Toxicity travels in a changing climate.

• Previous studies on contamination spread by flooding undercount sites. • 3.3 million people are at risk of contamination from flooding in US urban areas. • Due to changes in urbanization and climate change these figures are likely to increase. • These risks pose complex challenges for environmental managers and urban planners. Climate change is imposing substantial consequences across physical and social infrastructures. The extent of social disruption and risk to human health are, however, potentially much broader than these general consequences, taken individually, would suggest. To address this gap, we assess the distribution of contaminated sites in the United States (US) and then estimate the impact that flood hazards in urban areas will have on these contaminated sites. Using these measures, we draw inferences about the risk of contamination from climate-impacted extreme weather events, climate adaptation at the local level, social risk and how it is distributed, and a broader understanding of the potential global consequences of climate change. In this paper we address three critical points: 1) the role classification of contaminated sites on our understanding of risk due to climate change; 2) the relationship between contaminated sites and flood risk; and 3) the potential for climate adaption strategies to mediate this risk. We estimate that of the roughly one-third of the US population living in urban areas, up to 3,338,518 people, are living in high-risk flood zones near contaminated sites. Our results suggest severe potential implications for estimates of the negative consequences from climate change and contamination and provide critical insights into the relationship between climate change and the built environment for urban planners and environmental policy makers and managers alike. [ABSTRACT FROM AUTHOR]