Indoor Air Quality (IAQ)

Biological Pollutants' Impact on Indoor Air Quality

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Biological contaminants include bacteria, viruses, animal dander and cat saliva, house dust, mites, cockroaches, and pollen. There are many sources of these pollutants. By controlling the relative humidity level in a home, the growth of some sources of biologicals can be minimized. A relative humidity of 30-50 percent is generally recommended for homes. Standing water, water-damaged materials or wet surfaces also serve as a breeding ground for molds, mildews, bacteria and insects. House dust mites, the source of one of the most powerful biological allergens, grow in damp, warm environments.

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  • pollens, which originate from plants
  • viruses, which are transmitted by people and animals
  • mold
  • bacteria, which are carried by people, animals, and soil and plant debris
  • household pets, which are sources of saliva and animal dander (skin flakes)
  • droppings and body pats from cockroaches, rodens and other pests or insects
  • viruses and bacteria
  • The protein in urine from rats and mice is a potent allergen. When it dries, it can become airborne.
  • Contaminated central air handling systems can become breeding grounds for mold, mildew and other sources of biological contaminants and can then distribute these contaminants through the home

Many of these biological contaminants are small enough to be inhaled.

Biological contaminants are, or are produced by, living things. Biological contaminants are often found in areas that provide food and moisture or water. For example:

  • damp or wet areas such as cooling coils, humidifiers, condensate pans or unvented bathrooms can be moldy
  • draperies, bedding, carpet and other areas where dust collects may accumulate biological contaminants

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Health Effects From Biological Contaminants

Some biological contaminants trigger allergic reactions, including:

  • hypersensitivity pneumonitis
  • allergic rhinitis
  • some types of asthma

Infectious illnesses, such as influenza, measles and chicken pox are transmitted through the air. Molds and mildews release disease-causing toxins. Symptoms of health problems caused by biological pollutants include:

  • sneezing
  • watery eyes
  • coughing
  • shortness of breath
  • dizziness
  • lethargy
  • fever
  • and digestive problems

Allergic reactions occur only after repeated exposure to a specific biological allergen. However, that reaction may occur immediately upon re-exposure or after multiple exposures over time. As a result, people who have noticed only mild allergic reactions, or no reactions at all, may suddenly find themselves very sensitive to particular allergens.

Some diseases, like humidifier fever, are associated with exposure to toxins from microorganisms that can grow in large building ventilation systems. However, these diseases can also be traced to microorganisms that grow in home heating and cooling systems and humidifiers.

Children, elderly people and people with breathing problems, allergies, and lung diseases are particularly susceptible to disease-causing biological agents in the indoor air.

Mold, dust mites, pet dander and pest droppings or body parts can trigger asthma. Biological contaminants, including molds and pollens can cause allergic reactions for a significant portion of the population. Tuberculosis, measles, staphylococcus infections, Legionella and influenza are known to be transmitted by air.

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Reducing Exposure to Biological Contaminants

General good housekeeping, and maintenance of heating and air conditioning equipment, are very important. Adequate ventilation and good air distribution also help. The key to mold control is moisture control. If mold is a problem, clean up the mold and get rid of excess water or moisture. Maintaining the relative humidity between 30% - 60% will help control mold, dust mites and cockroaches. Employ integrated pest management to control insect and animal allergens. Cooling tower treatment procedures exist to reduce levels of Legionella and other organisms.

  • Install and use exhaust fans that are vented to the outdoors in kitchens and bathrooms and vent clothes dryers outdoors.
    These actions can eliminate much of the moisture that builds up from everyday activities. There are exhaust fans on the market that produce little noise, an important consideration for some people. Another benefit to using kitchen and bathroom exhaust fans is that they can reduce levels of organic pollutants that vaporize from hot water used in showers and dishwashers.
  • Ventilate the attic and crawl spaces to prevent moisture build-up.
    Keeping humidity levels in these areas below 50 percent can prevent water condensation on building materials.
  • If using cool mist or ultrasonic humidifiers, clean appliances according to manufacturer's instructions and refill with fresh water daily.
    Because these humidifiers can become breeding grounds for biological contaminants, they have the potential for causing diseases such as hypersensitivity pneumonitis and humidifier fever. Evaporation trays in air conditioners, dehumidifiers and refrigerators should also be cleaned frequently.
  • Thoroughly clean and dry water-damaged carpets and building materials (within 24 hours if possible) or consider removal and replacement.
    Water-damaged carpets and building materials can harbor mold and bacteria. It is very difficult to completely rid such materials of biological contaminants.
  • Keep the house clean. House dust mites, pollens, animal dander and other allergy-causing agents can be reduced, although not eliminated, through regular cleaning.
    People who are allergic to these pollutants should use allergen-proof mattress encasements, wash bedding in hot (130° F) water and avoid room furnishings that accumulate dust, especially if they cannot be washed in hot water. Allergic individuals should also leave the house while it is being vacuumed because vacuuming can actually increase airborne levels of mite allergens and other biological contaminants. Using central vacuum systems that are vented to the outdoors or vacuums with high efficiency filters may also be of help.
  • Take steps to minimize biological pollutants in basements.
    Clean and disinfect the basement floor drain regularly. Do not finish a basement below ground level unless all water leaks are patched and outdoor ventilation and adequate heat to prevent condensation are provided. Operate a dehumidifier in the basement if needed to keep relative humidity levels between 30 - 50 percent.

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Standards or Guidelines

There are currently no federal government standards for biologicals in school indoor air environments (as of 1999).

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Additional Resources

Publications/Fact Sheets

Biological Pollutants in Your Home, CPSC Document #425
Explains indoor biological pollution, health effects of biological pollutants and how to control their growth and buildup. One third of all structures have damp conditions that may encourage development of pollutants such as mold and bacteria, which can cause allergic reactions - including asthma - and spread infectious diseases. Describes corrective measures for achieving moisture control and cleanliness. This brochure was prepared by the American Lung Association and the U.S. Consumer Product Safety Commission.

Fact Sheet - Flood Cleanup: Avoiding Indoor Air Quality Problems
Discusses steps to take when cleaning and repairing a home after flooding. Excess moisture in the home is cause for concern about indoor air quality primarily because it provides breeding conditions for microorganisms. This fact sheet provides tips to avoid creating indoor air quality problems during cleanup. EPA 402-F-93-005, Revised October 2003

Indoor Allergens: Assessing and Controlling Adverse Health Effects, Andrew M. Pope, Roy Patterson and Harriet Burge, editors; Committee on the Health Effects of Indoor Allergens, Division of Health Promotion and Disease Prevention, Institute of Medicine. National Academy Press, 1993. 308 pages. ISBN 0-309-04831-1.
This project was supported by funds from the Environmental Protection Agency, National Institute of Environmental Health Sciences, National Institute of Allergy and Infectious Diseases, National Heart, Lung and Blood Institute, and Agency for Toxic Substances and Disease Registry. Copies of this book are available from the National Academy Press, call 1-800-624-6242 or 202-334-3313 (in the Washington DC metro area).

Indoor Air Fact Sheet No. 8 - Use and Care of Home Humidifiers
Explains that some types of home humidifiers can disperse microorganisms from their water tanks into the indoor air. Describes the different types of humidifiers and provides recommendations for their use and maintenance.

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