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Dr. Jackson Kung’u (PhD)- Mold Specialist.
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Acceptable levels of total aerobic bacteria, yeast and mold in buildings

Question: What is the “normal / acceptable” level of total aerobic bacteria and yeast & mold in homes / buildings

Answer: There are no universally agreed acceptable levels of total aerobic bacteria, yeast and mold in buildings. However, you may find levels suggested by various organisations. I would say that since there will always be bacteria/mold/yeast in houses, any levels that appear abnormally high is uncceptable. However, apart from the levels, you have also to consider what organisms are present since some are more harmful or destructive than others.

The tables below show some levels published by the Commission of the European Communities in Indoor Air Quality & its Impact on Man: Report No. 12: Biological Particles in Indoor Environments. ECSC-EEC-EAEC, Brussels-Luxembourg, 1993.

Categories of CFU/m3 (mixed populations of fungi) obtained with the Andersen six-stage sampler in combination with MEA, and with the N6-Andersen one-stage sampler in combination with MEA and DG18.

Category Fungal Counts (CFU/m3) in Houses Fungal Counts (CFU/m3) in non-industrial indoor environments
Very low <50 <25
Low <200 <1,000
Intermediate <1,000 <500
High <10,000 <2,000
Very High >10,000 >2,000

N.B.: These categories are based on the range of values obtained in indoor environments and not on a health risk evaluation.

 

Categories of CFU/g dust (mixed populations of fungi) obtained by direct
plating on V8 or DG18, and by suspension in peptone followed by plating on V8 or DG18, for houses and other non-industrial indoor environments

Category Method
  V8/directa DG18/directa V8/peptoneb DG18/peptoneb
Very low <1,000 <2,000 <10,000 <10,000
Low <2,500 <6,000 <20,000 <20,000
Intermediate <5,000 <9,000 <40,000 <50,000
High <10,000 <15,000 <100,000 <120,000
Very High >10,000 >15,000 >100,000 >120,000

a : direct plating of 30 mg dust

b: 100 mg dust suspended in a pepton solution (1 : 50), 0.1 ml of the solution plated on the medium

N.B. : These categories are based on the range of values obtained in indoor environments and not on a health risk evaluation.

 

Categories of CFU/m3 (mixed populations of bacteria) obtained with the
Andersen six-stage sampler or slit sampler (sampling time 10 – 15 min.,
incubation at 20 – 25°C for 3 – 5 days), for houses and non-industrial indoor environments.

Category Bacterial Counts (CFU/m3) in Houses Bacterial Counts (CFU/m3) in non-industrial indoor environments
Very Low <100 <50
Low <500 <100
Intermediate <2,500 <500
High <10,000 <2,000
Very High >10,000 >2,000

N.B.: These categories are based on the range of values obtained in indoor environments and not on a health risk evaluation

Pink Basement Mold

Question: My son and his family live in a small older rental home with a basement.  He called me this morning upset because he had seen some type of mold in the basement that was a pink, translucent color and as he looked at it released a puff of spores or something.   He continued to watch and the mold/fungi released these spores at intermittent intervals. 
 
Can you give me any idea of what type of mold/fungus this may be and if it is dangerous?
 
Thank you for your assistance.

 

Answer: I have no idea what the pink mold could be. Can your son take a good picture of the mold and send it to us by email? The picture might help us guess what the mold could be. Alternatively you could send a sample of the mold to our laboratory for testing. To take a sample, get clear scotch tape and cut 2-3 inches. With the sticky side facing the moldy surface, press the tape gently and then peel off the tape. Without folding, stick the tape onto a plastic bag such as a zip lock bag, place it in a suitable envelope and send it to us. You can find our mailing address at www.moldbacteria.com.

Mold from marijuana grow ops

Question: My tenant was growing marijuana in the basement bedrooms of our rental house, with plastic on the walls and ceilings. He was there for a month before being evicted. Do I need to worry about any mold from his growing operation? Need rent the house in a couple of weeks.
 

Answer: I would suggest you have the basement tested for possible mold and other hazards before renting it out again. If cleaning is required, hire a qualified professional. This way, if any of your future tenants sues you (for mold that presumably was caused by the marijuana operation), you’ll be able to defend yourself.

Mold and tenant’s rights

Question: What rights do I have as a renter when mold is present in my apartment? Who pays for the cost of the appraisal?
 
Answer: This is more of a legal question which we may not adequately answer. However, if the mold growth is due to the landlords neglect, then you have the right to ask them to clean it up and if they don’t you may be able to seek legal help. However, if mold growth is due to the occupants’ lifestyles or activities that generate too much moisture such as steam being generated through cooking, washing, bathing, showering and drying of clothes inside the house, then the landlord can even sue the tenant.

The landlord is responsible for mold growth from straightforward building defects, water leaks from windows, roof, downspouts, guttering, and internal plumbing or anything else that has nothing to do with the tenant.

Black mold on walls

Question: I had a lot of black mold or at least I thought that’s what it was so I took a blow torch and burned it off. It hasn’t come back but now I found a growth of some kind almost like a very fine hair, some of which is about an inch long and a gray color. I put the torch to it as well but this growth turned into a liquid and some would drop on the floor and some would stay on the walls and looked like a clear lacquer. I torched it about 4 days ago and now it has dried completely and the cement wall is a very light color and seems very dry as if it was dusted with powder. At one part I rubbed some grease on it and instantly fell to the floor and nothing seems to be growing back.
Any ideas what we may have here? It is quite damp in that area at times.

Answer:  From your description, it’s difficult for me to guess what type of black mold is on the walls in your home. I am also not sure if, when burned, mold would turn into a liquid that would drip. Obviously if the place is always damp, it’s liable to mold growth.