Chemo-mechanical synergy governs microplastic release from toothbrush bristles

Global toothbrush consumption exceeds billions of units annually, yet bristle wear as a microplastic source remains largely unquantified. Using a 5 × 3 × 3 design, we combined brushing experiments, 400-cycle simulations, and questionnaire data to investigate release drivers, ageing, and regional emissions.Single-use release was dominated by toothpaste type and brushing intensity (8.1-fold higher for Sensitivity care vs. cleansing; up to 82.3-fold across extremes), with no significant material main effect. High-intensity brushing increased release by 119.7%. Over 400 cycles, PET-based brushes exhibited early-burst or late-stage disintegration, whereas PE-based brushes reached gradual saturation. Particle size decreased by a factor of up to 4.27 with usage.Chemical ageing was material-dependent but uncorrelated with release; mediation analysis confirmed mechanical fatigue, not oxidation, governs emissions. Morphology was toothpaste-dependent: cleansing generated fragments, Brightening/Sensitivity care produced spheres; fibres accounted for <2%. Coupled with population data, annual emissions in Guangdong were estimated at 9.26 × 10¹³ particles (7.29 × 10⁵ per capita). Electric toothbrush users emitted more than manual users. These findings support material-specific replacement (~150 cycles for PET, ~250 for PE) over fixed intervals, demonstrating that behaviour-based interventions offer population-level mitigation leverage.全球牙刷年消费量已超数十亿支，但作为微塑料重要来源的刷毛磨损情况，目前仍基本未得到系统性量化研究。本研究采用5×3×3实验设计，结合刷毛磨损实验、400次循环模拟试验与问卷调研数据，系统探究了微塑料释放的驱动机制、材料老化规律与区域排放特征。 单次使用过程中的微塑料释放量主要受牙膏类型与刷牙强度的共同调控：抗敏感型牙膏的释放量为清洁型牙膏的8.1倍，极端工况下两者释放量差距可达82.3倍；而刷头材料本身未产生显著主效应。高强度刷牙可使微塑料释放量提升119.7%。经过400次循环使用后，聚对苯二甲酸乙二醇酯（PET）刷头会出现早期突发解体或晚期崩解现象，而聚乙烯（PE）刷头则呈现逐步饱和的释放模式。随着使用次数增加，微塑料粒径最高可缩减至初始尺寸的1/4.27。化学老化效应与刷头材料种类相关，但与微塑料释放量无显著关联；中介分析证实，微塑料排放主要受机械疲劳作用调控，而非氧化反应。微塑料的形貌特征受牙膏类型影响显著：清洁型牙膏对应生成碎片状颗粒，美白/抗敏感牙膏则产生球形颗粒；纤维状颗粒占比不足2%。 结合广东省人口统计数据估算，该省年微塑料排放量达9.26×10¹³颗，人均排放量为7.29×10⁵颗。电动牙刷使用者的微塑料排放量高于手动牙刷使用者。本研究结果支持按材料特性制定刷头更换周期（聚对苯二甲酸乙二醇酯刷头约150次循环、聚乙烯刷头约250次循环），而非采用固定时间间隔更换的方案，同时证明基于行为的干预措施可在人群层面实现有效的微塑料排放减缓。