Dust Characterization

Dusts are ubiquitous. They can be generated from many sources, indoors and outdoors, human/animal activities, construction, combustion, etc. As a matter of fact, our human bodies shed approximately 10 grams of skin scales each day, which is a significant portion of a typical household dust sample.

Unless you are allergic to dust, most people are immune to a normal amount of dust exposure. However, certain constituents in the dust can have some health consequences, such as pollen, fungal spores, and soot. People can get sick in an environment filled with allergens such as cat or dog danders or get skin rash from fiberglass exposure. Approximately 30% of Americans have an allergy and/or asthma, especially young children. Other constituents of the dust may not be a direct health concern themselves, but can be an indicator of something significant. For example, excessive percentage of skin cells in a dust sample may indicate an inefficient HVAC filtration system.

Dust characterization can be a very useful and important tool for industrial hygienists (IH) or indoor air quality (IAQ) professionals to evaluate a building related illness. Traditional IAQ investigation involves air sampling for a short period of time. For example, spore trap sampling for fungal spores are typically performed between 5 and 10 minutes. It’s really just a snapshot of the indoor air. In comparison, dust characterization can obtain crucial information about the history of the living environment ranging from weeks to even months as long as the selected surfaces have not been thoroughly cleaned for that period of time.

There are many ways for collecting samples for dust characterization analysis. The easiest way is to collect bulk dust from the concerned areas using microvac method or even a household vacuum cleaner. Alternatively, dusts can be collected using swab or tape lift method. If an investigator needs to know what’s in the air at the moment of sampling, spore trap or membrane filter sampling can be used. A good example of the latter is to find out if the air in a house is contaminated with soot after a nearby wildfire.

Polarized light microscopy (PLM) is the most common method for dust characterization because it is fast and affordable. Under this method, dust components are identified based on morphology and optical properties. The bulk dust is first examined under a stereoscope and then identified under PLM. Each component is semi-quantified using calibrated visual estimation. The detection limit of dust characterization using optical microscopy is 1%. At Eurofins, dust components are broken into four common categories: human/animal activities (e.g., skin scales, dandruff, animal fecal, hair, cellulose fibers, etc.), food particles (e.g., salt, sugar, starch, etc.), combustion product (e.g., ash, carbon, soot, iron oxides, etc.), building material (e.g., fiberglass, gypsum, calcite, silicates, paint, plaster, etc.), and miscellaneous (e.g., rubber, plastic, soil, stellate hair, air distribution system debris, etc.).

This method has its limitations. For example, it does not provide you with the chemical composition of the dust and it is difficult to identify small particles and especially at low concentrations. More advanced instrumentation such as SEM and/or TEM with EDS can be used for accurate identification of the constituents in the dust based on particle morphology and chemical composition.

Interpretation of results can be difficult because there is currently no regulation on acceptable dust constituents. There is also no accreditation for this type of analytical work. Therefore, it is imperative dust characterization samples be analyzed by experienced analysts. Eurofins Built Environment Testing has been performing this type of testing for our satisfied customers for over twenty years and helped them solved many IAQ mysteries.