From waste to workplace: Airborne microplastics and endotoxins in an indoor industrial environment

Airborne microplastics (MPs) and endotoxins are emerging occupational hazards, yet their co-occurrence in real workplaces is poorly documented. The study examined combined exposure in sludge-based fertilizer plant, where digestate handling and drying generate both polymer-rich dust and bioaerosols. Personal and stationary air samples were collected with calibrated pumps at three indoor hotspots: conveyor pipe, dryer, loading dock with an outdoor site. Microplastics were extracted in an ultra-clean laboratory and characterized by μ-FTIR imaging. Endotoxin levels were quantified by the LAL assay. Indoor air contained significantly higher MP counts (24-312 MP m^-3) than outdoor (13 MP m^-3), dominated by fragment-shaped particles (74%) vs fibres (26%) within the inhalable size fractions. Concentrations peaked near the sludge dryer unit and the conveyor, indicating process-related sources and resuspension of contaminated dust. Endotoxins (<0,7 - 30 EU m^-3) were consistently above outdoor levels and highest where sludge-derived material was agitated yet remained below occupational reference values (90 EU m^-3). Positive covariation between MP and endotoxin levels suggested that tasks and zones with high dust emissions also drive combined particle-biological exposure. The study provides one of the first integrated datasets on airborne MPs and endotoxin in a circular-economy fertilizer facility and demonstrates a practical, contamination-controlled protocol for joint assessment using coordinated sampling. The results show that workers can be simultaneously exposed to elevated levels of polymer particles and endotoxin, underscoring the need to include microplastics in exposure monitoring, risk assessment, and control strategies across biological-waste and related industrial environments.