Surface Sampling for Mold
Surface Sampling (Tape, Swab, Bulk, or Wipe)
- To determine whether or not the visible stain, discoloration, etc. is indicative of mold growth at the sample location.
- To determine and identify molds actually growing on the surface sampled, as opposed to the mere presence of mold spores.
- To determine whether the spore population on the surface represents a normal population or a skewed population of spore type. and also to note “marker” spore types that may indicate indoor mold growth.
Note: A direct microscopic examination that directly identifies fungal growth (and doesn’t just count the number of spores) is usually the best method of analysis for surface samples. While culturing a surface sample may help resolve a specific identification problem, used alone such a culture may result in an inaccurate characterization of the surface sampled.
Advantages and Disadvantages
- Surface sampling is inexpensive and (for a direct examination) may be analyzed immediately.
- A direct microscopic examination of a surface shows exactly what is there.
- Surface sampling may reveal indoor reservoirs of spores that have not yet become airborne.
- The presence of biological materials on a particular surface is not a direct indication of what may be in the air.
- Surface sampling for direct microscopic examinations usually requires no special equipment. Samples are typically tape lifts, swabs, or physical pieces of the suspect surfaces.
- Tape Sample
- Use a piece of absolutely clear (not frosted) tape that is one or two inches in length and 3/4 inch (2 cm) wide. Handle it by the ends only.
- Position the adhesive side of the tape over the suspect area and press firmly.
- Remove the tape from the surface and place it onto a clean microscope slide, then place the microscope slides into a slide box or other protective container. If microscope slides aren’t available, tape the tape sample directly onto the inside of a reclosable plastic bag adhesive side down, folding over one end for easy removal by the analyst.
- Do not fold the tape onto itself.
- Bulk Sample
- Remove a one or two square inch piece of the suspect material and place it inside a clean plastic reclosable bag.
- Swab Sample
- Swabs are a last choice for when the sampling area is difficult to reach, a bulk sample is not practical, or the surface is very wet and a tape sample will not adhere to the area of concern.
- Wipe Sample
- Wipes should only be used if sampling is not possible by any of the above methods mentioned. Wipes should not be the preferred method of sampling unless there is a proper justification to do so.
- Tapes and dry bulk samples require placement into a reclosable plastic bag.
- Swabs and wet bulk samples should be sent via overnight courier with a cold pack to retard growth during shipping. Refrigeration of wipe samples using a cold pack during transportation is also recommended to minimize changes.