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SMOG-CHAMBER TOXICOLOGY BETTER ESTIMATES THE TRUE TOXIC POTENTIAL OF ATMOSPHERIC MIXTURES
Citation:
DOYLE, M., K. SEXTON, K. DE BRUKINE, S. EBERVILLER, AND I. JASPERS. SMOG-CHAMBER TOXICOLOGY BETTER ESTIMATES THE TRUE TOXIC POTENTIAL OF ATMOSPHERIC MIXTURES. Presented at International Society of Exposure Assessment Annual Meeting, Tucson, AZ, October 30 - November 03, 2005.
Description:
The chemistry of hazardous air pollutants (HAPs) have been studied for many years, yet little is known about how these chemicals, once interacted with urban atmospheres, affect healthy and susceptible individuals. The toxic potential of these very reactive compounds once they interact with hydroxyl radicals and ozone (created by photochemical processes), to produce many identified and quantified but not yet identified, products is currently unclear. The UNC smog chambers have been used for over 30 years to investigate and develop chemical mechanisms of atmospheric species, utilizing natural environmental conditions (real sunlight and normal humidity) to simulate the chemistry of realistic mixtures of HAPs and NOx found in urban atmospheres, thus generating ozone and other 'smog' products. As transformation products are discovered, prioritized and regulated, natural simulation chemistry will need to be studied to predict potential changes in environmental risk assessments. The smog chamber/direct-gas-exposure system was designed to investigate the toxicity of chemicals before and after photochemical reactions and to investigate interactions of the urban atmosphere using representative in-vitro samples, avoiding the concern of compositional modifications caused by collecting in liquid or other techniques. Classical toxicological approaches to examine atmospheric pollutants do not allow for the study of unknown transformation products that may be important when assessing the risk of HAPs and their transformation products. By combining toxicological tests with suitable measurable endpoints, and the smog chamber exposure system using dynamic chemical mixtures generating full transformation products, allows the toxicity of the complete mixture to be determined even if it can not be fully characterized. Implementation of this system using isoprene, 1,3-butadiene and methanol suggests that their photochemically induced transformation products induce greater adverse effects, cytotoxicity and inflammatory gene expression (IL-8 and IL-6), than the original, unreacted HAP. Along with comparing the effects of photochemistry, a second objective of this study was to determine the role of ozone in the effects caused by the photochemically active HAPS mixtures. Taken together these results indicate, that unlike simplistic atmospheric models such as methanol, ozone does not significantly account for the effects seen in more complex atmospheric mixtures, such as those generated by BD and ISO, and therefore full photochemical transformations and interactions must be carefully evaluated when investigating adverse health effects induced by exposure to HAPS. This approach demonstrates the ability to better characterize and estimate the true toxic potential of atmospheric pollutants