PRACTICAL EXPERIENCES WITH MVOC AS AN INDICATOR FOR MICROBIAL GROWTH

Transcription

1 PRACTICAL EXPERIENCES WITH MVOC AS AN INDICATOR FOR MICROBIAL GROWTH W. Lorenz, T. Diederich and M. Conrad Institute of Indoor Diagnostic; Duesseldorf, Germany ABSTRACT The detection of hidden microbial growth in buildings by measuring airborne microbial particles is in many cases not successful. An alternative method is the measurement of microbial VOC, the volatile metabolism products of microorganisms, called MVOC. Fungi and bacteria emit MVOC during nearly all phases of their growth. The investigation of about 2000 buildings by measuring MVOC showed good results. An estimation scheme based on that and on additional measurements in emission chambers was developed, which can be used with very good reliability in practice under certain assumptions. INDEX TERMS MVOC, hidden microbial growth, emission chamber analysis, mould dog INTRODUCTION The most frequent reasons of indoor health problems are microbial sources caused by moisture damage. Between 1994 and 2001 we investigated indoor pollution problems in about 8000 buildings, and in 60 % of the cases microorganisms were found. We could see that people become ill regardless whether unusual quantities or species of airborne microbial particles were found, or not. Remarkably in most cases the damage is not visible, see table 1. Table 1 Indicators for microbial sources. In all cases sources were located Results of indoor inspection of 100 cases Cases in % Visible microbial growth 16 % Moldy or musty smell without visible microbial growth 11 % Moist building material, no visible mould, no musty smell 43 % Special construction (creep cellar, flat roof, covered walls,...), no visible 16 % mould, no musty smell Only typical health complaints, no other indication 14 % Hidden microbial growth occurs more frequently as visible mould since microorganisms grow at locations with high humidity, in areas which are mainly not ventilated or at rather hidden places, e.g. deeper layers of building materials. Experts are looking for a method to get indications whether there are hidden microbial sources or not. It is not acceptable to destruct wall or ceiling coverings or floor materials to look for sources without objective indication. That method must be effective and reliable. Measuring cultivable airborne microbial particles is often not successful in case of hidden microbial damage. Contact author lorenz@mail.isis.de 341

2 Swedish experts developed a method for measuring the volatile metabolism products of microorganisms and called them Microbial VOC = MVOC (Börjesson, Ström, West, Wessen et al, 1994). The Swedish experts recommended to think about microbial sources if the sum of certain MVOC compounds (1-octen-3-ol, 3-methylfurane, 3-methyl-1-butanol, dimethyldisulfide, 2-pentanol, 2-hexanone, 2-heptanone, 3-octanone) exceeds 0.1 µg/m³, because the outdoor concentrations in Sweden normally are < 0.1 µg/m³. In literature we could not find any methodical study of outdoor MVOC concentrations in correlation to different seasons and different regions, e.g. city centre or countryside. There were also no publications about average indoor values for rooms without microbial sources or about the influence of possible other sources like flower pots, garden mould, cooking, baking, dust, or waste. On the basis of 2000 investigations in buildings where we used MVOC measurements combined with other methods, we developed a valuation scheme which is proved in practical use successfully. METHODS In all cases we used MVOC measurements the inhabitants complained of health troubles. The symptoms could be caused by microbial sources. We measured MVOC only in cases in which no visible mould or musty smell occurred. The day before air sampling plants, pet cages, and waste were removed from flats or houses. At least 6 hours before sampling the room was ventilated, then closed and left unused. After ventilating till the end of sampling it was not allowed to smoke, cook, or bake. Sampling was made by SKC pumps and SKC anasorb tubes. Sample and pump periods were 240 minutes, the volume rate 0.5 l/min. The chemical analysis of the MVOC were made at the Institute Fresenius in Dresden, Germany, and at Pegasus Laboratory in Uppsala, Sweden, by solvent desorption, liquid injection and gaschromatography. At Fresenius Institute the ion-trap-method was used (Merten, Richter and Landrock, 1996). In the beginning we tried to locate microbial sources if 0.1 µg/m³ MVOC sum concentration was exceeded. Fist results showed that concentrations > 0.1 µg/m³ could be measured indoors without microbial damage. Therefore we started a search for sources at sum concentrations > 0.5 µg/m³ or when methylfurane, 1-octen-3-ol, or dimethyldisulfide were detected each with 0,05 µg/m³ or more. To localize microbial sources we measured moisture in walls, floors and ceiling. In difficult cases we used a mould dog (Lorenz and Diederich, 2001). Moist materials or materials which were marked by the mould dog were analysed at Umweltmykologie, Berlin, Germany, or at Pegasus Laboratories, Uppsala, Sweden, or Duesseldorf, Germany. Fungi and bacteria were analysed by the dilution plate method. Sample materials were suspended in a buffer solution, then shaken and diluted. 0.1 ml of the suspension were plated on DG 18 agar, maltagar and CASO agar. The plates were incubated at 24 C and analysed after three, six and twelve days. Measurements of outdoor air were made in the same way as indoor air. The sampling pump was placed in a distance of at least 3 meters from the building. The pump had to be protected against wind and rain. Emission analysis of materials were made with disposable glass chambers of 5 l volume or a 100 l chamber. To avoid contamination effects it was necessary either to take disposable 342

3 chambers or to measure the empty chamber prior to each emission analysis. 10 g material was filled in the chamber. Input air was cleaned with charcoal. For sampling SKC pump and SKC anasorb tubes were used. Pump time was 50 minutes and sampling time 1500 minutes. RESULTS Outdoor MVOC sum concentrations were < 0.1 µg/m³. Only in one case 0.14 µg/m³ was measured (country, May). The concentrations of the main indicators for microbial growth 1- octen-3-ol, 3-methylfurane, and dimethyldisulfide were always < 0.05 µg/m³. 3-methyl-1- butanol was not detected and there were only traces of 3-octanone. These results showed clearly that a relevant influence of outdoor MVOC can not be expected indoors. Table 2. Outdoor measurements Location Month MVOC 1-octensum 3-ol 3- methylfurane dimethyldisulfide 3-m-1- butanol 3- octanone 2- pentanol 2-hepta none 2-hexa none Small town Jan n.d traces n.d. traces n.d City Feb 0.04 n.d n.d. n.d. traces n.d City Mar n.d. n.d Village April traces n.d. n.d. n.d City April n.d. n.d. n.d Country April n.d. n.d. n.d. n.d Outskirts April n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. Small town May 0.05 n.d n.d. n.d. n.d. n.d Country May 0.14 n.d traces n.d. n.d Small town June traces n.d. n.d. n.d. traces City center June traces n.d. n.d City June 0.09 traces traces n.d. n.d. n.d Village July n.d. n.d. n.d Outskirts Oct traces n.d. traces traces Village Nov. traces n.d. traces n.d. n.d. n.d. n.d. traces n.d. Small town Dec. traces n.d. traces n.d. n.d. n.d. n.d. n.d. traces n.d. = In summer and autumn outdoor MVOC concentrations tend to higher values than in winter and spring. Statistical evaluation of 680 indoor measurements showed also higher values in the period between June and October. Table 3. Indoor MVOC measurements (buildings with microbial sources) Month January 1.02 µg/m³ (31 values) 1.22 µg/m³ (29 values) February 0.82 µg/m³ (15 values) 1.77 µg/m³ (30 values) March 1.23 µg/m³ (20 values) 1.88 µg/m³ (16 values) April 1.00 µg/m³ (33 values) 1.69 µg/m³ (22 values) May 1.41 µg/m³ (22 values) 1.27 µg/m³ (29 values) June 1.51 µg/m³ (29 values) 2.30 µg/m³ (17 values) July 2.56 µg/m³ (39 values) 1.52 µg/m³ (19 values) August 2.79 µg/m³ (32 values) 2.02 µg/m³ (22 values) September 2.02 µg/m³ (37 values) 1.56 µg/m³ (33 values) October 1.95 µg/m³ (41 values) 1.69 µg/m³ (22 values) November 1.69 µg/m³ (30 values) 1.01µg/m³ (24 values) December 1.77 µg/m³ (46 values) 1.12µg/m³ (15 values) Soil and garden mould contain high quantities of microorganisms. So we assumed that flower pots and garden mould will emit high amounts of MVOC. Measurements in creep cellars and 343

4 in a greenhouse showed astonishing results, however The MVOC concentrations were very low. In two creep cellars we found only traces of MVOC and in a greenhouse 0.50 µg/m³, lesser than the minimum average value of indoor air, see table 3. Usually there are a lot of soil and plants outdoors but the MVOC concentrations are also very low. Table 4. MVOC measurements in rooms with plants, garden mould and soil. Location MVOC sum 1-octen- 3-ol 3- methyl- dimethyl- 3-m-1- butanol 3-octanone 2- pentanol 2-heptanon 2-hexanone furane disulfide Creep cellar traces n.d. traces n.d. n.d. n.d. n.d. traces traces Creep cellar traces traces traces n.d. n.d. n.d. traces traces traces Greenhouse traces n.d. n.d Measuring emissions from garden mould as well as from plants we got low MVOC concentrations although the emission chamber was filled with quite a lot of material. Only 3- methylfurane and dimethyldisulfide could be detected in clear concentrations. These results showed that companion plants and garden mould might not have a significant influence. Table 5. Emission analysis of garden mould and flower pots in a 100 l chamber MVOC-component 150 g garden mould µg/m³ four different flower pots µg/m³ 1-octen-3-ol 3-methyl-1-butanol 2-pentanol 3-methylfurane dimethyldisulfide hexanone heptanone octanone 0.10 sum concentration In practice we became suspicious, seeing that the MVOC concentrations are remarkable higher in dirty rooms with a lot of sediment dust than in clean rooms. Therefore we measured the MVOC-emissions of dust in a 5 l emission chamber. Table 6. MVOC in a dirty room compared with emissions from dust. compound measurement in a room with significant dust sediments in µg/m³ emission analysis of house dust (10 g in 5 l chamber) in µg/m³ 1-octen-3-ol 3-methylfurane dimethyldisulfide 3-methyl-1-butanol 2-pentanol 2-hexanone 2-heptanone 3-octanone sum concentration: House dust is a strong source of MVOC. It is not yet clarified if microbial growth in the dust or adsorption and secondary emission of MVOC is the reason. 344

5 Measurements in rather new buildings have given MVOC concentrations always > 0,5 µg/m³, partly between 1 and 2 µg/m³. In new houses floor and walls are often not dry and also there are new materials like fresh wood, glue, adhesive. Emission analysis showed that new materials, especially wood oil and adhesive, can emit 2-hexanone and 2-heptanone. We investigated new insulation materials and gypsum board directly after purchasing and found high quantities of fungi and bacteria in these new materials. In rooms without adsorbing organic materials like wall papers, furniture, textiles, the MVOC concentrations were partly very low. E.g. in the corridor of a fire brigade building and also in a school hallway we got < 0.3 µg/m³ MVOC in spite of mould damages. Measurements after the reconstruction of buildings showed that 3-methylfurane was reduced quickly after the removal of the microbial sources. 1-octen-3-ol could be detected a long time afterwards, however. DISCUSSION We could see that the indication of a microbial damage by MVOC measurement is reliable. By measuring only cultivable particles much more hidden sources will be overlooked. Cases with a microbial damage and low MVOC concentrations are seldom. In rooms without organic materials we can see this effect. Probably the microorganism emit not enough quantities of MVOC to get detectable amounts in the air. Organic materials can adsorb MVOC and might become relevant secondary sources. VOC chamber measurements showed the same effect seen (Won, Corsi, and Rynes, 2001). Cases without microbial damages but with clear MVOC concentrations > 0.5 µg/m³ are rare. This observation was made in dirty rooms with big amounts of dust as well as in new buildings where are no damage but sources such as dust and new materials with microbial growth. In one case a big sized aquarium with a dirty filter was the source of MVOC. After searching for sources without success one should not be sure that there is no microbial damage. Sources may be overlooked. You get higher certainty using a mould dog. Beside microbial growth in building materials there might be other sources which emit MVOC, e.g. cooking and baking. Probably smoking will have an influence. 3-methylfuran was detected as an emission of tobacco smoke (Laussmann, 2001). We did not investigate these possible influences but we gave order not to smoke, to cook or to bake before and during measurement. Following rules should be considered by measuring MVOC: - 12 month after the construction works of a new building are finished, and the first 6 month after reconstruction MVOC measurements should not be performed. - Although the influence of flower pots might not be significant, they should be taken out of the room a day before measurement. Also waste and pet cages should be removed. - It is not allowed to smoke, cook or bake after ventilating and closing the rooms. Main indicators for microbial growth are the compounds: 3-methylfurane, 1-octen-3-ol and dimethyldisulfide. The clear detection one of these compounds ( > 0.05 µg/m³) indicates a microbial source reliably. Another main indicator, but with restriction, is 3-methyl-1-butanol. If only 3-methyl-1-butanol and no other main indicators are detected another kind of source is 345

6 possible, e.g. emissions from the kitchen or from fresh wood. Secondary indicators are hexanone and heptanone. These compounds emit also from different new materials, e.g. adhesives or from different moist materials without mould. No microbial source would be expected if only these compounds are detected. 2-pentanol and 3-octanone seem to be main indicators, but this must be cleared by further investigations. The basic indoor concentration of MVOC is normally higher than outdoors. Indoor MVOC sum concentrations < 0,3 µg/m³ and detection of only traces of the main indicators do not indicate microbial damage. MVOC sum concentrations between 0.3 and 0.5 µg/m³ can be expected in unhygienic dwellings with high amounts of sediment dust and in new buildings. In rooms without or with only a little furniture made of organic materials like classrooms, lounges or gymnasiums the measured MVOC concentrations are mostly very low even if there are microbial damages. Probably the MVOC concentrations depend on the presence of secondary sources, respectively contaminated organic material. New microbial damages mostly lead to lower MVOC values than older damages. This effect demonstrates that furnishing operates firstly as a sink and later as a secondary source. For evaluation we derived a valuation scheme from the results of the investigations of 2000 buildings. Table 7. MVOC - valuation scheme MVOC-sum concentration 0.5 µg/m³ sum concentration 0.6 to 1.0 µg/m³ sum concentration > 1.0 µg/m³ No detection of a main indicator probably no microbial source presumably no microbial source, but a hygienic problem a microbial source in the building is possible, but without main indicators uncertain Main Indicator 0.05 to 0.10 µg/m³ of at least one main indicator a small microbial source, a hygienic problem or a microbial source in a near part of the building a microbial source in the building is probable a microbial source in the examined room or in the rooms beside is very probable > 0.10 µg/m³ of at least one main indicator a microbial source is probable a microbial source is very probable a microbial source must be there An adaptation of the scheme may be necessary by using tenax-tubes and thermodesorption. REFERENCES Börjesson T Volatile fungal metabolites as indicators of mould growth in stored cereals, Ph.D.thesis, Swedish Univ. of Agricultural Sciences, Uppsala. Laussmann Robert-Koch-Institute, Berlin, Germany, personal information, Lorenz W, Diederich T How to find hidden microbial growth with a mould dog. Proceedings of IAQ 2001 ASHRAE Conference, San Francisco, USA Merten H, Richter H, Landrock A Ion-Trap GC/MS: Chemische Ionisierung mit Wasser. FIT Fachz. Lab., p , 10/ Ström G, West J, Wessén B, Palmgren U Quantitative Analysis of microbial volatiles in damp Swedish houses. In: Health implications of funghi in indoor environments, Elsevier, North-Holland Biomedical Press, Amsterdam. Won D, Corsi R L, Rynes M Sorptive Interactions between VOCs and Indoor Materials, Indoor Air, 11, p