United States Prevention, Pesticides EPA 712–C–02–189 

and Toxic Substances 

Agency (7101) 

Environmental Protection December 2002 

Health Effects Test


Guidelines


OPPTS 870.1000


Acute Toxicity Testing—


Background

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.). 

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 Internet Web site at http:/ 

/www.epa.gov/opptsfrs/home/guidelin.htm. 

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OPPTS 870.1000 Acute toxicity testing—background. 

(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 material for this revised harmonized test 

guideline is OPPTS 870.1000 Acute Toxicity Testing—Background, dated 

August 1998. 

(b) Purpose. The Agency considers the evaluation of toxicity following short term exposure to a chemical to be an integral step in the 

assessment of its toxic potential under the regulatory framework of its pesticide and toxic substances programs. In the assessment and evaluation 

of the toxic characteristics of a substance, acute toxicity is generally performed by the probable route of exposure in order to provide information 

on health hazards likely to arise from short-term exposure by that route. 

For pesticides, the short-term toxicity testing battery consists of acute toxicity tests by the oral, dermal, and inhalation routes; skin and eye irritation 

testing; and testing for dermal sensitization. Data from an acute study may 

serve as a basis for hazard categorization, labeling, or child-resistant packaging and may also serve to designate pesticides which may be applied 

only by certified applicators. It may also be an initial step in establishing 

a dosage regimen in subchronic and other studies and may provide information on absorption and the mode of toxic action of a substance. An 

evaluation of acute toxicity data should include the relationship, if any, 

between the exposure of animals to the test substance and the incidence 

and severity of all abnormalities, including behavioral and clinical abnormalities, the reversibility of observed abnormalities, gross lesions, body 

weight changes, effects on mortality, and any other toxic effects. 

(c) History—(1) Acute toxicity test guidelines. Test guidelines for 

acute toxicity were first published by the Agency in October 1982 as part 

of Subdivision F of the Pesticide Assessment Guidelines for the Office 

of Pesticide Programs (OPP) (see paragraph (g)(1) of this guideline) and 

in 40 CFR part 797 in September 1985 for the Office of Pollution Prevention and Toxics (OPPT). 

(2) Rejection rate analysis. In 1993, as part of its Pesticide Rejection 

Rate Analysis, Agency and industry scientists met to perform a guidelineby-guideline review of toxicology studies including acute toxicity studies. 

The purpose of this guideline-by-guideline review was to identify those 

factors that most frequently cause toxicology studies required for pesticide 

reregistration to be rejected. The results were published as the Pesticide 

Reregistration Rejection Rate Analysis: Toxicology (see paragraph (g)(2) 

of this guideline). In 1995, representatives from the Agency met with the 

American Crop Protection Association (ACPA), the Chemical Producers 

and Distributors Association (CPDA), the Chemical Manufacturers Asso1

ciation (CMA), Health Canada, and the California Department of Pesticide 

Regulation (CDPR) to discuss acceptable methods for the conduct of acute 

toxicity studies. The discussions of this meeting were incorporated into 

a preliminary Registration Division document titled Conduct of Acute Toxicity Studies (see paragraph (g)(3) of this guideline). These documents supplement the acute toxicology guidelines in Subdivision F. 

(3) Guideline harmonization. The Series 870 Health Effects test 

guidelines have been harmonized between OPP and OPPT and, where possible, with the Organization for Economic Cooperation and Development 

(OECD) test guidelines. Scientific considerations from both of the analyses 

described in paragraph (c)(2) of this guideline have been incorporated into 

the revised test guidelines. 

(d) Approaches to the determination of acute toxicity. (1) At 

present, the evaluation of chemicals for acute toxicity is necessary for the 

protection of public health and the environment. The Agency supports 

measures dedicated to reducing the use of animals in toxicity testing. 

When animal testing is required for this purpose, testing should be done 

in ways that minimize numbers of animals used and that take full account 

of their welfare. To this end, when conducting a test, the Agency stresses 

the simultaneous monitoring of several endpoints of toxicity in animals 

in a single acute study including sublethal effects as well as lethality. 

Dosed animals are observed for abnormal behavioral manifestations such 

as increased salivation or muscular incoordination, in addition to the recovery from these effects during the observation period. Both dead and surviving animals are necropsied to evaluate gross anatomical evidence of 

organ toxicity. In selected cases, additional testing may be justified to better characterize the kinds of abnormalities that have been found in the 

organs of the necropsied animals. These sound, scientific practices represent some of the means which maximize the utility of the data obtained 

from a limited number of test animals to achieve a balance between protecting humans and the environment, and the welfare and utilization of 

laboratory animals. 

(2) EPA recommends the following means to reduce the number of 

animals used to evaluate acute effects of chemical exposure while preserving its ability to make reasonable judgements about safety: 

(i) Use of data from structurally related substances or mixtures. In 

order to minimize the need for animal testing for acute effects, the Agency 

encourages the review of existing acute toxicity information on chemical 

substances that are structurally related to the agent under investigation. 

In certain cases, it may be possible to obtain enough information to make 

preliminary hazard evaluations that may reduce the need for further animal 

testing for acute effects. Similarly, mixtures or formulated products that 

are substantially similar to well-characterized mixtures or products may 

not need additional testing if there are sufficient bridging data available 

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for meaningful extrapolation. In those cases, classification would be extrapolated from the mixture already tested. 

(ii) EPA recommends the Up-and-Down Procedure (UDP), as detailed 

in this guideline and adopted by OECD as test Guideline 425 (see paragraph (g)(4) of this guideline), to access acute oral toxicity. This method 

provides a point estimate of lethality and confidence interval. A dedicated 

program (AOT425StatPgm) has been developed by EPA to assist laboratories in the conduct of this protocol. The Agency strongly recommends 

the use of this software package which is available on EPA’s Internet Web 

site at http://www.epa.gov/oppfead1/harmonization. Acute oral toxicity 

testing may also be performed using the Fixed Dose Method of OECD 

Guideline 420 (see paragraph (g)(5) of this guideline) or the Acute Toxic 

Class Method of OECD Guideline 423 (see paragraph (g)(6) of this guideline). These methods assess lethality within a dose range. 

(iii) Weight of evidence approaches to dermal and ocular irritation. 

Several factors should be considered in determining the corrosion and irritation potential of chemicals before testing is undertaken. Existing human 

experience and data and animal observations and data should be the first 

line of analysis, as it gives information directly referable to effects on 

the skin. In some cases, enough information may be available from structurally related compounds to make classification decisions. Likewise, pH 

extremes (pH <2 or >11.5) may indicate dermal effects, especially when 

buffering capacity is known, although the correlation is not perfect. Generally, such agents are expected to produce significant effects on the skin. 

It also stands to reason that if a chemical is extremely toxic by the dermal 

route, a dermal irritation/corrosion study may not be needed. Likewise, 

if there is a lack of any dermal reaction at the limit dose (2,000 mg/kg) 

in an acute toxicity study (for which observations of dermal reactions were 

made), a dermal irritation/corrosion study again may not be needed for 

labeling purposes. It should be noted, however, that often acute dermal 

toxicity and dermal irritation/corrosion testing are performed in different 

species that may differ in sensitivity. In vitro alternatives that have been 

validated and accepted may also be used to help make classification decisions. 

(iv) All of the available information on a chemical should be used 

in determining the need for in vivo dermal irritation testing. Although information might be gained from the evaluation of single parameters within 

a tier (e.g., caustic alkalies and acids with extreme pH (pH <2 or >11.5) 

should be considered as dermal corrosives), there is merit in considering 

the totality of existing information and making an overall weight of evidence determination. This is especially true when there is information 

available on some but not all parameters. 

(v) Use of limit testing. For chemicals judged to be relatively nontoxic, a single group of animals is given a large dose of the agent. If 

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no lethality is demonstrated, no further testing is pursued. The substance 

is classified in hazard categories according to the limit dose used. (See 

the following paragraph for a discussion of toxicity categories under 

FIFRA). 

(e) Regulatory applications under FIFRA. (1) Precautionary labeling provides the pesticide user with a general idea of the potential toxicity, 

irritation and sensitization hazard associated with the use of a pesticide 

(see EPA Label Review Manual (paragraph (g)(7) of this guideline) and 

40 CFR Part 156—Labeling Requirements for Pesticides and Devices). 

Precautionary labeling also identifies the precautions necessary to avoid 

exposure as well as any personal protective equipment which should be 

used when handling a pesticide and statements of practical treatment in 

case of accidental exposure. A globally harmonized system for classification and labeling has been approved through the United Nations. Implementation will be phased in by United Nations countries, with schedules 

to be announced. This section describes the current system in place for 

pesticides in the United States and will be revised and updated when the 

globally harmonized system is fully implemented. 

(2) Precautionary labeling which includes the signal word, personal 

protective equipment, hazard symbol, and statements of practical treatment 

is normally determined by six acute toxicity studies and product composition. The acute oral, acute dermal and acute inhalation studies are used 

to determine the LD50 of a product via the designated route of exposure. 

The primary eye irritation and primary skin irritation studies measure the 

severity of irritation or corrosivity caused by a product. The dermal sensitization study determines whether a product is capable of causing an allergic reaction. With the exception of the dermal sensitization study, each 

acute toxicity study is assigned a toxicity category as defined in the table 

below. All products falling into toxicity categories I–IV must bear a signal 

word and in some cases warning symbols. 

(3) Personal Protective Equipment. Personal protective equipment 

which includes use of protective clothing, chemical resistant gloves, protective eye gear, and respiratory protective devices, is determined by the 

results of six acute toxicity studies according to toxicity category (see 

table). The degree of protection required is graded according to the degree 

of acute toxicity and the hazard classification category of the chemical 

or product. These requirements are set forth in 40 CFR 170.240 in the 

Worker Protection Standard. 

(4) Restricted entry intervals. Agricultural products must display a 

restricted entry interval. A restricted entry interval is the time immediately 

following a pesticide application during which entry into the treated area 

is restricted. Restricted entry intervals are based on the most severe acute 

toxicity category assigned to the acute dermal, eye irritation and skin irritation data for all of the active ingredients in a pesticide product. The dura4

tion of restricted entry intervals is based on the severity of toxicity, with 

products classified in category I requiring intervals of 48 hours or more 

and products classified in category III or IV requiring intervals of 12 

hours. 

(5) Child-resistant packaging. FIFRA establishes standards with respect to pesticide packaging of products intended for use in residential 

settings in order to protect children or adults from serious illness or injury 

resulting from accidental ingestion or contact with pesticides. Criteria in 

40 CFR part 157 for which pesticides must be distributed or sold in childresistant packaging are based on classification according to the toxicity 

categories set forth in the table. 

(6) Restricted use pesticide. The Agency determines whether a pesticide must be applied under the direct supervision of a certified applicator. 

Such clarification for restricted use is based upon consideration of toxicity 

data, including acute toxicity, exposure, and intended use. 

(7) Biochemical pest control agents are tested in a special tiered progression. The technical grade biochemical pest control agent is always 

characterized by acute toxicity tests. However, because of their nontoxic 

mode of action against the target pest, further testing of the biochemical 

pest control agent is normally not required. Microbial pest control agents 

are tested using the OPPTS Harmonized Test Guidelines Series 885, Microbial Pesticide Test Guidelines, for pathogenicity/infectivity. In addition, 

all formulations of microbial pest control agents are tested for precautionary labeling using acute toxicity tests in the OPPTS Harmonized 

Test Guidelines Series 870, Health Effects Test Guidelines. 

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Toxicity Categories 

Study Category I Category II Category III Category IV 

Acute Oral Up to and including 50 

mg/kg 

>50 through 500 

mg/kg 

>500 through 

5000 mg/kg 

>5000 mg/kg 

Acute Dermal Up to and including 200 

mg/kg 

>200 through 

2000 mg/kg 

>2000 through 

5000 mg/kg 

>5000 mg/kg 

Acute Inhalation Up to and including 0.05 

mg/liter 

>0.05 through 0.5 

mg/liter 

>0.5 through 2 

mg/liter 

>2 mg/liter 

Eye Irritation Corrosive (irreversible 

destruction of ocular 

tissue) or corneal 

involvement or irritation 

persisting for more than 

21 days 

Corneal 

involvement or 

irritation clearing 

in 8-21 days 

Corneal 

involvement or 

irritation clearing 

in 7 days or less 

Minimal effects 

clearing in less 

than 24 hours 

Skin irritation Corrosive (tissue 

destruction into the 

dermis and/or scarring) 

Severe irritation at 

72 hours (severe 

erythema or 

edema) 

Moderate irritation 

at 72 hours 

(moderate 

erythema) 

Mild or slight 

irritation (no 

irritation or slight 

erythema) 

Study Study results Study results 

Dermal Sensitization Product is a sensitizer or is positive 

for sensitization 

Product is not a sensitizer or is 

negative for sensitization 

(f) Regulatory applications under TSCA. (i) Acute oral toxicity 

data are used to provide a basic understanding of acute effects and to 

serve as a starting point for human hazard and risk assessments focused 

on occupational and general population exposures. 

(ii) Acute oral toxicity testing is included in testing menus to obtain 

basic or ‘‘screening level’’ information on certain chemicals. These include higher volume/higher exposure new chemicals where TSCA section 

5(e) ‘‘exposure-based’’ testing authorities are used to obtain a basic level 

of hazard and environmental fate information; and High Production Volume existing chemicals (i.e., those produced and/or imported at or above 

1 million lbs/yr) information data set. 

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

(1) U.S. Environmental Protection Agency. Pesticide Assessment 

Guidelines, Subdivision F: Health Effects. EPA report 540/09–82–025, October 1982. 

(2) U.S. Environmental Protection Agency. Pesticide Reregistration 

Rejection Rate Analysis: Toxicology. EPA report 738–R–93–004. July 

1993. 

(3) U.S. Environmental Protection Agency. Conduct of Acute Toxicity 

Studies. EPA report 737–R–97–002. September 1997. 

(4) Organization for Economic Cooperation and Development, OECD 

Guidelines for Testing of Chemicals. Guideline 425: Acute Oral Toxicity– 

Up-and-Down Method. Approved: December 2001. 

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(5) Organization for Economic Cooperation and Development, OECD 

Guidelines for Testing of Chemicals. Guideline 420: Acute Oral ToxicityFixed Done Method. Adopted: December 2001. 

(6) Organization for Economic Cooperation and Development, OECD 

Guidelines for Testing of Chemicals. Guideline 423: Acute Oral ToxicityAcute Toxic Class Method. Adopted: December 2001. 

(7) U.S. Environmental Protection Agency. Label Review Manual 2nd 

Edition. EPA report 737–B–96–001. December 1996. 

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