Ethnocultural and socioeconomic disparities in exposure to residential greenness within urban Canada.

BACKGROUND: Residential greenness has been associated with health benefits, such as lower risk of mortality, cardiovascular disease, obesity, adverse birth outcomes and asthma and better psychological health. However, the variation in greenness across socioeconomic and demographic characteristics in urban areas of Canada has not been well documented. DATA AND METHODS: Respondents to the 2016 Census long-form questionnaire were assigned estimates of exposure to residential greenness based on the mean Normalized Difference Vegetation Index (NDVI) (from 2012 or the most recent year available) within a 500 m buffer around their home, based on postal code. Census weights were used to determine differences in average exposure to greenness according to selected demographic and socioeconomic characteristics. RESULTS: Mean residential greenness among the 5.3 million census respondents in urban Canada was 0.44 units of the NDVI (standard deviation = 0.18 units). Greenness was lower among immigrants (particularly recent immigrants), some groups designated as visible minorities (particularly people of Filipino ancestry), lower-income households and tenants (i.e., NDVI values ranging from 0.40 to 0.43 units). Greenness values were highest among White non-immigrants and higher-income households (i.e., NDVI values ranging from 0.46 to 0.47 units). DISCUSSION: Given the potentially multifaceted role that greenness plays in health outcomes, the inequalities in residential greenness described here may contribute to producing or exacerbating existing health inequalities in the Canadian population.

Evaluating the Sensitivity of PM2.5-Mortality Associations to the Spatial and Temporal Scale of Exposure Assessment.

BACKGROUND: The temporal and spatial scales of exposure assessment may influence observed associations between fine particulate air pollution (PM2.5) and mortality, but few studies have systematically examined this question. METHODS: We followed 2.4 million adults in the 2001 Canadian Census Health and Environment Cohort for nonaccidental and cause-specific mortality between 2001 and 2011. We assigned PM2.5 exposures to residential locations using satellite-based estimates and compared three different temporal moving averages (1, 3, and 8 years) and three spatial scales (1, 5, and 10 km) of exposure assignment. In addition, we examined different spatial scales based on age, employment status, and urban/rural location, and adjustment for O3, NO2, or their combined oxidant capacity (Ox). RESULTS: In general, longer moving averages resulted in stronger associations between PM2.5 and mortality. For nonaccidental mortality, we observed a hazard ratio of 1.11 (95% CI = 1.08, 1.13) for the 1-year moving average compared with 1.23 (95% CI = 1.20, 1.27) for the 8-year moving average. Respiratory and lung cancer mortality were most sensitive to the spatial scale of exposure assessment with stronger associations observed at smaller spatial scales. Adjustment for oxidant gases attenuated associations between PM2.5 and cardiovascular mortality and strengthened associations with lung cancer. Despite these variations, PM2.5 was associated with increased mortality in nearly all of the models examined. CONCLUSIONS: These findings support a relationship between outdoor PM2.5 and mortality at low concentrations and highlight the importance of longer-exposure windows, more spatially resolved exposure metrics, and adjustment for oxidant gases in characterizing this relationship.

Global estimates of mortality associated with long-term exposure to outdoor fine particulate matter.

Exposure to ambient fine particulate matter (PM2.5) is a major global health concern. Quantitative estimates of attributable mortality are based on disease-specific hazard ratio models that incorporate risk information from multiple PM2.5 sources (outdoor and indoor air pollution from use of solid fuels and secondhand and active smoking), requiring assumptions about equivalent exposure and toxicity. We relax these contentious assumptions by constructing a PM2.5-mortality hazard ratio function based only on cohort studies of outdoor air pollution that covers the global exposure range. We modeled the shape of the association between PM2.5 and nonaccidental mortality using data from 41 cohorts from 16 countries-the Global Exposure Mortality Model (GEMM). We then constructed GEMMs for five specific causes of death examined by the global burden of disease (GBD). The GEMM predicts 8.9 million [95% confidence interval (CI): 7.5-10.3] deaths in 2015, a figure 30% larger than that predicted by the sum of deaths among the five specific causes (6.9; 95% CI: 4.9-8.5) and 120% larger than the risk function used in the GBD (4.0; 95% CI: 3.3-4.8). Differences between the GEMM and GBD risk functions are larger for a 20% reduction in concentrations, with the GEMM predicting 220% higher excess deaths. These results suggest that PM2.5 exposure may be related to additional causes of death than the five considered by the GBD and that incorporation of risk information from other, nonoutdoor, particle sources leads to underestimation of disease burden, especially at higher concentrations.

Exposure to fine particulate matter air pollution in Canada.

BACKGROUND: Exposure to ambient fine particulate matter (PM2.5) has been associated with a greater risk of non-accidental, cardiovascular and respiratory mortality in Canada. Research based on Canadian cohorts suggests that exposure to PM2.5 varies by demographic and socioeconomic characteristics. Studies of NO2, another pollutant, indicate that persons of lower socioeconomic status and some visible minority groups have greater exposure in urban centres. DATA AND METHODS: National residential PM2.5 was estimated from a ~1 km² spatial layer for respondents to the 2006 Census long-form questionnaire. Weighted PM2.5 estimates from personal-level estimates were determined for white, Aboriginal, visible minority and immigrant populations, as well as for socioeconomic groups (household income, educational attainment) and stratified by urban core, urban fringe and rural residence. Descriptive statistics were provided for selected comparisons. RESULTS: In Canada, PM2.5 exposure was 1.61 µg/m³ higher for visible minority (versus white) populations, and 1.55 µg/m³ higher for immigrants (versus non-immigrants). When the relatively high percentages of these groups in large cities were taken into account, exposure differences in urban cores were much smaller. Exposure among urban immigrants did not decrease substantially with time since immigration (< 0.5 µg/m³ between any two years). In urban cores, residents of low-income households had marginally higher exposure (0.56 µg/m³) than did people who were not in low-income households. INTERPRETATION: Differences between specific population groups in exposure to PM2.5 are due, at least in part, to higher percentages of these groups living in urban cores where air pollution levels are elevated.

Socioeconomic differences in nitrogen dioxide ambient air pollution exposure among children in the three largest Canadian cities.

BACKGROUND: Nitrogen dioxide (NO2) is a marker for traffic-related air pollution, which exhibits strong spatial gradients in large cities. Previous studies have shown that in Canadian cities, exposure to ambient NO2 is greater in neighbourhoods of low socioeconomic status (SES). As a result of these differences in exposure, air pollution-related health problems may be more prevalent among children in lower SES urban neighbourhoods. DATA AND METHODS: Children younger than age 18 enumerated in the 2006 Census who lived in Toronto, Montreal or Vancouver were linked to published air pollution exposure land use regression models to assign exposure at the Dissemination Area (DA) level. Associations between both socioeconomic and visible minority status and exposure to ambient NO2 among children in these three cities were examined in a series of regression models (OLS and simultaneous autoregressive models that account for spatial autocorrelation). RESULTS: Children in lower income DAs in all three cities were exposed to higher NO2 concentrations than were children in higher income DAs (mean difference of 2 ppb between lowest and highest income quintiles). In some cities, DAs with larger percentages of children in lone-parent families and visible minority children were characterized by greater NO2 exposure. INTERPRETATION: The relatively high incidence of air pollution-related diseases (for example, asthma) among children in lower SES neighbourhoods may be attributable, at least in part, to variations in NO2 air pollution exposure within the same city.

Spatial associations between socioeconomic groups and NO2 air pollution exposure within three large Canadian cities.

Previous studies of environmental justice in Canadian cities have linked lower socioeconomic status to greater air pollution exposures at coarse geographic scales, (i.e., Census Tracts). However, studies that examine these associations at finer scales are less common, as are comparisons among cities. To assess differences in exposure to air pollution among socioeconomic groups, we assigned estimates of exposure to ambient nitrogen dioxide (NO2), a marker for traffic-related pollution, from city-wide land use regression models to respondents of the 2006 Canadian census long-form questionnaire in Toronto, Montreal, and Vancouver. Data were aggregated at a finer scale than in most previous studies (i.e., by Dissemination Area (DA), which includes approximately 400-700 persons). We developed simultaneous autoregressive (SAR) models, which account for spatial autocorrelation, to identify associations between NO2 exposure and indicators of social and material deprivation. In Canada's three largest cities, DAs with greater proportions of tenants and residents who do not speak either English or French were characterised by greater exposures to ambient NO2. We also observed positive associations between NO2 concentrations and indicators of social deprivation, including the proportion of persons living alone (in Toronto), and the proportion of persons who were unmarried/not in a common-law relationship (in Vancouver). Other common measures of deprivation (e.g., lone-parent families, unemployment) were not associated with NO2 exposures. DAs characterised by selected indicators of deprivation were associated with higher concentrations of ambient NO2 air pollution in the three largest cities in Canada.