Dogs. Archives of Biochemistry and Biophysics, 86:190–194.

Jemison, G. P. 2001. Poisoning the Sacred. Collection Forum, 17(1–

2):38–40.

woven cotton (p = 0.1135). For the case of mercury removal, it clearly showed that this could be achieved only for 

nonsulfur containing materials, such as paper and cotton.

CONCLUSIONS AND FUTURE 

RECOMMENDATIONS

Reduced lipoic acid solutions can be used to remove 

high concentrations of arsenic and mercury from materials that do not contain sulfur, such as paper and cotton. 

For sulfur-containing materials, such as wool and feathers, 

this method will only remove arsenic but not mercury. The 

treatment solutions and sequences developed show promising results for applications in decontaminating artifacts 

and other materials. A more comprehensive summary of 

the results can be found in the first author’s dissertation 

(Cross, 2007). The next level of scientific inquiry should 

examine the complexities of using the aqueous solutions 

to promote diffusion of toxins out of more complex threedimensional materials such as wood. It would also be useful to use α-lipoic acid to develop a technique to determine 

whether arsenic or mercury is inherent in a material or 

added as a contaminant. Combining this technique with 

the use of an organic solvent in the initial wetting step to 

dislodge the contaminant from the material bringing it to 

the surface, such as the surface activation technique, may 

also prove to be effective (Reuben, 2006).

Acknowledgments

This work was partially supported by a grant from 

the National Park Service and the National Center for Preservation Technology and Training. Its contents are solely 

the responsibility of the authors and do not necessarily 

TABLE 4. Percent removal of mercury from various materials 

contaminated with mercuric chloride after one cleaning sequence 

with and without lipoic acid and two cleaning sequences without 

lipoic acid. The amount removed in the second cleaning is calculated with respect to the original concentration.

Initial Percent Hg removed by treatment

Contaminated concentration 1 cleaning 1 cleaning 2 cleanings

material Hg (μg/cm2) (lipoic acid) (water) (water)

Filter paper 1548 >99.9 93 99.3

Cotton 1496 68.1 65.1 93.2

Wool 2161 0.0 8.7 36.7
num b e r 1 • 1 1

Reuben, P. A., 2006. Detection and Mitigation Strategies for Contaminated Nagpra Objects–The Seneca Nation’s Experience. Collection 

Forum, 20(1–2):33–41.

Saad, A., and M. A. Hassanien. 2001. Assessment of Arsenic Level in 

the Hair of the Nonoccupational Egyptian Population: Pilot Study. 

Environment International, 27(6):471–478.

Shacklette, H. T., and J. J. Connor. 1973. Airborne Chemical Elements 

in Spanish Moss. U.S. Geological Survey Professional Paper 574-­E.

Sheffy, T. B., and J. R. St. Amat. 1982. Mercury Burdens in Furbearers 

in Wisconsin. Journal of Wildlife Management, 46(4):1117–1120.

Stevens, R. T., T. L. Ashwood, and J. M. Sleeman. 1997. Mercury in Hair 

of Muskrats (Ondatra zibethicus) and Mink (Mustela vison) from 

the U.S. Department of Energy Oak Ridge Reservation. Bulletin of 

Environmental Contamination and Toxicology, 58:720–725.

Tack, F., M. G. Verloo, L. Vanmechelen, and E. Van Ranst. 1997. Baseline Concentration Levels of Trace Elements as a Function of Clay 

and Organic Carbon Contents in Soils in Flanders (Belgium). 

Science of the Total Environment, 201(2):113–123.

Veerle, J., D. Tom, P. Rianne, B. Lieven, B. Ronny, and E. Marcel. 2004. 

The Importance of Exogenous Contamination on Heavy Metal Levels in Bird Feathers. A Field Experiment with Free-Living Great 

Tits, Parus major. Journal of Environmental Monitoring, 6(4):356–

360.

Kocar, B. D., R. A. Garrott, and W. P. Inskeep. 2004. Elk Exposure to 

Arsenic in Geothermal Watersheds of Yellowstone National Park, 

USA. Environmental Toxicology and Chemistry, 23(4):982–989.

Monteiro, L. R., J. P. Granadeiro, and R. W. Furness. 1998. Relationship 

between Mercury Levels and Diet in Azores Seabirds. Marine Ecology Progress Series, 166:259–265.

Odegaard, N., .L. Boyer, M. Huber, L. Kaplan, C. Kunicka, T. Moreno, 

C. Podsiki, A. Sadongei, D. R. Smith, and W. Zimmt. 2003. “New 

Ideas for the Testing, Documentation, and Storage of Objects Previously Treated with Pesticides.” In AIC Objects Specialty Group 

Postprints 10, pp. 33–42. Washington, D.C.: American Institute for 

Conservation.

Oskarsson, A., B. J. Lagerkvist, B. Ohlin, and K. Lundberg. 1994. Mercury Levels in the Hair of Pregnant Women in a Polluted Area in 

Sweden. Science of the Total Environment, 151(1):29–35.

Palma, L., P. Beja, P. C. Tavares, and L. R. Monteiro. 2005. Spatial Variation of Mercury Levels in Nesting Bonelli’s Eagles from Southwest 

Portugal: Effects of Diet Composition and Prey Contamination. Environmental Pollution, 134(3):549–557.

Pesch, A., M. Wilhelm, U. Rostek, N. Schmitz, M. Weishoff-Houben, U. 

Ranft, and H. Idel. 2002. Mercury Concentrations in Urine, Scalp 

Hair, and Saliva in Children from Germany. Journal of Exposure 

Analysis and Environmental Epidemiology, 12(4):252–258.

Paper presented at the Pesticide Mitigation in 

Museum Collections workshop held at the Smithsonian’s Museum Conservation Institute in April 

2007 exploring possible methods and techniques 

that may become useful for the museum conservation field to reduce, mitigate, clean, or remediate 

undesirable pesticides on objects.

Robert Kaiser, Entropic Systems, Inc., 34d 

Holton Street, Woburn, Massachusetts 01801, 

USA (rkaiser@entropicsystems.com). Manuscript received 12 June 2008; accepted 26 June 

2009.

Solvent Cleaning of Fragile Artifacts without 

Mechanical Agitation

Robert Kaiser

ABSTRACT.  The removal of hazardous contaminants from fragile artifacts that cannot 

be treated by mechanical cleaning methods can be achieved by immersing the artifact into 

a solvent that dissolves the contaminant(s) of interest but is nonreactive with the artifact. 

By providing an adsorbent sink, such as activated carbon or an evaporative blotter, the 

dissolved contaminant is then removed from the solvent. Experiments were conducted in 

which a solvent soluble blue dye was removed from cotton gauze by placing the gauze 

in direct contact with an activated carbon fabric saturated with ethoxyperfluorobutane 

(3M’s HFE-7200). With sufficient time, the dye was completely removed from the gauze 

without the use of mechanical agitation.

Keywords:  organic pesticides, contaminated artifacts, activated carbon fabric, hydrofluoroethers, diffusive transfer, cleaning, removal.

INTRODUCTION

In terms of the decontamination of organic pesticides from museum artifacts of historic and cultural value, what immediately comes to mind is that 

one is dealing with unique and often irreplaceable objects that are likely to be 

mechanically fragile. Consequently, the objects must be handled with extreme 

care, and if the objects are of animal or vegetable origin, they also will be likely 

to interact with water, which could alter and mar their appearance.

In order to remove contaminants from a substrate under industrial conditions, such as with inertial guidance instruments, time plays an important role, 

and it becomes necessary to introduce a high level of shear in the cleaning medium so that the contaminants can be detached by convective mass transfer. 

Standard ways of attaining a high level of shear are, for example, to subject the 

object to a high-pressure spray, to place the object in a stirred or ultrasonic bath, 

or to rub it with a moistened fabric. Depending on the fragility of a museum or 

collection artifact, any one of these treatments could result in unnecessary damage or destruction. A big difference between the treatment of museum artifacts 

and that of precision industrial parts is that the time available for treatment is 

much longer for the former, presumably weeks or months compared with seconds or minutes for the latter.
1 4 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

Two types of dyes were used in these tests: (1) a HFEsoluble dye to simulate a soluble contaminant and (2) a 

water soluble, HFE-insoluble dye to simulate coloring that 

could be present in many museum objects.

REMOVAL OF A HFE-SOLUBLE 

CONTAMINANT BY DIFFUSION CLEANING

Experimental Procedure

1. Five, two-layer 1.75 inch (42.3 mm) diameter coupons 

of NU GAUZE pads (Johnson & Johnson) were each 

placed in a 50 mm diameter Petri dish and then contaminated with four drops of a HFE-soluble blue dye.

2. The Petri dishes were labeled IV to VIII. The coupons 

in these dishes were then subjected to the following 

treatments:

 a. Dish IV: 3 mL of HFE-7200 were added and the dish 

was covered.

 b. Dishes V and VI: a 1.75 inch diameter of 50K/100 

Micro activated carbon fabric coupon was placed 

on top of the contaminated fabric, 4 mL of HFE7200 were added, and three 1.75 inch diameter steel 

washers (weighing a total of 42 grams) were placed 

on top of the carbon fabric layer.

 c. Dishes VII and VIII: a second 1.75 inch diameter 

gauze coupon was placed on top of the contaminated fabric, 4 mL of HFE-7200 were added, and a 

steel washer was placed on top of each.

3.  In addition, an experiment was performed in a Petri 

dish labeled “0” where no HFE-7200 was added to 

serve as control.

4. Photographs of the five coupon stacks were taken (see 

Figure 1).

Given that the allowable time for museum artifact 

decontamination can be fairly long, it is possible to consider the use of molecular diffusion as a means of removing contaminants. The principle is based on the molecular 

diffusion of a soluble contaminant through a solvent that 

is then transferred from the surface or pores of the object 

being cleaned to an adsorption blotter that traps the contaminant (see “Diffusion Cleaning Process: Diagrams”).

The molecular diffusion decontamination process uses 

hydrofluoroethers (HFEs) as the liquid diffusion medium for 

the pesticide contaminants and an activated carbon fabric as 

the adsorption blotter. For example, HFE-7100 (methoxyperfluorobutane, CH3-­O-C4F9) and/or HFE-7200 (ethoxyperfluorobutane, C2H5-­O-C4F9), commercialized by 3M, 

can serve as the transfer solvents, given that they are capable 

of dissolving organophosphates, such as malathion, captan, 

or carbaryl, a class of compounds found in many pesticide 

formulations, because they are also compatible with a wide 

range of materials typically found in museum collections.

PHYSICAL DEMONSTRATION

In order to demonstrate the viability of the diffusion 

cleaning concept, a simple experiment was performed. First, 

a gauze pad was placed in a Petri dish and small amounts 

of colored dyes were added to the gauze. Then a piece of 

activated carbon fabric was placed on top of the dyed gauze. 

Sufficient HFE-7200 was added to soak the stack, and 

weights were placed on top of the activated carbon fabric to 

ensure firm contact between the different fabric layers. The 

Petri dish was covered and placed in a sealed bag to minimize solvent loss during the course of the experiment. The 

sample was periodically removed from the bag for visual 

examination and photography and then replaced in the bag.

FIGURE 1. Top view of the experimental stacks in Petri dishes.
num b e r 1 • 1 5

between the contaminated fabric and the activated carbon 

fabric, nor does the contaminant spread within the original fabric (see Figure 4).

CONTAMINANT MIGRATION INDUCED BY 

EVAPORATION OF THE TRANSFER LIQUID

The diffusion cleaning exercise described above and 

illustrated in Figure 3 was terminated after 116 hours of 

contact time for purposes of convenience. The damp fabrics and the steel washers were restacked in the Petri dish 

base but the cover was not replaced to allow the transfer 

solvent, HFE-7200, to evaporate.

The samples were left undisturbed overnight and examined the next morning (Figure 5, top). As shown in Figure 5, center, the contaminant in the three fabric samples 

that did not have an activated carbon coupon on top (i.e., 

samples IV, VII, and VIII) was concentrated in the areas 

from which the solvent could evaporate, that is, the center 

hole of the washer and the rim of the gauze coupon not 

covered by the washer.

The contaminant also migrated vertically as shown in 

the case of the two layer setups, V, VI, VII, and VIII (see 

Figure 5, bottom). The top fabric layer of plain gauze in 

samples VII and VIII was much bluer than the bottom one. 

This is a clear indication that the transfer solvent evaporates from the top of the stack and that the contaminant 

migrates with it. Because of the activated carbon fabric in 

samples V and VI, the bottom layer was as white, if not 

whiter, than the ones just covered with plain gauze. The 

visible absence of color shows that there is less dye left on 

the original item with the use of activated charcoal than 

with a simple absorptive material

This “evaporative cleaning” approach could be of 

value when undesired adsorptions occur on the activated 

carbon as would be the case if the transfer solvent is a mixture in which one of the solvent components may swamp 

the adsorptive sites. Saturation of the activated carbon 

would result in no further transfer of contaminant from 

the object being decontaminated. This could be determined 

by visual or instrumental examination of the contaminated 

object, and/or analysis of the activated carbon fabric. Further decontamination would entail replacing the used piece 

of activated carbon fabric with a fresh piece.1

MATERIAL COMPATIBILITY

The purpose of this section is to present experimental 

data that demonstrate that the diffusion cleaning process 

5. All five Petri dishes were placed in a one quart Ziploc 

plastic bag, as shown in Figure 2. They were allowed to 

stand for 116 hours (approximately 5 days).

6. Photographs were taken periodically of the contaminated fabrics.

Results

After 48 hours, the fabrics started to appear dry so 

that an extra 4 mL of HFE-7200 were added to samples 

V–VIII. The results obtained after 24, 48, and 116 hours 

of contact time, are illustrated by Figure 3.

Discussion

The photographs in Figure 3 clearly show that placing 

a contaminated fabric in contact with an activated carbon 

fabric in the presence of HFE-7200 results in the transfer of 

the contaminant from the former to the latter. The presence 

of HFE-7200 results in the migration of the contaminant 

throughout the gauze fabric, regardless of whether one is 

dealing with a single or two fabric coupons, an indication 

that relatively thick items can be treated by this process.

In the absence of a liquid diffusion medium (i.e., the 

HFE-7200 solvent), no transfer of the contaminant occurs 

FIGURE 2. Petri dishes in the Ziploc bag.
1 6 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

Experimental Procedure

1. Coupons of NU GAUZE pads (Johnson & Johnson), 

1.75 inch (42.3 mm) in diameter were each placed in 

50 mm diameter Petri dishes (labeled XIV and XV), 

and then stained with one drop each of red, green, and 

yellow Food Color and Egg Dye (McCormick). The 

poor solubility of these dyes in HFE-7200 is demonstrated by the photograph shown in Figure 6 in which 

one drop of each of these dyes was added to the HFE7200 solvent in an aluminum weighing dish.

can only be applied to species that are soluble in the transfer solvent. The diffusion cleaning process is of value only 

if it can selectively remove unwanted contaminants from 

the surface or body of an object without affecting other 

components, such as dyes or colorants that the object may 

contain.

To make this point, it was decided to examine the fate 

of fabric coupons stained with aqueous dyes that are not 

soluble in HFE-7200, and subject the stained fabrics to 

the diffusion cleaning process described in the previous 

section.

FIGURE 3. Removal of a hydrofluoroether (HFE) soluble contaminant by diffusion cleaning. Top left, at start of test just before adding HFE7200; top right, after 24 hours of contact with HFE-7200; bottom left, after 48 hours of contact with HFE-7200; and bottom right, after 116 

hours of contact with HFE-7200.
num b e r 1 • 1 7

both fabric and aluminum, and three 1.75 inch diameter steel washers were placed on top of the activated 

carbon fabric layer. The Petri dishes were covered and 

all three setups were placed in a one quart Ziploc plastic bag and allowed to stand for a 48 hours.

6. Photographs were taken periodically of the contaminated substrates.

2. The Petri dishes and the aluminum weighing dish were 

placed in an oven maintained at 105oC for four hours 

to remove the solvent and all volatile liquids.

3. The bottom of the weighing dish was punched out with 

a 1.75 inch diameter arch punch and placed in the Petri 

dish labeled XIII. Figure 7 depicts the three Petri dishes 

with the dried samples: the weighing dish and the two 

dyed gauze pads.

4. Five milliliters of HFE-7200 were added to each of the 

Petri dishes. The samples were visually examined to establish that the dyes did not dissolve or diffuse in the 

transfer solvent. Figure 8 shows the samples five minutes after adding the solvent.

5. A 1.75 inch diameter 50K/100 Micro activated carbon 

fabric coupon was placed on top of the dyed substrate, 

FIGURE 4. In the absence of a diffusion medium, no transfer is 

observed between the contaminated fabric and the activated carbon 

coupon. Top, at the beginning of the test; bottom, after 44 hours of 

contact between the contaminated fabric and the activated carbon 

coupon but without HFE.

FIGURE 5. Contaminant migration induced by evaporation of the 

transfer liquid overnight. Top, fabric stacks in open Petri dishes; center, view of top layer after removing steel washers; bottom, view of 

the second layer after removing first layer.
1 8 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

Results

The results after 24 and 48 hours are shown in Figures 9 and 10, respectively. Comparison of these photographs to those of Figures 7 and 8 demonstrate that no 

visual change can be observed. Testing of longer exposure 

times was not deemed necessary. The appearance of these 

samples after drying is shown in Figure 11, which can be 

compared to Figure 7.

FIGURE 6. Three drops of food dye, red, green, and yellow floating 

in HFE-7200.

FIGURE 7. The Petri dishes containing the base of the aluminum 

weighing dish and the stained gauzes after drying in the oven.

FIGURE 8. The same Petri dishes of Figure 7 five minutes after the 

addition of 5 mL of HFE-7200.

FIGURE 9. Petri dishes of Figure 8 after 24 hours of contact with 

activated carbon fabric in the presence of transfer solvent in a sealed 

environment.

FIGURE 10. Petri dishes of Figure 8 after 48 hours of contact with 

activated carbon fabric.
num b e r 1 • 1 9

an adsorbent material, such as activated carbon fabric, or 

an evaporative blotter.

Diffusion Cleaning Process: Diagrams

Diagrams 1–10 below sequentially illustrate the 

principles of how diffusion cleaning with HFE-wetted 

activated-carbon fabric works on porous surfaces.

CONCLUSIONS

Contaminants, such as organic pesticides, can be 

removed from a substrate by diffusion without any mechanical agitation. The requirements are (1) the presence 

of a suitable solvent that dissolves the contaminant and is 

compatible with the substrate being decontaminated and 

(2) a sink for the dissolved contaminant. This sink can be 

FIGURE 11. Left, petri dishes of Figure 10 after evaporation of the solvent before dismantling 

the stacks. Right, view after removal of metal washers and the activated carbon fabric layer.

Contaminant

Pore

Contaminated Porous Surface

Diagram 1
2 0 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

Diagram 2

Diagram 3

Pore

Contaminant

HFE- Wetted Activated Carbon Fabric

Vapor

Barrier

Pore

Contact HFE Wetted

Activated Carbon Fabric 

with Porous Surface

Vapor

Barrier
num b e r 1 • 2 1

Diagram 4

Diagram 5

Pore

HFE Displaces Air in Pores

and Dissolves Contaminant

Vapor

Barrier

Pore

Contaminant Diffuses in HFE

Vapor

Barrier
2 2 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

Diagram 6

Diagram 7

Pore

Contaminant Diffuses in HFE

Vapor

Barrier

Pore

Diffused Contaminant Adsorbs on ACF

Vapor

Barrier
num b e r 1 • 2 3

Diagram 8

Diagram 9

Pore

Adsorption Reduces Contaminant

Concentration in Pores

Vapor

Barrier

Adsorption Depletes Contaminant

From Pores

Vapor

Barrier
2 4 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

NOTE

1. This paper made use of research and findings presented at several 

annual Decontamination Commodity Area Conferences from 2002 to 

2006, as follows:

Kaiser, R. 2002. “Novel Decontamination Pads.” In DECON 2002, 4th 

Decontamination Commodity Area Conference, San Diego, Calif., 

CD-ROM.

Kaiser, R., A. Kulczyk, J. Minicucci, R. Willey, R. Spafford, and 

B. MacIver. 2005. “Adsorptive Wipes Using Activated Carbon Fabrics.” In DECON 2005, 6th Decontamination Commodity Area 

Conference, Tucson, Ariz., CD-ROM.

———. 2006. “Adsorptive Wipes Using Activated Carbon Fabrics.” In 

DECON 2006 Science & Technology Conference, Westminster, 

Colo., CD-ROM.

MacIver, B., R. Spafford, and R. Kaiser. 2002. “Precision Wiping Studies in Support of Block III Decontamination Efforts.” In DECON 

2002, 4th Decontamination Commodity Area Conference, San Diego, Calif., CD-ROM.

———. 2004. “Portable Decontamination: Preliminary Development 

and Evaluation of a Decontamination Wipe System.” In DECON 

2004, 5th Decontamination Commodity Area Conference, Tampa, 

Fla., CD-ROM.

Diagram 10

Clean Pores

Remove Contaminated

Activated Carbon Fabric

Allowing HFE to Evaporate from Pores

Vapor

Barrier

RECOMMENDATIONS

The results presented in this paper were based only on 

visual observation. More rigorous work still needs to be 

performed. It would be useful to have scientific testing carried out to confirm the complete removal of the pesticides 

from the substrate and to verify that no changes take place 

to the water-soluble components.

Materials and Suppliers

HFE-7200, 3M Electronic Materials Market Division, St. Paul, Minn.

Zorflex 50K Activated Carbon Fabric, Calgon Corp., Pittsburgh, Pa.

Zorflex 50K/Nylon Laminate, Entropic Systems, Inc., Woburn, Mass.

NU GAUZE Sterile Gauze Pads (Johnson & Johnson).

Water-Soluble Food Colors (McCormick).

Experimental Dye FC-3275 (HFE Soluble Blue Dye)—no longer commercially available (3M Electronics Materials Market Division).
ABSTRACT.  A novel strategy was developed for the mitigation of arsenic and mercury 

surface contaminants found on Haudenosaunee medicine masks. This strategy combined the replacement of specific components of the masks, the application of a surface 

active displacement solution (SADS), and the use of traditional cleaning methods. Initial 

efforts focused on the mitigation of medicine masks deemed highly contaminated with 

mercury; the results indicated more than 99% reduction in dislodgeable residues. The 

focus of this study was on the mitigation of arsenic residues after a single application of 

the SADS formulation as well as the removal and replacement of certain components of 

the masks. The results demonstrated that only trace amounts of arsenic remained and 

that the overall contaminant reduction was comparable with that previously obtained 

for mercury.

Keywords:  arsenic, mercury, Haudenosaunee medicine masks, surface active displacement solution (SADS), sodium lauryl sulfate, mitigation, cleaning, removal.

INTRODUCTION

Since enactment of the Native American Graves Protection and Repatriation Act in 1990, the Haudenosaunee have discovered the presence of arsenic 

and mercury pesticide residues on some of their repatriated medicine masks 

(Jemison, 2001). The Haudenosaunee (People of the Longhouse) include the 

Tonawanda Seneca Nation, Seneca Nation of Indians, Cayuga, Onondaga Nation, Mohawk Nation Council of Chiefs, the Council of Chiefs from the Six 

Nations Reserve at Oshweken, Ontario, and Tuscarora Nation. The Haudenosaunee Standing Committee on Burial Rules and Regulations in collaboration 

with the Seneca Nation’s Tribal Historic Preservation Office and the SenecaIroquois National Museum obtained National Park Service funding in 2002 to 

investigate methods of detection and mitigation of arsenic and mercury pesticide 

residues on their historic objects. The mitigation of these residues is of great importance given that the repatriated medicine masks will be used by traditional 

practitioners during ceremonies, and the masks will be stored in their homes, 

potentially affecting their families.

Paper presented at the Pesticide Mitigation in 

Museum Collections Workshop held at the Smithsonian’s Museum Conservation Institute in April 

2007 exploring possible methods and techniques 

that may become useful for the museum conservation field to reduce, mitigate, clean, or remediate 

undesirable pesticides on objects.

Peter A. Reuben, Seneca Nation of Indians, 

Tribal Historical Preservation Office, 467 Center Street, Salamanca, New York 14779, USA; email: reubpa58@yahoo.com. Manuscript received 

12 June 2008; accepted 26 June 2009.

Mitigation of Surface Contaminants on 

Haudenosaunee Medicine Masks

Peter A. Reuben
2 6 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

Solutions were applied using a Dynalon Quick Mist 

HDPE Sprayer bottle. Each solution was allowed to stand 

for two minutes before the next solution was applied. 

Soft bristled brushes were used in areas that were heavily 

soiled. Each cleaned mask was allowed to air dry before 

wipe sampling.

Surface wipe samples were obtained using premoistened Palintest dust wipes following a modified field procedure for surface wipe sampling (Brookhaven National 

Laboratory [BNL], 2002). The BNL procedure was modified to increase the sample area from 100 cm2 to half the 

surface area of the exterior painted side or the unpainted 

interior of the mask. Sampling was carried out before 

and after the SADS cleaning procedure. Sampling of the 

medicine mask followed the general format of two wipe 

samples per side using a vertical centerline to separate the 

surface into left and right sides. The wipe sample from the 

left side was arbitrarily assigned to be analyzed for arsenic 

and the wipe sample from the right side was analyzed for 

mercury.

RESULTS AND DISCUSSION

Given the unique cultural constraints and funding 

limitations for this project, a strategy was developed for 

detection and mitigation of surface contaminants on the 

repatriated medicine masks. Cultural constraints limited 

the mitigation and detection techniques to nondestructive 

methods only. This, in conjunction with funding limitations, led to the analysis of surface wipe samples as the 

primary means by which the progress of the mitigation 

could be documented. The objective of this project was 

to reduce dislodgeable arsenic and mercury contaminants 

(per wipe sample) to nanogram levels. This goal was suggested by a toxicologist and agreed upon by the traditional 

practitioners as reasonable for this project.

The mitigation strategy involved the removal of items, 

such as horsehair and headgear, and was performed with 

the approval and under the guidance of traditional practitioners. Any components removed were given to the traditional practitioners for disposal. The SADS formulation 

was then applied to the masks, followed by traditional 

cleaning methods, and finally the replacement of key components, such as horsehair by traditional practitioners.

Each of the six repatriated medicine masks in this study 

was screened for the presence of arsenic. To estimate the 

amounts of contamination, wipe samples were taken on 

each side of the mask. The sample area was equal to half 

of the surface area of the painted (exterior) or unpainted 

With the assistance of tribal representatives, a novel 

multistep strategy was developed to mitigate arsenic- and 

mercury-based pesticide residues. This strategy includes 

the use of a surface active displacement solution (SADS) 

(Reuben, 2006) and traditional cleaning methods. Because 

of the cultural sensitivity of the masks, sampling and mitigation methods were limited to nondestructive techniques 

only. The limitations of both nondestructive techniques 

and limited funding led to the use of surface wipe samples 

that were subsequently analyzed by atomic absorption 

spectroscopy or cold vapor atomic absorption spectrometry at a New York State certified environmental testing 

laboratory (TestAmerica).

Analyses of surface wipe samples from six recently repatriated medicine masks revealed high mercury levels—

levels that decreased significantly after treatment (Reuben, 

2006). During that study, additional surface wipes were 

analyzed for arsenic, but values for arsenic were not reported. This paper reports arsenic values for the same six 

medicine masks before and after treatment using the SADS 

formulation.

MITIGATION

Arsenic mitigation began with disassembly of the specific components of the masks, such as medicine bundles, 

horsehair, and headgear. The disassembly was accomplished using hand tools. Fasteners securing these items 

also were removed.

The SADS formulation is a multistep process that is 

tailored to the contaminating chemical agent and the surface from which it is to be removed. This concept has been 

recently used on heat exchangers and removal of microfouling films from delicate surfaces (Reuben, 2006). The 

first step of the SADS formulation in this study began with 

a 5% isopropyl alcohol solution sprayed directly onto the 

surface to be cleaned. This alcohol was acceptable to the 

traditional practitioners. The alcohol serves a potential 

solvent to the contaminant and provides the interfacial 

displacement action. The second step was a 5% aqueous 

solution of technical grade sodium lauryl sulfate, which 

emulsifies the stripped contaminant. The third step was 

a rinse with distilled water to minimize residues. Water 

is key component in the SADS concept because it carries 

the components of the formulation to the surface. As the 

water drains from the surface, it also carries the stripped 

and emulsified chemical contaminant. Rinsate from each 

step was collected and disposed of in the laboratory waste 

stream.
num b e r 1 • 2 7

for dislodgeable arsenic residues on painted and unpainted 

surfaces of the masks. This is comparable with the significant reduction in mercury residues previously reported 

(Reuben, 2006).

CONCLUSIONS

Six Haudenosaunee medicine masks were screened 

for arsenic residues. Analysis of surface wipe samples 

revealed high levels of arsenic on both the painted and 

unpainted surfaces of the medicine masks. A similar mitigation strategy was used for mercury mitigation on these 

masks. This included the removal of medicine bundles, 

horsehair, and headgear followed by a single application 

(interior) sides of the masks. The sample area was increased from the BNL procedure to better compensate for 

the potential uneven distribution of surface contaminates 

and to improve the estimate of dislodgeable residues from 

the surface. The surface wipe was able to follow irregular 

surface contours and reach into the many ornate features 

of the medicine mask.

It is important to remember the qualitative nature of 

the surface wipe sample with respect to this study. Other 

sampling techniques were reviewed and considered (Reuben, 2006, and references therein). This study requires 

a nondestructive sampling technique to estimate dosage 

for the toxicologist and a method of monitoring progress 

during mitigation that is within funding limitations. Although the analysis of the wipe sample is quantitative, 

the wipe sample is qualitative in nature. Reviews of the 

pros and cons for sampling techniques for museum objects 

have been published by Sirois and Sansoucy (2001). In a 

previous study with different medicine masks, analysis 

of field duplicate wipe samples produced nearly identical 

results when analyzed for arsenic and mercury residues 

as expected. Quality assurance/quality control programs

were used to assure that the results obtained were representative and defensible (BNL, 2003; P. A. Reuben, unpublished report for the Seneca Nation of Indians Tribal 

Historic Preservation Office: “Detection and Mitigation of 

Inorganic Pesticide Residues on Sacred Objects,” 2005). 

Previous attempts reported by Reuben (2006) had shown 

that both distilled water and distilled water/isopropyl alcohol mixture had little effect in the reduction of arsenic 

residues. On the basis of these observations, wipe samples 

have only a minor contribution to the overall mitigation. 

Also, pigment transfer to the wipe sample on the painted 

side was not observed during the sampling event. Results 

for arsenic and mercury levels on both the painted and the 

unpainted surfaces, before and after SADS treatment, are 

presented in Tables 1 and 2.

Arsenic was found on painted and unpainted surfaces 

of the medicine masks during the initial measurement of 

surface wipe samples. Arsenic levels on four of the six 

masks were determined to be above the mitigation goal 

of 0.999 μg/wipe. The same four masks also had elevated 

arsenic levels on the unpainted surfaces, whereas only 

two masks had measurable levels on the painted surface. 

Contamination ranged between 1,020 and 2,780 μg/wipe. 

After one treatment using the SADS formulation, arsenic 

values decreased significantly to 0.50–0.92 μg/wipe. The 

combination of removal of potentially contaminated components of the medicine masks and one application of the 

SADS formulation resulted in a greater than 99% removal 

TABLE 1. Arsenic and mercury values measured on wipes of 

painted exterior surfaces before and after treatment with surface active displacement solution formulation. Minimum detection level (MDL) As = 0.50 μg/wipe and MDL Hg = 0.012 μg/

wipe. Mercury data reproduced from Reuben, 2006; ND = not 

detected.

Arsenic (μg/wipe) Mercury (μg/wipe)

 Object Before After Before After

number treatment treatment treatment treatment

1 <0.50 0.53 830 0.172

2 <0.50 0.52 1770 0.885

3 2720 0.65 1320 0.680

4 <0.50 0.78 1540 0.443

5 ND ND 6860 2.38

6 1060 ND 140 0.123

TABLE 2. Arsenic and mercury values measured on wipes of unpainted surfaces (interior) before and after treatment with surface active displacement solution formulation. Minimum detection level (MDL) As = 0.50 μg/wipe and MDL Hg = 0.012 μg/

wipe. Mercury data reproduced from Reuben, 2006.

Arsenic (μg/wipe) Mercury (μg/wipe)

 Object Before After Before After

number treatment treatment treatment treatment

1 <0.50 0.56 330 0.087

2 <0.50 0.50 9160 1.495

3 1560 0.72 2120 0.088

4 1550 0.92 1470 0.093

5 1020 0.65 13200 5.06

6 2780 0.65 920 0.113
2 8 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

Materials

Palintest Wipes are available from Palintest USA, part number PT484 (reference #505).

Sodium lauryl sulfate (SLS) available from Fluka Chemicals part number 

71730-250g [Chemical Abstract Service registry no. 151-21-3].

Dynalon Quick Mist HDPE Sprayer bottle Fisher Scientific, part number 

03-438-12A. This may be substituted by a common spray bottle.

Isopropanol alcohol (70%) commercial grade.

REFERENCES

Brookhaven National Laboratory (BNL). 2002. Surface Wipe Sampling Procedure IH75190, Revision 7, pp.1–13. Upton, N. Y.: 

Brookhaven National Laboratory. http://www.bnl.gov/esh/shsd/

sop/pdf/IH_SOPS/IH75190.pdf (accessed 11 November 2003.

———. 2003. 2003 Site Environmental Report. pp. 9.1–9.12. Upton, 

N. Y.: Brookhaven National Laboratory. http://www.bnl.gov/ewms/

ser/2003.asp (accessed 6 June 2004).

Jemison, G. P. 2001. Poisoning the Sacred. Collection Forum, 17(1–

2):38–40.

Reuben, P. A. 2006. Detection and Mitigation Strategies for Contaminated Nagpra Objects—The Seneca Nation’s Experience. Collection Forum, 20(1–2):33–41.

Sirios, P. J., and G. Sansoucy. 2001. Analysis of Museum Objects for 

Hazardous Pesticide Residues: A Guide to Techniques. Collection 

Forum, 17(1–2):49–66.

of a SADS formulation. Analysis of wipe samples revealed 

that arsenic residues had been reduced significantly on all 

treated surfaces. The results from posttreatment levels of 

arsenic residues met the mitigation goal of 0.999 μg/wipe 

or less. These results are comparable with those obtained 

for the mitigation of high mercury levels on the same 

objects.

Acknowledgments

The author thanks Kathy Mitchell of the Seneca 

Nation Tribal Historic Preservation Office, the Haudenosaunee Standing Committee on Burial Rules and Regulations, and Sheree Bonaparte of the Saint Regis Mohawk 

Tribe’s Tribal Historical Preservation Office for allowing 

this information to be disseminated. Dr. Robert Baier of 

the Surface Science Center at the State University of New 

York at Buffalo is acknowledged for his assistance with 

the SADS concept. The author also thanks the Smithsonian’s Museum Conservation Institute for the opportunity 

to participate in the Mitigation of Pesticide on Museum Collections Workshop/Symposium. This research 

was funded by a National Park Service NAGPRA grant 

36-02-GP-324.
ABSTRACT.  This project investigated the removal of mercury, a nondegradable, persistent chemical, from museum materials by bacteria. Mercury-resistant bacteria have the 

ability to convert this element into a gaseous form. The isolation of a diverse bacterial 

community from mercury-treated items is reported. Two nonpathogenic bacterial isolates 

were capable of reducing 10 mg/L mercury concentrations. Arthrobacter sp. 2604 reduced the mercury associated with a gelatin medium by 30% and a paper matrix by 20% 

within 10 days at 28°C. Cupriavidus metallidurans CH34 reduced up to 50% and 60% 

of the mercury, respectively. Current work is focused on the optimization of conditions 

for bacterial mercury removal, including the nutritional requirements and appropriate 

environmental conditions for the remediation process.

Keywords:  mercury, bacteria, detoxification, remediation, removal, museum objects.

INTRODUCTION

Surveys are now routinely conducted to determine the extent of mercuryand arsenic-based pesticide contamination on botanical, ethnographic, and 

zoological specimens in museums worldwide. In the United States and Canada, 

estimates suggest that as much as 80% of ethnographic and natural history specimens have been treated with metal-based pesticides (Sirois, 2001; N. Odegaard, 

Arizona State Museum, personal communication, 2002). Methods for mercury 

and arsenic mitigation of these materials are needed because of the enactment 

of the Native American Graves Protection and Repatriation Act (NAGPRA) 

in 1990 and for the safety of museum personnel. In the work discussed herein, 

microorganisms associated with mercury-treated artifacts were investigated as a 

possible treatment source for mercury removal.

Mercury has a long history of use as a pesticide. It has been used as an antimicrobial in cosmetics, as an antifungal on grain seeds, and as an antibacterial 

in vaccines. Mercury is currently used in batteries, etching solutions, and various 

other industrial processes. It is available in a variety of chemical forms—elemental mercury (Hg0), mercuric chloride (HgCl2), ethyl mercury (CH3CH2Hg+), and 

mercuric sulfide, also known as cinnabar (HgS)—all of which are potentially 

Paper presented at the Pesticide Mitigation in 

Museum Collections Workshop held at the Smithsonian’s Museum Conservation Institute in April 

2007 exploring possible methods and techniques 

that may become useful for the museum conservation field to reduce, mitigate, clean, or remediate 

undesirable pesticides on objects.

Timberley M. Roane and Lisa J. Snelling, 

Department of Biology, Campus Box 171, P.O. 

Box 173364, University of Colorado Denver, 

Denver CO 80217-3364, USA. Corresponding 

author: T. Roane (Timberley.Roane@cudenver

.edu). Manuscript received 12 June 2008; accepted 26 June 2009.

Bacterial Removal of Mercury from Museum

Materials: A New Remediation Technology?

Timberley M. Roane and Lisa J. Snelling
3 0 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

Wagner-Dobler et al., 2000). In this study, it is hoped that 

the microorganisms will serve to reduce the amount of 

mercury associated with an object by conversion of the 

metal to a gaseous form without damaging the object.

The specific objectives of the work presented here were 

to (1) isolate mercury-resistant bacteria from the surfaces 

of mercury-treated museum materials and (2) evaluate the 

ability of the bacteria to decrease the mercury concentrations associated with different media.

EXPERIMENTAL

Mercury-­Treated Museum Materials

Access to mercury-impacted anthropological and 

herbarium materials was provided by the Arizona State 

Museum, Tucson. As materials could not be destructively 

sampled, Arizona State Museum personnel used a handheld X-ray fluorescence (XRF) spectrometer (NITON XLi 

700 Series Analyzer, Thermo Scientific, Billerica, Mass.) 

to identify objects impacted by mercury. This technique 

has been applied in the identification of objects containing 

arsenic (Seifert et al., 2000).

Collection, Identification, and Characterization

of Mercury-­Resistant Bacteria

The surfaces of museum materials were swabbed with 

sterile cotton applicators to collect bacteria, which were 

then transferred to bacterial media, brought back to the 

laboratory, and monitored for growth. Individual bacterial 

toxic. The widespread use of mercury has contributed to 

its prevalence in the environment where bacterial activity is one of the driving factors behind mercury’s chemical 

transformation.

Bacteria range in size from 1 to 2 μm, are ubiquitous in 

the environment, and can provide mechanisms to detoxify 

chemicals and reduce chemical concentrations (Figure 1).

Bacteria are ideal candidates for metal remediation 

studies because some have physiological means of reducing the toxicity associated with mercury (Roane and Pepper, 2001). The most widely used mechanism of mercury 

resistance by bacteria is the chemical reduction of mercury, 

i.e., the conversion of Hg2+ to Hg0 (Roane and Pepper, 

2000; Barkay et al., 2003). The resulting elemental mercury (Hg0) readily volatilizes as a gas, reducing the amount 

of mercury associated with a contaminated medium. The 

gaseous mercury can be collected and properly disposed of 

(von Castein et al., 2002; Boheme et al., 2005).

Mercury is toxic because of its global interference 

with all cellular processes in macro- and microorganisms. 

Mercury is just as toxic to bacteria as it is to humans, interfering with enzymatic functions, protein structure, and 

genetic integrity. Consequently, in order for an organism 

to avoid the toxic effects of mercury, the organism must 

be able to protect all of its cellular functions and reduce 

its exposure to mercury. One way to achieve this is to 

convert mercury into a gas, which will diffuse away from 

the cell, thereby reducing the concentration of mercury 

in direct contact with the cell. The use of such mercuryresistant bacteria to treat contaminated soils and waters is 

being widely investigated (Daly, 2000; Okino et al., 2000; 

FIGURE 1. Left: 1000× magnification of acridine orange-stained metal-resistant bacteria isolated from a soil. Each cell is 

approximately 1–2 μm in diameter. Right: A Petri plate containing a bacterial growth medium. Bacterial growth (as colonies) is evident on the surface of the plate.
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well contained a different carbon substrate as supplied by 

the manufacturer. A color change in a given well indicated 

bacterial growth and substrate use (Rusznyak et al., 2008).

RESULTS AND DISCUSSION

Several bacterial isolates were collected from mercurytreated items at the Arizona State Museum. Items sampled 

included several ethnographic objects, such as leather 

pouches and headdresses, and a Harvard cabinet housing botanical collections. The items examined had known 

mercury exposure—an assessment that was performed by 

Arizona State Museum personnel using XRF in most cases 

(Table 1). It should be noted that several locations on the 

objects were analyzed to confirm mercury presence.

The bacterial isolates obtained from the surfaces 

sampled represented commonly occurring bacteria. For 

example, Arthrobacter, Bacillus, and Pseudomonas spp. 

are readily found in soils. Five isolates, out of 20 total, 

were unidentifiable with the method used. These isolates 

may represent novel bacteria upon confirmation with additional techniques.

isolates were identified using the molecular method of 16S 

rRNA gene sequencing (Kassab and Roane, 2006; Marchesi et al., 1998). The DNA sequencing was performed 

at the University of Colorado Denver Cancer Center DNA 

Sequencing Core Facility (Denver, Colo.). The resulting 

16S rDNA sequences were analyzed with the BLAST program that is available from the National Center for Biotechnology Information (www.ncbi.com).

To examine mercury resistance, bacterial isolates 

were placed in varying concentrations of mercuric chloride (0–60 mg/L) and monitored for growth (Kassab and 

Roane, 2006; Roane and Pepper, 2000). Those isolates 

that did not grow in mg/L concentrations of mercury were 

placed in μg/L concentrations of mercury. The highest 

concentration of mercury an isolate grew in was recorded 

as the maximum mercury-resistance level.

Removal of Mercury from Different Media by

Mercury-­Resistant Bacteria

The Environmental Protection Agency (EPA) method 

3051, a microwave acid digestion technique (Walter et 

al., 2005), was modified for the dissolution of mercurytreated materials. Subsequent quantification of mercury 

used a PS200II Leeman Labs Cold Vapor–Atomic Absorption Spectrometry (CV-AAS) instrument (Hudson, N.H.) 

for laboratory treated materials (e.g., agar and paper), 

which could be destructively sampled. This instrument 

provided a total metal quantification method for assessing 

the ability of bacteria to remove mercury from the entire 

substrate. All instrumentation necessary for mercury analysis was provided by the Shared Analytical Services Laboratory at the University of Colorado’s downtown Denver 

campus. Three media were examined: (1) liquid broth for 

the initial screening of mercury removal; (2) agar, as a representative of a permeable substrate; and (3) paper as a 

representative of a complex substrate.

A mercuric chloride solution was used to contaminate these substrates to achieve a final concentration of 10 

mg/L mercury. Results from these initial media provide the 

basis for other materials in future research.

Substrate Usage

As a preliminary assessment of potential material degradation, the ability of one of the mercury-resistant isolates, Arthrobacter sp. 2604, to degrade different organic 

substrates was examined. Concentrated cells were placed 

in each well of a commercially available 96-well GN BIOLOG plate (BIOLOG, Hayward, Calif.) for analysis. Each 

TABLE 1. Bacterial isolate identification and maximum mercury 

resistance levels (MRL) from mercury-treated museum objects.

Here ND = not detected, although object had suffered mercury 

exposure according to museum personnel; (-) indicates mercury 

levels below detection limits <100 μg/L.

Mercury levels Isolate identification

Source material (μg/cm2) (mercury MRL)

Leather bag 93 Arthrobacter sp. 2604 (50 mg/L)

Turtle fetish ND Bacillus megaterium (5 mg/L)

Pseudomonas sp. (2 mg/L)

Korea rosea (-)

Bacillus sp. (-)

Arthrobacter sp. (-)

Pseudomonas tolassi (-)

Spear thrower 2147 Bacillus sp. (10 mg/l)

Headdress 1 280 Unknown (-)

Headdress 2 1076 Korea sp. (-)

Moccasin 23 Chelacoccus asaccharyorans (-)

Arthrobacter sp. (100 μg/L)

Harvard cabinet 300 Pseudomonas synxantha (1 mg/L)

Kaistobacter koreensis (-)

Arthrobacter sp. (100 μg/L)

Unknown (-)

Unknown (-)

Unknown (-)

Leather pouch ND Agrococcus jenensis (-)

Red textile 370 Unknown (100 μg/L)
3 2 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

lead, cadmium, and mercury, as well as other metals, and 

demonstrated mercury resistance up to 10 mg/L mercury.

Mercury removal from three substrates was examined. 

The initial screening of the isolates was carried out with 

broth cultures, followed by testing with agar and paper. 

Each substrate was amended with mercury to a concentration of 10 mg/L prior to bacterial treatment. In the case 

of the paper, it was allowed to air dry prior to bacterial 

application.

Each substrate was then inoculated with 107 cells/mL 

of either bacterial isolate—Arthrobacter sp. 2604 or C. 

metallidurans CH34—and then incubated to allow for 

bacterial growth and mercury removal. Uninoculated controls were used to monitor abiotic loss of mercury. Arthrobacter sp. 2604 was able to remove 20%, 30%, and 20% 

of the mercury from each substrate type, i.e., broth, agar, 

and paper, respectively, within 10 days (Figure 2). Cupriavidus metallidurans CH34 was able to remove up to 40%, 

Interestingly, the maximum mercury resistance level 

(MRL) of each of the bacterial isolates did not correlate 

with the amount of mercury associated with the item. Isolates with high resistance were found on items with lower 

mercury levels (as compared to other materials). Eight of 

the isolates were, however, able to tolerate from 100 ppb 

(μg/L) to 50 ppm (mg/L) levels of mercury.

One isolate, in particular, was chosen for further 

analysis. Arthrobacter sp. 2604, isolated from a leather 

pouch with 93 μg/cm2 mercury, could grow in up to 50 

mg/L of mercury. This extraordinary degree of resistance 

made this isolate an interesting candidate for use in the 

mercury removal studies. In addition to Arthrobacter sp. 

2604, another bacterial isolate, Cupriavidus metallidurans CH34, was used as a control organism in the mercury removal studies. Cupriavidus metallidurans CH34 is 

a soil bacterium originally isolated from zinc mine tailings 

(Legatzki et al., 2003). This organism is resistant to zinc, 

FIGURE 2. Mercury removal within 10 days by Arthrobacter sp. 2604 from broth, agar, and paper amended with 10 mg/L of mercury. Uninoculated controls 

containing 10 mg/L of mercury were used to assess abiotic loss of mercury. Standard error bars represent triplicate experiments.
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compounds. The BIOLOG test simultaneously monitors 

degradation of 95 different organic compounds. Table 2 

summarizes the organic substrates Arthrobacter sp. 2604 

preferred, such as sugars, amino acids, and organic acids. 

Continued analysis of organic substrate preference and resulting metabolic by-products will provide information regarding possible risks of material degradation during and 

after treatment. So far, Arthrobacter sp. 2604 shows little 

preference for the complex organics often associated with 

museum materials, e.g., cellulose, indicating a decreased 

risk for material influence. Cupriavidus metallidurans

CH34, however, is capable of autotrophic metabolism, 

meaning it can use CO2 to support its growth as opposed 

to organic compounds. The use of CO2 should substantially decrease the risk of material changes upon bacterial 

treatment.

50%, and 60% of the mercury, respectively (Figure 3). 

Mercury removal was measured against the uninoculated 

controls and so reflected actual bacterial mercury removal. 

Both isolates showed evidence of cell growth on each substrate within the 10 day period. Despite the porosity of the 

materials, both isolates removed more mercury from the 

solid substrates: agar and paper. This is promising given 

the types of museum materials requiring treatment. Additional studies will address the specific conditions needed 

for optimal microbial treatment and mercury removal. 

For example, bacterial mercury removal may be enhanced 

under a slightly elevated temperature or with supplied 

nutrients.

To begin to address the nutrients needed to sustain 

microbial activity, the isolate Arthrobacter sp. 2604 was 

screened for its ability to degrade various organic carbon 

FIGURE 3. Mercury removal within 10 days by Cupriavidus metallidurans CH34 from broth, agar, and paper amended with 10 mg/L of mercury. Uninoculated controls containing 10 mg/L of mercury were used to assess abiotic loss of mercury. Standard error bars represent triplicate 

experiments.
3 4 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

State Museum for access to collections and Jeff Boon of 

the Shared Analytical Services Laboratory, UCDHSC, for 

analytical support.

REFERENCES

Barkay, T., S. M. Miller, and A. O. Summers. 2003. Bacterial Mercury 

Resistance from Atoms to Ecosystems. FEMS Microbiology Reviews, 27:355–384.

Boheme, F., J. Rinklebee, H. J. Stark, R. Wennrich, S. Mothes, and H. U. 

Neue. 2005. A Simple Field Method to Determine Mercury Volatilization from Soils. Environmental Science and Pollution Research, 

12:133–135.

Daly, M. J. 2000. Engineering Radiation-Resistant Bacteria for Environmental Biotechnology. Current Opinion in Biotechnology, 11:280–

285.

Kassab, D. M., and T. M. Roane. 2006. Differential Responses of a Mine 

Tailings Pseudomonas Isolate to Cadmium and Lead Exposures. 

Biodegradation, 17:379–387.

Legatzki, A., G. Grass, A. Anton, C. Rensing, and D. H. Nies. 2003. 

Interplay of the Czc System and Two P-Type ATPases in Conferring 

Metal Resistance to Ralstonia metallidurans. Journal of Bacteriology, 185:4354–4361.

Marchesi, J. R., T. Sato, A. J. Weightman, T. A. Martin, J. C. Fry, S. J. 

Hiom, and W. G. Wade. 1998. Design and Evaluation of Useful 

Bacterium-Specific PCR Primers that Amplify Genes Coding for 

Bacterial 16S rRNA. Applied and Environmental Microbiology, 

64:795–799.

Okino, S., K. Iwasaki, O. Yagi, and H. Tanaka. 2000. Development of a 

Biological Mercury Removal-Recovery System. Biotechnology Letters, 22:783–788.

Roane, T. M., and I. L. Pepper. 2000. Microbial Responses to Environmentally Toxic Cadmium. Microbial Ecology, 38:358–364.

———. 2001. “Microoganisms and Metal Pollutants.” In Environmental Microbiology, ed. R. M. Maier, I. L. Pepper, and C. P. Gerba, pp. 

403–423. San Diego, Calif.: Academic Press.

Rusznyak, A., P. Vladar, P. Molnar, M. N. Reskone, G. Kiss, K. Marialigeti, and A. K. Borsodi. 2008. Cultivable Bacterial Composition 

and BIOLOG Catabolic Diversity of Biofilm Communities Developed on Phragmites australis. Aquatic Botany, 88:211–218.

Seifert, S. A., L. V. Boyer, N. Odegaard, and D. R. Smith. 2000. Arsenic Contamination of Museum Artifacts Repatriated to a Native 

American Tribe. The Journal of the American Medical Association, 

283:2658–2659.

Sirois, P. J., 2001. The Analysis of Museum Objects for the Presence of 

Arsenic and Mercury: Non-Destructive Analysis and Sample Analysis. Collection Forum, 16:65–75.

von Castein, H., S. Kelly, Y. Li, and I. Wagner-Dobler. 2002. Species 

Diversity Improves the Efficiency of Mercury-Reducing Biofilms 

under Changing Environmental Conditions. Applied and Environmental Microbiology, 68:2829–2837.

Wagner-Dobler, I., H. F. von Canstein, Y. Li, K. N. Timmis, and W.-D. 

Deckwater. 2000. Removal of Mercury from Chemical Wastewater 

by Microorganisms on Technical Scale. Environmental Science and 

Technology, 34:4628–4634.

Walter, P. J., S. Chalk, and H. M. Kingston. 2005. SamplePrep WebTM. 

http://www.sampleprep.duq.edu (accessed 11 November 2005).

CONCLUSIONS

A diverse bacterial community was identified on the 

surfaces of several mercury-treated museum collections. 

The presence of bacteria implies a possible remediation 

technology given the ability of certain microorganisms to 

convert various mercury compounds into gaseous forms 

of mercury. Gaseous mercury lends itself well to collection 

and appropriate disposal. The preliminary work presented 

here demonstrates the potential use of mercury-resistant 

bacteria in the removal of mercury from complex surfaces. 

In future work, this technology will need to be examined 

on actual museum materials prior to widespread use. 

However, current work is underway addressing optimization of the process and ensuring material preservation.

Acknowledgments

Funding for this work was provided by the National Center for Preservation Technology and Training 

under National Park Service grant number MT-2210-

04-NC-08. We thank Nancy Odegaard and the Arizona 

TABLE 2. Substrate utilization pattern for Arthrobacter sp. 2604 

based on the GN BIOLOG plate.

Type of substrate Specific substrate

Sugars α-D lactose

D-galactose

D-trehalose

D-melibiose

Amino acids L-alanine

L-proline

L-threonine

Organic compounds Acetic acid

Pyruvic acid methyl ester

Quinic acid

D-saccharic acid

L-alanyl glycine

Urocaric acid

 Inosine

Propionic acid

 Bromosuccine acid

Glucuronamide

α-ketobutyric acid

α-ketoglutaric acid

α-ketovaleric acid

β-hydroxybutyric acid
ABSTRACT.  Health hazards posed by the application of pesticide and heavy metal 

treatments of museum collections are problems that must be addressed. Surface cleaning 

will not remove poisonous substances embedded in the matrix of items. Efforts were undertaken to find a detoxification method that would better decontaminate objects, both 

individually and in groups. Carbon dioxide in its liquid or supercritical state offers alternative methods for better decontamination of objects. However, a detailed knowledge 

about the properties of the different materials is necessary in order to prevent any possible damage to those sensitive to liquid carbon dioxide (L-CO2) or supercritical carbon 

dioxide (SC-CO2). Sensitive materials should be excluded from the process given that 

damage to the object is unacceptable from a conservation point of view.

Keywords:  liquid carbon dioxide, supercritical carbon dioxide, dry cleaning, decontamination, ethnographic artifacts, cleaning, removal.

INTRODUCTION

In the past, ethnological objects were treated extensively with various pesticides, such as arsenic and mercury compounds, organochlorine insecticides, and 

other substances like naphthalene or camphor (see Figure 1) (Elert, 1994; Goldberg, 1996; Dawson, 1998; Davis and Caldararo, 2000; Hawks and Makos, 

2001; Odegaard and Sadongei, 2001, 2005; Schmidt, 2001; Sirois, 2001; Johnson and Henry, 2002; Martin and Kite, 2003; Klaus et al., 2005). However, this 

approach resulted in considerable contamination of indoor air as the pesticides 

in the matrix of the treated materials would contaminate the accumulated dust 

on them (Krooß and Stolz, 1993; Schieweck et al., 2005, 2007; Tello, 2006). 

Consequently, many objects had to be removed from public exhibition. It remains difficult to safely store and exhibit such objects given that solvent cleaning 

techniques can reduce surface contamination but cannot remove the embedded pesticide residues from their matrix. This is illustrated in Figure 2, where 

white dots of dichloro diphenyl trichloroethane (DDT) (detection by thin layer 

chromatography, TLC) are visible on a wooden flute from the collection of the 

Museum of Musical Instruments in Leipzig, Germany, previously sprayed with 

a wood preservative.

Paper presented at the Pesticide Mitigation in 

Museum Collections Workshop held at the Smithsonian’s Museum Conservation Institute in April 

2007 exploring possible methods and techniques 

that may become useful for the museum conservation field to reduce, mitigate, clean, or remediate 

undesirable pesticides on objects.

Helene Tello, Ethnological Museum, National 

Museums in Berlin, Arnimallee 27, D-14195 

Berlin, Germany. Achim Unger, Rathgen Research Laboratory, National Museums in Berlin, 

Schlossstrasse 1A, D-14059 Berlin, Germany. 

Corresponding author: H. Tello (h.tello@smb

.spk-berlin.de). Manuscript received 12 June

2008; accepted 26 June 2009.

Liquid and Supercritical Carbon Dioxide as 

a Cleaning and Decontamination Agent for 

Ethnographic Materials and Objects

Helene Tello and Achim Unger
3 6 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

• Evaporating DDT crystals and coatings from the surface using a laser.

• Removing pesticides in a vacuum drier or using a 

modified Thermo-Lignum process.

• Vacuum cleaning using water with surfactants.

• Dry cleaning with hydrocarbons or liquid carbon dioxide with surfactants

• Decontamination with supercritical carbon dioxide 

plus modifiers/cosolvents.

The present study evaluated the use of carbon dioxide 

in its liquid and supercritical state for the extraction of 

pesticides as well as for cleaning and degreasing ethnological objects with the aim of identifying the most appropriate conditions to achieve this goal.

Current conservation solutions to deal with contaminated objects include the following:

• Packing and sealing the objects in plastic that is impermeable to pesticide vapors.

• Enclosing and wrapping the objects with active carbon tissue.

• Storing objects in cabinets with an air circulation system.

• Installing special storage areas with air circulation systems.

Current methods for removal of pesticides from works 

of art include the following:

• Dry surface cleaning with special vacuum cleaners using HEPA filters.

FIGURE 1. Application of camphor to storage objects.
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THE CARBON DIOXIDE SYSTEM

Carbon dioxide, CO2, is a gas at ambient temperature 

and pressure. Changes in temperature and pressure may 

turn it into a solid, a liquid, or a supercritical fluid. Figure 

3 shows the phase diagram for this compound.

Solid carbon dioxide is usually referred to as “dry ice,” 

and in the form of particles (and even pellets), it is sprayed 

CLEANING PROCEDURES

The use of traditional wet methods for cleaning objects removes dust and soiling from their surfaces but has 

little impact on the matrix of artifacts. However, care must 

be taken to ensure that the cleaning procedures used for 

the removal of deleterious or toxic compounds do not affect the object itself, particularly if the soiling to be removed is composed of both lipophilic and hydrophilic 

materials. For example, indiscriminate removal of fats, 

oils, and waxes from objects such as wool, leather, and 

fur can make them particularly frail and brittle, thus putting them at risk for handling and future cleaning interventions. In addition, some organic solvents commonly 

used for cleaning, such as perchloroethylene, also may affect the conservator, given that most halogenated solvents 

used in museum environment are carcinogenic, as well 

as damaging to the ozone layer, thus affecting the global 

environment.

To overcome this dilemma, new methods using environmentally friendly solvents that can be reused are being 

developed. The regeneration of the solvent also simplifies 

the process of elimination of the soiling and toxic burden 

they may have extracted during use, so that these chemicals can be handled appropriately. One such solvent is 

carbon dioxide. This gas is more easily obtained than the 

expensive organic solvents presently used. Furthermore, it 

can be used in a liquid phase, or in a supercritical state, it 

is readily recycled given that the removal of the contamination products is straightforward.

FIGURE 2. Dichlorodiphenyltrichloroethane (DDT) spot deposits on a flute from the Museum of 

Musical Instruments in Leipzig, Germany.

FIGURE 3. Phase diagram for CO2.
3 8 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

serve as a solvent for nonpolar molecules, such as short hydrocarbon chains, i.e., fewer than 20 carbon atoms in length, 

as well as for aldehydes, ketones, and ethers. Even larger 

molecules, such as fats, oils, and waxes can at least be partly 

solubilized. However, it cannot remove polar compounds 

that occur in the contaminating materials, and for this purpose modifiers, such as tensioactive agents, are added.

Supercritical fluid (SC-CO2) is being used industrially 

for many purposes, such as extracting caffeine from coffee 

beans and hop extracts from hop cones. Since the 1970s, 

it has been used in the cosmetic and pharmaceutical industry to extract active ingredients from plant materials. 

It is also used as a carrier to impregnate timber with organic fungicides (Iversen et al., 2003) and to improve consolidation of waterlogged wood with polyethylene glycol 

(Chaumat et al., 1999). Other uses of SC-CO2 are the decontamination of wooden objects, with and without polychromy, from pesticide residues such as DDT, Lindane, 

and pentachlorophenol (PCP) (Unger, 1998; Jelen et al., 

under pressure to clean relatively flat and smooth surfaces. 

For example, it was used to remove the paint from the 

interior of the Statue of Liberty and is currently used in 

Germany to remove wax from wooden floors because the 

frozen wax particles detach easily from the wood, as does 

paint from metal. As dry ice sublimates directly into gaseous CO2, no residues are left.

The triple point for CO2, where the three phases—

solid, liquid, and gas—can coexist, is at approximately 5 

bar (0.5 MPa, ~5 atm) and –57oC (216°K). Carbon dioxide turns liquid at temperatures between 15°C and 20oC 

(288°K–293°K) and at 4–5 MPa pressure. The liquid is 

stable up to about 31oC (304°K) and 7.4 MPa where the 

critical point of CO2 lies. Above this temperature and pressure, only the supercritical fluid exists in which the physical differences between liquid and gas disappear, hence its 

denomination as “fluid.”

Liquid carbon dioxide (L-CO2) is nonpolar, but its polarity increases with increasing pressure. Therefore, it can 

FIGURE 4. Flow diagram of the UniClean process with L-CO2. Valves in the system are (1) autoclave (A) safety valve; (2) A filling valve; (3) 

purging valve; (4) storage tank ventilation valve; (5) gas recovery valve; (6) pressure valve; (7) gas recovery valve; (8) compressor (C) gas valve; 

(9) C liquid valve; (10) A draining valve; (11) distillation tank gas valve; (12) oil removal unit (ORU) gas valve; (13) ORU filling valve; (14) 

ORU draining valve.
num b e r 1 • 3 9

whose composition should be well known; otherwise, their 

use may have a negative effect on the treated objects.

Results

Preliminary testing of the procedure was carried out 

on several objects as described below.

Pinewood Panel. One half of a pinewood 

panel from the Green Vault of a room at the Staatliche 

Kunstsammlungen Dresden in Germany was used for the 

experiment. The panel previously had been treated with 

wood preservatives (“Hylotox 59” with 3.5% DDT and 

0.5% Lindane and probably also with “Hylotox IP” 

2003; Unger et al., 2004). Pesticides can also be extracted 

from textiles using SC-CO2 with the same approach (von 

Ulmann, 2003). The effect of SC-CO2 on color retention 

of different paint layers on wood has been addressed by 

Sungmo et al. (2004).

LIQUID CARBON DIOXIDE (L-CO2)

Methods

Two plants were used for the experiments reported 

herein. The first was the UniClean apparatus developed by 

the Union Engineering A/S Company in Fredericia, Denmark. This company also developed the procedure that 

industry uses to clean electronic accessories. The second 

system was the experimental plant at the wfk–Cleaning 

Technology Research Institute in Krefeld, Germany.

One experiment in cleaning, degreasing, and decontaminating ethnographic objects was carried out in the 

UniClean plant (Unger et al., 2006; Tello and Unger, 2006). 

Its flow diagram is schematically represented in Figure 4. 

The principal parts of the system are the reservoir holding 

the CO2, an autoclave that serves as the washing chamber, a distillation tank, the oil and fats separation tank, 

and a CO2 compressor. Figure 5 shows the appearance of 

the UniClean 450 model. The objects to be cleaned are 

placed in a stainless steel basket in the autoclave-washing 

chamber (see Figure 6). When the chamber is closed, it is 

flooded with L-CO2 that circulates through it, thus washing the objects placed in the basket. The process is carried 

out at 15°C–20oC and at 5–6 MPa. The time required for 

cleaning the objects varies from half an hour to 24 hours. 

When the chamber is drained, contaminated L-CO2 is sent 

to the distillation tank where it is separated from the soiling materials by evaporation, and the extracted contaminants are collected in the separation tank.

Another experiment was carried out at the experimental plant in Krefeld, Germany, shown in Figure 7. The 

same temperatures and pressures were used as for the UniClean system, and the cleaning time was between half an 

hour and one hour. In contrast to the UniClean apparatus and procedure, the washing cylinder of the wfk plant 

moved slowly.

All experiments with L-CO2 were performed without 

the addition of surfactants to determine the efficiency of 

the pure liquid. Although it would have been desirable to 

test special surfactants to improve the rate of decontamination, time constraints did not allow further tests. Surfactants are mostly used to remove polar substances, such 

as inorganic dirt particles, and for use on museum objects 

FIGURE 5. Appearance of the UniClean 450 plant.

FIGURE 6. Autoclave-washing chamber with stainless steel basket.
4 0 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

(Zujest, 2003). This means that the procedure has to be 

repeated to reach the desired safety levels.

Epitaph Fragment. A second sample was an 

epitaph piece from the Cathedral in Zwickau, Germany. 

In the early twentieth century, such wooden epitaphs had 

been found weakened from insect attack. Consequently, 

containing 5% PCP and 3% DDT because the presence of 

PCP was found on the sample). The sample clearly showed 

the presence of white DDT efflorescences on the dark 

brown background, as shown in Figure 8, top. The left 

half of the sample, with a weight of 184.8 g was subjected 

to L-CO2 cleaning in the UniClean plant.

Figure 8, bottom, shows the wood panel after cleaning with L-CO2. It can be seen that the color has intensified showing the color variations of the applied tincture 

and the disappearance of the white DDT crystals. Table 1 

presents the results of the analysis carried out before and 

after the treatment with L-CO2. As can be seen, there was 

a significant diminution of DDT and Lindane concentration. There was no significant change in the concentration 

for PCP; the slightly increased value can be attributed to 

uneven distribution of the contaminant in the sample. In 

spite of the positive results obtained it is to be noted that 

concentrations of DDT above 30 ppm and of Lindane 

above 100 ppm in wood remain high for these pesticides 

FIGURE 7. The experimental plant at wfk–Cleaning Technology 

Research Institute in Krefeld, Germany.

FIGURE 8. Pinewood panel with white efflorescences of DDT on 

the dark brown background (top), and after cleaning with L-CO2 

(bottom).
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cosolvents, were also unsuccessful (J. J. Morrell, Oregon 

State University, personal communication, 1997). These 

tests were carried out at 40oC, 4000 psi (~281 bar, 28 

MPa). Table 2 compares these results. It can be seen that 

CO2 is not effective in the removal of the aged linseed oil. 

Although the addition of dimethyl sulfoxide (DMSO) improved the extraction significantly, this is not a viable option of cultural heritage objects.

Gilded Leather Hanging. An eighteenthcentury gilded leather hanging from the Frens Palace (see 

Figure 9), presumably manufactured in the Netherlands, 

they were impregnated with linseed oil, using either a cold 

or hot procedure. Over the years, this treatment softened 

the wood and the linseed oil oxidation products partly 

oozed out. The objective of the test was the extraction of 

the polymerized linseed oil and its oxidation products.

The fragment, weighing 19.3 g, was subjected to a 

24 hour extraction with L-CO2. The minimal weight loss, 

around 1.7%, indicates that this method is not applicable 

for the removal of polymerized linseed oil and its decomposition products. It should be pointed out that tests on 

similar fragments using SC-CO2 by itself, and with various 

TABLE 1. Pesticide concentrations found on a pinewood panel 

before and after treatment with L-CO2. (DDT, dichloro diphenyl 

trichloroethane; PCP, pentachlorophenol; the dash indicates no 

reduction occurred.)

Contaminant value (ppm = mg/kg)

Treatment state DDT Lindane PCP

Before 1840 186 80.9

After 204 125 81.0

% Reduction 88.9 32.8 —

TABLE 2. Amount of aged linseed oil extracted by different 

methods (L-CO2, liquid carbon dioxide; SC-CO2, supercritical 

carbon dioxide; DMSO, dimethyl sulfoxide).

Amount

Method Cosolvent extracted (%)

L-CO2 none 1.7

SC-CO2 none 1.5

SC-CO2 3% Acetone 1.8

SC-CO2 3% Methanol 2.2

SC-CO2 3% DMSO 17.6

FIGURE 9. Leather hanging from the Frens Palace: left, front side, and right, back side.
4 2 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

remained at 44oC, and pH remained unchanged at around 

4.8–4.9.

The treated sample suffered a weight loss of about 6%, 

while the extraction of lipophilic materials was reduced by 

15.5%, showing the effectiveness of this method for the 

elimination of fatty materials. One of the advantages this 

procedure has for leather is that entire hides can be treated 

at a same time, ensuring a uniform extraction. However, 

additional tests are necessary to optimize the parameters 

needed for a practical application of this treatment.

Woolen Blanket. A Chilean Patagonia 

woolen blanket was yet another sample that was examined 

(see Figure 11). The white wool was partly dyed in red, orange, green, blue, and violet colors. The blanket showed 

moth holes and was darkened by soiling. The wool had 

a greasy feel, and the fibers appeared brittle. Some loose 

fibers were tested from this object (see Figure 12). Analyses showed that the object had been treated with organochlorine pesticides and that it was also contaminated with 

heavy metals.

After the cleaning, the woolen fibers felt softer and 

more elastic. The color was lighter and brighter, and microscopic observation confirmed the cleaning by the shine of 

also was tested. The calf or kid leather had been tanned 

with natural tanning agents. The hanging was greased 

successively with a synthetic wax (Lypoderm Fat A and 

Lypoderm from Licker SA), Montan wax, and Vaseline 

to simulate the application of fat-rich products generally 

used in the conservation of these objects (see Figure 10, 

left). For instance, fat contents of about 20% by weight 

have been found in leather that normally would contain 

about 5%–6% (J. Wouters, Institut Royal du Patrimoine 

Artistique, Brussels, personal communication, 1998).

The cleaning improved significantly the backside of 

the hanging, as shown in Figure 10, right, and the grease 

tackiness on the front side was reduced. However, the 

painted layer on the front side showed an increased tendency to flake off. It was difficult to determine whether or 

not this negative effect was due to the treatment or merely 

a consequence of object handling during this procedure. 

Microscopic examination of the surface showed that small 

white opaque areas had formed on top of the painting, 

and these could be attributed to a partial solubilization 

of the beeswax, which probably was applied as a coating. 

No negative effects on the shrinkage temperature of the 

leather or its pH were observed: the shrinkage temperature 

FIGURE 10. Back side of overlubricated leather hanging from the Frens Palace: left, before cleaning; right, after cleaning with L-CO2.
num b e r 1 • 4 3

showed that mercury levels could be reduced by 76% (Tello 

et al., 2005a, 2005b).

Seal Gut Parka. A piece of a translucent seal 

gut parka, about 37 μm (0.037 mm) thick and about 41 

× 6 cm, was taken and halved, one for treatment and the 

other as control. The piece was very undulated and wrinkled (see Figure 13, top), and the surface was sticky and 

had a waxy appearance. Darker spots of waxes and grease 

were visible on the surface because of conservation treatments carried out in the 1960s.

Previous cleaning attempts of some areas had been 

carried out using a mixture of isopropanol and isooctane 

(1:3) and were relatively successful (Weidner, 2000). However, treatment of the entire object could not be carried 

out because of health concerns and the lack of adequate 

installation and financial support.

The cleaning procedure reduced the weight of the 

sample by 4.4% mainly because of inorganic soiling materials removed by the process (Unger et al., 2006). The 

thickness of the seal gut strip was reduced from 37 to 35 

μm, and although it still was wrinkled, it was more pliable 

and no longer felt tacky (see Figure 13, bottom).

SUPERCRITICAL CARBON DIOXIDE (SC-CO2)

Methods

SC-CO2 tests were carried out using two different 

units. One was a 150 mL laboratory plant (see Figure 14) 

for screening experiments at the Fraunhofer Institute for 

Environmental Safety and Energy Technology (UMSICHT) 

in Oberhausen, Germany. The second was the 10 L highpressure plant of the Messer Griesheim HPE Technical Centre in Krefeld, Germany (see Figure 15) (Tello et al., 2005a).

For the extraction in the 150 mL high-pressure 

view cell, L-CO2 was compressed to 350 bar (35 MPa, 

the fibers. The weight loss of the sample during cleaning 

was of 4.7%. The reduction of contaminant concentration 

is reported in Table 3. Although the amount of DDT was 

reduced, the low content of Lindane was not significantly 

affected. Also, the amounts of mercury and arsenic may 

be misleading because the contamination is probably not 

uniform across the sample. Further testing with SC-CO2

FIGURE 11. Woolen blanket from Chilean Patagonia.

FIGURE 12. Woolen fibers from the Patagonian blanket before 

treatment with L-CO2.

TABLE 3. Concentrations of contaminants found on woolen fibers from a Patagonian blanket before and after treatment with 

L-CO2; the dash indicates no reduction occurred.

Contaminant value (ppm = mg/kg)

Treatment state DDT Lindane As Hg

Before 66.3 1.3 4 240

After 5.9 1.1 3 290

% Reduction 91.1 15.4 25.0 —
4 4 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

~350 atm), using a piston pump, and heated to supercritical conditions (40°C), in a heat exchanger, before it entered the view cell containing the samples. The pressure 

build up lasted 15 minutes, and the time of extraction was 

seven hours. The pressure release lasted one hour, and the 

mass flow of CO2 was recorded at 2 kg/h. The relatively 

high flow was chosen to obtain a strong decontamination 

effect and to prevent saturation of the CO2 with the pesticides. Ethanol served as a cosolvent with and without the 

additional use of the chelating agent trimercaptotriazine 

15 (TMT 15). Further details are given in an unpublished 

research report of the Fraunhofer Institute.

The high-pressure extraction plant in Figure 15 contains two 10 L extractors. For better handling of loose 

samples or bulk materials, a 7 L inner metal basket is 

used. By using one of the extractors, two experiments 

were carried out with the following parameters: extraction 

pressure, 250 bar (25 MPa, ~250 atm); extraction temperature, 40°C; extraction duration, three hours; CO2 flow 

FIGURE 13. Piece of a seal gut parka. Top, before treatment. Bottom, after treatment with L-CO2.

FIGURE 14. The 150 mL laboratory plant at the UMSICHT 

installation.

FIGURE 15. The 10 L high-pressure extraction plant at the Messer 

Griesheim Technical Centre.
num b e r 1 • 4 5

Figure 17 (right) shows the samples after extraction 

in the high-pressure view cell of the 150 mL laboratory 

plant. The fur and the wool tissue showed a partial loss 

in weight, which was probably caused by the removal of 

dust, grease, water, and pesticides. The haptic examination of all samples showed no difference before and after 

the extraction. The sample of fur was somewhat dry, the 

skin appeared to be more affected than the fur hair because it was degreased considerably. The visual and microscopic examination of the wool tissue suggested a positive 

cleaning effect, and the brilliance of the bundle of feathers 

was unchanged.

Table 4 presents the contaminant content before 

and after treatment with SC-CO2 for the fur, bundle of 

feathers, and wool tissue samples. As can be seen, a significant decrease in mercury and DDT concentration was 

achieved. Lindane was reduced to a high extent for the 

fur sample, but when found in low concentrations, it appeared not to be affected by the treatment. However, very 

rate, 20 kg/h. The 25 MPa pressure was reached within 34 

minutes. The pressure release took one hour (first experiment) and two hours (second experiment).

After closing the extractor, liquid CO2 was introduced 

from the collecting vessel. For further pressure build-up, a 

CO2 membrane pump was used and the CO2 from the collecting vessel was passed through a heat exchanger to cool 

it down to about 0°C to prevent cavitation due to vapor 

bubbles forming in a quickly moving solvent. During passage through the extractor, the CO2 accumulated the soluble components from the materials. After the set extraction 

time had passed, the mixture was depressurized to subcritical conditions (50–60 bar, ~50–60 atm, and 25°C–30°C) 

by means of a valve. By reducing the pressure and/or temperature to subcritical conditions, the CO2 returned to its 

gaseous state and the extracted materials precipitated in the 

7 L separator. The gaseous CO2 was again liquefied in a 

refrigerated condenser and collected in the collecting vessel.

To prevent the formation of L-CO2 or of dry ice respectively during expansion, the density of CO2 in the 

range between 100 and 50 bar (10–5 MPa, ~100–50 atm), 

was continuously changed in a linear manner. This also 

prevented damage to the inner structure of the materials 

and objects.

The conditions of the ethnographic samples were 

documented, examined macro- and microscopically and 

photographed before and after treatment. All specimens 

and objects were weighed. The amounts of heavy metals, 

DDT, Lindane, and PCP contamination on the materials 

also were determined before and after extraction.

Results

Preliminary testing of the procedure with SC-CO2

was carried out on several samples from materials and 

objects of the Ethnological Museum in Berlin, Germany. 

The entire range of sample specimens that were tested for 

the extraction with SC-CO2 is largely described by Tello 

(2006). A selection of some of these materials and objects 

is presented below.

Fur, Bundle of Feathers, and Wool 

Tissue. For testing in the 150 mL laboratory plant, 

the selected samples included a piece of fur from a small 

model (57 cm long, shown in Figure 16) of a fur coat from 

the Samojades, a feather bundle from the Amazon region, 

and archeological wool tissue (see Figure 17, left). Analyses showed that the different samples had been treated 

with inorganic (As and Hg compounds) and organic pesticides (DDT, Lindane, PCP).

FIGURE 16. Model of a fur coat from the Samojades.
4 6 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

FIGURE 17. Left column, from top to bottom, samples of fur, bundle of feathers, and wool tissue before extraction. Right column, samples 

after extraction with SC-CO2.
num b e r 1 • 4 7

terials were from Alaska and served as illustrative materials in the conservation laboratory of the Ethnological 

Museum in Berlin (see Figure 18). The experiment was to 

clarify whether or not damage of materials could be expected from this treatment. Table 5 reports the weight loss 

of the samples (grass blades 1.6% and caribou fur 5.3%) 

and the visual and haptic evaluation on the condition for 

these materials before and after the extraction experiment.

Visual evaluation after extraction showed a lightening 

effect on the grass blades that could be attributed to the 

removal of the small black spots that were in the grooves 

before extraction. Further examination by scanning electron microscopy clearly confirmed that loosely scattered 

and embedded dust was removed as a result of the extraction (Figure 19). Changes in tensile strength of the grass 

blades before and after extraction were evaluated by the 

measured modulus of elasticity.

The caribou fur showed slight differences in the haptic 

properties and residues were found in the pulp tissue of 

the sample (see Figure 20). These highly interesting observations lead to further analyses of the caribou fur using 

low concentrations of contaminants were not influenced 

by the treatment.

Blades of Grass and Caribou Fur.

Samples of grass blades and a piece of caribou fur were 

tested in the 10 L high-pressure extraction plant. The maTABLE 4. Concentrations of contaminants found on fur, feathers, and wool samples before and after treatment with SC-CO2; 

ND = not detected; a dash (-) indicates no reduction occurred or 

could be measured. 

Treatment

Contaminant value (ppm = mg/kg)

Object state DDT Lindane PCP As Hg

Fur Before 358 3.9 ND 8 800

After 8.4 0.3 0.2 19 94

% Reduction 97.6 92.3 — — 88.3

Feathers Before 66.3 0.1 ND <1 171

After 0.3 ND 0.2 2 16

% Reduction 99.6 — — — 90.6

Wool Before ND ND 0.4 <1 42

After 0.2 ND 0.3 4 10

% Reduction — — 25.0 — 76.2

FIGURE 18. Samples of the caribou fur (top) and grass blades before 

extraction with SC-CO2.

TABLE 5. Condition of grass blades and caribou fur before and 

after treatment with SC-CO2 in the 10-L high-pressure extraction plant.

Characteristic Condition before Condition after

Grass blades (weight loss = 1.6%)

Stability Stable No change

Flexibility Flexible, smooth No change

Color Yellowish gray Slight lightening of color

Residues Some soiling in the Visible cleaning effect

longitudinal grooves 

visible as small black 

spots

Surface Regular grooves No change

Caribou fur (weight loss = 5.3%)

Stability Skin/fur intact and flat No change

Flexibility Fur is soft and elastic No change

with firm grip; skin is 

flexible; edges are 

smooth

Color White and brown colors Skin is slightly white

of hair are well 

distinguishable

Residues Skin is greasy Skin is degreased; 

yellowish residues in pulp 

tissue

Surface Hair is slightly wavy; Hair is softer

structure of skin 

diaphragm is clearly 

visible, transparent
4 8 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

the fat itself. And, it is well known that aldehydes will lead 

to cross-linking of proteins, thus inducing their hardening, 

which may in turn cause damage to fur.

DISCUSSION AND CONCLUSIONS

The decontamination achieved with L-CO2 for the 

tested pinewood panel is similar to that obtained with SCCO2 for other wooden objects. For example, DDT content 

was reduced by 89% with the L-CO2 method, while the 

SC-CO2 method achieved values ranging between 97% 

and 27%, depending on the object, with the most frequent value being around 95% (Unger, 2003). In the case 

of Lindane, the content was reduced only by 15% with 

L-CO2 but ranged between 17% and 99%, with the most 

frequent value around 93%, for the SC-CO2 method. The 

poor performance of L-CO2 in the removal of Lindane can 

be attributed to the poor solubility of this pesticide in the 

liquid. Because of its higher polarity and hence lower solubility in CO2, PCP could not be extracted effectively with 

L-CO2 or SC-CO2. Further experiments with addition of 

surfactants/modifiers need to be carried out.

Arsenic and mercury compounds were not removed to 

a sufficient extent with L-CO2. In the case of inorganic pesticides, further tests using chelating agents are necessary.

The effect on the decontamination rate by variation 

of extraction pressure and extraction temperature using 

L-CO2 or SC-CO2 could not be suitably clarified and is the 

subject of future research.

pyrolysis gas chromatography/mass spectrometry. The 

results, shown in Figure 21, clearly demonstrate the noticeable impact of SC-CO2 on the caribou fur. This was unexpectedly very positive because the free fatty acids from 

the triglycerides in the fat and their degradation products, 

such as aldehydes, i.e., octanal, were extracted rather than 

FIGURE 19. Scanning electron microscope photomicrograph of a grass blade. Left, before treatment. Right, after extraction with SC-CO2.

FIGURE 20. Residues left on the paper tissue after extraction of the 

caribou fur with SC-CO2.
num b e r 1 • 4 9

Eisbein from the Landesamt für Denkmalpflege Sachsen in 

Dresden, Germany; Bernhard Trommer from the Forschungsinstitut für Leder und Kunststoffbahnen gGmbH 

Freiberg, Germany; and Beatrix Föllner and Georg Rohm 

from the wfk-Reinigungsinstitut Krefeld, Germany. Last 

but not least, we thank A. Elena Charola for her very 

helpful and patient collaboration during the manuscript 

preparation.

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Chaumat, G., Q. K. Tran, C. Perre, and G. Lumia. 1999. “Trials of Shape 

Recovering from Collapsed Waterlogged Wood by Treatment with 

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Davis, L., and N. Caldararo. 2000. The Repatriation Dilemma, Museum 

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Most objects did not show any marked changes in 

their properties during treatment with either L-CO2 or 

SC-CO2. One exception was found in the fur samples, 

wherein the extent of degreasing varied, depending on the 

test parameters. In the case of materials with oily and fatty 

components, treatment with SC-CO2 extracted mainly 

free fatty acids and the resulting degradation products 

from chemical aging processes of fat.

Acknowledgments

The cooperation of several colleagues in different 

institutions made possible the research presented in this 

paper. Among them we acknowledge Erich Jelen from 

the Fraunhofer-­Institut für Umwelt, Sicherheits- und Energietechnik UMSICHT Oberhausen; Frank Gockel and 

Thomas Berger from the Messer Group GmbH Application Technology Krefeld; Sørrn Lindex from the Union 

Engineering A/S Company Fredericia, Denmark; Manfried 

FIGURE 21. Pyrolysis–Gas Chromatography–Mass Spectromery (Py-GC-MS) results: top graph, backside of the caribou fur; middle, SC-CO2

extract found in the paper tissue; bottom, pure octanal.
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der Inuit. [Problems Posed by the Restoration of Ethnological Objects made from Seal-gut, as Illustrated by the Inuit Seal-gut Parka.] 

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für Technologie der Malerei der Staatlichen Akademie der Bildenden Künste, Stuttgart, Germany.

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Tello, H., 2006. Investigations on Super Fluid Extraction (SFE) with Carbon Dioxide on Ethnological Materials and Objects Contaminated 
ABSTRACT.  Because records for pesticide control procedures are often incomplete, a 

study was planned to determine if an unknown organic pesticide might be extracted as 

a residue on commonplace objects using supercritical carbon dioxide (SC-CO2). In this 

work, samples of chrome-tanned leather representing artifact material were treated with 

known quantities of a commercial Diazinon solution and, subsequently, with SC-CO2 for 

two minutes, to determine the extent of removal of the pesticide residue. Extraction effectiveness was improved using acetone as a cosolvent. Detection of the levels of extracted 

Diazinon was performed by toxicological screening using rat lung epithelial cell cultures. 

SC-CO2 may prove to be a viable solvent or cosolvent system to extract pesticides from 

artifacts without damaging fragile materials and without leaving a residue. A systematic 

study of museum materials and labeled pesticides should be carried out to define the utility of this method.

Keywords:  SC-CO2, cosolvents, pesticide removal, cleaning, Diazinon, museum 

objects.

INTRODUCTION

Often, in the past, cultural artifacts in museums were treated with a range 

of poisons and pesticides to prevent or retard deterioration, insects, rodents, and 

mold. Passage of the Native American Graves Protection and Repatriation Act 

(NAGPRA) in 1990 has established a mechanism for Native American groups to 

reclaim certain museum artifacts and return them to cultural use. In the meantime, new developments have led to the recognition and banning of many of the 

old poisons and pesticides. Consequently, there is an increased need to identify 

and report objects that pose human health risks and an increased urgency to 

develop methods to mitigate hazards posed through direct human contact (Odegaard and Sadongei, 2005). In May 2003, funding from the University of Arizona Vice President for Research was awarded to initiate an interdepartmental 

collaborative program to study pesticide removal techniques that would enable 

objects to return to cultural use.

Many pesticides are short lived and degrade in the environment. Others are

persistent and may remain on artifacts several decades after application. Methods 

Paper presented at the Pesticide Mitigation in 

Museum Collections Workshop held at the Smithsonian’s Museum Conservation Institute in April 

2007 exploring possible methods and techniques 

that may become useful for the museum conservation field to reduce, mitigate, clean, or remediate 

undesirable pesticides on objects.

Werner Zimmt, Teresa K. Moreno, and Nancy 

Odegaard, Preservation Division, Arizona State 

Museum, 1013 East University Boulevard, Building 26, University of Arizona, Tucson, Arizona 

85721, USA. Rachael A. Turner and Mark R. 

Riley, Agricultural and Biosystems Engineering, 

Shantz Building, Room 403, 1177 East Fourth 

Street, University of Arizona, Tucson, Arizona 

85721, USA. Bo Xie and Anthony J. Muscat, 

Chemical and Environmental Engineering, 

Harshbarger 134, P.O. Box 210011, University 

of Arizona, Tucson, Arizona 85721, USA. Corresponding author: W. Zimmt (wsz@ag.arizona

.edu). Manuscript received 12 June 2008; accepted 26 June 2009.

Pesticide Extraction Studies Using 

Supercritical Carbon Dioxide

Werner S. Zimmt, Nancy Odegaard, Teresa K. 

Moreno, Rachael A. Turner, Mark R. Riley, 

Bo Xie, and Anthony J. Muscat
5 2 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

insoluble (Politzer et al., 1993). The solubility of molecules in SC-CO2 is also a function of the density of the 

fluid, which can be manipulated by changing the pressure 

and temperature (Jones et. al., 2004). Testing the effectiveness of SC-CO2 for the extraction of organic pesticide 

residues required the application of a technique to assess 

the concentration of the pesticide on the sample before 

and after cleaning. In this study, that concentration was 

equated to the toxicity of the pesticide in the sample before and after the pesticide removal process. Such toxicity testing was provided here by RLE cell culture analyses 

(Riley et al., 2003).

MATERIALS PREPARATION AND HANDLING

To develop a protocol and evaluate the ability of SCCO2 to remove pesticides from a diverse array of museum 

artifacts, two types of surrogate materials (leather and 

feathers) were investigated. The particular leather and 

feather samples were selected because they were readily 

available. The protocol for contaminating the simulated 

artifact material consisted in the application of dilute pesticide solutions to 5 × 5 cm chrome-tanned leather samples 

that previously had been cleaned and tested for inherent 

toxicity (i.e., baseline reactivity) with the RLE cell culture 

technique. The RLE cell response is an indirect approach 

and was considered appropriate because of its ability to 

detect a wide range of pesticide toxins on artifacts with 

unspecified pesticide residues. Therefore, it was used as 

an indicator rather than traditional analytical detection 

methods.

The impact of SC-CO2 on brightly dyed feathers was 

also assessed in order to determine if the color or texture 

of a delicate material would be affected by the extraction 

process. The feathers were bought in a craft store, and 

digital pictures were taken before and after the extraction 

with SC-CO2. On the basis of visual and photographic 

comparison, the extraction process had no effect on the 

color or texture (see Figure 1). No microscopy examination was carried out for this preliminary assessment.

A broad spectrum commercial pesticide labeled 

“Ortho Diazinon, 25% active material” was purchased 

in a local garden supply store, as it was one of the few 

organic pesticides available. Although it was not a commonly used museum pesticide, it was considered to be 

suitable for the purposes of this study given its characteristics of polarity and SC-CO2 solubility. It has since been 

withdrawn from use indoors and on lawns and gardens. 

Diazinon is an organophosphate, the chemical name is o, 

to decontaminate museum objects treated with pesticides 

have been of critical interest to museums holding contaminated collections and to Native American tribes seeking to 

return these objects to cultural use. Many techniques that 

had been previously discussed in the museum and conservation literature include the use of high-efficiency particulate air (HEPA) filtered vacuums, compressed air, washing, 

ultraviolet light, chemical alteration, freeze-drying, lasers, 

and microbial detoxification (Odegaard, 2001). The applicability of supercritical carbon dioxide (SC-CO2) as a 

pesticide removal technique for museum objects has been 

studied (Jelen et al., 2003; von Ulmann, 2003; Kang et 

al., 2004; Tello et al., 2005; Tello, 2006). However, these 

studies address the use of unmodified SC-CO2. The purpose of the present study involved two areas of research 

with the following aims:

• Develop a protocol for methods that would test the 

use of SC-CO2 for the removal of an organic pesticide 

from simulated artifacts.

• Assess the effectiveness of the pesticide residue removal through the use of rat lung epithelial (RLE) 

cell culture technique as it relates to potential human 

health risk.

Supercritical CO2 is a solvent that has the potential to 

extract chemicals without leaving a residue of its own. The 

use of SC-CO2 for removing pesticides from solid objects 

has several advantages over other methods. A low surface 

tension and viscosity allows SC-CO2 to wet the surface of 

any object and rapidly penetrate porous materials. Releasing the system pressure causes CO2 to go directly from a 

supercritical fluid state to a gas without becoming a liquid. 

An object consequently comes out dry after processing. 

CO2 has low toxicity and is nonflammable, and as a gas 

it is readily separated from chemical additives and products that have much lower vapor pressures. Furthermore, 

this treatment may be considered acceptable by tribes because the use of SC-CO2 involves minimal handling during the cleaning process, utilizes natural materials, and 

does not permanently introduce new products. The aim 

of the study was to determine if adding small quantities of 

a polar solvent to the SC-CO2 would improve its removal 

of more polar pesticides. The substrate for the particular 

pesticide to be studied was not important; the focus was 

the pesticide, which had to be polar and mostly insoluble 

in pure SC-CO2.

Generally, low molecular weight organic compounds 

are soluble in SC-CO2, but high molecular weight organic compounds, especially if they are polar, are nearly 
num b e r 1 • 5 3

The Soxhlet extractor is used to separate a contaminant of limited solubility, i.e., the pesticide, from the solvent. It consists of a distillation flask where the solvent is 

vaporized and goes to a reflux condenser via a side arm. 

The condenser drips the condensed liquid into a cylindrical chamber that contains the sample to be extracted 

and fills the chamber, allowing the extractable material to 

dissolve. A siphon on the side of this chamber allows the 

solvent to flow back into the distillation flask so that the 

system can be kept running as long as necessary. Although 

this Soxhlet process is not appropriate for artifacts, it did 

provide a rigorous and efficient means of removing the

pesticide from the samples and was therefore important 

in evaluating the effectiveness of the SC-CO2 procedure. 

Dilutions of these Soxhlet extracts were then introduced 

to RLE cells to evaluate the presence of any toxic material. 

Industrial grade acetone was not sufficiently pure for this 

process as it contained impurities that interfered with the 

RLE testing. The dose/response curves of the cells to the 

test solution provide a measure of the quantity of pesticide

on the leather samples.

The experimental SC-CO2 system used to process the 

leather samples consisted of a 200 mL stainless steel reactor fed by a liquid CO2 bottle (see Figure 3). Samples were 

placed upright on the bottom of the reactor with the top 

edge leaning against the reactor wall. A disposable syringe 

was used to introduce 0.2 or 2 mL of acetone (analytical 

reagent grade) into the bottom of the reactor as far from a 

sample as possible to avoid direct contact. The reactor was 

closed, cooled to 8°C in an ice bath, and charged with liquid CO2 (99.99%, Air Liquide Coleman grade) to a pressure of approximately 60 atm (6 MPa). When filled with 

liquid CO2, given the 200 mL volume of the reactor, the 

acetone concentration in the fluid was either 0.1 or 1 vol%.

The reactor was heated requiring approximately 12 

minutes to cross into the supercritical CO2 region, which 

typically occurred at 31°C and approximately 150 atm 

o-diethyl o-(2-isopropyl-6-4-pyrimidinyl) phosphorothioate. Its use as a museum pesticide is documented by Pool 

et al. (2005). The product was diluted with reagent grade 

acetone to concentrations of 2 or 4 mg active ingredient 

per milliliter solution. The pesticide solution was applied 

slowly from a hypodermic syringe so that the leather samples were uniformly saturated. When all of the solution 

had been absorbed by the leather, the samples were allowed to dry while suspended in a gentle stream of ambient air. The samples were divided into two groups for 

pesticide removal. One set was subjected to Soxhlet acetone extraction. The other set was treated with supercritical CO2 as the primary removal method, followed 

by the Soxhlet acetone extraction. A comparison of the 

two acetone extracts, made before and after the SC-CO2

process, served to show what was extracted by the use of 

supercritical CO2. The flow of this experimental process is 

depicted in Figure 2.

FIGURE 2. Diagram of experimental flow.

FIGURE 1. Effect of supercritical carbon dioxide (SC-CO2) extraction on color and texture of three feathers: left, before extraction; 

right, after extraction.
5 4 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

be completely removed. The addition of a cosolvent such 

as acetone is known to increase the solubility of slightly 

water-soluble contaminants (Xie et al., 2005).

Rat Lung Epithelial Cell Culture Methods

for Toxicity Testing

The lethal dosage for rats from inhaling an acute, 

short-term exposure of pesticide can be defined in milligrams per liter (of air) in hours. Thus, rat lung tissue was 

thought to be a good model to use to test the exposure 

to pesticides. One of the goals of this work was to use 

RLE-6TN (T-antigen negative) cell cultures to determine 

the effectiveness of the SC-CO2 extraction procedure. This 

technique is a standard method of determining toxicity by 

exposing well-defined cultures to suspected toxic materials and determining the dilution of the toxins required to 

allow 50% of the cells to survive (LD50) (Okeson et al., 

2004; Riley et al., 2005). If appropriate, this test for toxicity would obviate the need of isolating or identifying them. 

In this study, the RLE cells were useful for testing the protocol and the effectiveness of the SC-CO2 extraction process. The tests for toxicity were conducted according to 

accepted protocols (Riley et al., 2003; Tello, 2006).

PESTICIDE REMOVAL RESULTS

To evaluate the ability of SC-CO2 to remove the organophosphate pesticide from simulated artifacts without 

damaging their material structure or losing pigmentation, 

it was necessary to validate methods of extraction and the 

application of the RLE cell culture method for pesticide 

detection. Rat lung epithelial cell cultures are highly responsive to a variety of common pesticides that may have 

been used to treat artifacts in storage. Extracts displaying 

no toxicity would be expected to yield a cellular metabolic activity of 100% equal to the control (e.g., no cell 

damage). Decreases below this level result from cellular 

damage to membranes, mitochondria, or the protein components of cells and serves as a marker of toxic impact.

In initial tests, samples treated with the organophosphate pesticide and extracted with pure SC-CO2 retained 

about 50% of the pesticide on the basis of dilution experiments. After acetone was added to the SC-CO2 extraction 

process, no pesticide residue was detected. Some test result 

inconsistencies were shown to be due to the use of an industrial grade acetone, which reduced cell activity at a 1:50 

dilution. Higher dilutions with industrial grade acetone 

showed no such decline in cell activity. The impurity from 

(15 MPa), and another three minutes to reach the steady 

state processing temperature, in the range of 50°C–60°C, 

and pressure, in the range of 100–250 atm (10–25 MPa). 

The temperature and pressure ranges were chosen to vary 

the SC-CO2 density from approximately 0.5 to 0.9 g/

cm3 based on the Peng-Robinson equation of state. The 

resistively–heated jacket and insulation covering the reactor allowed a temperature set point to be reached within 

±5°C using a thermocouple and controller. Pressure was 

read using a Bourdon tube with an accuracy of ±20 psi 

(1.4 atm or 0.14 MPa) in the range 0–5,000 psi (340.2 

atm or 34 MPa). All experiments were run as batch processes for a two minute soak time at steady state conditions. Cross-contamination was minimized by running 

pure SC-CO2 through the system between experiments.

After processing, the reactor pressure was released 

quickly through a 1⁄4 inch (6.35 mm) needle valve reaching 

ambient in less than 1 minute. The high mass flow rate out 

of the reactor was sufficient to entrain chemicals that were 

dissolved in the fluid during processing because no liquid 

residue was observed on the samples.

The extremely low viscosity and surface tension of 

SC-CO2 makes it an ideal solvent for removal of contaminants from both exterior and interior of the object being 

cleaned. The organophosphate pesticide itself is a polar, 

slightly water-soluble material, while SC-CO2 has the solvating character of n-hexane. Initial experiments showed 

that Diazinon was not sufficiently soluble in SC-CO2 to 

FIGURE 3. Schematic drawing of the SC-CO2 reactor system. After 

loading, the reactor was chilled to 8°C and fed with liquid CO2 to 

approximately 60 atm. The cylinder was closed, and the reactor was 

heated using a heating jacket and set point controller until the desired steady state conditions were reached. After processing, the fluid 

was exhausted through a needle valve.
num b e r 1 • 5 5

from the commercial organophosphate, were as follows: 

three inorganic compounds: arsenic trioxide (As2O3), mercury bichloride (HgCl2), and zinc fluosilicate (ZnF6Si); a 

chlorinated hydrocarbon: Lindane (γ-hexachloro cyclohexane); and another organophosphate: Malathion [2-

(dimethoxyphosphinothioylthio) butanedioic acid diethyl 

ester]. The results are shown in Figure 5.

The commercial grade Diazinon used in this study 

caused similar declines in metabolic activities as As2O3

and HgCl2 at similar amounts of active ingredient; increasing amounts of each induced decreased cellular function in 

a classic dose response relationship. There is no statistical difference between the magnitudes of effects of these 

three pesticides. ZnSiF6 is somewhat less toxic and shows 

a slower decline in cell function. Malathion and Lindane 

the industrial grade was not identified; analytical grade 

acetone was used for all later experiments. These results 

provide an indication of the sensitivity of the test method.

Extracting samples with 1% by volume of acetone 

dissolved in SC-CO2 maintained high cellular metabolic 

activity with a response similar to that obtained with unexposed controls (see Figure 4). By using the response of 

the initial 25% active ingredient in Figure 4 as a standard, 

it can be concluded that the addition of 1% by volume of 

acetone removed >99% of the organophosphate and the 

0.1% by volume solutions removed approximately 75% 

of the organophosphate.

Rat lung epithelial cell cultures were exposed to several pesticide solutions at increasingly higher dilutions 

until their LD50 was reached. The pesticides tested, apart 

FIGURE 4. Metabolic activity of rat lung epithelial (RLE-6TN) cells exposed to extracted samples using SC-CO2 and acetone as cosolvent. 

Samples labeled 4D were treated with 4 mg commercial formulation of the organophospate pesticide Diazonon; samples labeled 0D were not 

exposed to any pesticide (0 mg) and served as controls. The decrease in metabolic activity at the 1:50 dilution ratio is most likely a consequence 

of impurity in the acetone used in the Soxhlet extraction but not used as a cosolvent with the SC-CO2.
5 6 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

effectiveness of SC-CO2 along with added cosolvents. It 

was found that SC-CO2 alone removed only part of the 

organophosphate residue; however, introduction of acetone as a cosolvent significantly improved removal. For 

example, 1% volume to volume acetone added to SC-CO2

removed more than 95% of the active ingredient in the 

commercial formulation tested. Overall, this approach is 

shown to have been successful for pesticide removal with 

minimal damage to leather or feathers.

A further goal was to achieve this removal without 

having to determine the specific pesticide present. This 

approach, based on the use of the RLE culture detection 

system, has worked very well in the tests reported here 

and should work well with other artifacts and pesticides. 

The study used a total extraction method; however, other 

methods of residue sampling (i.e., swabs) could also 

be adapted for use with the RLE cell culture detection 

system.

show the lowest toxicity, reducing cellular function only at 

active ingredient concentrations of greater than 0.001%.

CONCLUSIONS

The recognition and subsequent removal of pesticides 

from museum artifacts is an important issue for collections 

managers, conservators, researchers, and educators who 

use museum collections. This issue has recently become 

of significantly greater concern as a result of NAGPRA, 

which allows repatriation of artifacts and their handling 

during traditional cultural uses.

A goal of this work was to develop a protocol and 

to evaluate the utility of SC-CO2 for the removal of pesticides from surrogate museum artifacts while causing 

minimal damage to the artifact. The work presented here 

provides a possible quantitative approach to assessing the 

FIGURE 5. Response of RLE-6TN cells to a variety of pesticides. The decrease in metabolic activity indicates the presence of toxic effects.
num b e r 1 • 5 7

Okeson, C. D., M. R. Riley, and E. Riley-Saxton. 2004. In-­Vitro Alveolar 

Cytotoxicity of Soluble Components of Airborne Particulate Matter: Effects of Serum on Toxicity of Transition Metals. Toxicology 

in Vitro, 18:673–680.

Riley, M. R., D. E. Boesewetter, A. M. Kim, and M. P. Sirvent. 2003. Effects of Metals Cu, Fe, Ni, V and Zn on Rat Lung Epithelial Cells. 

Toxicology, 190:171–185.

Riley, M. R., D. E. Boesewetter, R. A. Turner, A. M. Kim, J. M. Collier, and A. Hamilton. 2005. Comparison of the sensitivity of three 

lung derived cell lines to metals from combustion derived particuate 

matter. Toxicology in Vitro, 19(3):411–419.

Tello, H. E. 2006. Investigation on Super Fluid Extraction (SFE) with 

carbon dioxide on ethnological materials and objects contaminated 

with pesticides. Thesis, Fachhochschule für Technik und Wirtschaft 

[University for Applied Sciences], Berlin.

Tello, H. E., E. Jelen, and A. Unger. 2005. Decontamination of ethnological collections using supercritical carbon dioxide. Collection 

Forum, 19:45–48.

von Ulmann, A. 2003. “Non-polluting removal of pesticides from historic textiles−A project at the Germanisches National Museum 

Nürnberg and the Deutsche Bundesstiftung Umwelt (1999-2001).” 

In Cultural Heritage Research: A Pan-European Challenge, ed. 

R. Kozlowski, R. M. Chapuis, M. Drdácký, R. Drewello, J. Leissner, P. Redol, and J. M. Vallet, pp. 334–336. Cracow: Polish Academy of Sciences.

Xie, B., C. C. Finstad, and A. J. Muscat. 2005. Removal of copper from 

silicon surfaces using hexafluoroacetylacetone (hfacH) dissolved in 

supercritical carbon dioxide. Chemistry of Materials, 17:1753.

Acknowledgments

This work was supported by The University of Arizona’s Vice President for Research Small Grant Program.

REFERENCES

Jelen, E., A. Weber, A. Unger, and M. Eisbein. 2003. Detox Cure for Art 

Treasures. Pesticide Outlook, 14:7–9.

Jones, C. A., A. Zweber, J. P. DeYoung, J. B. McCain, R. Carbonell, and 

J. M. DeSimone. 2004. Applications of “Dry” Processing in the 

Microelectronics Industry Using Carbon Dioxide. Critical Reviews 

in Solid State and Materials Sciences, 29:97–109.

Kang, S. M., A. Unger, and J. J. Morrell. 2004. The Effect of Supercritical Carbon Dioxide Extraction on Color Retention and Pesticide 

Reduction of Wooden Artifacts. Journal of the American Institute 

for Conservation, 43:151–160.

Odegaard, N., and A. Sadongei. 2005. Old Poisons, New Problems. 

Walnut Creek, Calif.: AltaMira Press.

Odegaard, N., 2001. Methods to Mitigate Risks from Use of Contaminated Objects, Including Methods to Decontaminate Affected Objects. Collection Forum, 17:117–121.

Politzer, P., J. S. Murray, P. Lane, and T. Brinck. 1993. Relationships 

between Solute Molecular Properties and Solubility in Supercritical 

Carbon Dioxide. Journal of Physical Chemistry, 97(3):729–732.

Pool, M., N. Odegaard, and M. J. Huber. 2005. “Identifying the Pesticides: Pesticide Names, Classification, and History of Use.” In Old 

Poisons, New Problems. Walnut Creek, Calif.: AltaMira Press.

ABSTRACT.  The removal of pesticide residues from museum objects is an ongoing concern. Historic information on pesticide residues and their detection, toxicity, and removal 

from artifacts have been the focus of numerous pervious studies at the University of Arizona and elsewhere. This paper proposes four potential approaches for the removal of 

pesticide residues including cosolvent additives to supercritical carbon dioxide (SC-CO2), 

other supercritical gases, CO2 snow cleaning, and fluidized bed cleaning. The aim of this 

paper is to point out those research areas most likely to prove fruitful in developing and 

adapting these techniques so as to make them safe for use on ethnographic materials.

Keywords:  supercritical gases, cosolvents to supercritical carbon dioxide, carbon dioxide snow cleaning, fluidized bed cleaning, pesticide removal, remediation.

INTRODUCTION

Many objects in museums have been preserved with the use of pesticides 

based on a wide variety of chemical products to prevent their destruction by insects. A need to remove these poisons is based on the concern that their presence 

represents a threat to the health of museum workers, researchers, and visitors. 

Another important concern is the health hazard posed to Native Americans if 

objects are repatriated under the Native American Graves Protection and Repatriation Act or various state laws and are returned for cultural use. The applied 

pesticides may bond to the material, be surface deposited, or in some cases, 

both, depending on the chemical(s) and the application methods used. In all 

cases, removal is desirable, but the method to be used may differ, depending on 

the pesticide, the material, and the way the pesticide is attached to it.

General approaches to pesticide remediation based on methods such as 

washing, physical removal, chemical removal, and biological removal, in addition to object replacement and object containment has been discussed previously (Odegaard, 2001). Although it is clear that there are several possible 

methods for removing pesticide residues from objects, there are also numerous 

problems to overcome. This paper will be limited to discussing four potential 

approaches for the removal of pesticide residues from museum objects. These 

Paper presented at the Pesticide Mitigation in 

Museum Collections Workshop held at the Smithsonian’s Museum Conservation Institute in April 

2007 exploring possible methods and techniques 

that may become useful for the museum conservation field to reduce, mitigate, clean, or remediate 

undesirable pesticides on objects.

Werner S. Zimmt, Nancy Odegaard, and 

David R. Smith, Arizona State Museum, 1013 

East University Boulevard, Building 26, University 

of Arizona, Tucson, Arizona 85721, USA. Corresponding author: W. Zimmt (wsz@ag.arizona

.edu). Manuscript received 12 June 2008; accepted 26 June 2009.

The Potential for Adapting Some Cleaning 

Methodologies to Pesticide Removal 

from Museum Objects

Werner S. Zimmt, Nancy Odegaard, 

and David R. Smith
6 0 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

composition or may at least be effective in lowering their 

concentration. Given that CO2 is a nonpolar solvent and 

many pesticides are somewhat polar, additives such as acetone or ethanol would greatly enhance the effectiveness 

of the system.

One could list a number of chemicals that might make 

effective additives. Generally, they should be low boiling, 

nonodorous, and nontoxic. Such a composition, in conjunction with the method of determining the presence of 

most toxins without having to identify the specific one involved, would allow museums to detoxify a large number 

of objects at reasonable cost. A well-designed program 

that includes as many different pesticides as can be collected and tested against mixtures of SC-CO2 and different 

additives would go a long way toward this goal.

Although the use of this technique for the removal 

of most organic pesticides should be relatively simple, it 

may be more difficult to find substances that will readily 

remove inorganic poisons, such as lead, mercury, or arsenic. Studies have shown that even unmodified SC-CO2 can 

reduce the amount of mercury found on an object (Tello 

et al., 2005). However, the possibility exists that a welldesigned adjuvant that will make the metal/chelate combination soluble in SC-CO2 would be very useful. Work 

undertaken at the University of Arizona in the Department 

of Chemical and Environmental Engineering has shown 

that trace amounts of unwanted metallic copper can be removed from computer chips by SC-CO2 containing small 

amounts of the proper chelating agent (Xie et al., 2005).

Because metal-based pesticides can be more readily identified, specific compounds for specific metals would be useful 

in these cases. Because objects treated by museums before 

the 1920s were often treated with mercury or arsenic compounds, such a process would be extremely practical.

SUPERCRITICAL FLUIDS OTHER THAN 

CARBON DIOXIDE

Supercritical CO2 is the most convenient and the least 

expensive gas that becomes supercritical in a convenient 

range of pressures and temperatures. Other gases, in addition to carbon dioxide, could be made supercritical in a 

reasonable temperature and pressure range. For some purposes, the use of other gases may provide solubility advantages over SC-CO2 and even if the alternative gas is more 

expensive, it may provide a cost-effective solution. Table 

1 lists some other gases and their critical points collected 

from various different sources.

are (1) cosolvent additives to supercritical carbon dioxide (SC-CO2); (2) other supercritical gases; (3) CO2 snow 

cleaning; and (4) fluidized bed cleaning.

The first of these has been successfully tested by our 

laboratory, as described in another paper (Zimmt et al., 

2010 [this volume]) and has also been reported by others. The other three suggested methods still require further 

work. They are merely presented as potential methods that 

should be investigated further, considering that no discussion of these approaches focus on the decontamination of 

ethnographic museum collections.

SC-CO2 AND ADDITIVE COSOLVENTS 

OTHER THAN ACETONE

Supercritical (or hypercritical) carbon dioxide (SCCO2) has been shown to effectively remove organic pesticide residues from museum objects without causing 

additional damage (Jelen et al., 2003; von Ulmann, 2003; 

Kang et al., 2004; Tello et al., 2005; Tello, 2006). These 

studies indicated that removal of nonpolar pesticides can 

be accomplished with unmodified SC-CO2. Tello et al. 

(2005) also showed that mercury, but not arsenic, can be 

removed by this technique.

However, other research has shown that when the 

pesticide is an even mildly polar compound, the addition 

of small quantities (1%) of a polar cosolvent is necessary 

(Zimmt et al., 2010). Collaborative work at the University 

of Arizona among the Conservation Laboratory of the Arizona State Museum, the Department of Agricultural and 

Biosystems Engineering, and the Department of Chemical 

and Environmental Engineering has shown the ability of 

supercritical CO2, to remove Diazinon [O,O-diethyl-­O-(2-

isopropyl-4-methyl-6-pyrimidinyl) phosphorothioate] from 

museum-like objects. It has also shown that by the addition 

of very small quantities of acetone, at the 1% level, the 

removal effectiveness can be improved significantly. Other 

SC-CO2 studies have found the addition of 5% methanol to 

be highly beneficial (Tavlarides et al., 2001).

More than 90 different pesticides have been used on 

museum objects; however, documentation on what pesticide may have been applied to which object is largely 

lacking (Pool et al., 2005). On the basis of the literature 

of what pesticides have been used, the probability is high 

that many of them could be removed using a properly 

modified SC-CO2 (Page et al., 1992). Other adjuvants 

may be equally or more effective. They might also allow 

the removal of a broad range of pesticides with a single 
num b e r 1 • 6 1

An initial literature review has found very little information on the use of other gases. Only one patent1 discusses the use of gases other than SC-CO2 in extracting 

specific ingredients from animal tissue (Kamarei, 1988), 

but contains no specific data. Because no reference on the 

use of other supercritically cooled gases for the removal 

of pesticides from museum collections has been found, it 

appears evident that further research is this area may be 

fruitful.

CO2 SNOW CLEANING

Solid particles of dry ice pellets or “snow” have been 

shown to remove dust, soot, and small particles from even 

the most delicate surfaces without causing scratches or 

other damage (Fong, 1974; Wolbers, 2000; Silverman, 

2006.). In cases where the pesticide is not chemically 

bound to the surface of an object, this approach may constitute a safe and easy way to remove it.

When pressurized liquid CO2 is allowed to expand 

adiabatically into a gas, the temperature drops to the point 

that some of the gas solidifies into small particles, forming 

CO2 snow. Advantage has been taken of this effect to develop a system to remove particles and dust from a variety 

of surfaces (Hoenig, 2001; Young, 2003). The system consists of a source of liquid CO2 (usually in a gas cylinder) 

and a device that allows the required rapid expansion. The 

particles, because they sublime rapidly and therefore are 

surrounded by an envelope of gas, never come into direct 

contact with the surface of the object being cleaned. Because this system is dry, nonconductive, nonabrasive, nontoxic, and leaves no residue, it has found wide approval in 

fields like astronomy, where it can keep the delicate mirrors and lenses clean without causing scratches or other 

damage.

This approach would allow the removal of pesticide 

particles adhering to an object, even if the object does not 

have a smooth surface, such as fur or feathers, because 

the force of the gas stream moving the dry ice particles 

would dislodge the pesticide. Because the dry ice particles 

are enveloped in a blanket of gas, they would not damage 

the object being cleaned.

Further work needs to be carried out in a closed system so that the pesticide particles can be filtered and collected for proper disposal. The major difference between 

this system and the solvent cleaning procedures is that the 

dry ice will only remove surface contamination. However, 

in many cases that would be all that is required.

It is evident that some gases listed in Table 1 would 

not be suitable either because the temperature required to 

become supercritical is too high or because they are toxic. 

However, nitrous oxide (N2O), trifluoromethane (CHF3), 

and some of the other fluorinated molecules are worth 

considering. Their chemical properties are substantially 

different from CO2, and they may be able to solubilize a 

range of substances unaffected by CO2.

Trifluoromethane and fluoromethane (CH3F) have 

some properties, such as weak acidity, that may allow 

them to remove metals and basic species. The chemical 

properties of supercritical fluids can be changed by relatively small changes in pressure (Egorov and Rabani, 

2002). One of the solvents tested was trifluoromethane. 

Drawbacks for the use of some of these fluorinated gases 

include cost and environmental considerations.

Nitrous oxide (N2O) might be considered isoelectronic 

with CO2 since both have 16 valence electrons. However, 

the arrangement of the electrons is different and so are 

the chemical properties of the gases. For a start, N2O is 

far more polar and so would dissolve a different range of 

substances. It also has relatively low toxicity. Studies have 

used both SC-CO2 and SC-N2O to extract dioxins from 

sediments (Onuska and Terry, 2005). Furthermore, there 

are a substantial number of references on the use of SCN2O in chromatography.

TABLE 1. Some gases that form supercritical liquids along with 

their values for critical temperature (TC), critical pressure (PC), 

and density (δ).

    δ (g/mL)

Gas Name TC (°C) PC (atm) at 40 MPa

CO2 Carbon dioxide 31.3 72.9 0.96

N2O Nitrous oxide 36.5 72.5 0.94

NH3 Ammonia 132.5 112.5 0.40

C2H6 Ethane 32.5 48.2 —

n-C4H10 Butane 152.0 37.5 0.50

CCl2F2 Dichloro difluoro methane 111.8 40.7 1.12

CHF3 Trifluoro methane 25.9 46.9 —

BrCF3 Bromo trifluoro methane 66.8 45.3 —

CH3F Fluoro methane or 44.55 59.9 —

methyl fluoride

CF4 Tetrafluoro methane 33.3 38.9 —

C2F6 Hexafluoro ethane, 19.7 29.2 —

perfluoroethane, or

carbon hexafluoride

CH3CHF2 1,1 difluoro ethane or 30.1 43.8 —

ethylidene fluoride

CClF3 Chloro trifluoro methane 28.8 38.2 —
6 2 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

a cleaning process as envisioned here. The air velocity is just 

high enough to gently suspend the powder particles. There 

are many references to this technology, but those dealing 

with powder coatings are probably the most relevant.

The possible Process I

• A powder of controlled particle size is suspended in a 

stream of air.

• The powder exhibits liquid-like properties.

• Penetration into the substrate occurs whenever the 

particle is smaller than the opening into which the air 

is flowing.

The possible Process II

• A powder is selected that promotes adhesion between 

itself and unwanted particles on the object’s surface.

• The article to be cleaned is submerged in the “liquefied” powder for a given amount of time, withdrawn, 

and shaken to remove as much loose powder as 

possible.

• The article is vacuumed to remove the remaining 

loose powder.

• The powder can be reused several times and is then 

disposed off according to extant regulations.

Fluidized beds are used in large numbers in several industries, and their engineering principles have been studied 

thoroughly. The internet contains thousands of references 

to fluidized bed technology. Many include illustrations, tables, and information. They present an interesting concept 

and deserve further study. Some are listed here.

Free Patents Online

Vortex effect electrostatic fluidized bed coating method and apparatus (U.S. 

Patent 4606928), http://www.freepatentsonline.com/4606928.html

Understanding Fluidized Bed Powder Coating, http://www.pfonline.com/

articles/1004qf1.html

ArsenXnp Arsenic Removal, http://www.purolite.com

The Fluidized Bed Reactor Page, http://faculty.washington.edu/finlayso/Fluidized_Bed/

CONCLUSIONS

There are numerous possible approaches to the removal of pesticide residue contaminants that have not 

been tested or investigated for use on cultural objects. This 

FLUIDIZED BED CLEANING

Another potential solution for the removal of solid 

pesticides applied as powders is the use a fluidized bed 

process. The fluidized bed process is a well-established 

technique in the chemical and oil industries for catalyzed 

reactions in large volume, and it has also been useful in 

coating applications and with odd-shaped objects (Howard, 1989). A fluidized bed is a vessel that contains finely 

divided powder, usually in the micrometer range size, that 

is levitated by a stream of air introduced through a fine 

screen at the bottom, so that it suspends the powder and 

allows it to behave like a liquid. Any object suspended in 

the vessel is surrounded by the powder as though it was 

suspended in a liquid. If a gas or liquid is moved through 

the suspended powder that acts as a catalyst, it will be exposed to a large amount of the surface because each particle is fully surrounded by the reactants, and consequently, 

the reaction rate is greatly increased. Large refineries use 

fluidized beds to move huge masses of catalyst powders 

that allow the refining and modification of petroleum fractions into gasoline, kerosene, aviation fuel, etc.

This method could be combined with standard techniques such as vacuuming because it can effectively enter 

into crevices of the object and adsorb the pesticide. Solid 

pesticides that were applied as powders can potentially be 

removed using a fluidized bed process.

Solid, dry materials have been used for cleaning various substrates for many years. In the 1930s a dry but 

gummy material was used to remove dust and grime from 

wall paper by rubbing over the paper and repeatedly folding the cleaner over to provide a fresh cleaning surface. 

Powders containing cleaning agents have been used to remove dirt as the stains are absorbed into them. The powders can be sprinkled or sprayed on rugs and upholstery, 

rubbed in, and then removed, usually by vacuuming. All 

these uses involve surface cleaning.

Over the years, some museum objects were dusted with 

powders to protect them from insects, mold, rodents, and 

other deteriorating agents. The pesticide on most of these 

objects is confined to their surfaces. The problem is that 

these are generally not smooth surfaces but have areas that 

are not readily cleaned, such as seams, feathers, folds, etc. 

One possibility might be to combine the cleaning ability of 

appropriate powders with the fluidized bed technique.

Fluidized beds containing powder coatings are routinely used to paint small and irregularly shaped objects 

because they are highly efficient and avoid losses due to 

overspray encountered in air spraying of objects. The 

equipment used for coating is the most likely candidate for 
num b e r 1 • 6 3

Page, S. H., S. R. Sumpter, and M. L. Lee. 1992. Fluid Phase Equilibria in Supercritical Fluid Chromatography with CO2-­Based Mixed 

Mobile Phases: A Review. Journal for Microcolumn Separations, 

4:91–122.

Pool, M., N. Odegaard, and M. J. Huber. 2005. “Identifying the Pesticides: Pesticide Names, Classification, and History of Use.” In Old 

Poisons, New Problems, ed. N. Odegaard and A. Sadongei, pp. 

5–31. Walnut Creek, Calif.: AltaMira Press.

Silverman, R., 2006. Fire and Ice: Soot Removal Technique Using Dry Ice 

Blasting. International Preservation News, 39:20–24.

Tavlarides, L. L., W. Zhou, and C. Anitescu. 2001. “Supercritical Fluid 

Technology for Remediation of PCB/PAH-Contaminated Soils/

Sediments.” In Proceedings of the 2000 Conference on Hazardous Waste Research, ed. L. E. Erickson and M. M. Rankin, pp. 

239–255. Manhattan: Kansas State University.

Tello, H. E. 2006. Investigation on Super Fluid Extraction (SFE) with 

Carbon Dioxide on Ethnological Materials and Objects Contaminated with Pesticides. Thesis, Fachhochschule für Technik und 

Wirtschaft [University for Applied Sciences], Berlin.

Tello, H. E., E. Jelen, and A. Unger. 2005. Decontamination of Ethnological Collections Using Supercritical Carbon Dioxide. Collection 

Forum, 19:45–48.

von Ulmann, A. 2003. “Non-polluting Removal of Pesticides from Historic textiles−A Project at the Germanisches National Museum 

Nürnberg and the Deutsche Bundesstiftung Umwelt (1999–2001).” 

In Cultural Heritage Research: A Pan-European Challenge, ed. 

R. Kozlowski, R. M. Chapuis, M. Drdácký, R. Drewello, J. Leissner, P. Redol, and J. M. Vallet, pp. 334–336. Cracow: Polish Academy of Sciences.

Wolbers, R. 2000. “Os produtos de substituição.” [Substitution Products.] In II Encontro Nacional, pp 43–48. Lisbon: Instituto de Desenvolvimento e Inspecção de Condicões de Trabalho.

Xie, B., S. R. Finstad, and A. J. Muscat. 2005. Removal of Copper from 

Silicon Surfaces using Hexafluoroacetylacetone (hfacH) Dissolved 

in Supercritical Carbon Dioxide. Chemistry of Materials, 17:1753–

1764.

Young, F. C. 2003. “Cleaning with Solid Carbon Dioxide Pellet Blasting.” In Surface Contamination and Cleaning, ed. K. L. Mittal, Volume 1, pp. 151–158. New York: VSP.

Zimmt, W. S., N. Odegaard, T. K. Moreno, R. A. Turner, M. R. Riley, 

B. Xie, and A. J. Muscat. 2010. “Pesticide Extraction Studies Using Supercritical Carbon Dioxide.” In Pesticide Mitigation in Museum Collections: Science in Conservation, ed. A. E. Charola and 

R. J. Koestler, pp. 51–57. Smithsonian Contributions to Museum 

Conservation, No. 1. Washington, D.C.: Smithsonian Institution 

Scholarly Press.

brief discussion points out several directions that appear 

to be promising and that could be pursued in addition to 

the current efforts underway. It should be understood that 

the objective of this paper is to broaden the range of possible approaches for the removal of pesticides from museum 

collections not to report research already done. This was 

in line with the goal of the Mitigation Workshop, where it 

was presented orally.

NOTE

1. Ahmad R. Kamarei, U.S. Patent No. 4749522.

REFERENCES

Egorov, S. A., and E. Rabani. 2002. Chemical Equilibrium in Supercritical Fluids: Solvent Effects on Dimerization Equilibrium Constants. 

Journal of Chemistry and Physics, 116(19):8447–8454.

Fong, C. 1974. Taking the Sand Out of Blasting. American Machinist, 

118:67.

Hoenig, S. A. 2001. Cleaning Up with Dry Ice. Photonics Spectra, 

36:115–116.

Howard, J. R. 1989. Fluidized Bed Technology: Principles and Applications. New York: Adam Higler.

Jelen, E., A. Weber, A. Unger, and M. Eisbein. 2003. Detox Cure for Art 

Treasures. Pesticide Outlook, 14:7–9.

Kamarei, A. R. 1980. Supercritical Fluid Extraction of Animal Derived 

Materials. U.S. Patent 4,749,522; filed 31 October 1985, issued 7 

June 1988.

Kang, S. M., A. Unger, and J. J. Morrell. 2004. The Effect of Supercritical Carbon Dioxide Extraction on Color Retention and Pesticide 

Reduction of Wooden Artifacts. Journal of the American Institute 

for Conservation, 43:151–160.

Odegaard, N. 2001. Methods to Mitigate Risks from Use of Contaminated Objects, Including Methods to Decontaminate Affected Objects. Collection Forum, 17:117–121.

Onuska, F. E., and K. A. Terry. 2005. Supercritical Fluid Extraction of 2,

3,7,8-Tetrachlorodibenzo-p-Dioxin from Sediment Samples. Journal of High Resolution Chromatography, 12:357–361.

ABSTRACT.  The Smithsonian Institution’s museums and research units have been working to address the challenges posed by contaminated museum collections and, to that 

end, organized the Pesticide Mitigation in Museum Collections Workshop to learn more 

about potential approaches for remediation of contaminants. The papers assembled here 

result from the workshop and represent experimental attempts to use a wide assortment 

of mitigation and remediation technologies on simulated and real cultural objects. These 

and other theoretical approaches hold great promise for decontamination of collections 

for the safety of all who work with them.

Keywords:  repatriation, mitigation, remediation, cleaning, removal, museums 

collections.

INTRODUCTION

Potentially hazardous collections in museums have existed for as long as 

museums have been collecting. Reasons include the inherent composition of the 

objects as well as pest-control treatments to which they have been subjected. 

However, widespread recognition of the health and safety risks posed by handling these types of objects and specimens, and the need for adequate exposure 

controls, has been growing more recently. Over the past two decades, awareness 

of the problem has spread in conjunction with broadening access and use of 

collections and increased understanding of the potential risks to human health. 

Naturally, concomitant with the increased awareness of the existence of the potential hazards is the pressure to answer the question “What can be done about 

it”? There are many responsible safe work practices, including the use of personal protective equipment that can effectively minimize personal exposure to 

the health hazards posed by these agents. However, in the hierarchy of controls, 

permanent elimination or significant reduction of the hazard agent itself is the 

ultimate goal. The Smithsonian’s Mitigation of Pesticides on Museum Collections Workshop and the resulting papers assembled here represent the current 

ability to address this important question and the hope for future advances toward tackling these problems.

Paper presented at the Pesticide Mitigation in 

Museum Collections Workshop held at the Smithsonian’s Museum Conservation Institute in April 

2007 exploring possible methods and techniques 

that may become useful for the museum conservation field to reduce, mitigate, clean, or remediate 

undesirable pesticides on objects.

R. Eric Hollinger, Supervisory Archaeologist, 

Anthropology Department, Repatriation Office, 

National Museum of Natural History, Smithsonian Institution, P.O. Box 37012, MRC 138, 

Washington, DC 20013-7012, USA. Greta Hansen, Head of Conservation, Anthropology Conservation Laboratory, National Museum of Natural History, Museum Support Center, Smithsonian 

Institution, 4210 Silver Hill Road, Suitland, Maryland 20746, USA. Corresponding author: E. Hollinger (hollingere@si.edu). Manuscript received 

12 June 2008; accepted 26 June 2009.

Discussion: Mitigation of Contaminated 

Collections

R. Eric Hollinger and Greta Hansen
6 6 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

required they be made accessible to Native Americans for 

religious purposes.

For the Smithsonian, repatriations of remains and objects began in the early 1980s before being required by law 

by the repatriation provisions in the 1989 National Museum of the American Indian Act (20 U.S. Code [U.S.C.], 

sec. 80q) and the 1996 amendments to the act. These 

repatriation provisions were extended to the rest of the 

United States by the Native American Graves Protection 

and Repatriation Act (NAGPRA) of 1990 (25 U.S.C., sec. 

3001–3013). These statutes require museums to return 

remains, funerary objects, sacred objects, and objects of 

cultural patrimony when requested by the culturally affiliated tribe, Native Hawaiian organization, or Alaska 

Native Village. Although neither of these laws make mention of pesticides or other treatments, the regulations for 

carrying out the NAGPRA, which were promulgated in 

1995, require that museums inform recipients of repatriated items of any presently known treatment of the objects 

“with pesticides, preservatives, or other substances that 

represent a potential hazard to the objects or to persons 

handling the objects” (43 C.F.R., 10.10 (4)e).

Present Position of the

Smithsonian Institution

Although the Smithsonian museums are not subject to 

these regulations, the NMNH and the National Museum 

of the American Indian (NMAI) have adopted policies of 

notification of treatments and have gone beyond any legal 

requirements by proactively testing objects for heavy metals and other substances.

Because some repatriated objects, particularly sacred 

objects, go back into use within their communities, it is 

critical that repatriation recipients be informed of any 

known or potential hazards that might come with the 

objects. Consequently, hundreds of museums across the 

country have notified indigenous communities through 

consultations or resultant repatriations that objects to 

which they are affiliated may have been contaminated. 

Some tribes have even taken to carrying out their own 

programs of testing for contaminants, while others have 

declared a moratorium on repatriations until they understand the issues more fully.

In the Repatriation Office of the NMNH we have seen 

the reactions of tribal representatives learning for the first 

time of the nature and possible extent of contamination 

of collections. Inevitably, after learning of potential contaminants inherent in the construction materials and the 

PAST SMITHSONIAN INSTITUTION 

EXPERIENCE

It is appropriate that the Smithsonian Institution, the 

world’s largest museum complex, take a lead in the effort 

to address the problem of contaminated collections. The 

Smithsonian Institution, including 19 museums and galleries and the National Zoological Park, as well as research 

facilities, was founded in 1846 and is the oldest research 

and museum institution in the United States. It is today the 

custodian of more than 137 million objects.

Beginning with its founding collection, the Wilkes U.S. 

Exploring Expedition of 1843, the collections were treated 

with a wide range of substances from tobacco to arsenic 

and mercury. Research into museum records by conservators at the Anthropology Department of the National 

Museum of Natural History (NMNH), which houses 

the largest—with 125 million objects—and oldest of the 

Smithsonian’s collections, showed that dozens of different 

substances have been used over the years to treat natural 

history collections (Goldberg, 1996; Hawks and Williams, 

1996). It should be noted that early collections staff were 

not fully aware of the potential risks these poisons posed. 

However, Otis T. Mason, a Curator of Ethnology at the 

U.S. National Museum, described the procedures used for 

ethnological materials that were “sent to the poisoning 

department, where it is subjected to a close scrutiny. The 

curator has devoted much time to this subject, for it is 

encumbered with many difficulties, each kind of material 

demanding a different treatment” and he noted that one 

of the problems needing to be solved was “to reduce the 

danger to the curator and others to the lowest amount” 

(Mason, 1886:87–88). Even so, it seems that the need to 

protect collections from the attacks of insects and other 

pests superseded any concerns of risk to those who might 

come into contact with them in the future.

REPATRIATION SPURS INCREASED INTEREST

The publication of the pesticide findings from museum records fueled wider interest in identifying potential 

hazards in collections and simultaneous with this an increasing concern for the problem on the part of the general 

public and Native American tribes in particular. This has 

been due in large part to the increased access to museum 

collections and repatriation of human remains and cultural 

objects from museums. Even before repatriation laws were 

passed, regulations for the curation of federal collections 

(36 Code of Federal Regulations [C.F.R.], Part 79, 1990) 
num b e r 1 • 6 7

sought to explore the potentials for decontamination and 

collaborated with MCI to host a workshop for researchers 

who have experimented with mitigation or remediation. 

The goal was to bring together scientists who developed 

or applied methods and technologies for removing or otherwise reducing contaminants on museum collections and 

have them to present their research primarily to Smithsonian staff. With this information, the Working Group will 

identity and prioritize various decontamination methods 

and technologies for future testing. Although the primary 

target audience was Smithsonian staff, notices were sent to 

other museums, tribes, and federal agencies with interests 

in the topic and the final audience represented a cross section of these stakeholders. With the exception of the paper 

by Madden et al. (2010) and this paper, each of the papers 

in this volume is the written version of the presentations 

shared at the workshop.

THE WORKSHOP: 

PAPERS AND DISCUSSIONS

All of the invited participants embraced the opportunity to present their research and the potentials of the 

mitigation approaches in which they specialized and to 

share their knowledge with others working to tackle similar problems. The presenters are an exceptional group of 

people who have dedicated considerable time, energy, and 

careful thought to solving the problems of chemical hazards in collections and making objects safer for handling.

The paper by Madden et al. (2010) provides an introduction to the volume and the issues by outlining some 

of the broader contexts in which pesticides or other contaminants should be understood in conjunction with efforts to mitigate them. The fundamental challenges of the 

contaminated collections problem include the detection, 

characterization, and quantification of the potential hazard; the assessment of the potential risks posed by that 

hazard; and the mitigation or remediation of the hazard.

Madden et al. (2010) rightly point out that in order to 

attempt to remove contaminants, it is critical to assemble 

information about what is actually present on the object 

and ideally to quantify those substances so that one can 

gauge the effectiveness of mitigation efforts. Many institutions, including the Smithsonian, have turned to portable 

XRF analyzers for their speed and nondestructive ability 

to detect the heavy metals lead, mercury, arsenic, and bromine. The efforts of Smithsonian researchers, as Madden 

et al. describe, have focused on refining the methodologies 

for XRF testing. These efforts have made great progress, 

treatment histories of the objects, as well as the efforts of 

the museums to test for contaminants, the representatives 

always ask what can be done to clean the objects or otherwise make them safer for handling. Only a few years ago 

we would have answered that there was no way to remove 

contaminants from cultural objects. Today, we can confidently reply that, as seen by the research presented in the 

papers gathered here, there are techniques under development that hold promise for cleaning objects of pesticides 

or other residues.

At the Smithsonian Institution, occupational hazard 

determinations and hazard communication outreach is 

handled by several venues. Line management supervision in each unit is responsible, under prevailing federal 

regulations, to “provide a safe and healthful workplace” 

for its employees by identifying hazards inherent to the 

unit’s tasks and controlling safety and health risks. The 

Office of Safety, Health and Environmental Management 

(OSHEM) assists units in evaluating those risks (through 

exposure sampling and biological monitoring) against established health standards and recommending appropriate 

controls measures, as well as providing staff training and 

other hazard communication, and environmental monitoring and hazardous waste determinations. The working units have also established the Smithsonian Pesticide 

Working Group to network on merging pesticide-artifact 

contamination issues, collaborate on hazard identification 

instrumental analyses and conservation remediation techniques, and share information on public disclosure information sanctioned by the Smithsonian Institution.

The Smithsonian Pesticides Working Group is based 

on the collaboration between four units of this institution. 

These are: the Anthropology Department of the National 

Museum of Natural History and the National Museum of 

the American Indian, the two major collecting units; the 

Office of Safety Health and Environmental Management 

(OSHEM) and the Museum Conservation Institute (MCI), 

which provides scientific research and analytical assistance 

to collecting units.

Although all of the member units have been actively 

identifying the presence of heavy metal or bromine-based 

pesticides by means of equipment such as portable X-ray 

fluorescence (XRF) analyzers and have utilized OSHEM 

for exposure monitoring, health risk assessment, and 

development of safe work procedures, little research or 

experimentation has been conducted at the Smithsonian 

into the actual removal (decontamination) of the pesticide 

hazard itself from contaminated collections. The Smithsonian Pesticides Working Group, recognizing the need to 

comprehensively address contaminated collections issues, 
6 8 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

This approach employs special, engineered solvents to 

dissolve the targeted contaminants and blotters or adsorbent materials, such as activated carbon fabric, as sinks 

to capture the dissolved contaminant. Experiments were 

conducted using test samples of dyes on fabric to simulate 

a contaminated material and showed that, given sufficient 

time, the dyes were almost completely removed. Crucial 

to the success of this method is the identification of the 

targeted contaminant so that an efficient solvent that is 

harmless to the object material can be used. The method 

may prove particularly valuable for decontamination of 

materials too fragile to withstand cleaning with mechanical agitation.

Reuben’s (2010) paper describes the work of the 

Haudenosaunee Standing Committee on Burial Rules and 

Regulations, the Seneca Nation’s Tribal Historic Preservation Office, and the Seneca-­Iroquois National Museum 

to mitigate contaminated Haudenosaunee medicine masks 

that had been repatriated from museums. The mitigation 

procedures employed a mixed approach that included removal and replacement of materials such as horsehair, the 

spray application of a surface active displacement solution 

consisting of sodium lauryl sulfate, and traditional physical and ritual methods of cleaning. Wipe tests had detected 

arsenic and mercury on the interiors and painted exteriors 

of the masks prior to cleaning and after treatment all of 

the tested surfaces showed reductions of more than 99%. 

The success of this method with real objects that continue 

to be used in ceremonies illustrates the importance of integrated approaches tailored to the needs being addressed.

The research presented by Roane and Snelling (2010), 

using bioremediation, demonstrates the resourcefulness 

being applied to the search for mitigation solutions. They 

harness the natural biological processes of bacteria to convert mercury compounds to a gaseous form that can be 

collected and removed. They have identified bacteria living on mercury-contaminated museum objects, cultured 

them, and then applied them to mercury contaminated 

broth, agar, and paper. In their experiments, one bacterial 

isolate was able to reduce the mercury in the test samples 

by as much as 30% in 10 days, while another was able to 

reduce levels by as much as 60%. Although a great deal 

of research still needs to be conducted before it is practical for treating objects, the potential of this approach is of 

particular interest to many Native Americans because it 

simply directs and encourages a natural process already at 

work on mercury contaminated objects.

Tello and Unger (2010) present results of their research and experimentation using liquid and supercritical 

carbon dioxide to clean museum objects. This technology 

although there is no one Smithsonian standard protocol for 

XRF testing. Staff of NMAI and NMNH who conducted 

XRF testing of cultural objects have shared methods and 

information in an effort to standardize their protocols 

where feasible, but differences between the protocols employed at these two museums remain because of their different collection treatment histories and approaches.

At the NMNH Anthropology Department, XRF testing protocols are continually evolving with experience, 

improving technology, and consultation with tribal representatives, risk assessment experts within the OSHEM, 

XRF experts, and other museums working to develop 

testing protocols. Testing is carried out on all objects requested for repatriation or loaned to other institutions by 

systematic sampling of all surfaces, materials, and areas 

of handling. With an emphasis on full disclosure, all sampling data and raw spectra are provided to object recipients along with interpretations and recommendations for 

handling. All museums are likely to develop XRF testing 

procedures that are unique to their collections and goals 

although standardization of approaches, where practical, 

remains a worthy goal.

As Madden et al. (2010) and Odegaard (2001) note, 

most of the risk mitigation approaches explored in this 

volume are more accurately classified as remediation because they seek to reduce the potential hazard by removal 

of contaminants. The first three papers present research 

into chemical solution remediation techniques. The next 

paper by Roane and Snelling (2010) describes a novel 

method of bioremediation of pesticides on cultural objects. The final set of three papers addresses the use of supercritical gases such as carbon dioxide to clean objects. 

The last paper by Zimmt et al. (2010b) presents additional 

methods that may hold great potential for remediation of 

pesticides from cultural objects.

Cross’ (2010) paper describes her research on the use 

of alpha lipoic acid in a solution to wash arsenic and mercury from test samples of contaminated wool, feathers, 

cotton, and filter paper. Her experiments showed a 93%–

99.8% reduction in the metals from the feathers, cotton, 

and paper after two cleanings and a 99.7% reduction in 

arsenic from wool. Because the wool contained sulfur, the 

lipoic acid was only able to remove 36.7% of the mercury 

from the wool sample. Cross’ experiments suggest great 

potential for remediation of heavy metals from cultural 

objects, and because alpha lipoic acid is a naturally occurring chemical, it is considered more appropriate for use on 

culturally sensitive objects by Native Americans.

Kaiser’s (2010) paper presents research on decontamination of materials using a diffusion-cleaning method. 
num b e r 1 • 6 9

is the application of carbon dioxide “snow” blown over 

the object to remove pesticides or other substances from 

the surface without abrasive action. Finally, the authors 

explore the potential of fluidized beds, a technology commonly used in industry, as cleaning technology. Fluidized 

beds have the potential to be adapted to treat museum objects by immersing them in powders that adhere to surface 

contaminants and then removing the powders by shaking 

and vacuuming. These methods represent the potential for 

innovations and adaptations of technologies to tackle the 

problems of contaminated collections.

CONCLUSIONS

As our awareness of health and environmental hazards presented by pesticides and other contaminants on 

museum collections continues to increase, so, too, will the 

pressures to find ways of reducing or removing those hazards. Museum collections around the world are becoming increasingly more accessible to researchers, indigenous 

communities, and the public at large. As direct physical 

contact with collections increases, the impetus to make 

sure that collections are as safe as possible for handling by 

visitors, recipients of repatriated collections, and museum 

staff who come into contact with collections on a regular 

basis is gaining greater urgency. In the interim, it is incumbent upon museum supervisors to ensure that safe work 

practices with appropriate personal protective equipment, 

cleaning procedures, use of local ventilation, and other 

risk reduction measures are incorporated into all protocols. Visitors to collections need to be made aware of these 

issues and follow any departmental requirements for safe 

handling or research (such as offering protective gloves). 

Although the inherent toxicity hazard of these heavy metals and other pesticides may be significant, the actual health 

risk to the employee or object handler may be low depending on frequency and duration of contact and efficacy of 

work practice controls. Therefore, arranging for personal 

exposure monitoring and health risk assessments overseen 

by qualified industrial hygienists and occupational health 

clinicians is key to establishing perspectives on hazard and 

risk in any given work situation. However, the ultimate 

risk control is the mitigation of the hazard itself.

The papers assembled here represent some of the first 

steps toward developing technologies to decontaminate 

museum collections. These approaches represent the diversity of methods that will be necessary to deal with the broad 

array of materials represented by museum collections. Although it is unlikely that there will ever be a single method 

has been applied for some time in industrial contexts such 

as dry cleaning. In their experiments, five ethnographic objects or pieces of objects were subjected to treatment using 

liquid carbon dioxide and three samples were subjected to 

supercritical carbon dioxide. Pretreatment analysis of the 

objects had already shown the presence of various contaminants. Objects treated with liquid carbon dioxide showed 

marked reduction in dichloro diphenyl trichloroethane 

(DDT), a slight to significant decrease in Lindane, and 

no real change in arsenic or mercury levels. The museum 

samples treated with supercritical carbon dioxide showed 

reduction of DDT, Lindane, and mercury, but little change 

in the amount of pentachlorophenol (PCP) and arsenic. 

The majority of the test samples showed little change in 

the condition of the material other than becoming visually 

cleaner, although fur appeared to have improved by softening. The authors do note that this technique may not be 

appropriate for sensitive materials.

Zimmt et al. (2010a) also present experiments using 

supercritical carbon dioxide to remove pesticides from 

simulated collections materials. In their research, pieces of 

leather and dyed feathers were intentionally contaminated 

with known amounts of the organic pesticide Diazinon. 

The materials were then treated using supercritical carbon 

dioxide, which by itself only removed part of the Diazinon 

residue from the test materials. When small amounts of 

acetone were added to the supercritical carbon dioxide as 

a cosolvent, the process removed more than 95% of the 

Diazinon with no visible damage or loss of color to the 

materials being tested. The amounts of pesticides in this 

experiment were measured using a toxicological screening 

method of exposing the treated materials to rat lung epithelial cell cultures and watching for any decrease in cellular 

metabolic activity. A benefit of this method, versus the use 

of XRF, wipes, or other methods which detect specific targeted substances, is its ability to tell if exposure to the object 

is potentially harmful without knowing the contaminant.

The final paper by Zimmt et al. (2010b) continues the 

discussion of the research carried out by the University of 

Arizona and suggests additional approaches that in theory hold great promise for decontamination of museum 

objects. Building on their observations that cosolvents 

were necessary for supercritical carbon dioxide cleaning, 

they note that other chemicals such as ethanol might also 

make good cosolvents. They also explore the potential 

for a number of gases other than carbon dioxide to be 

applied in supercritical form for the cleaning of museum 

collections. The properties of these gases may facilitate 

the removal of substances that are not removed by supercritical carbon dioxide. Another potential method offered 
7 0 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

sonian Institution. Journal of the American Institute for Conservation, 35(1):23–43.

Hawks, C. A., and S. L. Williams. 1996. Arsenic in Natural History Collections. Leather Conservation News, 2(2):1–4.

Kaiser, R. 2010. “Solvent Cleaning of Fragile Artifacts without Mechanical Agitation.” In Pesticide Mitigation in Museum Collections: Science in Conservation, ed. A. E. Charola and R. J. Koestler, pp. 13–

24. Smithsonian Contributions to Museum Conservation, No. 1. 

Washington, D.C.: Smithsonian Institution Scholarly Press.

Madden, O., J. Johnson, and J. R. Anderson. 2010. “Pesticide Remediation in Context: Toward Standardization of Detection and Risk 

Assessment.” In Pesticide Mitigation in Museum Collections: Science in Conservation, ed. A. E. Charola and R. J. Koestler, pp. 1–6. 

Smithsonian Contributions to Museum Conservation, No. 1. Washington, D.C.: Smithsonian Institution Scholarly Press.

Mason, O. T. 1886. Report on the Work in the Department of Ethnology in the U.S. National Museum for Year Ending June 30, 1886. 

Smithsonian Institution Annual Report for the year 1886, Part II, 

Report of the United States National Museum, pp. 87–92. Washington, D.C.: U.S. Government Printing Office.

Odegaard, N. 2001. Methods to Mitigate Risks from Use of Contaminated Objects, Including Methods to Decontaminate Affected Objects. Collection Forum, 17(1–2):117–121.

Reuben, P. A. 2010. “Mitigation of Surface Contaminants on Haudenosaunee Medicine Masks.” In Pesticide Mitigation in Museum 

Collections: Science in Conservation, ed. A. E. Charola and R. J. 

Koestler, pp. 25–28. Smithsonian Contributions to Museum Conservation, No. 1. Washington, D.C.: Smithsonian Institution Scholarly Press.

Roane, T. M., and L. J. Snelling. 2010. “Bacterial Removal of Mercury 

from Museum Materials: A New Remediation Technology?” In 

Pesticide Mitigation in Museum Collections: Science in Conservation, ed. A. E. Charola and R. J. Koestler, pp. 29–34. Smithsonian 

Contributions to Museum Conservation, No. 1. Washington, D.C.: 

Smithsonian Institution Scholarly Press.

Tello, H., and A. Unger. 2010. “Liquid and Supercritical Carbon Dioxide as a Cleaning and Decontamination Agent for Ethnographic 

Materials and Objects.” In Pesticide Mitigation in Museum Collections: Science in Conservation, ed. A. E. Charola and R. J. Koestler, 

pp. 35–50. Smithsonian Contributions to Museum Conservation, 

No. 1. Washington, D.C.: Smithsonian Institution Scholarly Press.

Zimmt, W. S., N. Odegaard, T. K. Moreno, R. A. Turner, M. R. Riley, 

B. Xie, and A. J. Muscat. 2010a. “Pesticide Extraction Studies Using Supercritical Carbon Dioxide.” In Pesticide Mitigation in Museum Collections: Science in Conservation, ed. A. E. Charola and 

R. J. Koestler, pp. 51–57. Smithsonian Contributions to Museum 

Conservation, No. 1. Washington, D.C.: Smithsonian Institution 

Scholarly Press.

Zimmt, W. S., N. Odegaard, and D. R. Smith. 2010b. “The Potential 

for Adapting Some Cleaning Methodologies to Pesticide Removal 

from Museum Objects.” In Pesticide Mitigation in Museum Collections: Science in Conservation, ed. A. E. Charola and R. J. Koestler, 

pp. 59–63. Smithsonian Contributions to Museum Conservation, 

No. 1. Washington, D.C.: Smithsonian Institution Scholarly Press.

for cleaning all types of objects or materials, these approaches show great promise for future applications. While 

some of the research presented here includes experimentation with remediation on actual cultural objects, considerably more research and experimentation is needed before 

most museums will be comfortable applying remeditiation approaches to collections on a large scale. Even then, 

some methods may not be culturally appropriate or may 

not meet requirements for conservation of particular objects requiring us to fall back to mitigating the risk through 

containment, personal protective measures, and handling 

protocols. It is likely that there will always be need for such 

measures, but there is also a clear need for more research 

into developing portable equipment for the analysis of organic pesticides, developing standards for the quantification 

of contamination, as well as developing experimentation 

into remediation of contaminated collections.

Acknowledgments

We thank Kathryn Makos, Industrial Hygienist with 

the Smithsonian Institution’s Office of Safety, Health and 

Environmental Management, for her assistance over the 

years with development of the Anthropology Department’s 

approach to the problems of contaminated collections and 

for her help with this paper. We also thank Robert Koestler and Paula DePriest for hosting the Mitigation of Pesticides on Museum Collections Workshop and for inviting 

us to contribute to this volume. We also thank A. Elena 

Charola for her patience and assistance in overseeing the 

editing process for these papers.

REFERENCES

Cross, P. S., N. Odegaard, and M. Riley. 2010. “Aqueous α-Lipoic Acid 

Solutions for Removal of Arsenic and Mercury from Materials 

Used for Museum Artifacts.” In Pesticide Mitigation in Museum 

Collections: Science in Conservation, ed. A. E. Charola and R. J. 

Koestler, pp. 7–11. Smithsonian Contributions to Museum Conservation, No. 1. Washington, D.C.: Smithsonian Institution Scholarly Press.

Goldberg, L. 1996. A History of Pest Control Measures in the Anthropology Collections, National Museum of Natural History, Smith-
TABLE A.1. Organic compounds most commonly used as pesticides for museum collections.

Common name Chemical name Chemical formula

Camphor d-2-Damphanone or C10H16O

d-2 keto-1,7,7-trimethylcamphane

Carbolic acid Phenol C6H5OH

Carbon disulphide Carbon disulphide CS2

Carbon tetrachloride Carbon tetrachloride CCl4

Carboxide Mixture of ethylene oxide and CH2CH2O (90%)

carbon dioxide (90-10%) + CO2 (10%)

Chlorotenea 1,1,1 Trichloro ethane Cl3C-CH3

Diazinon O,O-diethyl-O-(2-isopropyl-4-methyl- [C(CH3)2CHC4N2H(CH3)O]

6-pyrimidinyl)phosphorothioate PS(OC2H5)2

Dichlorobenzene p-Dichlorobenzene or C6H4Cl2

1,4 Dichlorobenzene

Dichlorvos or DDVP 2,2 Dichlorovinyl dimethyl phosphate (CH3O)2POOCH:CCl2

Dimethyl formamide (DMF) N, N-dimethyl formamide HCON(CH3)2

DDa Mixture of 1,3 dichloropropene ClCH:CHCH2Cl

and 1,2 dichloropropane + ClCH2CHClCH3

DDT Dichloro diphenyl trichloroethane, or more correctly (pClC6H4)2CHCl3

1,1,1-Trichloro-2,2-bis(p-chloro phenyl) ethane

Dowfume G Mixture of carbon tetrachloride, ethylene dichloride, CCl4 + ClCH2CH2Cl

and ethylene dibromide, or more correctly, + BrCH2CH2Br

1,2 dichloroethane and 1,2 dibromoethane

Dowfume 75 Mixture of ethylene dichloride (1,2 dichloroethane) ClCH2CH2Cl (70%)

and carbon tetrachloride (70:30 %) + CCl4 (30%)

Dowfume 85 Contains 85% ethylene dibromide (1,2 dibromoethane) —

Ethylene dibromide or EDBa 1,2 Dibromoethane BrCH2CH2Br

Ethylene dichloridea 1,2 Dichloroethane ClCH2CH2Cl

Ethylene oxidea Epoxyethane CH2CH2O

Larvex Contains organochlorine compounds

Lindane or gammaxene g Hexachloro cyclohexane C6H6Cl6

or benzene hexachloride

(continued)

Appendix: Common Museum Pesticides
7 2 • S m i ths o n i an C o ntr i b ut i o ns t o mus e um c o ns e rvat i o n

TABLE A.1. (Continued)

Common name Chemical name Chemical formula

Malathion 2-(Dimethoxyphosphinothioylthio) C10H19O6PS2

butanedioic acid diethyl ester

Menthol Methyl-hydroxyisopropyl-hexane CH3C6H9(C3H7)OH

Methyl bromidea Methyl bromide CH3Br

Naphthalenea Naphthalene C10H8

Nemagon or DBCPa 1,2 Dibromo-3 chloro propane CH2BrCHBrCH2Cl

Paradichlorobenzene or PDBa 1,4 Dichlorobenzene C6H4Cl2

PCP Pentachlorophenol C6OHCl5

Telone IIa 1,3 Dichloropropene ClCH:CHCH2Cl

Thymol 5-Methyl 2-isopropyl 1-phenol CH3(C3H7)C6H3OH

or isopropyl m-cresol

Vapam or Metama Sodium N-methyldithiocarbamate CH3NH(S:)CSNa

Vapona (See Dichlorvos) —

Vikane a Sulfuryl fluoride SO2F2

a Fumigant.
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