The perpetuation of the misconception that rats receive a 3–5 times lower lung tissue dose than humans at the same ozone concentration

Abstract

This paper highlights the pervasive misconception concerning 1994 findings from Hatch et al. about ozone (O3) tissue dose in humans versus rats. That study exposed humans to 0.4 ppm and rats to 2 ppm 18O-labeled O3 and found comparable incorporation of 18O into bronchoalveolar lavage constituents. However, during O3 exposure humans were exercising, which increased their ventilation rate five-fold, while rats were at rest. This resulted in similar O3 tissue doses between the two species, and predominantly explained the comparable 18O incorporation at five-fold different concentrations. The five-times higher exercising human inhalation rate offset the five-times lower concentration, producing the same human dose expected at rest at 2 ppm (i.e. 0.4 ppm × 4686 L/2 hour ≈ 2 ppm × 998 L/2 hour). In 2013, Hatch et al. showed that resting humans and resting rats experienced fairly comparable 18O incorporation at the same O3 exposure concentration and activity state into BALF cells. Despite these findings, we show here that in the peer-reviewed literature a substantial proportion of researchers continue to perpetuate the misunderstanding that human lung tissue doses of O3 are simply 3–5 times greater than rat doses at the same O3 concentration, due to interspecies differences, and not considering activity state. It is important to correct this misconception to ensure an appropriate understanding of the implications of O3 studies by the scientific community and policy experts making regulatory decisions (e.g. the US Environmental Protection Agency’s National Ambient Air Quality Standards for O3).