Indoor mold on the head jamb of the window in a multi-story building
Indoor mold (American English) or indoor mould (British English), also sometimes referred to as mildew, is a fungal growth that develops on wet materials in interior spaces. Mold is a natural part of the environment and plays an important part in nature by breaking down dead organic matter such as fallen leaves and dead trees; indoors, mold growth should be avoided. Mold reproduces by means of tiny spores. The spores are like seeds, but invisible to the naked eye, that float through the air and deposit on surfaces. When the temperature, moisture, and available nutrient conditions are correct, the spores can form into new mold colonies where they are deposited.[1] There are many types of mold, but all require moisture and a food source for growth.
Mold is ubiquitous, and mold spores are a common component of household and workplace dust. In large amounts they can lead to mold health issues to humans, potentially causing allergic reactions and respiratory diseases.
Infants in homes with mold have a much greater risk of developing asthma and allergic rhinitis.[5][4] Infants may develop respiratory symptoms as a result of exposure to Penicillium, a fungal genus. Signs of mold-related respiratory problems in an infant include a persistent cough or wheeze.
Mold exposure has a variety of health effects, and sensitivity to mold varies. Exposure to mold may cause throat irritation, nasal stuffiness, eye irritation, cough and wheezing and skin irritation in some cases. Exposure to mold may heighten sensitivity, depending on the time and nature of exposure. People with chronic lung diseases are at higher risk for mold allergies, and will experience more severe reactions when exposed to mold. Damp indoor environments correlate with upper-respiratory-tract symptoms, such as coughing and wheezing in people with asthma.[6]
Some mold produce mycotoxins, chemical components of their cell walls, that can pose serious health risks to humans and animals. "Toxic mold" refers to mold which produce mycotoxins, such as Stachybotrys chartarum.[7] Exposure to high levels of mycotoxins can lead to neurological disorders and death[citation needed]. Prolonged exposure (for example, on a daily basis) can be particularly harmful. Mycotoxins can persist in the indoor environment even after death of the fungi. They can adhere to dust particles and can spread through the air attached to these dust particles or spores.[8] There must be very specific temperature and humidity conditions in order for fungi to produce mycotoxins.[8]
Causes and growing conditions
Mold is found everywhere and can grow on almost any substance when moisture is present. It reproduces by spores, which are carried by air currents. When spores land on a moist surface suitable for life, they begin to grow. Mold is normally found indoors at levels that do not affect most healthy individuals.[citation needed]
Black indoor mold growing in a humid bathroom
Because common building materials are capable of sustaining mold growth and mold spores are ubiquitous, mold growth in an indoor environment is typically related to water or moisture exposure and may be caused by incomplete drying of flooring materials (such as concrete). Flooding, leaky roofs, poor building maintenance, or indoor plumbing problems can lead to interior mold growth.[9]Water vapor commonly condenses on surfaces cooler than the moisture-laden air, enabling mold to flourish.[citation needed] This moisture vapor passes through walls and ceilings, typically condensing during the winter in climates with a long heating season. Floors over crawl spaces and basements, without vapor barriers or with dirt floors, are mold-prone. The "doormat test" detects moisture from concrete slabs without a sub-slab vapor barrier.[citation needed] Inorganic materials, such as metal or polished concrete, do not support mold growth, although surface mold growth is still possible.
Significant mold growth requires moisture and food sources and a substrate capable of sustaining growth. Common cellulose-based building materials, such as plywood, drywall, furring strips, finish carpentry, cabinetry, wood framing, composite wood flooring, carpets, and carpet padding provide food for mold. In carpet, organic load such as invisible dust and cellulose are food sources. After water damage to a building, mold grows in walls and then becomes dormant until subsequent high humidity; suitable conditions reactivate mold. Mycotoxin levels are higher in buildings which have had a water incident.
Although this home experienced minor exterior damage from Hurricane Katrina, small leaks and inadequate airflow permitted mold infestation.
Hidden mold
Mold is detectable by smell and signs of water damage on walls or ceiling and can grow in places invisible to the human eye. It may be found behind wallpaper or paneling, on the inside of dropped ceilings, the back of drywall, or the underside of carpets or carpet padding. Piping in walls may also be a source of mold, since they may leak (causing moisture and condensation).[10]
Spores need three things to grow into mold: nutrients – cellulose (the cell wall of green plants) is a common food for indoor spores; moisture – to begin the decaying process caused by mold; and time – mold growth begins from 24 hours to 10 days after the provision of growing conditions.
Mold colonies can grow inside buildings, and the chief hazard is the inhalation of mycotoxins. After a flood or major leak, mycotoxin levels are higher – even after a building has dried out.[citation needed]
Food sources for mold in buildings include cellulose-based materials such as wood, cardboard and the paper facing on drywall and organic matter such as soap, textiles, and dust containing skin cells. If a house has mold, the moisture may originate in the basement or crawl space, a leaking roof or a leak in plumbing pipes.[11] Insufficient ventilation may accelerate moisture buildup. Visible mold colonies may form where ventilation is poorest and on perimeter walls (because they are nearest the dew point).
If there are mold problems in a house only during certain times of the year, the house is probably too airtight or too drafty. Mold problems occur in airtight homes more frequently in the warmer months (when humidity is high inside the house, and moisture is trapped), and occur in drafty homes more frequently in the colder months (when warm air escapes from the living area and condenses). If a house is artificially humidified, by the use of a humidifier, during the winter, this can create conditions favorable to mold. Moving air may prevent mold from growing, since it has the same desiccating effect as low humidity. Mold grows best in warm temperatures, 25 to 30°C (77 to 86°F), although growth may occur between 0 and 35°C (32 and 95°F).[citation needed]
Removing one of the three requirements for mold reduces (or eliminates) new mold growth: moisture; food for the mold spores (for example, dust or dander); and warmth since mold generally does not grow in cold environments.
Heating, ventilation, and air conditioning (HVAC) systems can produce all three requirements for mold growth. The air conditioning system creates a difference in temperature, encouraging condensation. The high rate of dusty air movement through an HVAC system may furnish ample food for mold. Since the air-conditioning system is not always running, warm conditions are the final component for mold growth.
Prevention
Mold growth can be inhibited by keeping surfaces at conditions that are further from condensation, with relative humidity levels below 75%. This usually translates to a relative humidity of indoor air below 60%, in agreement with the guidelines for thermal comfort that recommend a relative humidity between 40 - 60%. Moisture buildup in buildings may arise from water penetrating areas of the building envelope or fabric, from plumbing leaks, rainwater or groundwater penetration, or from condensation due to improper ventilation, insufficient heating or poor thermal quality of the building envelope.[12] Even something as simple as drying clothes indoors on radiators can increase the risk of mold growth, if the humidity produced is not able to escape the building via ventilation.[13]
Residential mold may be prevented and controlled by cleaning and repairing rain gutters, to prevent moisture seepage into the home; keeping air-conditioning drip pans clean and drainage lines clear; monitoring indoor humidity; drying areas of moisture or condensation and removing their sources; ensuring that there is adequate ventilation by installing an exhaust fan in your bathroom; treating exposed structural wood or wood framing with a fungicidal encapsulation coating after pre-cleaning (particularly homes with a crawl space, unfinished basement, or a poorly-ventilated attic).[10]
Assessment
An observation of the indoor environment should be conducted before any sampling is performed. The area should be surveyed for odors indicating mold or bacterial growth, moisture sources, such as stagnant water or leaking pipes, and water-damaged building materials.[14] This can include moving furniture, lifting (or removing) carpets, checking behind wallpaper or paneling, checking ventilation ductwork and exposing wall cavities. Efforts typically focus on areas where there are signs of liquid moisture or water vapor (humidity), or where moisture problems are suspected. In many cases, if materials have failed to dry out several days after the suspected water event, mold growth can be suspected even if it is not immediately visible. Often, quick decisions about the immediate safety and health of the environment can be made by these observations before sampling is even needed.[8] The United States Environmental Protection Agency (EPA) does not generally recommend sampling unless an occupant of the space has symptoms. In most cases, if visible mold growth is present, sampling is unnecessary.[15] Sampling should be performed by a trained professional with specific experience in mold-sampling protocols, sampling methods and the interpretation of findings. It should be done only to make a particular determination, such as airborne spore concentration or identifying a particular species.
Sampling
Before sampling, a subsequent course of action should be determined.
Air is the most common form of sampling to assess mold levels. Although, the Environmental Protection Agency (EPA) does not have any current testing protocols. Air sampling is considered to be the most representative method for assessing respiratory exposure to mold.[17] Indoor and outdoor air are sampled, and their mold spore concentrations are compared. Indoor mold concentrations should be less than or equal to outdoor concentrations with similar distributions of species. A predominant difference in species or higher indoor concentrations can indicate poor indoor air quality and a possible health hazard.[8] Air sampling can be used to identify hidden mold and is often used to assess the effectiveness of control measures after remediation. An indoor mold air sampling campaign should be performed over the course of at least several days as the environmental conditions can lead to variations in the day-to-day mold concentration. Stationary samplers assess a specific environment, such as a room or building, whereas personal samplers assess the mold exposure one person receives in all of the environments they enter over the course of sampling. Personal samplers can be attached to workers to assess their respiratory exposures to molds on the job. Personal samplers usually show higher levels of exposure than stationary samples due to the "personal cloud" effect, where the activities of the person re-suspend settled particles.[17] There are several methods that can be used for indoor mold air sampling.
Swab and surface sampling
Culture dish with A. fumigatus colonies, a species commonly found in indoor air
Surface sampling measures the number of mold spores deposited on indoor surfaces. With swab, a cotton swab is rubbed across the area being sampled, often a measured area, and subsequently sent to the mold testing laboratory. The swab can rubbed on an agar plate to grow the mold on a growth medium. Final results indicate mold levels and species located in the suspect area. Surface sampling can be used to identify the source of mold exposure. Molecular analyses, such as qPCR, may also be used for species identification and quantification. Swab and surface sampling can give detailed information about the mold, but cannot measure the actual mold exposure because it is not aerosolized.[17]
Bulk and dust sampling
Bulk removal of material from the contaminated area is used to identify and quantify the mold in the sample. This method is often used to verify contamination and identify the source of contamination. Dust samples can be collected using a vacuum with a collection filter attached. Dust from surfaces such as floors, beds, or furniture is often collected to assess health effects from exposure in epidemiology studies. Researchers of indoor mold also use a long-term settled dust collection system where a dust cloth or a petri dish is left out in the environment for a set period of time, sometimes weeks.[17] Dust samples can be analyzed using culture-based or culture-independent methods. Quantitative PCR is a DNA-based molecular method that can identify and quantify fungal species. The Environmental Relative Moldiness Index (ERMI) is a numerical that can be used in epidemiological studies to assess mold burdens of houses in the United States. The ERMI consists of a list of 36 fungal species commonly associated with damp houses that can be measured using qPCR.[18][17] Like swab and surface sampling, bulk and dust sampling can give detailed information about the mold source, but cannot accurately determine the level of exposure to the source.[17]
Remediation
Mold remediation
In a situation where there is visible mold and the indoor air quality may have been compromised, mold remediation may be needed. The first step in solving an indoor mold problem is to remove the moisture source;[19] new mold will begin to grow on moist, porous surfaces within 24 to 48 hours. There are a number of ways to prevent mold growth. Some cleaning companies specialize in fabric restoration, removing mold (and mold spores) from clothing to eliminate odor and prevent further damage to garments.
The effective way to clean mold is to use detergent solutions which physically remove mold. Many commercially available detergents marketed for mold cleanup include an antifungal agent.[20][21]
Mold will start to grow once moisture and organic material come together. This can happen anywhere in a property including bathrooms, walls, garages, bedrooms, kitchens, etc. A smell is a good indicator that there is mold growth that needs immediate attention. If not attended to, the growth can spread through the property contributing to adverse health problems and causing secondary damage to the structure and its contents. Significant mold growth may require professional mold remediation to remove the affected building materials and eradicate the source of excess moisture. In extreme cases of mold growth in buildings, it may be more cost-effective to condemn the building than to reduce mold to safe levels.[citation needed]
The goals of remediation are to remove (or clean) contaminated materials, preventing fungi (and fungi-contaminated dust) from entering an occupied (or non-contaminated) area while protecting workers performing the abatement.[22]
Cleanup and removal methods
The purpose of cleanup is to eliminate mold and remove contaminated materials. Killing mold with a biocide is insufficient, since chemical substances and proteins causing reactions in humans remain in dead mold. The following methods are used.
Evaluation: Before remediation, the area is assessed to ensure safety, clean up the entire moldy area, and properly approach the mold. The EPA provides the following instructions:[10]
HVAC cleaning: Should be done by a trained professional.[23]
Dry brushing or agitation device: Wire brushing or sanding is used when microbial growth can be seen on solid wood surfaces such as framing or underlayment (the subfloor).
Dry-ice blasting: Removes mold from wood and cement; however, this process may spray mold and its byproducts into surrounding air.
Wet vacuum: Wet vacuuming is used on wet materials, and this method is one of those approved by the EPA.[citation needed]
Damp wipe: Removal of mold from non-porous surfaces by wiping or scrubbing with water and a detergent and drying quickly.
HEPA (high-efficiency particulate air) vacuum cleaner: Used in remediation areas after materials have been dried and contaminated materials removed; collected debris and dust is stored to prevent debris release.
Debris disposal: Sealed in the remediation area, debris is usually discarded with ordinary construction waste.
Thermographic camera, infrared thermal-imaging cameras to identify secondary moisture sources.
Hepa Vacuum, also known as High Efficiency Particulate Filter is commonly used with mold remediation for safely removing any mold spores from the surface and building materials to deter these pores from becoming airborne.
Protection levels
During mold remediation in the U.S., the level of contamination dictates the protection level for remediation workers.[24] Contamination levels have been enumerated as I, II, III, and IV:[citation needed]
Level I: Small, isolated areas (10 square feet (0.93m2) or less); remediation may be conducted by trained building staff;
Level II: Mid-sized, isolated areas (10–30 square feet (0.93–2.79m2)); may also be remediated by trained, protected building staff;
Level III: Large, isolated areas (30–100 square feet (2.8–9.3m2)): Professionals experienced in microbial investigations or mold remediation should be consulted, and personnel should be trained in the handling of hazardous materials and equipped with respiratory protection, gloves and eye protection;
↑ Sullivan, John B. Jr.; Krieger, Gary R. (2001). Clinical environmental health and toxic exposures (2nded.). Philadelphia: Lippincott Williams & Wilkins. ISBN0-683-08027-X. OCLC41606485.
Mold health issues refer to the harmful health effects of molds and their mycotoxins. However, recent research has shown these adverse health effects are caused not exclusively by molds, but also other microbial agents and biotoxins associated with dampness, mold, and water-damaged buildings, such as gram-negative bacteria that produce endotoxins, as well as actinomycetes and their associated exotoxins. Approximately 47% of houses in the United States have substantial levels of mold, with over 85% of commercial and office buildings found to have water damage predictive of mold. As many as 21% of asthma cases may result from exposure to mold. Substantial and statistically significant increases in the risks of both respiratory infections and bronchitis have been associated with dampness in homes and the resulting mold.
A mold or mould is one of the structures that certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. Not all fungi form molds. Some fungi form mushrooms; others grow as single cells and are called microfungi.
Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present.
Indoor air quality (IAQ) is the air quality within buildings and structures. Poor indoor air quality due to indoor air pollution is known to affect the health, comfort, and well-being of building occupants. It has also been linked to sick building syndrome, respiratory issues, reduced productivity, and impaired learning in schools. Common pollutants of indoor air include: secondhand tobacco smoke, air pollutants from indoor combustion, radon, molds and other allergens, carbon monoxide, volatile organic compounds, legionella and other bacteria, asbestos fibers, carbon dioxide, ozone and particulates. Source control, filtration, and the use of ventilation to dilute contaminants are the primary methods for improving indoor air quality.
Mildew is a form of fungus. It is distinguished from its closely related counterpart, mold, largely by its colour: molds appear in shades of black, blue, red, and green, whereas mildew is white. It appears as a thin, superficial growth consisting of minute hyphae produced especially on living plants or organic matter such as wood, paper or leather. Both mold and mildew produce distinct offensive odours, and both have been identified as the cause of certain human ailments.
Sick building syndrome (SBS) is a condition in which people develop symptoms of illness or become infected with chronic disease from the building in which they work or reside. In scientific literature, SBS is also known as building-related illness (BRI), building-related symptoms (BRS), or idiopathic environmental intolerance (IEI).
A mycotoxin is a toxic secondary metabolite produced by fungi and is capable of causing disease and death in both humans and other animals. The term 'mycotoxin' is usually reserved for the toxic chemical products produced by fungi that readily colonize crops.
A humidifier is a household appliance or device designed to increase the moisture level in the air within a room or an enclosed space. It achieves this by emitting water droplets or steam into the surrounding air, thereby raising the humidity.
Stachybotrys chartarum (, stak-ee-BO-tris char-TARE-əm, also known as black mold is a species of microfungus that produces its conidia in slime heads.
Radon mitigation is any process used to reduce radon gas concentrations in the breathing zones of occupied buildings, or radon from water supplies. Radon is a significant contributor to environmental radioactivity and indoor air pollution. Exposure to radon can cause serious health problems such as lung cancer.
Structural dampness is the presence of unwanted moisture in the structure of a building, either the result of intrusion from outside or condensation from within the structure. A high proportion of damp problems in buildings are caused by ambient climate dependent factors of condensation and rain penetration. Capillary penetration of fluid from the ground up through concrete or masonry is known as "rising damp" and is governed by the shape and porosity of the construction materials through which this evaporation-limited capillary penetration takes place. Structural damp, regardless of the mechanisms through which it takes place, is exacerbated by higher levels of humidity.
Bioaerosols are a subcategory of particles released from terrestrial and marine ecosystems into the atmosphere. They consist of both living and non-living components, such as fungi, pollen, bacteria and viruses. Common sources of bioaerosols include soil, water, and sewage.
Mold control and prevention is a conservation activity that is performed in libraries and archives to protect books, documents and other materials from deterioration caused by mold growth. Mold prevention consists of different methods, such as chemical treatments, careful environmental control, and manual cleaning. Preservationists use one or a combination of these methods to combat mold spores in library and archival collections.
Airborne transmission or aerosol transmission is transmission of an infectious disease through small particles suspended in the air. Infectious diseases capable of airborne transmission include many of considerable importance both in human and veterinary medicine. The relevant infectious agent may be viruses, bacteria, or fungi, and they may be spread through breathing, talking, coughing, sneezing, raising of dust, spraying of liquids, flushing toilets, or any activities which generate aerosol particles or droplets.
Indoor bioaerosol is bioaerosol in an indoor environment. Bioaerosols are natural or artificial particles of biological origin suspended in the air. These particles are also referred to as organic dust. Bioaerosols may consist of bacteria, fungi, viruses, microbial toxins, pollen, plant fibers, etc. Size of bioaerosol particles varies from below 1 μm to 100 μm in aerodynamic diameter; viable bioaerosol particles can be suspended in air as single cells or aggregates of microorganism as small as 1–10 μm in size. Since bioaerosols are potentially related to various human health effects and the indoor environment provides a unique exposure situation, concerns about indoor bioaerosols have increased over the last decade.
Interstitial condensation is a type of condensation that may occur within an enclosed wall, roof or floor cavity structure, which can create dampening.
Wallemia sebi is a xerophilic fungus of the phylum Basidiomycota.
Aspergillus versicolor is a slow-growing species of filamentous fungus commonly found in damp indoor environments and on food products. It has a characteristic musty odor associated with moldy homes and is a major producer of the hepatotoxic and carcinogenic mycotoxin sterigmatocystin. Like other Aspergillus species, A. versicolor is an eye, nose, and throat irritant.
Soil stabilization is a general term for any physical, chemical, mechanical, biological, or combined method of changing a natural soil to meet an engineering purpose. Improvements include increasing the weight-bearing capabilities, tensile strength, and overall performance of unstable subsoils, sands, and waste materials in order to strengthen road pavements.
Healthy building refers to an emerging area of interest that supports the physical, psychological, and social health and well-being of people in buildings and the built environment. Buildings can be key promoters of health and well-being since most people spend a majority of their time indoors. According to the National Human Activity Pattern Survey, Americans spend "an average of 87% of their time in enclosed buildings and about 6% of their time in enclosed vehicles."
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