Evaluation of adverse human lung function effects in controlled ozone exposure studies.

The US EPA is evaluating controlled human ozone exposure studies to determine the adequacy of the current ozone National Ambient Air Quality Standard of 75 ppb. These studies have shown that ozone exposures of 80 ppb and greater are associated with lung function decrements. Here, we critically review studies with exposures below 80 ppb to determine the lowest ozone concentration at which decrements are causally associated with ozone exposure and could be considered adverse using the Adverse Effects/Causation Framework. Regarding causation, the framework includes consideration of whether exposure-related effects are primary or secondary, statistically significant, isolated or independent, or due to study limitations. Regarding adversity, the framework indicates one should consider whether effects are adaptive, compensatory, precursors to an apical effect, severe, transient and/or reversible. We found that, at exposures below 72 ppb ozone, lung function effects are primary effects, but are isolated, independent and not statistically different compared to effects observed during filtered air exposure, indicating a lack of causation. Up to 72 ppb, lung function effects may be precursors to an apical effect, but are not likely adverse because they are transient, reversible, of low severity, do not interfere with normal activity and do not result in permanent respiratory injury or progressive respiratory dysfunction. Overall, these studies do not demonstrate a causal association between ozone concentrations in the range of the current National Ambient Air Quality Standard and adverse effects on lung function.