SAMPLING SOFT-SURFACE ITEMS - CLEAN OR DISCARD?

INTRODUCTION

One of the biggest areas of disagreement in mold remediation often involves personal possessions: should they be cleaned or discarded? I believe part of the reason may be due to the selection of the sampling method. If the sampling method can not differentiate between “contamination” and “colonization”, then sample results may be available, but they may be difficult to interpret.

Let's define contamination as mold spores simply lying on a dry surface. This can occur when airborne spores settle onto a soft-surface item, such as a couch or chair. Since this often occurs during mold-related incidents, HEPA-vacuuming and cleaning soft-surface items as part of a mold remediation is a prudent practice. Generally, soft-surface items that are simply contaminated are easily cleaned. Unless the user is especially sensitive, a thorough cleaning by HEPA-vacuuming the item is often sufficient. However, we have to be aware that such items, when exposed to water in either the liquid or vapor form (high relative humidity), can accumulate enough moisture to promote the growth of the settled spores.

If a soft-surface item becomes wet as the result of a water intrusion incident, then colonization can occur. I will define colonization as mold growth within the material, such as the fabric, cushions, particle board, etc. Once colonization has occurred, it becomes almost impossible to clean the item to acceptable levels. Discarding the item then becomes the most cost-effective solution.

If, in general, we can say that contaminated items can be cleaned, but that colonized items should be discarded, then we have the basis for a rational decision. Following this logic, we would prefer to use a sampling method that can differentiate between items that are simply contaminated and those that are colonized, since the sample results provided by that method allow us to make a decision.

In order to pursue this logic, I have to make the following assumptions:

• A sampling method that collects the sample from the surface of a soft-surface item is only testing for surface contamination. An example is the closed-face cassette depicted in Figure 1.
• A sampling method that collects the sample from below the surface (as well as the surface) is testing for both colonization and contamination. The open-face cassette in Figures 2 is an example of this method.

Since the decision to clean or discard is based on colonization rather than contamination, the preferred sampling method would collect the sample from below the surface, from the interior of the material.

MICRO-VACUUM SAMPLING METHODS

Ideally, a soft-surface sampling method should satisfy the following goals:

• First, it should be quantitative. That is, it should have the ability to detect differences in mold concentrations between two or more items (carpets, chairs, etc.).

• Second, it should be reproducible. By this I mean there should be a reasonable chance that two field technicians would collect samples in the same way, so that the sample results collected on different projects could be compared.

• Third, the sample results should allow the investigator to differentiate between items that can be cleaned and those that should be discarded.

In order to meet these goals, the sample results have to be “standardized” (in this case by area), the sampling parameters have to be constants, and the sampling protocol has to be well-defined and simple to implement.

A micro-vacuum sampling method is one that uses a high-volume air sampling pump (suction device) attached to a filter cassette (sample collection device) to collect mold from surfaces. There are two basic micro-vac methods for collecting surface dust samples, by weight and by area.

The first method uses a closed-face 25 mm filter cassette to collect a weighable amount of dust. Sometimes, but not always, the area sampled is measured and reported. The sample is then cultured for fungi and/or bacteria. The airflow rate of the sampling pump may or may not be calibrated. A short piece of beveled plastic tubing is attached to the inlet of the cassette. The beveled tip is then brushed across the area of material to be sampled until a weighable amount of dust has been collected. This method primarily samples the surface of an item.

The method discussed in this article used a more consistent approach. The airflow rate of the sampling pump was calibrated at 20 liters per minute, a 30-cm by 30-cm (centimeter) template was used to enclose the area sampled, and the sample time was two minutes.
The second method discussed in this article uses an open-face 25 mm filter cassette to collect dust from soft-surface materials. The open face of the cassette has an area of about 4.9 cm², so sampling 20 different spots yields a sample area of 98 cm². This method not only samples the surface, but the interior of the material as well.
If the objective is to sample for culturable fungi, then a standard 25 millimeter (mm) filter cassette can be used as the collection device. If a fast turn-around spore count is required, or if both total spores and culturable fungi are being sampled, then a dual-trace Bi-Air cassette may be used as the collection device (moldinspectionproducts.com). The sample results are reported on an area basis (mold per 100 square centimeters of surface) [mold/100 cm²], for example.

SAMPLING SOFT-SURFACE ITEMS

The best way to address this issue is to discuss some actual data. Approximately 19 soft-surface items were sampled by Leila Brickus, Ph.D., CIH (Clark Seif Clark, Inc., Chatsworth, CA). Her data are a direct comparison of the closed-face and open-face sampling methods. However, my intent is not to present her data, but to simply offer my opinion as to the interpretation of the summarized data.

The 19 items that were sampled had been HEPA-vacuumed, removed from the subject property, and stored in a warehouse operated by a restoration company. The question: were the items in a suitable condition to be returned to the owner, or should they be discarded? I based my recommendation on the data summarized in Table 1.

Table 1. Median Concentrations of Cladosporium and Aspergillus/Penicillium Type Spores (spores/100 cm²).

My interpretation of the data in Table 1 was based on the following four assumptions:

• The closed-face cassette with beveled tip primarily sampled the surface of an item.

• The open-face cassette sampled the surface as well as the interior of an item.

• Cladosporium species are common environmental fungi, the spores are almost always present in the air, and those spores settle onto surfaces.

• Aspergillus and Penicillium, when detected at elevated concentrations in soft-surface items, are contaminant fungi resulting from a water intrusion incident.

Both sampling methods produced similar results for Cladosporium, with concentrations of 283 spores/100 cm² (closed-face) and 378 spores/100 cm² (open-face). Therefore, about 75 % of the Cladosporium was detected on the surfaces of the items. These results suggested that the Cladosporium was due to the settling of airborne spores. The data suggest that either method could be used to sample the surfaces of items.

The closed-face cassette did not detect the presence of elevated concentrations of AspPpen type spores, indicating that Asp/Pen type spores were not present on the surfaces of the items in significant concentrations. However, there was a dramatic difference in the concentrations of Asp/Pen type spores between the two sampling methods. The closed-face cassette detected a median concentration of 75 spores/100 cm², while the open-face cassette was able to detect a median concentration of 6,193 spores/100 cm² of Asp/Pen type spores. The median concentration detected using the open-face cassette was over 80-times greater than with the closed-face cassette.

The data obtained with the open-face cassette indicated that the Asp/Pen spores, which were assumed to be contaminant spores, were located primarily in the interiors of the items, not on the surfaces of the items.

The sample results from the closed-face and open-face cassette led to completely opposite conclusions, and decisions. The decision based on the results from the closed-face sampling method was that the items were in an acceptable condition, and could be returned to the owner. The results from the open-face cassette showed high concentrations of residual contaminant spores, the items had not been adequately cleaned, and were not in an acceptable condition.

Therefore, using the closed-face cassette is the “defense method”, while using the open-face cassette is the “plaintiff method”.

However, the unbiased approach would be to use both sampling methods in what is referred to as differential sampling. Use the closed-face cassette to sample the surfaces of the items, and the open-face cassette to sample both the surfaces and the interiors of the items. The difference in sampling results could provide a rational basis for classifying items as either “contaminated” (clean) or “colonized” (discard).

CLEAN OR DISCARD?

One question that has not been addressed is: Why discard colonized items, why not just clean them too? Again, I can best address this issue by presenting and discussing sample results. The data in Table 2 were collected from office chairs and padded office dividers as part of a mold investigation in a commercial building.

Table 2. Concentrations of Culturable Penicillium in Soft-Surface Items Measured with Closed Face and Open Face Cassettes. (cfu/100 cm²).

Fortunately, one wing of the facility had not been involved in the water intrusion incident, and items from that wing served as controls. The Penicillium concentrations in the soft-surface items from that wing were considered to be typical of “clean” office furniture. The items in the remainder of the facility, the contaminated area in Table 2, had been exposed to either direct contact with water or high humidity for an extended period.

The sample results in Table 2 were post-cleaning. Each of the soft-surface items had been HEPA-vacuumed three times by a professional restoration contractor, and sprayed each time with an antimicrobial agent, prior to sampling.

Based on the results for the closed-face cassette, the average concentration of Penicillium was about 6-times greater (4 v. 24 cfu/100 cm²) in the items from the contaminated area. However, the contractor characterized the difference as “not significant”, and the owner was asked to accept the furniture for re-use.

I was then asked by the owner to re-sample the items, which I did using the open-face cassette. The Penicillium concentration, even after HEPA-vacuuming three times, was about 140-times greater (9 v. 1,235 cfu/100 cm²) in the items from the contaminated area compared to those in the control area, and the owner decided not to accept the items for re-use.

The concept that soft-surface items, once colonized by mold, can not be adequately cleaned is generally accepted within the community of microbial indoor air quality consultants. The items in Table 2 had been HEPA-vacuumed three times by a professional contractor prior to sampling. Was it worth HEPA-vacuuming them a fourth time? Probably not. Once a soft-surface item has been characterized as colonized by mold, the most cost-effective approach may be to discard the item rather than try to clean it.

SUMMARY

This article describes micro-vacuum methods for sampling mold in fabric-covered couches, bedding, and other soft-surface items. The advantages of the open-face cassette method is that it is often able to differentiate between items that are simply contaminated and those that are colonized by mold. If an item can be placed into one of these two categories, then a rational decision can be made as to whether or not it can be cleaned.

There is an old adage that is applied to computer-generated data: garbage in, garbage out. This same concept applies to sample results. If the sampling method is not appropriate for the intended task, then we start with “garbage in”. The open-face sampling method