.... United States Environmental Protection Agency Prevention, Pesticides and Toxic Substances (7101) EPA 712–C–96–204 June 1996 

# Health Effects Test Guidelines OPPTS 870.3465 Subchronic Inhalation Toxicity

‘‘Public Draft’’

### i 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 theNational 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 proceduresthat 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 theEPA 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.’’

### 1 OPPTS 870.3265 Subchronic Inhalation toxicity. (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 used in developing this harmonized OPPTS test guideline are 40 CFR 798.2450 Inhalation Toxicity; OPP 82–4 90–Day Inhalation—Rat (Pesticide Assessment Guidelines, Subdivision F—Hazard Evaluation; Human and Domestic Animals) EPAreport 540/09–82–025, 1982; and OECD 413 Subchronic Inhalation Toxicity: 90–Day. (b) Purpose. In the assessment and evaluation of the toxic characteristics of a gas, volatile substance, or aerosol/particulate, determination of subchronic inhalation toxicity may be carried out after initial information on toxicity has been obtained by acute testing. The subchronic inhalationstudy has been designed to permit the determination of the no-observedeffect level (NOEL) and toxic effects associated with continuous or repeated exposure to a test substance for a period of 90 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 health hazards likely to arise from repeated exposures by the inhalation route over a limited period of time. It will provide information on target organs and the possibilities of accumulation, and can be of use in selecting dose levels for chronic studies and establishing safety criteria for human exposure. Hazards of inhaled substances are influenced by the inherent toxicity and by physical factors such as volatility and particle size. (c) Definitions. The definitions in section 3 of the Toxic SubstanceControl Act (TSCA) and the definitions in 40 CFR Part 792—Good Laboratory Practice Standards apply to this test guideline. The following definitions also apply to this test guideline. Aerodynamic diameter is defined as the diameter of a unit densitysphere having the same terminal settling velocity as the particle in question, whatever its size, shape, and density. It is used to predict where in the respiratory tract such particles may be deposited.

Concentration in a subchronic inhalation study is the amount of testsubstance administered via inhalation for a period of 90–days. Concentration is expressed as weight of the test substance per unit volume of air (milligrams per liter or parts per million). Cumulative toxicity is the adverse effects of repeated doses occurringas a result of prolonged action on, or increased concentration of the administered test substance or its metabolites in susceptible tissues.

### 2 Inhalable diameter refers to that aerodynamic diameter of a particle which is considered to be inhalable for the organism. It is used to referto particles which are capable of being inhaled and may be deposited anywhere within the respiratory tract No-observed-effect-level (NOEL) is the maximum dose used in a study which produces no adverse effects. The NOEL is usually expressed in terms of weight of test substance per unit volume of air (milligrams per liter or parts per million). Mass median aerodynamic diameter (MMAD) is the geometric mean aerodynamic diameter and along with the geometric standard deviation(GSD) is used to describe the particle size distribution of any aerosol statistically based on the weight and size of the particles. Fifty percent of the particles by weight will be smaller than the median diameter and 50 percent of the particles will be larger. Subchronic inhalation toxicity is the adverse effects occurring as a result of the repeated daily exposure of experimental animals to a chemical by inhalation for part (approximately 10 percent) of a life span. (d) Limit test. If exposure at a concentration of 1 mg/L (expected human exposure may indicate the need for a higher dose level), or wherethis is not possible due to physical or chemical properties of the test substance, the maximum attainable concentration produces no observabletoxic effects, then 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. A variety of rodent species may be used, although the rat is the preferred species. Commonly used laboratory strains should be employed. If another mammalian species is used, the tester should provide justification/reasoning for its selection. (ii) Age/weight. (A) Testing should be started with young healthy animals as soon as possible after weaning and acclimatization. (B) Exposure should commence no later than 8 weeks of age.(C) At the commencement of the study the weight variation of animals used should not exceed ± 20 percent of the mean weight for each

sex. (iii) Sex. (A) Equal numbers of animals of each sex should be used at each dose level. (B) Females should be nulliparous and nonpregnant. (iv) Numbers. (A) At least 20 rodents (10 females and 10 males) should be used for each test group. If another mammalian species is se-

### 3 lected (e.g. dog, rabbit, or nonhuman primate), at least eight animals (four males and four females) should be used. (B) If interim sacrifices are planned, the number of animals should be increased by the number of animals scheduled to be sacrificed before the 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 should be assigned a unique identification number. Dead animals, their preserved organs and tissues, and microscopic slides should be identified by reference to the animal’s unique number. (v) Husbandry. (A) Animals may be group-caged by sex, but the number of animals per cage must not interfere with clear observation of each animal. The biological properties of the test substance or toxic effects (e.g., morbidity, excitability) may indicate a need for individual caging.Animals must be housed individually in inhalation chambers during exposure. (B) The temperature of the experimental animal rooms should be at 22 ± 3 ° C. (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 h light/ 12 h dark. (E) Control and test animals should be fed from the same batch andlot. The feed should be analyzed to assure adequacy of nutritional requirements of the species tested and for impurities that might influence the outcome of the test. Animals should be fed and watered ad libitum with food replaced at least weekly. For nonrodents feeding should be at least daily and water ad libitum. (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. (2) Control and test substances. (i) Whenever it is necessary to formulate the test substance with a vehicle for aerosol generation, the vehicleshould not elicit toxic effects or substantially alter the chemical or toxicological properties of the test substance.(ii) One lot of the test substance should be used, if possible throughout the duration of the study, and the research sample should be stored under conditions that maintain its purity and stability. Prior to the initiation

### 4of the study, there should be a characterization of the test substance, including the purity of the test substance and, if technically feasible, the name and quantities of unknown contaminants and impurities. (3) Control groups. A concurrent control group is required. This group should be an untreated or sham-treated control group. Except for treatment with the test substance, animals in the control group should be handled in a manner identical to the test group animals. Where a vehicle other than water is used to generate a substance, a vehicle control group should be used. If the toxic properties of the vehicle are not known or cannot be made available, both untreated 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 concentration level for 90 days andobserved for reversibility, persistence, or delayed occurrence of toxic effects for a post-treatment period of appropriate length, normally not less than 28 days. In addition a control group of 20 animals (10 animals of each sex) should be added to the satellite study. (5) Concentration levels and concentration selection. (i) In subchronic toxicity tests, it is desirable to have a concentration-response relationship as well as a NOEL. Therefore, at least three concentrationlevels plus a control and, where appropriate, a vehicle control (corresponding to the concentration of vehicle at the highest exposure level) should be used. Concentrations should be spaced appropriately to produce test groups with a range of toxic effects. The data should be sufficient to produce a concentration-response curve. (ii) The highest concentration should result in toxic effects but notproduce an incidence of fatalities which would prevent a meaningful evaluation. (iii) The intermediate concentrations should be spaced to produce a gradation of toxic effects. (iv) The lowest concentration should produce no evidence of toxicity. (v) In the case of potentially explosive test substances, care should be taken to avoid generating explosive concentrations. (6) Administration of the test substance. Animals should be exposed to the test substance for 6 h per day on a 7–day per week basisfor a period of at least 90 days. Based primarily on practical considerations, exposure for 6 h per day on a 5–day per week basis is acceptable. (7) Observation period. The animals should be observed for a periodof 90 days. Animals in the satellite group (if used) scheduled for followup observations should be kept for at least 28 days further without treatment to assess reversibility.

### 5 (8) Exposure specifications. (i) The animals should be tested in dynamic inhalation equipment designed to sustain a minimum air flow of 10 air changes per hour, an adequate oxygen content of at least 19 percent, and uniform conditions throughout the exposure chamber. Maintenance of slight negative pressure inside the chamber will prevent leakage of the test substance into the surrounding areas.(ii) The selection of a dynamic inhalation chamber should be appropriate for the test substance and test system. Where a whole body chamber is used, individual housing must be used to minimize crowding of the test animals and maximize their exposure to the test substance. To ensure stability of a chamber atmosphere, the total volume occupied by the test animals should not exceed 5 percent of the volume of the test chamber. It is recommended, but not required, that nose-only or head-only exposure be used for aerosol studies in order to minimize oral exposures due to animals licking compound off their fur. The animals should be acclimated to the chambers and heat stress minimized.(iii) The temperature at which the test is performed should be maintained at 22 ± 2 ° C. The relative humidity should be maintained between 30 and 70 percent, but in certain instances (e.g., use of water vehicle) this may not be practicable. (9) Physical measurements. Measurements or monitoring should be made of the following: (i) The rate of air flow should be monitored continuously but recorded at least every 30 minutes.(ii) The actual concentrations of the test substance should be measured in the animal’s breathing zone. During the exposure period, the actualconcentrations of the test substance should be held as constant as practicable, monitored continuously or intermittently depending on the method of analysis, and recorded at least at the beginning, at an intermediate time, and at the end of the exposure period. Whenever the test substance is a formulation, or it is necessary to formulate the test substance with avehicle for aerosol generation, the analytical concentration must be reported for the total formulation, and not just for the active ingredient (AI). If, for example, a formulation contains 10 percent AI and 90 percent inerts, a chamber analytical limit concentration of 2 mg/L would consist of 0.2 mg/L of the AI. It is not necessary to analyze inert ingredients provided the mixture at the animal’s breathing zone is analogous to the formulation; the grounds for this conclusion must be provided in the study report. If there is some difficulty in measuring chamber analytical concentration due to precipitation, nonhomogeneous mixtures, volatile components, or other factors, additional analyses of inert components may be necessary. (iii) During the development of the generating system, particle size analysis should be performed to establish the stability of aerosol concentra-

### 6 tions with respect to particle size. During exposure, analysis should be conducted as often as necessary to determine the consistency of particle size distribution in the animal’s breathing zone. The MMAD particle size range should be between 1–4 μm. The particle size of hygroscopic materials should be small enough when dry to assure that the size of the swollen particle will still be within the 1–4 μm range. (iv) Temperature and humidity should be monitored continuously but should be recorded at least every 30 minutes. (10) Feed and water during exposure period. Feed should be withheld during exposure. Water may also be withheld during exposure. (11) Observation of animals. (i) During and following exposure, observations are made and recorded systematically; individual records should be maintained for each animal. (ii) Observations should be made at least once 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). (iii) A careful clinical examination should be made at least once weekly. Observations should be detailed and carefully recorded, preferably using explicitly defined scales. Observations should include, but not belimited to, evaluation of skin and fur, eyes and mucous membranes, respiratory and circulatory effects, autonomic effects such as salivation, central nervous system effects, including tremors and convulsions, changes in the level of motor activity, gait and posture, reactivity to handling or sensory stimuli, grip strength, and stereotypies or bizarre behavior (e.g., self-mutilation, walking backwards).(iv) Signs of toxicity should be recorded as they are observed including the time of onset, degree and duration. (v) Individual weights of animals should be determined shortly before the test substance is administered, weekly thereafter, and at death. (vi) Food consumption should also be determined weekly if abnormal body weight changes are observed.(vii) Moribund animals should be removed and sacrificed when noticed and the time of death should be recorded as precisely as possible. (viii) At termination, all survivors in the treatment groups should be sacrificed. (12) Clinical pathology. Hematology and clinical chemistry examinations should be made on all animals, including controls, of each sex in each group for rodents and all animals when nonrodents are used as test

### 7 animals. For rodents, the hematology and clinical chemistry parameters should be examined at terminal sacrifice. For nonrodents, the hematologyand clinical chemistry parameters should be examined once prior to initiation of dosing, at monthly intervals or midway through the test period and at termination. (i) Hematology. The recommended parameters are: Hemoglobin and hematocrit concentrations, red blood cell count, white blood cell count,differential leukocyte count, platelet count, and a measure of clotting potential such as prothrombin time or thromboplastin time. (ii) Clinical chemistry. Parameters which are considered appropriate 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 clinical toxicity. Suggested blood clinical chemistry determinations: (A) Electrolytes. ( 1 ) Calcium. ( 2 ) Chloride. ( 3 ) Magnesium. (4 ) Phosphorous. ( 5 ) Potassium. ( 6) Sodium. (B) Enzymes. ( 1 ) Alkaline phosphatase. ( 2 ) Alanine aminotransferase. ( 3 ) Aspartate aminotransferase. (4 ) Gamma glutamyl transferase. ( 5 ) Sorbitol Dehydrogenase. (C) Other. ( 1 ) Albumin. ( 2 ) Blood creatinine. ( 3 ) Blood urea nitrogen. (4 ) Globulin. ( 5 ) Glucose (fasting).

### 8 ( 6) Total bilirubin. ( 7 ) Total cholesterol. ( 8) Total serum protein.Other determinations which may be necessary for an adequate toxicological evaluation include analyses of lipids, hormones, acid/base balance, methemoglobin and cholinesterase activity. Additional clinical biochemistry may be employed where necessary to extend the investigation of observed effects. (iii) Urinalysis is not recommended on a routine basis, but only when there is an indication based on expected or observed toxicity. (13) Optional immunotoxicity screen. To fulfill, in part, requirements for an immunotoxicity screen, subpopulation of splenic or peripheral blood lymphocytes in the rodents should be enumerated and quantified. Total T-, Total B-, Total T-helper, T-suppressor/cytotoxic and Natural Killer (NK) cell populations should be determined on at least 10 rodents of each sex in each group at the end of 90 days. (14) Ophthalmological examination. Using an ophthalmoscope or an equivalent device, ophthalmological examinations 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. (15) Gross pathology. (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) At least the liver, kidneys, lungs, brain, spleen, and gonads should be trimmed and weighed wet, as soon as possible after dissection to avoid drying.(iii) The following organs and tissues, or representative samples thereof, should be preserved in a suitable medium for possible future histopathological examination: (A) Digestive system. ( 1 ) Salivary glands. ( 2 ) Esophagus. ( 3 ) Stomach. (4 ) Duodenum. ( 5 ) Jejunum.

### 9 ( 6) Ileum. ( 7 ) Cecum. ( 8) Colon. ( 9 ) Rectum. ( 10) Liver. ( 11 ) Pancreas. ( 12 ) Gallbladder (dogs). (B) Nervous system. ( 1 ) Brain (multiple sections). ( 2 ) Pituitary. ( 3 ) Peripheral nerve(s). (4 ) Spinal cord (three levels). ( 5 ) Eyes (retina, optic nerve). (C) Glandular system. ( 1 ) Adrenals. ( 2 ) Parathyroids. ( 3 ) Thyroids. (D) Respiratory system. ( 1 ) Trachea. ( 2 ) Lung. ( 3 ) Pharynx. (4 ) Larynx. ( 5 ) Nose. (E) Cardiovascular/hematopoietic system. ( 1 ) Aorta (thoracic). ( 2 ) Heart. ( 3 ) Bone marrow. (4 ) Lymph nodes.

### 10 ( 5 ) Spleen. ( 6) Thymus. (F) Urogenital system. ( 1 ) Kidneys. ( 2 ) Urinary bladder. ( 3 ) Prostate. (4 ) Testes. ( 5 ) Epididymides. ( 6) Seminal vesicle(s). ( 7 ) Uterus. ( 8) Ovaries. (G) Other. ( 1 ) All gross lesions and masses. ( 2 ) Sternum and/or femur. (16) Histopathology. (i) The following histopathology should be performed: (A) Full histopathology on the respiratory tract and other organs and tissues, listed under paragraph (e)(15(iii) of this guideline, of all animals in the control and high exposure groups. (B) All gross lesions in all animals. (C) Target organs in all animals.(D) Lungs, liver and kidneys of all animals. Special attention to examination of the respiratory tract should be made for evidence of infectionas this provides a convenient assessment of the state of health of the animals.(E) When a satellite group is used, histopathology should be performed on tissues and organs identified as showing effects in the treated groups.(ii) If excessive early deaths or other problems occur in the high exposure 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.

### 11 (iv) Tissues and organs designated 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 trimming. Tissues should be trimmed to a maximum thickness of 0.4 cm for processing. (f) Data and reporting—(1) Treatment of results. (i) Data should be summarized in tabular form, showing for each test group the 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) All observed results (quantitative and qualitative) should be evaluated by an appropriate statistical method. Any generally accepted statistical method may be used; the statistical methods including significance criteria should be selected during the design of the study. (2) Evaluation of study results. The findings of the subchronic inhalation toxicity study should be evaluated in conjunction with the findings of preceding studies and considered in terms of the observed toxic effectsand the necropsy and histopathological findings. The evaluation will include the relationship between the concentration of the test substance andduration of exposure, and the presence or absence, the incidence and severity, of abnormalities, including behavioral and clinical abnormalities, gross lesions, identified target organs, body weight changes, effects on mortality and any other general or specific toxic effects. A properly conducted subchronic test should provide a satisfactory estimation of a no-effect level. 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, 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 number. (C) Physical properties. (D) Purity/impurities. (E) Identification and composition of any vehicle used. (ii) Test system should contain data on: (A) Species and strain of animals used and rationale for selection if other than that recommended.

### 12 (B) Age including body weight data and sex (C) Test environment including cage conditions, ambient temperature, humidity, and light/dark periods. (iii) Test procedure should include the following data: (A) Method of randomization used. (B) Full description of experimental design and procedure. (C) Dose regimen including levels, methods, and volume.(D) Test conditions. The following exposure conditions must be reported: ( 1 ) Description of exposure apparatus including design, type, dimensions, source of air, system for generating particulate and aerosols, method of conditioning air, treatment of exhaust air and the method of housing the animals in a test chamber. ( 2 ) The equipment for measuring temperature, humidity, and particulate aerosol concentrations and size should be described. (E) Exposure data. These should be tabulated and presented with mean values and a measure of variability (e.g., standard deviation) and should include: ( 1 ) Airflow rates through the inhalation equipment. ( 2 ) Temperature and humidity of air. ( 3 ) Actual (analytical or gravimetric) concentration in the breathing

zone. (4 ) Nominal concentration (total amount of test substance fed into the inhalation equipment divided by volume of air). ( 5 ) Particle size distribution, calculated mass median aerodynamic diameter (MMAD) and geometric standard deviation (GSD). ( 6) Explanation as to why the desired chamber concentration and/ or particle size could not be achieved (if applicable) and the efforts taken to comply with this aspect of the guidelines. (iv) Test results. (A) Group animal data. Tabulation of toxic response data by species, strain, sex and exposure level for: ( 1 ) Number of animals exposed. ( 2 ) Number of animals showing signs of toxicity. ( 3 ) Number of animals dying.

### 13 (B) Individual animal data. Data should be presented as summary (group mean) as well as for individual animals. ( 1 ) Time of death during the study or whether animals survived to termination. ( 2 ) Time of observation of each abnormal sign and its subsequent

course. ( 3 ) Body weight data. (4 ) Feed consumption data, when collected. ( 5 ) Results of ophthalmological examination, when performed. ( 6) Results of Hematological tests performed. . ( 7 ) Results of clinical chemistry tests performed. ( 8) Results of urinalysis tests performed. ( 9 ) Results of immunotoxicity screen, when performed. ( 10) 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 andequipment. The study must be conducted in compliance with GLP regulations. (h) References. The following references should be consulted for additional background information on this test guideline:(1) Cage, J.C. Experimental Inhalation Toxicology, Methods in Toxicology. Ed. G.E. Paget. (Philadelphia: F.A. Davis Co. 1970, pp. 258-277. (2) Casarett, L.J. and Doull, J. Chapter 9. Toxicology: The Basic Science of Poisons (New York: Macmillan Publishing Co. Inc. 1975).(3) Environmental Protection Agency. Office of testing and evaluation. Proposed health effects test standards for toxic substances control act test rules. 40 CFR Part 772. Standard for development of test data. Subpart D. Federal Register. Vol. 44, No.91. Pp. 27350-27362. (4) Environmental Protection Agency. Interim policy for particle size and limit concentration issues in inhalation toxicity studies. 2/1/94. Health effects division, Office of Pesticide Programs.

### 14 (5) MacFarland, H.N. Respiratory Toxicology, Essays in Toxicology. Ed. W.J. Hayes. Vol. 7 (New York: Academic Press, 1976) pp. 121-154. (6) National Academy of Sciences. Principles and Procedures for Evaluating the Toxicity of Household Substances, a report prepared bythe Committee for the Revision of NAS Publication 1138, under the auspices of the Committee on Toxicology, National Research Council, National Academy of Sciences, Washington, DC (1977). (7) Organization for Economic Co-operation and Development. Guidelines for testing of chemicals, section 4-health effects, part 413 Subchronic Inhalation Toxicity Studies, paris, 1981. (8) World Health Organization. Part I. Environmental Health Criteria6, Principles and Methods for Evaluating the Toxicity of Chemicals. (Geneva: World Health Organization, 1978). (9) World Health Organization. Principles for pre-clinical testing of drug safety, WHO Technical Report Series No. 341. (Geneva: WHO, 1966).