Cardiovascular effects of nickel in ambient air

Abstract

Background: Fine particulate matter (FPM) in ambient air causes premature mortality due to cardiac disease in susceptible populations.

Objective: Our objective in this study was to determine the most influential FPM components.

Methods: A mouse model of atherosclerosis (ApoE-/-) was exposed to either filtered air or concentrated FPM (CAPs) in Tuxedo, New York (85 microg/m3 average, 6 hr/day, 5 days/week, for 6 months), and the FPM elemental composition was determined for each day. We also examined associations between PM components and mortality for two population studies: National Mortality and Morbidity Air Pollution Study (NMMAPS) and Hong Kong.

Results: For the CAPs-exposed mice, the average of nickel was 43 ng/m3, but on 14 days, there were Ni peaks at approximately 175 ng/m3 and unusually low FPM and vanadium. For those days, back-trajectory analyses identified a remote Ni point source. Electrocardiographic measurements on CAPs-exposed and sham-exposed mice showed Ni to be significantly associated with acute changes in heart rate and its variability. In NMMAPS, daily mortality rates in the 60 cities with recent speciation data were significantly associated with average Ni and V, but not with other measured species. Also, the Hong Kong sulfur intervention produced sharp drops in sulfur dioxide, Ni, and V, but not other components, corresponding to the intervention-related reduction in cardiovascular and pulmonary mortality.

Conclusions: Known biological mechanisms cannot account for the significant associations between Ni with the acute cardiac function changes in the mice or with cardiovascular mortality in people at low ambient air concentrations; therefore, further research is needed.

Figure 1

Elemental concentrations and HR and HRV (mean ± SE) for 14 days when winds were from the northwest and for the 89 days with winds from all other directions, and the differences in heart rates in ApoE^−/− mice exposed to CAPs and filtered air. CAPs concentrations are shown in μg/m³, elemental concentrations in ng/m³, HR in beats/min, and HRV (as logSDNN) in milliseconds.

Figure 2

Back trajectories of all 14 days when winds were from the northwest based on the National Oceanic and Atmospheric Administration (NOAA) HYSPLIT model (NOAA 2006). Abbreviations: EDAS, Eta Data Assimilation System; UTC, coordinated universal time. *Location of the nickel smelter in Sudbury, Ontario, Canada.

Figure 3

Differences in daily group–averaged HR (A) and HRV (logSDNN) (B) between mice exposed to CAPs and filtered air for the 89 days when winds were from other directions and for the 14 days when winds were from the northwest (and Ni, Cr, and Fe were elevated) with the corresponding data for 1 and 2 days after the days with wind from the northwest. Boxes represent 25th and 75th percentiles, lines within boxes indicate medians, error bars indicate 10th and 90th percentiles, and diamonds indicate outliers.

Figure 4

Daily group averaged HR (A) and HRV (logSDNN) (B) in mice exposed to CAPs or filtered air.

Figure 5

Differences in mortality risk coefficients shown as the 5th–95th percentile difference in concentrations of FPM and FPM components for the 60 NMMAP MSAs for which FPM speciation data were available. Abbreviations: EC, elemental carbon; OC, organic carbon.