Journal of Environmental Protection, 2011, 2, 1062-1068
doi:10.4236/jep.2011.28122 Published Online October 2011 (
Copyright © 2011 SciRes. JEP
Libby Amphibole Contamination in Tree Bark
Surrounding Historical Vermiculite Processing
Mohamed I. Elashheb1, Terry M. Spear2, Julie F. Hart2, James S. Webber3, Tony J. Ward1,*
1Center for Environmental Health Sciences, The University of Montana, Missoula, USA; 2Department of Safety, Health and Indus-
trial Hygiene, Montana Tech of the University of Montana, Butte, USA; 3New York State Department of Health, Wadsworth Center,
Albany, USA.
Email: *
Received August 13th, 2011; revised September 15th, 2011; accepted October 3rd, 2011.
Over a 70-year period, a mine near Libby, MT supplied nearly 80% of the world’s vermiculite. Raw vermiculite, wh ich
was contaminated with naturally occurring amphibo le in veins throughout the deposit, was shipped to processing sites
throughout the Un ited States for exfoliation. In this pilot stud y, tree ba rk samples were collected near pr ocessing facili-
ties in Spokane, WA, Santa Ana, CA, Newark, CA, and Phoenix, AZ in an effort to determine if areas surround ing these
facilities are today contaminated with Libby amphibole asbestos (AA). From areas surrounding each of the four his-
torical processing sites, Libby AA was detected in a subset of the bark samples. At the Santa Ana, Newark and Phoenix
facilities, actinolite-tremolite and other high Fe Ca-bearing amphibole were also measured from the bark samples. In
addition, chrysotile was frequently measured in samples collected from each of the sites. From the results of this pilot
study, it is evident that tree bark can serve as reservoirs of asbestos, and indicators of past and current co ntamination.
These data also suggest that areas outside of these historical processing facilities may today have some level of existing
contamination resulting from the operation of these facilities.
Keywords: Vermiculite, Asbestos, Amphibole, Libby, Exfoliation, Tree Bark
1. Introduction
Prior to 1990, up to 80% of the world’s vermiculite was
derived from a mine near Libby, Montana [1]. The ver-
miculite ore mined from Zonolite Mountain seven miles
northeast of Libby was contaminated with fibrous and
asbestiform amphibole in veins throughout the deposit
[2], containing a combination of winchite (84%), rich-
terite (11%) and tremolite (6%) [3]. As a result of this
contamination, occupational exposure to Libby amphi-
bole asbestos (AA) has led to a significant increase of
serious respiratory diseases such as lung cancer, pleural
cancer and asbestosis among the former mine workers
[4-6]. In addition, pleural abnormalities have been de-
fined in 17.8% of the 6668 participants who lived or
worked in the Libby area prior to 1991 [7]. In October
2002, Libby was added to the Environmental Protection
Agency’s (EPA) National Priorities List, and in June
2009 the town of Libby was designated a public health
emergency. This is the only time EPA has made such a
Libby AA has been measured outside of Libby as well.
Between the 1920s and 1990s, vermiculite mined from
Libby (estimated in the millions of tons) was shipped by
railroad to 245 facilities within the US for processing via
exfoliation [13]. Exfoliation refers to a commercial pro-
cess where vermiculite is rapidly heated to expand it into
low-density, accordion-like nuggets [13]. At the facili-
ties, the raw vermiculite was typically unloaded manu-
ally by workers using shovels and front loaders, and
stored on site until transferred to an exfoliation furnace
where it was heated to a temperature between 1500 and
2000 °F [14]. The processed vermiculite was then stored
on site until packaged in various forms for commercial
use such as attic insulation. In facilities such as the West-
ern Mineral Products Site in Minneapolis, Minnesota
additional products such as Monokote (a fire proofing
material that combined vermiculite and chrysotile asbes-
tos) were also produced [15].
In 2008, ATSDR released a study in which 28 out of
Libby Amphibole Contamination in Tree Bark Surrounding Historical Vermiculite Processing Facilities1063
245 sites were selected for detailed evaluation for on-site
Libby AA contamination. At many of these facilities,
Libby AA was found in exterior soil and indoor dust in
areas where vermiculite and waste rock were unloaded or
stored. At the present time, many of these former exfo-
liation sites are occupied with commercial and industrial
operations not related to the original exfoliation pro-
cesses. In addition to on-site contamination, we hypothe-
size that airborne emissions of Libby amphibole fibers
from exhaust stacks and fugitive emissions from vermi-
culite storage sites may have been dispersed into the ar-
eas surrounding these locations.
In this manuscript, we report on a study in which tree
bark samples were collected surrounding historical Libby
vermiculite processing facilities located in Spokane
(WA), Newark (CA), Santa Ana (CA), and Phoenix (AZ).
The goal of this research project was to determine if
Libby AA emanated from the industrial sites during the
periods of operation of these facilities, and if trees sur-
rounding these facilities are today contaminated with
Libby AA.
2. Materials and Methods
Tree bark samples were collected in areas surrounding
the former vermiculite processing facility in Spokane,
WA, on March 9, 2009. Between June 8 and June 10,
2010, tree bark samples were collected in areas surround-
ing three other former facilities in Newark, CA, Santa
Ana, CA and Phoenix, AZ. Bark samples were also
collected in Missoula, MT to serve as control samples.
The Spokane site (located approximately 160 kilometers
from Libby) was selected because it is one of the closest
former processing facilities to Libby. The remaining
three sites were selected based on a ranking system, con-
sidering 1) the tonnage of raw vermiculite processed, 2)
the year that exfoliation work was terminated at the site,
3) the population density within one mile of the site and
4) the total duration of site operation. Table 1 presents
the characteristics of each site.
2.1. Tree Bark Sampling
At each location, bark was collected from several tree
species native to the area. A pry-bar or spatula was used
to collect a ~ 200-gram piece (with surface area between
50 - 150 cm2) of bark from approximately four feet
above the base of each tree. These were placed into
labeled plastic bags. The spatula/pry-bar was wiped down
after each sample collection with isopropyl alcohol and
laboratory tissues. In total, 22 samples were collected
from around the Spokane facility. At the Santa Ana,
Newark, and Phoenix facilities, 40, 22 and 25 samples,
respectively, were collected in proximity to the facilities.
Because asbestos fibers can become airborne and easily
dispersed, the majority of samples were collected in
areas predominantly downwind of the facilities.
2.2. Tree Bark Analyses
Following the MD Webber method [8], samples of ap-
proximately 1 gram (normalized to 10 cm2 surface area)
were weighed, dried to stable mass at 60 to 100˚C, ashed
at 450˚C for ~16 hours, and re-weighed to determine
percentage loss of organic material. Residue, typically
5% of original mass, was suspended in filtered deionized
water, thoroughly mixed, and filtered through 0.4-um
polycarbonate filters before being prepared for transmis-
sion electron microscopy (TEM) analysis using carbon
coating and ethylene-diamine dissolution onto TEM
All 22 samples from the Spokane site were analyzed
whereas funding constraints limited us to only five sam-
ples per site from the Santa Ana, Newark, and Phoenix
sites. As the goal of this project was to detect Libby am-
phibole in the areas surrounding the historical facilities,
the five samples from the latter three sites were chosen
Table 1. Description of Vermiculite proce ssing facilities in Spokane, WA, Santa Ana, CA, Newark, CA and Phoenix, AZ.
Factor/Site Spokane, WAA Santa Ana, CAB Newark, CAC Phoenix, AZD
Years of Operation 1951-1973 1971-1993 1966-1993 1964-1992
Tons Processed 10,317
(between 1967 and 1973) 453,000 337,100 254,900
Pop. Within 1 mile 17,214 35,832 10,183 12,915
Surrounding area use Commercial
and residential
Light industrial and commercial,
elementary school (1950-present)
200 yards away
Mixed commercial, industrial
and residential
Industrial, commercial
and residential
Prevailing wind Southwest Southwest Northwest
Variable, west in the
daytime and east
in the evening
Sample collection
direction from facility All directions, primarily
north and northeast
All directions, primarily north and
All directions, primarily
northeast and southeast
All directions,
primarily east
AATSDR, Vermiculite northwest, Spokane, WA [16]; BATSDR, Fact sheet, Santa Ana, CA [17]; CATSDR, Fact sheet, Newark, CA [18]; DATSDR, Fact sheet,
Phoenix, CA [19].
Copyright © 2011 SciRes. JEP
Libby Amphibole Contamination in Tree Bark Surrounding Historical Vermiculite Processing Facilities
from trees close to and downwind of the facility. For
each sample, four different dilutions were prepared from
the ashed bark in an effort to eliminate both over and
under-loading of TEM grids.
Once the grids were prepared, they were sent to ALS
Laboratories (Cincinnati, OH) for TEM analysis. TEM
analysis was performed at a screen magnification of at
least 15,000× on a Philips CM-12 TEM with EDAX
Genesis System providing Energy-dispersive X-ray ana-
lysis (EDXA) capabilities. Identification and measure-
ment of asbestos structures were conducted according to
AHERA protocol [20].
3. Results
Table 2 presents the summary of findings from the
Spokane site, while Table 3 presents the results from
Table 2. Summary of tree bark results from the Spokane site.
Asbestos Concentration (s/cm2)
Total asbestos <5 µm Total asbestos >5 µm Type of tree Distance from Facility (meters)
Sample ID AA Chrysotile AA Chrysotile
SPK_1 ND 939,506 ND ND American Elm 122
SPK_2 2,400,640 ND 800,213 ND Douglas fir 61
Note: AA: Libby Amphibole Asbestos; ND: None detected.
Table 3. Summary of tree bark analysis results of Santa Ana, Newark and Phoenix sites.
Asbestos Concentration (s/cm2)
Total Asbestos < 5 µm Total Asbestos > 5 µm
Sample ID Dilution
Prep AA A-T Chrysotile AA A-T ChrysotileOther Conc.
(s/cm2) Type of tree Distance from
Facility (meters)
A. Santa Ana Site
Eastern cottonwood 366
SA_2 6 469,716 ND ND ND ND ND ND
Blue gum Eucalyptus 457
American Elm 610
SA_4 3
ND American Elm 732
B. Newark Site
NEW_1 4 ND ND 1,266,526 ND ND ND ND
Blue gum Eucalyptus 701
Eastern cottonwood 152
NEW_3 2
429,191 California redwood 61
Australian pine 213
Australian pine 305
C. Phoenix Site
PHX_1 3
ND Snow Gum eucalyptus 274
PHX_2 4 ND ND 681,027 ND ND ND 681,027 Snow Gum eucalyptus 152
PHX_3 3
479,941 Ash-leaf Maple 610
Note: A-T: Actinolite-Tremolite; AA: Libby Amphibole Asbestos; Other fibers: refers to fibers that may be a high Fe Ca-bearing amphibole; ND: None detected.
opyright © 2011 SciRes. JEP
Libby Amphibole Contamination in Tree Bark Surrounding Historical Vermiculite Processing Facilities1065
Santa Ana, Newark, and Phoenix, respectively. Chry-
sotile and Libby AA were detected in samples collected
from trees surrounding the Spokane facility. At the Santa
Ana, Newark and Phoenix facilities, actinolite-tremolite
(A-T) and other asbestos structures were identified in
addition to chrysotile and Libby AA. The term “other
fibers” is used in this paper to refer to fibers that appear
to be a high Fe Ca-bearing amphibole.
3.1. Spokane Site
Libby AA did not predominate in tree bark samples
collected surrounding the Spokane site. Of the 22 bark
samples collected and analyzed, only one sample yielded
Libby AA (2,400,640 s/cm2 < 5 µm in length, and
800,213 s/m2 > 5 µm in length). Another sample revealed
chrysotile structures, with a concentration of 939,506
s/cm2 (<5 µm in length).
3.2. Santa Ana Site
Four of the 40 samples collected were analyzed, on the
basis of their location predominantly downwind and near
the facility. Two samples yielded AA structures with
concentrations ranging from 463,192 to 1,704,683 s/cm2.
Actinolite-tremolite structures (568,228 s/cm2) were de-
tected in a third sample, while another sample contained
Fe Ca-bearing amphibole (concentration of 744,062 s/cm2).
In addition to AA, chrysotile structures were found in
three of the four samples with concentrations ranging
from 333,559 s/cm2 to 744,062 s/cm2 (Table 3).
3.3. Newark Site
One of the five samples revealed Libby AA with a
concentration of 530,103 s/cm2 (Table 3). The majority
of samples yielded chrysotile structures with concen-
trations ranging between 480,088 s/cm2 and 2,120,412
s/cm2. Actinolite-tremolite structures were detected in
two samples with concentrations of 807,883 s/cm2 and
530,103 s/cm2, respectively. Fe Ca-bearing amphibole
fibers were detected in three samples with concentrations
ranging between 429,191 s/cm2 to 671,128 s/cm2.
3.4. Phoenix Site
Only one of the three samples analyzed from the Phoenix
site indicated the presence of Libby AA (479,941 s/cm2),
while another sample revealed actinolite-tremolite fibers
with a concentration of 473,892 s/cm2 (Table 3). Chry-
sotile was detected in all three samples that were ana-
lyzed from the Phoenix site, with concentrations ranging
from 681,027 s/cm2 to 1,371,575 s/cm2. Fe Ca-bearing
amphibole fibers were identified in two samples, with
concentrations from 479,941 to 685,787 s/cm2.
3.5. Control Samples
All 11 control samples used for this study were collected
from Douglas fir (Pseudotsuga menziesii) trees at The
University of Montana campus in Missoula. Control
samples were treated with the same analytical protocol as
the actual samples. For the Spokane bark analytical pro-
gram, two control bark samples were analyzed in an ef-
fort to detect any potential sources of contamination. No
Libby AA were detected in any of the nine control sam-
ples that were analyzed when processing the samples
from the Santa Ana, Newark and Phoenix sites. However,
it should be noted that one chrysotile fiber was measured
in one of the control bark samples. This chrysotile fiber
could have actually been on the control sample (given
the historical ubiquity of chrysotile in the 20th century),
or it could have been contamination that occurred either
during the sample preparation or during lab analysis. At
any rate, we are confident that this single chrysotile fiber
does not indicate a contamination problem with the ana-
lytical program.
4. Discussion
Tree bark has been used since the late 1980s as bio-
monitors for both inorganic and organic pollutants [21].
Specifically, polychlorinated dibenzo-p-dioxins and di-
benzofurans [22], polyaromatic hydrocarbons [23], poly-
chlorinated bipheynls [24-26], organochlorine pesticides
[27-28], radioactive analytes [29-30], trace metals [31-
39], and persistent organic pollutants [40] have all been
In the present study, Libby AA was detected at each of
the four sites in a subset of the trees surrounding the his-
torical processing facilities. Meeker et al. [3] conducted
the first comprehensive study on Libby asbestos to de-
termine the mineralogy and morphology of both fibrous
and non-fibrous amphiboles, supporting the earlier re-
sults of Wylie and Verkouteren [41] and Gunter et al.
[42]. They described the Libby AA as winchite, richterite,
tremolite, and magnesioriebeckite, with the majority of
structures displaying a gradient of morphologies between
prismatic crystals and asbestiform fibers. Libby amphi-
bole has a standard elemental composition of Si > Mg >
Ca > Fe > Na > K, with fibers having a mean length of
4.9 μm, and mean aspect ratio of 17. These characteris-
tics were all used when identifying the Libby AA in bark
samples collected surrounding the four historical pro-
cessing facilities.
The non-Libby AA asbestos structures included acti-
nolite-tremolite (EDXA spectra with just Mg-Ca-Fe-Si
peaks present, and occasionally minimal Al) and amphi-
bole fibers that were high in iron and calcium were iden-
tified in the bark samples. Chrysotile fibers were also
detected in tree bark samples collected around the pro-
cessing facilities at each of four sites. This finding is not
surprising, as chrysotile was widely used in thousands of
Copyright © 2011 SciRes. JEP
Libby Amphibole Contamination in Tree Bark Surrounding Historical Vermiculite Processing Facilities
commercial products from the 1930s through the 1970s,
and is still used in asbestos cement, friction materials,
roof coatings and gaskets [43]. It is possible that chry-
sotile’s wide spread usage in industry could contribute to
its ubiquity in the ambient environment.
Table 4 shows a comparison between asbestos fiber
dimensions measured from the bark samples collected in
Libby, Spokane, Santa Ana, Newark, and Phoenix. From
the tree bark samples collected surrounding the aban-
doned vermiculite mine in Libby, the majority of the AA
measured are less than 5 micrometers in length (mean =
3.4 µm), with a mean diameter of 0.39 µm[8]. Libby
AA fibers measured in the Spokane, Santa Ana, Newark,
and Phoenix samples were comparable to what was
measured in Libby, with mean diameters of 0.37 - 0.50
µm and mean lengths of 2.8 - 5.6 µm. Chrysotile fibers
that were measured at each of the sites had mean diame-
ters of ~0.1 µm and mean lengths of ~1.6 µm.
There were limitations to this investigative pilot study.
We encountered a problem in determining the correct
loading for the grids prior to the TEM analysis of the
Santa Ana, Newark, and Phoenix bark samples. The pro-
tocol we had developed previously for coniferous trees in
northwest Montana [8] did not work as well for trees
from other parts of the country. Samples collected from
the Santa Ana, Newark and Phoenix sites were from se-
veral different regional species of trees [Douglas fir
(Pseudotsuga menziesii), American elm (Ulmus Ameri-
cana), Eastern cottonwood (Populus deltoids), Blue gum
Eucalyptus (Eucalyptus globulus), California redwood
(Sequoia sempervirens), Australian pine (Casuarina equi-
setifolia), Snow Gum eucalyptus (Eucalyptus pauciflora)
and Ash-leaf Maple (Acer negundo)]. Hence a series of
dilutions were used (for each sample) in preparing the
TEM grids before the correct loading was achieved.
Overall, this impacted the number of samples we could
analyze from each of the sites due to funding constraints.
5. Conclusions
An EPA assessment published in 2009 showed that
Libby amphibole was detected in the soil and indoor dust
at the Newark, Santa Ana, and Phoenix historical Libby
vermiculite processing facilities [44]. The results from
tree bark analyses collected near these same areas (also
including the Spokane facility) indicate that trees in the
residential/commercial areas surrounding these facilities
can serve as reservoirs for asbestos fibers. In addition to
amphibole asbestos, chrysotile structures were also de-
tected from the tree bark samples. While amphibole as-
bestos is most likely associated with the historical Libby
vermiculite processing facilities, it is difficult to deter-
mine the source of chrysotile structures.
Ewing [45] discusses concentrations of surface dust
found in a variety of settings and suggests that a concen-
tration of 1,000 s/cm2 may be considered clean, whereas
concentrations >100,000 fibers indicate contamination.
Results from the present study revealed concentrations of
chrysotile up to 2 million s/cm2, concentrations of Libby
AA from ND to 2.8 million s/cm2, actinolite-tremolite
from ND to 800,000 s/cm2, and other fibers ranging from
ND to 700,000 s/cm2. Many of these samples were col-
lected in areas near residential areas, and in some cases
near schools. For comparison, the levels measured in
Libby were a great deal higher than what was measured
in the present study. Specifically, bark samples collected
in proximity to the abandoned vermiculite mine in Libby
measured over 100 million s/cm2 bark surface.
Adgate et al. (2011) estimated potential cumulative
asbestos exposures to non-occupational individuals in
areas surrounding a historical Libby vermiculite pro-
cessing facility in Minneapolis, Minnesota [46]. In addi-
tion to these findings, the results from our study suggest
a potential fiber exposure to persons who perform work
activities associated with contaminated trees surrounding
these facilities. Surfaces other than trees, such as soil,
building structures, etc., may be contaminated in these
areas as well. Recommendations for future studies in-
clude determining the risk of exposure to persons per-
forming work activities on trees in these areas, as well as
determining if there is an elevated health risk to the ge-
neral public when amphibole-contaminated trees are dis-
Table 4. Summary of the average dimensions of asbestos fibers measured from the bark samples in Libby, Spokane, Santa
Ana, Newark, and Phoenix.
Amphibole Chrysotile
Site Avg. diameter
Avg. Length
Avg. aspect
ratio (AR)
Avg. diameter
Avg. Length
Avg. aspect ratio
Libby, MT 0.39 3.4 11.5 N/A N/A N/A
Spokane, WA 0.37 3.6 9.42 N/A N/A N/A
Santa Ana, CA 0.49 5.6 11.2 0.10 1.7 16.0
Newark, CA 0.44 2.8 6.52 0.08 1.5 21.6
Phoenix, AZ 0.50 3.7 7.21 0.11 1.6 17.6
Note: Amphibole represents Libby amphibole and actinolite-tremolite fibers.
opyright © 2011 SciRes. JEP
Libby Amphibole Contamination in Tree Bark Surrounding Historical Vermiculite Processing Facilities1067
6. Acknowledgements
Special thanks to Anna Ristich at ALS Laboratories in
Cincinnati, OH. The majority of the work was supported
by an NIH COBRE grant p20-RR017670.
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