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One question we often receive is whether there are some molds that are specific to marijuana grow ops.

Well, if there were some, we could use them as forensic tools to detect buildings that were ever used as grow ops long after the operations were discontinued.

Recent research has shown that molds can effectively be used as forensic tools to help investigators to connect a victim and suspect, determine a location of crime, help define cause of death, estimate interval since death, and determine whether a body has been moved.

Therefore, molds are already being used, though not widely as they should be as forensic tools.

But how can we use molds as forensic tools in building investigations?

Understanding the behaviour or requirements of various types of indoor molds can be very helpful during your investigations. A study that was conducted in Norway showed that some molds are commonly found in insulated outer walls in basements, others grow almost exclusively on wood in cold attics while some prefer cold basements and crawl spaces.

Members of some common molds such as Aspergillus and Penicillium can grow under a wide range of building conditions and therefore may not be very useful indicators of the building conditions.

One of the growth requirements that easily determines where and when a mold grows is water availability on material that is subject to mold decay. The level of available or free water on a material is measured on a scale of 0 (i.e., dry) to 1 (very wet). Available water, what scientists like calling water activity, differentiates 3 broad categories of molds.

Water loving (hydrophilic) molds. These are molds that require high amounts of available water, usually at a scale of 0.9 and and above. If the free water in the building materials is not 0.9 or more then the growth of these molds is not optimal. Moderately hydrophilic molds. This category of molds typically grows on continuously damp building materials that have free water in the range between 0.80 and 0.90. Dry loving (xerophilic) molds. This category of molds is able to grow on materials with available water below 0.8. These molds are very common in buildings since they don’t require excessive moisture to grow.

For the water loving molds to grow, the building materials must remain nearly saturated for more than 7 days before growth appears. Once they grow and the available water declines to a level where it cannot support their growth, the molds either become dormant or die – but they don’t disappear.

They remain on the building material as a forensic clue that the building had water damage at some point in time. These molds, for example Chaetomium and Stachybotrys are referred to as “Indicator molds” or “Signature Molds.” Their presence, either in air or on a surface indicates that the moisture damage has been going on for a long time, and that the building does not dry up during warmer periods.

Their absence indicates either that there was no water impact, or that water was not retained for an adequate period of time for them to commence growth.

Research in Norway had also shown that some indoor molds are almost exclusively found in certain locations in buildings and on certain types of building materials. For example Cladosporium, Acremonium, Ulocladium and Actinomycetes are found in the same locations in buildings but they differ in type of building material preference.

Cladosporium prefers growing on wood, Acremonium on wind barriers, Ulocladium on gypsum boards and Actinomycetes prefer growing on concrete. The same study showed that Chaetomium, Stachybotrys and Trichoderma grow on wet constructions. The three molds grow well on building materials containing cellulose. However, Chaetomium prefers chipboards, Stachybotrys gypsum boards, and Trichoderma wood.

Conclusion

An understanding of the ecology and behaviour of molds is crucial if we are to utilize their potential as forensic tools. Knowing where certain species of molds are likely to be found can help us in locating hidden molds.

Contact Mold & Bacteria Consulting Laboratories if you have any questions about this article or would like to inquire about how to test for mold, contact us by telephone or email.

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