OECD TG 403 is the standard for “Acute Inhalation Toxicity, ” which is listed in Section 4 (Health Effects) of the OECD Test Guidelines for the Testing of Chemicals. It was first adopted in 1981 and updated in 2009. The test is an in vivo toxicity test designed to evaluate the acute toxic effects of a substance following a single exposure via the respiratory tract.
The primary objective of the test is to determine the local and systemic toxic effects following inhalation, the LC50 value, and the GHS/CLP classification. Inhalation is the primary route of exposure for volatile chemicals, gases, vapors, aerosols, and inhalable particles.
The basic principle of the test is as follows:
- The test substance is administered to the animals via inhalation using a suitable inhalation exposure system.
- Common exposure systems include whole-body systems, nose-only systems, and head-only systems. “Nose-only” systems are often preferred because they minimize secondary exposure via the oral and dermal routes.
- The physical state of the test substance (gas, vapor, aerosol, dust) directly affects the preparation and characterization of the test atmosphere.
- The exposure duration is generally 4 hours; however, depending on regulatory requirements, other time periods may also be used.
- In the test atmosphere, both the nominal concentration and the actual (analytical) concentration must be measured and reported.
- When exposed to aerosols and particles, the particle size distribution (e.g., mass-median aerodynamic diameter, MMAD, and geometric standard deviation, GSD) must be determined.
- The animals are kept under clinical observation for at least 14 days; respiratory findings, signs of toxicity, reversibility, changes in body weight, and mortality are recorded.
- At the end of the study, a necropsy is performed; macroscopic findings, particularly those of the respiratory tract and lungs, are documented; if necessary, a histopathological examination is conducted.
The key parameters reported in the study are:
- The exposure concentrations used (mg/L, ppm, or mg/m³)
- Duration of exposure and exposure pattern (whole body, nose only, head only)
- Actual concentration in the test atmosphere and analytical measurement method
- Physical state (gas, vapor, or aerosol) and particle size distribution (MMAD, GSD)
- Clinical observations (breathing difficulties, nasal discharge, cyanosis, lethargy, etc.)
- Changes in Body Weight
- Mortality and Survival Times
- Autopsy findings and, if applicable, histopathological findings
- LC50 value and confidence interval
GHS/CLP category for acute inhalation toxicity (separately for gas, vapor, dust/mist) and rationale for the classification; animal species, sex, age, and environmental conditions (temperature, humidity, airflow) used; data on measurement uncertainty and repeatability
Why is this being done?
OECD TG 403 is being conducted for the following scientific and regulatory purposes:
- Determination of Acute Inhalation Toxicity: Assessment of Local and Systemic Toxic Effects Occurring Following a Single Inhalation Exposure
- Determination of the LC50 Value: Quantitative Assessment of Acute Inhalation Toxicity Potential
- GHS/CLP Classification: Determination of the acute inhalation toxicity category of the substance (gas, vapor, dust/mist) and establishment of labeling requirements
- Evaluation of the target organs of the respiratory tract: Assessment of local effects in the upper respiratory tract, the lungs, and associated tissues
- Support in the preparation of regulatory submissions: Used in safety assessments of chemicals, pesticides, biocidal products, pharmaceuticals, and industrial chemicals
- Contribution to Risk Assessment: Provision of Baseline Data for Risk Assessment in Inhalation Exposure Scenarios
- Selection of the route of exposure: Provision of baseline toxicity data for volatile substances for which the oral or dermal route is not appropriate
- Labeling and Transportation: Data on acute inhalation toxicity are used in the classification of chemicals for labeling and transportation purposes
- Evidence-Based Approach: A Contribution to the Holistic Assessment of the Substance in Conjunction with Other Toxicological, Physicochemical, and Exposure Data
OECD Guideline 403 is the standard method for assessing acute inhalation toxicity. Depending on the regulatory context, alternative approaches such as OECD Guideline 433 (Fixed Concentration Procedure) and OECD Guideline 436 (Acute Toxic Class Method) may also be used.
The results should be interpreted in the context of the substance's physicochemical properties, other data on acute toxicity, repeated-dose toxicity, and the exposure assessment.
As part of our nano-testing services, we conduct acute inhalation toxicity studies in accordance with OECD TG 403, applying scientific rigor and utilizing our accredited laboratory infrastructure and quality management system.
Our scope of services includes the following:
Study Design and Protocol Development
- Preparation of a study protocol in accordance with OECD TG 403
- Selection of the exposure system (whole-body, nose-only, head-only) based on the physical state (gas, vapor, aerosol, dust) and the physicochemical properties of the test substance
- Scientific justification for the concentration levels and the design of the preliminary tests based on existing toxicity data and structural similarities
- Selection of a suitable carrier (vehicle); evaluation of solubility, volatility, and stability
- Determination of species, sex, age, and environmental conditions (temperature, humidity, airflow)
- Compliance with Ethical Review and Animal Welfare Requirements
- If necessary, draft a preliminary test (range-finding)
For information on study design, selection of the exposure system, characterization of the test atmosphere, sample collection conditions, the test schedule, and reporting procedures for your acute inhalation toxicity studies in accordance with OECD TG 403, please contact Nano-Test.