Thermal degradation and microplastic emission in polypropylene infant bottles: A laser direct infrared imaging study for exposure risk assessment

Abstract

The rapid quantification and identification of microplastic (MPs) released from feeding bottles (FBs) represent a critical challenge in environmental and biomedical research. Existing studies have primarily focused on MPs release quantities under isolated conditions and fail to identify MPs. Laser direct infrared (LDIR) imaging was employed to quantify MPs released from polypropylene-FBs (PP-FBs) under simulated infant-care scenarios, including ambient washing (35 °C), formula preparation (70 °C), sterilization (95 °C), drying (75 °C), and multi-cycle usage. Dynamic MPs release was observed across all conditions, with concentrations escalating from 62 ± 5 to 243 ± 9 particles/10 ml under thermal stress. Repeated heating cycles amplified MPs emissions by 32.5 % to 264.2 %, while prolonged sterilization (30 vs. 15 min) and drying (60 vs. 15 min) increased release by 45.2–51.6 % and 195.7 %, respectively. LDIR-based size profiling identified dominant 10–30 μm particles (50–59 %), with polyamide (PA), polyvinyl chloride (PVC), and vinyl chloride (VC) as primary polymers. Notably, silicone nipples contributed dual MPs sources: PA/PVC leaching (42 %) and siloxane oligomer shedding (4 %). Endocrine-disrupting PA particles (10–30 μm) constituted the majority of released MPs, raising concerns about current safety guideline, suggesting instead dynamic replacement intervals between 28 and 112 days. This work underscores the urgency revision of sterilization protocols, material standards, and infant-product monitoring protocols through advanced tools like LDIR to minimize early-life MPs exposure.