Photograph of toxic gas testing devices. Mold MVOCs, Moldy or Musty Odors, Toxic Mold & Toxic Gas Testing Guide

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MVOCs and mold:

This article explains MVOCs or mold volatile organic compounds, what makes MVOCs, the meaning of the presence or absence of moldy smells in buildings, and MVOC testing.

This article series lists and compares classes of mold, air, gas, test methods used in indoor air quality investigation methodology in searching for possible causes of respiratory illness, asthma, immune system disorders, rashes, skin disease, psychological and neurological disorders, eye infections, or other symptoms which may have a physiological and environmental component.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Sampling for Mold Volatile Organic Compounds - MVOCs and other Mold-Related Gases in Buildings

Airborne debris indoors (C) Daniel Friedman

As we explain below in our comments about mold sniffing dogs, not all molds generate MVOCs, and even molds that do generate MVOC's don't do so all the time.

If the humidity, temperature, light, and other factors don't cause a particular MVOC-generating mold to release this gas, you're not going to detect it on the day of the inspection and test. Just later.

At MOLD ODORS, MUSTY SMELLS we discuss the variations in the indoor environment that can turn on or turn off mold smells in a building.

Production of toxins and microbial volatile organic compounds (MVOCs) by fungi in an environmental sample is dependent upon many factors, such as the substrate on which mold is growing, relative humidity and temperature in the moldy environment; the relative importance of each of these factors in toxin production is poorly understood.

But it is clear that the level of MVOCs in a building varies widely from none detected to high, even when the genera/species of mold present include MVOC-producing molds. That is, even an MVOC-producing mold species will not always produce detectable odors and gases.

Indoor and outdoor microbial environments are complex, dynamic and transient in nature, and sampling results will change with time. Viability of bacteria and fungi is influenced by environmental conditions such as relative humidity, available nutrients and temperature. Important microbial ecology factors, such as the presence of competing bacteria, fungi, production of anti fungal and antibacterial metabolites, and insects greatly influence viability.

According to a US EPA Mold and Water Damage Study, Some micro-organisms, including molds, also produce characteristic volatile organic compounds (VOCs) or microbial VOCs (mVOCs). Molds also contain substances known as beta glucans; mVOCs and beta glucans might be useful as markers of exposure to molds.

Some molds are capable of producing toxins (sometimes called mycotoxins) under specific environmental conditions, such as competition from other organisms or changes in the moisture or available nutrient supply. Molds capable of producing toxins are popularly known as toxigenic molds; however, use of this term is discouraged because even molds known to produce toxins can grow without producing them (6). Many fungi are capable of toxin production, and different fungi can produce the same toxin.

MVOC Testing Does Not Generally IDentify the Source of the mold smell or musty odor problem

Even if we detect MVOCs, is that the problem mold in the building? If we don't detect MVOC's does that promise there is no problem mold? No.

Photograph of toxic gas testing devices.

Toxic or irritating gases such as mold-produced VOC's, MVOC's, or other odors, toxic chemicals, and combustion products can be important as life-safety concerns may be involved. Unfortunately no single test or tool can detect all possible building contaminants.

We use methods and equipment which can test for common contaminants. If the identity of a specific contaminant is known in advance we can also test for a very large number of specific contaminant gases in buildings.

We use gas sampling equipment provided by the two most reliable companies in the world, Draeger-Safety's detector-tubes and Drager accuro™ bellows pump, the Gastec™ cylinder pump and detector-tube system produced by Gastec or Sensidyne, and we also use Sensidyne's Gilian air pump.

For broad screening for combustibles and a number of other toxic gases and for leak tracing we also use Amprobe's Tif8850. All of these instruments, their applications, and sensitivities (minimum detectable limits) for specific gases are described in our Gas Sampling Plan online document.

Our Indoor Gas Sampling Plan for Residential Buildings describes gas testing procedures, instruments, detection limits, and it lists some of the toxic (or other) indoor gases for which we can test, depending on the building complaint and building conditions.

Health Effects of MVOC Exposure

Depending on individual sensitivity and health, indoor air quality complaints about moldy odors or smells or MVOCs range from none to allergic or asthmatic reaction to complaints of disorientation and neurological effects.


We distinguish between building related complaints - reports from individuals that an illness appears to be related to spending time in a particular building, and scientific controlled-case studies which have documented certain relationships between exposure to various substances (such as mycotoxins) and illnesses in humans or other animals. Anecdotal evidence associating building related illnesses and mold is often compelling even when the medical research data remain incomplete.


Mold Sniffing Dogs as a Building Screen for Mold

Client Comment on experience with mold-sniffing dog

I know you don't give much credence to the mold dog but he did point to the outer wall of the closet that was not remediated. (The inspector put a hole in the wall and tested the spot and it came out nothing.) The dog also pointed to the wall in the dining room but a little further away from where the remediation left off. (Again, the inspector did a test and found nothing.) It was uncanny that the dog identified the 2 spots that were very close to the remediation. The dog also pointed to the HVACs which were cleaned thoroughly twice (once by XXX and again by YYY.)

Mold sniffing dogs are unreliable, even though though they're fun. For details, see INEFFECTIVE MOLD PRODUCTS for an explanation of why mold sniffing dogs make poor mold detectives and why it's not good for them anyway.

There's no doubt that a dog can be trained to smell mold. Dogs have a very sensitive sense of smell and can detect very low levels of what they are trained for. What is the dog smelling? MVOCs. But there are a few shortcomings of relying on animals as mold investigators:

MVOCs often remain at low levels even in areas where mold remediation has been carried out; if our little buddy sniffs and points to a wall that has been remediated we're unsure if it's a new problem or a few molecules left from a remediated problem. There are no independent, peer reviewed studies demonstrating that we can relate a mold-dog's sniff-and-point to the completeness of a building survey for problematic mold reservoirs.

Not all molds generate MVOCs, and even molds that do generate MVOC's don't do so all the time. If the humidity, temperature, light, and other factors don't cause a particular MVOC-generating mold to release this gas, you're not going to detect it on the day of the inspection and test. Just later. Even if we detect MVOCs, is that the problem mold in the building?

Beagles & most other dogs are short as dogs go - certainlyh less than 6' 8" tall, and therefore, are not good at sniffing out MVOC's that telltale a mold problem high in a building wall or in a ceiling. Have you ever seen the mold-dog handler swing his/her partner through a loop to make a pass at a ceiling or at the top of a wall?

Beagles are cute, though.

MVOC Smell or Odor Removal

Spraying a biocide at a mold remediation project (C) Daniel Friedman

The steps in curing a moldy smell or MVOC odor complaint or getting rid of MVOCs from various sources in buildings have been moved to a separate article.

Mold & MVOC & IAQ Articles


And because mold-related volatile organic compounds (MVOCs) are not the only source of VOCs in buildings, readers should also see VOCs VOLATILE ORGANIC COMPOUNDS.


Continue reading at MYCOTOXIN EFFECTS of MOLD EXPOSURE or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.




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