More on Moulds in the Home

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Cladosporium cladosporioides

I got a call from an old colleague of mine who retired many years ago. He is now 88 and a little frail. He and his wife recently moved into a retirement home and he is putting up his home for sale. Apparently, there were moulds growing on the walls and windows inside is house and the people acting on his behalf were concerned about this. He called in a ‘mould expert!’ who offered to clean it up the offending moulds and quoted a fee of $1200!  This concerned my collegue and he sought my help and opinion.  So I arranged with his relatives to visit the home and have a look. Sure enough, when I got to the house I saw colonies or patches of moulds, here and there, growing on the bedroom walls, living room windows etc. and, to be honest, I was quite surprised by the amount of mould growth. Visible mould colonies on the walls of bedrooms at ground level or higher is not too common under normal circumstances

I took a few samples by sticking ‘Scotch Tape’ to the affected areas then stripping of the moulds stuck to the tape.   Later, in the lab, I put these samples on a slide directly under the microscope.  With this simple technique, in most cases I can identify the fungus present to genus and sometimes even to species.  At any rate there was no Stachybotrys (=Toxic Mould!) present but there was a lot of Cladosporium on the walls and scattered, as small colonies, over the panes of the large picture window (click here for more information on Cladosporium). Cladosporium is a very common household mould in bathrooms, around tubs, shower stalls, or window frames and even bathroom walls and ceilings.  It requires free water for growth.  Around the edge of the tub there is water from splashing or water running down the wall from the shower.  The water just sits around the edge of the tub and may evaporate very slowly.  On walls and ceilings  the steamy air results in condensate, especially on colder, outer walls.  The spores of Cladosporium are ubiquitous and will germinate in this available water and  very quickly little dark brown colonies start to grow.  Eventually there will be an olive- brown to blackish brown edge around the tub. This is Cladosporium.   In basements in homes, it is usually Penicillium and Aspergillus that are the major problems.

How did it happen?

As I mentioned only the prolonged presence of water allows Cladosporium to grow and form colonies.  Excluding water from leaks and floods for the moment***, this requires very high humidity for extended periods, resulting in condensation.  It is difficult for me to imagine, under normal conditions, the relative humidity in the above ground portion of a home would reach the level to cause condensation of free water for such extended periods on the walls etc.   If someone makes a mistake, however, and the humidification system (normally used in the winter months) is turned on during the summer then this could raise the relative humidity to the dew point and condensation might take place.  Alternatively, if a person has respiratory problems and uses a portable humidifier in a small room to alleviate the problem, then condensation on the walls could take place.  For a short period no problem.  Long term humidification in a confined area with the doors and windows closed could result in mould growth on the walls.  This is especially true by the way in electrically heated apartments which are often sealed pretty tightly against the external environment

***It is a different story where there is  water leaks and/or serious flooding that traps water behind walls, beneath floors, inside cupboards etc. for prolonged periods.

In my friends home, in the bedroom with the mould growth, you could see the faint tracks running down the wall left by tiny rivers of condensation. This is not normal and could only result, I suspect, from some supplementary humidification system.   All of this is conjecture and my friend could not explain how this might have happened.  However, from my Scotch Tape sample, I could tell that the fungus material was not  fresh growth and looked pretty old.  So the possible high humidity episode must have happened some time before and was no longer happening.  It is important to know this as it means that once the mould growth is cleaned up it will not reoccur.

What About Toxic Moulds.

Whatever you’ve heard about toxic moulds take with a big grain of salt.  The people who are stirring the pot often have vested interests.   Sort of ‘putting the 'foxes in charge of the chickens’ syndrome.   Tell people that their house is full of ‘Toxic Mould’ and they will pay any price (almost) for a ‘cure’.  I asked my friend to ask his mould expert what he intended to do for the $1200.  Apparently, he said the house could be full of toxic mould lurking behind the walls and that would take a lot of work to clean up.   Then again, maybe not!   Remember many of the moulds in   the home are allergenic but they are not toxic!

How I would solve the problem

Use household Javex or a similar product using the manufacturers recommendations. i.e. a bleach solution.  Make it up in a pail.   Using a long handled sponge mop wipe down the walls slowly and gently. The idea is to wet, and thus kill, the moulds on the wall with bleach while disturbing them as little as possible.  This might even work with a paint roller.  Afterwards, wipe down the walls with clean water (plus a little detergent) and allow to dry. That’s it!   You could do the whole job for a few dollars. After that, a new coat of paint would spruce the place up and certainly work wonders for the selling price.

Cladosporium and the Clean-up Crew

What about the respiratory dangers of Cladosporium initiating asthma in my colleague who lived in the house and of course for the innocents who will clean up the mould?  This fungus is one of the most common causes of mould allergies.  However, 90% + of the population are not affected by it at all.  My colleague said that neither he nor his wife had any respiratory problems in the house.

In the Great Outdoors, Cladosporium is one of the dominant fungi that grows on senescent grasses including small grains and corn.  If you ever look at corn late in the season the tan surfaces of the senescent leaves become spotted  and eventually sometimes covered with dark brown to blackish brown colonies. These are Cladosporium and Alternaria growing on the surface of the leaves. When the corn is harvested there is a black cloud above the combine.  The cloud is fungus spores by the hundreds of billions.  The so-called clean country air can contain 10,000 fungus spores per cubic metre. And, of course a large percentage of these will be Cladosporium.  In days gone by, when I first came to Guelph, we had no air conditioning in the labs. In late summer and fall, however, we had to keep the windows in our laboratory closed because there was so much Cladosporium blowing in the windows that it caused serious contamination of our Petri plates.

Way back in 1878 a French scientist called Miquel, working in a park near Paris, estimated that there were as many as 200,000 fungal spores per cubic metre of air.  So!  There you have it! Cleaning up the moulds in my colleague’s house wouldn’t be much different than a walk in the park!

News Flashes:

"To rid themselves of toxic mold that savaged their lives, Steve and Karen Porath burned down their home"      People Magazine - 9th July, 01.

"Beware: Toxic Mold - Fungus in the floorboards is making some Americans sick. Panic and lawsuits abound."      Time Magazine - 2nd July, 01

" Mould problems identified in 58 government buildings"                                                            Toronto Star - 11th July, 01

What about all this stuff?  Where have the toxic moulds been hiding for the last hundred years or more?  Is this as serious a problem as many claim or is it blown all out of proportion?  Who decides if a mould is toxic or not.  Should we really be worried about moulds in the home or work place?  If so, what moulds should we be worried about and at what concentrations?  What about storms, floods and other natural disasters on mould growth! As they say ‘All this and more’ sometime down the line.