Revisions to Spacecraft Maximum Allowable Concentrations for Acetaldehyde

Spaceflight Maximum Allowable Concentrations (SMACs) were previously developed for acetaldehyde in 1994. Acetaldehyde is commonly detected at low levels on the International Space Station, and at higher concentrations it might be expected to cause respiratory and eye irritation. Since 1994, numerous exposure studies in human volunteers and laboratory animals have deepened our understanding of potential effects associated with exposure to acetaldehyde vapor.

A comprehensive literature search was conducted using principles of systematic review to identify toxicological data on acetaldehyde published since 1994. This search was supplemented by the use of summary sources for setting other safety values (i.e., safety values from the U.S. Environmental Protection Agency, occupational limits, etc.).

There were 13 primary toxicology studies identified in this exercise, prompting a re-evaluation of SMACs for all durations. Though the toxicity of acetaldehyde has traditionally been understood as a function of the metabolism of ingested ethanol, scientific publications after 1994 greatly increased our understanding of the toxicological effects of inhaling acetaldehyde vapor. In particular, the development of a physiology-based pharmacokinetic model generated data that was critical to the development of updated SMAC values.

The availability of newer data enabled the generation of SMACs for acetaldehyde that are markedly higher than the prior values. The shorter-duration SMACs increased by approximately 10-fold, and the longer-duration SMACs rose by twofold. The proposed values will appropriately protect astronaut health and performance and provide critical information for the design of life-support systems for low Earth orbit and beyond. Williams ES, Tapia CM, Ryder V. Revisions to spacecraft maximum allowable concentrations for acetaldehyde. Aerosp Med Hum Perform. 2025; 96(11):1019-1023.