|Teach Yourself Environmental Home Inspecting|
First, here is my “cheat sheet” used as the basis for various talks, etc., on mold. This is like a summary sheet for Mold 101:
Let’s go over the above chart.
The growth cycle of mold
Think of a plant and what happens with a seed, only with mold, the seed is known as a spore and the roots and branches are “hyphae.” The fruit is made by the fruiting body. The whole plant is known as the mycelium.
A spore lands on a nutrient source, typically cellulose, and sends down hyphae. The hyphae are the stomach of the mold. Digestive juices work on the cellulose and release nutrients for continued growth.
Hyphae grow above the nutrient source and soon may form fruiting bodies, which produce more spores.
Spores are not the only concern with growing mold:
The mold may give off biologically active gases known as MVOCs, or volatile organic gases produced by mold;
Some molds under some conditions may make mycotoxins, which are not volatile.
Parts of the mold might dry out and break up into tinier microparticles, some of which are inflammagens.
Remediation parallels mold growth
Set up containment and negative pressure (discussed later) so that mold particulates from contaminated areas do not spread into clean
areas of the home.
Remove loose mold material with HEPA vacuuming (discussed later).
If there is visible mold, wipe off with a cleaning solution (discussed later).
Encapsulate (like, paint) to kill residual mold and seal in buried hyphae.
Finish cleaning up the work area.
There are about five common black molds – discussed below
Stachybotrys, the so-called “toxic black mold,” but more precisely, a toxigenic mold, i.e., a mold that is capable of producing toxins. (Many mold are toxigenic but the mycotoxin that Stachybotrys can make can be especially hurtful. Trichoderma also can make these trichothecenes.)
There are two common green/white molds
That’s it for the Mold 101 chart.
In the next section, you’ll see actual photos that I made of mold under a microscope, but first we’ll talk more about the above genera of mold. “Genus” is the main biological category that ranks below family and above species. The family here is Fungus. The genus is Aspergillus. There are 200+ species of Aspergillus in the genus.
There are numerous websites providing photos of what different fungi look like under the microscope. Just do a search on the mold you want: “Penicillium + picture + microscope.” Dennis Kunkel, www.denniskunkel.com, has exceptional pictures of mold under an electron microscope. His photos are works of art.
Again, one or more of these genera are the main players at most houses with mold:
- Alternaria – club-like spores, sometimes in short chains; the largest of the common spores
- Aspergillus – chains of spherical spores, produced from fruiting bodies that look like a flower
- Chaetomium – lemon-shaped spores formed in sea urchin-shaped structures
- Cladosporium – varying shapes of spores, such as narrow ovoid (three-dimensional oval) sometimes with black connection points on ends where they once joined to other spores; bi-cellular spores (spores with two cells); banana, torpedo, shield-shaped, etc., spores
- Penicillium – chains of spherical spores, extending off the ends of brush-like structures
- Stachybotrys – mottled black grape-like spores, at the end of a stalk like a bunch of balloons or grapes. “Stachybotrys” means “grapes on a stick.”
- Ulocladium – segmented and broadly ovoid, somewhat like an elongated berry or a hand-grenade
And then, there are other molds, such as Acremonium, Trichoderma, Mucor, Syncephalastrum, and Rhizomucor, but in the average house, I find the ones listed above to be more common.
Some observations on the more common indoor molds
First, let’s stop and talk for moment about black molds, and what makes black molds black. These molds contain melanin, as do we, to protect them from UV C in sunlight. The mold could be wiped off, such as Cladosporium from a bathroom ceiling, but the melanin stain will remain. That could be treated with a mold stain remover or painted over.
Interestingly, since Cladosporium is the most common mold to grow on AC coils, adding UV light to the coils may not do too much to retard mold growth. Save your money, and get a better filter – discussed elsewhere.
Aspergillus and Penicillium
These molds are often found wherever moisture is found: in damp basements, under steps to the basement, behind finished basement walls, in attics with inadequate ventilation and too much moisture, at plumbing or roof leaks, inside sink cabinets, below-grade on wood or OSB (oriented stand board) in new construction, on AC coils and in contaminated ductwork, on ceilings and insulation in damp crawl spaces, growing on books and clothing stored in basements, and on furniture in houses shut up in a humid season.
Because Aspergillus and Penicillium spores look similar and because characteristic fruiting bodies aren’t always seen, the general term for these molds is “Aspergillus or Penicillium-like,” or, simply, “Asp-Pen.” If I see a half dozen stray spherical spores on a tape sample, I don’t know whether they belong to Aspergillus or Penicillium (or some other mold producing spherical spores). I call them “Asp/Pen” in my notes.
Health effects from either Aspergillus or Penicillium can be similar. If a few spores are inhaled, there may be allergic or asthmatic responses. If there is a lot of growth, and gases are breathed in, maybe there would be neurological responses, such as headache, depression, or inability to concentrate. The immune system may become compromised from being in a state of alert at home.
If someone lives in a terribly moldy basement or tore down moldy walls, maybe a fungal infection of the lungs would follow.
When growing on a Petri dish, both molds have various colors, ranging from green to white, orange, yellow, or black (Aspergillus niger). I started colored-pencil drawings of the coloration of Penicillium colonies and filled up three pages of variations before I gave up. The colors of some colonies were exquisite.
Under a microscope you’ll see all sorts of differentiations, from the size and texture of the mold spores to how much dye they absorb, to the width, texture, and segmentation of the hyphae or differences in size, shape and textures of the structures that produce the spores. It is these details that a lab technician looks at to help determine the kind of mold being cultured. Science is moving on, however, to computerized DNA testing, which is more precise, with results available much quicker, and for a fancier price.
Alternaria is a dark grayish brown mold, associated with asthmatic or allergic reactions. One boy discovered the mold growing on the back wall of his closet when he had an asthmatic reaction at the closet due to a chronic leak due at the adjacent bathroom shower. Sealant was missing on tile under the shower entry ledge and it was later found that water had seeped under the shower pan and onto the wood support.
The wood had been chronically wet and was a heavy source of Alternaria. The parents opted for a shower enclosure, rather than replacement tiles at the shower, to reduce the risk of future leakage.
I once saw visible Alternaria growing all over a basement foundation wall in new construction. The homeowners bought the house, went on vacation, and came back to all the discoloratoin. There must have been some additive in the concrete that pleased the Alternaria. It was quite a sight, and I do not know what steps were taken to clean and prevent future growth.
Chaetomium is another black allergenic mold, usually associated with leaks. This is the mold that frequently is present on a few rafters in the attic or on some ceiling joists in the basement. Many times, it is old, dried out mold, especially in the attic. Under the microscope, I see just broken up pieces of hyphae, with no spores. This is non-viable mold; it can’t grow again. You could just scrub it off with Borax solution, though a dark stain may remain. See the next mold for a discussion of the stain.
Chaetomium is sometimes found in DNA testing of AC supply vents – see Testing Options, a previous tab. At one house, 3 swabs were taken at AC supply vents for each zone. One test result showed high Chaetomium, and when the remediator went poking around, he found a source of leakage, perhaps a drainage issue though I no longer recall, for that one unit, which was subsequently replaced. Chaetomium, similar to Stachybotrys, needs more water for growth to start.
Cladosporium is an allergenic mold that also can give off some mycotoxins. Because its spores have multiple shapes, I pick out a few distinctive ones to look for under the microscope. I know the mold is Cladosporium if I see elongated oval spores with black dots on either end, or if I see bi-cellular spores (spores with two cells) or the shield-shaped (or banana or torpedo-shaped) spores. Cladosporium is the black mold that often grows on windows or windowsills, on the bathroom ceiling, near the top corners in a closet on an outside wall, at AC units or their insulation, and on attic sheathing if there is too much moisture and too little ventilation.
Cladosporium is invariably found in room air, because it is a common outdoor mold, but indoors, I find it to be a pretty well-behaved mold. That is, it doesn’t give off spores the way some other molds, such as Aspergillus and Penicillium, do. Cleaning it up from – say – windowsills and bathroom ceilings – is a homeowner's maintenance job.
I once tried to scrub Cladosporium out of wood grain with Borax. It didn’t work. Cladosporium can be hard to clean off a surface. Though I haven’t seen this in action, I wonder if Fiberlock’s Advanced Peroxide Cleaner would do the trick, or 9% hydrogen peroxide. You can buy 27% hydrogen peroxide at a swimming pool supply store and then cut it down to 9% (2 parts of water and 1 part hydrogen peroxide) – but wear goggles and gloves and a mask, because 27% hydrogen peroxide can burn and should only be handled outside and with care.
Stachybotrys, like Chaetomium, needs wetness to start growing. Stachybotrys is more likely to grow where there has been a flood or a leak than in a chronically damp basement. It likes drywall, so if you see lots of black mold growing on wet, or previously wet, drywall, there’s a good chance it’s Stachybotrys. I have never seen it grow on concrete – except once, at a very small area of concrete. I found it practically covering the back wall of a bathroom sink cabinet due to a chronic leak at the faucet fixture. The lesson is: Fix leaks right away and remove wet building materials, before mold grows. Here the cabinet was a loss.
Sometimes, floor cleaning activities result in water continually being sloshed against molding. Stachybotrys could grow under that molding. Don’t push water against molding; draw the damp mop along and away from the molding. I sometimes find Stachybotrys or other molds under the edges of molding in bathrooms. If there is a gap between the bottom of the molding and the floor covering, look into a low-VOC caulk that could seal the gap.
Stachybotrys has been associated with pulmonary hemorrhages in babies. There is some evidence for permanent neurological damage due to chronic exposure to mycotoxins from some species of Stachybotrys.
Stachybotrys gives off many compounds, among them close to 200 versions of trichothecenes, which are potent mycotoxins.
Trichoderma (not pictured on the summary chart above)
Trichoderma is a fast-growing green mold that also can give off trichothecenes and also needs more dampness, if not wetness, to grow. A few of my clients have been extremely sensitive to this mold. Occasionally I see it in tape samples, not very often. For me, the tell-tale signs of Trichoderma under a microscope are green bunches of tiny clumped spores, somewhat like clusters of tiny grapes. The spores grow out of pyramidal-like branches, best seen at the end of a central stalk.
Ulocladium is another moisture-loving black mold commonly found in leak areas. I’ve seen it covering the sheathing in an attic lacking adequate ventilation. Spores are brown, shaped like hand grenades.
Mucor, Rhizomucor, and others are genera that like chronic dampness, either long-term ambient dampness or shorter-term floods and leaks that weren’t cleaned up right away.
Let’s pause for a moment and consider bacteria.
As research progresses, one of my microbiology professors may be proved right, that bacteria growing in homes may prove to be of more importance for health than mold. Or, mold and bacteria could interact or be synergistic, that is, health effects from the sum of their interactions would be greater than the sum of either one’s added together.
Bacteria are single-celled organisms that are smaller than mold when viewed under a microscope and obtain their nourishment by dissolving and absorbing organic matter. At 600x, there might be a film visible on the tape, with lots of little rods or ovals in the film. You might only know that bacteria are present by seeing the edge of the film, kind of like the edge of a cloud.
Bacteria need food and water to grow, but they die or form spores when they dry out, so they are more often found in chronically wet or damp areas. Like mold, bacteria give off toxins and other substances, contributing to health reactions similar to those from mold exposure. Bacteria can grow in films, spreading over a surface, with the film taking on characteristics of its own.
Bacteria grow faster than mold. If there is water damage, bacteria will be on the scene before mold. For example, Stachybotrys often grows together with Streptomyces.
Mold may be said to be a surrogate for bacteria, and also for dust mites. If the indoor environment is controlled for mold, it will likely also be controlled for bacteria and dust mites. Dust sampling is available for endotoxins. We’ll be talking more about pressured dehumidification later.
Bacteria, such as Pseudomonas, can also be found in some filtered water when proper maintenance is not kept up. That will be discussed in the water section later.
Biofilms are a relatively recent field of study, thanks to new developments in laser microscopy. Biofilms are an aggregation of bacteria, mold, or a mix. This incredible definition, from the website, www.MedicineNet.com, sounds right out of science fiction:
“Biofilm: An aggregate of microbes with a distinct architecture. A biofilm is like a tiny city in which microbial cells, each only a micrometer or two long, form towers that can be hundreds of micrometers high. The “streets” between the towers are really fluid-filled channels that bring in nutrients, oxygen and other necessities for live biofilm communities.”
Biofilms are common health hazards with various medical conditions, such as in periodontal disease and cystic fibrosis pneumonia, as well as in contamination of urinary catheters and medical implants. Millions of people are affected annually by biofilms.
Biofilms are also present in the environment, such as inside water pipes. Chlorine doesn’t kill bacterial films growing in and around flaking pipe interiors. Some communities are adding ammonia to public water to try to get rid of bacteria missed by chlorine, as well as to cut down on levels of carcinogenic chlorine by-products. An Internet search on “biofilms” will bring up many interesting sites.