Systematically evaluating and integrating evidence in National Ambient Air Quality Standards reviews

Meta-analysis of the association between low concentration PM2.5 and cardiovascular mortality in the United States and Canada

OBJECTIVES

The adverse effects of fine particulate matter (PM2.5), including cardiovascular outcomes, are well established. This review and meta-analysis investigates the association between long-term exposure to low concentration PM2.5 (<12 µg/m3) and CVD mortality in U.S. and Canadian populations.

METHODS

We conducted a literature search and completed random effect meta-analyses.

RESULTS

Twenty-four studies were reviewed, with 12 from each of the U.S. and Canada. Fifteen of eighteen studies that reported hazard ratios (HRs) for total CVD mortality reported statistically significant positive associations with low concentration PM2.5. For cause-specific CVD mortality, more consistent results were shown for ischemic heart disease (IHD) mortality, with all eleven studies reporting statistically significant associations (HR = 1.09 to 2.48). Only three of 12 studies evaluating cerebrovascular mortality reported statistically significant associations (HR = 1.10 to 1.27). Studies that restricted analyses to participants with mean exposures <12 µg/m3 found statistically significant associations between PM2.5 and at least some of the CVD mortality outcomes of interest. However, the shape of the concentration-response functions varied widely. Only six studies controlled for at least one additional air pollutant, and multi-pollutant models generally showed an attenuated impact of PM2.5. Despite existing gaps in understanding the association between low concentrations of PM2.5 and cardiovascular mortality, this review highlights the critical importance of ongoing efforts to improve air quality for public health benefits.

CONCLUSIONS

Continued focus on understanding the shape of the concentration-response function for PM2.5, the impact of co-pollutants on observed effects, and how particle composition may impact effect estimates, is recommended.

Characteristics of ambient air quality and its air quality index (AQI) model in Shanghai, China

Long-term observations indicate that, the ambient air quality in Shanghai continues to improve, however the synergistic effects between the air pollutants PM2.5, O3 and NO2 are also increasing. The concentration of chemical components included in PM2.5 is higher in moderately polluted air containing multiple pollutants. This suggests that air pollution metrics based on multi-pollutant synergy are more descriptive of ambient air quality than single-pollutant air quality index (AQI) models that may ignore the effect of synergy between pollutants on ambient air quality forecasts. Therefore, this study proposes a new multi-pollutant air quality index model (NMAQI) based on four air pollutants (PM2.5, SO2, NO2 and O3) that emphasizes the relationship between PM2.5, NO2 and O3 in ambient air. The model successfully categorized observational data into classes of good, moderate, and polluted air quality ratings. Verification of the NMAQI model using the PM2.5 chemical composition spectrum shows that the NMAQI model can more accurately classify samples with high concentrations of chemical components (often misclassified by AQI) into high pollution levels. The model has an improved capacity to assess the degree of pollution in urban ambient air and to reduce the risk of public exposure to highly polluted atmospheric environments.

Does ozone inhalation cause adverse metabolic effects in humans? A systematic review

We utilized a practical, transparent approach for systematically reviewing a chemical-specific evidence base. This approach was used for a case study of ozone inhalation exposure and adverse metabolic effects (overweight/obesity, Type 1 diabetes [T1D], Type 2 diabetes [T2D], and metabolic syndrome). We followed the basic principles of systematic review. Studies were defined as "Suitable" or "Supplemental." The evidence for Suitable studies was characterized as strong or weak. An overall causality judgment for each outcome was then determined as either causal, suggestive, insufficient, or not likely. Fifteen epidemiologic and 33 toxicologic studies were Suitable for evidence synthesis. The strength of the human evidence was weak for all outcomes. The toxicologic evidence was weak for all outcomes except two: body weight, and impaired glucose tolerance/homeostasis and fasting/baseline hyperglycemia. The combined epidemiologic and toxicologic evidence was categorized as weak for overweight/obesity, T1D, and metabolic syndrome,. The association between ozone exposure and T2D was determined to be insufficient or suggestive. The streamlined approach described in this paper is transparent and focuses on key elements. As systematic review guidelines are becoming increasingly complex, it is worth exploring the extent to which related health outcomes should be combined or kept distinct, and the merits of focusing on critical elements to select studies suitable for causal inference. We recommend that systematic review results be used to target discussions around specific research needs for advancing causal determinations.