Debates over science, facts, and values are pivotal in the struggle for environmental justice. For decades, environmental justice activists have campaigned against the misuse of science, engaging in community-led citizen science that champions knowledge produced by and for ordinary people living with environmental risks and hazards. However, post-truth politics have threatened science itself. Toxic truths examines the relationship between environmental justice and citizen science, focusing on enduring issues and new challenges in a post-truth age. The volume features a range of community-based participatory environmental health and justice research projects that seek to establish different ways of sensing, witnessing, and interpreting environmental injustice. From struggles in American hog country and contaminated indigenous communities, to local environmental controversies in Spain and China, this volume examines political strategies for seeking environmental justice. With international, interdisciplinary contributions from distinguished authors, emerging scholars and community activists, Toxic truths is essential reading for those seeking to understand the cutting edge of citizen science and activism around the world.