Exposure limits to black mold
Many times we’re asked the exposure limits to black mold. Unlike other indoor pollutants, there are no exposure limits to mold. Exposure limits to mold would be difficult to set because human beings differ in their susceptibility to mold. Similarly, the molds themselves differ in their ability to cause health problems.
Molds may affect human beings in three different ways:
- Allergenicity
- Infection
- Toxicity
As concerns common indoor molds the most likely effect is allergenicity. Very few fungi (molds and yeasts) are known to cause infection to healthy individuals. Toxicity is most likely to occur if one eats food contaminated with the fungal toxins. While toxicity is also possible through inhalation of spores or dust containing toxins, little is known about this possibility.
Generally, elderly people, infants, sick people and other individuals with weak immune systems are at higher risk of suffering from mold exposure related diseases than healthy people.
Black Mold
The black mold, Stachybotrys chartarum, is the mold feared most by the general public. It’s one of the molds used as indicators of moisture damage in a building. Black mold thrives on wet materials rich in cellulose. It’s commonly isolated from soil and decaying plant matter such as straw. In buildings black mold is found growing on very wet gypsum board, wallpaper, cotton fabrics and textiles, and other materials containing cellulose.
Unlike some other indoor molds such as Aspergillus and Penicillium that produce dry spores, spores of black mold (Stachybotrys) are produced in wet form. This means that the spores of Stachybotrys do not easily become airborne until they dry out or get disturbed say during renovations. Therefore, if pre-remediation air samples, for example, contain a few spores of black mold, it’s important to try and locate the source of those spores. The mold is most likely to be located in areas with a history of moisture damage.
Medical Significance Of Black Mold
While black mold is highly publicized as the cause of all sorts of health problems, it’s medical significance still remains controversial.
How To Test For Mold
Mold testing has 2 components:
- Assessment of the extent of mold growth in the building
- Laboratory testing of the samples collected during the building assessment
Assessment of the extent of mold growth
This component of mold testing is very important because the results of this assessment are used to determine the level of remediation required. Mold assessment in a building should be performed by a qualified professional.
Laboratory Testing Of Samples
Laboratory testing of samples for mold is necessary especially in situations where mold is suspected to be the cause of illness to the building occupants. The samples tested for mold include the following:
- Bulk and Surface Samples: These include samples such as pieces of carpet, carpet dust, drywall, wallpaper, swabs, tape lift samples or any other material suspected of mold contamination.
- Air Samples. Air samples may be collected on culture media or on inert non-culture media depending on the objectives of the mold investigation.
White Mold Picture
We received this amazing picture showing white mold growing on wood in a crawlspace from one of our site visitors. We wish to thank them for giving us permission to use the picture for training people about mold. For confidentiality reasons we will not mention their names here. The picture was taken from the crawlspace of a new building which has a wood basement floor and wooden joists with a crawlspace under. The crawlspace was lined with poly vapor barrier and gravel poured over the poly to hold it in place. Unfortunately, prior to roofing, it rained and the water collected on top of the poly, creating a “pool” of water over the poly/gravel and under the wood floor.
The pool of water sat in this confined space with no air movement and no drainage until power was connected and a pump could be placed in the sump to pump it out. In approximately 8 – 10 weeks, the white mold began to grow. When it was first noticed, it varied in length from 1/4″ in length to 1″ and covered approx. 25% of the wood joists. Within 2 weeks, it had grown from 1 inch to 4 inches in length (approx. 4 times!).
What could the white mold be?
From the picture, it’s difficult to tell for sure. However, there are a number of common wood-rotting fungi that infest damp or water-damaged wood. We shall discuss this in detail in the next post.
Could this mold be a health hazard?
Probably not. However, if it’s not completely removed, it could destroy the wooden joists completely thus compromising the structural integrity of the basement floor.
Mold Resources
Below are some of the most common referenced mold documents.
Directory of Mold Testing Professionals and Companies
Directory of Canadian companies offering mold testing services, searchable by province and city.
Mold Articles
Limitations and Considerations in Air Sampling, Sample Analysis and Result Interpretation for Airborne Mould Spores
. Inoculum, September 2004.
Guidance for Clinicians on the Recognition and Management of Health Effects Related to Mold Exposure and Moisture Indoors
The University of Connecticut and USEPA
Fungal Contamination in Public Buildings: Health Effects and Investigation Methods
Health Canada – This document is a revision of an earlier version published by Health Canada and the Federal-Provincial Advisory Committee on Environmental and Occupational Health (CEOH) in 1995.
Mould Guidelines for the Canadian Construction Industry
Canadian Construction Association (CCA) – Recent rerelease of CCA 82. Hard copies can also be purchased from your local construction associations.
Guidelines on Assessment and Remediation of Mold in Indoor Environments
New York City Department of Health and Mental Hygiene
Common Molds In Historic Buildings
Old, dusty and damp historic buildings provide perfect conditions for mold growth. In such buildings mold will be found growing on wall surfaces, the ceiling and on interior decorations.
Before any restoration work, it’s important to conduct a microbiological investigation to document the types of microorganisms present and their quantities. Some of the common molds in historic buildings include:
- Aspergillus niger
- Aspergillus flavus
- Aureobasidium pullulans
- Chaetomium globosum
- Cladosporium spp
- Fusarium spp
- Penicillium spp
- Stachybotrys spp
- Trichoderma spp
These molds are not only allergenic (trigger allergic reactions) but also potential producers of mycotoxins. For example, Aspergillus flavus is a producer of the highly carcinogenic (cancer causing) Aflatoxin. Restoration workers are, therefore, exposed to allergenic molds and also most likely to mold toxins.
Mold Training Course
The mold training course is being expanded to include a full-day mold remediation training. The first day of the course will primary focus on how to recognize indoor mold, how to develop effective sampling strategies, and how to interpret laboratory results. The second day will dedicated to how to perform effective mold remediation/abatement. Dates for this unique mold training course will be posted soon.