Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
Mold Standards for Exposure & Testing:
This InspectAPedia technical article describes various current & proposed mold standards as well as the very substantial shortcomings in any mold exposure standard whatsoever.
Here we also explain reasons for substantial variation in and interpretation of the meaning of airborne mold spore counts, moldy surface density, and other measures of the exposure level of allergenic, infectious, and levels of toxic mold in buildings. At what level is allergenic or toxic mold considered a problem in buildings? How do we obtain an accurate and meaningful measurement of mold exposure indoors?
Green links show where you are. © Copyright 2017 InspectApedia.com, All Rights Reserved.
[Click to enlarge any image]
Warning: fungal spore counts in indoor air, whether "viable" or "non-viable" counts, as well as swab and culture methods to identify just what mold is present in a building are questionable methods to characterize the presence or absence of a mold problem indoors.
From experience carefully inspecting many buildings for mold problems and simultaneously collecting many types of field samples and examining them in our lab, our view is that anyone who makes one or a few indoor air measurements or relies on culture plates or swabs to "characterize" the mold level and mold species in a building is risking being way off target, particularly if the "test results" show low numbers.
"Mold Levels" warning: single number "mold levels" are unreliable as a measure of health risk in buildings for several reasons including at least the following:
See ACCURACY OF AIRBORNE MOLD SPORE COUNTS for more details about these issues. That said, here is a sampling of some indoor air mold spore exposure level criteria and comments
1. Baxter et als: Mold contamination is considered present in a building when the total mold spore concentration per cubic meter is above 10,000. Our own field and lab experience confirms this view. However in special cases, even low quantitative levels of certain particles or particle types (such as Pen/Asp spore chains in an un-treated building) may be diagnostic and may indicate a hidden mold reservoir that at least merits further investigation.
2. The National Allergy Bureau, reporting the NAB SCALE (National Allergy Bureau) of mold and pollen counts, considers mold counts in outdoor air of 0-6499 spores per cubic meter of air as low, to 6500 to 12,999 spores per cubic meter of air as moderate, to 13,000 to 49,999 spores per cubic meter of air as high, and above 50,000 as very high. At "high" levels most individuals with any sensitivity will experience
AAAAI also provides absent, low, moderate, high, and very-high level level definitions for grass, tree, and weed pollen grains counted per cubic meter of outdoor air.
Acceptable levels for individual species vary since species toxicity varies widely as does spore size, weight, and other features which affect risk to building occupants. E.g. Aspergillus/Penicillium in a "clean" residential building study was at a mean of 230, in buildings known to have a moisture or flooding problem it was at 2235 and in mold contaminated buildings the figure was 36,037.
AAAAI provides an important qualification about mold and pollen counts as reported by that agency which we quote just below:
"These mold levels were determined based on outdoor exposure to natural occurring spores in the environment and should not be applied to indoor exposure which may represent an entirely different spectrum of spore types.
These definitions would allow comparison between sites across the country. They are based on ecological measurements, not health effects. However, assuming dose/response relationships are the same across the country, the definitions are probably more appropriate than a definition based on local numbers. This does mean that, for some stations, some categories will never be high." - AAAAI.
3. The University of Minnesota data presents this table for mold levels expressed in colony forming units per gram. WARNING: mold spores may be not viable (dead), wrong culture media may be used, or one species can overgrow another, etc. - so don't produce any colonies, but may be toxic if inhaled (such as some species of Penicillium). So we would not rely on culture data. But here it is:
WARNING: about interpreting mold cultures: this is a very very inaccurate method for screening buildings for the level of mold contamination for many reasons, including that only 10% of all molds will grow on any culture under any condition. So this approach begins as 90% "wrong".
Other mold level variables include the differences in settlement rate out of air as a function of particle size and weight, proximity to a mold contamination reservoir, and the problem that a serious toxic mold may be overgrown (if it grows at all) in the culture by a second mold species which hides the first one. See INDOOR AIR QUALITY METHODS COMPARED for details of these issues.
4.The American Conference of Government Industrial Hygienists (ACGIH) stated (Harriet Burge et. al) stated in 1987 that indoor mold levels are generally less than 1/3 the outdoor level and that when indoor mold is at more than this level remedial action should betaken to find the source of the elevated counts and to clean it up.
WARNING: this is an inaccurate and unreliable method for screening buildings for mold for many reasons, including:
See INDOOR AIR QUALITY METHODS COMPARED for details of these issues.
5. Other proposals for Mold Exposure Standards have included a limit of 500 CFU/ of mold spores per cubic meter of air in winter indoors in sub arctic climates (Reponen et al.1990). CFU means "colony forming units" of mold.
We suspect that focusing only on "colony-forming-units" (that is, viable mold that will grow) is not a very reliable way to check out a building. That's because
At MOLD CULTURE PLATE TEST ERRORS we have cited the range of errors and limitations of using cultures to check for viable mold, and we point out that depending on the particular mold genera and species present in a building, even non-viable mold may be allergenic or toxic. That is why experts in mold testing and remediation advise that the object is to remove mold or clean up mold in a moldy indoor environment, rather than attempting to "kill" mold indoors.
Also see INDOOR AIR QUALITY METHODS COMPARED for details of these issues.
Single number "mold levels" are very unreliable as a measure of health risk in buildings for several reasons including at least the following:
Particle levels vary widely over short time periods: The actual level of indoor particles in air varies by several orders of magnitude over very short few-minute intervals, making reliance on any single measurement questionable, particularly if the measurement does not show evidence of a problem.
The absolute level of airborne particles in buildings varies enormously, possibly by a factor of hundreds to thousands, over intervals as short as a few minutes. Simple mechanical disturbance like turning on or off a fan can completely change individual measurement results. Short term measurements are therefore inaccurate and even longer term measurements are inaccurate if they do not consider the in-use variations in dust disturbance in a building.
Human sensitivity to mold varies: Individual susceptibility to mold/mycotoxin/aflatoxin-related or allergy-related illness varies widely and human exposure is complex because people move among a variety of environments
Finally, because of wide variation in individual human reaction and risk to mold, variation in allergenicity, pathogenicity, and toxicity among mold genera and individual species, and even additional variation in these levels depending on specific environmental conditions such as the substrate upon which a mold is growing (its food), quantitative risk-levels are better used as an overall indication of building cleanliness before and after a mold cleanup, and not as an absolute level of risk to building occupants.
There is very wide variance among the toxicity of individual mold species, ranging from none to probably highly toxic, pathogenic, or even carcinogenic
Mold Spore size varies widely from less than 1 u to over 200u, so a large spore contains potentially more harmful material than a small spore of the same "toxicity," making a "count" that does not identify the particle and particle size ambiguous
Mold spore toxicity may vary, even within an individual species, depending on what substrate the species is growing on in a particular instance, e.g. wood vs. drywall.
These mold spores vary in significance: procedures that use cultures to identify "viable" spores may omit high levels of non-viable spores which nonetheless remain highly toxic. Methods that rely on culturing have a high risk of identifying a mold which is present but is not the dominant or even the most problematic mold in the building.
For more details see Mold Spore Counts: are indoor fungal spore counts valid?for further explanation.
For the standards and references below, numbers are spores per cubic meter of air and do not consider individual or viable/non-viable or genera-species specific levels. There is a serious limitation of the standards since the spores of different genera and species vary widely in total size, mass, and toxicity.
The level of airborne particles indoors varies enormously, by orders of magnitude, from moment to moment, making the strict interpretation of any "indoor air mold test" unreliable, as we discuss
at ACCURACY OF AIRBORNE MOLD SPORE COUNTS. -DF
Note: Previous data provided at this web article had been obtained from a presentation by J.R. Tucker, EMS-sales, who presented data at the NC/SC Environmental Information Association 2005 Conference, Myrtle Beach, SC citing mold exposure standards from Brazil, mold exposure standards for Czechoslovakia, Mold exposure guidelines for Finland, Mold exposure standards set by the Nordic Council, mold standards cited by the World Health Organization WHO, and mold exposure standards for the Netherlands and lastly, mold exposure standards for Poland.
Those figures were quoted in this article from the material provided at that conference. Mold exposure standard numbers were expressed spores per cubic meter of air and did not consider individual or viable/non-viable or genera-species specific levels. We have removed those data points at the request of Dr. Robert Brandys who informed us that he was and remains the original author.
Mycotoxins are produced by some common molds found in buildings, including Aspergillus, Penicillium, Fusarium, Stachybotrys, and even Alternaria. Common classification groups of mycotoxins include aflatoxins, fumonisins, trichothecens, and ergot alkaloids. Arora has pointed out that the following conditions are necessary for mycotoxins to affect humans:
Given even these stringent criteria, field investigations of moldy buildings that we have conducted from 1986 to present, included both human building occupants and in some cases pets who appeared exhibit complaints or symptoms consistent with mycotoxin exposure. Some of these clients and their physicians confirmed that exposure by appropriate medical tests.
A fellow aerobiologist who also has experience raising sheep, Larry Syzdek (PAAA member) informed us of a mold-related illness well known to occur in sheep which Syzdek explained has occurred in his experience in sheep exposed to moldy straw, called in lay terms, "sheep circling disease" (Listeriosis, however Listeria moncytogenes is the specific bacterium - not a mold - known to cause listeriosis, a disease which can affect both other animals and also humans, particularly pregnant women who are 20 times more likely than other healthy adults to get listeriosis).
The author of this web article, (Friedman) has described field observations of dogs appearing to exhibit strange behavior (running in circles, falling down, disorientation, and occasional uncharacteristic aggressive behavior, and in one case, fatal internal bleeding after severe exposure to S. chartarum during a building demolition. These animals were pets of clients whose homes were severely mold-contaminated.
With Syzdek, we have speculated on the possibility that other animals than sheep may be similar affected by exposure to some indoor molds and may be exhibiting behavior similar to that caused by Listgeriosis though the etiology of this disease is suspected to be different.
At MOLD RELATED ILLNESS GUIDE or in the FAQs section of that article we include a 2014 report from a Salem Oregon family who describe drunken behaviour of dogs after the dogs spend time outdoors.
These hypothetical remarks presented here intend to solicit additional field reports and data, possibly in support of future controlled studies. Readers should not assume that we have drawn conclusions from the suggestive anecdotal data currently at hand.
Some species specific acceptable levels have been addressed and vary considerably by species, environmental conditions, and proponent.
REFERENCE:A number of resources cited here are reviewed more carefully in "Comparisons of seasonal fungal prevalence in indoor and outdoor air and in house dusts of dwellings in one Northeast American County," Ping Ren,
Thomas M. Jaunkun and Brian P. Leaderer, Division of Environmental Health Sciences, Department of Epidemiology and Public Health, Yale University School
of Medicine, New Haven Ct. and appearing in the Journal of Exposure Analysis and Environmental Epidemiology (1999) 9, 560-568.
See references below for important additional information such as mold testing, cleanup and mold remediation guideline resources.
According to A.S. Arora: Stachybotrys chartarum strain s72 contains 1.0x10-4 nanograms of satratoxin H per spore. 10 billion spores of s72 S. chartarum must be present in a single cubic meter of air to produce one milligram of satratoxin H per meter of air.
Dr. Arora continues: "... it was calculated that a no-effect dose [in rats] corresponds to a 24-hour exposure to 3 billion spores per cubic meter of air for an infant [human], 9.5 billions spores per meter for school-age children, and 22 billion spores per cubic meter for adults."
Dr. Arora did not expand his discussion to address any potential cumulative toxicity of longer term exposure to lower levels of mycotoxins in buildings.
This "toxic black mold," Stachybotrys chartarum, infamous thanks to media attention, is not designed for airborne transmission, being large and sticky. The Stachybotrys family of molds appear to have evolved to be spread by sticking to the cow's foot as it walked through moldy straw.
Indeed we often find S. chartarum mold spores present in air samples when a dense colony of such mold is being mechanically disturbed, such as during demolition.
But we have never seen it in air anywhere close to the levels cited as the "no-effect dose." We believe that we've been barking up the wrong mold-tree, and that one would be smarter to look in buildings for the Penicillium and Aspergillus families which spread throughout a building easily by airborne transmission
REFERENCE: Content of this section paraphrased and others quoted from a guest column, "Understanding the Health Effects of Mold," by Dr. Ajit S. Arora, MD, PhD, appearing in AIHA's magazine "The Synergist," September 2003, in the AIH Diplomate section, Pages vi-vii. Dr. Arora is a forensic medical examiner and medical toxicologist in Los Angeles. See partheniamedical.com.
"Clean" residential buildings are typically 230/m3 +/- 630.
Buildings with evidence of flooding are typically much higher: 2200/m3 and
mold-damaged buildings are typically extremely high in comparison: 36,000/m3.
We usually find only trace levels of Penicillium/Aspergillus indoors in residential buildings and offices, so counts even close to the "clean" level may make further investigation a reasonable course of action, particularly where the building houses occupants have complaints possibly due to mold, or occupants who may be at extra risk.
Holmberg (1987) associated Aspergillus spore levels over 50 CFU / cubic meter with sick building syndrome.
We comment elsewhere that depending on culturing mold in buildings is unreliable since toxic or allergenic particles may be present but may be of a species or genera which either does not grow on a culture medium, or which is overgrown by something else on the medium.
Further, relying on settlement plates to culture mold produces quantitatively skewed results since different particles settle out of air at different rates, confounding an estimate of their numbers. Anderson™ multi-stage samplers which develop culturable samples attempt to overcome the particle size problem.(C)Trap DJ Friedman
Aspergillus sp. may be the most common and serious airborne mold problems in buildings: Opinion: from the author (DJ Friedman) based on extensive field investigations and laboratory work, we suspect that several species of Aspergillus are probably the most common and widespread problem mold found indoors in buildings.
These spores are small, easily airborne, grow on a variety of surface materials, and move readily throughout a building almost like a gas (due to their small size) riding on building convection currents and remaining airborne for long periods of time.
Continue reading at MOLD TEST vs. PROBLEM DIAGNOSIS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.
Or see MOLD EXPOSURE RISK LEVELS
Or see MOLD LEVEL REPORTING
Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia
Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Please see MOLD COUNT FAQs
(Mar 12, 2016) Concerned Mother said:
We recently had an air quality test completed throughout the house, due to illness in the family. These came back as being high in the lower level (LL), main level (ML) and upper level (UL). Are these levels high enough to cause a true concern? Should the basement be gutted or cleaned and gutted where the mold is seen at? What should be done on the main and upper levels of the house?
I appreciate your guidance!
Aspergillus/Penicillium LL 6667 ML 293 UL 373
Chaetomium LL 33 ML 13 UL 13
Stachybotrys / Mennoniella LL 133
(Sept 25, 2016) Cindy said:
Had an air test done and stachybotus came back as 2 on only room in house. Penicillin and Aspergillus came back zero. Is there a reason to worry or do further testing? Thanks great info on this sight.
- See more at: https://InspectAPedia.com/mold/Mold-Exposure-Standards.php#sthash.MBJ9FgMG.dpuf
Concerned and Cindy:
Regrettably the test results alone, without a competent and thorough building inspection for mold reservoirs, both visible and if appropriate, hidden, for building leak history, for occupant vulnerability and IAQ complaints, is nearly worthless - certainly it is not diagnostic. I see variation from 1 to 4 orders of magnitude in airborne particle counts depending on how a test was conducted so an accurate mold level that produced an airborne spore "count" of 13 might be anywhere from 1.3 spores/cubic meter of air to 4000 times that amount. Sorry I can't say what should be done based on so little information.
My best advice is to ask for your mold test money back since the person who was in your home, where your money and health are at risk, has apparently thrown a test result over the wall (figuratively) without answering even the most basic questions.
(Apr 30, 2016) Sorry Susan said:
I brought some dusty books into my home and they were sitting on carpet. What is the most practical thing to do now? Is vacuuming and airing out the room a bad idea? Vacuuming the carpet? There is not a high level of humidity and no visible signs of mold.
I meant shampooing the carpet after vacuuming and airing?
Normal housecleaning and vacuuming sound sufficient to me.
(Aug 26, 2016) Anna levis said:
Why mold cause sever health problems just because of the people not take any action when they found mold in their house and after that the mold increases in growth and cause severe health issues to homeowners. They spend their day in that environment which is highly affected with the Toxic black mold which can also harmful to your health and cause a permanent damage.
Homeowners never realize the affter effects of that black mold until they practically go through it. Toxic black mold cause problems such as mental disability, damaging internal organs, and sometimes a purpose of death. You can just have a quick checklist to remove Black mold without killing the environment as i have found both of the articles helpful for me
Please search InspectApedia.com for MOLD KILLING GUIDE to read about the problem you discuss.
(Oct 17, 2016) Casey Lee said:
Aspergillus Penicillium in my bathroom is at 89% and the count is at 800m3 and the living room is at a count of 2300. I have been having bad breathing problems rashes eye irritation as well as loosing hair and just plan wore out all the time.
I have been expierencing this for a year now and my apartment won't do anything about it even when I found the leak behind my toilet inside the walls that had rotted out all the wood and caused serious damage to building and observed them cover it up without cleaning or replacing wood!
And leaving the wall open for weeks for me and my 10 year old daughter to get even worse, even our dogs started itching and loosing they're coats. 😞 I don't know what else to do. I hired a mold inspector at $750 (out of my rent here! But the management don't know yet) and the results basically are saying there's a lot of different moods but no dominating ones. It hasn't been dissmissed but they want ta recheck at a later date. I can't keep living like this
Advice for your situation is at RENTERS & TENANTS: MOLD ADVICE
Questions & answers or comments about standards for acceptable or unacceptable toxic mold spore counts, levels, or measurements in building interiors.
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
Search the InspectApedia website