Chemo-mechanical synergy governs microplastic release from toothbrush bristles
Description
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.
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Steps to reproduce
Methods 2.1 Experimental Materials Five commercial toothbrushes (B1–B5; B1–B4 electric, B5 manual) were purchased in 2025. Bristle polymers were identified by FTIR against reference spectra (Aytulun et al., 2025; Ren et al., 2025) (SI Table S1): B1 (PE/PET), B2 and B3 (PE), B4 (PET/PE), and B5 (PET/PVC). Three fluoride-containing toothpastes (cleansing, P1; Brightening, P2; and sensitivity care, P3) were selected; all contained hydrated silica as the primary abrasive. A standard plaster denture model was used for simulation experiments. 2.2 Human Toothbrushing Experiment Fifteen healthy volunteers (7 males, 8 females; 20–30 years old) were recruited from a university campus between September and November 2025. Eligibility criteria included absence of periodontal disease, no ongoing orthodontic treatment. Participants were drawn from a relatively homogeneous pool to minimise inter-individual variability in oral health status and brushing habits; age and gender were not treated as experimental factors, as the study focused on material-toothpaste-mechanics interactions. The study was restricted to daily toothbrushing and rinse water collection, with no invasive medical procedures. A randomized block design was employed, with toothbrush type (B1–B5) and toothpaste type (P1–P3) as fixed factors. Fifteen volunteers were allocated to 15 toothbrush–toothpaste combinations via stratified randomization (one volunteer per combination). Each volunteer completed 15 brushing sessions (3 intensities × 5 replicates) twice daily (ca. 08:00 and 20:00) in campus dormitories under consistent ambient conditions. The intensity sequence was fixed from S1 to S2 to S3 to minimise cross-interference: starting with the lowest intensity (S1, Light mode) established a sensory baseline, while postponing the highest intensity (S3, Brightening mode) prevented early bristle damage and microplastic carryover from confounding lower-intensity measurements. Prior to the experiment, each volunteer received a new assigned toothbrush and a sealed tube of designated toothpaste, with instructions to maintain habitual oral care. For each session, 0.3 g of toothpaste was dispensed using a vacuum pump (discarded and re-dispensed if air bubbles appeared) and evenly spread onto the bristles. Volunteers brushed for 2 min. For B1–B4 (electric toothbrushes), built-in modes were used directly: S1 (sensitive/light), S2 (clean/normal), and S3 (Brightening/high). For B5 (manual toothbrush), volunteers were trained in a standardized Bass brushing technique and executed self-rated force levels: S1 corresponded to light force, S2 to Medium force, and S3 to High force. After brushing, volunteers rinsed with purified water (Wahaha Group, China); all rinse water was collected in pre-cleaned sterile glass bottles. Samples were transported to the laboratory, adjusted to 150 mL, of which 20 mL was taken for microplastic extraction (SI Text 1) and the remainder was stored at 4 °C.
Institutions
- South China Agricultural UniversityGuangdong, Guangzhou