Nanoparticles and Engineered Nanomaterials: Emerging Dust Hazards in Australian Workplaces

Engineered nanomaterials (ENMs) — materials with at least one dimension between 1 and 100 nanometres — are incorporated in products ranging from sunscreens (nano-TiO₂) and textiles (nano-silver) to composite materials (carbon nanotubes) and electronic components (quantum dots). Workers who manufacture, process or handle ENMs in powder or suspension form may inhale or otherwise be exposed to nanoparticles with poorly characterised health effects. The occupational hygiene challenge is that traditional mass-based dust monitoring may not adequately characterise nano-specific hazards, and health-based WES values are absent for most ENMs.

Why Nanoparticles Are a Different Kind of Hazard

The toxicology of nanoscale materials differs fundamentally from bulk equivalents of the same chemical composition, for several reasons:

• Surface area dominance: As particle size decreases, surface area-to-mass ratio increases exponentially. A 10 nm TiO₂ particle has approximately 100× the surface area per unit mass of a 1 µm particle. Surface area — not mass — drives most particle-induced biological reactions (oxidative stress, inflammatory cytokine release)
• Novel properties: Nanoscale materials may exhibit quantum effects, altered electron conductivity, different optical properties and different reactivity compared to bulk materials
• Greater lung deposition efficiency: Nanoparticles (particularly <20 nm) deposit efficiently in the alveolar and tracheobronchial regions; some may translocate via olfactory nerve to the brain or be absorbed into systemic circulation through the alveolar membrane
• Biopersistence: Some ENMs (carbon nanotubes, some ceramic fibres) are biopersistent — they resist degradation by lung macrophages and persist in the lung for years, potentially driving chronic inflammation

Key ENMs of Occupational Concern

Carbon Nanotubes (CNTs)

Single-walled (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) are of particular concern due to their high aspect ratio (length:diameter) analogous to asbestos fibres. Animal inhalation studies have demonstrated granulomatous pulmonary inflammation, progressive fibrosis and — for long, rigid MWCNTs — mesothelioma-like pleural pathology. NIOSH has established a recommended exposure limit (REL) of 1 µg/m³ elemental carbon for CNTs. Australia has no specific WES but ALARA applies.

Titanium Dioxide Nanoparticles (nano-TiO₂)

Used in sunscreens, paints and coatings. IARC classifies TiO₂ as Group 2B (possibly carcinogenic) based on animal data — exposure is primarily during manufacturing and not from topical skin application. NIOSH REL is 0.3 mg/m³ (fine TiO₂) and 0.03 mg/m³ (ultrafine/nano-TiO₂).

Nano-Silver

Used for antimicrobial properties in textiles, wound dressings and food packaging. Nano-silver can be cytotoxic and genotoxic in cell culture studies. Inhalation exposure during manufacturing requires precautionary controls. Systemic toxicity (argyria) is a concern with chronic silver exposure.

Silica Nanoparticles

Amorphous silica nanoparticles (fumed silica, precipitated silica) are widely used as flow agents in food, pharmaceuticals and rubber. Unlike crystalline silica, amorphous silica is considered less hazardous but the nano-specific effects of high-surface-area amorphous silica warrant caution. The WES for amorphous silica is 10 mg/m³ — but this was established for bulk material, not nano-silica.

Exposure Monitoring: What Metric to Use?

The fundamental challenge for nano-monitoring is that mass concentration — the primary metric for traditional dust monitoring — may not be the relevant dose metric for nanoparticle toxicity. Alternative metrics:

• Particle number concentration (#/cm³): Measured in real-time by condensation particle counters (CPC). Detects even tiny mass releases of nanoparticles. Not material-specific — cannot distinguish workplace ENMs from background ultrafine particles (vehicle exhaust, combustion)
• Surface area concentration (µm²/cm³): Measured by electrical mobility analysis or estimated from number/size distributions. Correlates well with surface-area-driven toxicity mechanisms. Instruments: nano-SMPS (scanning mobility particle sizer), ELPI (electrical low-pressure impactor)
• Mass concentration (mg/m³): Captured on filters for gravimetric analysis and electron microscopy (TEM/SEM with EDX) — definitive characterisation of material identity but lower sensitivity for nano-specific hazards

A tiered approach is recommended: real-time particle number monitoring for initial assessment and control verification, with filter-based TEM/SEM analysis for material characterisation when elevated particle numbers are detected.

Precautionary Controls for ENMs

In the absence of established WES values for most ENMs, the precautionary principle and ALARA govern Australian practice. Controls follow the standard hierarchy:

• Substitution: Use bulk material form where feasible; use aqueous suspensions rather than dry powder forms of ENMs
• Engineering controls: Isolated glove boxes or isolator systems for high-hazard ENMs (CNTs, high-toxicity nanoparticles); LEV with HEPA filtration at dry handling operations; enclosed transfer systems
• Administrative controls: Designate nano-working areas; restrict access; wet cleaning procedures
• PPE: Gloves (non-porous, impermeable); P3 or HEPA-filtered respirator for airborne ENM exposure; Tyvek coverall for body protection during powder handling

Australian Regulatory Position

Safe Work Australia has published a guidance note on engineered nanomaterials that recommends treating ENMs as hazardous substances in the absence of WES-specific data, applying the precautionary principle, and conducting workplace risk assessments. The Australian Industrial Chemicals Introduction Scheme (AICIS) requires assessment of new chemicals — including novel ENMs — before introduction into Australia. Employers have a general WHS duty to identify and manage hazards including those from new and emerging materials.