This paper examines the tensions of sustainable development in Seattle, Washington, a commonly recognised urban environmental leader. Drawing on the perspective of sustainability as a conflicted process, this research expected a negative relationship between gentrification and environmental justice when affluent residents outcompete less affluent ones for neighbourhoods with fewer environmental hazards. The methods combine geographic cluster analysis and longitudinal air toxic emission comparisons to analyse socioeconomic changes in Seattle Census block-groups between 1990, 2000, and 2009 coupled with measures of relative potential risk and pollution volume. The property and development conflicts embedded within sustainability lead to pollution exposure risk and socioeconomic vulnerability converging in the same areas and reveal one of the ‘Emerald City’s’ significant environmental challenges. Inequitable development and environmental injustice remain overlooked dimensions of sustainability that interdisciplinary research should address.