Health Hazard Evaluation Report 2013-0061-3244 Page 1

Evaluation of Erionite and Silica Exposure 

During Forestry Activities

HHE Report No. 2013-0061-3244

November 2015

Catherine Beaucham, MPH, CIH

Martin Harper, PhD, CIH FAIHA, 

CChem FRSC

Bradley King, PhD, MPH, CIH

Alan Dozier, PhD, MS

U.S. Department of Health and Human Services

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health
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Contents

Highlights...............................................i

Abbreviations ..................................... iii

Introduction......................................... 1

Methods ............................................... 5

Results and Discussion ....................... 8

Conclusions........................................ 14

Recommendations .............................14

Appendix A ........................................ 17

Appendix B ........................................ 19

Appendix C ........................................ 23

References ......................................... 26

Acknowledgements .......................... 31

The employer is required to post a copy of this report for 30 days at or near the 

workplace(s) of affected employees. The employer must take steps to ensure 

that the posted report is not altered, defaced, or covered by other material.

The cover photo is a close-up image of sorbent tubes, which are used by the HHE 

Program to measure airborne exposures. This photo is an artistic representation that may 

not be related to this Health Hazard Evaluation. Photo by NIOSH.
Health Hazard Evaluation Report 2013-0061-3244 Page i

We took air samples for erionite 

mineral fibers and respirable 

crystalline silica during forestry 

activities and collected bulk 

rock and soil samples in the 

vicinity of the employees. 

All employees were exposed 

to erionite mineral fiber. We 

recommended against repairing 

roads with aggregate that 

contained erionite. We also 

recommended controlling 

dust exposures with ventilated 

vehicle cabs, wet methods, and 

other work practices.

Highlights of this Evaluation

The Health Hazard Evaluation Program received a request from a federal government 

agency. This employer was concerned about potential employee exposures to erionite mineral 

fibers during forestry activities in areas where erionite had been confirmed or was suspected 

to be present. 

What We Did

● We observed employees thinning, felling, and bucking trees; digging fireline; spraying 

invasive weeds; mowing campgrounds; using a Bobcat® to masticate timber and grade 

roads; and reclaiming a push pit.

● We took personal air samples for mineral fibers 

and respirable crystalline silica.

● We took rock and soil samples to analyze 

for erionite.

What We Found

● We developed a revised approach to confirm 

erionite in air samples.

● Most of the personal air samples contained erionite.

● The rock and soil samples contained erionite.

● Some task-based personal air samples 

contained respirable crystalline silica.

What the Employer Can Do

● Do not repair roads with aggregate that 

contains erionite.

● Keep the windows and doors to the equipment 

operators’ cabs closed when operating equipment or driving down dirt roads.

● Maintain air filters in the equipment regularly and improve air filtration in the vehicle cabs.

● If soil is dry, wet it before doing dust-generating activities.

● Provide clean hearing protection on work trucks.

● Wash personal protective equipment, such as turnout gear, regularly to remove dust and dirt.

What Employees Can Do

● Change hearing protection more frequently and do not reuse when dirty.

● When personal protective equipment, such as turnout gear, is contaminated, ask the 

employer to have it cleaned. Do not take personal protective equipment home for cleaning.
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Health Hazard Evaluation Report 2013-0061-3244 Page iii

Abbreviations

μm Micrometer

Al Aluminum 

Ca Calcium

EDS Energy-dispersive spectroscopy

FBAS Fluidized bed asbestos segregator

f/cc Fibers per cubic centimeter

g Grams

K Potassium

MERV Minimum efficiency reporting value

Na Sodium

NIOSH National Institute for Occupational Safety and Health

OEL Occupational exposure limit

OSHA Occupational Safety and Health Administration

PEL Permissible exposure limit

PCM Phase contrast microscopy

PLM Polarized light microscopy

PPE Personal protective equipment

REL Recommended exposure limit

Si Silicon

TEM Transmission electron microscopy

TLV® Threshold limit value

TWA Time-weighted average

WEELTM Workplace environmental exposure level

XRD X-ray diffraction
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Health Hazard Evaluation Report 2013-0061-3244 Page 1

Introduction

The Health Hazard Evaluation Program received a request from a management representative 

at a federal government agency whose employees work in the Sioux Ranger District of the 

Custer National Forest. The requestor was concerned about potential employee exposures to 

erionite mineral fibers when employees worked in areas where erionite was known or suspected 

to be present. We visited these areas in July 2013 and September 2014. We sent summary letters 

with preliminary recommendations in July 2013, April 2014, September 2014, and March 2015.

Erionite and Respirable Crystalline Silica

Erionite is a member of the zeolite mineral family. It is a naturally occurring mineral found 

in some geologic environments, including extensive fine-grained volcanic ash deposits 

of a certain age that have been altered by weathering and ground water. Erionite deposits 

have been identified in all of the western states except Washington [USGS 1996, 2010]. In 

the Sioux Ranger District of the Custer National Forest, the geologic formations that may 

contain erionite are the Arikaree Formation and White River Group, specifically the Chadron 

and Brule formations [Van Gosen et al. 2012]. Exposure to erionite fibers is associated with 

health effects similar to those typically seen with exposure to asbestos, including malignant 

mesothelioma [Carbone et al. 2001; Kliment et al. 2009]. Health effects associated with 

exposure to erionite are described in Appendix B.

Crystalline silica is another mineral commonly found in many geologic formations, 

usually as quartz. Occupational exposure to respirable crystalline silica has been associated 

with silicosis, lung cancer, and other airway diseases [NIOSH 2002]. Erionite fibers and 

crystalline silica only pose a health hazard when they are airborne.

Thinning, Felling, and Bucking Trees

Thinning tree growth is done to prevent forest fires. Removing slower growing or defective 

trees creates more space between trees. By creating more space, it becomes more difficult 

for a fire to spread from tree to tree. Felling is the process of downing individual trees, while 

bucking is the process of cutting a felled and delimbed tree into logs. Personal protective 

equipment (PPE) worn by the sawyers included hearing protection (canal caps, ear plugs, or 

ear muffs), hard hat, chainsaw chaps, and safety glasses (Figure 1).
Page 2 Health Hazard Evaluation Report 2013-0061-3244

Digging Fireline

Fire fighters perform many tasks besides direct fire suppression during a wildland firefight. 

A fireline is a break in fuel (e.g., grasses, trees, shrubs) made by cutting, scraping, or digging 

to remove all plant debris; firelines usually range from 6 inches to 3 feet wide, with the width 

depending on the type of fuel and slope of the land. The fireline needs to be wide enough 

to prevent smoldering or burning embers from blowing or rolling across the line to ignite 

additional fuel and perpetuate the fire. While digging fireline can be done by mechanized 

equipment such as bulldozers, it is more commonly done using hand tools. Fire fighters may 

spend 12 hours or more digging fireline per shift once a fire has started. Their PPE includes 

hard hats, leather gloves, and safety glasses. In addition, all fire fighters wear fire resistant 

clothing and carry an approximately 50-pound wildland fire pack that contains a self-rescue 

tent and water (Figure 2).

Figure 1. Thinning tree growth around the Reva Gap campground in the Slim Buttes. Photo by the 

National Institute for Occupational Safety and Health (NIOSH).
Health Hazard Evaluation Report 2013-0061-3244 Page 3

Figure 2. Employees using hand tools to dig fireline in the Ekalaka Hills. Photo by NIOSH.

Spraying Invasive Species

The agency employees used universal terrain vehicles to access pastures off the main roads 

to search for invasive plant species. When an invasive plant was discovered, the employee 

sprayed it with a pesticide mixture to kill it. The employee then sprayed the plant with a blue 

dye to indicate it had been treated. PPE for the pesticide applicator included rubber gloves, a 

Tyvek® suit, and safety glasses (Figure 3).

Figure 3. Using a universal terrain vehicle to access off-road locations to spray invasive weed species 

with pesticides. Photo by NIOSH.
Page 4 Health Hazard Evaluation Report 2013-0061-3244

Mowing Campground

The agency was responsible for maintaining the national forest campgrounds in their district. 

Maintaining the campgrounds included using push and riding lawnmowers and operating 

weed whackers. PPE for these employees included leather gloves, safety glasses, and hearing 

protection (ear muffs or ear plugs). Employees on the riding lawn mowers also wore hard hats.

Figure 4. Campground maintenance. Castle rock, an erionite containing rock formation, can be seen 

in the background. Photo by NIOSH.

Vegetation Mastication

A masticator attached to a Bobcat® grinds woody vegetation into wood chips that are 

deposited onto the forest floor. The masticator cuts down and grinds up whole standing trees 

in a single, continuous process. The operator remained inside of the closed vehicle cab of the 

Bobcat. PPE worn by the employee included disposable foam ear plugs and a hard hat.
Health Hazard Evaluation Report 2013-0061-3244 Page 5

Figure 5. Masticator. Photo by NIOSH.

Push Pit Reclamation

Push pits were dug to explore for uranium in the late 1950s and early 1960s. An agency 

employee uses a Bobcat to refill the pit by pushing the dirt that was removed from the pit into 

the trench, and then another employee spreads grass seed on the newly filled-in trench. The 

activity involves a Bobcat operator, a safety manager to evaluate radiation levels, and grass 

seed applicators. PPE for the Bobcat operator included ear plugs and a hard hat. No PPE was 

required for other team members.

Methods

Our objectives were to:

1. Assess employee exposure to erionite and respirable crystalline silica during 

forestry activities. 

2. Determine if erionite was present in certain rock formations within the national forest. 

3. Develop a revised approach to more accurately detect and measure erionite in air 

samples from this location.

Air Sampling

We took air samples to evaluate employee exposure to erionite and respirable crystalline 

silica. We did this during forestry activities including thinning, felling, and bucking trees; 

digging fireline; spraying invasive weed species; mowing campgrounds; using a Bobcat to 

masticate timber and grade roads; and reclaiming push pits. These activities took place within 

the Arikaree and White River rock formations in July 2013 and September 2014. 
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During the July 2013 visit we took 36 task-based personal air samples for erionite and 37 

task-based personal air samples for respirable quartz. During the September 2014 visit, we 

took 14 full-shift personal air samples for erionite and 14 full-shift personal air samples for 

respirable quartz.

We collected and analyzed the erionite samples according to NIOSH Method 7400 [NIOSH 

2015]. We then used transmission electron microscopy (TEM) with energy dispersive 

spectroscopy to analyze the erionite samples according to a modified NIOSH Method 7402 

for asbestos [NIOSH 2015]. Initially, we attempted to confirm the presence of erionite by 

TEM using the method described by Dogan and Dogan [2008]. In doing so, we discovered 

limitations of the Dogan and Dogan method, which are described in Appendix A. As a result 

of those limitations, we developed and used the following methodology. The fibers that we 

found in the air samples were easily visualized using TEM (Figure 6). Fibers meeting certain 

size parameters (length greater than 5 micrometers [μm], and length to width aspect ratio 

greater than 3:1) underwent energy-dispersive spectroscopy (EDS) to identify the chemical 

composition of the fiber. A fiber was considered erionite if it contained major peaks of silicon 

(Si) and aluminum (Al) and minor peaks of at least one of the elements calcium (Ca), sodium 

(Na), or potassium (K).

Figure 6. Erionite fiber under TEM. Photo by Bureau Veritas North America.

We collected the respirable crystalline silica samples on preweighed, 5-μm pore size 

polyvinyl chloride filters with a Dorr-Oliver nylon cyclone at a nominal flow rate of 1.7 

liters per minute in July 2013, and with a BGI cyclone at a nominal flow rate of 4.2 liters per 

minute in September 2014. The July 2013 samples were task-based and the September 2014 

samples were full-shift. We analyzed the samples according to NIOSH Method 7500 [NIOSH 

2015] with modification. The modification included wiping the interior walls of the filter 

cassette with the back side of the sample filter to collect particles on the inside of the cassette 

walls as recommended by NIOSH [2014a]. 
Health Hazard Evaluation Report 2013-0061-3244 Page 7

Bulk Rock and Soil Samples

We collected bulk rock samples and soil samples to determine if erionite was present in the 

rock formations surrounding the areas where employees worked. We analyzed all the bulk 

rock samples collected in 2013 by phase-contrast microscopy (PCM) to look for fibers. In 

the laboratory, we gently crushed small amounts of material into a fine powder between two 

glass slides and mounted the material in a drop of mounting medium. A few of these samples 

were also analyzed in different laboratories for confirmation of erionite by polarized light 

microscopy (PLM), x-ray diffraction (XRD), and TEM-EDS.

During the September 2014 visit, we collected 10 bulk soil samples according to a bulk 

sampling method for asbestos developed by the U.S. Environmental Protection Agency 

[EPA 2013]. Each of these 10 samples was collected as a composite consisting of a total 

of 50 grams (g) of soil from 30 individual sampling points equidistant from each other and 

representative of the 1,500-square-foot cell around each worker. We identified the location of 

each cell using GPS coordinates.

In the laboratory, the sample was shaken to homogenize it. From each sample we split two 

10-g portions into different containers; the remaining 30 g of soil was not analyzed. One 10-g 

portion was analyzed according to a modified NIOSH Method 9002 for bulk asbestos by 

PLM [NIOSH 2015]. The modification includes identifying erionite in lieu of asbestos. The 

second 10-g portion was analyzed by XRD. Approximately 1 g of the sample was added to a 

mortar and ground to a fine powder with a pestle. The ground powder was wet sieved through 

a 45-μm sieve using 2-propanol, which was then evaporated. Approximately 0.5 g of sample 

powder was placed into an aluminum sample plate, which was then placed in the automated 

sample changer. A fast, full range XRD scan of the powder was performed to determine the 

primary sample constituents. Slow scans for selected regions were then done to confirm 

erionite presence. The sample peak identifications were assigned referencing known mineral 

data found in the American Mineralogist crystal structure database and Jade 8.0 software 

[Bish and Chipera 1991].

We also analyzed the bulk samples by a fluidized bed asbestos segregator (FBAS). We 

blended 1-g aliquots of the soil sample with 19 g of clean sand and mixed them together. 

We then placed the soil-sand combination in the glass vessel of the FBAS according to 

a procedure developed by U.S. Environmental Protection Agency researchers [Januch et 

al. 2013]. Filtered air was passed through the vibrated sample, and a portion of the outlet 

air was collected on a 25-mm diameter mixed-cellulose ester filter in a conductive plastic 

cassette. We then examined the filter under PCM. We identified fibers as erionite using their 

morphology and refractive index and then counted and measured them. We calculated an 

estimate of fiber mass per unit area of filter from the dimensions and the density of erionite, 

and converted the result to a mass per gram of soil concentration using the known area of 

filter and the air flows through the sample and filter.
Page 8 Health Hazard Evaluation Report 2013-0061-3244

Results and Discussion

Erionite Air Sampling

The July 2013 visit took place in the following areas: (1) Slim Buttes, (2) Long Pines, 

(3) East Short Pines, and (4) the Ekalaka Hills. All of these locations were located within 

outcrops of the Arikaree and White River rock formations and included soils developed 

from those locations. We took air samples for the entire duration of dust-generating tasks, 

though not for the entire work shift, which included long commute times into and out of 

forest service lands. Erionite concentrations ranged from not detected to 0.36 fibers per 

cubic centimeter (f/cc). The tasks (Table 1) that resulted in the highest airborne mineral fiber 

concentrations included operating the masticator in the East Short Pines (0.36 f/cc), mowing 

in the Slim Buttes/Reva Gap campground (0.26 f/cc), digging fireline in Ekalaka Hills with 

the polaski tool (0.11 f/cc), and chainsaw operations in the East Short Pines (0.11 f/cc). These 

exposures cannot be directly compared to the NIOSH recommended exposure limit (REL) 

of 0.1 f/cc for asbestos because the definition of airborne asbestos fibers does not explicitly 

encompass elongate mineral particles from other micro-fibrous minerals such as erionite. 

Table 1. Task-based personal air sample results by location and activity, July 2013

Location: activity

(Number of employees sampled)

Erionite 

(f/cc)

Sample duration 

(minutes)

Slim Buttes/Reva Gap: campground maintenance

Felling and bucking (11 employees) Not detected*–0.056 155–233

Mowing (5 employees) 0.012–0.26 54–290

Long Pines: universal terrain vehicle operation

Operator and assistant (4 employees) 0.0077–0.015 302–336

East Short Pines: thinning, bucking, felling, mastication

Chainsaw operation (6 employees) 0.024–0.11 141–225

Masticator (1 employee) 0.36 213

Log stacker (1 employee) 0.061 214

Skid loading (1 employee) 0.078 164

Ekalaka Hills: digging fire line

Polaski† (2 employees) 0.025 and 0.11 204 and 206

Combi† (2 employees) 0.081 and 0.026 203 and 321

Rogue hoe† (2 employees) 0.016 and 0.057 218 and 324

McCloud† (1 employee) 0.0081 320

*Not detected means no fibers were seen after counting 100 TEM grids.

†These are the names of the tools that the employees used while digging fire line.

We returned to the East Short Pines and the Slim Buttes areas in September 2014 to 

re-evaluate the full-shift exposure for the tasks that previously contributed to the highest 

airborne mineral fiber concentrations. Table 2 lists the results of these full-shift samples. The 

concentrations ranged from 0.009–0.096 erionite f/cc. We collected these samples while it 

was raining and snowing. Airborne concentrations would likely be higher in dry weather.
Health Hazard Evaluation Report 2013-0061-3244 Page 9

Table 2. Full-shift personal air sample results by location and activity, September 2014

Location: activity

(Number of employees sampled)

Erionite 

(f/cc)

Sample duration 

(minutes)

East Short Pines: thinning, bucking, felling, mastication

Chainsaw operation (4 employees) 0.012–0.096 516–522

Masticator (1 employee) 0.015 501

Driving (1 employee) 0.013 496

Slim Buttes/Reva Gap: campground maintenance and 

push pit reclamation

Mowing (3 employees) 0.0010–0.0020 296–298

Seeding push pit (2 employees) 0.0050 and 0.0060 595 and 597

Safety at push pit (2 employees) 0.0030 and 0.0040 564 and 569

Bobcat operator (1 employee) 0.009 585

Respirable Crystalline Silica

Respirable crystalline silica was present, but below the minimum quantifiable concentration 

in some task-based personal air samples collected in July 2013 (Table 3). Quartz was the only 

form of crystalline silica detected. The concentration estimates were based on short duration 

samples and cannot be directly compared to full-shift occupational exposure limits (OELs). 

Respirable crystalline silica was not detected in any of the full-shift air samples collected 

in September 2014. The minimum detectable concentration ranged from 0.002–0.004 

milligrams per cubic meter, which is below the ACGIH threshold limit value (TLV) of 0.025 

milligrams per cubic meter. Health effects associated with exposure to respirable crystalline 

silica are described in Appendix B. Although we did not find detectable silica concentrations 

in full-shift samples taken on the follow-up evaluation, crystalline silica was detected in some 

short-term air samples on the initial evaluation, a finding that was consistent with our results 

during another health hazard evaluation involving outdoor work in federal land known or 

suspected to contain erionite [NIOSH 2014b]. In addition, samples from September 2014 were 

taken while it was raining and snowing; airborne concentrations could be higher in dry weather. 
Page 10 Health Hazard Evaluation Report 2013-0061-3244

Table 3. Task-based personal air sample results for silica by location and activity, July 2013

Location: activity

(Number of employees sampled)

Quartz 

(milligrams per cubic meter)

Sample duration 

(minutes)

Slim Buttes/Reva Gap: campground maintenance

Felling and bucking (11 employees) Not detected 155–233

Mowing (4 employees) Not detected 54–290

Long Pines: universal terrain vehicle operation

Operator and assistant (4 employees) Not detected 302–336

East Short Pines: thinning, bucking, felling, 

and mastication

Chainsaw operation (6 employees) Not detected–(0.02)* 141–225

Piler/stacker (2 employees) Not detected 139 and 219

Masticator (1 employee) (0.02) 213

Log stacker (1 employee) (0.02) 214

Skid loading (1 employee) Not detected 164

Ekalaka Hills: digging fire line

Polaski† (2 employees) (0.03 and 0.05) 204 and 206

Combi† (2 employees) (0.03 and 0.03) 203 and 321

Rogue hoe† (2 employees) (0.01 and 0.03) 218 and 324

McCloud† (1 employee) (0.01) 320

Minimum detectable concentration 0.01–0.02 —

Minimum quantifiable concentration 0.030–0.070 —

*Parentheses are used when results were between the minimum detectable concentration and the 

minimum quantifiable concentration, making these estimated results due to greater uncertainty 

associated with these values.

†These are the names of the tools that the employees used while digging fire line.

Bulk Rock and Soil Samples

In July 2013, we collected bulk rock samples from various locations in the Arikaree and 

White River Formations in the Sioux Ranger District of the Custer National Forest. These 

locations included the cliffs above the campground at Reva Gap, in the Castles area of 

Slim Buttes, and in the Capitol Rock area of Long Pines. All samples contained fibrous 

minerals. Some of these samples were sent for further identification in other laboratories. All 

laboratories confirmed that the fibrous minerals in each sample included erionite. Some of 

these laboratories also compared reference erionite samples from Rome, Oregon, and Karain, 

Cappadocia, Turkey. We observed some differences in composition and mineralogy between 

the reference erionites and the Custer National Forest erionite samples, which may have a 

bearing on toxicity (Appendix C).

We observed the highest concentration of fibrous minerals in the samples collected in the 

Arikaree Formation, about 30 meters above the White River Formation. The area of fibers 

by point-counting is high (Figure 7), but because of the much larger volume of the accessory 

mineral grains (mainly quartz) the weight percentage of erionite is low (about 1%).
Health Hazard Evaluation Report 2013-0061-3244 Page 11

Figure 7. Scanning electron microscopy image at 100x of erionite. Photo by NIOSH.

We split each of the bulk soil samples into three separate groups and analyzed each split 

by PLM, FBAS/PCM, and XRD. The variability in the analytical results is believed to 

be due to method variability. The bulk soil samples that we collected in September 2014 

and analyzed by PLM consisted mostly of particles of calcite, gypsum, quartz, opaque 

minerals, and cellulose fibers. Most of the fibers seen (8%–10%) were cellulose fibers. The 

percentage of erionite fibers in the soil samples analyzed by PLM ranged from not detectable 

to approximately 5% (Table 4). The soil samples collected in the East Short Pines had the 

highest percentage of erionite.

Table 4. Soil sample results collected in September 2014

Task description Latitude Longitude Elevation

(feet)

PLM 

erionite 

(%)

FBAS 

erionite 

(%)

XRD 

erionite 

(%)

East Short Pines

Masticating 45°22.629N 103°43.366W 3915 5 5.1 10

Masticating 45°22.710N 103°42.906W 3986 3 3.9 10

Sawing 45°22.612N 103°43.168W 3946 < 1 1.0 5

Masticating 45°22.683N 103°42.630W 3940 < 1 1.3 1

Sawing 45°22.618N 103°43.195W 4051 < 1 1.4 2

Slim Buttes

Mowing 45°31.559N 103°10.714W 3301 2 2.5 6

Mowing 45°31.684N 103°10.613W 3342 3 4.2–4.6 7

Mowing 45°31.887N 103°10.711W 3299 ND 0.1 4

Mowing 45°31.852N 103°10.719W 3347 ND 0.1 7

Push pit 45°34.965N 103°11.918W 3632 ND ND 4

ND = not detectable
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The soil samples analyzed by a fast qualitative XRD scan (5 to 80 two-theta degrees) 

identified quartz, clinoptilolite (another zeolite that can crystallize in a needle-like or fibrous 

form, but which is not considered carcinogenic), alkali feldspar, and calcite. We found 

zeolites in all samples. In addition, some samples had low levels of erionite (Table 4), which 

required further confirmation with a slow scan below 20 two-theta degrees so that erionite 

could be confirmed in the presence of interfering minerals. A high purity (80%–85%) erionite 

reference sample was obtained from Rome, Oregon. Two lower concentration erionite 

reference samples were prepared from the Rome, Oregon, reference erionite material. 

Reference A contained 0.7% erionite, while reference B contained 5.1% erionite. The 

reference A sample was created to investigate the limit of detection, while reference B was 

prepared to investigate the erionite fingerprint and compare it to the bulk soil samples. The 

values in Table 4 for XRD should be considered rough estimates. 

We took photographs of representative erionite fibers seen with PLM and PCM after FBAS 

concentration (Figures 8 and 9). We anticipated the FBAS results would be similar to 

concentrations seen in the PLM analysis, but with more precision, because of the similarities 

of the two methods (Table 4). Erionite mineral fibers can clearly be seen in both microscopic 

photographs and can be visually differentiated from other types of fibers. Interestingly, the 

erionite fibers found in this region differed from erionite fibers found in Cappadocia, Turkey, 

and Rome, Oregon. Appendix C contains a description of these differences.

Figure 8. Photograph collected using PLM. Photo by Bureau Veritas North America.
Health Hazard Evaluation Report 2013-0061-3244 Page 13

Figure 9. Photograph collected using PCM after FBAS concentration. Photo by NIOSH

Observations

Hearing protection was required for certain tasks. In those cases the employees used it 

diligently. However, their disposable foam ear plugs were often covered in dirt and oil. 

Using dirt- and oil-coated ear plugs can introduce these contaminants into the ear canal 

and can also alter the fit of the ear plug and therefore potentially limit its effectiveness. 

Employees told us that new ear plugs were not available on the work trucks. In addition, 

the agency-issued turnout gear was dirty and had oil on it. Some employees indicated to us 

that they only washed their turnout gear a few times a year. The National Fire Protection 

Association recommends that fire fighter protective clothing be kept clean to ensure its proper 

performance. Soiled or contaminated turnout gear is a hazard to fire fighters because oils and 

contaminants can be flammable, toxic, or carcinogenic. In addition, dirty ensembles can have 

reduced protective performance [NFPA 2011, 2014]. 

One seasonal employee who was applying pesticides and dye to invasive weed species did 

not know about the hazards of the pesticides and reported he had neither seen the safety data 

sheets nor received chemical-specific health and safety training.

The Bobcat Skid Steer was used for multiple tasks, including vegetation mastication, grading 

roads, removing plants from the center of the roadway, and filling in the push pit with dirt. 

The Bobcat had two cabin air filters, one on the fresh air intake and one on the recirculating 

air intake. We observed accumulated dust inside the cab. Recent NIOSH studies have shown 

that an effective vehicle cab filtration system includes both a powered and pressurized 

air intake as well as filtered circulation air to reduce respirable dust [Cecala et al. 2012; 

Organiscak et al. 2013; Cecala et al. 2014]. The ventilation system on the Bobcat Skid Steer 

was not powered, and there was no change-out schedule for its air filters. Also, we were 

unable to determine the minimum efficiency reporting value (MERV) for the filters for 

comparison with recommendations. 
Page 14 Health Hazard Evaluation Report 2013-0061-3244

Conclusions

Erionite mineral fibers were found in the personal air samples and in the bulk rock and soil 

samples collected in rock formations within the national forest. We defined erionite as fibers 

that had a length greater than 5 μm, and a length to width aspect ratio greater than 3:1 with 

major peaks of silicon and aluminum and minor peaks of at least one of the elements Ca, 

Na, or K. Although OELs specific to erionite have yet to be developed, and toxicological 

studies of the health effects of the various forms of erionite are ongoing, health hazards of 

erionite exposure have been identified elsewhere. Characterizing and minimizing potentially 

hazardous exposures until an evidence-based OEL for erionite is developed is necessary. 

Although we did not measure overexposures to respirable crystalline silica during this 

evaluation, detectable silica concentrations were found in several task-based personal air 

samples and we have previously identified overexposures among employees performing 

similar outdoor tasks on other federal land. Therefore, minimizing dust exposure during dustgenerating activities is prudent.

Recommendations

On the basis of our findings, we recommend the actions listed below. We encourage the agency 

to use a labor-management health and safety committee or working group to discuss our 

recommendations and develop an action plan. Involve those who do the work in the national forest.

Our recommendations are based on an approach known as the hierarchy of controls. This 

approach groups actions by their likely effectiveness in reducing or removing hazards. In 

most cases, the preferred approach is to eliminate hazardous materials or processes and 

install engineering controls to reduce exposure or shield employees. Until such controls 

are in place, or if they are not effective or feasible, administrative measures and personal 

protective equipment may be needed. 

Elimination and Substitution

Eliminating or substituting hazardous processes or materials reduces hazards and protects 

employees more effectively than other approaches. Prevention through design, considering 

elimination or substitution when designing or developing a project, reduces the need for 

additional controls in the future.

1. Do not use aggregate known or suspected to contain erionite to build or repair roads.

Engineering Controls

Engineering controls reduce employees’ exposures by removing the hazard from the process or by 

placing a barrier between the hazard and the employee. Engineering controls protect employees 

effectively without placing primary responsibility of implementation on the employee. 

1. Keep the windows and doors to the equipment operators’ cabs closed when operating 

equipment or driving down dirt roads.

2. Maintain equipment air filters regularly as recommended by the equipment 
Health Hazard Evaluation Report 2013-0061-3244 Page 15

manufacturers. Change the gaskets and seals when signs of age (cracking or wear) or 

damage occur. Air intake filters should have a MERV of 16 and should be part of a 

powered, pressurized system. Ensure the enclosed cab has the structural integrity to 

achieve pressurization. The recommended flow rate should be 40–140 cubic feet per 

minute. The filtration efficiency of the recirculation filter should be between a MERV-14 

and MERV-16 filter at a flow rate of 200–300 cubic feet per minute [Cecala et al. 2014].

3. Wet wash equipment and vehicle exteriors, and vacuum the inside of work trucks with 

a high-efficiency particulate air filtered vacuum to minimize the buildup of dust in the 

cab of the vehicles.

Administrative Controls

The term administrative controls refers to employer-dictated work practices and policies 

to reduce or prevent hazardous exposures. Their effectiveness depends on employer 

commitment and employee acceptance. Regular monitoring and reinforcement are necessary 

to ensure that policies and procedures are followed consistently.

1. Educate employees on the health effects and hazards of crystalline silica and the 

potential health effects of erionite, where they are likely to encounter these hazards, 

which tasks are likely to expose them, and how they can protect themselves. Inform 

employees of the need to use dust control methods during any dust-generating work, 

and train them on dust control techniques. Links for information on silica exposure 

and dust control techniques that will help you develop a comprehensive training 

program are available at http://www.cdc.gov/niosh/topics/silica/.

2. Wet the soil or aggregate before disturbing it to reduce dust generation. It is common practice 

at construction and other outdoor work sites to use water trucks for dust suppression.

3. Restrict, whenever possible, dust-generating activities to times when environmental 

conditions are conducive to minimizing dust generation (e.g., snow, rain, calm 

weather). Avoid dust-generating tasks on windy days. Whenever possible, schedule 

dust-generating tasks on days when the soil is already moist.

4. Establish standard operating procedures for reducing dust exposure for vehicles used 

on dirt/gravel roads (i.e., drive slowly, vents closed, windows up).

5. Characterize fire fighter exposure to erionite during fire suppression activities 

(wildland fires and prescribed burns). 

6. Ensure an effective hazard communication program so that employees understand the 

hazards associated with workplace chemicals and know how to protect themselves. 

Follow the guidelines available at https://www.osha.gov/dsg/hazcom/.
Page 16 Health Hazard Evaluation Report 2013-0061-3244

Personal Protective Equipment

Personal protective equipment is the least effective means for controlling hazardous 

exposures. Proper use of personal protective equipment requires a comprehensive program 

and a high level of employee involvement and commitment. The right personal protective 

equipment must be chosen for each hazard. Supporting programs such as training, changeout schedules, and medical assessment may be needed. Personal protective equipment should 

not be the sole method for controlling hazardous exposures. Rather, personal protective 

equipment should be used until effective engineering and administrative controls are in place.

1. Provide employees with clothes (i.e., turnout gear) and boots that are solely designated 

for work activities, and prevent employees from washing these work clothes at home. 

Require employees who have been working in dusty areas to change into clean 

clothing before leaving the worksite.

2. Wash protective clothing and other equipment (chaps, hard hats, and tools) regularly to 

remove dust, dirt, and other contaminants.

3. Inspect hearing protection devices prior to each use. When contaminated, clean them if 

they are reusable or throw them away if they are disposable. Ensure that replacement 

hearing protection devices are available to employees working in the field. 
Health Hazard Evaluation Report 2013-0061-3244 Page 17

Appendix A: Sampling and Analytical Methods

Air samples for erionite were first analyzed by PCM according to NIOSH Method 7400 to 

identify fibers [NIOSH 2015]. Fibers are defined as those particles having a length-to-width 

aspect ratio equal to or greater than 3:1. Fibers longer than 5 μm are counted until either 

a minimum of 100 fibers is counted in 20 or more fields, or a maximum of 100 fields is 

examined. Samples with a high fiber count were then selected for a second analysis using TEM.

We analyzed samples from our first visit with TEM per NIOSH Method 7402 and then 

applied a method developed by Dogan and Dogan [2008] to determine if the fibers were 

erionite. Portions of the mixed cellulose ester filters were transferred to a glass slide and then 

placed on a 200-mesh copper TEM grid. Structures that had a width to length aspect ratio of 

greater than 3:1 and a minimum length of 5 μm were selected for further evaluation. We first 

identified a fiber by morphology then evaluated its elemental makeup using EDS. The Dogan 

and Dogan paper recommended that to confirm erionite, the fibers have a magnesium content 

of < 0.8 atoms per unit cell, and a balance error (E%) of ≤ 10%. Atomic percentages of the 

elements, not weight percentages, should be used when computing the balance error formula.

The E% was determined using the following formula: 

E% = [(Al+Fe)−(Na+K)−2(Ca+Mg)]/[(Na+K)+2(Ca+Mg)]*100 

Note the minus sign in front of the 2, which was accidentally left out in the published Dogan 

and Dogan paper [2008]. The balance error formula is applicable to erionite crystals from 

vesicles in mafic volcanic lavas but works less well when applied to erionites that have 

formed in a sedimentary environment [Dogan 2012]. The erionites from the Custer National 

Forest were formed in a sedimentary environment; therefore, the Dogan and Dogan method 

might not work well for these fibers.

When using a TEM for the EDS analysis of erionite, two problems are encountered that can 

have a large impact on accuracy: the beam sensitivity of erionite and the accuracy of the 

analysis software package. The beam sensitivity problem is most notable by the observation 

of Na reduction under electron beam exposure during the EDS analysis. To address this 

problem, we used a JEOL 2100F high resolution TEM with scanning capability and detectors 

for EDS and electron energy-loss spectroscopy for sample analysis. We analyzed three bulk 

samples of highly concentrated erionite from (1) Rome, Oregon; (2) Custer National Forest, 

South Dakota; and (3) Cappadocia, Turkey. To prepare the samples for analysis, the three 

samples were crushed to a fine powder in a negative pressure hood. We then transferred a 

small portion of each fine powder to a lacey carbon TEM grid for analysis. We performed 

EDS analysis of a reference zeolite material from the National Institute of Standards and 

Technology (8851A) to find acceptable beam conditions for EDS analysis. The Na content in 

8851A is very beam sensitive, meaning if the beam is left in one spot for even a short period 

of time, the Na content may degrade. Beam conditions tested were standard TEM imaging 

mode with a small condenser aperture and small spot size to minimize beam dose, and 

scanning TEM imaging mode with different spot sizes. While 8851A does not have certified 

values for major and minor trace element contents, as do standard reference materials, 8851A

does provide information values and a common source of zeolite material for measurement 
Page 18 Health Hazard Evaluation Report 2013-0061-3244

comparisons. We found only the smallest scanning TEM spot size of 0.2 nanometers with 

a 25-μm condenser aperture would not produce alteration in composition of the 8851A

standard or the erionite. In addition, the scanning TEM probe could not be stopped but 

always had to be scanning a small region to prevent the reduction in Na content.

As mentioned earlier, another factor affecting EDS results is the quantification software used 

to obtain atomic and weight percentages for the elements present. The currently available 

commercial EDS quantification software functions as a “black box,” without the user’s 

knowledge of the analytical parameters or the accuracy of the quantification algorithms used. 

We obtained our analytical results with two commercial EDS software packages, Gatan and 

Oxford, and compared them to the 8851A elemental values. After the EDS data acquisition 

conditions and analysis method were determined, the ten samples from each of the three 

types of “known” erionite from Rome, Oregon, Custer National Forest, and Cappadocia 

Turkey were analyzed. Percent errors (by the percent error formula or balance equation) 

were computed for each sample using each type of commercial software packages. The 

average percent error for Rome, Oregon using the Oxford software was 54.2 (range 17–95) 

and 178.8 (range 36 – infinity) using the Gatan Software. For the Custer National Forest 

samples, the average percent error was 311.8 (range 28 – 975) using Oxford and 386.6 

(range 85 – infinity) using Gatan. The Cappadocia, Turkey samples had a percent error of 

311.8 (range 28–975) with Oxford and 386.6 (range 84.8 – infinity) with Gatan. These results 

show that the percent error formula could not be used to identify erionite with either type of 

analytical software because not one fiber analyzed passed the less than 10% rule.

Because of the problems associated with using the balance equation for erionite 

identification, we developed a new way to confirm erionite. We again used the “known” 

erionite samples to compare the Gatan and Oxford software, but this time only for Na, Al, 

and Si. The Gatan software produced results differing from the reference weight percentages 

of Na, Al, and Si by 23.8, 7.2, and 12.9 percent, whereas the Oxford analysis differed from 

the reference by 6.4, 3.2, and 2.0 percent respectively. This comparison shows that the Gatan 

analysis software had a maximum deviation from the reference of 23.8 percent whereas 

the Oxford software had a maximum deviation of 6.4 percent. These comparisons were 

done with the 0.2 nm probe that was used for the analysis of all samples. This indicates that 

accurate and reproducible EDS analyses of erionite can be obtained from a TEM/scanning 

TEM microscope as long as a careful assessment is made of the EDS quantitative software 

and beam exposure using a beam sensitive EDS standard.

Our revised method to identify erionite included the following: we first identified a fiber then 

evaluated its elemental makeup using electron dispersive spectroscopy. We defined erionite 

mineral fiber as any particle longer than 5 μm, with an aspect ratio of equal to or greater than 

3:1 length to width, with strong peaks for Si and Al and minor peaks for at least one of the 

elements Na, Ca, or K. 
Health Hazard Evaluation Report 2013-0061-3244 Page 19

Appendix B: Occupational Exposure Limits and 

Health Effects

NIOSH investigators refer to mandatory (legally enforceable) and recommended OELs for 

chemical, physical, and biological agents when evaluating workplace hazards. OELs have 

been developed by federal agencies and safety and health organizations to prevent adverse 

health effects from workplace exposures. Generally, OELs suggest levels of exposure that 

most employees may be exposed to for up to 10 hours per day, 40 hours per week, for a 

working lifetime, without experiencing adverse health effects. However, not all employees 

will be protected if their exposures are maintained below these levels. Some may have 

adverse health effects because of individual susceptibility, a pre-existing medical condition, 

or a hypersensitivity (allergy). In addition, some hazardous substances act in combination 

with other exposures, with the general environment, or with medications or personal habits of 

the employee to produce adverse health effects. Most OELs address airborne exposures, but 

some substances can be absorbed directly through the skin and mucous membranes.

Most OELs are expressed as a time-weighted average (TWA) exposure. A TWA refers to 

the average exposure during a normal 8- to 10-hour workday. Some chemical substances 

and physical agents have recommended short-term exposure limit or ceiling values. Unless 

otherwise noted, the short-term exposure limit is a 15-minute TWA exposure. It should not be 

exceeded at any time during a workday. The ceiling limit should not be exceeded at any time.

In the United States, OELs have been established by federal agencies, professional 

organizations, state and local governments, and other entities. Some OELs are legally 

enforceable limits; others are recommendations. 

● The U.S. Department of Labor Occupational Safety and Health Administration (OSHA) 

permissible exposure limits (PELs) (29 CFR 1910 [general industry]; 29 CFR 1926 

[construction industry]; and 29 CFR 1917 [maritime industry]) are legal limits. These 

limits are enforceable in workplaces covered under the Occupational Safety and Health 

Act of 1970. 

● NIOSH RELs are recommendations based on a critical review of the scientific and technical 

information and the adequacy of methods to identify and control the hazard. NIOSH 

RELs are published in the NIOSH Pocket Guide to Chemical Hazards [NIOSH 2010]. 

NIOSH also recommends risk management practices (e.g., engineering controls, safe work 

practices, employee education/training, personal protective equipment, and exposure and 

medical monitoring) to minimize the risk of exposure and adverse health effects.

● Other OELs commonly used and cited in the United States include the threshold limit 

values (TLVs), which are recommended by the American Conference of Governmental 

Industrial Hygienists, a professional organization, and the workplace environmental 

exposure levels (WEEL), which are recommended by the American Industrial Hygiene 

Association, another professional organization. The TLVs and WEELs are developed 

by committee members of these associations from a review of the published, peerreviewed literature. These OELs are not consensus standards. TLVs are considered 
Page 20 Health Hazard Evaluation Report 2013-0061-3244

voluntary exposure guidelines for use by industrial hygienists and others trained in 

this discipline “to assist in the control of health hazards” [ACGIH 2015]. WEELs have 

been established for some chemicals “when no other legal or authoritative limits exist” 

[AIHA 2015].

Outside the United States, OELs have been established by various agencies and organizations 

and include legal and recommended limits. The Institut für Arbeitsschutz der Deutschen 

Gesetzlichen Unfallversicherung (Institute for Occupational Safety and Health of the German 

Social Accident Insurance) maintains a database of international OELs from European Union 

member states, Canada (Québec), Japan, Switzerland, and the United States. The database, 

available at http://www.dguv.de/ifa/GESTIS/GESTIS-Internationale-Grenzwerte-fürchemische-Substanzen-limit-values-for-chemical-agents/index-2.jsp contains international 

limits for more than 1,500 hazardous substances and is updated periodically. 

OSHA requires an employer to furnish employees a place of employment free from 

recognized hazards that cause or are likely to cause death or serious physical harm 

[Occupational Safety and Health Act of 1970 (Public Law 91–596, sec. 5(a)(1))]. This is 

true in the absence of a specific OEL. It also is important to keep in mind that OELs may not 

reflect current health-based information.

When multiple OELs exist for a substance or agent, NIOSH investigators generally 

encourage employers to use the lowest OEL when making risk assessment and risk 

management decisions. NIOSH investigators also encourage use of the hierarchy of controls 

approach to eliminate or minimize workplace hazards. This includes, in order of preference, 

the use of (1) substitution or elimination of the hazardous agent, (2) engineering controls 

(e.g., local exhaust ventilation, process enclosure, dilution ventilation), (3) administrative 

controls (e.g., limiting time of exposure, employee training, work practice changes, medical 

surveillance), and (4) personal protective equipment (e.g., respiratory protection, gloves, 

eye protection, hearing protection). Control banding, a qualitative risk assessment and risk 

management tool, is a complementary approach to protecting employee health. Control 

banding focuses on how broad categories of risk should be managed. Information on control 

banding is available at http://www.cdc.gov/niosh/topics/ctrlbanding/. This approach can be 

applied in situations where OELs have not been established or can be used to supplement 

existing OELs.

Erionite

Erionite is a naturally occurring mineral that belongs in a group of hydrated aluminosilicate 

minerals called zeolites [NTP 2011]. Erionite has three forms: erionite-Ca, erionite-Na, 

and erionite-K, each determined by the predominant element [Coombs et al. 1998; Dogan 

et al. 2008]. The International Agency for Research on Cancer has determined that there 

is sufficient evidence in humans to classify erionite as carcinogenic to humans, and that 

it causes mesothelioma [IARC 2004]. This determination was made primarily because of 

exposure studies of villagers in the Cappadocia region of Turkey, and did not examine the 

variability of the different forms of erionite. Extensive toxicological and epidemiological 

research has been done on exposure to erionite in the Cappadocia region of Turkey [Baris et 
Health Hazard Evaluation Report 2013-0061-3244 Page 21

al. 1978; Baris and Grandjene 2006; Carbone et al. 2007]. Pulmonary fibrosis and mesothelioma 

have been associated with people who live and work in areas of the western United States known 

to have erionite [Rom et al. 1983; Ilgren et al. 2008]. Dogan [2012] determined that erionite-K 

was positively identified in Oregon, Nevada, Germany, and the Cappadocia region of Turkey. 

Research on health effects of erionite-Na and erionite-Ca is sparse.

Airborne erionite fibers have no specific OELs. NIOSH has established an REL for asbestos 

of 0.1 fibers greater than 5 μm in length per cubic centimeter of air as determined in a sample 

collected over any 100-minute period at a flow rate of 4 liters per minute. In 1990, NIOSH 

revised the REL to include elongated mineral particles that also met the same length (> 5 μm) 

and aspect ratio (3:1 length:width) definition of asbestos and expanded the method to use 

NIOSH Method 7400 or equivalent (e.g., NIOSH Method 7402). The revised definition of 

airborne asbestos fibers did not explicitly encompass elongated mineral particles from other 

micro-fibrous minerals (e.g., erionite) that are known to be associated with health effects similar 

to those caused by asbestos [NIOSH 2011]. Therefore, for the purpose of this report, we use 

0.1 f/cc OEL only as a point of reference. Characterizing and minimizing potentially hazardous 

exposures until an evidence-based OEL for erionite is developed remains a necessity.

Respirable Crystalline Silica

Silica, or silicon dioxide, occurs in a crystalline or noncrystalline (amorphous) form. 

In crystalline silica, the silicon dioxide molecules are oriented in a fixed pattern versus 

the random arrangement of the amorphous form. The more common crystalline forms 

in workplace environments are quartz and cristobalite, and to a lesser extent, tridymite. 

Occupational exposures to respirable crystalline silica (quartz and cristobalite) have been 

associated with silicosis, lung cancer, pulmonary tuberculosis, and airway diseases. 

Silicosis is a fibrotic disease of the lung caused by the deposition of fine crystalline silica 

particles in the lungs. It is the disease most often associated with exposure to respirable 

crystalline silica. This lung disease is caused by the inhalation and deposition of crystalline 

silica particles that are 10 μm or less in diameter. Particles 10 μm and below are considered 

respirable particles and classified as having the potential to reach the lower portions of the 

human lung (alveolar region). Although particle sizes 10 μm and below are considered 

respirable, some of these particles can be deposited before they reach the alveolar region 

[Hinds 1999]. Symptoms of silicosis usually develop insidiously, with cough, shortness of 

breath, chest pain, weakness, wheezing, and nonspecific chest illnesses. Silicosis usually 

occurs after years of exposure (chronic), but may appear in a shorter period of time (acute) 

if exposure concentrations are very high. Acute silicosis is typically associated with a 

history of high exposures from tasks that produce small particles of airborne dust with a 

high silica content [NIOSH 1986]. Even though the carcinogenicity of crystalline silica in 

humans has been strongly debated in the scientific community, the International Agency 

for Research on Cancer in 1996 concluded that there was “sufficient evidence in humans 

for the carcinogenicity of inhaled crystalline silica in the form of quartz or cristobalite from 

occupational sources” [IARC 1997]. A NIOSH publication also lists several other serious 

diseases from occupational exposure to crystalline silica. These include lung cancer and 
Page 22 Health Hazard Evaluation Report 2013-0061-3244

noncarcinogenic disorders including immunologic disorders and autoimmune diseases, 

rheumatoid arthritis, renal diseases, and an increased risk of developing tuberculosis after 

exposure to the infectious agent [NIOSH 2002]. 

When proper practices are not followed or controls are not maintained, respirable crystalline 

silica exposures can exceed the OSHA PEL, NIOSH REL, or the ACGIH TLV. For general 

industry, the OSHA PEL for respirable dust containing 1% or more of quartz is calculated 

by dividing 10 milligrams per cubic meter (mg/m3) by the percent quartz in the sample, plus 

two [OSHA 2014]. NIOSH recommends an exposure limit of 0.05 mg/m3 as a TWA for up to 

a 10-hour work day to reduce the risk of developing silicosis, lung cancer, and other adverse 

health effects [NIOSH 2010]. The ACGIH TLV for quartz is 0.025 mg/m3, as an 8-hour TWA 

[ACGIH 2015].
Health Hazard Evaluation Report 2013-0061-3244 Page 23

Appendix C: Comparison of Erionite from the 

Custer National Forest with Erionites from 

Cappadocia, Turkey, and Rome, Oregon 

Morphological Differences

Figure C1a shows Euparal-mounted slide preparations of bulk rock material from Reva 

Gap, Custer National Forest (Arikaree Formation) and C1b shows similarly mounted slides 

from Karain, Cappadocia, Turkey, under phase-contrast microscopy at 400x magnification. 

In each case, a small quantity of the volcanic tuff was pressed between two glass slides to 

liberate individual mineral particles, but there was no aggressive attempt to pulverize the 

material. The particles liberated with the Custer National Forest fibers are long and thick, 

with a distinct appearance of being bundles. The Turkish particles, in contrast, are commonly 

shorter, thinner fibers, with an appearance of being single fibers, although under higher 

magnification they are comprised of bundles of finer fibers. Rome, Oregon, erionite particles 

(NIOSH research material) are similar in appearance to the Arikaree Formation particles at 

this level of magnification (not shown), but differences appear at higher magnification.

Figure C1. Using PCM to compare Custer National Forest (C1a) and Cappadocia, Turkey, (C1b) 

erionites. Photo by NIOSH.
Page 24 Health Hazard Evaluation Report 2013-0061-3244

Figure C2a shows high-resolution TEM images of the same Arikaree Formation material 

compared to erionite from Rome, Oregon, in Figure C2b. Many of the Arikaree Formation 

particles appear to consist of ribbon-like fibers approximately 0.1–0.15 μm in diameter, while 

the particles from Rome, Oregon, although they are of similar size, appear to be bundles of 

finer “fibrils” around 30–40 nanometers in diameter.

Figure C2. High resolution TEM image of C2a. Custer National Forest and C2b. Rome, Oregon, 

erionite fibers. Photo by NIOSH.

Figure C3. Field-emission scanning electron microscope image of C3a. Custer National Forest and 

C3b. Rome, Oregon erionite samples. Photo by NIOSH.

However, individual nanometer-scale fibers were found in all samples, including the Arikaree 

Formation material, as in the image in Figure C3, obtained with a field-emission scanning 

electron microscope.
Health Hazard Evaluation Report 2013-0061-3244 Page 25

Chemical Differences

Zeolites are a silicate structure where Al atoms can substitute for Si. Because the valency of Si is 

4 and Al only 3, cations such as Na, K, and Ca are incorporated in the aluminosilicate structure 

to level out the charge imbalance. All of the erionites we have examined from volcaniclastic 

sedimentary environments have ratios of Si to Al that are much higher than anticipated from 

published analyses of erionite crystals removed from vesicles in mafic volcanic rocks. A 

publication comparing 26 samples of erionite from mafic volcanic rocks from various regions 

across the globe shows that they have a tight range of ratios around an average of 2.6, which is 

compatible with the typical erionite formula of Si26Al10 [Passaglia et al. 1998]. However, all the 

sedimentary erionites we have analyzed (Cappadocia, Turkey; Rome, Oregon; Custer National 

Forest Arikaree; South Killdeer Mountain Arikaree; Reese River, Nevada) have a tight range of 

average ratios around 4.0, which is closer to a formula Si29Al7. Fewer cations are required for 

balance, but when these particles are analyzed very carefully by scanning TEM with EDS or 

electron microprobe with wavelength-dispersive spectroscopy, the cation content is found to be 

insufficient even to meet this lower requirement. Thus the minerals do not meet the cation-balance 

formula requirement for cations, and are likely balanced instead by acidic H+ ions.

Large variations in cation contents are found between different particles even in the same 

sample, so that large numbers of analyses are required to provide average cation contents for 

comparison between different samples. Differences exist in the average cation contents between 

sedimentary erionites from different sources, with erionite from Cappadocia, Turkey, having 

the largest total cation content [USGS 2010]. Differences also exist in the relative abundance 

of cations, with the erionite from Cappadocia, Turkey, having more Na and Ca than others. 

However, as noted, there is considerable variation (order of magnitude) between individual 

particle analyses, so that the range of cation contents in erionites from different sources has 

considerable overlap. A possible indicator of toxicity is iron. Iron is typically present at low 

levels (less than 1 percent by weight) in these particles, although individual particles can show 

high levels. Erionite from Rome, Oregon, has the highest average iron content, with a large 

proportion of particles having iron content in the percent range [Harper and Shvedova 2015]. 

Ballirano has suggested that nanometer-sized clusters of iron atoms on the exterior of Rome, 

Oregon, erionite particles may be a factor in the toxicity of that material [Ballirano et al. 2009]. 

Toxicity Differences

In preliminary NIOSH laboratory studies, toxicity differences between erionites from 

different sources have been seen. However, these experiments have involved whole rock. 

The erionite content of different rock samples varies dramatically, so that it is not possible 

to conclude at this time whether the observed differences in toxicity are due to differences in 

erionite dosage or even associated with the other minerals in the samples. For example, while 

the Custer National Forest Arikaree samples appear to have lower toxicity than samples from 

Rome, Oregon, on an equal rock weight basis, the weight percent erionite in Rome, Oregon, 

has been calculated to be around 15% while that in the Custer National Forest Arikaree is 

around 1% [Harper and Shvedova 2015]. Thus additional work with purified extracts will be 

required to fully interpret the results.
Page 26 Health Hazard Evaluation Report 2013-0061-3244

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Keywords: North American Industry Classification System 924120 (Administration of 

Conservation Programs), chemical, South Dakota, Montana, erionite, respirable crystalline 

silica, fireline maintenance
Health Hazard Evaluation Report 2013-0061-3244 Page 31

The Health Hazard Evaluation Program investigates possible health hazards in the workplace 

under the authority of the Occupational Safety and Health Act of 1970 (29 U.S.C. § 669(a)

(6)). The Health Hazard Evaluation Program also provides, upon request, technical assistance 

to federal, state, and local agencies to investigate occupational health hazards and to prevent 

occupational disease or injury. Regulations guiding the Program can be found in Title 42, Code 

of Federal Regulations, Part 85; Requests for Health Hazard Evaluations (42 CFR Part 85).

Disclaimer

The recommendations in this report are made on the basis of the findings at the workplace 

evaluated and may not be applicable to other workplaces.

Mention of any company or product in this report does not constitute endorsement by NIOSH.

Citations to Web sites external to NIOSH do not constitute NIOSH endorsement of the 

sponsoring organizations or their programs or products. NIOSH is not responsible for the 

content of these Web sites. All Web addresses referenced in this document were accessible as of 

the publication date.

Acknowledgments

Analytical Support: Alan Dozier, Martin Harper, and Bureau Veritas North America

Desktop Publisher: Shawna Watts 

Editor: Ellen Galloway 

Industrial Hygiene Field Assistance: Karl Feldmann, Greg Burr, and Donnie Booher

Logistics: Donnie Booher, Kevin Moore

Availability of Report

Copies of this report have been sent to the employer, employees, and union at the 

facility. The state and local health department and the Occupational Safety and Health 

Administration Regional Office have also received a copy. This report is not copyrighted 

and may be freely reproduced. 

This report is available at http://www.cdc.gov/niosh/hhe/reports/pdfs/2013-0061-3244.pdf.

Recommended citation for this report:

NIOSH [2015]. Health hazard evaluation report: evaluation of erionite and silica 

exposure during forestry activities. By Beaucham C, Harper M, King B, Dozier A. 

Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease 

Control and Prevention, National Institute for Occupational Safety and Health, NIOSH 

HHE Report No. 2013-0061-3244.
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