The extractive classroom: indoor school environments as reservoirs of mining legacy.

The global energy transition is accelerating the demand for copper and other energy-transition minerals worldwide, potentially expanding the existing large-scale mining across the Global South. Sustainability assessments of mining currently focus primarily on ambient outdoor concentrations of chemicals (metals) and commonly assume that buildings can buffer human exposure. Here we test this assumption in Calama, Chile, a desert city downwind of one of the world's largest copper-mining complexes (Chuquicamata). We combined elemental, isotopic, and mineralogical analyses with oxidative potential measurements and zebrafish embryo assays to examine paired indoor and outdoor settled dust from 38 schools in Calama. Indoor concentrations of Cu, As, Pb, and Mo closely tracked outdoor levels and exceeded regional desert background by up to one order of magnitude, with minimal attenuation for As and Pb. Mineralogical and isotopic evidence indicated that the dust is not connected to fresh vehicles or combustion emissions, but rather to the mining industry. Additionally, the evidence showed enrichment in oxidized mining-derived particles, and indoor dust exhibited substantial oxidative potential. Zebrafish embryos exposed to dust extracts showed elevated heart rate under sublethal conditions. These results indicate that indoor environments in intensive mining landscapes, including classrooms, may be physically integrated into the surrounding extractive environment and should be incorporated into regular environmental monitoring, mine-closure planning, and just-transition governance.