On November 5th, 2015, Fundão tailings dam in Mariana (Minas Gerais) collapsed. This was considered the biggest environmental disaster in Brazil and one of the largest in the world. Mud wastes (more than 50 million m3) were dumped downstream of the Doce River basin. Hundreds of thousands of people living along the rivers have been affected. The aim of this study was to characterize dust samples collected after the mud deposition. Although iron mining wastes were classified as “not-hazardous” materials, our chemical analyses results pointed out the occurrence of potentially hazardous elements as As, Al, Mn and Pb at very high levels in the collected particulate material.