National Ambient Air Quality Objectives For Ground-Level Ozone- Summary - Science Assessment Document

7. Birds And Mammals

Very little information on the effect of ozone on birds and wildlife is available. Only three studies were found that reported on effects on birds, and all of these involved domesticated birds and their response to acute exposures. Lung haemorrhage was noted in all three studies, and therefore this appears to be a consistent effect in birds in response to exposure to ozone. The absence of data on potential effects of chronic exposures is clearly a weakness of the current database.

Eleven studies on the effects of acute exposure to ozone on mammals were reviewed, all on domesticated mammals. Most of these studies were on sheep, because sheep have been proposed as a potential animal model for human effects. The most consistently observed responses include adverse effects on red blood cells and inflammatory responses. Red blood cell effects appear to be the most sensitive endpoint for assessment of effects of ozone on mammals based on the evidence presented. No studies were found that dealt with chronic exposures.

For both birds and mammals, the only significant exposure route is inhalation. Therefore, as is the case with humans, the effects of concern have to do with impacts on the respiratory system. There are notable differences, however, between the lung-air sac respiratory system of avian species and the mammalian bronchoalveolar lung. Among the most important of these are that birds have a higher mass-specific minute ventilation, higher mass specific effective ventilation of gas-exchange tissues, cross-current and counter-current gas-exchange mechanisms and a gas diffusion barrier half the thickness of that of mammals. While these differences may predispose birds to greater sensitivity to inhaled toxicants, there is insufficient information at present to make any predictions concerning relative sensitivities. There appears to be a complex relationship between a species' respiratory physiology, its pathophysiologic response to a toxic gas and other physiologic factors.

There was insufficient information to develop concentration-response relationships and very limited information on which to base effect levels for both birds and mammals. Given the paucity of experimental data and the lack of experimental exposures that reflect ambient conditions, no general conclusions can be drawn at this stage about possible effect levels in either birds or mammals.