What’s in House Dust?

House dust can contain many different particles and contaminants.  The type of dust and the composition can vary depending on climate, region, the number of occupants, and the activities performed in the space.  Researchers estimate that one-third of dust originates from indoor sources such as fabric fibers, human skin cells, animal fur, decomposing insects, food debris, and lint.  Approximately, two-thirds come from soil and particles from the outdoors.  I also found out that household dust may also contain several dangerous chemical contaminants.

In one study, researchers found multiple types of plasticizers and flame retardants in 90-100% of the dust samples taken.  Plasticizers are used to soften plastics in vinyl flooring, food containers, and cosmetics.  Phthalates are common chemical compounds that makeup plasticizers.  Different types of phthalates were found in the dust samples.  This result is concerning because phthalates are known as endocrine disruptors.  The human endocrine system regulates hormone levels inside the body.  The endocrine disruptors negatively affect the body by causing developmental problems, cancer, and birth defects among other issues.  

Research is still being conducted on the chemicals that can be found inside of dust but I think the evidence so far shows how common house dust can be a real problem in terms of indoor air quality.  In a future blog post, I’ll cover the most notorious contaminant in dust… dust mites.


Layton, D. W., & Beamer, P. I. (2009). Migration of Contaminated Soil and Airborne Particulates to Indoor Dust. Environmental Science & Technology, 43(21), 8199–8205.

Consumer Product Chemicals in Indoor Dust: A Quantitative Meta-analysis of U.S. Studies  Susanna D. Mitro, Robin E. Dodson, Veena Singla, Gary Adamkiewicz, Angelo F. Elmi, Monica K. Tilly, and Ami R. Zota Environmental Science & Technology 2016 50 (19), 10661-10672 DOI: 10.1021/acs.est.6b02023

Foreclosures And Hidden Mold

A funny thing happened during a recent inspection.  The client had purchased a home roughly four years ago.  She was concerned when a visiting relative complained of having symptoms of her mold allergy while in the property.  The client called a mold company to come in and do air testing.  Picture her shock when she discovered highly elevated levels mold in her basement.  She called our company to get a second opinion and I was on the case.  

And what a complex case it was.  Our air samples confirmed that there were elevated levels of Chaetomium in the air, but there were no visible signs of mold growth.  I cut holes in the basement walls, but couldn’t find mold growth on any drywall.  This didn’t make any sense.  Typically, when you see these levels, there is a moisture source and there should be some kind of evidence of mold growth somewhere in the basement.  

Finally, in exasperation, I asked if they purchased the home as a foreclosure.  When the answer turned out to be “yes”, our investigation dug deeper.  After further investigation (and more wall cutting) we discovered what had happened.  The property appeared to have had a past flooding event from an upstairs bathroom.  This water continued down into the basement and mold growth developed on the drywall, wood framing, and ceiling.  

What happens so many times in a foreclosure is that contractors start to cut corners.  Sure, they removed the drywall that contained some of the mold, but they never bothered to remove the physical mold on the basement ceiling joists and wall studs.  They just covered it up with new drywall.  What could go wrong?  

Mold growth on wood studsMold growth on ceiling joists

What did go wrong was that the inside of the walls and ceiling had hidden mold growth.  Because the basement drywall was dry at the time of the inspection, it made it next to impossible to locate the growth.  The current owners walked in and saw a great house at a great price in a great location.  What they bought was a basement with hidden mold.  

In addition to the above example, there can be other sources for moisture to get into a distressed property.  During a foreclosure, the home can be unoccupied for several months.  When these properties are occupied during a humid summer, there is air conditioning that removes moisture out of the home.  But during many foreclosures, the electricity is shut off; this stops this dehumidification of the air and cuts power to the sump system.  The end result can be moisture in the home and then mold growth.

If you see a little mold in a distressed property, chances are there is a great deal more hidden somewhere else.  Try to detect any moldy odors by the walls.  Pull up the corner of carpeting and see if there are any dark stains on the carpet tack strips.  Be very cautious if you see any water lines on unpainted walls behind furnaces or water heaters.   

And above all, hire a professional mold inspection company to inspect a distressed property.  When you are worried about hidden mold, be sure to include air sampling.  Our clients were happy to finally find the source of the mold, but it did come at a cost.  Foreclosures can be tricky, but it pays to take the proper precautions and save yourself the headaches later on.

Questions From The Field


mold under the microscope

During one of my recent inspections, a client presented me a list of questions after the assessment. I often encounter these questions in the field, so I picked out some of the best questions and I am providing the answers below.

Q1. Is everything in a room where mold spores are present assumed to have mold spores?

A1. Mold spores are everywhere and under normal conditions are generated in the outdoor air. They typically settle over time and are a common component of house dust. If there is an elevated spore count in a room, there will likely be additional spores settling on the contents in the affected room, joining the normal, background spores already on the surface.

Q2.How do I decide which items can be kept vs what can be cleaned vs what must be thrown away?

A2. If the items do not sustain mold growth, it can be cleaned and/or HEPA vacuumed to remove settled spores. If the item is sustaining mold growth and is a porous material, it should be discarded. If the item is sustaining mold growth and is non-porous, the item can be wiped clean.  If the item is wood and is sustaining mold growth, we generally recommend roughing the surface using a wire brush or sandpaper to remove the mold.

Q3. When do I clean my air ducts?

A3. Currently, the EPA does not recommend routine cleaning under most circumstances. The reason is that there is not enough concrete evidence showing that duct cleaning may improve air quality. However, duct cleaning should be performed if visible mold is seen in the ducts or other HVAC components.

Q4. Under what conditions do mold spores grow and multiply?

A4. Think of spores as being like seeds of a plant. Spores grow when there is adequate moisture and a nutrient source. Adequate moisture can come from flood water, exterior moisture intrusion, condensation and elevated humidity. Nutrient sources from mold are commonly dust, drywall’s paper facing, and wood.

Q5. What is the relative value of ERMI tests when compared with air tests?

A5. ERMI tests give insight into historical mold activity, whereas air samples tell current conditions. Because of this difference, ERMI tests and air samples running concurrently may yield vastly different results. Please note that the EPA currently recommends the ERMI tests for research purposes only.  We can still perform ERMI testing, but we do it in conjunction with a more traditional mold inspection.

Mold Testing In Winter

Winter brings a unique situation for environmental consultants. With the colder weather and snow cover on the ground that comes with winter in Chicago, there are usually very low outdoor mold levels. Occasionally we can even see outdoor air samples that have no spores present. If you recall from my last blog post on interpreting mold results, environmental professionals use outdoor air samples as a primary guide for determining if there is evidence of indoor mold growth. In areas where there are consistent sub-freezing outdoor temperatures or where snow cover persists for the entirety of winter, some inspectors will choose not to collect an outdoor sample. Here in Chicago, our winters can be dynamic. We can go from 40 degrees and no snow cover to sub-zero and 5” of snow on the ground in the blink of the eye. Even periods of a brief thaw can cause outdoor fungal levels to spike, and therefore affect the natural levels of mold in the indoor air. Because of this, we always collect an outdoor reference sample. So, how do they know if something is elevated when the outdoor control sample is very, very low?


Without the scope of an outdoor air sample, we have to be extra careful with interpreting the indoor results. We use indoor control samples in unaffected areas as one guide. This helps establish what “normal” levels would be expected in the building. Moderate levels of common outdoor types such as Aspergillus/Penicillium and Cladosporium indoors, which in the warmer months may be similar to the outdoor levels, in winter can be signs of possible indoor mold growth when an outdoor source can be ruled out. Also, any amount of water damage indicating mold found indoors, such as Chaetomium, Stachybotrys, or Fusarium to name a few, found in the indoor samples raise concern.


Interpreting air samples can be one of the largest challenges for an environmental professional. There are no concrete guidelines available and the results are unique to each job. Having someone who is well trained and experienced reviewing your results is one of the most important factors in identifying mold concerns indoors.

It Can Happen to Me – AGAIN!!!

Just as I thought that I would have my hands full with the issues in my attic, I was forced to contend with another issue – radon!

As I have mentioned in previous blog posts, we want the radon levels in our home to be under 4.0 pCi/L.  I have tested the levels in my unfinished basement and discovered that my levels were at 5.0 pCi/L.  I tested this a few more times to make certain that there was no mistake, but to no avail.  I need to have a mitigation system installed in my home.  

And so off I go in search of a mitigation company.  Some companies come to the property to provide a more accurate quote.  Others provide a quote over the phone after answering a series of questions.  And some don’t bother returning your phone calls.

What should one look for when looking for a mitigation expert?  First and foremost, you should confirm that the person doing the work is licensed as a radon mitigation professional.  Illinois requires a state license, but most other states do not have a licensure program.  In addition to actually returning your calls, we recommend hiring a company that is bonded and insured.  They should also have an excellent reputation for the quality of their work. This can be verified on several websites such as Angie’s List and Yelp.

Other things you may want to consider is if the company will send you a written estimate and if they offer any warranties.  Is the warranty written in clear, unambiguous language?  Will they warranty the effectiveness of the system unconditionally?  Are parts covered?  For how long?  The pricing may vary, but just because they are cheap doesn’t mean that they will ensure the quality of their work.  You may also want to see if the warranty will include new owners to the property.  

Case in point, I have heard of one company that reportedly told his client that he couldn’t guarantee that the levels of radon will be under 4.0 pCi/L after the system is installed.  I am here to tell you that if I am paying this company any kind of money, the very least I will expect is that it will be under the EPA and IEMA recommended level of 4.0 pCi/L!  And it will also be covered under some kind of warranty for parts and labor.   

As for now, I think I have selected the right company.  They are licensed, bonded and insured.  They have an excellent reputation and they warranty their work.  They actually came out to the property for a physical inspection – and they were the cheapest!  As I have discovered, when it comes to your family’s safety, it is important to do the necessary research.  

Fundamentals of Mold Remediation

My new book, “Fundamentals of Mold Remediation“, was published this week.  Over the past few years, I have been collecting my thoughts from designing and evaluating countless mold remediation projects.  I have seen some mold projects done right, and many more projects done wrong.

There are a number of guidelines and standards on mold remediation, so why did I find it necessary to publish a book on the topic?  The available guidelines don’t always agree with each other, and they often deviate from the common practices done in the field.  Also, the formality of standards and guidelines often make them difficult to read.  My target was a 100-page book that was easy to read and reference.  Although the book was written with mold professionals in mind, a homeowner, building engineer, or maintenance staff can readily understand and apply the concepts.


The book is now retailing for $65 on Amazon, but if you are a client of Indoor Science, you’ll be able to pick up a free copy at our office starting November 15, 2017.  More than selling books, my goal for this project was to help individuals who are serious about doing mold remediation right.  In some small way, I hope I can help the profession become more standardized and elevate the quality of work.

Patio Doors That Make You Weep

Several of our clients have experienced water intrusion around sliding glass doors.  There is a mixed bag of flashing problems that can cause water intrusion.  Flashing materials, weep holes, and weep ropes are used to drain water that gets behind the masonry.  

In this image, the black material beneath the vertical bricks is the flashing that drains the water out and away from the building.  The weep rope is supposed to help draw water out from behind the masonry to the outside.  This main issue with this picture is that the weep hole looks small and the rope looks pinched.  


Here we can see that a translucent sealant was placed right on top of the flashing.  This sealant prevents the water from moving to the outside and traps it behind the masonry.  The sealant was only present towards this end of the patio door and not the other.  Inside, a lot of moisture was found directly behind this section of the door and not on the other side where the sealant was absent.

At this property some flashing was present but it did not extend far away enough from the masonry.  The flashing should come out and overlap.  In this image, rust is visible between the door frame and the concrete.  This is a good indication that moisture is actively getting into this patio door.


Here, it appears that new mortar was placed to seal up the weep hole.  It may have been confused for just a simple opening. They probably sealed it up trying to prevent water from coming in, not realizing they were preventing water from coming out! Weep holes don’t always contain weep ropes.  A mesh screen can be placed over the weep hole to prevent insects and debris from entering the cavity. No matter what type, they should not be sealed shut.


In all of the properties shown above, there was moisture detected behind the patio doors.  To prevent mold growth you need to address the underlying moisture issue that is causing the dampness.  If there’s moisture surrounding a glass sliding door, it would be wise to check out the exterior of the patio door to determine if there are any anomalies that could cause water intrusion.  


Asbestos samples were positive. Now what?


So you just bought your new home or are conducting renovations in your property and you discover a material that you suspect is asbestos containing. You decide to have the material tested by a licensed inspector and discover it is in fact asbestos. Now the decision comes of what to do with it.


The first option is leaving the material alone. If the material is in good condition and it will not be disturbed by renovation activities it is acceptable to the leave the material in place. There is a minimal health risk if the asbestos containing material is left undisturbed. However, if the material is damaged or at risk of disturbance other options must be pursued.


When dealing with damaged asbestos containing materials, there are two options you may choose. Either encapsulating the material or removal. Asbestos abatement is an expensive option which many homeowners may not be able to do. Instead encapsulating can prevent the asbestos fibers from becoming airborne by placing a sealant or barrier on the material and is cheaper than removal. One example of this for floor tiles would include placing a sealant or barrier over the tiles instead of abatement. However, in a situation where the material has to be removed due to renovation we recommend having it properly abated and removed by a licensed abatement company. Never attempt to remove or repair asbestos containing materials without a licensed professional as this may lead to asbestos exposure and potentially contaminating the area of removal.

Is October “Mold Season” in Chicago?

“This is the time of year for mold around Chicago.” This isn’t a quote from an allergist, but rather Dusty Baker, the manager of the Washington Nationals (and past Cubs manager).  He made this statement at a press conference after game 4 of the NLDS baseball playoffs, which was postponed due to rain. This was in response to ace pitcher Stephen Strasburg feeling under the weather and declining to start game 4. This blog will examine Dusty Baker’s observation and let you know… is October mold season in Chicago?

There are many factors that influence the outdoor mold levels at any given time. The time of year, precipitation, wind speed and direction can all be factors. Seasonally, winter has the lowest levels of outdoor mold. With snow cover, we can even see outdoor levels at or very close to zero. In my experience, the highest levels that I see in the lab are during a wet spring period, and late summer. At these times we can see total outdoor counts over 10,000 spores per cubic meter of air.


Usually, by October, I start to see outdoor mold levels start to fall off towards their winter lows. This fall Chicago has been unseasonably warm, and over the past week, we have had rain off-and-on. Rain can cause higher levels of many common outdoor mold types such as basidiospores. The American Academy of Allergy, Asthma & Immunology’s National Allergy Bureau Pollen and Mold Report reported a “High” designation for the Chicago area on October 10, 2017. All of these factors are telling me that while it isn’t the common time for high mold levels in Chicago, we are seeing unseasonably high levels currently.

At the end of the day the mold didn’t seem to bother Stephen Strasburg and the Nationals too much, as they shutout the Cubs 5-0.

It Can Happen To Me

I have been living in my home for a number of years now and really don’t have any reason to go up in my attic.  I would need to get a ladder out and set it up in the middle of my hallway and access the attic through a small door in the ceiling.  But one day I came to the conclusion after doing my job for a number of years that it was time that I perform a visual inspection to see what’s going on.  I dragged my feet for years.  Now was the time.

And what I found shocked me.

I discovered dark stains on the north side sheathing of my attic (See Photo #1).  These stains surrounded several roofing nails on this side.  This is especially concerning because my bathroom exhaust is located in this area and I noticed that the bathroom duct was not properly connected to the outdoors (See Photo #2).  It is highly likely that humid air from the bathroom is hitting this attic wall to create condensation.  With this condensation, we have the distinct possibility that the dark stains are mold growth.

Photo #1 – Stains on attic sheathing

Photo #2 – Improperly connected duct


I am sure that I will be writing about how we will respond to this in the future.  However, if this new discovery will teach me anything, it will be a new found sense of greater empathy for those who encounter this exact same problem.  So please take my advice as we start to go into this winter season.  Poke your head into your attic space and examine your attic walls to see if there are any stains or water damage.  Check to see if your bathroom exhaust is properly connected to the outdoors.  If your attic has a wood floor, examine if there are dark spots on the flooring that might indicate water dripping from the roofing nails.  And most importantly, don’t do what I did and put it off.  Regularly checking your attic (even if there were no problems in the past) will save you a load of headaches later.  Trust me, it can happen to me.

ERMI Testing Vs. Air Samples

Very often we receive calls from very concerned people that need help determining if they need an Environmental Relative Moldiness Index (ERMI) test or not.  The range of knowledge in the general public for this type of test varies.  In this post, I will highlight a few points to keep in mind when deciding on doing an ERMI test.First, let me provide some information per the Environmental Protection Agency’s (EPA) website on ERMI testing.  ERMI stands for Environmental Relative Moldiness Index.  The analysis from this test can be used by researchers to estimate the levels and types of mold inside a property.  The test is done by collecting a dust sample.  Since mold spores can settle onto dust, the DNA from the mold in the dust can be identified, thereby providing information on what types of mold are present.  However (and this is highlighted in bold lettering on the EPA website), “the ERMI should be used only for research.  The ERMI has not been validated for routine public use in homes, schools, or other buildings.”  The EPA also recommends that water damage is assessed during the inspection since moisture issues are what cause most mold problems.  

Our company performs several types of mold tests including ERMI and air samples.   Air samples differ from ERMI because no settled dust is used.  Instead, air is drawn through a cassette and any spores present are deposited onto a glass slide in the cassette and ultimately viewed through a microscope.  The laboratory analysis can tell us the concentration of mold that was found in the air along with the types of mold (generally, down to the genus level).  

So the main difference is that ERMI collects spores and DNA from dust, whereas air samples collect spores from the air.  What’s the big difference?  The spores settled in the dust provide more historical information and air samples provide more current information.  Is one better?  Not really, they are just different.  Analysis between the two types is another main difference with ERMI detecting DNA via polymerase chain reaction and most air samples being analyzed via the microscope.

ERMI tests use a statistical formula to provide a single ERMI number.  Interpreting that ERMI number can be a big challenge.

When potential clients ask us to perform an ERMI test, we first recommend that we do a visual inspection and moisture evaluation.  We recommend that they also do more traditional spore trap testing alongside ERMI.  This way we can provide them with both historical and current information regarding the mold levels in their home.   

This blog article is just scratching the surface about ERMI.  Please leave a comment if you have any questions.

EPA Website:

Featured Asbestos – Chrysotile



Did you know that there are different types of asbestos?  There are six different minerals that we collectively call “asbestos”.  

Chrysotile is the most commonly found mineral in asbestos-containing materials. According to OSHA, Chrysotile makes up 95% of the asbestos found in asbestos-containing materials in the United States.

Chrysotile fibers are typically more curly while other (amphibole) asbestos fibers are more needle-like. While the fibers can still cause serious health effects such as lung cancer and mesothelioma, it is generally considered less toxic than amphiboles. This is due to the fact that the needle-like amphiboles are able to go deeper into the lung tissue and more durable than Chrysotile.

For my fellow geology enthusiasts, here are some facts about its origin. Chrysotile is a white asbestiform mineral and the only asbestos mineral that is from the serpentine group, while the other five are from the amphibole group. Chrysotile typically appears white in color and has a curly fibrous crystal habit.  Chrysotile forms when metamorphic serpentinite is hydrothermally altered, which causes Chrysotile to form in veins of the source rock. The source of most of the Chrysotile used in American products originates from Canadian mines. Serpentine is the state rock of California. Because of its relation to Chrysotile, there have been numerous attempts to remove it from its status.

In my undergrad years, I remember during a mineralogy lecture my professor bringing out several minerals to the lab table. My fellow colleagues and I walked over to see this strange looking fibrous bundle. One of the students in the class enthusiastically picked up the mineral, before our professor rushed over quickly to inform us it was asbestos. Little did I know at the moment, I would encounter this mineral many more times in the future.

More on the Interpretation of Mold Air Samples

Are you staring at the results of a mold test and struggling to figure out what it all means?  Let me try to help you.


The most common method used for mold air testing is uses a spore trap cassette. Because there is always a background amount of airborne mold spores, a key step in collecting air samples is to have a “reference” sample collected from the outdoor air at the time of the indoor testing. Since there are no guidelines on acceptable mold levels in the air, an outdoor sample is the best tool for interpreting the results of the indoor samples. Without the outdoor sample, you are limited in what you can gather from the results of the indoor samples.


There are various D.I.Y. air tests you can pick up at your local hardware store requiring you to place out a petri dish for several hours. Most of those tests are not very helpful in giving you any sort of usable data to evaluate the air in your home and as a general suggestion should be avoided.


Interpreting mold levels can be tricky. If you would like feedback on your mold air sampling results, please comment below and I will do my best to give any feedback I can in my free time. The views expressed in the blog post and comments are my own, and not necessarily those of Indoor Science. If you need a more immediate response regarding your results you can book a 30-minute phone consultation for $98 by clicking here.

Common Errors to Watch For in Mold Remediation

The drill goes something like this.  A mold expert is called into to your home and you find out the bad news that you have mold in your home.  The remediation company is called in and after a few hours or a few days worth of work, they report that you are clear of the mold.  What a relief!  That is until your mold expert is called back in to reinspect the work.  It’s been my experience that the remediation company can leave three major items incomplete during the remediation.  

  1.  Killing, not removing, mold

I have had some clients inform me that “The only good mold is dead mold.”  I usually correct them and say “No, the only good mold is physically removed mold.”  Whether it’s on drywall, wood, or dust, the only way to be sure that mold is not going to pose a danger is to safely remove it.  Some companies might see mold growth on attic sheathing and spray anti-microbial fungicide to kill it.  We call these companies “Spray and Pray” because the fungicide can often times look like white primer paint and it is difficult to determine if the mold is properly removed.  Then they pray the mold doesn’t come back!  Remember, even dead mold can be allergenic and toxigenic.  Be sure to physically remove that mold!

  1. Not scrubbing the air

The second issue that can ruin a remediation job occurs when the air is not properly cleaned of mold spores.  When workers are tearing down walls or scraping the mold away, we find that a large number of spores have been released into the air.  The air after remediation can have a higher level of airborne spores than before the work began.  This is why containment is so important; the plastic walls prevent large numbers of spores from going throughout the rest of the building.  Another issue is not running the air scrubbers or negative air machines for a long enough period of time to properly clean the air.  Air scrubbers can suck the spores through a HEPA filter, but a better method is to have them act as a negative air machine (or NAM) to suck the spores, trap them in a filter, and properly exhaust anything left through ducting to the outdoors.  It’s not enough to remove the mold, the spores in the air need to also be removed to ensure a healthy environment.

  1. Not addressing the moisture source

The third issue, which seems to be a no-brainer, is to address and fix the moisture problem that initially allowed the mold to grow.  It seems obvious, but I have seen it more than once or twice.  The homeowner has paid thousands of dollars to have remediation performed, but will have the exact same problem in a year or two because the moisture source that created the mess, to begin with, was never addressed.  Fix the moisture source!

So for review, if you ever have remediation performed on your property, keep in mind these three objectives:  1.) Physically remove the mold.  2.) Properly clean the air of mold spores.  And finally 3.) Fix the moisture source that caused the problem to begin with.  Then you can be assured that the problem has been fixed once and for all.  

Microbiomes, Buildings, and Human Health

An informative report was published by the National Academies of Sciences, Engineering, and Medicine. The report highlights how a building can influence changes in the microbiology inside the building which can impact human health.  In this blog post, I summarize some of the key points from the consensus study report.  
It may be helpful to keep the definition of microbiome in mind when reading this post.  A microbiome is defined by Merriam-Webster as “a community of microorganisms (such as bacteria, fungi, and viruses) that inhabit a particular environment.” Popular press commonly describes the microbiome of the human body, but buildings also have a microbiome.

The report points out that damp, water-damaged buildings can provide the right environment for microorganisms to flourish.  These organisms can have adverse effects on the human respiratory system.  This problem is exasperated in poorly ventilated buildings.  Currently, many well-sealed homes do not introduce much outdoor air besides through the occasional open window.  Mechanical ventilation can help introduce outdoor air into a tight building.  The report argues that having controlled, mechanical ventilation to introduce outdoor air is preferred over infiltration through cracks, crevices, gaps in openings for pipes, or other unintentional pathways.

It makes sense that ventilation can impact indoor air quality which can then affect human health.  However, the report points out that even water temperature in plumbing systems can affect the viability of microbes which can then impact human health.  Clearly, there is more than one aspect of a building that can impact people but the report does highlight a few means to better monitor microbes in a building.  Sensors that measure temperature and humidity can help monitor the dampness of a building which can inhibit microorganism growth.  Sampling of different microbes in a building can also be done to get a better understanding of microbes that can adversely impact humans.  However,  few organisms can be cultured which can make it difficult to get accurate information about a building.    The sampling methods of the future are through genomics, proteomics and other advanced laboratory procedures that can provide more data about the microbes living inside buildings.

A link to the report can be found here:

Bio-Contaminants in Water-Damaged Buildings

[The following is a chapter I submitted for a workshop on water damage, with a target audience of property managers.  It is a good primer on the contaminants found during water damage.]


Microorganisms are all around us.  In fact, they are in and on our bodies as well!  The vast majority of these organisms are harmless to humans, with many even having beneficial effects.  The human cells in your body are outnumbered by the bacterial cells in your body 10 to 1.  And some speculate that your human cells are outnumbered 100 to 1 when compared to viruses.  These mostly good microorganisms help our bodies function and are often referred to as our “microbiome”.


Even buildings can have a microbiome.  Normal types of bacteria and fungi are found in the air, dust and surfaces throughout.  Many of these microorganisms are normal and expected to be found in homes, offices, schools and other buildings. However, when water damage occurs, the indoor microbiome can change and have a negative effect on health.  


This chapter will describe the three most important microorganisms: fungi (mold), bacteria and viruses.


Fungi (Mold)

Mold belongs to the taxonomic kingdom of fungi. Fungi are not plants because they are unable to make their own energy via photosynthesis.  That means fungi don’t need light to grow.   Besides mold, other fungi include mushrooms and yeast. Fungi is a scientific term, whereas “mold” is more of a layman’s term.  Mildew is a term with several disparate definitions but is essentially the same thing as mold.


There are over a million different species of fungi with an estimated 30,000 types of mold. Mold gives off tiny spores, which are similar to plant seeds.  Once these spores land on ideal environmental conditions, they can grow into a colony (similar to how a seed grows into a plant).  Mold spores are ubiquitous in outdoor and indoor air, but because they are microscopic, you cannot see them.  They are typically about 2-10 microns in diameter, which is about 10 times smaller than the width of a human hair.  Even a normal home, office or school will commonly have more than 1,000 spores per cubic meter.


What do mold spores need in order to grow?  There are two primary environmental conditions: nutrients and moisture.


Mold needs nutrients to grow.  Just like there are enzymes in our digestive tract to break down food, each mold species has unique enzymes too.  Because of their enzymes, some molds prefer to grow on leather, whereas others prefer to grow on paper, leaves, drywall, soil, dust, or other organic materials.  Mold can grow in every building because the indoor environment is filled with organic materials.  Mold can even grow on an inorganic surface such as concrete by using nutrients from the paint or the dust accumulation on the surface.


Mold also needs moisture to grow. When organic materials are dripping wet, mold can certainly grow.  But what about environments where there is no liquid water, just high humidity?  There is a wide variety of humidity preference between the different species.  Relative humidity (RH) is used to measure moisture in the air and “equilibrium relative humidity” (ERH) is used to describe moisture within a material or substrate.  When a substrate such as drywall is in a room with 80% RH, it will generally approach an ERH of 80%.  Surfaces above 60% ERH are at risk for mold growth, but the vast majority of species require an ERH above 80%.


When a spore lands on a surface with the right nutrients and moisture, it will germinate, grow into a colony, and give off more spores.  That can happen as quickly as 24-48 hours for some species when conditions are ideal.  Therefore, it is important to dry materials quickly.  If mold grows but then dries out, it will stay dormant until more moisture comes back.  If the surface is dry for long enough, the colony and its spores will eventually die.  However, dead mold is still potentially allergenic and toxigenic.


The primary health concerns about mold are allergy and respiratory symptoms, such as asthma and cough.  Although there are no reliable numbers, it is estimated that about 15% of the US population has an allergy to at least one mold type.  Beyond these effects, mold can cause infections in immunocompromised individuals. These rare infections may happen in a hospital or nursing home, but some fungal infections can affect even healthy individuals (e.g. Valley Fever).  The most controversial effects of mold are the mycotoxins that some species can produce. The toxins are not released as a gas but are present on the colony and travel on the spores. There is a wide range of opinion regarding the exact effects of mycotoxin inhalation. Lastly, there are musty odors produced during growth that also have an effect on human health, although the effects are not well understood.


Although there are many species of mold, there are a few common types of which it is important to be aware. The following are water damage indicators which are uncommon in normal buildings, but common where there is chronic dampness:

  • Stachybotrys (sometimes referred to as “black mold” or “toxic mold”)
  • Chaetomium (pronounced K-toe-me-um)
  • Ulocladium
  • Fusarium
  • Trichoderma
  • Acremonium



Furthermore, some species of the following types can indicate water damage:

  • Aspergillus
  • Penicillium
  • Cladosporium




Bacteria belong to an entirely different kingdom than mold.  Their cells are unique in that they lack a nucleus.  Unlike other organisms, bacteria can be found in extreme environments from the tops of mountains to the bottom of oceans.  Although it is estimated that there are over 10 million species of bacteria, the vast majority do not cause human illness.  


The following are examples of building-related diseases caused by bacteria:

  • Legionnaires’ Disease
  • MRSA
  • Tuberculosis
  • Digestive tract and respiratory disease from fecal bacteria


With water damage, the primary concern is fecal bacteria, which are those species found in sewage.  Pathogenic fecal bacteria include:


  • Escherichia coli
  • Enterococcus
  • Fecal Streptococcus
  • Clostridium difficile
  • Leptospira
  • Helicobacter pylori


Besides the risk of infections from these fecal bacteria in sewage, certain bacteria produce endotoxins.  These toxins are found in the cell wall of Gram-negative bacteria, which can be commonly found in sewage.  When breathed in, endotoxins can affect respiratory function.  It is important to note that even when Gram-negative bacteria are killed, their endotoxins may not be diminished.  Therefore, it is critical to clean flood-damaged areas, not just use disinfectant.  


When areas are impacted with sewage, it is important to verify that fecal bacteria has been properly removed prior to reoccupancy.  The highest standard is to check surfaces for DNA related to fecal bacteria.  Culture plate methods may provide a “false negative” because the remnant, dead bacteria doesn’t grow on a petri dish (although its DNA could be detected).  Performing clearance testing puts people at ease when re-occupying a room impacted by raw sewage.



Viruses are the most unique microorganisms to be found with water damage.  Viruses do not have the means to reproduce by themselves.  They invade cells and commandeer the machinery to reprogram the cell to produce more viruses.  They can be 100 times smaller than a single bacteria cell as they generally range in size from .02 – 0.4 microns in diameter.  


There are a few pathogenic viruses associated with water damage:

  • Hepatitis A
  • Enteroviruses
  • Norovirus
  • Rotavirus

Viruses are very difficult to measure, so their impact on sewage-damaged properties is not fully understood.

Assessment and Remediation

When there is water damage, it is common to hire an industrial hygienist to assess environmental concerns before and after the remediation process.  The industrial hygienist can perform several functions, including:

  • Confirm mold growth or presence of other organisms
  • Identify the types present
  • Investigate the underlying moisture source
  • Determine the extent of the problem
  • Develop a scope of work for the remediation contractor to follow
  • Perform clearance testing when remediation is complete to verify the work was successful

Some states require that an assessment is performed both before and after remediation by a party independent from the contractor.  Although Illinois does not have such a requirement, it is still a good idea.


When selecting an industrial hygienist to assess biological contamination, look for certifications such as the Certified Industrial Hygienist (CIH) which has the most rigorous education, experience, and testing requirements.  Other acceptable certifications are from the organization American Council for Accredited Certification (ACAC).  Experience and knowledge are also important factors when selecting an industrial hygienist, as not everyone has a specialty in biological contamination.  



It is important to act quickly when there is water damage.  Delays can turn a small water problem into a large mold project.  If a water loss leads to biological growth, it is advisable to hire an industrial hygienist to evaluate the problem prior to remediation taking place.  Mold and sewage problems must be taken seriously as sensitive individuals may experience symptoms from the exposure. Being proactive can quickly resolve an issue that might otherwise lead to a drawn out lawsuit.

Vermiculite and Asbestos

You may have come across something called “vermiculite” in potting soil or in attic insulation.  Why is it often associated with asbestos?

Vermiculite is a mineral that appears in a pebble-like form. It is often gray, silver, and gold in color and can shimmer in light. Because of its insulating properties and versatility, vermiculite was used in a wide variety of purposes such as insulation and potting materials. While vermiculite alone isn’t harmful, it can often contain asbestos.

The bulk of vermiculite found in US homes is directly from Libby, Montana. The EPA estimates that 70% of vermiculite sold between 1919 to 1990 originated from there. In the vermiculite mines, there was an asbestos deposit that formed alongside it. As the mineral was mined, large quantities of asbestos fibers were thrown into the air which caused many properties of Libby to become contaminated. While some of the asbestos content in Libby is regulated fibrous Tremolite, many of the asbestiform minerals found are known as Libby amphiboles, which are not regulated.

The term Libby amphiboles refers to two asbestiform minerals known as Richterite and Winchite. These minerals typical form from contact metamorphism of limestone. In their fibrous forms, they share similar physical properties to the regulated five amphibole asbestos minerals. There are no current federal regulations on Libby amphiboles although they may have similar health effects to other regulated types.

The EPA has spent hundreds of millions of dollars on the cleanup of Libby.  They recommend that if you find suspected vermiculite insulation in your home, you should assume it to be asbestos-containing. There are tests that can be performed, but they are more expensive than standard asbestos testing.  


Mold Clearance Testing

One of the key parts of an effective mold remediation project is one that is often overlooked. “Post remediation verification” (PRV), or “clearance” is the process that evaluates the performance of a mold remediation project. This step should always be done by an unaffiliated, third-party testing company to assure an unbiased assessment. This assessment is so important that some states require it by law.  It is also key that this assessment is scheduled at the proper stage in a remediation project. A verification assessment should be done after all of the mold has been removed, but before the containment has been removed, antimicrobial coatings have been applied, and build-back of the building materials.

The specific steps taken for a post remediation verification assessment are dependent on the specific mold remediation project, however a few basic steps should be followed: assessing the containment, visual inspection for remaining mold growth or mold damaged materials, verifying there are no musty odors present, and checking that the work area is clean.  Although there is no consensus on sampling for clearance, air samples are commonly collected to see if the levels in the air have been returned to background amounts.


We occasionally get calls from clients who have been told by their remediation company NOT to have a post remediation verification inspection done. They typically say it is a waste of money.  These unscrupulous companies don’t want anyone to review their work because in our experience even the best companies often miss things. You can imagine what might be missed by companies who like to cut corners! In our experience, we find something that was missed in about 50% of all post remediation verifications. This can range from small areas of missed growth or a slight elevation of airborne fungal levels to large issues like major moisture problems and mold damaged materials remaining in place.


The key goal of a mold remediation project is to return the affected areas to a “pre-loss state”. This can help avoid future issues from a problem you thought was already addressed.  One of the most compelling reasons to have PRV testing done is to provide a “clearance letter”.  This is a document you can share with the future purchaser of your home when disclosing the past mold problem.  Having an independent evaluation determine that the project was successful can put everyone’s’ mind at ease.  For all these reasons, we strongly recommend having a post remediation verification assessment done.

Radon Part III – When Radon Hits Home

In my recent blogs, I have written in some detail about radon and how it can affect your health.  But just recently, I had a call from my brother who was concerned about the possibility of radon in his home.  When talking with a next door neighbor who was selling his home, he discovered that the neighbor had elevated levels of radon.  Naturally, my brother was curious about his own home and called for my expertise.

The radon levels for a residential property should be under 4.0 pCi/L.  Picture both my brother’s and my surprise when we tested his home and discovered that it was between 26 and 27 pCi/L!!  Yikes!!

Needless to say, my brother called a professional to install a mitigation system.  A mitigation system usually involves drilling a hole through the basement floor and installing a perforated pipe which has a fan continuously sucking the radon gas from the ground before it has a chance to enter into the living space.  The gas travels through a pipe that exhausts it outdoors where the gas mixes with ambient air and no longer poses as a safety hazard.

It was interesting to note that my brother’s neighbors on each side of his house had radon levels measuring roughly 10 pCi/L, but his home had an elevated level of 27 pCi/L.  There are several possible explanations for this.  One is that there could have been a larger store of uranium directly underneath my brother’s home.  Another explanation could be that my brother had recently installed new windows and extensive insulation; this worked at making his home more airtight and therefore made it more difficult for radon gas to escape.

Regardless of the reason, my brother is feeling much better about his situation.  After having a mitigation system installed in his home, I had the chance to retest his property.  The radon level had dropped from 27 pCi/L to  0.9 pCi/L.  Significantly better and much safer.

Website Review for “IDPH Guidelines for Indoor Air Quality”

The intention of this blog post is to review a website from the Illinois Department of Public Health (IDPH).  The website can be found here:

The website provides some general guidelines for indoor air quality.  Some details about each parameter are discussed.  Parameters ranging from humidity and temperature to formaldehyde and particulates in the air.  It also provides a table that summarizes the guidelines for the following parameters from four different agencies, including IDPH:

  • Humidity
  • Temperature
  • Carbon dioxide
  • Carbon monoxide
  • Hydrogen sulfide
  • Ozone
  • Particulates
  • Formaldehyde
  • Nitrogen dioxide
  • Radon

The “IDPH Guidelines for Indoor Air Quality” website gives recommendations for improving indoor air quality.  Proper thermostat location along with HVAC maintenance are a few of those recommendations.  Source control is also mentioned.  It is generally better to remove the source of contamination, rather than trying to filter it out or dilute it with ventilation.  The problem is often hunting down the source.

Additionally, the site provides contact information for other agencies and groups that offer educational information related to indoor air quality.  National Institute for Occupational Safety and Health (NIOSH), Illinois Department of Labor, and Occupational Safety and Health Administration (OSHA) are mentioned.

Towards the end of the website, a bullet list of recommendations for indoor air investigations is provided.

This site does not provide a lot of detail but it does cover a large scope of information related to indoor air quality.  Indoor Science follows many of the items covered by the IDPH website when doing an investigation for indoor air quality contaminants.  If you have any concerns please feel free to reach out to us at (312) 920-9393.