Libby Amphibole Contamination in Tree Bark Surrounding Historical Vermiculite Processing Facilities

doi:10.4236/jep.2011.28122

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Journal of Environmental Protection, 2011, 2, 1062-1068

doi:10.4236/jep.2011.28122 Published Online October 2011 (http://www.scirp.org/journal/jep)

Libby Amphibole Contamination in Tree Bark

Surrounding Historical Vermiculite Processing

Facilities

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: *Tony.Ward@mso.umt.edu

Received August 13th, 2011; revised September 15th, 2011; accepted October 3rd, 2011.

ABSTRACT

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

declaration.

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

grids.

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

east

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].

Libby Amphibole Contamination in Tree Bark Surrounding Historical Vermiculite Processing Facilities

1064

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

SA_1

2.5

3.5

1,704,683

333,559

1,136,456

463,192

568,228

Eastern cottonwood 366

SA_2 6 469,716 ND ND ND ND ND ND

Blue gum Eucalyptus 457

SA_3

1.5

2.5

744,062

428,992

713,842

744,062

American Elm 610

SA_4 3

3.5

543,881

649,360

ND American Elm 732

B. Newark Site

NEW_1 4 ND ND 1,266,526 ND ND ND ND

Blue gum Eucalyptus 701

NEW_2

1.5

2.5

807,883

634,753

1,485,125

842,188

Eastern cottonwood 152

NEW_3 2

2.5

530,103

2,120,412

429,191 California redwood 61

NEW_4

2.5

3.5

1,599,152

2,013,383

1,137,822

671,128

Australian pine 213

NEW_5

480,088

776,296

645,265

Australian pine 305

C. Phoenix Site

PHX_1 3

473,892

924,072

ND Snow Gum eucalyptus 274

PHX_2 4 ND ND 681,027 ND ND ND 681,027 Snow Gum eucalyptus 152

PHX_3 3

1,371,575

479,941

685,787

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.

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

studied.

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

Libby Amphibole Contamination in Tree Bark Surrounding Historical Vermiculite Processing Facilities

1066

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-

turbed.

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

(µm)

Avg. Length

(µm)

Avg. aspect

ratio (AR)

Avg. diameter

(µm)

Avg. Length

(µm)

Avg. aspect ratio

(AR)

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.

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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