Hydrogen sulfide and particle matter levels associated with increased dispensing of anti-asthma drugs in Iceland's capital

Background: Air pollutants in Iceland's capital area include hydrogen sulfide (H ₂S) emissions from geothermal power plants, particle pollution (PM ₁₀) and traffic-related pollutants. Respiratory health effects of exposure to PM and traffic pollutants are well documented, yet this is one of the first studies to investigate short-term health effects of ambient H ₂S exposure. Objectives: The aim of this study was to investigate the associations between daily ambient levels of H ₂S, PM ₁₀, nitrogen dioxide (NO ₂) and ozone (O ₃), and the use of drugs for obstructive pulmonary diseases in adults in Iceland's capital area. Methods: The study period was 8 March 2006 to 31 December 2009. We used log-linear Poisson generalized additive regression models with cubic splines to estimate relative risks of individually dispensed drugs by air pollution levels. A three-day moving average of the exposure variables gave the best fit to the data. Final models included significant covariates adjusting for climate and influenza epidemics, as well as time-dependent variables. Results: The three-day moving average of H ₂S and PM ₁₀ levels were positively associated with the number of individuals who were dispensed drugs at lag 3-5, corresponding to a 2.0% (95% confidence interval [CI] 0.4, 3.6) and 0.9% (95% CI 0.1, 1.8) per 10μg/m ³ pollutant concentration increase, respectively. Conclusion: Our findings indicated that intermittent increases in levels of particle matter from traffic and natural sources and ambient H ₂S levels were weakly associated with increased dispensing of drugs for obstructive pulmonary disease in Iceland's capital area. These weak associations could be confounded by unevaluated variables hence further studies are needed.