Industrial hygienists have an interest in surface mold growth

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1 Journal of Occupational and Environmental Hygiene, 3: ISSN: print / online Copyright c 2006 JOEH, LLC DOI: / Controlled Study of Mold Growth and Cleaning Procedure on Treated and ntreated Wet Gypsum Wallboard in an Indoor Environment Michael Krause, 1 William Geer, 1 Lonie Swenson, 1 Payam Fallah, 2 and Coreen Robbins 1 1 Veritox, Inc., Redmond, Washington 2 Environmental Microbiology Laboratory, San Diego, California The basis for some common gypsum wallboard mold remediation practices was examined. The bottom inch of several gypsum wallboard panels was immersed in bottled drinking water; some panels were coated and others were untreated. The panels were examined and tested for a period of 8 weeks. This study investigated: (a) whether mold growth, detectable visually or with tape lift samples, occurs within 1 week on wet gypsum wallboard; (b) the types, timing, and extent of mold growth on wet gypsum wallboard; (c) whether mold growth is present on gypsum wallboard surfaces 6 inches from visible mold growth; (d) whether some commonly used surface treatments affect the timing of occurrence and rate of mold growth; and (e) if moldy but dried gypsum wallboard can be cleaned with simple methods and then sealed with common surface treatments so that residual mold particles are undetectable with typical surface sampling techniques. Mold growth was not detected visually or with tape lift samples after 1 week on any of the wallboard panels, regardless of treatment, well beyond the hours often mentioned as the incubation period. Growth was detected at 2 weeks on untreated gypsum. Penicillium, Cladosporium, and Acremonium were early colonizers of untreated panels. Aspergillus, Epicoccum, Alternaria, and locladium appeared later. Stachybotrys was not found. Mold growth was not detected more than 6 inches beyond the margin of visible mold growth, suggesting that recommendations to remove gypsum wallboard more than 1 foot beyond visible mold are excessive. The surface treatments resulted in delayed mold growth and reduced the area of mold growth compared with untreated gypsum wallboard. Results showed that simple cleaning of moldy gypsum wallboard was possible to the extent that mold particles beyond normal trapping were not found on tape lift samples. Thus, cleaning is an option in some situations where removal is not feasible or desirable. In cases where conditions are not similar to those of this study, or where large areas may be affected, a sample area could be cleaned and tested to verify that the cleaning technique is sufficient to reduce levels to background or normal trapping. These results are generally in agreement with laboratory studies of mold growth on, and cleaning of, gypsum wallboard. Keywords cleaning, drywall, gypsum wallboard, mold growth, sanitation Address correspondence to: Michael Krause, Veritox, Inc., Redmond-Fall City Road, Redmond, WA 98052; mkrause@ veritox.com. This work was not funded by any manufacturer of products mentioned, nor was any other outside funding received to support this work. Mention of these products does not constitute an endorsement of their use by the authors. INTRODCTION Industrial hygienists have an interest in surface mold growth as a potential source of mold exposure. Disturbance of surface mold may result in mold spores or particles becoming airborne and thus being available for inhalation. Due to this concern for potential mold exposure, hygienists often become involved in recommending cleanup and treatment procedures for moldy indoor surfaces. The most commonly cited New York City Department of Health and Environmental Protection Agency (EPA) mold guidelines state that drying of gypsum wallboard (GWB) within 24 to 48 hours must be done to prevent mold growth. (1,2) There is no supporting information. If visible mold arises, the guidelines recommend that intact GWB with small amounts of growth (less than 10 square feet) be cleaned with detergent solutions or high-efficiency particulate air (HEPA) vacuums. The guidelines stress physical removal of all mold particles. They do not promote the use of biocides, like chlorine, reasoning that if spores not cleaned off may be killed by the biocide, but potentially allergenic particles will remain. They infer that biocides will be misused (simply sprayed on surfaces), that wiping or vacuuming is highly effective, and that particles left behind are an airborne hazard. Although the guidelines allow cleaning of surfaces, mold consultants often require that GWB with any visible mold growth be cut out and discarded. Removal of GWB over 1 foot beyond any visible mold growth is commonly required. The unsupported assumption is that invisible mold is present well beyond the visible margins of growth. Journal of Occupational and Environmental Hygiene August

2 Obviously, removal of moldy GWB may sometimes be more economical than surface cleaning or may be expedient for other reasons, such as to aid thorough drying of wall cavities. However, in other cases, removal of moldy GWB is not feasible (e.g., in pipe chases), is extremely costly (e.g., behind brick or concrete), or may appear unwarranted (e.g., small areas of growth). Surface coatings could allay concerns that residual mold particles may be left after cleaning. The New York City Department of Health and EPA guidelines do not promote the treatment of cleaned surfaces, such as wallboard or studs, with encapsulating and/or fungicidal materials. However, the efficacy of these treatments in eliminating surface mold particles as potential sources of airborne spores is unknown. ASTM International has several methods for evaluating the resistance of materials and treatments to staining and mold growth. ASTM G21 Standard Practice for Determining Resistance of Synthetic Polymeric Materials to Fungi is used to test the mold resistance of polymeric films (paints, etc.). A chip of the cured material is covered with a mixed spore suspension in a petri dish containing nutrient agar. The sample is maintained under optimal conditions for mold growth for a period of 28 days. (3) Samples are rated from zero to four, with zero indicating no growth, and four indicating that 60% of the agar surface is covered with observed growth. ASTM D3273 Standard Test Method for Resistance to Growth of Mold on the Surface of Interior Coatings in an Environmental Chamber uses an environmental chamber to better model humid conditions. Treated panels are placed in an environmental chamber for 4 weeks at 95 98% humidity at 90 ± 2 F. Nutrient-rich soil and water in the bottom of the chamber is inoculated with mold. Mold growth on panel surfaces within the chamber is observed. (4) Although these tests can help ascertain the relative resistance of different coatings to mold growth, they are not conducted under conditions of a typical building environment. They are not useful in determining whether mold growth on GWB can be cleaned and sealed so that mold spores are not available on the surface once the material is dried or the source of moisture otherwise controlled. Different aspects of mold growth on GWB have been studied. Mycotoxin production from artificially inoculated and naturally infested wallboard was measured by Nielsen and colleagues. (5) They were able to detect different types of mycotoxins in response to different temperature, water activity, and material composition but acknowledged the need for further research to relate their results to health risks. Gao and Martin (6) measured microbial volatile organic compounds (MVOCs) from mold growth on inoculated wallboard. Fewer MVOCs were detected when the wallboard was inoculated with S. chartarum, and the MVOCs were different from those seen with Aspergillus species. (6) Murtoniemi et al. (7) also studied the growth of inoculated Stachybotrys on different types of wallboard in the laboratory. They found no Stachybotrys growth when the wallboard paper was treated with biocide. Other researchers have conducted laboratory investigations concerning growth of inoculated Stachybotrys on small pieces of wallboard and the effect of cleaning with quaternary ammonium compounds with and without chlorine. (8) These researchers also examined the effect of microbial coatings on regrowth of mold on the cleaned wallboard. In Price and Ahearn s (8) study, wallboard that was cleaned and coated did not support Stachybotrys growth for over 35 days. The study also noted that commercial wallboard contains a baseline bioburden, including Stachybotrys. Tests of mold growth, pretreatment effects, and cleaning and sanitizing studies conducted on a room-size scale under typical office conditions have not been published. The current study used half-sheets of GWB with the bottom edges immersed in water in a room that is typical of offices in the Pacific Northwest, with normal conditions of temperature, humidity, and ambient spores. This was intended to better represent mold growth on wet GWB in a typical indoor office setting. This study investigated (a) whether mold growth, detectable visually and with tape lift samples, occurs within 48 hours on wet gypsum wallboard; (b) the types, timing, and extent of mold growth on wet gypsum wallboard; (c) whether invisible mold is present on gypsum wallboard surfaces over 1 foot from visible mold growth; (d) whether some commonly used surface treatments affect the timing of occurrence and rate of mold growth; and (e) whether moldy, gypsum wallboard can be dried and cleaned with simple methods and then sealed with common surface treatments so that residual mold particles are undetectable with typical surface sampling techniques. METHODS Phase 1 Mold Growth Trials Five standard 4 ft 8ft 0.5 inch interior GWB panels were purchased from a nationwide hardware retail store and cut in half lengthwise. Three half-panels (hereafter called panels or sheets) were coated with either BORA-CARE, Kilz Premium, or Foster on the kraft paper side with separate, disposable 4-inch paint rollers. This was to simulate treatment of GWB in awall cavity. Five panels were used as untreated wet controls and two as dry controls. One end of all sheets was marked with lines at 1 inch (water line) and then at 3-inch intervals above the water line to the end (bottom) to facilitate the visual estimation of mold growth area (Figure 1). BORA-CARE (Nisus Corp., Rockford, Tenn.) is usually used by contractors on wooden structural members as an insecticide and for the control of wood decay fungi. The label states that it can be used on other cellulosic materials... in and around homes. The active ingredient listed on the label is an EPA-registered borate compound (disodium octaborate tetrahydrate). Kilz Premium (Masterchem Industries, Inc., Imperial, Mo.) is a water-based, stain-blocking primer widely sold in hardware stores for both interior and exterior wallboard surfaces as a mildew resistant coating. No active ingredients are listed on the label. Foster (Foster Products, Inc., Oakdale, Minn.) is a white fungicidal protective coating that contains EPA-registered compounds. It is used in the mold 436 Journal of Occupational and Environmental Hygiene August 2006

3 FIGRE 1. Week 5 Typical untreated gypsum wallboard half sheet in water tray showing kraft paper side with 3-inch grid lines and mold growth at cleanup industry on interior wallboard and wall cavities. The active ingredients listed on the label are barium metaborate and 3-iodo-2 propynyl butylcarbamate. Panels were hung from the top of a wooden rack. The bottom 1 inch of each of the eight wet panels was immersed in water contained in a clean wallpaper tray (Figure 1). Drinking water in 5-gal bottles from a nationwide hardware retailer was chosen for cleanliness, consistency, low chlorine, and ease of handling. Two panels were hung as dry controls. All of the work took place in a 12 ft 16 ft 10 ft high, painted, carpeted, office-like room with baseboard heat controlled by a manual thermostat. There was no air conditioning or mechanical ventilation system in this room, but there was some infiltration of outdoor air through the front door. The room maintained typical Northwest spring daytime and nighttime temperatures (60 65 Fatnight, and F during the day, with some sunny afternoon peaks in the low 80s). Relative humidity (RH) in the room typically ranged from 45% to 65% RH, except for short transient lows to 30% RH when afternoon sunshine heated the space. Conditions were monitored manually with an electronic residential thermometer/hygrometer (Radio Shack thermo/hygrometer, model ; Fort Worth, Texas). Long-term temperature and humidity were monitored at each end of the rack with two data logging temperature/rh meters (Hobo 8 data loggers, Onset Computer Corp., Bourne, Mass.). Panels were observed daily for mold growth and digitally photographed. The time of the appearance of mold growth was noted, and the area of mold growth was estimated weekly. Tape lift samples were collected from the kraft paper sides with transparent cellophane tape and placed on glass microscope slides for transport. Surface tape samples were collected prior to panel immersion and then once per week for 8 weeks. Initially, samples were collected within a few inches of the water line and again approximately 6 inches away from the water line in a different area each week. After visible mold appeared (at the third week post immersion), samples were collected of random mold colonies and then at 6 inches above the highest point of visible mold growth. Samples were sent to an AIHA-accredited laboratory for analysis of mold presence and genera. The laboratory determines whether the number of spores and other mold structures present indicate actual mold growth versus simply a normal mix of settled spores, called normal trapping. If mold growth is present, the genus is identified and a qualitative assessment of the relative abundance of mold spores is indicated. Tape sampling ended after 8 weeks. Phase 2 Cleaning Effectiveness Trials This work was designed to model a moisture intrusion episode involving discovery and correction of the water source, drying of materials, and cleaning of mold growth. Journal of Occupational and Environmental Hygiene August

4 The water was removed from all pans, and panels were allowed to dry for 2 weeks. The panels initially treated with Kilz Premium, BORA-CARE, or Foster were set aside and not included in the subsequent testing. Three uncoated control panels with similar, contiguous, abundant mold growth were used for cleaning and coating tests (Figure 1). One dry panel with no growth was used for comparison. One moldy panel was simply brushed off outdoors using a dry, stiff-bristled brush and then rehung. A second moldy panel was wiped with clean paper towels after being sprayed with a 10:1 solution of ltra Clorox Germicidal Bleach containing 6% sodium hypochlorite (Colorox Company, Oakland, California). The third test panel was wiped after being sprayed with a 10:1 solution of Clorox Outdoor Bleach Cleaner (sodium hypochlorite 6 7% and detergent/surfactant ingredients). The same cleaning method was used on the kraft paper side (hereafter called the front side) and the finished paper side (back side) of each panel. Although vegetative growth was removed, the paper faces remained intact but stained. The Clorox-treated panels appeared less stained than the panel that was brushed. The cleaned panels were allowed to dry for 2 more weeks. Then, a 1-foot wide strip down the middle of both sides of those panels and the dry control was vacuumed with a filtered, canister-type home vacuum with a horsehair brush attachment. This was done to determine the added effectiveness of vacuuming on previously dry-brushed and chlorine-wiped surfaces. Tape-lift and swab samples (BBL CultureSwab; Becton Dickenson, Franklin Lakes, N.J.) were collected from all panels from the vacuumed and nonvacuumed areas. Cultured swab sampling was added to determine whether any viable spores remained after wiping with chlorine cleaners. The laboratory cultured the samples and reported colonies by species. The test panels and dry control were then coated with Kilz Premium on one half of the front and back and Foster on the other half of the front and back. Clean, 4-inch rollers were used for each area to avoid cross contamination. After drying, tape lift and swab samples were collected from the same vacuumed and nonvacuumed areas that were sampled prior to coating. RESLTS Phase 1 Mold Growth Trials No mold growth was detected with tape samples on any panel at the beginning of the study or after 1 week. Some colorless hyphae were detected on four out of five untreated panels after 2 weeks had elapsed. Mold growth was not clearly visible until 3 weeks on the uncoated panels. The growth started as dispersed colonies that completely filled in later to cover an area of up to approximately 2 square feet (Figure 2). The height of mold growth on the kraft paper side (front) varied by several inches between untreated panels and was consistently lower than growth on the finished paper side (back). No mold growth was detected on the dry controls. The mold genera and the approximate timing of their appearance on treated and untreated panels are shown in Table I. The common molds Penicillium and Cladosporium were early colonizers of the untreated GWB panels, with spores first detected on the third week. Aspergillus was first detected FIGRE 2. Area of mold growth versus time in water for untreated and treated gypsum wallboard 438 Journal of Occupational and Environmental Hygiene August 2006

5 TABLE I. Mold First Detected with Tape Lifts on Wet Wallboard vs. Time Mold Structures Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 7 Week 8 A,B Hyphae only B Spores/growth Acremonium Penicillium Cladosporium Aspergillus Epicoccum Alternaria locladium Phoma Notes: = untreated panels; B = BORA-CARE treated surface. A Kilz Premium treated surface: No spores or hyphae detected. B Foster treated surface: No spores or hyphae detected. at the fourth week and locladium at 6 weeks. Stachybotrys was never detected. The appearance of mold occurred at least 1 week later on the treated panel surfaces compared with the untreated panels. Colorless hyphae were found on the BORA-CARE-treated panel surface at Week 4, but spores were not detected through Week 8. Mold grew on the uncoated back side of the BORA- CARE panel, but it appeared later and covered less area than on the untreated panels. No mold growth was visible or detected on the coated (kraft) side of the Kilz Premium and Foster panels. Visible mold growth on the uncoated back side of the Kilz panel ended up at a similar height to that of untreated panels but was more dispersed. Mold growth on the back side of the Foster treated panel appeared later and covered much less area than any of the other panels. Mold growth was not detected on any sample collected 6 inches beyond visible mold growth. Also, all visible mold growth stopped below the upper limit of the water marks about 18 inches high due to wicking up the wallboard. Phase 2 Cleaning Effectiveness Trials After cleaning with household chlorine compounds, very few mold spores and/or hyphae were found on tape lift samples, similar to the dry control panel (Table II). Tape lifts were positive for mold growth and mold colonies were cultured from swab samples of the panel cleaned only with dry brushing. No colonies resulted from swab samples of the panels cleaned with spraying and wiping. These results show that viable spores were undetectable with swab samples on the panels sprayed and wiped with bleach-containing solutions. Vacuuming appeared to have little effect on the dry brushed panel, which still showed mold growth on tape lifts and viable colonies in one swab sample. The number of loose spores analyzed from the wet cleaned panels was slightly reduced by the addition of vacuuming. TABLE II. Mold Growth Detected After Cleaning and Treating Moldy Panels Cleaning Method After Cleaning, Prevacuuming After Vacuuming After Kilz After Foster Panel side Tape Swab Tape Swab Tape Swab Tape Swab Dry control Finished N 0 N Kraft N 0 N 0 N ltra Clorox Finished N 0 N 0 N Kraft N 0 N Dry brushing Finished MG Pen, lo, Clad MG Pen Kraft MG Pen, lo MG hyphae Clorox Outdoor Finished N Kraft N 0 hyphae Notes: N = normal trapping, very few spores; 0 = no mold spores, hyphae, or colonies detected; MG = mold growth; Pen = Penicillium species colonies, lo = locadium, Clad = Cladosporium. Journal of Occupational and Environmental Hygiene August

6 Regardless of the cleaning method used, results from all swab samples collected from panels that had been coated showed no viable mold spores. On tape lift samples, no loose spores or hyphae were found for Foster treated panels. No spores to normal trapping was seen on the Kilz-treated panel and the dry control panel. DISCSSION Results show that invisible mold structures on untreated wet GWB, detectable with tape samples, was restricted to hyphae at Week 2. Visible mold colonies and samples of conidia indicating growth of Penicillium, Cladosporium, and Acremonium were found at Week 3. This is well in excess of the 48-hour period that is often cited as the time suggested for mold growth. (2) It is possible that some dispersed invisible mold growth was present but not detected in the first 2 weeks. However, the exposure potential from mold particles present at levels undetectable by these methods is expected to be low. Price (8) reported that growth was often not observed with the unaided eye on noninoculated wallboard until 4 weeks of incubation; however, wallboard inoculated with Stachybotrys had nearly confluent colonization after days. Small pieces of wallboard (64 cm 2 ) were inoculated with Stachybotrys spores, or naturally occurring mold was allowed to grow in humid chambers. Although these researchers found Stachybotrys on noninoculated wallboard, this genus was not detected in the current study on any swab or tape sample. This does not preclude its presence, since it may have occurred in untested areas. Price (8) studied the disinfection of wallboard with Stachybotrys and other molds on it. Mold growth was cleaned by rinsing, brushing, and flushing with quaternary ammonium compounds (quats), with and without chlorine. Resampling showed that no viable mold remained. These methods appeared to be effective in killing and eliminating mold spores. The current study results indicate that it is possible to sanitize moldy GWB, to the extent that viable mold spores are not detected on swab culture samples after fairly dilute bleach solutions are sprayed on and wiped with a paper towel. The current results generally agree with those reported by Price, 8 but the current study suggests practical methods that can be implemented on a larger scale. Dry brushing and use of a household vacuum with a soft brush did not effectively remove all mold growth, as measured with tape lift or swab samples. However, results indicate that it is possible to treat or coat even dry-brushed and vacuumed GWB to the extent that mold spores and hyphae are not detectable at any more than normal background (normal trapping) levels, at least under the conditions of this study. Price (8) also examined the potential for mold regrowth on wallboard pieces that were cleaned and then treated with a clear acrylic coating designed to coat aluminum air-conditioner heat exchange coils, or with a white-pigmented, water-based, metal-priming paint. After 3 weeks at >95% relative humidity, the acrylic coating was penetrated by pinpoint fungal colonies observed under a microscope. Growth was observed on the uncoated edges of the metal primer-painted wallboard at about 5 weeks; however, the painted areas remained free of colonies for an additional 3 weeks. The current study results generally agree with Price s findings, since initial mold growth was delayed for weeks by the original coatings on the wet GWB. Mold regrowth on GWB similarly may be inhibited by the use of coatings. Since only bottled drinking water was used in this study, results concerning growth time may not be representative of cases where dirty water from floods or plumbing may provide nutrients and initial inocula that could result in mold growth in a shorter time period. The IICRC Standard and Reference Guide for Water Damage Restoration S500 recommends that drywall be replaced when contaminated by category 3 black water (sewage and flooding). (9) The current study was carried out under normal Pacific Northwest indoor office conditions; therefore, changes in the environmental parameters are likely to influence the timing and extent of mold growth. CONCLSIONS Mold growth was not detectable with tape lift samples on wet, untreated, interior GWB within 2 weeks in environmental conditions of a typical Pacific Northwest office building with baseboard heat. This is well beyond the 24 to 48 hours often cited. Penicillium and Cladosporium were early colonizers of untreated GWB panels. Aspergillus, Alternaria, and locladium appeared later. Stachybotrys spores or growth were not found. Mold growth was not detected with tape lifts at distances 6ormore inches beyond visible mold growth. Therefore, any requirement to remove GWB at least 1 foot beyond visible mold is unsupported. Although the current study and earlier work by Price (8) used different methods of subjecting GWB to moisture and different cleaning techniques, both studies indicate that GWB can be sanitized and cleaned of mold growth. Results show that cleaning of GWB is an option in some situations where removal is not feasible or desirable. In cases where conditions are not similar to those of this study, or where large areas may be affected, a sample area could be cleaned and tested to verify that the cleaning technique is sufficient to achieve background or normal trapping. Future trials of industrial strength vacuums and abrasive brush attachments may illustrate better cleaning efficiency than the household vacuum used in this study. Further research is needed on the effectiveness of other cleaning and sanitizing wipes and solutions available, including those that contain quaternary ammonium compounds (quats). Treatment of GWB slows the appearance and reduces the extent of mold growth, suggesting that this may be a useful step in places where recurring wetness and/or humidity can occur, such as bathrooms. Although other researchers have found inhibition of regrowth with mold-inhibiting coatings, 440 Journal of Occupational and Environmental Hygiene August 2006

7 full-scale studies specific to GWB remain to be conducted to determine the timing and extent of regrowth with moisture reexposure after applying the cleaning and treatment methods in this study. REFERENCES 1. D Andrea, C. (ed.): Guidelines on Assessment and Remediation of Fungi in Indoor Environments. New York: New York City Department of Health, Environmental Protection Agency (EPA): Mold Remediation in Schools and Commercial Buildings (EPA 402-K ). Washington, D.C.: EPA, ASTM International (ASTM): Standard Practice for Determining Resistance of Synthetic Polymeric Materials to Fungi (G 21-96). [Standard] West Conshohocken, Pa: ASTM International, ASTM International (ASTM): Standard Test Method for Resistance to Growth of Mold on the Surface of Interior Coatings in an Environmental Chamber (D ). [Standard] West Conshohocken, Pa.: ASTM International, Nielsen, K.F., S. Gravesen, P.A. Nielsen, B. Andersen,. Thrane, and J.C. Frisvad: Production of mycotoxins on artificially and naturally infested building materials. Mycopathologia 145: (1999). 6. Gao, P., and J. Martin: Volatile metabolites produced by three strains of Stachybotrys chartarum cultivated on rice and gypsum board. Appl. Occup. Environ. Hyg. 17: (2002). 7. Murtoniemi, T., A. Nevalainen, and M.-R. Hirvonen: Effect of plasterboard composition on Stachybotrys chartarum growth and biological activity of spores. Appl. Environ. Microbiol. 69: (2003). 8. Price, D.L. and D.G. Ahearn: Sanitation of wallboard colonized with S. Chartarum. Curr. Microbiol. 39: (1999). 9. Institute of Inspection, Cleaning and Restoration Certification (IICRC): Standard and Reference Guide for Water Damaage Restoration (IICRC S500). [Standard] Vancouver, Wash.: IICRC, Journal of Occupational and Environmental Hygiene August