Indoor Biological Contaminants: Sources, Health Risks, and Mitigation

Biological Contaminants in Indoor Environments

Biological contaminants are living or once-living organisms that can negatively affect indoor air quality and human health. Key types include:

• Bacteria: Carried by people, animals, soil, and plant debris.
• Viruses: Primarily transmitted by people and animals.
• Moulds: Grow on water-damaged materials or wet surfaces.
• Pollens: Originate from plants.
• Animal Dander: Sources include household pets.
• Saliva: Mainly from cats and rabbits.
• Dust Mites: Thrive in damp, warm environments.
• Insects and Pests: Including ants, cockroaches, mice, and rats.

Humans as Sources of Indoor Contamination

Human activities significantly contribute to indoor biological contamination:

• During sneezing, between 4,000 and 40,000 small drops of mucus and saliva are released into the indoor air, potentially spreading bacterial infections.
• Shed skin particles (dander) can trigger asthma.
• Clothing and bed linen are major sources of bacteria and dust mites. Note: For effective killing of most bacteria, the washing temperature should be higher than 85 °C (185 °F).

Components of Domestic Dust

Domestic dust is a complex mixture that acts as a breeding ground for microbes, which produce mVOCs (microbial volatile organic compounds). Typical components include:

• Organic Particles: Dead insects, plant debris, hairs, and eyelashes.
• Inorganic Particles: Sand, particles from paints, textiles, etc.
• Pollen and spores of moulds.
• Bacteria and dust mites.
• Fecal particles (excrements).

Activities That Increase Contaminant Levels

Common household activities can dramatically increase the concentration of germs and spores in the air:

• Vacuum Cleaning: Vacuuming carpets can increase the amount of germs and spores of moulds (e.g., Aspergillus, Alternaria, Cladosporium, Penicillium, Stachybotrys) in indoor air by 14 times.
• Sweeping: Sweeping floors results in a 10 times higher amount of germs.
• Mould Removal: Mechanical removal of moulds from moulded surfaces may induce a 3,000 times higher amount of spores.
• Cellar Access: Opening doors to a cellar with moulded walls causes 1.5 times higher amount of spores in the living area. Penicillium spores often dominate.
• Firewood: Placing six birch logs into a fireplace causes a 100 times greater amount of germs in the indoor air initially. One hour later, the amount remains 30 times higher.
• Cleaning Mouldy Food: Cleanup of mouldy bread or opening a jar with mouldy jam induces 500 times higher amount of spores. 30 minutes later, the amount was 170 times greater. Penicillium spores dominated.
• Pets Returning: A dog or cat returning from a walk results in 10 times higher amount of spores. 30 minutes later, the amount decreases to 30% of the peak. Cladosporium spores dominated.
• Pet Bedding: Replacing hamster or rabbit bedding (if bred indoors) increases the amount of germs in indoor air up to 20,000/m³.
• Bedding Changes: Replacement of the bed sheet causes 3 times higher amount of germs in the bedroom. After 60 minutes, concentration drops back to original values.

Health Symptoms Related to Biological Exposure

Exposure to biological contaminants can cause various health issues, including:

• Sneezing
• Watery eyes
• Coughing
• Shortness of breath
• Dizziness
• Lethargy
• Fever
• Digestive problems
• Allergic reactions
• Asthma

Understanding Allergic Reactions

Allergic reactions occur only after repeated exposure to a specific biological allergen. These reactions include:

• Hypersensitivity pneumonitis
• Allergic rhinitis
• Some types of asthma
• Skin irritation (dermatitis)