Inhalation toxicity 90 days – OECD 413
Description
OECD 413 is the reference study for characterizing the toxicity of a substance when repeatedly inhaled over 90 days. It is the test expected by regulatory agencies when establishing a legally binding threshold value for prolonged respiratory exposure—that of workers in a specific job, or consumers in regular use.
Thirteen weeks of exposure allow us to observe what a four-week study cannot show: the progressive retention of poorly soluble materials in the lung, the establishment of a chronic inflammatory response, and the systemic damage resulting from the passage of the substance into the circulation.
Objective of the analysis
- Determine the NOAEC and LOAEC with statistical power suitable for small amplitude effects.
- Distinguish between local effects on the respiratory system and systemic effects.
- Characterize the pulmonary retention of poorly soluble materials, a phenomenon that only manifests itself over time.
- Documenting pulmonary inflammation by bronchoalveolar lavage.
- Establish the reversibility of the effects using a satellite group exposed to the highest concentration.
OECD Methodology 413
| Guideline | OECD 413 (2018 version) |
| Preferred species | Rat |
| Exhibition route | Inhalation — nose-only mode preferred |
| Duration | 13 weeks, or a minimum of 90 days — 6 hours per day, 5 days per week |
| Experimental groups | 3 concentrations + control exposed to air and/or vehicle |
| Staff | 10 males and 10 females per group |
| Satellite group | 10 males and 10 females at the highest concentration, recovery of at least 14 days |
| Required particle size | MMAD of 1 to 3 µm, geometric standard deviation of 1.5 to 3.0 |
| Product result | NOAEC, LOAEC, target organs, pulmonary retention, reversibility |
Seven-day-a-week exposure is permitted for certain specific applications, subject to justification. The atmospheric control requirements—exposure method, weekly particle size analysis, measurement of actual concentration several times a day, ambient conditions—are identical to those of the 28-day test and are detailed in our OECD Fact Sheet 412.
Parameters evaluated
Clinical monitoring — daily observations, body weight, food and water intake throughout the duration of the study.
Ophthalmological examination — performed before the start of the trial and then at its end. It detects eye damage related to direct contact with the exposure atmosphere.
Biological analyses — complete hematology and clinical biochemistry.
Bronchoalveolar lavage — recommended when the lower respiratory tract is the primary site of deposition. It quantifies the pulmonary inflammatory response before lesions become histologically evident.
Necropsy, organ weighing and histopathology — complete examination of the respiratory tree, from the nasal passages to the alveoli, and of the systemic organs.
Further investigations — the guideline allows for the integration, depending on the issues at stake, of a kinetic study, biomonitoring, respiratory function testing, measurement of the retention of poorly soluble materials, and observation of behavioral changes. These parameters are decided at the study design stage, never afterward.
Interpretation and regulatory consequences
The CLP regulation guideline values for the STOT-RE are established precisely on the basis of a 90-day study. Test 413 therefore applies directly to this, without the extrapolation step required by a 28-day study—a real advantage, since this extrapolation is a classic point of contention for the assessor.
| Physical fitness | Category 1 | Category 2 |
|---|---|---|
| Gas | C ≤ 50 ppmV/6 h/day | 50 < C ≤ 250 ppmV/6 h/day |
| Vapors | C ≤ 0.2 mg/L/6 h/day | 0.2 < C ≤ 1.0 mg/L/6 h/day |
| Dust, fog, smoke | C ≤ 0.02 mg/L/6 h/day | 0.02 < C ≤ 0.2 mg/L/6 h/day |
Under REACH, subchronic exposure assessment becomes a standard reporting requirement when the threshold of 100 tonnes per year per reporting entityis exceeded, with the respiratory route being the primary focus when it corresponds to the actual exposure scenario. The resulting NOAEC also informs the calculation of occupational exposure limits.
Sectors and applications concerned
- Chemical industry — volatile substances, gases, solvents and high tonnage powders.
- Materials, polymers and nanomaterials — evaluation of pulmonary retention of poorly soluble particles.
- Biocides and plant protection products — active substance approval dossiers.
- Cleaning products, aerosols and propellants — repeated domestic or professional use.
- Animal health and nutrition — occupational exposure to premix dust.
Why use YesWeLab?
A 90-day inhalation study combines the two most costly challenges of regulatory toxicology: the duration and the technical complexity of the exposure. Thirteen weeks of generating a controlled atmosphere, continuously monitored and documented daily, represents a commitment that very few laboratories can meet, and that no industry is willing to repeat.
We connect you with partner laboratories equipped for inhalation exposure and operating according to Good Laboratory Practices, a condition for the study to be admissible in a regulatory file.
Our intervention lies precisely where it changes the outcome of the study: validating the suitability of the respiratory route, deciding between 28 and 90 days, determining the concentration plan, and, most importantly, choosing which additional investigations to include from the outset—bronchoalveolar lavage, pulmonary retention, and functional testing. These decisions cannot be reversed once the study has begun.
Frequently Asked Questions
What is the expected timeframe for an OECD 413 test?
Thirteen weeks of exposure, preceded by the development and characterization of the atmosphere generation system, and followed by histopathology and report writing. An overall timeframe of nine to fifteen months is realistic, and the availability of inhalation facilities is often the limiting factor.
Is it necessary to carry out an OECD 412 beforehand?
A preliminary concentration determination study is strongly recommended in the absence of data. This avoids the most costly scenario: a poorly calibrated high concentration that renders the group uninterpretable after thirteen weeks of exposure. If your tonnage immediately exceeds 100 tonnes per year, a short preliminary phase is preferable to a full 412 test.
What does the study of pulmonary retention reveal?
For poorly soluble materials, it measures the progressive accumulation in the lungs and the body's clearance capacity. This is a crucial parameter for powders and particles, and it can only be assessed over a long period.
Is a 28-day study sufficient?
It meets the applicable requirement for volumes between 10 and 100 tonnes per year. Beyond this, a 90-day study is required, and test 412 is not a substitute: its observation window does not allow for the observation of pulmonary retention or the detection of slowly developing effects.
See also
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