Particle size and morphology drive the kinetic parameters that govern how external exposure translates into internal dose — specifically airway and lung deposition fractions, as well as placental, gut and pulmonary translocation fractions. These fractions are retrieved from a size- and morphology‑based kinetic lookup table derived from published values (see documentation). Clearance kinetics are not currently modelled; the framework currently assumes that once MNPs enter the systemic circulation they are not cleared. Polymer and chemical toxicity scores [Christopher et al. 2024] combine with automatic size/morphology modifiers to produce the final hazard score.
Particle Size
Source: [van Boxel 2025; ICRP 66]Morphology
Source: [Sturm 2012; Zhou 1996]Polymer & Chemical Profile
Source: [Christopher et al. 2024]Defaults are set for a high-concern scenario (mouthing of high-priority polymer toys). Adjust the Polymer Toxicity score for safer toy materials.
Body Weight (BW) [kg]
Source: [WHO Child Growth Standards]Normalisation Metric
Source: [Standard RA Practice vs. Particle-Specific]Applies to both pathways: particles/kg-bw/day and µg/kg-bw/day when normalized.
Dust Ingestion Rate (IR_dust) [mg/day]
Source: [EPA ExpoBox - General Population]Dust Concentration (C_dust) [p/mg]
Source: [Zhang et al. 2021; Jenner et al. 2022]Default revised from 500 to 50 p/mg following the Phase 0 audit (Issue #4b). Consistent with the infant model. Jenner et al. (2022) report typical indoor settled dust MNP concentrations of 2–90 p/mg for inhalable fibres; 50 p/mg is a conservative mid-range value.
Mass-based approach per Aurisano, N. et al. (2022), J Expo Sci Environ Epidemiol 32, 94–102. Replaces the former surrogate particle-based toy emission rate with a validated chemical migration model.
Chemical Migration Rate (Rmgr) [µg/10cm²/min]
Source: [Aurisano et al. 2022 — PVC plasticizer migration rates]Conservative default for DINP plasticizer in PVC soft toys (upper empirical range ~10 µg/10cm²/min).
Mouthing Duration (t_mouthing) [min/hr]
Source: [Aurisano et al. 2022, Table 2 — citing US EPA EFH]Corrected unit: min/hour (not min/day). Mean 1.8, 99th percentile 6.3 min/hr for toddlers (2–3 yrs).
Active Hours per Day [hr/day]
Source: [Aurisano et al. 2022 — typical toddler awake window]Contact Area [cm²]
Source: [Aurisano et al. 2022 — standard mouthing surface area]Standardised mouthing contact area (default: 10 cm² per Aurisano et al. 2022).
Inhalation pathway added in Phase A, citing Ni, Y. et al. (2026), J Expo Sci Environ Epidemiol. Toddlers resuspend settled dust through active play; the resuspended concentration, breathing rate, active hours, and deposition fraction together determine the inhaled particle dose. Note: This pathway combines with Section 3 (Direct Dust Ingestion) into a single combined particle dose — both produce particles/day in the same kinetic framework.
Resuspended Dust Conc. (C_resus) [p/m³]
Source: [Kacprzak 2025; Hassan 2025 — indoor resuspension]Active Breathing Rate (IR_breath) [m³/hr]
Source: [Ni et al. 2026 — RR=30.4, VT=82.6mL, MV=2.51 L/min → ~0.3 m³/hr active]Active Hours [hr/day]
Source: [EPA EFH — age-resolved, toddler range]Exposure Thresholds (Particle Pathway)
Source: [User Defined]Note on Thresholds
Exposure thresholds are currently arbitrary and user-definable. What constitutes Low, Medium and High in terms of daily particle exposures is to be resolved by scientific consensus.