Indoor Environmental Biological Contaminants

Sources, Control Factors and Sampling Techniques

By:

Vik Ahuja, CIAQP

The average residential or office environment is host to a variety of biological contaminants, which include bacteria, mold, mildew, viruses, animal dander, dust mites, cockroaches, and pollen. There are as many sources of these pollutants as there are pollutants themselves.

Pollens originate from plants; people and animals transmit viruses; people, animals, and soil and plant debris carry bacteria; and household pets are sources of saliva and animal dander. 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.

The best way to control the growth and proliferation of many typical indoor environmental contaminants is to control the relative humidity level in the environment.  This will minimize the growth of some sources of biological contaminants. The American Society of Heating and Refrigeration Engineers (ASHRAE) generally recommends relative humidity be in the range of 30 and 60 percent (ASHRAE 62-1989). As humidity and moisture are an important factor to the growth of mold, standing water, water-damaged materials, or wet surfaces should be mitigated to eliminate areas that may serve as a breeding ground for molds, mildews, bacteria, and insects. House dust mites are the source of one of the most powerful biological allergens.  The house dust mite grows in damp, warm environments such as bathrooms.

Molds, such as Aspergillus and Penicillium, release disease-causing toxins called mycotoxins. Symptoms of health problems caused by exposure to mycotoxins include sneezing, watery eyes, coughing, and shortness of breath, dizziness, lethargy, fever, and digestive problems. Some biological contaminants trigger allergic reactions, including hypersensitivity pneumonitis, allergic rhinitis, and some types of asthma.

Repeated exposure to specific biological allergens can cause allergic reactions. That reaction, however, 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.

Exposure to toxins from microorganisms that can grow in large building ventilation systems are implicated in some diseases, like humidifier fever and legionnaires disease. These diseases can also be traced to microorganisms that grow in residential heating and cooling systems and humidifiers. Those most susceptible to disease-causing biological agents in the indoor environment are children, elderly people, and people with breathing problems, allergies, and lung diseases.

Sampling for Indoor Environmental Contaminants – 2 Methods

1. Non-Cultureable Direct Microscopy

In this technique, specimens can be collected directly from surfaces or from the ambient air.  Surface samples are easily collected using transparent cellotape on microscope slides.  The cellotape, prepared on the microscope slide, is peeled off, pressed against the contaminated surface to trap the specimen, and then adhered back to the slide.

 An ambient air sample can be collected with the aid of a specialized air sampling pump and a slide preparation (i.e. Air – O – Cell Cassette, Burkhard Spore Trap, Cyclex-D).  Airborne particulates are trapped on gel coated microscope slides within cartridges as air is drawn into them based on principles of impaction due to suction, rotation or gravity.  The slides are then observed under a microscope  and the results are tabulated based on the qualitative and quantitative visual examination of the trapped particles.

Advantages of Non-Cultureable Direct Microscopy

·         User friendly – can be easily operated by facilities, risk or safety personnel

·         Rapid turn around time – as quickly as 24 hours

·         Both qualitative and quantitative estimation of the bioparticulates at a given time and place.

·         Cost Effective – Surface Microscopy Preparations with analysis can be obtained from $35.00

·         Can give data on other non-viable particulate such as fiberglass, dust, insect biodetritus, etc…

Disadvantages of Non-Cultureable Direct Microscopy

·         Efficacy of sampling varies on the type of instrument used.

·         Not suitable for very large (i.e. plant trichomes, intact insects, large protozoan cysts) or very small bioparticulate (i.e. viruses and bacteria).

·         Viability of the microorganism can not be determined

·         Accurate identification cannot be made after a certain taxonomic level (no speciation).

2. The Cultureable Technique

In this method the airborne particulates are isolated on a culture plate from the ambient air using air samplers (i.e. Andersen’s, etc.) and are allowed to grow on the media under certain controlled conditions for further analysis. Slides are prepared from growing microorganisms on specific media and are then observed under a microscope for further identification and analysis.

Advantages of the Cultureable Technique

·         Qualitative and Quantitative estimation of viable aerobiota (to a reasonable degree of approximation) is possible.

·         Viability of the isolated aerobiota can be determined.

·         Identification of isolated bioparticulates is more specific and accurate (i.e. up to species levels).

·         Biochemical (other analyses) for the various chemicals / toxins etc. of isolated organisms can be done.

Disadvantages of the Cultureable Technique

·         Much scientific training is required (e.g. MPH and Ph.D level mycology and bacteriology).

·         Microorganisms are media-specific.

·         Unable to give data of non-viable particles in the atmosphere.

·         Microorganisms take time to grow, hence a longer turn-around-time (14 days).

·         Antagonism of microorganisms can produce pseudo-identification of biota.

·         Expensive - analysis of media plates begins at about $65.00 per plate.

Which of these two sampling techniques is best to use?  Comparison between the two techniques reveals that the Direct Microscopy Technique coupled with the Culture Technique is the most effective diagnostic tool to assess the severity of a problem potentially caused by microorganisms in the indoor environment. Using both of these techniques also helps to design abatement strategies for controlling problems due to biological aeropollutants in the indoor environment that may affect human health.

Keep in mind, when developing sampling strategies for routine-building assessments (developing baseline conditions) is critical to include both the outdoor air and inside air in the assessment.  This will allow you to compare the inside to outside fungal propagul ratios and determine the similarity of ecological conditions that may affect the quality of indoor air.   

For more information: http://www.pureaircontrols.com

Contact: Vahuja@PureAirControls.com

Phone: (800) 422-7873, ext. 804