Episodic Exposure to Eucalyptus Smoke during Sperm Maturation Impairs Sperm Motility in Long Evans Rats

Epidemiologic studies have suggested a relationship with firefighting and exposure to wildland fire smoke with a heightened risk of male infertility. Herein, 12-week-old Long-Evans rats were exposed to smoldering eucalyptus smoke with concentrations ranging from 3.52-23.7 mg/m³ for 7 total days (1 h/day) over a 10-day period, aligning with sperm maturation. An additional subset of rats was exposed to the filtered fraction of the lowest concentration, removing particulate matter from the smoke emission. At ∼24 h following the final exposure, the percentage of sperm with progressive tracking was reduced with whole smoke exposure (11 mg/m³). This reduction was accompanied by a decrease in the average path velocity (VAP) of sperm. While these effects were lost at the 3.52 mg/m³ concentration, interestingly, filtration of the particulate matter from this exposure reduced progressive motility and nearly all measures of sperm kinetics including VAP, straight line velocity (VSL), and the amplitude of lateral head displacement (ALH). Data from this study provides evidence that acute exposure to eucalyptus smoke during a sensitive window of the sperm lifecycle (maturation) impairs sperm motility, an effect that may be attributed to the volatile phase of eucalyptus combustion.