Drawing from sociology, anthropology and history, this symposium will examine the different forms of participatory and citizen knowledge produced in these territories, as well as their effects on the work of agencies, state administration, and the actions of public authorities. Is there a specificity to citizen science depending on the types of environmental pollution studied? To what extent do these new forms of expertise reframe what “science” is in the already well-established institutional system of expertise production? What are the effects of citizen science on public action?