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Are There Moulds That Can Be Used As Indicators Of Marijuana Grow Operations In A Building?

With increasing grow ops in residential houses many home buyers, home inspectors and indoor air quality consultants wonder if there were some types of mould species that can be used as ‘fingerprints’ or indicators for homes formerly used for marijuana grow ops. Currently we are not aware of species of moulds that can strictly be associated with marijuana grow ops. However, the dominant moulds in a building environment are generally indicative of the moisture levels prevailing over a long period of time.

The environments tends to select and maintain certain micro-organisms as the “home microflora”. This “home microflora” is usually determined by the types of nutrients available, water activity, pH and temperature. In building environments, moisture is the growth limiting factor for moulds. Moulds differ in their water requirements. A small group of moulds requires high levels of available water (water activities of more than 0.9). This group, referred to as hydrophilic or tertiary colonizers can be used as indicators for water/moisture damaged buildings. Such moulds include species of Chaetomium, Fusarium, Memnoniella, Stachybotrys, Trichoderma, Ulocladium and a few others. The largest group of moulds requires continuous damp conditions (or water activities between 0.80 and 0.90). This group is referred to as secondary colonizers. Examples of secondary colonizers include common indoor contaminants such as Cladosporium spp and some species of Aspergillus and Penicillium. Another small group of noulds, the xerophilic or xerotolerant, is able to grow at water activities below 0.80. This group, also referred to as primary colonizers, include Aspergillus restrictus, Aspergillus versicolor, Eurotium spp., Penicillium aurantiogriseum, P. brevicompactum, P. chrysogenum and Wallemia sebi. Xerophilic moulds are indicators of relatively dry environments.

Moulds commonly associated with marijuana in storage include species of Aspergillus, Penicillium, Fusarium, Mucor, Rhizopus, Alternaria, and Curvularia. These moulds cannot be used as indicator moulds for marijuana grow ops since they are also found on many other substrates.

Secondary colonizers are likely to be the most common in houses used for grow ops but they are not unique to the grow ops. In conclusion no moulds are currently known to be strictly associated with marijuana grow operations.

Indoor Marijuana Growing Operations: Questions from Home Buyers

Use of residential houses for marijuana growing operations (simply referred to as grow ops) is increasing at an alarming rate. Buyers of houses across the country want to know if their potential properties were ever used for grow ops. The question I have been asked several times is, “if a house was renovated after these operations, is there a simple test that can be conducted to tell if the house was ever used for these operations?” Their major concern is mould. Unfortunately there is no mould test that I know of that can tell whether a property was ever used for marijuana growing. As a potential buyer my concern would not be whether the property was used for grow ops or not, unless the fact that it was ever used for grow ops would bother me or my family. I would be concerned about 2 things:

  1. Whether the property was structurally sound and met all the building codes. Grow ops may involve tempering with some of the building systems thus violating the building codes. Also, due to high humidity, mould growth may damage and weaken the wooden structure of the building.
  2. Whether there were abnormally high concentrations of hazardous contaminants such as pesticides, biological contaminants (mould, bacteria, mites, etc.), and other well known indoor contaminants.

If I am happy with 1 & 2 above, only other considerations would stop me from buying the property if I liked it.

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