United States

Environmental Protection

Agency

Prevention, Pesticides

and Toxic Substances

(7101)

EPA712–C–96–228

June 1996

Health Effects Test

Guidelines

OPPTS 870.5460

Rodent Heritable

Translocation Assays

‘‘Public Draft’’
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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 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. Environmental Protection Agency under the Toxic Substances Control Act (15

U.S.C. 2601) and the Federal Insecticide, Fungicide and Rodenticide Act

(7 U.S.C. 136, et seq.).

Public Draft Access Information: This draft guideline is part of a

series of related harmonized guidelines that need to be considered as a

unit. For copies: These guidelines are available electronically from the

EPA Public Access Gopher (gopher.epa.gov) under the heading ‘‘Environmental Test Methods and Guidelines’’ or in paper by contacting the OPP

Public Docket at (703) 305–5805 or by e-mail:

guidelines@epamail.epa.gov.

To Submit Comments: Interested persons are invited to submit comments. By mail: Public Docket and Freedom of Information Section, Office

of Pesticide Programs, Field Operations Division (7506C), Environmental

Protection Agency, 401 M St. SW., Washington, DC 20460. In person:

bring to: Rm. 1132, Crystal Mall #2, 1921 Jefferson Davis Highway, Arlington, VA. Comments may also be submitted electronically by sending

electronic mail (e-mail) to: guidelines@epamail.epa.gov.

Final Guideline Release: This guideline is available from the U.S.

Government Printing Office, Washington, DC 20402 on The Federal Bulletin Board. By modem dial 202–512–1387, telnet and ftp:

fedbbs.access.gpo.gov (IP 162.140.64.19), or call 202–512–0132 for disks

or paper copies. This guideline is also available electronically 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 870.5460 Rodent heritable translocation assays.

(a) Scope—(1) Applicability. This guideline is intended to meet testing 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 harmonized OPPTS test guideline are OPPT 40 CFR 798.5460 Rodent Heritable Translocation Assays and OECD guideline 485 Genetic Toxicology:

Mouse Heritable Translocation Assay.

(b) Purpose. This test detects transmitted chromosomal damage

which manifests as balanced reciprocal translocations in progeny descended from parental males treated with chemical mutagens.

(c) Definitions. The definitions in section 3 of TSCA and in 40 CFR

Part 792—Good Laboratory Practice Standards (GLP) apply to this test

guideline. The following definitions also apply to this test guideline.

Diakinesis and metaphase I are stages of meiotic prophase scored

cytologically for the presence of multivalent chromosome association characteristic of translocation carriers.

A heritable translocation is one in which distal segments of

nonhomologous chromosomes are involved in a reciprocal exchange.

(d) Test method—(1) Principle. When a balanced reciprocal

translocation is induced in a parental male germ cell, the resulting progeny

is translocation heterozygote.

(i) Basis for fertility screening. Male translocation heterozygotes

may be completely sterile. This class consists of two types of

translocations:

(A) Translocations between nonhomologous chromosomes in which

at least one of the breaks occurs close to one end of a chromosome.

(B) Those that carry multiple translocations. The majority of male

translocation heterozygotes are semisterile—they carry one or (rarely) two

translocations. The degree of semisterility is dependent upon the proportions of balanced and unbalanced (duplication-deficiency) gametes produced in the ejaculate as a function of meiotic segregation. Balanced and

unbalanced sperm are equally capable of fertilizing an egg. Balanced

sperm lead to viable progeny. Unbalanced sperm result in early embryonic

lethality.

(ii) Basis for cytological screening. The great majority of male

translocation heterozygotes can be identified cytologically through analysis

of diakinesis metaphase I spermatocytes. Translocation heterozygotes are

characterized by the presence of multivalent chromosome association such
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as a ring or chain of four chromosomes held together by chiasmata in

paired homologous regions. Some translocation carriers can be identified

by the presence of extra long and/or extra short chromosomes in

spermatogonial and somatic cell metaphase preparations.

(2) Description. Essentially, two methods have been used to screen

for translocation heterozygosity—one method uses a mating sequence to

identify sterile and semisterile males followed by cytological examination

of suspect male individuals; the other method deletes the mating sequence

altogether and all F1 male progeny are examined cytologically for presence

of translocation. In the former approach, the mating sequence serves as

a screen which eliminates most fully fertile animals for cytological confirmation as translocation heterozygotes.

(3) Animal selection—(i) Species. The mouse is the species generally

used, and is recommended.

(ii) Age. Healthy sexually mature animals shall be used.

(iii) Number. The number of male animals necessary is determined

by the following factors:

(A) The use of either historical or concurrent controls.

(B) The power of the test.

(C) The minimal rate of induction required.

(D) Whether positive controls are used.

(E) The level of significance desired.

(iv) Assignment to groups. Animals shall be randomized and assigned to treatment and control groups.

(4) Control groups—(i) Concurrent controls. No concurrent positive or negative (vehicle) controls are recommended as routine parts of

the heritable translocation assay. However, investigators not experienced

in performing translocation testing shall include a substance known to

produce translocations in the assay as a positive control reference chemical.

(ii) Historical controls. At the present time, historical control data

must be used in tests for significance. When statistically reliable historical

controls are not available, negative (vehicle) controls shall be used.

(5) Test chemicals—(i) Vehicle. When appropriate for the route of

administration, solid and liquid test substances should be dissolved or suspended in distilled water or isotonic saline. Water-insoluble chemicals may

be dissolved or suspended in appropriate vehicles. The vehicle used shall
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neither interfere with the test chemical nor produce toxic effects. Fresh

preparations of the test chemical should be employed.

(ii) Dose levels. At least two dose levels shall be used. The highest

dose level shall result in toxic effects (which shall not produce an incidence of fatalities which would prevent a meaningful evaluation) or shall

be the highest dose attainable or 5 g/kg body weight.

(iii) Route of administration. Acceptable routes of administration

include oral, inhalation, admixture with food or water, and IP or IV injection.

(e) Test performance—(1) Treatment and mating. The animals

shall be dosed with the test substances 7 days per week over a period

of 35 days. After treatment, each male shall be caged with two untreated

females for a period of 1 week. At the end of 1 week, females shall be

separated from males and caged individually. When females give birth,

the day of birth, litter size, and sex of progeny shall be recorded. All

male progeny should be weaned, and all female progeny should be discarded.

(2) Testing for translocation heterozygosity. When males are sexually mature, testing for translocation heterozygosity shall begin. One of

two methods shall be used; the first method involves mating, determining

those F1 progeny which are sterile or semisterile and subsequent

cytological analysis of suspect progeny; the other method does not involve

mating and determining sterility or semisterility; all progeny are examined

cytologically.

(i) Determination of sterility or semisterility—(A) Conventional

method. Females are mated, usually three females for each male, and each

female is killed at midpregnancy. Living and dead implantations are counted. Criteria for determining normal and semisterile males are usually established for each new strain because the number of dead implantations varies

considerably among strains.

(B) Sequential method. Males to be tested are caged individually

with females and the majority of the presumably normal males are identified on the basis of a predetermined size of one or two litters. Breeding

pens are examined daily on weekdays beginning 18 days after pairing.

Young are discarded immediately after they are scored. Males that sire

a litter whose size is the same as or greater than the minimum set for

a translocation-free condition are discarded with their litter. If the litter

size is smaller than the predetermined number, a second litter is produced

with the same rule applying. Males that cannot be classified as normal

after production of a second litter are tested further by the conventional

method or by cytological confirmation of translocation.
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(ii) Cytological analysis. For cytological analysis of suspected

semisteriles, the air-drying technique is used. Observation of at least two

diakinesis-metaphase 1 cells with mutivalent association constitutes the required evidence for the presence of a translocation. Sterile males are examined by one of two methods, those with testes of normal size and sperm

in the epididymis are examined by the same techniques used for

semisteriles. Animals with small testes are examined by squash preparations or, alternatively, by examination of mitotic metaphase preparations.

If squash preparations do not yield diakinesis-metaphase 1 cells, analysis

of spermatogonia or bone marrow for the presence of unusually long or

short chromosomes should be performed.

(f) Data and report—(1) Treatment of results. (i) Data shall be

presented in tabular form and shall include the number of animals at risk,

the germ cell stage treated, the number of partial steriles and semisteriles

(if the fertility test is used), the number of cytogenetically confirmed

translocation heterozygotes (if the fertility test is used, report the number

of confirmed steriles and confirmed partial steriles), the translocation rate,

and either the standard error of the rate or the upper 95 percent confidence

limit on the rate.

(ii) These data shall be presented for both treated and control groups.

Historical or concurrent controls shall be specified, as well as the

randomization procedure used for concurrent controls.

(2) Statistical evaluation. Data shall be evaluated by appropriate statistical methods.

(3) Interpretation of results. (i) There are several criteria for determining a positive result, one of which is a statistically significant doserelated increase in the number of heritable translocations. Another criterion

may be based upon detection of a reproducible and statistically significant

positive response for at least one of the test points.

(ii) A test substance which does not produce either a statistically significant dose-related increase in the number of heritable translocations or

a statistically significant and reproducible positive response at any one of

the test points is considered nonmutagenic in this system.

(iii) Both biological and statistical significance should be considered

together in the evaluation.

(4) Test evaluation. (i) Positive results in the heritable translocation

assay indicate that under the test conditions the test substance causes heritable chromosomal damage in the test species.

(ii) Negative results indicate that under the test conditions the test

substance does not cause heritable chromosomal damage in the test species.
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(5) Test report. In addition to the reporting recommendations as

specified under 40 CFR part 792, subpart J, the following specific information shall be reported:

(i) Species, strain, age, weight, and number of animals of each sex

in each group.

(ii) Test chemical vehicle, route and schedule of administration, and

toxicity data.

(iii) Dosing regimen, doses tested, and rationale for dosage selection.

(iv) Mating schedule and number of females mated to each male.

(v) The use of historical or concurrent controls.

(vi) Screening procedure including the decision criteria used and the

method by which they were determined.

(vii) Dose-response relationship, if applicable.

(g) References. The following references should be consulted for additional background material on this test guideline.

(1) Generoso, W.M. et al. Heritable translocation test in mice. Mutation Research 76:191–215 (1980).

(2) [Reserved]