Submarine exposure guideline recommendations for carbon dioxide based on the prenatal developmental effects of...

To protect crewmember health, the U.S. Navy sets exposure limits for more than 200 components of submarine atmospheres. The addition of females to nuclear submarines required a reevaluation of these exposure limits, originally established for all-male crews. In the case of carbon dioxide (CO₂ ), the only available data suitable for deriving an exposure limit were from a 2010 study sponsored by the British Royal Navy that reported a debatable interpretation casting doubt on whether current U.S. Navy exposure limits served to protect fetal developmental health.

About 120 time-mated female Sprague-Dawley rats (Crl: CD[SD]) were exposed to CO₂ at levels of 1.5%, 2.0%, 2.5%, and 3.0% from gestation days 6 to 20. Dams were euthanized and fetuses were examined.

Findings with implications for exposure limits for CO₂ during pregnancy were an increased mean litter proportion of early resorptions and a lower mean litter proportion of viable fetuses in the 3.0% CO₂ group.

The results yield a No Observed Adverse Effect Level (NOAEL) of 2.5% and a Lowest Observed Adverse Effect Level (LOAEL) of 3.0%. The results reasonably allow a point of departure of 2.5% CO₂ for deriving an exposure recommendation. An interspecies uncertainty factor was applied to derive a recommended 90-day continuous exposure limit (CEL) of 0.8% for CO₂ . As reproductive endpoints that are developmental in nature must be assumed to result from a single exposure at a critical point during gestation, it is further recommended that the 24-hr emergency exposure limit (EEL) also be 0.8%.