13.7.1 Encapsulants

Research to control biological growth using three separate antimicrobial encapsulants which were spray-painted on FGDL contaminated with Aspergillus versicolor (see Figs 13.6 and 13.7) has been performed in both field and laboratory testing ASTM 6329-98 (ASTM 6329-98, 2003; VanOsdell et al., 1996; Menetrez and Foarde, 2002) using visual inspection to estimate growth on coupons. The estimation of growth was made by optical inspection of the coupon surfaces. The numerical ranking of mold growth was:

Triplicate sample coupons were processed for surface growth on encap sulant-coated FGDL. The results indicate differences in antimicrobial efficacy for the period of testing (ASTM 6329-98, 2003; Menetrez et al., 2007, 2008a; Menetrez and Foarde, 2002; VanOsdell et al., 1996). An encapsulant or coating is a covering that is applied (spray paint as in Fig. 13.6) to a surface. The aim of applying coatings is to improve surface properties of a bulk material, usually referred to as a substrate (as in Fig. 13.7).

Three common HVAC (or HAC) antimicrobial encapsulants were evaluated for their use on FGDL in both laboratory and field application experiments. The antimicrobial encapsulants tested are manufactured for use in HVAC system components and on duct surfaces. Coating I was a poly-acrylate copolymer containing 9% barium metaborate and 0.16% iodo-2-propynyl butylcarbamate. Coating II was an acrylic coating containing decabromodiphenyl oxide and antimony trioxide. Coating III was an acrylic primer containing phosphoric acid compounds with a phosphated quaternary amine complex (diethanolamine n-coco alkyl derivatives; 2,2’-(coco ankylimino) bis-ethanol).

The results of the chamber experiments are shown in Tables 13.1 and 13.2, for sections of FGDL that were removed from the test house. Surface samples indicated that the population of A. versicolor on untreated FGDL increased by 3 logs (1000-fold) by the end of the first month (see Table 13.1), and remained approximately level through the 3.5-month study.

Table 13.1 shows a slight variation (an increase followed by a decrease) in the A. versicolor population for Coatings I and III on FGDL, for the period of 3.5 months. This was in contrast to the increased populations observed in samples with Coating II. The increase in fungi population for Coating II was comparable to that observed in the untreated samples, as compared with successful limiting of growth accomplished by Coatings I and III.

Soiled FGDL experiments resulted in similar populations of A. versicolor for untreated and Coating II samples, as shown in Table 13.2. The results were again similar for Coatings I and III, in which variations in fungi populations were observed to increase in month 1, and then decrease. The results indicate that antimicrobials can remain effective with moderate dust loading.

A comparison of the results obtained with dynamic and static chamber testing is shown in Table 13.3. The additional static chamber testing was performed at 70, 85, 90, and 94% RH, for comparison with the 94% RH dynamic chamber testing. Table 13.3 indicates that static chamber results at 94% RH are in good agreement with dynamic chamber results at 94% RH. Studies also demonstrated that static chamber fungi growth decreases with decreasing RH. Both methods indicate greater effectiveness in controlling growth with Coatings I and III.

Laboratory SMTC experiments conducted at 21.7°C (71°F) and from 65% to saturated relative humidity showed differences in degrees of efficacy for three antimicrobial coatings. Two antimicrobial coatings limited fungal contamination for the duration of testing. The most effective coatings were Coatings I and III while Coating II was ineffective. Although all three antimicrobials are registered with the EPA, they were not equally effective, nor should they be expected to perform equally in field use (Menetrez et al., 2004, 2007, 2008a; Menetrez and Foarde, 2002).

Although the importance of efficacy testing cannot be overstated, it has not received priority until the last 10 years. Additional methods of testing antimicrobial efficacy need to be standardized to evaluate differences in products having or seeking EPA registration. The standard methods should cover treatment techniques pertaining to liquids, fumigants and irradiation. The following text addresses these research subjects and is the first step in the development of standard methods. Additionally, the series of experiments described in Menetrez and Foarde (2002), are adequate tests for viable mold (ASTM 6329-98, 2003; Menetrez et al., 2004, 2007, 2008a; Menetrez and Foarde, 2002; VanOsdell et al., 1996). However, in addition to viable mold antimicrobial efficacy, additional testing may be needed for viable bacteria (bacteria cells and spores), nonviable mold (mycotoxins) and bacteria (endotoxins), as well as viruses and some forms of allergens (e.g., dust mites), to determine whether the manufacturers’ claims apply (Foarde et al., 1997a, 1997b, 1997c; Menetrez and Foarde, 2002; Menetrez et al., 2007, 2008a). The results demonstrated a significant variation in the antimicrobial efficacy of encapsulants. This variation indicates a need for product efficacy testing (Menetrez et al., 2007; Menetrez and Foarde, 2002).

13.7.2 Cleaners

Mold-contaminated materials are often not entirely removed from problem buildings. These colonized porous materials frequently have surface cleaners applied in an attempt to alleviate the problem. The efficacy of antimicrobial cleaners to remove, eliminate or control mold growth on surfaces can easily be tested on nonporous surfaces. However, the testing of antimicrobial cleaner efficacy on porous surfaces, such as those found in the indoor environment (e.g., gypsum board), can be more complicated and prone to incorrect conclusions regarding residual organisms and microbial toxins (Foarde et al., 1997a, 1997b, 1997c; Menetrez and Foarde, 2002; Menetrez et al., 2004). The mold Stachybotrys chartarum has been found to be associated with idiopathic pulmonary hemorrhage in infants and has been studied for toxin production and its occurrence in water-damaged buildings. Growth of S. chartarum on building materials such as gypsum wallboard has been frequently documented. Research to control S. chartarum growth using 13 separate antimicrobial cleaners on contaminated gypsum wallboard has been performed in laboratory testing. Laboratory SMTC experiments conducted at 21.1°C (70.0°F) and 100% relative humidity showed differences in degrees of efficacy. Common brands of cleaning products were tested by following directions printed on the product packaging and are listed in Table 13.4. A variety of gypsum wallboard surfaces were used to test these cleaning products at high relative humidity using a modification of ASTM 6329-98 (Foarde et al., 1997a, 1997b, 1997c; Menetrez and Foarde, 2002; Menetrez et al., 2004).

Visual inspection for S. chartarum regrowth of the coupons within static chambers extended up to six months. Only those samples that exhibited heavy amounts of regrowth were stopped prior to six months. The estimation of regrowth was made by optical inspection of the coupon surfaces. The numerical ranking of mold growth followed was:

Triplicate sample coupons were processed for each of the 14 cleaning products and six GWB surface types. Visual inspection for S. chartarum regrowth of the coupons within the static chambers occurred for six months or until it was judged to have extensive growth (a numerical ranking of 5). The results were numerically ranked from best (0 represented no growth) to worst (5 represented extensive growth) and are listed in Table 13.5. Six varieties of surfaces were used to evaluate S. chartarum growth. The surfaces were constructed over standard GWB and were as follows:

The object of this research was to test the antimicrobial efficacy of these cleaning and disinfectant products for removing and preventing S. chartarum, or restricting its growth, on the six varieties of GWB surfaces listed above, and with variations in RH.

The mean results (of triplicate samples) for 14 cleaning products for the six types of GWB surfaces varied extensively (see Tables 13.5 and 13.6). However, three cleaning products exhibited significantly better results than others. Lysol All-Purpose Cleaner-Orange Breeze (full strength) demonstrated results which ranked among the best in five of the six surfaces tested. Both Borax and Orange Glo Multipurpose Degreaser demonstrated results which ranked among the best in four of the six surfaces tested (Menetrez et al., 2007).

Other cleaning products ranked among the best in at least one surface test: Formula 409, Lysol IC, Pine Sol, Bleach, Spray Nine, Mildew Stain Remover with bleach, SporKlenz, Tilex, Fantastik Orange Action, and Lysol All-Purpose Cleaner-Orange Breeze (diluted). Every product tested demonstrated to be among the best in at least one surface test (Menetrez et al., 2007).

The results of S. chartarum regrowth listed in Table 13.5 were sorted in a comparative ranking of antimicrobial efficacy performance. Those products listed in Table 13.5 which best limited regrowth were given a ranking of 1, and those that demonstrated the most regrowth were given a ranking of 5. The 14 products tested are listed from 1 (best performance) to 14 (worst performance) in Table 13.6. Numerous products received the same equivalent ranking in Table 13.6 when their test results listed in Table 13.5 were equal. Table 13.6 compares antimicrobial cleaning product performance (Menetrez et al., 2007).

The results indicate differences in antimicrobial efficacy for the six-month period of testing by not allowing mold regrowth (Menetrez et al., 2007). The preferred antimicrobial cleaner to choose is often dependent on the type of surface to be cleaned of S. chartarum contamination. For Plain GWB, no paint, the best cleaners were Borax, Lysol All-Purpose Cleaner-Orange Breeze (full strength), Orange Glo Multipurpose Degreaser, and Fantastik Orange Action (Menetrez et al., 2007). For vinyl (100% vinyl, removed, cleaned and replaced) covered GWB, the best cleaners were Formula 409, Lysol IC, Pine Sol, Borax, Lysol, Bleach, Spray Nine, Mildew Stain Remover with bleach, Tilex, and Orange Glo Multipurpose Degreaser (Menetrez et al., 2007). For GWB with vinyl-coated wallpaper removed before cleaning and replaced, the best cleaners were Lysol All-Purpose Cleaner-Orange Breeze (full strength) and Orange Glo Multipurpose Degreaser (Menetrez et al., 2007). For GWB with vinyl coated wallpaper not removed before cleaning, the best cleaners were Lysol All-Purpose Cleaner-Orange Breeze (full strength), and Orange Glo Multipurpose Degreaser and Lysol All-Purpose Cleaner-Orange Breeze (diluted) (Menetrez et al., 2007). For GWB with oil-based paint, the best cleaners were Lysol All-Purpose Cleaner Orange Breeze (full strength), Lysol and Borax (Menetrez et al., 2007). For GWB with acrylic (latex) paint, the best cleaners were Borax, Lysol AllPurpose Cleaner-Orange Breeze (full strength) and SporKlenz (Menetrez et al., 2007).

Lysol All-Purpose Cleaner-Orange Breeze (full strength) demonstrated results which ranked among the best in five of the six surfaces tested. Both Borax and Orange Glo Multipurpose Degreaser demonstrated results which ranked among the best in four of the six surfaces tested. Every product tested was demonstrated to be among the best in at least one surface test (Menetrez et al., 2007).

13.7.3 Paints

Employing antimicrobial paints can in some cases prevent mold regrowth. The accepted recommendation in handling S. chartarum-contaminated gypsum wallboard is removal and replacement. This practice is, however, not always followed completely. Often mold contaminated building materials are not properly removed, some surface cleaning is performed, and paint is applied in an attempt to alleviate the problem. The efficacy of antimicrobial paints to eliminate or control mold regrowth on surfaces can easily be tested on nonporous surfaces. However, the testing of antimicrobial efficacy on porous surfaces found in the indoor environment such as gypsum wallboard can be more complicated and prone to incorrect conclusions regarding residual organisms. Growth of S. chartarum on building materials such as gypsum drywall has been frequently documented (Vesper and Vesper, 2002; Dearborn et al., 1999; Vesper et al., 2000, 2004; Scheel, 2001; Brunekreef et al., 1989; Mahmoudi and Gershwin, 2000). Research to control S. chartarum growth using seven separate antimicrobial paints and two commonly used paints on contaminated gypsum wallboard has been performed in laboratory testing. The nine paint products and manufacturers tested are listed in Tables 13.7 and 13.8 along with the product active ingredients (Menetrez et al., 2008a).

Laboratory SMTC experiments conducted at 21.1°C (70.0°F) and 100% relative humidity showed differences in degrees of efficacy. Manufacturers’ directions were followed and common gypsum wallboard was used as the base to test these products at high relative humidity. The results indicate differences in antimicrobial efficacy for the six-month period of testing by not allowing mold regrowth. When the cost of replacing walls may prevent remediation, antimicrobial paint can lend a possible low-cost alternative (Menetrez et al., 2008a). Each coupon is visually assigned a numerical ranking of mold growth from 0 to 5 for the entire averaged coupon surface. Each paint result was the average of three coupons’ surfaces. Inspection for S. chartarum regrowth of the coupons within the static chambers extended up to six months. The estimation of regrowth was made by visual inspection of the coupon surfaces. Triplicate sample coupons were processed for each of the nine paint products and two cleaning techniques. The numerical ranking of mold growth followed was:

Two techniques of preparing the GWB surfaces were used (cleaned with water only and cleaned with a bleach and water solution) to test these paint products at high relative humidity using a modification of ASTM 6329-98. The observed regrowth results were averaged for each of the seven antimicrobial paint products and the two standard paint products listed in Tables 13.9 and 13.10. Results of regrowth of S. chartarum on GWB are listed in Table 13.9. The test results of Table 13.9 list paint used on water-cleaned GWB, and paint used on bleach and water-cleaned GWB (the method recommended by most manufacturers) (Menetrez et al., 2008a).

Results for the nine types of paint products on GWB surfaces varied. However, three antimicrobial encapsulant paint products exhibited no mold regrowth. Permawhite, M-1 Additive, and Portersept demonstrated results which ranked among the best in tests (see Table 13.9). Mil-Kil ranked among the best for water-cleaned GWB (Table 13.9), and near the best for bleach and water-cleaned GWB (Table 13.10). The remaining three antimicrobial encapsulant paints and two common paints did not perform as well. The Kilz performance was not even as good as the acrylic/latex or oil-based paint (Menetrez et al., 2008a).

The results of S. chartarum regrowth listed in Table 13.9 were sorted in a comparative ranking of antimicrobial efficacy performance. The nine products tested are listed from 1 (best performance) to 9 (worst performance) in Table 13.10. Numerous products received the same equivalent ranking in Table 13.10 when their test results listed in Table 13.9 were equal. Table 13.10 compares antimicrobial paint product performance (Menetrez et al., 2008a).

Based on the study results, the best antimicrobial encapsulant paints for dealing with S. chartarum contamination on GWB were Permawhite, M-1 Additive, and Portersept. The results for Mil-Kil were close in comparison. Although two of these four products contain titanium dioxide, they all contain unique formulations that make it difficult to draw conclusions regarding antimicrobial performance (Menetrez et al., 2008a).

These results are not meant to endorse the incomplete removal of mold contaminated building materials. However, it is recognized that complete removal may not always be economically possible. Solutions to control mold regrowth can contribute to reduced occupant exposure. In some instances when mold damage is not substantial, cleaning surfaces and then painting with Permawhite, M-1 Additive, Portersept, or Mil-Kil can offer a practical alternative. In most cases, current recommendations of removal and replacement of porous building materials should be followed (Menetrez et al., 2008a).

13.7.4 UVC irradiation

Ultraviolet (UV) irradiation has been used for the disinfection of air streams for many years (Cole and Foarde, 1999; Shechmeister, 1991). The range of UV wavelengths found to be most effective was 220 to 300 nanometers (nm), and the peak effectiveness was determined to be 265 nm (VanOsdell and Foarde, 2002). The production of UV light employs an electrical discharge through low-pressure mercury vapor enclosed in a quartz glass tube (VanOsdell and Foarde, 2002). This technique produces a tube-type bulb with a primary wavelength of 253.7 nm, and is within the ‘C’ band of UV (UVC) (VanOsdell and Foarde, 2002). The UVC or UV germicidal (UVGI) form of irradiation has been demonstrated to deactivate bacteria, fungi, viruses, and mycoplasmas (Morey, 1988; Lidwell, 1994; Calvo et al., 1999; Slieman and Nicholson 2000; Peccia et al., 2001).

Ultraviolet irradiation has commonly been used in the indoor environment to eliminate or control infectious diseases in medical care facilities. HVAC system components such as duct-liners, cooling coils, drip-pans, interior insulation and areas subjected to high levels of moisture can create an environment which is prone to the establishment of biological microorganisms (Foarde et al., 1997a, 1997b, 1997c; Menetrez et al., 2004). The movement of indoor air is dominated by HVAC system operation. Biological contaminants that have become established in HVAC components, or that have been brought into the HVAC intake air (unintentionally or intentionally), can become distributed throughout the building interior. Air supplied to the building interior can carry these biological contaminants which expose numerous occupants to potential toxigenic, allergenic, and pathogenic bioaerosols.

A single UVC light was placed inside a galvanized steel square HVAC duct mock-up. The exposure chamber was maintained at room temperature, which was 22°C (71.6°F). A method to determine the antimicrobial efficacy of UVC irradiation was developed and tested on the surface of agar plates with four species of vegetative bacteria (Deinococcus radiodurans, Pseudomonas fluorescens, Serratia marcescens, and Staphylococcus epider-midis), three species of yeast (Candida albicans, Geotrichum candidum, and Rhodotorula mucilaginosa), four species of mold (Aspergillus versicolor, A. fumigatus, Penicillium chrysogenum, and Cladosporium cladosporioides) and eight varieties of Bacillus bacteria spores (B. subtilus var. orange, B. subtilus var. cream, B. stearothermophilus, B. pumilus, B. megaterium, B. cereus, B. thuringiensis, and B. anthracisstern.) exposed to UVGI irradiation (Menetrez et al., 2006, 2008b). Most of these microorganisms have been identified as being present in HVAC air-handling units (Levetin et al., 2001) and responsible for the transmission of airborne disease (Brickner et al., 2003). B. anthracis surrogates were used for their expected similar inactivation responses to UVC irradiation. The exposure time (from 5 to 900 seconds depending on the microorganism) was initiated when an internal guillotine was very quickly lifted, allowing the UV light to travel down the duct to impact the plates. At the end of the exposure time, the guillotine was quickly lowered back into the duct mock-up. In all experiments, the plates were kept the same distance from the light (144.0 cm, or 56 in). With distance and irradiance constant, time of exposure is the controlling variable. The percent kill and k value for each organism were calculated for various periods of exposure (Menetrez et al., 2006, 2008b).

For constant and uniform irradiance, the disinfection effect of UVC on a population of microorganisms can be expressed by the following set of equations (Philips Lighting Division, 1992):

[13.1]

where:

The concentration–time product calculated in Equation 13.1 depicts the exponential decay of a population of viable organisms with constant exposure to UVC. Equation 13.1 can also indicate the ability of populations of microorganisms to withstand low to high doses of UVC irradiation (Brickner et al., 2003; Levetin et al., 2001; Menetrez et al., 2006, 2008b; Philips Lighting Division, 1992).

The plates were incubated until moderate growth was visible, then the colony forming units (CFUs) were counted. The percentage killed was obtained by the following equation:

[13.2]

where C_E is the number of colonies on the side of the plate exposed to UV (N_t) and C_NE is the number of colonies on the side of the plate not exposed to UV (N₀). Significant kill was achieved with increasing periods of exposure (up to a high kill rate of 81% for a 120-second exposure). HVAC surfaces such as cooling coil fins within an air-handler which is exposed to a constant dose of UV irradiation would be expected to be relatively free of biological growth. This research demonstrated that UVC lamp irradiation inactivated biological growth to a reproducible degree with conditions of controlled doses. The k value and kill rate were calculated with the above equations (Brickner et al., 2003; Levetin et al., 2001; Menetrez et al., 2006, 2008b; Philips Lighting Division, 1992).

In one experiment, eight varieties of Bacillus spores were tested and exhibited similar effects to UVGI irradiance. Each species had large variations in surviving populations, and no significant difference in resistance between species. The k values ranged from a high of 7.46e^–5 cm²W-s (for B. s. orange) to a low of 3.23e^–5 cm²W-s (for B. megaterium) (Menetrez et al., 2006).

In another experiment, the k value results showed variability for three normally susceptible vegetative bacteria from 1.05e^–3 cm²μW-s to 3.60e^–5 cm²μW-s (with a range of relative standard deviation from 74% to 105%); yeast varied from 1.83e^–4 cm²μW-s to 1.73e^–5 cm²μW-s (with a range of relative standard deviations from 68% to 166%); and mold varied from 2.78e^–5 cm²μW-s to 7.39e^–6 cm²μW-s (with a range of relative standard deviation from 56% to 139%). Although highly variable, the k values are both reproducible and similar for all varieties tested. D. radiodurans (bacteria), R. mucilaginosa (yeast), and C. cladosporioides (mold) were the most difficult organisms to destroy in their groups. As anticipated, the four species of mold required a period of exposure in excess of 300 seconds to exhibit significant die-off, about twice that required for vegetative bacteria. It is difficult to infer further UVC exposure effects between microorganisms as comparatively diverse as fungi and bacteria (Menetrez et al., 2008b). The ability to eliminate microorganism contaminants within commercial HVAC and residential HAC systems should contribute toward reducing occupant exposure and the opportunity for the spread of these organisms based on infectious diseases.

An example of the results of this work is listed in Fig. 13.8 which depicts the percent kill as a function of the period (in seconds) of UV exposure. D. radiodurans (bacteria), R. mucilaginosa (yeast), and C. cladosporioides (mold) were the most difficult organisms to destroy. G. candidum and C. albicans of the yeast, and S. epidermidis, S. marcescens and P. fluorescens of the bacteria, were the organisms which were most rapidly destroyed. Other than these specific microorganisms the four species of mold microorganisms, required a longer period of exposure to exhibit significant die-off. It is difficult to infer further UV exposure effects between microorganisms as comparatively diverse as fungi and bacteria.

Heating, ventilating, and air-conditioning (HVAC) systems become colonized by microorganisms after a period of use, and distribute those organisms as well as those in the return air. Depending on the amount and type of microorganisms (bacteria, viruses and mold), the amount of dust and stationary film, cooling coil fouling may occur. It has been suggested that this fouling biofilm is responsible for a diminished coil capacity and increased energy consumption. UVC used to maintain HVAC equipment can potentially result in lower energy costs while providing cleaner air. This could also greatly reduce occupant exposure and the opportunity for the spread of disease and allergic reactions (Brickner et al., 2003; Levetin et al., 2001; Menetrez et al., 2006, 2008b; Philips Lighting Division, 1992).

13.7.5 Ozone

This work evaluated the effects of exposing a variety of microorganisms (two bacteria and two fungi) to elevated gaseous ozone concentrations ranging from 100 to 1000 ppm. In order to evaluate ozone under realistic ‘real world’ conditions, the test organisms were inoculated onto the surfaces of building materials (Menetrez et al., 2009). Inoculated organisms were allowed to dry on selected coupon surfaces. The concentration of organisms in colony forming units (CFU) was based on levels of contamination ranging from 10³ to 10⁷ CFU/cm² which have been isolated from surfaces of contaminated buildings. Inoculated materials were exposed to a range of RH levels, specifically low RH (20–45%) and high RH (80–95%). Temperature and RH were measured by a factory-calibrated EdgeTech Model 2000 Series DewPrime dew point hygrometer (Menetrez et al., 2009).

The microorganism exposure experiments were carried out in a commercially available desiccator cabinet constructed of polished stainless steel and glass. The interior dimensions of the chamber were approximately 30 × 25 × 30 cm (L × W × H). The total chamber volume was approximately 22 liters. The chamber was set up for use by opening the test gas entry, exit, and sampling ports, placing the support shelves within the chamber, and placing the test surfaces (glass microscope slides and glass Petri dishes holding squares of gypsum wallboard). A steady-state ozone concentration was established at the desired concentration, with measurement in the chamber center and at various locations to ensure that the test gas was well mixed. The air flow rates and ozone production were then adjusted to achieve the desired ozone concentration and RH for each experiment (Menetrez et al., 2009).

The objective of this study was to evaluate the effects of exposing a variety of microorganisms to elevated gaseous ozone concentrations. Both porous and nonporous building materials were used to represent actual indoor surfaces, and controlled chamber exposures were conducted to maintain consistent exposure concentrations (Menetrez et al., 2009).

Both gypsum wallboard (porous) and glass slide (nonporous) building materials were employed as the test surfaces in a series of experiments. Four separate microorganisms and two levels of relative humidity (RH) were tested. The four organisms selected for testing in this study were Rhodotorula mucilaginosa, Penicillium brevicompactum, Bacillus atrophaeus, and Staphylococcus epidermidis. Two fungal organisms (R. mucilaginosa (vegetative yeast cells) and P. brevicompactum (mold spores)) and two bacterial organisms (B. atrophaeus (Gram-positive bacterial spores) and S. epidermidis (vegetative bacterium)) were used (Menetrez et al., 2009).

The ozone efficacy results varied for the organisms inoculated on the surface of glass slides and gypsum wallboard coupons. Exposures on the glass slides at low RH had no observed effect on the concentration of B. atrophaeus and R. mucilaginosa, while the S. epidermidis and P. brevicompactum both decreased at least 4 logs at the maximum exposure. The high RH exposures on both glass slides and gypsum wallboard affected all of the organisms. However, the R. mucilaginosa were inactivated by 4 logs. On the gypsum wallboard at low RH, none of the organisms exposed was inactivated by as much as 2 logs. The organisms exposed to high concentrations of gaseous ozone were more readily killed on glass slides than on gypsum wallboard. Additionally, increasing RH was found to increase the biocidal capability of high levels of ozone (Menetrez et al., 2009).

The overall results of this study indicate that, even at concentrations of ozone approaching 1000 ppm, it is difficult to get significant inactivation of organisms on surfaces. In agreement with earlier experiments conducted at low ozone concentrations, the organisms exposed to high concentrations of gaseous ozone were more readily killed on glass slides than on gypsum wallboard. Increasing RH increases the biocidal capability of high levels of ozone (Menetrez et al., 2009). However, unlike the application of previously discussed antimicrobial treatments such as cleaners, paints or UV irradiation, the efficacy result for gaseous ozone indicates that it is not a realistic alternative for remediating biological contamination (Menetrez et al., 2009).

Although the specific results vary according to each of the four test organisms and the test surfaces, the overall results of this study indicate that, even at relatively high concentrations of ozone, it is difficult to get significant inactivation of organisms on surfaces. Maintaining consistently high concentrations of 1000 ppm of ozone gas could be difficult throughout the volume of air contained in a building remediation application due to unwanted reactions with building materials. Achieving a significant reduction of biocontamination concentrations on surfaces, as well as inside porous materials, wall cavities and voids, within a building would be very difficult and impractical (Menetrez et al., 2009). In addition to the difficulty in achieving these elevated concentrations, and the inadequate ability of gasphase ozone to reduce concentrations of microorganisms, the high risk to human health of exposure makes this treatment technique both ineffective and hazardous (Menetrez et al., 2009).

13.10.1 Microbial-resistant building materials product evaluation – gypsum wallboard

When building materials become exposed to moisture by weather events, leaks in the building envelope, or inadequate control of relative humidity, absorption and transport of moisture through those materials often render it susceptible to the growth of biological contaminants. Microbial colonization, and the rapid growth and dispersion of mold, can expose building occupants and produce severe illnesses including pulmonary, immunologic, neurological and oncogenic disorders. Removal of substrates from building materials, or the incorporation of antimicrobial agents in the manufacturing of building products, may prevent mold growth and the spread of contaminants. The manufacture of microbial-resistant building materials (such as wallboard, ceiling tiles and flooring) can inhibit or prevent mold growth. Limiting or preventing mold growth by the manufacture of microbial-resistant building materials creates a product which can sustain temporary adverse conditions and is less likely to become a source of biological contamination, or to need replacement.

The manufacture of wallboard that has a greater ability to withstand moisture and prevent mold growth will be less problematic and in need of replacement. Possible methods of gypsum wallboard improvement are being studied, including treatment with antimicrobials, ozone and heat during the manufacturing process. The ability to produce wallboard that may impair or prevent mold growth could greatly impact indoor air quality and reduce the need to remove and dispose of wallboard in landfills.

The manufacture of microbial-resistant gypsum wallboard has been initiated by a number of companies producing building materials. Each company has established its own manufacturing strategy for producing this material. The resultant wallboard materials could potentially have a longer product life and be both environmentally friendly and less likely to need replacing.

13.10.2 Microbial-resistant building materials product evaluation – ceiling tiles and flooring

Analogous to wallboard, the generation of ceiling tiles and flooring that has a greater ability to withstand moisture and prevent mold growth will be less problematic and in need of replacement. Possible methods of ceiling and flooring improvement should be studied. The prevention of mold growth could prevent contamination, human exposure and having to remove and landfill these products. This would ultimately create product sustainability which is the focus supported by the EPA.

Analogous to wallboard, the evaluation of ceiling tiles and carpet flooring would test the following: (1) microbial growth, (2) moisture absorption, and (3) VOC emission. The same established methods developed for wallboard would be used to form the basis of evaluation.

Acoustic ceiling tiles and carpeting used as building materials should be evaluated by this grading process. The impact on the building product industry and the consumer public can be significant, with both gaining advantages through the sales of better products.

13.10.3 HVAC biological film (biofilm) research

The presence of moisture on HVAC system cooling coils and drip-pans from condensate flow establishes conditions favorable for microbial growth. The established microbial growth can then be responsible for releasing gases (microbial volatile organic compounds or MVOCs, ‘Dirty Socks Syndrome’) or particles (BioPM) into the conditioned airstream. The presence of a microbial film on the cooling coils is also responsible for loss of heat transfer efficiency, overall component operation and the possible cause of condensate ‘blow-by’ into the supply air-duct. The characterization of fungal organisms and their byproducts (MVOCs and BioPM) which are responsible for this condition and the most effective form of treatment (UV) would give building owners, building occupants, and building remediators accurate information in identifying and dealing with this problem.

The use of UV to destroy any biofilm which has been established on HVAC surfaces and not to allow regrowth is the most efficacious manner of long-term treatment. The use of UV to deactivate airborne biological contaminants transported within existing HVAC systems adds additional benefit to this treatment alternative. Also, the prevention of biofilm buildup on cooling-coil surfaces increases thermal transfer efficiency and decreases HVAC system energy use while preventing organisms from establishing a foothold in the indoor environment, increasing the sustainability of current building systems.

MVOC characterization of gases and polymerase chain reaction (PCR) identification of particles will be used to find the best way to identify biofilms. UV treatment of an HVAC system which has an established biological film will be performed. Measurements of biological contaminants and heat transfer efficiency from before and after treatment will be conducted. Laboratory and field demonstrations will be performed concurrently.

13.10.4 Reduced infectious disease

The spread of infectious disease in humans can be attributed to communication by touch, and inhalation of the infectious agents (virus and bacteria). Air conveyance through the HVAC can transport the infectious agents along with other particles throughout a building. One infectious person can spread viable organisms to many other through the conveyance of conditioned air.

Research should focus on developing optimal air treatment techniques of fine and ultrafine biological particles (viral, bacterial) which are responsible for the spread of infectious disease. Biological surrogates of viral and bacterial organisms will be inoculated into the airstream traveling through an HVAC system. Improving methods of treatment can result in less transmission of infectious disease as well as better biological indoor air quality.

Research will involve ultraviolet (UV) irradiation to destroy viral and bacterial microorganisms on a surface and in a moving stream of air. The use of UV to destroy Bacillus spores and mold has been demonstrated. However, the antiviral or anti-pneumonial efficacy of UV on surfaces and in a moving airstream is largely unknown. The use of UV to clean air within an existing HVAC system can have other beneficial effects such as preventing fungal growth and decreasing energy use.

13.11.1 Books and publications

13.11.2 Online resources

Andersen, B., Nissen, A.T. Evaluation of media for detection of Stachybotrys and Chaetomium species associated with water-damaged buildings. International Biodeterioration and Biodegradation. 2000; 46:111–116.

Andersen, B., Nielsen, K.F., Jarvis, B.B. Characterization of Stachybotrys from water-damaged buildings based on morphology, growth, and metabolite production. Mycologia. 2002; 94:392–403.

ASTM 6329–98. Standard Guide for Developing Methodology for Evaluating the Ability of Indoor Materials to Support Microbial Growth Using Static Environmental Chambers. West Conshohocken, PA: ASTM; 2003.

Brickner, P.W., Vincent, R.L., First, M., Nardell, E., Murray, M., Kaufman, W. The application of ultraviolet germicidal irradiation to control transmission of airborne disease: bioterrorism countermeasure. Public Health Reports. 2003; 118:99–114.

Brunekreef, B., Dockery, D.W., Speizer, F.E., Ware, J.H., Spengler, J.D., Ferris, B.G. Home dampness and respiratory morbidity in children. American Review of Respiratory Disease. 1989; 140:1363–1367.

Calvo, M.A., Agut, M., Calvo, R.M., Larrondo, J. Effect of ultraviolet light irradiation and nitrosoguanidine on viability of 46 strains of Arthinium and their antibiotic production. Microbios. 1999; 98:179–187.

Chang, J., Foarde, K.K., VanOsdell, D.W. Assessment of fungal (Penicillium chrysogenum) growth on three HVAC duct materials. Environment International. 1995; 22:425–431.

Chang, J., Foarde, K.K., VanOsdell, D.W. Evaluation of fungal growth (Penicillium glabrum) on a ceiling tile. In: Morawska L., Bofinger N.D., Maroni M., eds. Indoor Air – An Integrated Approach. Australia: International Society of Indoor Air Quality and Climate (ISIAQ), Gold Coast; 1995:265–268.

Chang, J., Foarde, K.K., VanOsdell, D.W. Growth evaluation of fungi (Penicillium and Aspergillus spp.) on ceiling tiles. Atmospheric Environment. 1995; 29:2331–2337.

Cole, E.C., Foarde, K.K., Biocides and antimicrobial agents Chapter 16Macher J., ed. Bioaerosols: Assessment and Control. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, 1999.

Crook, B., Burton, N. Indoor moulds, Sick Building Syndrome and building related illness. Fungal Biology Review. 2010; 24:106–113.

Dearborn, D.G., Iwona, Y., Sorenson, W.G., Miller, M.J. Overview of investigations into pulmonary hemorrhage among infants in Cleveland, Ohio. Environmental Health Perspectives. 1999; 107(Suppl. 3):495–499.

Etzel, R.A. Stachybotrys. Current Opinion in Pediatrics. 2003; 15:103–106.

Foarde, K.K., VanOsdell, D.W., Chang, J. Susceptibility of fiberglass duct lining to fungal (Penicillium chrysogenum) growth. Proceedings of the Air and Waste Management Association Specialty Conference, Engineering Solutions to Indoor Air Quality Problems. 1995; VIP-51:629–638.

Foarde, K.K., VanOsdell, D.W., Chang, J. Static chamber method for evaluating the ability of indoor materials to support microbial growth. In: Characterizing Sources of Indoor Air Pollution and Related Sink Effects. West Conshohocken, PA: ASTM STP 1287. ASTM; 1996:87–97.

Foarde, K.K., VanOsdell, D.W., Chang, J. Evaluation of fungal growth on fiberglass duct materials for various moisture, soil, use, and temperature conditions. Indoor Air. 1996; 6(2):83–92.

Foarde, K.K., VanOsdell, D.W., Chang, J. Amplification of Penicillium chrysogenum on three HVAC duct materials. Nagoya, Japan,. Indoor Air ‘96: Proceedings of the 7th International Conference on Indoor Air Quality and Climate. 1996; 3:197–202.

Foarde, K.K., VanOsdell, D.W., Chang, J. Effectiveness of vacuum cleaning on fungally contaminated duct materials. Proceedings of the Air and Waste Management Association Specialty Conference, Engineering Solutions to Indoor Air Quality Problems. 1997; VIP-75:325–335.

Foarde, K.K., VanOsdell, D.W., Myers, E.A., Chang, J. Investigation of contact vacuuming for remediation of fungally contaminated duct materials. Environment International. 1997; 23:751–762.

Foarde, K.K., VanOsdell, D.W., Owen, M.K., Chang, J. Fungal emission rates and their impact on indoor air. Proceedings of the Air and Waste Management Association Specialty Conference, Engineering Solutions to Indoor Air Quality Problems. 1997; VIP-75:581–592.

Foarde, K.K., VanOsdell, D.W., Menetrez, M.Y., Chang, J. Investigating the influence of relative humidity, air velocity, and amplification on the emission rates of fungal spores. Indoor Air 99. 1999; 2:507–512.

Foarde, K.K., VanOsdell, D.W., Menetrez, M.Y. Investigation of the potential antimicrobial efficacy of sealants used in HVAC systems. Proceedings of the Air and Waste Management Association Specialty Conference, Engineering Solutions to Indoor Air Quality Problems. 343–347, 2000.

Gent, J.F., Ren, P., Belanger, K., Triche, E., Bracken, M.B., Holford, T.R., Leaderer, B.P. Levels of household mold associated with respiratory symptoms in the first year of life in a cohort at risk for asthma. Environmental Health Perspectives. 2002; 110:A781–A786.

Gravesen, S., Nielsen, P.A., Iversen, R., Nielsen, H.F. Microfungal contamination of damp buildings – Examples of risk constructions and risk materials. Environmental Health Perspectives. 1999; 107(Suppl. 3):505–508.

Kuhn, D.M., Ghannoum, M.A. Indoor mold, toxigenic fungi, and Stachybotrys chartarum: Infectious disease perspective. Clinical Microbiology Reviews. 2003; 16:144–172.

Levetin, E., Shaughnessy, R., Rogers, C.A., Scheir, R. Effectiveness of germicidal UV radiation for reducing fungal contamination within air-handling units. Applied and Environmental Microbiology. 2001; 67(8):3712–3715.

Lidwell, O.M. Ultraviolet radiation and the control of airborne contamination in the operating room. Journal of Hospital Infection. 1994; 28:245–248.

Mahmoudi, M., Gershwin, M.E. Sick building syndrome. III. Stachybotrys chartarum. Journal of Asthma. 2000; 37:191–198.

Meklin, T., Haugland, R.A., Reponen, T., Varma, M., Lummus, Z., Bernstein, D., Wymer, L.J., Vesper, S.J. Quantitative PCR analysis of house dust can reveal abnormal mold conditions. Journal of Environmental Monitoring. 2004; 6:615–620.

Menetrez, M.Y., Foarde, K.K. Testing antimicrobial efficacy on porous materials. Indoor Built Environment: Journal of the International Society of the Built Environment. 2002; 11:202–207.

Menetrez, M.Y., Foarde, K.K., Webber, T.D., Dean, T.R., Betancourt, D.A. Growth responses of Stachybotrys chartarum to moisture variation on common building materials. Indoor Built Environment: Journal of the International Society of the Built Environment. 2004; 13:183–188.

Menetrez, M.Y., Foarde, K.K., Webber, T.D., Dean, T.R., Betancourt, D.A. Efficacy of UV irradiation on eight species of Bacillus. Journal of Environmental Engineering and Science. 2006; 5(4):329–334.

Menetrez, M.Y., Foarde, K.K., Webber, T.D., Dean, T.R., Betancourt, D.A. Testing antimicrobial cleaner efficacy on gypsum wallboard contaminated with Stachybotrys chartarum. Journal of Environmental Science and Pollution Research. 2007; 14(7):523–528.

Menetrez, M.Y., Foarde, K.K., Webber, T.D., Dean, T.R., Betancourt, D.A. Testing antimicrobial paint efficacy on gypsum wallboard contaminated with Stachybotrys chartarum. Journal of Occupational and Environmental Hygiene. 2008; 5:1–4.

Menetrez, M.Y., Foarde, K.K., Dean, T.R., Betancourt, D.A. The effectiveness of UV irradiation on vegetative bacteria and fungi surface contamination. Chemical Engineering Journal. 2008; 157:443–450.

Menetrez, M.Y., Foarde, K.K., Webber, T.D., Dean, T.R., Betancourt, D.A. An evaluation of the antimicrobial effects of gas-phase ozone. Ozone: Science and Engineering. 2009; 31(4):316–325.

Morey, P.R. Microorganisms in buildings and HVAC systems. A summary of environmental studies. In: Proceedings of IAQ’88 – Engineering Solutions to Indoor Air Problems. Atlanta, GA: American Society of Heating, Refrigerating and Air Conditioning Engineers, Atlanta, GA; 1988:10–25.

Murtoniemi, T., Nevalainen, A., Suutari, M., Toivola, M., Komulainen, H., Hirvonen, M.R. Induction of cytotoxicity and production of inflammatory mediators in TAW264.7 macrophages by spores grown on six different plasterboards. Inhalation Toxicology. 2001; 13(3):233–247.

Nielsen, K.F. Mycotoxin production by indoor molds. Fungal Genetics and Biology. 2003; 39:103–117.

Novotny, W., Dixit, A. Pulmonary hemorrhage in an infant following 2 weeks of fungal exposure. Archives of Pediatric and Adolescent Medicine. 2000; 154:271–275.

Peccia, J., Werth, H.M., Miller, S., Hernandez, M. Effects of relative humidity on the ultraviolet induced inactivation of airborne bacteria. Aerosol Science and Technology. 2001; 35:728–740.

Philips Lighting Division, Disinfection by UV-radiation, 1992. [Booklet 3222 C34; 00671.].

Scheel, C.M. Possible sources of sick building syndrome in a Tennessee middle school. Archives of Environmental Health. 2001; 56(5):413–418.

Shechmeister, I.L. Sterilization by ultraviolet radiation. In: Block S.S., ed. Disinfection, Sterilization, and Preservation. Phildelphia: Lea & Febiger; 1991:553–565.

Slieman, T.A., Nicholson, W.L. Artificial and solar UV radiation induces strand breaks and cyclobutane pyrimidine dimers in Bacillus subtilus spore DNA. Applied and Environmental Microbiology. 2000; 66(1):199–205.

Sudakin, D.L. Stachybotrys chartarum, current knowledge of its role in disease. Medscape www.medscape.com/viewarticle/408038, 2000. [E11].

VanOsdell, D., Foarde, K.K., Defining the effectiveness of UV lamps installed in circulating air ductwork. ARTI-21CR/610-40030-01. Air-Conditioning and Refrigeration Technology Institute, Arlington, VA, 2002.

VanOsdell, D.W., Foarde, K.K., Chang, J. Design and operation of a dynamic test chamber for measurement of biocontaminant pollutant emission and control. In: Characterizing Sources of Indoor Air Pollution and Related Sink Effects. West Conshohocken, PA: ASTM STP 1287. ASTM; 1996:44–57.

Vesper, S.J., Vesper, M.J. Stachylysin may be a cause of hemorrhaging in humans exposed to Stachybotrys chartarum. Infection and Immunity. 2002; 70:2065–2069.

Vesper, S.J., Dearborn, D.G., Yike, I., Allen, T., Sobolewski, J., Hinkley, S.F., Jarvis, B.B., Haugland, R.A. Evaluation of Stachybotrys chartarum in the house of an infant with pulmonary hemorrhage: Quantitative assessment before, during, and after remediation. Journal of Urban Health. 2000; 77:68–85.

Vesper, S.J., Varma, M., Wymer, L.J., Dearborn, D.G., Sobolewski, J., Haugland, R.A. Quantitative polymerase chain reaction analysis of fungi in dust from homes of infants who developed idiopathic pulmonary hemorrhaging. Journal of Occupational and Environmental Medicine. 2004; 46(6):596–601.