The inhalation acute toxic class method: test procedures and biometric evaluations

Area of Science:

• Toxicology
• Chemical Safety
• Animal Welfare

Background:

• The classical LC50 test for inhalation acute toxicity requires a significant number of animals.
• Existing oral acute toxicity classification (ATC) methods, adopted by OECD and EU, provide a basis for developing alternative in vivo approaches.
• There are 12 international classification systems for inhalation toxicity based on LC50 values, varying in units (mg/L or ppm) and exposure times (1-4 h).

Purpose of the Study:

• To present a novel method for inhalation acute toxicity (ATC) classification.
• To demonstrate that the proposed method uses significantly fewer animals than the classical LC50 test.
• To establish the reliability of the inhalation ATC method as an alternative to the LC50 test.

Main Methods:

• The inhalation ATC method is a stepwise procedure, adapted from the oral ATC method.
• Three animals of each sex are tested simultaneously per concentration.
• The method was developed with three starting concentrations and two reference systems (ppm and mg/L), and biometrically evaluated using the probit model.

Main Results:

• The inhalation ATC method uses, on average, 50-80% fewer animals compared to the classical LC50 test (which uses at least 30 animals).
• Classification probabilities were calculated for all 12 current international classification systems.
• The method demonstrates reliability and provides expected numbers of experimental and moribund/dead animals for various scenarios.

Conclusions:

• The inhalation ATC method is a reliable alternative to the classical LC50 test, significantly reducing animal usage.
• The method's validity is supported by biometric evaluation and classification probability calculations.
• There is no need for further validation of the inhalation ATC method using experimental animals.