Factors Affecting Inhalability
- Form: Metals themselves are not inhaled in atomic form, but as components of dust, fumes, or aerosols. Vapors (e.g., mercury) and fumes (e.g., cadmium oxide) have greater inhalation risk than coarse dust.
- Particle size: Must be small enough to penetrate respiratory defenses.
- Solubility: Affects bioavailability once deposited in the lungs.
- Heavy metals <10 microns (PM 10 µm): Are typically small enough to be inhaled into the lungs, with those <2.5 µm deposited into the alveoli and bloodstream, with those <0.1 µm able to cross blood brain barrier.
Heavy Metals That Are Typically Inhalable
| Heavy Metal | Typical Form Inhaled | Source | Health Risks |
|---|---|---|---|
| Lead (Pb) | Dust, fumes (PbO, PbCl2) | Paint, battery plants, smelting | Neurotoxicity, anemia, renal effects |
| Cadmium (Cd) | Fine dust, oxide fumes | Welding, batteries, smelting | Lung cancer, kidney damage |
| Arsenic (As) | Arsenic trioxide fumes | Mining, smelting, coal combustion | Carcinogenic (lung, skin, bladder) |
| Mercury (Hg) | Vapor (elemental), aerosols | Coal burning, gold mining | Neurotoxicity, immunotoxicity |
| Chromium (Cr, esp. Cr⁶⁺) | Dust, Cr(VI) aerosols | Welding, plating, pigments | Lung cancer, respiratory damage |
| Nickel (Ni) | Nickel sulfate dust | Alloy production, refinery | Respiratory cancer, allergic asthma |
| Beryllium (Be) | Inhalable dust or fume | Aerospace, electronics | Chronic beryllium disease, lung cancer |
| Manganese (Mn) | Dust or fumes (MnO₂) | Welding, mining, steel | Neurotoxicity (manganism) |
| Cobalt (Co) | Dust or fumes | Batteries, pigments | Lung/heart damage, cancer risk |
| Antimony (Sb) | Dust or fumes (Sb₂O₃) | Smelting, flame retardants | Respiratory irritation, pneumoconiosis |
| Tellurium (Te) | Dust or fume | Mining, metal refining, thermoelectric devicesproduction, semiconductor manufacturing, CdTe solar panels | Headache, metallic taste, respiratory irritation, garlic odor, liver/kidney damage |
Particle Size and Lung Penetration
| Particle Size | Inhalability | Penetration |
|---|---|---|
| >10 µm | Mostly filtered by nose | Rarely reaches lungs |
| 2.5–10 µm | Respirable, trapped in bronchi | Irritates upper lungs |
| <2.5 µm | Deep lung penetration | Enters alveoli and bloodstream |
| <0.1 µm (Ultrafine) | Deepest penetration | May cross blood–brain barrier |
Occupational and Environmental Relevance
- Occupations at risk: Welders, smelters, miners, battery plant workers, construction workers.
- Environmental exposure: Wildfires, polluted urban air, lead-based paint or soil contamination.