United States Prevention, Pesticides EPA712-C-98-201
Environmental Protection and Toxic Substances August 1998
Agency (7101)
&EPA Health Effects Test
Guidelines
OPPTS 870.3200
21/28-Day Dermal
Toxicity
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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, chap-
ter I, subchapter R of the Code of Federal Regulations (CFR), the Office
of Pesticide Programs (OPP) which appeared in publications of the Na-
tional Technical Information Service (NTIS) and the guidelines published
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. 136, etseq. ).
Final Guideline Release: This guideline is available from the U.S.
Government Printing Office, Washington, DC 20402 on disks or paper
copies: call (202) 512-0132. This guideline is also available electronically
in PDF (portable document format) from EPA's World Wide Web site
(http://www.epa.gov/epahome/research.htm) under the heading "Research-
ers and Scientists/Test Methods and Guidelines/OPPTS Harmonized Test
Guidelines."
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OPPTS 870.3200 21/28-Day dermal toxicity.
(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 material used in developing this har-
monized OPPTS test guideline are OPP 82-2 21-Day Dermal (Pesticide
Assessment Guidelines, Subdivision F—Hazard Evaluation; Human and
Domestic Animals) EPA report 540/09-82-025, 1982; and OECD guide-
line 410 Repeated Dose Dermal Toxicity: 21-28 Day.
(b) Purpose. A 21/28 day repeated dose dermal study will provide
information on possible health hazards likely to arise from repeated dermal
exposure to a test substance for a period of 21/28 days. This study is
not capable of determining those effects that have a long latency period
for development (e.g., carcinogenicity and life shortening). Extrapolation
from the results of this study to humans is valid only to a limited degree.
It can, however, provide useful information on the degree of percutaneous
absorption, target organs, the possibilities of accumulation, and can be of
use in selecting dose levels for longer-term studies and for establishing
safety criteria for human exposure.
(c) Definitions. The definitions in section 3 of the Toxic Substance
Control Act (TSCA) and the definitions in 40 CFR Part 792—Good Lab-
oratory Practice Standards apply to this test guideline. The following defi-
nitions also apply to this test guideline.
Cumulative toxicity is the adverse effect of repeated doses occurring
as a result of prolonged action or increased concentration of the adminis-
tered test substance or its metabolites in susceptible tissues.
Dose in a 21/28 day repeated dose dermal study is the amount of
test substance applied daily to the skin for 21/28 days. Dose is expressed
as weight of the test substance (grams, milligrams), or as weight of the
test substance per unit body weight of test animal (milligrams per kilo-
gram), or as weight of test substance per unit of surface area (milligrams
per square centimeter)
No-observed-effect level (NOEL) is the maximum dose used in a
study which produces no adverse effects. The NOEL level is expressed
in terms of the weight of a test substance given daily per unit weight
of test animal (milligrams per kilogram per day).
Repeated dose dermal study is used to embrace the toxic effects asso-
ciated with repeated doses of a chemical over part of a life span of the
test animal. Dosing periods lying between a single dose and 10 percent
of life span are often referred to as subacute. The term subacute is semanti-
cally incorrect. To distinguish such a dosing period from the classical sub-
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chronic period, it may be described as short-term repeated dose study.
Study durations have been 14, 21, or 28 days.
Target organ is any organ of a test animal showing evidence of an
effect induced by a test substance.
(d) Limit test. If a test at one dose level of at least 1,000 mg/kg
body weight (expected human exposure may indicate the need for a higher
dose level), using the procedures described for this guideline, produces
no observable toxic effects, or if toxic effects would not be expected based
upon data on structurally related compounds, a full study using three dose
levels might not be necessary.
(e) Test procedures—(1) Animal selection—(i) Species and strain.
A mammalian species should be used for testing. The rat, rabbit, or guinea
pig may be used. Commonly used laboratory strains should be employed.
If other mammalian species are used, the tester should provide justifica-
tion/reasoning for their selection. When a subchronic dermal study is con-
ducted as a preliminary to a chronic study, the same species and strain
should be used in both studies.
(ii) Age. (A) Testing should be started with young healthy animals
as soon as possible after weaning and acclimatization.
(B) Dosing should generally begin in guinea pigs between 5-6 weeks
of age, in rats between 8-9 weeks of age, and in rabbits at least 12 weeks
old.
(C) At the commencement of the study, the weight variation of ani-
mals used should not exceed 20 percent of the mean weight for each sex.
(iii) Sex. Equal numbers of animals of each sex with healthy skin
should be used at each dose level. The females should be nulliparous and
nonpregnant except for specially designed studies.
(iv) Numbers. (A) For studies where the data will form the definitive
basis for a risk assessment, e.g., where a NOEL for risk assessment is
needed, 10 animals/sex/dose will be needed. For screening studies, 5 ani-
mals/sex/dose will generally be sufficient.
(B) If interim sacrifices are planned, the number should be increased
by the number of animals scheduled to be sacrificed before completion
of the study.
(C) To avoid bias, the use of adequate randomization procedures for
the proper allocation of animals to test and control groups is required.
(D) Each animal must be assigned a unique identification number.
Dead animals, their preserved organs and tissues, and microscopic slides
should be identified by reference to an animal's unique number.
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(v) Husbandry. (A) Animals should be housed in individual cages.
(B) The temperature of the experimental animal rooms should be at
22 + 3 °C for rodents and 20 + 3 °C for rabbits.
(C) The relative humidity of the experimental animal rooms should
be 30 to 70 percent.
(D) Where lighting is artificial, the sequence should be 12 hours light/
12 hours dark.
(E) Control and test animals should be fed from the same batch and
lot. The feed should be analyzed to assure adequacy of nutritional require-
ments of the species tested and for impurities that might influence the
outcome of the test. For feeding, conventional laboratory diets may be
used with an unlimited supply of drinking water.
(F) The study should not be initiated until animals have been allowed
a period of acclimatization/quarantine to environmental conditions, nor
should animals from outside sources be placed on test without an adequate
period of quarantine. An acclimation period of at least 5 days is rec-
ommended.
(2) Control and test substances, (i) Where necessary, the test sub-
stance is dissolved or suspended in a suitable vehicle. If a vehicle or dilu-
ent is needed, the vehicle should not elicit toxic effects or substantially
alter the chemical or toxicological properties of the test substance. It is
recommended that, whenever possible, the usage of an aqueous solution
be considered first, followed by consideration of a solution of oil and then
solution of other vehicles.
(ii) One lot of the test substance should be used, if possible, through-
out the duration of the study, and the research sample should be stored
under conditions that maintain its purity and stability. Prior to the initiation
of the study, there should be a characterization of the test substance, in-
cluding the purity of the test compound and if technically feasible, the
name and quantities of unknown contaminants and impurities.
(iii) If the test substance is dissolved or suspended in a vehicle, the
period during which the test substance is stable in such a mixture should
be determined prior to the initiation of the study. Its homogeneity and
concentration should be determined prior to the initiation of the study and
periodically during the study. Statistically randomized samples of the mix-
ture should be analyzed to ensure that proper mixing, formulation, and
storage procedures are being followed, and that the appropriate concentra-
tion of the test or control substance is contained in the mixture.
(3) Control groups. A concurrent control group is required. This
group should be an untreated or sham-treated control group or, if a vehicle
is used in the application of the test substance, a vehicle control group.
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If the toxic properties of the vehicle are not known or not available, both
untreated/sham-treated and vehicle control groups are required.
(4) Satellite group. A satellite group of 20 animals (10 animals per
sex) may be treated with the high-dose level for 21/28 days and observed
for reversibility, persistence, or delayed occurrence of toxic effects for a
post-treatment period of 14 days. In addition a control group of 20 animals
(10 animals of each sex) should be added to the satellite study.
(5) Dose levels and dose selection, (i) For the repeated dose study,
it is desirable to determine a dose-response relationship as well as a
NOEL. Therefore, at least three dose levels plus a control and, where ap-
propriate, a vehicle control (corresponding to the concentration of vehicle
at the highest-dose level) group should be used. Doses should be spaced
appropriately to produce test groups with a range of toxic effects. The
data should be sufficient to produce a dose-response curve.
(ii) The highest-dose level should result in toxic effects but not
produce severe skin irritation or an incidence of fatality which would pre-
vent a meaningful evaluation. If application of the test substance produces
severe skin irritation, the concentration may be reduced, although this may
result in a reduction in, or absence of, other toxic effects at the high-
dose level. If the skin has been badly damaged early in the study, it may
be necessary to terminate the study and undertake a new one at lower
concentrations.
(iii) The intermediate dose levels should be spaced to produce a gra-
dation of toxic effects.
(iv) The lowest-dose level should not produce any evidence of toxic
effects.
(6) Preparation of animal skin. Fur should be clipped from not less
than 10 percent of the body surface area shortly before testing for applica-
tion of the test substance. In order to dose approximately 10 percent of
the body surface, the area starting at the scapulae (shoulders) to the wing
of the ileum (hipbone) and half way down the flank on each side of the
animal should be shaved. Shaving should be carried out approximately
24 hours before the test. Repeated clipping or shaving is usually needed
at approximately weekly intervals. When clipping or shaving the fur, care
should be taken to avoid abrading the skin (which could alter its per-
meability).
(7) Preparation of test substance, (i) Liquid test substances are gen-
erally used undiluted, except as indicated in paragraph (e)(5)(ii) of this
guideline.
(ii) Solids should be pulverized when possible. The substance should
be moistened sufficiently with water or, when necessary, a suitable vehicle
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to ensure good contact with the skin. When a vehicle is used, the influence
of the vehicle on toxicity of, and penetration of the skin by, the test sub-
stance should be taken into account.
(iii) The volume of application should be kept constant, e.g. less than
300 (iL for the rat; different concentrations of test solution should be pre-
pared for different dose levels.
(8) Administration of test substance, (i) The duration of exposure
should be at least for 21/28 days.
(ii) The animals should be treated with test substance for at least 6
h/day on a 7-day per week basis. However, based on practical consider-
ations, application on a 5-day per week basis is acceptable. Dosing should
be conducted at approximately the same time each day.
(iii) The test substance should be applied uniformly over the treatment
site.
(iv) The surface area covered may be less for highly toxic substances.
As much of the area should be covered with as thin and uniform a film
as possible.
(v) During the exposure period, the test substance should be held in
contact with the skin with a porous gauze dressing (less than or equal
to 8 ply). The test site should be further covered with nonirritating tape
to retain the gauze dressing and the test substance and to ensure that the
animals cannot ingest the test substance. Restrainers may be used to pre-
vent the ingestion of the test substance, but complete immobilization is
not recommended. The test substance may be wiped from the skin after
the six-hour exposure period to prevent ingestion
(9) Observation period. The animals should be observed for a period
of 21/28 days. Animals in the satellite group, (if one is used) scheduled
for follow-up observations should be kept for at least 14 days further with-
out treatment to assess reversibility.
(10) Observation of animals, (i) Observations should be made at
least twice each day for morbidity and mortality. Appropriate actions
should be taken to minimize loss of animals to the study (e.g., necropsy
or refrigeration of those animals found dead and isolation or sacrifice of
weak or moribund animals).
(ii) A careful clinical examination should be made at least once prior
to the initiation of treatment (to allow for within subject comparisons) and
once weekly during treatment in all animals. These observations should
be made outside the home cage, preferably in a standard arena, and at
similar times on each occasion. Effort should be made to ensure that vari-
ations in the observation conditions are minimal. Observations should be
detailed and carefully recorded, preferably using scoring systems, explic-
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itly defined by the testing laboratory. Signs noted should include, but not
be limited to, changes in skin, fur, eyes, mucous membranes, occurrence
of secretions and excretions and autonomic activity (e.g., lacrimation,
piloerection, pupil size, unusual respiratory pattern). Changes in gait, pos-
ture and response to handling as well as the presence of clonic or tonic
movements, stereotypies (e.g., excessive grooming, repetitive circling) or
bizarre behavior (e.g., self-mutilation, walking backwards) should be re-
corded.
(iii) Once, near the end of the exposure period and in any case not
earlier than in week 3/4, assessment of motor activity, grip strength, and
sensory reactivity to stimuli of different types (e.g., visual, auditory, and
proprioceptive stimuli) should be conducted. Further details of the proce-
dures that could be followed are described in the references listed under
paragraphs (h)(l), (h)(3), (h)(4), (h)(5), (h)(6), and (h)(9) of this guideline.
(iv) Functional observations conducted towards the end of the study
may be omitted when data on functional observations are available from
other studies and the daily clinical observations did not reveal any func-
tional deficits.
(v) Exceptionally, functional observations may be omitted for groups
that otherwise reveal signs of toxicity to an extent that would significantly
interfere with functional test performance.
(vi) Individual weights of animals should be determined shortly be-
fore the test substance is administered, weekly thereafter, and at death.
(vii) Food consumption should also be determined weekly if abnormal
body weight changes are observed.
(viii) Moribund animals should be removed and sacrificed when no-
ticed. The time of death should be recorded as precisely as possible.
(ix) At termination, all survivors in the treatment groups should be
sacrificed.
(11) Clinical pathology. Hematology and clinical chemistry examina-
tions should be made on all animals, including controls, of each sex in
each group. The hematology and clinical chemistry parameters should be
examined at terminal sacrifice at the end of the study. Overnight fasting
of the animals prior to blood sampling is recommended. Overall, there
is a need for a flexible approach in the measures examined, depending
on the observed or expected effects from a chemical, and in the frequency
of measures, depending on the duration of potential chemical exposures.
(i) Hematology. The recommended parameters are red blood cell
count, hemoglobin concentration, hematocrit, mean corpuscular volume,
mean corpuscular hemoglobin, and mean corpuscular hemoglobin con-
centration, white blood cell count, differential leukocyte count, platelet
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count, and a measure of clotting potential, such as prothrombin time or
activated partial thromboplastin time.
(ii) Clinical chemistry. (A) Parameters which are considered appro-
priate to all studies are electrolyte balance, carbohydrate metabolism, and
liver and kidney function. The selection of specific tests will be influenced
by observations on the mode of action of the substance and signs of clini-
cal toxicity.
(B) The recommended clinical chemistry determinations are potas-
sium, sodium, glucose, total cholesterol, urea nitrogen, creatinine, total
protein and albumin. More than 2 hepatic enzymes, (such as alanine
aminotransferase, aspartate aminotransferase, alkaline phosphatase, sorbitol
dehydrogenase, or gamma glutamyl transpeptidase) should also be meas-
ured. Measurements of addtional enzymes (of hepatic or other origin) and
bile acids, may also be useful.
(C) If a test chemical has an effect on the hematopoietic system,
reticulocyte counts and bone marrow cytology may be indicated.
(D) Other determinations that should be carried out if the test chemi-
cal is known or suspected of affecting related measures include calcium,
phosphorus, fasting triglycerides, hormones, methemoglobin, and
cholinesterases.
(iii) Optionally, the following urinalysis determinations could be per-
formed during the last week of the study using timed urine volume collec-
tion: appearance, volume, osmolality or specific gravity, pH, protein, glu-
cose, and blood/blood cells.
(12) Ophthalmological examination. Ophthalmological examina-
tions using an ophthalmoscope or an equivalent device should be made
on all animals prior to the administration of the test substance and on
all high-dose and control groups at termination. If changes in the eyes
are detected, all animals in the other dose groups should be examined.
(13) Gross necropsy, (i) All animals should be subjected to a full
gross necropsy which includes examination of the external surface of the
body, all orifices, and the cranial, thoracic and abdominal cavities and their
contents.
(ii) The liver, brain, kidneys, spleen, adrenals, testes, epididymides,
uterus, ovaries, thymus, and heart should be trimmed and weighed wet,
as soon as possible after dissection.
(iii) The following organs and tissues, or representative samples there-
of, should be preserved in a suitable medium for possible future
histopathological examination:
(A) Digestive system.
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(7) Salivary glands.
(2) Esophagus.
(3) Stomach.
(4) Duodenum.
(5) Jejunum.
(6) Ileum.
(7) Cecum.
(8) Colon.
(9) Rectum.
(10) Liver.
(11) Pancreas.
(72) Gall bladder (when present).
(B) Nervous system.
(7) Brain (multiple sections, including cerebrum, cerebellum, and me-
dulla/pons).
(2) Pituitary.
(3) Peripheral nerve(sciatic or tibial, preferably in close proximity to
the muscle).
(4) Spinal cord (three levels, cervical, mid-thoracic, and lumbar).
(5) Eyes (retina, optic nerve).
(C) Glandular system.
(7) Adrenals.
(2) Parathyroids.
(3) Thyroids.
(D) Respiratory system.
(7) Trachea.
(2) Lung.
(3) Pharynx.
(4) Larynx.
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(5) Nose.
(E) Cardiovascular/Hematopoieitic system.
(7) Aorta.
(2) Heart.
(3) Bone marrow (and/or fresh aspirate).
(4) Lymph nodes (preferably one lymph node covering the route of
administration and another one distant from the route of administration
to cover systemic effects).
(5) Spleen.
(6) Thymus.
(F) Urogenital system.
(7) Kidneys.
(2) Urinary bladder.
(3) Prostate.
(4) Testes.
(5) Epididymides.
(6} Seminal vesicles.
(7) Uterus.
($) Ovaries.
(9) Female mammary gland.
(G) Others.
(7) All gross lesions and masses.
(2) Skin (both treated and adjacent untreated areas).
(14) Histopathology. (i) The following histopathology should be per-
formed:
(A) Full histopathology on the organs and tissues, listed under para-
graph (e)(13)(iii) of this guideline, of all animals in the control and high-
dose groups.
(B) All gross lesions in all animals.
(C) Target organs in all animals.
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(D) When a satellite group is used, histopathology should be per-
formed on tissues and organs identified as showing toxic effects in the
treated groups.
(ii) If excessive early deaths or other problems occur in the high-
dose group, compromising the significance of the data, the next dose level
should be examined for complete histopathology.
(iii) An attempt should be made to correlate gross observations with
microscopic findings.
(iv) Tissues and organs designed for microscopic examination should
be fixed in 10 percent buffered formalin or a recognized suitable fixative
as soon as necropsy is performed and no less than 48 hours prior to trim-
ming.
(f) Data and reporting—(1) Treatment of results, (i) Data should
be summarized in tabular form, showing for each test group—number of
animals at the start of the test, the number of animals showing lesions,
the types of lesions and the percentage of animals displaying each type
of lesion.
(ii) When applicable, all observed results, quantitative and qualitative,
should be evaluated by an appropriate statistical method. Any generally
accepted statistical method should be used; the statistical methods includ-
ing significance criteria should be selected during the design of the study.
(2) Evaluation of study results. The findings of a 21/28 day dermal
toxicity study should be evaluated in conjunction with the findings of pre-
ceding studies and considered in terms of toxic effects, and the necropsy
and histopathological findings. The evaluation should include the relation-
ship between the dose of the test substance, the incidence and severity
of abnormalities including behavioral and clinical abnormalities, gross le-
sions, identified target organs, body weight changes, effect on mortality
and any other general or specific toxic effects. A properly conducted 217
28 day dermal toxicity study should provide information on the effects
of repeated application of a substance and a satisfactory estimation of a
NOEL. It also can indicate the need for an additional longer-term study
and provide information on the selection of dose levels.
(3) Test report. In addition to reporting requirements specified under
EPA Good Laboratory Practice Standards at 40 CFR part 792, subpart
J and 40 CFR part 160, and the OECD principles of GLP (ISBN 92-
64-12367-9), the following specific information should be reported:
(i) Test substance characterization should include:
(A) Chemical identification.
(B) Lot or batch numbers.
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(C) Physical properties.
(D) Purity/impurities.
(E) Identification and composition of any vehicle if used.
(ii) Test system should contain data on:
(A) Species and strain of animals used and rationale for selection
if other than that recommended.
(B) Age including body weight data and sex.
(C) Test environment including cage conditions, ambient temperature,
humidity, and light/dark periods.
(D) Identification of animal diet.
(E) Acclimation period.
(iii) Test procedure should include the following data:
(A) Method of randomization used.
(B) Full description of experimental design and procedure.
(C) Dose regime including levels, method, and volume.
(iv) Test results should include:
(A) Group animal data: Tabulation of toxic response data by species,
strain, sex, and exposure level for:
(7) Number of animals exposed.
(2) Number of animals showing signs of toxicity.
Number of animals dying.
(B) Individual animal data. Data should be presented as summary
(group mean) as well as for individual animals.
(7) Date of death during the study or whether animals survived to
termination.
(2) Date of observation of each abnormal sign and its subsequent
course.
Body weight data.
(4) Feed consumption data, when collected.
(5) Results of ophthalmological examination.
(6) Results of the hematology tests performed.
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(7) Results of the clinical chemistry tests performed.
(8) Results of urinalysis, when performed.
(9} Results of the observations made.
(Iff) Necropsy findings, including absolute and relative organ weight
data.
(11) Detailed description of all histopathological findings.
(12} Statistical treatment of results, where appropriate.
(g) Quality control. A system should be developed and maintained
to assure and document adequate performance of laboratory staff and
equipment. The study must be conducted in compliance with GLP regula-
tions.
(h) References. The following references should be consulted for ad-
ditional background material on this test guideline.
(1) Crofton K.M., Howard J.L., Moser V.C., Gill M.W., Leiter L.W.,
Tilson H.A., MacPhail, R.C. Interlaboratory Comparison of Motor Activity
Experiments: Implication for Neurotoxicological Assessments.
Neurotoxicol. Teratol. 13, 599-609. (1991)
(2) Draize, J.H. Dermal toxicity, Appraisal of Chemicals in Food,
Drugs and Cosmetics. The Association of Food and Drug Officials of the
United States, 3rd printing 1975. pp. 46-59 (1959).
(3) Gad S.C. A Neuromuscular Screen for Use in Industrial Toxi-
cology. Journal of Toxicology and Environmental Health. 9, 691-704.
(1982)
(4) International Programme on Chemical Safety. Principles and
Methods for the Assessment of Neurotoxicity Associated with Exposure
to Chemicals. Environmental Health Criteria Document No. 60. (1986)
(5) Meyer O.A., Tilson H.A., Byrd W.C., Riley M.T. A Method for
the Routine Assessment of Fore- and Hind-Limb Grip Strength of Rats
and Mice. Neurobehav. Toxicology. 1, 233-236. (1979)
(6) Moser V.C., McDaniel K.M., Phillips P.M. Rat Strain and Stock
Comparisons using a Functional Observational Battery: Baseline Values
and Effects of Amitraz. Toxicology and Applied Pharmacology. 108, 267-
283 (1991)
(7) National Academy of Sciences. Principles and Procedures for
Evaluating the Toxicity of Household Substances. A report prepared by
the Committee for the Revision of NAS Publication 1138, under the aus-
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pices of the Committee on Toxicology, National Research Council, Na-
tional Academy of Sciences, Washington, DC (1977).
(8) Organization for Economic Cooperation and Development. Guide-
lines for Testing of Chemicals, Section 4—Health Effects, Part 410, Re-
peated Dose Toxicity Study, Paris (1981).
(9) Tupper, D.E., Wallace R.B. Utility of the Neurologic Examination
in Rats. Acta. Neurobioloical Exp. 40, 999-1003 (1980).
(10) Weingand K., Brown G., Hall R. et al. Harmonization of Animal
Clinical Pathology Testing in Toxicity and Safety Studies. Fundamental
and Applied Toxicology. 29:198-201. (1996)
(11) World Health Organization. Part I. Environmental Health Criteria
6, Principles and Methods for Evaluating the Toxicity of Chemicals.
(World Health Organization, Geneva) (1978).
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