United States
Environmental Protection
Agency
Industrial Environmental Research
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-82-063 Sept. 1982
Project Summary
Chemical Stabilizers for the
Control of Fugitive Asbestos
Emissions from Open Sources
Paul K. Ase, Roger Koch, and George Yamate
Quarried serpentinite, recently
found to contain asbestos, is used as
aggregate for surfacing secondary
roads. Emission concentrations of
0.6 x 106 to 8 x 10* fibers/m3 were
collected 20m downwind from a
serpentinite surfaced roadway. These
levels correspond to emission factors
of 34x1010 to 370x1010 fibers/km-
vehicle at vehicular traffic speed of
13.4 m/sec (30 mph).
Chemical treatments were tested
for controlling these asbestos emis-
sions. Laboratory tests were developed
for screening 51 candidate commer-
cial materials. Four of the most
promising were field tested. Asbestos
emission reductions of up to 90%
were achieved with chemical treat-
ments at application rates ranging
from $0.08/m2 to $0.25/m2. Similar
emission reductions were observed
with traffic speeds reduced to 6.7
m/sec (15 mph).
This Project Summary was devel-
oped by EPA's Industrial Environ-
mental Research Laboratory, Cincin-
nati. OH. to announce key findings of
the research project that is fully
documented in a separate report of the
same title (see Project Report ordering
information at back).
Introduction
Quarried serpentinite crushed stone
is the major source of crushed stone
where it is readily available and in
localities where access to limestone is
limited. Limestone is preferred because
it is a sedimentary material, and
therefore has better weathering prop-
erties. Serpentinite is used as road
aggregate material for parking lots,
driveways, and country roads. It is also
used as base course for highways, as
concrete aggregate, and as binder filler
for asphalt paving. Serpentinite rock
formations occur at or near the earth's
surface in many regions of eastern
United States. Belts of serpentinite
extend from Maine to Alabama, covering
much of the Appalachian Moutains.
Serpentinite is native to extensive
regions of the western United States
also.
The bulk of serpentinite quarried in
the United States for crushed stone is
made up of antigorite. However, chryso-
tile, tremolite, deweylite, talc, antho-
phyllite, and other silicate minerals
have been reported to occur in serpen-
tinite. Dustfall collected along roads and
trails in a western recreational area
located over a serpentinite massif
contained 90 percent chrysotile. On the
other hand, the average concentrations
of asbestos in quarried serpentinite
crushed stone ranged from 10 * 1010
fibers/g to 100 * 10'° fibers/g, repre-
senting roughly 0.1 to 1% by weight
asbestos in the quarried stone.
The erosive action of vehicular
passage is much more intensive than
the action of wind alone. The large dust
plume in the wake of an automobile on a
dirt road gives visible demonstration to
the intense dust generating forces that
accompany vehicular traffic on unpaved
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roadways (See Figure 1). The mechan-
ical action of the tires on the road
surface kicks up dust particles and
places them directly into suspension.
The simultaneous turbulence of vehic-
ular movement adds more suspension
in the wake. Large dust plumes are
formed which are easily dispersed by
the faintest air currents.
On unpaved crushed stone roadways,
the pressure of vehicular tires on the
road surface applies an intense grinding
action on the unbound rock which
replenishes the fines lost to suspension.
Since the effect of vehicular traffic is
much more severe than the action of
wind alone, the amount of stabilizer
material needed to control roadway
emissions is also much greater than
that required to control wind erosion.
The present program was undertaken
to determine the extent to which dust
control agents might provide control
over asbestos emissions from the use of
crushed serpentinite rock on unpaved
roadways. Laboratory tests were devel-
oped to screen control agents and levels
of their application. In all, 69 materials
were considered. Of these, 51 were
screened in the laboratory tests. Three
levels of application, based on cost of
control agents, were tested. Transmis-
sion electron microscope (TEM) analysis
of air samples collected near the
roadway were used to evaluate the
effectiveness of four of the most
promising control agents in field appli-
cations.
Conclusions
Serpentinite is native to many parts of
eastern and western United States.
Serpentinite rock in some of these
regions is quarried and is used locally as
aggregate for surfacing material on
secondary roads. The quarried ser-
pentinite is known to contain asbestos.
Chemical stabilizers were tested for
controlling asbestos emission from
unpaved roadways surfaced with crushed
serpentinite. Significant asbestos emis-
sions over background levels were
measured on the untreated roadway.
Emission factors of 34 x 1010 to 370 x
1010 fibers/km-vehicle were reached
for a vehicular traffic speed of 13.4
m/sec (30 mph). These emission
generation levels corresponded to
ambient concentrations of 0.6 x 106 to 8
x 106 f/m3 at 20 m downwind from the
road. Fiber emission reductions of 80 to
90 percent were achieved with chemical
treatment. Similar reductions were
Figure 1. Large dust plume in the
wake of an automobile on a
serpentinite crushed stone
road.
achieved with reduction in traffic speed
to 6.7 m/sec (15 mph).
The asbestos emissions were essen-
tially all chrysotile asbestos. The
observed fibers were all in the respirable
range and averaged <0.1 fjm indiameter
and <2 //m in length. The emission
fibers were classified in terms of four
structural forms: individual fibers,
matrices, bundles, and clusters. The
fiber structures found in the roadway
emissions were mostly either single
fibers or fibers attached to rock matrix
material. Very few bundles or clusters of
fibers were found. Fiber structures
found in the emission from the untreated
roadway section and the treated roadway
sections were indistinguishable.
Respirable emission levels were
much lower than projected from the
concentration of asbestos fibers in the
dust from fresh quarry crushed aggre-
gates. This may be due, in part, to the
manner in which the serpentinite tends
to break up along asbestos-containing
seams during crushing. It may also be
due, in part, to the presence of larger
aggregates in which the fibers are still
bound and not released.
The field-tested treatments showed
that they were each capable of control-
ling asbestos emissions. The treatment
choice would depend on a number of
factors including: availability of treat-
ment, equipment on hand, and local
climatic conditions. More extensive
testing could be used to refine application
strategies. These should be tailored to
the physical nature of the individual
treatments and anticipated local condi-
tions. Under the most severe weather
conditions, traffic controls could also be
used to hold down emissions. Alterna-
tively, significant emissions reductions
might be achieved by removing the
initial fines from the freshly produced
aggregates.
Methodology
There is no data on the comparative
effectiveness of stabilizers for the
present application, i. e., to control
emission of asbestos from crushed
stone roadways. Stabilizers were se-
lected from those which showed prom-
ise in other applications such as soil
stabilizers, as palliatives for treatment
of unpaved roadways, and for application
on asbestos waste piles, as well as other
more recent commercial materials. Of
69 chemical agents originally selected,
51 were laboratory tested.
A number of desirable properties for
chemical agents are needed for them to
act as effective stabilizers including low
application cost, water solubility, high
bondability to the particles, long life and
stability, resistant to heat and cold,
nonphytotoxicity, biodegradability, no
drainage water pollution problems,
ease of cleaning from application
devices, and effectiveness at low
dilutions. In addition, for roadway use it
would be useful for the chemical agents
to have a regenerative capacity in order
to maintain control action in spite of the
continual generation of fresh particu-
lates from the pulverization of surface
materials.
The stabilizer cost was used as a basis
for comparing stabilizer effectiveness in
the laboratory tests. Application rates of
$0.01/m2, $0.05/m2, and $0.25/m2
were selected. These rates were based
on bulk material prices and the amount
of each material required for a 1 m2 x
2.54 cm (1 in.) deep application.
Laboratory Tests
In the laboratory screening tests, the
main emphasis was placed on the
measurements of treatment control
effectiveness. Ball milling was selected
to simulate the wear action of vehicular
traffic over crushed stone road beds,
and the fine fractions, measured by
sieve analysis, were used to determine
stabilizer effectiveness. The overall
laboratory test procedure used a series
of six consecutive steps:
1. Sample Preparation — Weighing
and Drying,
2. Initial Sieve Analysis,
3. Treatment Application,
4. Rain Cycling,
5. Traffic Simulation, and
6. Final Sieve Analysis.
The treatment effectiveness of each
stabilizer treatment was calculated as
the weight fraction of fines <140 mesh
found in each sample after the traffic
simulation compared to the weight
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fraction of fines <140 mesh found
initially in each sample. The treatment
effectiveness is referred to here as the
Treatment Score (TS):
TS _ Final Wt % <140 mesh
Initial Wt % <140 mesh
where the Wt % is based on the total dry
sample weight. The treatment effec-
tiveness, TS (treatment), is further
normalized by comparison with the
treatment effectiveness of the control,
TS (control), treated with water only.
The value for the normalized treatment
effectiveness is referred to as Relative
Treatment Score (RTS):
TS (treatment)
Wind
TS (control)
The RTS is the ratio of the treatment
effectiveness for a particular stabilizer
at a selected treatment level (e.g.,
$0.01 /m2, $0.25m2) compared to the
effectiveness with only water (control).
The value for TS (control) was calculated
from the average of randomly selected
control samples.
Field Tests
Four of the most highly ranked
laboratory treatments were selected for
field testing: Coherex (oil byproduct
emulsion), SS-1H (asphalt emulsion),
Liquidow (aqueous calcium chloride),
and Orzan GL-50 (ammonium liquo-
sulfonate). These treatments were
applied on the roadway and upwind and
downwind high volume air sampling
stations were positioned to collect
emissions. The collected high volume
filter samples were analyzed by trans-
mission electron microscope (TEM)
methods for ambient air asbestos.
A public secondary road in Maryland,
surfaced with crushed serpentinite,
was selected for field testing. The
crushed serpentinite rock used on the
road was produced locally. This aggre-
gate material is used on approximately
60 miles of unpaved secondary roads
throughout the country. Fresh crushed
serpentinite, crusher No. 6 (~<7.5 cm)
was applied during the summer along a
5OO-m field test section.
The field treatments were applied
in the fall. A section of roadway was
prepared for each of the four treatments
and a fifth was used as a control section
with no treatment, as shown in Figure
2. Applications were made with readily
available road working equipment: a
water sprinkler truck and a road grader.
The grader was used to serape the road
surface to a depth of 2.5 cm (1 in.), and
this was done just before each treatment
UpwindSamp/ing Sites D-
--D
6
N
t
5.
-+ j I\|\\\N t,
Test Sections
4. 3.
\v\\N_-
Holy Cross Road Ammonium Coherex
Lignosulfonate 20m
twnwind Sampling Sites d
5
-D--
30m
2.
-i\\\\TLi\\\\s/ _
QJI Calcium
EmulsionChloride
--D D--
432
1.
fs ^ x \ \N
Control
--D
'
Weather O ' <
Station
Figure 2. Field test sections on crushed serpentinite roadway, each 5.5m x 67.5m.
Table 1. Comparison of Laboratory and Field Application Rates.
Application Rate
Laboratory
Treatment
Coherex (oil byproduct emulsion)
SS-1H (asphalt emulsion)
Liquidow (calcium chloride)
Orzan GL-50 (lignosulfonate)
1/m2
1.8
2.3
7.2
7.2
(gal. /yd2)
(0.4)
(0.5)
(1.6)
(1.6)
Field
1/m2*
1.5
2.3
2.3
2.3
(gal. /yd2)
(0.33)
(0.5)
(0.5)
(0.5)
*Treatments were diluted for ease of application and applied at the rate of 4.5 1/m2 (1
gal./yd2) of the diluted treatment.
application. The treatment and their
application rates are shown in Table 1.
The test sections, each 67.5 m (220ft)
long and 5.6 m (18.5 ft) wide, were
separated by 23 m (75 ft) long inhibited
sections on which the emulsion oil was
applied to minimize "cross talk" between
the sections. (Figure 3.)
All treatments, except the SS-1H,
emulsion oil, were applied from the
water truck. All treatments were made
as single applications. The amount
needed for a 2.5 cm (1 inch) depth was
mixed for each test area in the sprinkler
truck and applied through a sprinkler
bar. Between 6 to 10 passes of each
treatment were used to get uniform
application and to permit the treatments
to soak in. (Figure 4).
After each treatment application, the
grader was used to mix the treatment
into surface layer by blading. (Figure 5).
In this operation the wetted, treated
aggregates were bladed to the center of
the road from each side. Then the
central pile was spread out and a crown
formed in the middle of the road. (Figure
6). This procedure was used to provide
intimate mixing of the aggregates with
the treatment. Several additional passes Figure 4. Application of a treatment
were then made by the grader to roll out from the water truck to a test
the surface. section.
Figure 3. Emulsion oil application to
minimize "cross talk"
between test sections.
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Figure 5. Grader used to mix the treat-
ment into surface layer by
blading.
Figure 6. Central pile spread out to
provide intimate mixing of
the aggregates with the
treatment.
Upwind/downwind air samples were
collected immediately after application
of treatments and six months later, in
the spring. These ambient air samples
were collected with high volume sam-
plers on 20.3 cm x 25.4 cm membrane
filters. The downwind high volume
samplers were located 20 m downwind
of the road centerline and aligned with
the average wind direction through the
middle of each roadway test section.
Two upwind stations were located 30 m
upwind of the roadway, 150 m apart. At
the beginning and end of each run high
volume sampler flow rates were verified
with a magnehelic gauge calibrated
with a high volume air sample calibrator.
Meterological information was obtained
continuously from a recording weather
station which was located in an open
field 40 m south of the control section.
The instrument readout was used to
align the sampling stations with the test
sites and the current average wind
direction. Tests were conducted only
when the average wind direction was
perpendicular to the roadway.
Ambient air samples were collected
on membrane filters. The bulk of the
samples were collected on 0.4 /um pore
diameter polycarbonate membrane
filters. In addition, 0.8 fjm pore size
cellulose mixed ester membrane filters
were used to collect emission from the
control section in parallel with the
polycarbonate filter samplers. A What-
man 41 cellulose filter was used as a
backup support filter for each membrane
filter. At the end of each run, filter
sections were stored in 150 mm petri
dishes and returned to the laboratory for
analysis.
The filter samples were prepared and
analyzed in accordance with EPA's
provisional methodology for ambient air
asbestos. The EM grid samples were
examined with a JEOL 100C analytical
electron microscope in the Transmission
Electron Microscope (TEM) mode. Grid
samples were screened initially under
low magnification by TEM to determine
suitability for further examination. In this
inspection the grid was examined for
loading, uniformity, lack of processing
contamination, adequacy of clearing,
and damage. Inadequate grids were
either reprocessed or discarded and
reprepared from another filter section.
Acceptable prepared samples were
examined at a 20.000X magnification
for chrysotile and amphibole asbestos
fibers. Fibers with length to width ratios
of greater than 3:1 and substantially
parallel sides were recorded. The fibers
were classified as:
• chrysotile asbestos
• amphibole asbestos
• ambiguous (incomplete spot pat-
tern)
• non-asbestos (definitely some
other mineral)
• no pattern (unknown, no spot
pattern).
Fibers were classified based on mor-
phology and recognition of selected area
electron diffraction (SAED) pattern.
TEM morphology and SAED patterns
from standard samples were used as
guides for fiber identification. Fibers
showing the tubular structure of chry-
sotile are tentatively classified as
chrysotile but morphological features
alone are not sufficient to distinguish
chrysotile and amphibole from other
fibrous minerals. A recognizable SAED
pattern is used to confirm identification.
Pattern recognition is not always easy
for ambient air samples which can
include interference from nearby part-
icles and attached aggregates. Due to
the very light fiber loading encountered
in the field samples, the procedures for
counting at low loading levels were
followed. The entire grid opening was
scanned and the entire grid openinc
was considered as a single field. Each
grid opening was scanned in a series ol
parallel scans across the grid until a
total of 10 grid openings or 100 total
fibers were counted, whichever occurred
first. In the roadway emission samples,
fibers were identified in several contexts
with other particulates, not currently
considered under the provisional meth-
odology.
These were characterized as asbestos
structures. The effective concentration
and desposition pattern in the respiratory
system will be affected by the asbestos
content and on the aerodynamic size of
individual asbestos structures. The
individual "fiber" is a form of asbestos
structure which is isolated from all
other particulates. The other structural
forms are "bundles", "clusters", and
"matrices", by themselves or in com-
binations. A bundle is a single entity
composed of fibers in a parallel ar-
rangement with each fiber closer
together than one fiber diameter. A
cluster is a single entity composed of
numerous fibers in random orientation
with all other fibers intermixed in a
single group. A matrix is a fiber with one
end free and the other end embedded in
some other material. Each of these
asbestos structures were included as
single asbestos entities in the analysis
for asbestos fibers, provided it met the
test for asbestos by morphology and
SAED pattern.
Results
The transmission electron microscope
was used as the principal analytical tool
for the field sample measurements. In
general, the filter loadings were all very
light. The asbestos fiber concentrations
on a count basis were mainly all
chrysotile. The overall amphibole fiber
concentration was <3 percent. While
the amphiboles found were all single
fibers, chrysotile occurred about equally
as single fibers and as matrix fibers.
Bundles and clusters were only occa-
sionally observed.
The asbestos emissions concentra-
tions from the road were determined as
the difference between upwind and
downwind concentrations based on the
TEM fiber counts. These observed levels
of asbestos concentrations were used to
estimate emission factors. In the control
section, the emission factor (f/km-
vehicle) varied from 32 x 10'° to 370 x
1010 fibers/km-vehicle corresponding
to net emission concentrations of 0.6 x
-------
10e to 7.7 x io» fibers/m2. The lowest
levels were collected in mid-fall just
after treatment application while the
highest levels were collected during the
following spring. With chemical treat-
ment, overall fiber emission reductions
of 80 to 90 percent were achieved.
Two stabilizer mechanisms for asbes-
tos emission control were identified:
1) Stabilizer which forms a solid,
water resistant surface coating
and binds road aggregates togeth-
er — This type is represented by
SS-1H and Coherex, both of which
are petroleum byproducts. After 6
months, they still retained better
than 80 percent emission reduction
when applied at the level of
$0.20/m2 to $0.25/m2.
2) Stabilizer which forms a water
soluble surface matrix which
binds surface particles together —
This type may not control aggregate
wear as well as the first, but is
able to rewet new particulates and
repair worn surfaces to minimize
emission. This type is represented
by Liquidow (calcium chloride) and
Orzan GL-50 (ligno-sulfonate).
The first is hygroscopic and main-
tains a high moisture presence in
the road surface. The second fills
the voids and can be redispersed
by precipitation. These showed
little emission control after 6
months when applied at the rate of
$0.08/m2, but periodic reapplica-
tion can be used to maintain
emission control.
Essentially all of the asbestos found in
the downwind air samples were within
the respirable range, (<3.5 /urn in
aerodynamic diameter). A large fraction
of the fibers were still attached to matrix
particulates. This suggests that the
fibers in serpentinite, which occur in
thin veins and bundles, are in intimate
association with the matrix rock but are
easily separated into small, thin fibers
which are then emitted.
However, the concentration of asbes-
tos collected from the control section
emissions were much lower than
expected based on the level of fines in
the road surface aggregates and the on
average concentration of asbestos
found in fresh quarried crushed stone.
Several factors may contribute to this
reduced level of asbestos emissions
found.
When fresh aggregate is laid on the
road, the fiber release may be relatively
high. However, the original free fibers
may soon be depleted by being emitted
into the air or by being washed away.
When subsequent grinding of the larger
aggregates replaces the original fines
with others which contain reduced
concentrations of asbestos, the long-
term asbestos emissions from the road
will be reduced correspondingly.
Those fibers buried in the aggregates
could not be identified and were not
counted. Thus, the presence of these
fibers would not be evident under EM
analysis. Also, much of the fugitive dust
ejected from an unpaved road are large
particulates, which deposit close to the
edge of the road. Fibers bound in such
large particles did not reach the
samplers and thus were also excluded
from analysis.
Paul K. Ase, Roger Koch, and George Yamate are with IIT Research Institute.
Chicago, IL 60616.
Mary K. Stinson is the EPA Project Officer (see below).
The complete report, entitled "Chemical Stabilizers for the Control of Fugitive
Asbestos Emissions from Open Sources," (Order No. PB 82-249 905; Cost:
$9.00. subject to change) wilt be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Industrial Pollution Control Division
Industrial Environmental Research Laboratory—Cincinnati
U.S. Environmental Protection Agency
Edison, NJ 08837
. S. GOVERNMENT PRINTING OFFICE: 1982/659-095/539
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