A Toxicologist Looks at Mold Remediation

The book of Leviticus makes it clear that if mold is still present after remediation, the home is unsafe. This is a radical approach to mold, one shared by leading toxicologist Dr. Jack Thrasher. Dr. Thrasher, author of the article The Biocontaminants and Complexity of Damp Indoor Spaces: More Than What Meets the Eyes, says it is best to flee a home rather than remediate when serious health issues exist and when a serious infestation is involved. According to Dr. Thrasher:

I have always been skeptical regarding the successful remediation of homes and buildings contaminated with fungi and bacteria from water intrusion. Buildings and homes are complicated structures. The spores of both bacteria and fungi, as well as their by-products (fine particles less than one micron to those equal or greater than the mold spores), are present in dust. The dust can be found in all nooks and crannies of a building, e.g. refrigerator insulation and coils, areas not normally dusted, even in carpeting that has been vacuumed, under carpeting, and in wall cavities. Finally, little attention is paid to the contaminants in buildings that result from Gram negative and positive bacteria.

I will give some examples below:

Two buildings in Bermuda. These buildings had been remediated prior to our testing. Also, just before we arrived to do testing, the buildings had been cleaned and painted. Aggressive air sampling revealed the presence of hidden fungal spores up to 150,000 spores per cubic meter. Q-PCR revealed the presence of Stachybotrys and several species of Aspergillus and Penicillium, along with other fungi. Culturing for presence of bacteria revealed pathogenic Gram negative and positive bacteria. Interestingly, the occupants of one building had recurrent episodes of food-like poisoning (diarrhea and lower abdominal cramping and pain). In this building we detected high levels of Bacillus cereus, a bacterium that causes food poisoning. Also, we found high concentrations of endotoxins (lipopolysaccharides) released by Gram negative bacteria. Moisture measurements revealed moisture content of walls from 58% to 98% in both buildings. Finally, disturbing the air around a work station that had computers produced spores of Stachybotrys at 7,000 per cubic meter. Thus, workers pounding on keyboards most likely were inhaling these spores along with finer particulates. Samples of dust were positive for endotoxins and 2-3-beta-D-glucans.


House that had been remediated twice. The occupants were still ill. Moisture measurements showed moisture was coming up through the cement slab, which had numerous cracks. This was in all rooms of a 4-bedroom home. Q-PCR revealed Stachybotrys, several species of Aspergillus and Penicillium in three different dust samples (carpeting, living area, kitchen cabinet dust). Results for endotoxins were elevated. Mycotoxins were detected in the dust. Two windows had evidence of elevated moisture content below the window. Tests revealed wall cavity fungi that were active and grew when cultured. Gram negative and positive bacteria were cultured from dust. The fireplace area with a TV alcove had high moisture content with Stachybotrys present (this had been previously remediated). The master bath still had high moisture content with Stachybotrys isolated (this had been remediated). The moral of this story is to check cement slabs as well as check below every window in the home.
1. I have done other homes with similar results. I always culture for bacteria and endotoxins, test for mycotoxins, and do Q-PCR on several different dust samples. We have to remember that air spore counts alone do not tell the story. The fine particulates (less than one micron) have been shown to be up to 500 times more concentrated than the airborne spores. The fine particulates contain the antigens and toxins. Finally, recent peer-reviewed literature has shown that the bacteria in water-damaged structures also release toxins into the indoor environment. Therefore, both bacterial and fungal toxins are present and should be considered in risk assessments with respect to animal and human health.

As for the implications of this for those who are genetically challenged, Thrasher says:

People who are genetically challenged would be those who are genetically susceptible to such exposures. This would involve not only HLA genes but also genetic polymorphism of detoxification pathways such as Glutathione transferases and Cytochrome P450. Thus these people should receive full disclosure when renting or buying.