United States Prevention, Pesticides EPA712-C-96-037
Environmental Protection and Toxic Substances August 1996
Agency (7101)
&EPA Product Properties
Test Guidelines
OPPTS 830.7520
Particle Size, Fiber
Length, and Diameter
Distribution
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INTRODUCTION
This guideline is one of a series of test guidelines that have been
developed by the Office of Prevention, Pesticides and Toxic Substances,
United States Environmental Protection Agency for use in the testing of
pesticides and toxic substances, and the development of test data that must
be submitted to the Agency for review under Federal regulations.
The Office of Prevention, Pesticides and Toxic Substances (OPPTS)
has developed this guideline through a process of harmonization that
blended the testing guidance and requirements that existed in the Office
of Pollution Prevention and Toxics (OPPT) and appeared in Title 40,
Chapter I, Subchapter R of the Code of Federal Regulations (CFR), the
Office of Pesticide Programs (OPP) which appeared in publications of the
National Technical Information Service (NTIS) and the guidelines pub-
lished by the Organization for Economic Cooperation and Development
(OECD).
The purpose of harmonizing these guidelines into a single set of
OPPTS guidelines is to minimize variations among the testing procedures
that must be performed to meet the data requirements of the U. S. Environ-
mental Protection Agency under the Toxic Substances Control Act (15
U.S.C. 2601) and the Federal Insecticide, Fungicide and Rodenticide Act
(7U.S.C. I36,etseq.).
Final Guideline Release: This document is available from the U.S.
Government Printing Office, Washington, DC 20402 on The Federal Bul-
letin Board. By modem dial 202-512-1387, telnet and ftp:
fedbbs.access.gpo.gov (IP 162.140.64.19), internet: http://
fedbbs.access.gpo.gov, or call 202-512-0132 for disks or paper copies.
This guideline is available in ASCII and PDF (portable document format)
from the EPA Public Access Gopher (gopher.epa.gov) under the heading
"Environmental Test Methods and Guidelines."
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OPPTS 830.7520 Particle size, fiber length, and diameter distribu-
tion.
(a) Scope—(1) Applicability. This guideline is intended to meet test-
ing requirements of both the Federal Insecticide, Fungicide, and
Rodenticide Act (FIFRA) (7 U.S.C. 136, et seq.} and the Toxic Substances
Control Act (TSCA) (15 U.S.C. 2601).
(2) Background. The source materials used in developing this har-
monized OPPTS test guideline are the OPPT guideline under 40 CFR
796.1520 Particle Size Distribution/Fiber Length and Diameter Distribu-
tions and OECD guideline 110 Particle Size Distribution/Fibre Length and
Diameter Distributions.
(b) Introductory information. Method A: Particle size distribution
(effective hydrodynamic radius). Method B: Fiber length and diameter dis-
tributions.
(1) Prerequisites. Method A: Water insolubility. Method B: Informa-
tion on fibrous nature of product; Information on stability of fiber shape
under electron-microscopic conditions.
(2) Guidance information. Method A: Melting point. Method B:
Melting point.
(3) Qualifying statements. Both test methods can be applied to pure
and commercial grade substances.
(i) Method A: (A) This method can only be applied to water-insolu-
ble (<10-6 g/L), powdered type products.
(B) The equivalence of the six national and international standard
methods for particle size distribution was not tested, and is currently not
known. There is a particular problem in relation to sedimentation and
Coulter counter measurements.
(ii) Method B: This method applies only for fibrous products. The
effect of impurities on particle shape should be considered.
(4) Recommendations. Method A: Equivalence of the methods for
determination of particle size distribution should be tested in the labora-
tory.
(5) Standard documents. The "Effective Hydrodynamic Radius De-
termination" is based on the following standards (refer to paragraph (e)
of this guideline for more information):
(i) ASTM—D 3360, D422.
(ii) NF-T 30044.
(iii) DIN—66115.
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(iv)DIN—66116, part 1.
(v) ASTM—C 678.
(vi) ANSI—C 690-75.
and on a test principle described in Chemie Ingenieur Technik 146: 729
(see paragraph (e) of this guideline).
(c) Method—(1) Introduction, purpose, scope, relevance, applica-
tion and limits of test. (i)(A) Many methods are available for particle
size measurements, but none of them is applicable to the entire size range.
Sieving, microscopic sedimentation and elutriation techniques are most
commonly employed. Moreover, in the case of airborne particles (dusts,
smokes, fumes), radiation scattering and inertial methods prove particularly
useful. Finally, appropriate sampling procedures should be selected in
order to prepare specimens really representative of the material under test
(method A).
(B) The first method described in this guideline (method A) is de-
signed to provide information on the transportation and sedimentation of
insoluble particles in water and air. In the special case of materials which
can form fibers, an additional set of measurements (method B) is also
recommended to help identify potential health hazards arising from inhala-
tion or ingestion.
(C) Method A is generally applicable, frequent in use and hydro-
dynamic in character; method B is comparatively specialized, infrequently
required and involves microscopic examination. It should be borne in
mind, however, that the original particle size distribution is highly depend-
ent on the industrial processing methods used and can also be affected
by subsequent environmental or human transformations.
(D) These tests are applicable only to water insoluble (solubility <10-6
g/L) substances. Method B for fibers will be applied only if light micro-
scopic examination, similarities to known fibrous or fiber-releasing sub-
stances or other data indicate a likelihood that fibers are present. In this
context, a fiber is a water insoluble particle, of aspect ratio (length/diame-
ter) >3 and diameter <100 (im. Fibers of length <5 (im need not be consid-
ered. Method A, which determines the effective hydrodynamic radius, Rs,
will be used for both fibrous and nonfibrous particulates without prior in-
spection. It is useful only in the range 2 (im < Rs < 100 (im.
(ii) Definitions and units. (A) For method A the parameter of interest
is the effective hydrodynamic radius, or effective Stokes radius Rs. The
terminal velocity of a small sphere falling under the influence of gravity
in a viscous fluid is given by:
v = 2gRs2(di-d2)/9ri
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where
v = velocity (m/sec),
g = gravitation constant (m/sec2),
Rs = Stokes radius (m)
di = density of sphere (kg/m3),
d2 = density of fluid (kg/m3),
T| = dynamic viscosity (Nsec/m2 = Pa s) of the the fluid
(B) In other situations, similar relationships apply. Particle size is usu-
ally measured in micrometers (a micrometer = 10~6 m = (im).
(C) Method B provides histograms of the length (1) and diameter
(d) distributions of fibers. The ordinate is the absolute number of particles
in each interval of 1 or d. Typical plots are provided in figures 1 and
2 under paragraph (c)(l)(iv) of this guideline.
(iii) Reference substances. (A) Five reference substances of defined
particle size covering the overall range 0.35 to 650 (im (excepting the
50 to 200 (im region) have been certified with respect to the cumulative
mass distribution of particles versus equivalent settling rate diameter or
equivalent volume diameter. The materials will be made available from
the Community Bureau of Reference of the European Economic Commu-
nity and they will be issued with certificates of measurement. The certifi-
cation report under paragraph (e)(4) of this guideline will also be available
from the Community Bureau of Reference.
(7) The certification report of five reference materials will be avail-
able from: Commission of the European Community, Directorate—General
for Research, Science and Education, Community Bureau of Reference
BCR, rue de la Loi 200, B-1049 Brussels.
(2) Filter equipment for sample preparations according to method B
is available commercially through the following manufacturers:
(/) Nuclepore Corporation, 7035 Commerce Circle, Pleasanton, Cali-
fornia 94566.
(//) Millipore Corporation, Order Service Department, Bedford, Mas-
sachusetts 01730.
(///) Whatman Filters, W&R Balston Limited, England.
(B) Calibration materials—(7) Method A. A binary or ternary mixture
of latex spheres (2 (im < d < 100 (im) is suggested.
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(2) Method B. No standard reference materials are readily available.
(C) Evaluation materials—(7) Method A. A ternary mixture of latex
spheres, 2, 50, and 100 (im (which provides a discrete calibrated distribu-
tion) plus a sample of crushed quartz (continuous distribution).
(2) Method B. Fibrous chrysotile asbestos is recommended (specific
properties not essential as long as enough of a throughly mixed sample
is available for identical distribution in a ring test).
(iv) Principle of the test methods—(A) Method A. (7) There are sev-
eral standard methods available which meet the sensitivity requirements
(refer to paragraph (e) for more information):
Principle
Sedimentation
Centrifugation
Coulter counter
ASTM— D 3360, D 422,
ASTM— C 678 Chemie
ANSI-C 690-75.
Methods
NF-T 30044 DIN— 66-115
Ingenieur Technik 146' 729
(1 974)
(2) The comparability of these methods (especially the sedimentation)
and the other methods must be determined.
(3) The sample should also be subjected to a simple light microscopic
examination to determine the approximate nature of the particles (e.g,
plates, needles, etc.).
(B) Method B. Since data must be collected on small diameter fibers
(>0.1 (im), scanning electron microscope (SEM) or transmission electron
microscopy (TEM) is required. There is no standard procedure at present,
and those currently under development for asbestos contamination (in
which the fibrous material is already identified and in high concentration)
are often more complex and expensive than necessary for the needs of
this program. Extreme care must still be taken during sample preparation
to avoid fiber breaking, clumping and contamination. A simple initial pro-
cedure is suggested below (Description of the test procedures). The length
and diameter of the fiber images can be measured manually,
semiautomatically or automatically and the results tabulated in histogram
form (see the following figures 1 and 2):
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FIGURE i—SAMPLE FIBER LENGTH DISTRIBUTION (METHOD B)
FIGURE 2—SAMPLE FIBER DIAMETER DISTRIBUTION (METHOD B)
_
S
i-
BE
B,
Li.
o
EC
to
1,4 5.0
DIAMETER
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(v) Quality criteria—(A) Repeatability. (7) The effective hydro-
dynamic radius distribution (method A) should be measured three times,
with no two values differing by more than 20 percent.
(2) The length and diameter distributions of fibers (method B), if re-
quired, should be measured at least twice—using separate samplings and
preparations—with at least 70 fibers per histogram. No two values in a
given histogram interval should differ by more than 50 percent or 3 fibers,
whichever is larger. Such repeatability should be sufficient for the model-
ing and decision-making procedures currently envisaged; however, the
presence of long, thin fibers—due to their potential adverse health ef-
fects—would indicate a need for further, more precise measurements.
(B) Sensitivity. In the general case (method A) particles as small as
2 (im and as large as 200 (im must be measurable. The method requires
that sufficient numbers of radius intervals be used to resolve the radius
distribution curve. In the case of fibers (method B), diameters as small
as 0.2 (im and as large as 100 (im and lengths as small as 5 (im and
as large as 300 (im, must be measurable.
(C) Specificity. See paragraph (c)(l) of this guideline.
(D) Possibility of standardization. The method procedures can be
readily standardized, if desired, but nonuniformity of sampling, preparation
and prior handling may still cause considerable variation in results in meth-
od B.
(E) Possibility of automation. Automation or semiautomation of these
procedures if possible. Full automation of fiber 1 and d measurements and
analysis is also possible.
(2) Description of the test procedures—(i) Preparations—(A)
Method A. The small quantities used as samples must be representative
of product batches comprising many kilograms; therefore, sampling and
sample handling require great care. For example, small particles often form
agglomerates; therefore, sample pre-treatment (e.g., the addition of dispers-
ing agents, agitation, or low-level ultrasonic treatment) may be required
before the primary particle size can be determined. However, great care
must be taken to avoid changing the particle size distribution. In the case
of highly stable aggregates, a strict distinction between primary particles
and agglomerates is not always useful. Some representative sample prepa-
ration methods will be found in the standard procedures listed in Principle
of the test methods (method A) under paragraph (c)(l)(iv) of this guide-
line.
(B) Method B. Two simple sample preparation procedures (B-l, B-
2) for scanning electron microscopy can be suggested.
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(7) Sample preparation B-l. Suspend a given amount of sample
in 10-100 mL of filtered distilled or deionized water (the suspension
should be relatively light, not a slurry). Distribution of the particles in
suspension may be aided by use of a surfactant, such as small amounts
(~1 part/100) of absolute ethyl alcohol or a nonionic detergent. Suspension
of the powder is achieved by gentle hand agitation, vortex mixing or mag-
netic stirring. Filter the suspension directly onto a 47 mm diameter
Nuclepore® filter overlaying a 47 mm diameter Millipore® membrane fil-
ter housed in a 47 mm diameter Millipore® filter holder (Hydrosol, stain-
less) using gentle vacuum. Ensure that the powder has not precipitated
out of suspension. Depending on the size of particles of interest various
pore-sized filters may be used. The concentration of suspended particles
determines the amount filtered. A less concentrated suspension will give
a more even distribution of particles on the filter surface under paragraph
(e)(2) of this guideline. Remove the Nuclepore® filter from the filter hous-
ing, being careful not to disturb the particles on the surface. Place the
filter—particle-coated face upward—into a glass or plastic Petri dish con-
taining Whatmann No. 1 filter paper; cover Petri dish and store in a dry
box or under vacuum. When completely dried, the filter is cut into pieces
of appropriate size and mounted, filter face up, onto copper tape which
has been previously mounted onto an SEM specimen holder (using double
face tape). To ensure stickiness of the tape, preheat using infrared or simi-
lar heat source for 5 to 15 min. Trim the edge of the filter to fit the
SEM specimen holder.
(2) Sample preparation B-2. An alternate sample preparation meth-
od is the direct transfer of the dry powder onto copper tape (adhesive
electrical tape) which has been mounted onto a scanning electron micro-
scope (SEM) specimen holder. The powder may also be sprayed onto the
copper tape surface by using an atomizer or pipet equipped with a large
rubber bulb.
(ii) Test conditions and apparatus—(A) Method A. Ambient condi-
tions. Measuring apparatus for all methods are readily available. Pipets
and sedimentation balances are used for the sedimentation methods.
(B) Method B. (7) Contamination by air-borne fibers can be a prob-
lem. A hood or "clean room" should be used if available.
(2) A small electron microscope and support equipment are required.
(iii) Performance of the tests. (A) methods:
(7) Method A. To be selected from standard procedures listed above
(Principle of the test methods).
(2) Method B. Both preparation methods (B-l and B-2) provide a
particulate sample on filter paper or copper tape mounted on an SEM spec-
imen holder. This can then be examined in the SEM, or first coated with
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metal film using a sputtering device or vacuum evaporator. Representative
fields within the sample surface are photographed at various magnifica-
tions to yield a representative sample of the population of interest. (If de-
sired, energy dispersive X-ray analysis (EDXA) of representative par-
ticles—to check sample contamination—could be performed at this time.)
(B) Particle size distribution can be determined by measuring the
screen directly or from measurements on photographs. If the SEM is
equipped with an image analysis system, population statistics can be deter-
mined directly. Such measurements can be automated or semi-automated
when desired (see paragraph (e)(3) of this guideline). If the image indicates
the sample is too concentrated, repeat again with a more dilute solution.
(iv) Analysis. Measuring the physical parameters by different meth-
ods can result in somewhat different particle size distributions; therefore,
the measuring techniques used should always be reported. Representative
analysis methods are discussed in reference under paragraphs (e)(l)
through (e)(6) of this guideline, and the following "Summary of the Usual
Methods for the Determination of Particle Size and the Important Granular
Size Classes," (adapted from G. Miiller, Methoden der
Sedimentuntersuchungen, 1964, p. 303, Stuttgart, revised with appropriate
supplements):
8
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FIGURE 3.—SUMMARY OF METHODS
100 10 ; 1
0.1 0.01 J 0.001 mm 1 0.01|i
I ELECTRON-MICROSCOPE
1 ULTRA-MICROSCOPE
1 LIGHT MICROSCOPE AND UV LIGHT
MICRO-HARD LENS WITH SPECIAL SCALE } 1 „.».„««,.,.... 1
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PERFORATED SHEET METAL SIEVES
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HICROMESH-SieVES 1
j
1 1 1 SIEVING 1
200 63 20 6.3 2 0.2 0.02,.
ASTM 0 2862-70 ASTM 1921-63(75) , . ASTM 2947-74
ASTM 1705-61
ASTM 0 422-63(72)
DIN 19 683
NFX 11-507
GRAVITATIONAL !
, I
1
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INDEX GRAIN TEST SEDIMENTATION APPARATUS | 1 OHAVITATIONAL METHODS 1
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ASTM O 422-63(72)
BS 3406 PART 2: 1963
MFT 30-044
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BS 3406: PART 3: 1961
I
( J | OTHER METHODS |
I " "'
| . C 690-75 COULTER.COUNTER
i
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I i
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' 1 1 1 1 1 t. ____.
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(d) Data and reporting—(1) Data—(i) Method A: Data should be
obtained for 3 size ranges: >200 (im, <2(im and the region 2 to 200 (im.
Only in the latter range should the distribution curve be prepared. It should
have sufficient (im increments to resolve the curve (subpopulations). A
histogram presentation is required plus a statement on the weight percent
of material >200 (im and <2 (im.
(ii) Method B: Full length (1) and diameter (d) data are needed on
fibers of dimensions d > 0.1 (im and 1 > 5 (im. Two histogram distribu-
tions, based on examination of at least 50 fibers each, should be prepared.
For diameters, the ranges should be 0.1-0.5, 0.5-1.0, 1-2, 2-3, 3-5 (im
and >5 (im. For lengths they should be 0-5, 5-10, 10-15, 15-20, (im
(etc.). This is illustrated in figures 1 and 2 in paragraph (c)(l)(iv)(B) of
this guideline.
(2) Test report—(i) Method A: The following information should
be presented:
(A) Expected percent change of reported values in the future (e.g.,
variations between production batches).
(B) Sample preparation methods used.
(C) Analysis methods used.
(D) Approximate information on particle shape (e.g., spherical, plate-
like, needle shaped).
(E) Lot number, sample number.
(F) Suspending medium, temperature, pH.
(G) Concentration.
(H) Stoke's (effective hydrodynamic) radius Rs distribution for 2 <
Rs < 200 (im.
(I) Mean value and approximate "area" (percent) of any resolvable
peaks in Rs distribution.
(J) Percent of particles with Rs < 2 (im.
(K) Percent of particles with Rs > 200 (im.
(ii) Method B: The following information should be presented:
(A) Sample description, method description.
(B) Number of particles per field.
(C) Total number of fibers measured.
(D) 1, d distributions (histograms).
10
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(E) Mean value and approximate "area" (percent) of any resolvable
peaks in the Rs distribution.
(e) References. The following references should be consulted for ad-
ditional background material on this test guideline.
(1) Allen, T., Particle Size Measurement. (Chapman and Hall: Lon-
don, 1975).
(2) Irani, R.R., and Callis, C.F., Particle Size Measurement. Interpre-
tation and Application.
(3) Orr, S., and Dallavalle, J.M., Fine Particle Measurement.
(4) Certification Report on Particles of Defined Particle Size. (Com-
munity Bureau of Reference: Brussels, 1979).
(5) McGrath, P.P., and Ewell, J.B., "Application of Electron Micros-
copy to Problem of Particulate Contaminants in Food, Drugs and
Biologicals," Scanning Electron Microscopy, part III (1976).
(6) Symposium on Electron Microscopy of Microfibers, ed. Asher
I.M., and McGrath, P.P., Proceedings of the First FDA Office of Science
Summer Symposium, (August 23-25, 1976).
(7) Chemie Ingenieur Technik 146: 729 (1974).
(8) American Society for Testing and Materials, ASTM, 1916 Race
St., Philadelphia PA 19103. Annual Book of ASTM Standards (latest edi-
tion).
(9) British Standards Institution, BSI. American National Standards
Institute, Sales Department, 1430 Broadway, New York, NY 10018. Book
of British Standards (latest edition).
(10) Das 1st Norm., DIN. American National Standard Institute, Sales
Department, 1430 Broadway, New York, NY 10018. Book of British
Standards (latest edition).
(11) American National Standards Institute, ANSI, Sales Department,
1430 Broadway, New York, NY 10018. Book of British Standards (latest
edition).
(12) Organization for Economic Cooperation and Development,
Guidelines for The Testing of Chemicals, OECD 110, Particle Size Dis-
tribution/Fibre Length and Diameter Distributions, OECD, Paris, France.
11
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