What is Mold?

Molds are fungi similar to mushrooms and yeast. There are over 100,000 species of mold and at least 1,000 are common in the United States. Fungi are heterotrophic, they do not produce their own food like plants. They must get their food from their environment. They do this by secreting digestive enzymes to dissolve organic and inorganic materials. They absorb the soluble products from digestion. Molds can be found almost anywhere; they can grow on virtually any organic substance, as long as moisture and oxygen are present. Mold growth will often occur when excessive moisture accumulates in buildings or on building materials, particularly if the moisture problem remains undiscovered or unaddressed.

Molds reproduce by releasing spores that usually cannot be seen without magnification. Mold spores float through the indoor and outdoor air continually. When these spores land on a damp or wet surface indoors, they may begin growing and digesting whatever they land on in order to survive. Molds gradually destroy the things they land on. There are many types of molds that exist and there are many types of molds that only grow in an indoor environment that has had water damage. All molds have the potential to cause adverse health effects. Molds can produce allergens that can trigger allergic reactions or even asthma attacks in people allergic to mold. Others are known to produce potent toxins and/or irritants like Stachybotrys, Chaetomium and Ulocladium to name a few. Potential health effects and property damage are important reasons to prevent mold growth and to remediate any existing indoor mold growth.

Molds are microscopic organisms found virtually everywhere, indoors and outdoors.Mold is alive, but it is neither a plant nor an animal. Mold is a type of fungus. It is part of a group of living organisms that are very common and serve an important role in the environment. Penicillin, an antibiotic that has saved many lives, is a type of mold, as is yeast.Mold is formed by microscopic creatures belonging to the Fungi Kingdom. When tiny airborne spores of mold burst, and then land on a favorable surface, they proliferate into visible colonies, and find new favorable surfaces on which to further develop. Fungal growth requires oxygen, adequate temperature, nutrients and water.

Temperature tolerance: Thermophiles – 35ºC + human pathogens such as Aspergillus FumigatusMesophiles – 18ºC to 35ºCPsychrophiles – some fungi grow at 4ºC or below.

Nutrients: Paper, wallpaper, wallboard, sugars (fruits, vegetables), fabrics, wood, dust, etc

How does mold grow?

Mold seeks MOISTURE, WARMTH, and FOOD, and all three conditions are necessary for it to grow. Mold is most likely to find a place to grow in a bathroom, basement or kitchen, but it can grow in other rooms if conditions are favorable. The climate where you live and the living habits in your household can affect the ability of mold to grow. Mold spores can thrive and reproduce in wet or damp parts of your home: areas that have had flooding or where leakage has occurred in roofs, pipes, or walls, or areas around house plants, especially ones that sometimes are over-watered. In just 48 hours, a moist environment combined with room-temperature conditions and an organic food source can lead to mold growth.

Some places where mold can grow in your home are:

  • carpet
  • drapes
  • upholstery
  • leather
  • wood products
  • clothing
  • paper
  • cardboard
  • books
  • rags
  • wallboard
  • cloth
  • ceiling tiles
  • ductwork
  • paint
  • wallpaper
  • household dust

After it gets the food it needs, mold can move to virtually any kind of surface. Mold growth prefers temperatures between 40 and 100 degrees Fahrenheit. If a warm enough area in your home is humid or damp and contains items that mold likes to eat, your home could develop a mold problem.


Why Test For Mold?

Mold testing shows the type and quantity of mold present. The primary reason to test for mold is because under certain conditions, indoor mold has the potential to damage property and cause health problems in humans and animals. Not all molds spores are harmful – they fall into the following categories: Allergenic, Hyper- Allergenic and Toxic.

Some have called it “The Silent Killer”. That may be on the extreme side, but with all the information available about mold and its potential for harm, there are plenty of valid reasons to perform mold testing. For example, we now know that some molds produce toxins which may be linked to severe cases of asthma, respiratory problems which include bleeding lungs, and several other serious ailments including immune system disorders. Medical and legal communities are now taking mold contamination very seriously. With so much overwhelming evidence to support the dangers of exposure to mold, mold testing is the first step in properly assessing whether an abnormal or elevated mold condition exists.

Some may tell you that mold is no big deal and mold testing is not necessary. It is interesting to note that those who make such irresponsible statements also disclaim everything they say by warning you to wear a respirator and rubber gloves when cleaning mold. Why? If mold is “no big deal”, why bother protecting your lungs and skin from it? The answer is because mold can be a very big deal and the only way to really know for sure is by proper testing for mold.

Whenever you hear statements that seem extremely biased to one side of the mold testing issue or the other, be cautious. Our advice is to make sure the person testing for mold has no personal interest in how your mold tests come out. The truth is, under certain conditions, mold does have the potential to cause very costly damage to property and poses a serious health threat to humans and animals. However, not all mold problems are catastrophic by default.

Again, the best way to get an accurate and unbiased assessment of your mold condition is to have proper mold testing done by an independent and certified third party mold inspector. The difference between a minor mold problem and a major problem is: (a)how long before you discover it; and (b)how long you wait to do something about it.

When Is A Good Time To Test For Mold?

  • Whenever you smell a musty or moldy odor
  • After any flooding or water damage event
  • Whenever you find a leak that has been present for more than 24 hours
  • Whenever you smell a moldy odor
  • Unusual stains appear on furniture or building material
  • You suspect mold but do not see any visible mold growth
  • Residents of your home or personnel experience a long-term medical condition without a known cause.

Reasons To Test:

1) Create a baseline for future testing. This allows a mold professional to track and evaluate the progress of mold abatement activities. If current levels are unknown, it is difficult to establish that progress has been made.

2) Establish the presence of mold and the justification for remediation. Many remediation and insurance companies will not authorize or undertake mold remediation if the presence of mold growth is not scientifically demonstrated.

3) Set the parameters for remediation. Many remediation companies will not initiate an abatement project without the input of a testing company to define the boundaries of the affected area needing remediation.

4) Identify the types of mold present (i.e., “natural” or “toxic”). In many cases, residents are interested in the types of mold present and the possible relation to medical symptoms they may be experiencing. Certain mold species may cause serious illness in the elderly, infants and people who have weak immune systems due to chemotherapy or AIDS. Testing can assure the indoor environment is free of mold species that may cause infection in vulnerable people.

5) Establish the levels present. Although mold is mold, and its presence calls for remediation, it is useful to know if the ambient airborne levels are in a range of thousands, or hundreds of thousands. For example, this may affect decisions regarding the timeliness of remediation, and the continued occupancy of the premises.

6) Find “hidden mold”. Mold growth may often not be visible in a house, but known water intrusion or a moldy odor provides cause for concern. Testing will identify if there is a mold problem, even when there is no visible mold growth.

7) To “clear” a remediation; that is, to show that all mold is gone after remediation. Often, mold remediation will miss a mold-contaminated area. Testing of the air in the contained work area will assure that the levels inside the work area are reduced to ambient levels. This also provides documentation for future real estate transfers that the mold was properly and effectively removed.

8) To confirm the “lack of mold”, as in a home purchase. Sometimes a homebuyer will have concerns about mold when purchasing a new home. This may be as a result of a bad experience with mold in their previous residence. Mold testing can provide the peace of mind that there are no problems with elevated airborne mold in the new residence.

9) Confirm that a flood has not yet created mold growth. Floods in homes and offices can occur due to breaks in plumbing lines, or failure of plumbing fixtures. After drying, it is useful to test for mold to assure occupants that mold has not grown as a result of the flooding.

10) Support a legal case. A lawyer or plaintiff usually needs to have objective evidence of the presence or absence of mold and mold exposure to support a legal action. Testing can show scientifically whether mold was or was not present.

If you suspect you have a mold problem, whether mold is visible or not, one call to PrimeAire Mold Services is all it takes to be sure. Our only interest is in providing our clients with accurate reporting of the data we collect during the course of a comprehensive mold inspection process. We provide reliable results of mold tests and samples.


Mold & Property Damage

Mold and Property Damage

Should I have my home tested for Mold?If visible mold is present then it should be remediated. If mold is suspected but not visibly detectable then you should hire a professional that can perform an inspection including but not limited to moisture, temperature and humidity readings. After an inspection it may be necessary to collect air samples to reveal mold colonies and determine the extent of contamination throughout the building if any. This serves well to provide a written protocol that will properly get rid of your mold and its source. Sampling for airborne mold spores can also indicate whether the molds are typical of indoor/outdoor air or unusual at the time of testing.

Who should clean up the Mold?

You want a company who specializes and is certified in mold remediation. Not your local handyman or contractor. Clean Earth Restorations specializes in water and mold remediation and has the experience to handle your unique needs. Mold Property Damage. Mold does two things: Damages property and makes people sick. Either way, mold is most dangerous when you can’t see it. Undetected mold often causes irreversible damage before it is discovered. Mold remediation can become impossible. The most common mistake people make is to assume that only visible mold is a problem. In vain, they attempt to wash mold with bleach or cover it with paint or wallpaper, only to have it come back worse than before. Bleach does not kill spores.


Mold Health Effects

Can Mold cause health problems?

Molds release spores similar to the way some plants release pollen as part of its reproduction cycle. The spores that are released can cause allergies in some people. Mold can also cause other problems ranging from irritation to eyes, skin, nose and throat to conditions even more serious. There are some molds such a Stachybotrys, Chaetomium, and Ulocladium that can produce toxins.

Who is affected by Mold?

There is a wide range of people that are more at risk from mold exposure that include:

  • Infants and children
  • Elderly people
  • Pregnant women
  • Individuals with respiratory conditions such as allergies and asthma
  • Individuals with weakened immune systems

Not all of the health risks that are said to be cause by molds have been substantiated. However, one thing is certain – mold is an asthma trigger and over 5,000 asthma related deaths are reported in the U.S. alone each year, (mostly children). For that reason, periodic home inspections and mold testing is prudent. Mold Health Effects on your family is serious. All indoor mold issues should be addressed immediately. People with asthma should avoid contact with molds and limit their exposure to moldy environments.


Radon Testing and Information

Radon Testing and Radon Information - Surgeon General’s health advisory

“Indoor radon is the second-leading cause of lung cancer in the United States and breathing it over prolonged periods can present a significant health risk to families all over the county,” Dr. Carmona said. “It’s important to know that this threat is completely preventable. It can be detected with a simple test and fixed through well-established venting techniques.” January 13, 2005

Radon Gas

You can’t see or smell it, but you do have it. How can I make such a statement? Because it is a natural occurring gas that emanates from the soil, ground water and even the oceans of the world. Thus a zero level is not a possibility. Regrettably the chances are great that your indoor radon level in your home is higher than out on the back porch.
Why is this case?…Well how do we build houses? We dig a hole in the ground in order to place the foundation for a building in it. We have in effect taken the cork out of a portion of the earth.Yes the top soil and vegetation serves as a cap for the earth. Next we build a dwelling that is as air tight as possible. So we have just corked the bottle with our house and we now live inside of it. All appears to be safe and secure. But houses do breathe. Actually a house is like a big vacuum cleaner. Think of it this way…We heat our homes in the winter. Where does the warm air go? Yes, it rises up through the roof, thus a portion of this air is replaced or suctioned into our homes from the ground. This condition also occurs whenever the wind blows or the barometric pressure changes. The result is that soil gases in the vicinity of of your basement will enter your home through cracks and penetrations in the basement floor and walls.What should you do?  Please test your home! Radon is a radioactive gas!

Why There is No Radon Hysteria

“Consider the danger of radon gas.If there is one environmental problem that is real, it is radon…thereis no hysteria over radon…because it’s natural…”Rush Limbaugh, 1992
“Radon is natural. Radon is not a by-product of industrial or consumer activities. Because there is no one to “blame,” it has been difficult to inflame the passions of the public. Even outdoor air has some amountof radon in it.”Kent Jeffreys


Mold Glossary

Absidia sp – A zygomycete fungus which is considered common to the indoor environment. Reported to be allergenic. May cause mucorosis in immune compromised individuals. The sites of infection are the lung, nasal sinus, brain, eye, and skin. Infection may have multiple sites. Absidia cormbifera has been an invasive infection agent in AIDS and neutropenic patients, as well as, agents of bovine mycotic abortions, and feline subcutaneous abscesses. Acremonium species may be confused with Fusarium species that primarily produce microconidia in culture. Fusarium genera are generally much more rapid growers and produce more aerial mycelium.

Acremonium sp (Cephalosporium sp.) – Reported to be allergenic. Can produce a trichothecene toxin which is toxic if ingested. It was the primary fungus identified in at least two houses where the occupant complaints were nausea, vomiting, and diarrhea. Asexual state of Emericellopsis sp., Chaetomium sp., and Nectripsis sp. It can produce mycetomas, infections of the nails, onychomycosis, corneal ulcers, eumycotic mycetoma, endophthalmitis, meningitis, and endocarditis.

Alternaria sp – Extremely widespread and ubiquitous. Outdoors it may be isolated from samples of soil, seeds, and plants. It is commonly found in outdoor samples. It is often found in carpets, textiles, and on horizontal surfaces in building interiors. Often found on window frames. The species Alternaria alternata is capable of producing tenuazonic acid and other toxic metabolites which may be associated with disease in humans or animals. Alternaria produces large spores having sizes between 20 – 200 microns in length and 7 – 18 microns in width, suggesting that the spores from this fungi are deposited in the nose, mouth, and upper respiratory tract. It may be related to bakers asthma. It has been associated with hypersensitivity pneumoniti, sinusitis, deratomycosis, onychomycosis, subcutaneous phaeohyphomycosis, and invasive infection. Common cause of extrinsic asthma (immediate-type hypersensitivity: type I). Acute symptoms
include edema and bronchiospasms, chronic cases may develop pulmonary emphysema.

Arthrinium phaeospermum– Widespread saprophyte on dead plant material, particularly swampy grasses. Should be considered an allergen. This fungus has also been documented in various subcutaneous infections. No toxic related diseases are of record to date.

Ascomycete.– One of the major classes of fungal organisms. This class contains the the”sac fungi” and yeasts. Some ascomycete spores can be identified by spore morphology, however; some care should be excersised with regard to specific identification. Many ascomycete spores are reported to be allergenic.

Aspergillus sp – A genus of fungi containing approximately 150 recognized species. Members of this genus have been recovered from a variety of habitats, but are especially common as saprophytes on decaying vegetation, soils, stored food, feed products in tropical and subtropical regions. Some species are parasitic on insects, plants and animals, including man. Species within this genus have reported Aw’s (water activities) between 0.75 – 0.82. All of the species contained in this genus should be considered allergenic. Various Aspergillus species are a common cause of extrinsic asthma (immediate-type hypersensitivity: type I). Acute symptoms include edema and bronchiospasms. Chronic cases may develop pulmonary emphysema. Members of this genus are reported to cause a variety of opportunistic infections of the ears and eyes. Sever pulmonary infections may also occur. Many species produce mycotoxins which may be associated with disease in humans and other animals. Toxin production is dependent on the species or a strain within a species and on the food source for the fungus. Some of these toxins have been found to be carcinogenic in animal species. Several toxins are considered potential human carcinogens.

Aureobasidium pullulans – A cosmopolitan fungus with the main habitat apparently on the aerial parts of plants. Frequently found in moist environments. This fungus should be considered allergenic. This species has been associated with deratitis, peritonitis, pulmaonary infection, and invasive disease in AIDS patients. Probably aquired by traumatic implantation. May be recovered as a contaminant from human cutaneous sites. No toxic diseases have been documented to date.

Basidiomycetes – One of the major classes of fungal organisms. This class contains the mushrooms, shelf fungi, puffballs, and a variety of other macrofungi. It is extremely difficult to identify a specific genera of mushrooms by using standard culture plate techniques. Some basidiomycete spores can be identified by spore morphology, however; some care should be exercised with regard to specific identification. Many basidiomycete spores are reported to be allergenic.

Bipolaris sp – A widespread fungus that is most frequently associated with grasses, plant material, decaying food, and soil. It is common to both indoor and outdoor environments. Older obsolete names include Drechslera and Helminthosporium. This fungus produces large spores which would be expected to be deposited in the upper respiratory tract. Various species of this fungus can produce the mycotoxin – sterigmatocystin which has been shown to produce liver and kidney damage when ingested by laboratory animals.

Candida sp– This genus contains a variety of organisms that have been isolated from the environment, as well as human skin and mucous membranes.

Chaetomium sp. – Large ascomycetous fungus producing perithecia. It is found on a variety of substrates containing cellulose including paper and plant compost. It can be readily found on the damp or water damaged paper in sheetrock.

Chrysosporium sp – Widespread, common in the soil and on plants. Rare agents of onychomycosis, skin lesions, endocarditis, and uncommon agents of the pulmonary mycosis adiaspiromycosis. No toxic diseases have been documented to date.

Cladosporium sp. (Hormodendrum sp.) – Aw (water activity) in the range of 0.84 to 0.88. Most commonly identified outdoor fungus. The outdoor numbers are reduced in the winter. The numbers are often high in the summer. Often found indoors in numbers less than outdoor numbers. It is a common allergen. Indoor Cladosporium sp. may be different than the species identified outdoors. It is commonly found on the surface of fiberglass duct liner in the interior of supply ducts. A wide variety of plants are food sources for this fungus. It is found on dead plants, woody plants, food, straw, soil, paint and textiles. It can cause mycosis. Produces greater than 10 antigens. Antigens in commercial extracts are of variable quality and may degrade within weeks of preparation. Common cause of extrinsic asthma (immediate-type hypersensitivity: type I). Acute symptoms include edema and bronchiospasms, chronic cases may develop pulmonary emphysema.

Curvularia sp. – Reported to be allergenic. It may cause corneal infections, mycetoma and infections in immune compromised hosts.

Dreschlera sp – Conidia (spores) dimensions 40-120 x 17-28 microns. Found on grasses, grains and decaying food. It can occasionally cause a corneal infection of the eye.

Epicoccum sp. – Conidia (spores) dimensions 15-25 microns. A common allergen. It is found in plants, soil, grains, textiles, and paper products.

Fusarium sp– Aw (water activity) 0.90. A common soil fungus. It is found on a wide range of plants. It is often found in humidifiers. Several species in this genus can produce potent trichothecene toxins (5, 27). The trichothecene (scirpene) toxin targets the following systems: circulatory, alimentary, skin, and nervous. Produces vomitoxin on grains during unusually damp growing conditions. Symptoms may occur either through ingestion of contaminated grains or possibly inhalation of spores. The genera can produce hemorrhagic syndrome in humans (alimentary toxic aleukia). This is characterized by nausea, vomiting, diarrhea, dermatitis, and extensive internal bleeding. Reported to be allergenic. Frequently involved in eye, skin and nail infections.

Geotrichum sp. – Aw (water activity) 0.90. Conidia (spores) dimensions 6-12 x 3-6 microns. Aw (water activity) 0.90. A common contaminant of grains, fruits, dairy products, paper, textiles, soil and water, and often present as part of the normal human flora. The species Geotrichum candidum can cause a secondary infection (geotrichosis) in association with tuberculosis. This rare disease can cause lesions of the skin, bronchi, mouth, lung, and intestine.

Mucor sp. – Often found in soil, dead plant material, horse dung, fruits, and fruit juice. It is also found in leather, meat, dairy products, animal hair, and jute. A Zygomycetes fungus which may be allergenic (skin and bronchial tests) (7, 17). This organism and other Zygomycetes will grow rapidly on most fungal media. May cause mucorosis in immune compromised individuals. The sites of infection are the lung, nasal sinus, brain, eye, and skin. Infection may have multiple sites.

Nigrospora sp – Reported to be allergenic.

Paecilomyces sp – Commonly found in soil and dust, less frequently in air. P. variotii can cause paecilomycosis. Linked to wood-trimmers disease and humidifier associated illnesses. They are reported to allergenic. Some members of this genus are reported to cause pneumonia. It may produce arsine gas if growing on arsenic substrate. This can occur on wallpapers covered with paris green.

Papulospora sp. – This fungi is found in soil, textiles, decaying plants, manure, and paper.
Penicillium sp – Aw (water activity) 0.78 – 0.88. A wide number of organisms have placed in this genera. Identification to species is difficult. Often found in aerosol samples. Commonly found in soil, food, cellulose, and grains (17, 5). It is also found in paint and compost piles. It may cause hypersensitivity pneumonitis and allergic alveolitis in susceptible individuals. It is reported to be allergenic (skin) (7, 17). It is commonly found in carpet, wallpaper, and in interior fiberglass duct insulation (NC). Some species can produce mycotoxins. Common cause of extrinsic asthma (immediate-type hypersensitivity: type I). Acute symptoms include edema and bronchiospasms, chronic cases may develop pulmonary emphysema.

Periconia sp – No information available, more to come.

Phoma sp. – A common indoor air allergen. It is similar to the early stages of growth of Chaetomium sp. The species are isolated from soil and associated plants (particularly potatoes). Produces pink and purple spots on painted walls (3, 17). It may have antigens which cross-react with those of Alternaria sp. It will grow on butter, paint, cement, and rubber. It may cause phaeohyphomycosis, a systematic or subcutaneous disease.

Pithomyces sp. – Grows on dead grass in pastures. Causes facial eczema in ruminants.

Rhizomucor sp. – The Zygomycetous fungus is reported to be allergenic. It may cause mucorosis in immune compromised individuals. It occupies a biological niche similar to Mucor sp. It is often linked to occupational allergy. The sites of infection are the lung, nasal sinus, brain, eye, and skin. Infection may have multiple sites.

Rhizopus sp – The Zygomycetous fungus is reported to be allergenic. It may cause mucorosis in immune compromised individuals. It occupies a biological niche similar to Mucor sp. It is often linked to occupational allergy. The sites of infection are the lung, nasal sinus, brain, eye, and skin. Infection may have multiple sites.

Rhodotorula sp – A reddish yeast typically found in moist environments such as carpeting, cooling coils, and drain pans. In some countries it is the most common yeast genus identified in indoor air. This yeast has been reported to be allergenic. Positive skin tests have been reported. It has colonized in terminally ill patients. Sporotrichum sp – Reported to be allergenic. See also Sporothrix sp. as there is some taxonomic confusion between these two genera. This genera does not cause sporotrichosis.

Stachybotrys sp. – Aw (water activity) – 0.94, optimum Aw (water activity) – >0.98. Several strains of this fungus (S. atra, S. chartarum and S. alternans are synonymous) may produce a trichothecene mycotoxin- Satratoxin H – which is poisonous by inhalation. The toxins are present on the fungal spores. This is a slow growing fungus on media. It does not compete well with other rapidly growing fungi. The dark colored fungi grows on building material with a high cellulose content and a low nitrogen content. Areas with relative humidity above 55% and are subject to temperature fluctuations are ideal for toxin production. Individuals with chronic exposure to the toxin produced by this fungus reported cold and flu symptoms, sore throats, diarrhea, headaches, fatigue, dermatitis, intermittent local hair loss, and generalized malaise. The toxins produced by this fungus will suppress the immune system affecting the lymphoid tissue and the bone marrow. Animals injected with the toxin from this fungus exhibited the following symptoms: necrosis and hemorrhage within the brain, thymus, spleen, intestine, lung, heart, lymph node, liver, and kidney. The mycotoxin is also reported to be a liver and kidney carcinogen. Affects by absorption of the toxin in the human lung are known as pneumomycosis. This organism is rarely found in outdoor samples. It is usually difficult to find in indoor air samples unless it is physically disturbed. The spores are in a gelatinous mass. Appropriate media for the growth of this organism will have a high cellulose content and a low nitrogen content. The spores will die readily after release. The dead spores are still allergenic and toxigenic. Percutaneous absorption has caused mild symptoms.

Stemphylium sp. – Reported to be allergenic. Isolated from dead plants and cellulose materials.

Syncephalastrum sp. – Can cause a respiratory infection characterized by a solid fungal ball.

Trichoderma sp – It is commonly found in soil, dead trees, pine needles, paper, and unglazed ceramics. It often will grow on other fungi. It produces antibiotics which are toxic to humans. It has been reported to be allergenic (7, 17). It readily degrades cellulose.

Trichophyton sp – Can cause ring worm, athlete’s foot, skin, nail, beard, and scalp (5, 6). Reported to be allergenic. Found on soil and skin.

Ulocladium sp – Has an Aw (water activity) of 0.89. Isolated from dead plants and cellulose materials. Found on textiles.

Verticillium sp – Conidia (spores) dimensions 2.3-10 x 1-2.6 microns. Found in decaying vegetation, on straw, soil, and arthropods. A rare cause of corneal infections.

Wallemia sp – Has an Aw (water activity) of 0.75. Conidia (spores) dimensions 2.5-3.5 microns. Found in sugary foods, salted meats, dairy products, textiles, soil, hay, and fruits.

Yeast – Various yeasts are commonly identified on air samples. Some yeasts are reported to be allergenic. They may cause problems if a person has had previous exposure and developed hypersensitivity. Yeasts may be allergenic to susceptible individuals when present in sufficient concentrations.