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Fine Ambient Particulate and Ozone Co-Exposures in Durham, North Carolina: Influence of Season on Particle Chemistry and Cardiovascular Responses in Rats
Citation:
Farraj, A., L. Walsh, N. Coates, F. Malik, D. Winsett, K. Kovalcik, J. Mcgee, M. Higuchi, AND M. Hazari. Fine Ambient Particulate and Ozone Co-Exposures in Durham, North Carolina: Influence of Season on Particle Chemistry and Cardiovascular Responses in Rats. Presented at Society of Toxicology, Phoenix, AZ, March 22 - 27, 2014.
Impact/Purpose:
This is the first study conducted at the US EPA that examines the health effects of co-exposures to CAPS and ozone in experimental models while also assessing the impacts of season. Data from this study may help reduce uncertainty in standard setting and improve risk assessment particularly as it relates to effect modification by exposure to a co-pollutant and the impact of season on particle chemistry.
Description:
Epidemiological studies have shown that the presence of one air pollutant modifies the cardiovascular health effects of another while controlled exposure studies in humans have documented synergistic effects of co-exposure to ambient particulate matter (PM) and ozone (O3) on blood pressure, conduit artery vasoconstriction, and dispersion of ventricular repolarization. An added complicating factor is seasonal variation of the physicochemical characteristics of PM. Thus, there is a growing need to assess the health effects of exposure to multipollutant air pollution mixtures and determine associated impacts of seasonal variation. To assess the impacts of season on particle chemistry and cardiovascular responses, we conducted summer and winter co-exposures to concentrated ambient particulates (CAPs) and O3 in Durham, NC. We hypothesized that CAPs and O3 co-exposures during the summer will elicit more adverse cardiovascular effects in rats than winter co-exposures. Rats implanted with telemeters to monitor heart rate and electrocardiogram (ECG) were exposed once for 4 hrs by whole-body inhalation to fine CAPs with/without 0.2 parts per million O3 or filtered air using a Harvard Fine Particle Concentrator. Sensitivity to arrhythmia was measured in a separate cohort 24 hr after exposure as the threshold dose of aconitine required to produce ventricular premature beats (VPB), ventricular tachycardia (VT), and ventricular fibrillation (VF). CAPs concentrations ranged from 75-200 g/m3 with particle sizes from ~155 nm to ~325 nm. Winter exposure’s ambient PM mass had a lower ratio of fine to ultrafine particles; therefore, CAPs concentrations and PM size were approximately half of summer exposures. PM elemental composition and organic and elemental carbon fractions were analyzed by high resolution inductively coupled plasma – mass spectrometry and thermo-optical pyrolytic vaporization, respectively. Preliminary assessments indicate that rats exposed to summer CAPs or ozone alone developed VPB’s and VT at significantly lower doses of aconitine than air controls; CAPs and ozone co-exposures did not augment the response. There was no effect of exposure on arrhythmia sensitivity during the winter. Particle chemistry and ECG and heart rate variability are currently being analyzed (This abstract does not reflect EPA policy).