Assessment of Recent Health Studies of Long-Term Exposure to Ozone

Report no. 3/14: This report summarises the assessment of the policy relevant long-term health studies published since the last update of the ozone Air Quality Limit Value (AQLV). This project was undertaken in preparation for the European Union 2013 Year of Air discussions on the Air Quality Directives, and the impact of new health science on the AQLV for key pollutants, including ozone.

The types of studies reviewed in this assessment included chronic mortality and morbidity air pollution epidemiology studies and repeat-dose toxicology and mechanistic studies. For each study, a summary of the findings as reported was prepared along with a critical review identifying the strengths and weaknesses of the study, In total thirteen chronic mortality studies, nine respiratory morbidity studies, nine epidemiology studies evaluating long-term exposure to zone and pulmonary function and nine repeat dose animal inhalation studies were reviewed. Reliability scores were provided for both the epidemiology and toxicology studies, and a weight-of evidence approach was implemented to determine causality.

In summary, for chronic mortality, the data were considered not sufficient to draw a causal conclusion between long-term exposure to zone and mortality. The available toxicology and mechanistic data did not support the mortality hypothesis at current ambient ozone levels since much higher levels (500 ppb) were required to produce serious effects. For chronic morbidity, the data were considered insufficient to establish a causal relationship between long-term exposure to ozone and new onset asthma. In addition, the data do not indicate that long-term exposure to ozone at current ambient levels causes reductions in lung function development. Short-term exposure to higher levels of ozone can cause transient change in lung function which, if accompanied with symptoms, could be considered as adverse.

The serious effects in animals as a result of repeated high level (500 ppb) exposure are not expected to occur in humans exposed to ambient levels. In summary, the quality of the evidence to evaluate the association between chronic exposure to ozone and mortality is highly unreliable, and information to support an objectively-based Air Quality Target Values (AQTV) is lacking.