Facts About Air Filter

The Air we Breathe

Indoor air is 100 times more polluted than outdoor air. Bad, stale air in your home can cause:

  • Eye, nose, throat and lung irritations
  • Colds and flu, sneezing and wheezing
  • Headaches, fatigue, asthma and allergy symptoms
  • Waking up with puffy eyes, a sore throat, or a stuffed up nose

What you can’t see CAN hurt you. 99% of pollutants are so small that they are invisible to the naked eye!

  • Bacteria
  • Asbestos
  • Viruses
  • Pollen
  • Dust Mites
  • Formaldehyde
  • Germs
  • More…

Filter facts

Dust contains 2% aluminum.

There are over two million dust mites in every double bed.

Ozone can kill mould.

A human hair is .75 microns thick. Bacteria is .22 microns. A virus is .01 microns. The Nutri-Tech cartridge filters down to 0.03 microns.

Scientists believe that while air pollution probably doesn’t cause asthma, other respiratory conditions or heart problems, it certainly aggravates them. And new research suggests that some of the smallest pollutants (too small to be measured until recently) may be linked to lung cancer.

U.S. polution is part of the problem.


By Pat Moffat
First published in Chatelaine’s October 1996 issue.
© Pat Moffat

Every breath I take hurts,” says Judy LeBlanc, one of Saint John’s most vocal campaigners for clean air. Stricken for more than 10 years with a severe respiratory disease, bronchiectasis, and maintained by medications whose side effects include heart palpitations, nausea and weight loss, the 43?year?old mother of two teenagers continues to fight local air pollution despite
her doctors’ warnings to slow down. She knows the air is making her sicker.

Part of LeBlanc’s motivation is to fulfill a pact she made with her friend and fellow
campaigner Cynthia Marino, who died during an asthma attack in May 1995. “Cindy and I
promised that if one of us died, the other would continue the work,” says LeBlanc.

In several urban trouble spots?Vancouver, Saint John and the Quebec City?Windsor corridor?air pollution is taking a toll on human health. Studies are showing that people with respiratory and heart conditions are at risk of premature death in polluted cities and that children can be seriously affected. Some of the most dangerous pollutants are ozone (which contributes to smog and comes primarily from vehicles), sulfate (an acidic aerosol formed largely from industrial and power?plant emissions of sulfur dioxide), carbon monoxide (largely from vehicles) and very fine particles (primarily from industrial emissions) that penetrate deeply into the lungs. This “particulate matter” is measured in microns as PM10 or PM2.5; a human hair, by comparison, is 100 microns thick.

Scientists believe that while air pollution probably doesn’t cause asthma, other respiratory conditions or heart problems, it certainly aggravates them. And new research suggests that some of the smallest pollutants (too small to be measured until recently) may be linked to lung cancer.

Saint John receives hefty amounts of pollutants from the United States. But it’s a local problem that’s made the city’s air notorious. In Saint John’s east end, an oil?fired electricity plant, a pulp?and?paper mill and the biggest oil refinery in Canada, owned by the Irving family, all emit sulfur dioxide, which, in the city’s frequent fogs, becomes sulfuric acid. “Saint John is certainly not the most polluted city in Canada, but it has the most acidic air we’ve ever measured,” says Health Canada scientist Rick Burnett. Unfortunately, neither Environment Canada’s air quality index nor our supplemental data fully reflect the amount of corrosive sulfuric acid in
the air. That’s why Saint John scores higher than it probably should in our air quality rankings (see “The regulatory haze.”)

In southern Ontario, on the other hand (where up to half the air pollution comes from the United States), and Vancouver (where most is homegrown), ozone and fine particles are of greatest concern. A study by Burnett and Haluk Ozkaynak at the Harvard School of Public Health, which correlated nonaccidental deaths with daily levels of ozone and other pollutants over 20 years in Metro Toronto, concluded that 30 deaths each month are related to high levels of air pollution.

“Among asthmatics and people with allergies, even a low exposure to ozone can increase their sensitivity to allergens,” says Dr. David Bates, professor emeritus of medicine at the University of British Columbia and an authority on air pollution and health. “Studies are also showing that PM10 has a long?term and highly significant health impact, not only for asthma but possibly also for lung cancer and cardiovascular diseases.” People doing aerobic exercise in peak smog times, the elderly, infants and children are especially susceptible. Health Canada’s Rick Burnett has found that 15 percent of the summer hospitalizations of babies in southern Ontario are linked to high levels of air pollution.

In the west, Calgary and Edmonton contend with hydrogen sulfide from the petroleum industry and traffic exhaust. Winnipeg’s wheat?stubble burning in the fall and swirling sand in the spring (from winter de?icing) help explain its mediocre position in our air quality rankings. And in near?pristine Saskatoon, which scores among the best on the pollutants Environment Canada reports, teacher Judith Benson is seeing more children with “puffers” for asthma. She also worries about cancer from pesticide residues. “In the summer, there’s grit on my furniture,” says
Benson. “If we’re getting topsoil as household dust, we must be getting the pesticides too.” So far, there are no studies to ease?or confirm?her fears.

Compared with much of the world, Canada enjoys enviable air quality. Yet the fact remains that Canadians are getting sick and dying from air pollution. And unanswered questions beg for better regulations and monitoring. It’s citizens who often drive change. In Saint John, Judy LeBlanc is proud of what “two housewives” and other volunteers in the Citizens’ Coalition for Clean Air have helped accomplish in two years: a new Clean Air bill before the legislature and a
toughening of the provincial standard for industrial sulfur dioxide emissions. And now that LeBlanc no longer lives in the pollution?plagued east end her family moved last winter she has more energy to campaign for a respiratory clinic.

The regulatory haze

First, the bad news. Our guidelines are old, our laws have no teeth and change is a political
football. The good news? There’s a committee studying the problem…

By Pat Moffat
First published in Chatelaine’s October 1996 issue.
© Pat Moffat

Last year we had egg on our face. Our ranking of Saint John as top city for air quality triggered a torrent of protests, including a letter from 14?year?old asthmatic Amy Evans.

What went wrong? Our rankings relied entirely on Environment Canada’s air quality index, the main source of national pollution data, reporting acceptable or unacceptable levels of ozone, sulfur dioxide, total suspended particulate, carbon monoxide and nitrogen dioxide in most Canadian cities. According to the index, one of the worst cities for people with respiratory diseases came out on top.

“Many things have a greater effect on health than what’s in the air quality index,” says Tom Dann, head of air toxics in Environment Canada’s Environmental Protection Service. In Saint John, acidic aerosols and very fine particles just 2.5 microns or less in diameter (known as PM2.5) appear to be causing the problems. Yet they’re not part of the main index.

Why not? Government regulations catch up with changing scientific knowledge slowly. In several areas, Canada’s guidelines lag behind U.S. standards. Although the gaps in air quality guidelines are particularly glaring, similar problems are found in surface?water and drinking?water guidelines. (For an explanation of how we tried to improve this year’s ranking, see “How we graded them”)


We’ve been pushing for an objective for PM2.5 since 1987,” says a frustrated Environment Canada official who asked for anonymity. While stations have monitored PM10 and PM2.5 since 1984, the main air quality index includes only “total suspended particulate,” a grab bag of different?size particles that most experts now consider irrelevant as a measure for health effects. The United States has had a national standard for PM10 since 1987, and the push is on to extend the law to PM2.5.

One difficulty in trying to ensure that regulations protect human health is that for some substances there may be no way of confirming at what point they cause problems. “People get hospitalized when the ozone is less than 82 parts per billion, which is the federal objective for acceptable levels,” explains Health Canada scientist Rick Burnett. “The system of how we set national objectives may not be appropriate anymore.”

Toxics?including benzene, dioxins and heavy metals are another disturbing unknown. Although 40 stations monitor for many different airborne toxic chemicals across the country, no national air quality objectives cover them.

What’s needed now

Some of Canada’s most serious problems with air and water pollution can’t be solved without the cooperation of our closest neighbour. Three years after a bilateral air quality agreement was signed in 1991, officials of both countries began working on the trans?boundary smog problem in central and Eastern Canada, where up to 50 percent of air pollution comes from south of the border. Pete Christich, senior international officer for U.S.?Canada relations at the U.S. Environmental Protection Agency in Washington, D.C., says that for the past five years the United States has been “encouraging” Canada to work with British Columbia to “make progress in treating Victoria’s sewage,” 91 percent of which is dumped untreated into the shared Juan de Fuca Strait. (So far, progress has been slow.)

The two countries take different approaches to air and water quality. In the United States, federal laws govern environmental standards, and polluters face fines and possible jail terms. In Canada, the federal government sets guidelines for air and water quality, which the provinces may turn into enforceable regulations. (In July, for example, Ontario bowed to political pressure and announced its intention to crack down on auto emissions. Days later, a government report showed plans to
dismantle a slew of other environmental regulations in the interests of unburdening industry.)

It’s natural for environmentalists to get fed up with Canada’s kinder, gentler approach, to wish our laws had more teeth and that governments enforced them more rigorously. “The federal government doesn’t have the stomach to do what must be done in controlling polluters,” charges Daniel Green, Co-President of the Société pour vaincre la pollution (a Quebec organization similar to Pollution Probe) in Montreal. He’s referring to the industries and municipal wastewater plants
that dump mercury, lead, PCBs and other chemicals into the St. Lawrence River?polluters that could be charged under the powerful but little?used Federal Fisheries Act if the government chose to do so. When Ottawa has acted, its laws have proven effective. Banning leaded gasoline in
1990 reduced airborne lead?blamed for neurological problems in children?to very low levels. The federal environment minister’s implementation of stricter standards for auto emissions this past June, which aim to meet the U.S. standards for the 1998 model year, is a step in the right direction. And revisions to the Canadian Environmental Protection Act of 1988 may have the most far?reaching consequences yet, says Ann McMillan, member of a federal?provincial working group on air quality objectives and guidelines. The aim: to tighten regulations and strengthen the federal government’s ability to prosecute polluters. But as past experience proves, it’s a long slow road from good intentions to regulatory clout. In the meantime, we all pay the price. Airborne toxics are another disturbing unknown. No national objectives govern benzene, dioxins or heavy metals

A guide to understanding air cleaning terms.

CFM (Cubic Feet per Minute) a measurement of air flow.

Although there is no universally accepted method for comparing air-cleaning devices, several investigators of portable air-cleaning units have expressed their results as a “Clean Air Delivery Rate” or CADR. The CADR is the product of the unit efficiency and the airflow rate, and is a measure of the number of CFM of air it cleans of a specific material.

Revolutions Per Minute (RPM) is a measure of speed for any rotating device. Typically found in specifications for motors.


The DOP Military Standard is the standard set by the federal government to rate particle reduction by HEPA filters. This test rates high-efficiency filters by the percentage of 0.3 micron size particles of dioctylphthalate (DOP) smoke they remove.

HEPA stands for High Efficiency Particulate Air, and like the name says, these filters are designed to remove 99.97% of all airborne pollutants 0.3 microns or larger from the air that passes through the filter (these include tobacco smoke, household dust and pollen).

Pounds per Square Foot (PSF). A measurement of air pressure

Carbon, the sixth most abundant element in the universe, has been known since ancient times. Many natural substances of base materials are used to make carbon. The most common of these are wood, coal, lignite, and coconut shell.
Amorphous carbon is formed when a material containing carbon is burned without enough oxygen for it to burn completely.


Activated carbon is the generic term used to describe a family of carbonaceous adsorbents with a highly crystalline form and extensively developed internal pore structure. Activation creates a fast internal pore network and imparts certain surface chemistries (functional groups) inside each particle. Thus activation gives carbon its unique filtering characteristics.

Zeolite is a mineral with a unique interconnecting lattice structure. This lattice structure is arranged to form a honeycomb framework of consistent diameter interconnecting channels and pores. Negatively charged alumina and neutrally charged silica tetrahedral building blocks are stacked to produce the open three-dimensional honeycomb framework. Zeolites actually attract odors & gases and trap them in its crystalline structure.


A pre filter is the primary layer of filtration that collects large particles before they reach the HEPA filter. Eliminating these larger particles, dust and hair extends the life of your HEPA filter. Occasional vacuuming of the exterior of the unit will help extend life of the filters and will also prolong the HEPA filter life.

When a gas or vapor is brought into contact with a solid, the solid takes up part of it. The molecules that disappear from the gas either enter the inside of the solid, or remain on the outside attached to the surface. The former phenomenon is termed absorption (or dissolution) and the latter adsorption.

Trap is the process of gasses and particulate matter attaching to the surface of the carbon and or zeolite structures.

There are many simple electronic devices that claim to clean the air in your home by making negative ions and ozone. The claim is accurate–they do make both ozone and negative ions, and they do clean the air in your home. However, that’s not the whole story. Also ozone gives off the “fresh” smell that occurs after a thunderstorm (a potent producer of ozone)

Ozone is produced indirectly by ion generators.

A micron is a unit of length equal to 1 millionth of a meter or .000039th (39 millionth) of an inch. Another name for micron is micrometer.

Particulate Matter Up to 10 Microns in Diameter (PM10)
The number 10 refers to the particle size measured in microns.
PM 10’s are widely considered the most dangerous to human health.

3-Speed refers to a variable speed selection control on your air cleaner. This control allows you to operate your air cleaner on low, medium or high settings depending upon your needs.

The blower wheel is a squirrel cage type wheel whose purpose is to move the air through the room. A blower wheel is more efficient than a fan as it will move more air and resists clogging.

A standard developed for measuring particulate matter in a pre defined area.

The Association of Home Appliance Manufacturers (AHAM) is an organization that represents the manufacturers of home appliances and creates standards with large manufacturers. While it has an admirable mission, it is important to note that AHAM is not a HEPA standard and seems to have been developed to resemble the output of electrostatic precipitators, a technologically inferior air cleaning method. It is for that reason that the output ratings are only valid for the first 72 hours (3 days) of operation.


The electrostatic stage filters the air using static electricity by having a static charge on the filter to allow airborne particles to “stick” to the filter, just like static-charged clothing sticks together.

Ion generators act by charging the particles in a room so that they are attracted the unit. Ion generators remove small particles (e.g., tobacco smoke) from the indoor air. These devices provide a benefit by rectifying a hypothesized ion imbalance.

A warranty is legal concept or doctrine that holds manufacturers or sellers responsible, or liable, for harm caused by defective products sold in the marketplace.

A limited warranty is a warranty that imposes certain limitations, and is therefore not a full warranty.

The main filter cartridge in Nutri-Tech air purifiers is backed by the 1 year pro-rated warranty. Under this pro-rated warranty the user of a Nutri-Tech Air cleaner becomes eligible to receive a new filter cartridge at a partial cost if the unit fails within the duration period of the pro-rated warranty period. This warranty applies to the Nutri-Tech units used under normal residential conditions only. Under the pro rated warranty the sooner you have to replace the filter, the less money you pay.

A guarantee is an assurance for the fulfillment of a conditions put forth by the manufacturer.

Is the American Society of Heating, Refrigerating and Air-Conditioning Engineers. ASHRAE publishes Standards for Ventilation for Acceptable Indoor Air Quality.

Molds produce tiny spores to reproduce, just as plants produce seeds. Mold spores waft through the indoor and outdoor air continually. When mold spores land on a damp spot indoors, they may begin growing and digesting whatever they are growing on in order to survive. There are molds that can grow on wood, paper, carpet, and foods. When excessive moisture or water accumulates indoors, mold growth will often occur, particularly if the moisture problem remains undiscovered or unaddressed. Molds can trigger asthma episodes in individuals with an allergic reaction to mold.

The term “sick building syndrome” (SBS) is used to describe situations in which building occupants experience acute health and comfort effects that appear to be linked to time spent in a building, but no specific illness or cause can be identified. The complaints may be localized in a particular room or zone, or may be widespread throughout the building.
The following have been cited causes of or contributing factors to sick building syndrome:
Inadequate ventilation: Inadequate ventilation, which may occur if heating, ventilating, and air conditioning (HVAC) systems do not effectively distribute air to people in the building.
Chemical contaminants from indoor sources: Most indoor air pollution comes from sources inside the building. For example, adhesives, carpeting, upholstery, manufactured wood products, copy machines, pesticides, and cleaning agents may emit volatile organic compounds (VOCs), including formaldehyde. Environmental tobacco smoke contributes high levels of VOCs, other toxic compounds, and respirable particulate matter. Research shows that some VOCs can cause chronic and acute health effects at high concentrations, and some are known carcinogens. Low to moderate levels of multiple VOCs may also produce acute reactions. Combustion products such as carbon monoxide, nitrogen dioxide, as well as respirable particles, can come from unvented kerosene and gas space heaters, wood stoves, fireplaces and gas stoves.
Chemical contaminants from outdoor sources: The outdoor air that enters a building can be a source of indoor air pollution. For example, pollutants from motor vehicle exhausts; plumbing vents, and building exhausts (e.g., bathrooms and kitchens) can enter the building through poorly located air intake vents, windows, and other openings. In addition, combustion products can enter a building from a nearby garage.

Particle Count per Cubic Foot is a unit of measure to classify the amount of a particular size of particles in a cubic foot of air.

An air cleaner must constantly recirculate indoor air in order to effectively reduce concentrations of airborne particulate contamination. Cleaning the total volume of air contained within a room is the equivalent of completely changing the air in that room. Air cleaner filtration capacity is expressed as the number of air changes per hour (ACH). For air cleaners of equivalent filter effectiveness, a higher ACH rating yields higher levels of air quality improvement.

Room air cleaners help with allergies by helping people live in cleaner, healthier environments. By sleeping in a room with an air cleaner, you will breathe much cleaner air all night long. And by also having an air cleaner in your office, or any other room where you spend a lot of time, you will maximize your clean air intake and minimize the allergens you breathe. Even if you have a good filter on your central air conditioning system, a room air cleaner will increase the purity of the air you breathe.

Many room air cleaners can go with you. If your den and your bedroom are similar sizes, you can move your air cleaner to the room you’re in.


What are carbon and zeolite used for?
Carbon and zeolite are used to remove gases and odors. Both have properties that allow them to adsorb gaseous materials.

What are the guarantees?
The motor, fan and other working parts come with a limited lifetime warranty and a conditional 10 mechanical warranty.

What would cause a filter to fill up in less time?
Having many pets, new carpeting, paint fumes, heavy smoking, city pollution, etc

How long do you think my unit will last?
The unit should last well over 10 years or more if properly maintained. It is the filter that must be replaced when needed.

Where should I place the unit for maximum effectiveness?
It can be placed anywhere in a room, including corners. Ideally close to an air intake vent. The air cleaner should be placed in the bedroom at night with the door closed in order to produce the best personal results. The best room in the house to use a single machine is the bedroom.

How much space does the air cleaner effectively clean?
It will clean an average bedroom in about 10 minutes with the door closed. In technical terms, it cleans up to 1,600 square feet per hour. The Compact model cleans up to 700 square feet. (All estimates assume 8 ft. ceilings.)

Does the unit require any special maintenance?

Periodic (once a month) vacuuming of the front of the pre-filter with the brush attachment of your vacuum cleaner is the only regular maintenance required for the air cleaner.

How much electricity is required to run the air cleaner?
Your Nutri-Tech uses an ordinary 120 volt outlet. Maximum draw is about 135 watts on the high setting or 1 cent per hour, average cost.

Your online guide to air purifiers: Learn the basics before you buy

For most people, buying air purifiers is very confusing. HEPA filters, negative ionizers, electrostatic precipitators– the terminology alone sounds like a foreign language!

Not to worry though, we’ve broken down the whole, convoluted world of air purifiers into one, straightforward page covering the basics. From here, you can check out other pages on aspects that interest you, or go straight to our air purifier page for specific recommendations. Here we go!

Why air purifiers are needed

Air purifiers have become very widespread over the years due to several factors. Over the last 20 years the number of people with asthma has increased 100 times. It is also estimated that now 1 out of every 3 adults and children have either asthma or allergies. Why is this? Why has the EPA (Environmental Protection Agency) declared indoor air quality as the nations worst environmental health problem? Why did The American College of Allergies recently announce that 50% of all illness is aggravated or caused by polluted indoor air?

The main reason is the insulation of homes and offices in response to the energy crisis in the 1970s. To save on energy costs, and for other reasons, indoor spaces are now tightly insulated. These air-tight, energy-efficient indoor spaces are perfect for trapping in all kinds of pollutants and particles.

Our respiratory tracts struggle daily against the contaminants that are in the air. Poor air quality causes headaches, digestive problems, fatigue, restlessness, congestion, and many other health problems. This is why there is such a need for air purifiers in most indoor environments.

What air purifiers clean

Air purifiers attempt to eliminate or reduce a host of airborne contaminants.

Here is a list of the most common elements that are found in the air of most homes, schools, and offices:

Animal Dander
Dust Mites
Tobacco Smoke

The sources of these pollutants are many. They include dust, people, animals, carpet, plywood, mattresses, furniture, cleaning products, aerosol, humidity, food, and insecticides.

Benefits of air purifiers

Good air purifiers will generally make an immediate difference in the lives of most people. After using an air purifier, many people report sleeping better, having more energy, being more alert, being more creative, breathing better, and just feeling better overall.

Technologies available in air purifiers

Due to advances in science and technology, there are now four methods that are used in air cleaners. Most air purifiers use more than one technology to better clean the air. Most of the machines recommended in our air purifier reviews section, utilize more than one of these:

1. HEPA – a specially designed filter effective against many particles.

2. Ionic – electronically charges particles causing them to attract to collector plates or fall to the floor.

3. Ozone Generato r – creates ozone, which seeks out contaminants.

4. Carbon Filter – removes chemicals, fumes, and smoke.

We’ve created separate pages for each of these air purifier technologies should you want more detailed information. We suggest you check each of them out.


What to look for in an air purifier

OK. We know that air purifiers are necessary and we know why we need them and what they can do. Now, we’ve assembled a list of things to consider when searching for an air purifier for your home or office.

1. Appropriate room size : Make sure the air purifier can change the air several times an hour.

2. Air filtering efficiency: Obviously, you want a air purifier that effectively cleans the air.

3. Air purification technology: Which of the four technologies does the unit use.

4. Noise level: You want this to be as low as possible, but realize some of the better air purifiers do make noise. Quieter doesn’t necessarily mean better.

5. Cost of replacement parts: Find out what it costs to replace filters and other parts

.6. Electricity costs: Know how much it costs to run an electronic air cleaner.

7. Warranty: Learn about the warranty available for the unit you are considering.

8. Indicator lights for filter changes: Some units have this, it’s not necessary but is very convenient

9. Separate filters: Does the unit have a pre-filter to increase HEPA filter efficiency.

10. Size and look of the air purifier: Some air purifiers are big and ugly, others are sleek and pleasing to the eye.


Hopefully this page has given you a solid, helpful introduction to air purifiers and what they can do. Everyday, it seems many people and the medical community are becoming increasingly aware of the need for clean air.

Whole home air purifiers may not be as effective and convenient as portable

There are basically two different ways to go about cleaning your air using an air purifier. You can either get a whole home air purifier or a room air purifier (also called portable). Home air purifiers are in one way or another tied in with the current air conditioning/heating system already present in your home. In contrast, room air purifiers are stand-alone units that can be moved from room-to-room.

Home air purifiers are designed to clean the air over an entire house or office. Most operate by having some type of filter (i.e. activated carbon) over or inside the air vents. As air is pushed in and out, the filters are designed to remove particles.

There are several reasons why home air purifiers are not always the most efficient method of purifying your air. The filters commonly available do not clean the air as efficiently as the HEPA filters in portable air purifiers. Using a HEPA filter in a central ventilation system would restrict the airflow to unacceptable levels.

Also, the current created by air conditioning/heating units is not sufficiently strong enough to get the air cleaned and back into the filter or unit. This does not apply to all systems of course, but it does to many.

Another drawback with home air purifiers is the fact that they can only remove particles 1 to 1.5 microns in size and larger, and they do nothing to remove gases and odors. They are not designed to remove the smaller particulates, which tend to cause the most health problems.

Another consideration as far as cost in involved, most whole home air purifiers require professional installation. This can run anywhere between $200 and more depending on where you live.

ACGIH – American Conference of Governmental Industrial Hygienists

acute – occurring over a short period of time; used to describe brief exposures and effects which appear promptly after exposure

acute exposure – a single exposure to a toxic substance or microorganism which results in severe biological harm or death. Acute exposures are usually characterized as lasting no longer than a day.

algae – microscopic plants which contain chlorophyll and live floating or suspended in water. They also may be attached to structures, rocks or other submerged surfaces. They are food for fish and small aquatic animals. Excess algal growths can impart tastes and odors to potable water. Algae produce oxygen during sunlight hours and use oxygen during the night hours. Their biological activities appreciably affect the pH and dissolved oxygen of the water.

algal bloom – sudden, massive growths of microscopic and macroscopic plant life, algae, and cyanobacteria, which develop in lakes, reservoirs, and marine waters

algicide – any substance or chemical specifically formulated to kill or control algae

allergen – something that causes an allergy, allergic response, or hypersensitivity

allergy – an exaggerated or inappropriate immune response initiated by exposures to antigens such as mold spores, pollen, or certain drugs and foods

ambient – environmental or surrounding conditions

amplification – (amplification source) the process of indoor growth leading to an increased indoor microbial concentration compared to the immediate outdoor environment 

anaphylaxis – (anaphylactic shock)  a severe and life-threatening allergic reaction. These rare reactions can occur following exposure to biological or chemical antigens  such as microbes, insect stings, drugs, and even certain types of foods.

anion – a negatively charged ion in an electrolyte solution, attracted to the anode under the influence of a difference in electrical potential. Chloride (CI-) is an anion.

antagonism – interference or inhibition of the effect of one chemical by the action of another chemical

antibodies – proteins in the blood that are generated in reaction to foreign proteins or polysaccharides; also called “immunoglobulins” 

Anderson sampler – a sieve-type air sampling device that uses a vacuum pump to draw air through a radial pattern of 300 small holes, impacting particles in each of the small streams of air onto the surface of microbial growth medium. 

antigen – a substance or molecule that is recognized by the immune system. The molecule can be from a foreign material such as bacteria or viruses.

antihistamine drugs – group of drugs that block the effects of histamine, a chemical released in body fluids during an allergic reaction.  These drugs may reduce itching, sneezing, and runny nose.

aspergillosis – a group of diseases caused by the fungus Aspergillus; affected tissues may include lungs, bronchial airways, sinus cavities, ears, and eyes

asthma – an immediate hypersensitivity (allergy) resulting in respiratory symptoms such as wheezing, coughing, shortness of breath, and a feeling of constriction within the chest or bronchial airways

autotroph – an organism that can produce its own food from inorganic molecules and sunlight. All photosynthetic plants are autotrophs.


B cells – small white blood cells crucial to the immune defenses; also known as B lymphocytes, they come from bone marrow and develop into blood cells called plasma cells, which are the source of antibodies

background level – the average presence of a chemical substance or microorganism in the environment, originally referring to naturally occurring phenomena

bacteria – microorganisms with prokaryotic cell organization (lacking membrane-bounded nucleus and other specialized features); bacteria are also typically much smaller than fungi (molds)

bioaerosol – an airborne dispersion of particles containing whole or parts of biological entities, such as bacteria, viruses, dust mites, fungal hyphae, or fungal spores 

biocide – substances such as antibiotics, bacterialcides, or fungicides that are capable of destroying living organisms 

biochemical oxygen demand (BOD) – the amount of oxygen consumed by microorganisms (mainly bacteria) and by chemical reactions in the biodegradation of organic matter

black water – liquid and solid human body waste and the carriage water generated through toilet usage

blastomycosis – a disease caused by the fungus Blastomyces dermatitidis; may infect lungs, skin, mucous membranes, bones, internal organs, and joints  

bronchitis – an inflammation of the bronchi (lung airways), resulting in persistent cough that produces consideration quantities of sputum (phlegm)

bronchodilator drugs – a group of drugs that widen the airways in the lungs

brown-rot fungi: fungi that are capable of utilizing the cellulose and hemicellulose portions of wood but are incapable of decomposing brown lignin; rot characteristics include crumbly appearance and brown coloration 

BRI – building-related illness: a recognized disease that can be attributed to airborne building bioaerosols or chemical pollutants


CFUs – Colony Forming Units; individual regions of growth attributed to a single reproductive unit such as a spore or vegetative cell

carcinogenic – cancer-producing or cancer-causing

carriers – seeminglyly healthy people who harbor disease-causing microbes in the body and who can infect others by passing the microbes on to them

cation – a positively charged ion in an electrolyte solution, attracted to the cathode under the influence of a difference in electrical potential. Sodium ion (Na+) is a cation

cell – the smallest and most fundamental unit of life

central nervous system – portion of the nervous system which consists of the brain and spinal cord; CNS

chlorination – The application of chlorine to water, generally for the purpose of disinfection, but frequently for accomplishing other biological or chemical results (aiding coagulation and controlling tastes and odors)

chlorine demand – Chlorine demand is the difference between the amount of chlorine added to water and the amount of residual chlorine remaining after a given contact time. Chlorine demand may change with dosage, time, temperature, pH, and nature and amount of the impurities in the water. Chlorine Demand, mg/L = Chlorine Applied, mg/L – Residual, mg/L

chlorine requirement – The amount of chlorine which is needed for a particular purpose. Some reasons for adding chlorine are reducing the number of coliform bacteria (Most Probable Number), obtaining a particular chlorine residual, or oxidizing some substance in the water. In each case a definite dosage of chlorine will be necessary. This dosage is the chlorine requirement.

chronic – occurring over a long period of time, either continuously or intermittently; used to describe ongoing exposures and effects that develop only after a long exposure

chronic exposure – long-term, low-level exposure to a toxic chemical or microorganism

coccidioidomycosis – a disease caused by the fungus Coccidioides immitis; may infect lungs, internal organs, bones, joints, and skin  

colony – a discrete growth usually discernable by the naked eye; this term is usually used in reference to growth originating from a single spore or cell

contact dermatitis – a rash or inflammation of the skin caused by contact with biological or chemical substances. The reaction may be an immunologic response or a direct toxic effect of the substance. Among the more common causes of a contact dermatitis reaction are detergents, metals, chemicals in rubber gloves and condoms, certain cosmetics, plants such as poison ivy, and topical medications.

corticosteroid drugs – a group of anti-inflammatory drugs similar to the natural corticosteroid hormones produced by the cortex of the adrenal glands. Among the disorders that often improve with corticosteroid treatment include asthma, allergic rhinitis, eczema and rheumatoid arthritis.

cryptococcosis – a disease caused by the fungus Cryptococcus neoformans; may infect lungs, central nervous system, skin, and lining of body cavity  

cytotoxin – a chemical compound that is poisonous to cells


DNA (deoxyribonucleic acid) – a complex molecule found in the cell nucleus which contains an organism’s genetic information

decomposition – the conversion of chemically unstable materials to more stable forms by chemical or biological action. If organic matter decays when there is no oxygen present (anaerobic conditions or putrefaction), undesirable tastes and odors are produced. Decay of organic matter when oxygen is present (aerobic conditions) tends to produce much less objectionable tastes and odors.

degradation – chemical or biological breakdown of a complex compound into simpler compounds

dermal exposure – contact between a microorganism (or chemical) and the skin

dermatophytes – a fungus that causes skin disease in humans or other animals

Der p 1 – an allergen found in house dust mite droppings. A common cause for irritations and allergic reactions usually attributed to dust.

dew point – the temperature at which water would condense from the air if the air mass were cooled. In general, when the relative humidity is high, the dew point will be close to the air temperature. At 100% relative humidity, the dew point is equal to the air temperature. When the relative humidity is low, the dew point is much lower than the air temperature.

diatom – unicellular algae capable of photosynthesis and characterized by producing a thin outer shell made of silica (glass)

dinoflagellates – a diverse assemblage of biflagellate unicellular organisms, which constitute an important component of marine, brackish, and fresh bodies of water

disease – a state in which a function or part of the body is no longer in a healthy condition

dose-response – a quantitative relationship between the dose of a chemical or microorganism and an effect caused by the chemical or microorganism

dose-response curve – a graphical presentation of the relationship between degree of exposure to a chemical or microorganism (dose) and observed biological effect or response

dust mite – a house dust mite (Dermatophagoides pteronyssinus), sometimes abbreviated by allergists to HDM, is a small insect that is a common guest in human habitation. The dust mite droppings are the most common cause of allergic rhinitis and asthma on this planet – they contain an allergen that can irritate a person, or cause an allergic reaction.


endotoxin – a lipopolysaccharide component of the membrane of gram-negative bacteria that is heat stable and toxic; a secreted toxin produced by bacteria is termed an “exotoxin”

epidemic – a widespread outbreak of a disease, or a large number of cases of a disease in a single community or relatively small area. Disease may spread from person to person, and/or by the exposure of many persons to a single source, such as a water supply.

epidemiology – a branch of medicine which studies epidemics (diseases which affect significant numbers of people during the same time period in the same locality). The objective of epidemiology is to determine the factors that cause epidemic diseases and how to prevent them.

eutrophication – the increase in the nutrient levels of a lake or other body of water; this usually causes an increase in the growth of aquatic animal and plant life

exposure assessment – the determination or estimation (qualitative or quantitative) of the magnitude, frequency, duration, route, and extent (number of people) of exposure to a chemical or microorganism

extrapolation – estimation of unknown values by extending or projecting from known values

extrinsic asthma – asthma that is triggered by an allergic reaction, usually something that is inhaled


fecal coliform bacteria – bacteria found in the intestinal tracts of animals. Their presence is an indicator of pollution and possible contamination by other pathogens.

FEV1 – the forced expiratory volume (FEV) in 1 second – the amount of air blown out in the first second, means how much someone can breathe out in one second, trying as hard as possible.

FEV6 – the forced expiratory volume (FEV) in 6 seconds is how much someone can breathe out in six seconds, trying as hard as possible.

FVC – the forced vital capacity (FVC) – the maximum volume of air that can be forcibly expired from the lungs.

flagellates – microorganisms that move by the action of tail-like projections

free available residual chlorine – that portion of the total available residual chlorine composed of dissolved chlorine gas cl2), hypochlorous acid (HOCl), and/or hypochlorite ion (OCl-) remaining in water after chlorination. This does not include chlorine that has combined with ammonia, nitrogen, or other compounds.

fungus – (pl. fungi) a kingdom of organisms (equal in rank to the Plant Kingdom or the Animal Kingdom) defined technically as a parasite or saprobeic, filamentous or single-celled eukaryotic organism, devoid of chlorophyll and characterized by heterotrophic growth, and the production of extracellular enzymes.  Fungi include yeasts, molds, mildews, and mushrooms.  

fungicide – a chemical compound capable of inhibiting or destroying the growth of fungi


gastroenteritis – an inflammation of the stomach and intestine resulting in diarrhea, with vomiting and cramps when irritation is excessive. When caused by an infectious agent, it is often associated with fever.

genes – units of genetic material (DNA) that carry the directions a cell uses to perform a specific function

genus – a grouping of similar species according to taxonomic criteria, for example, humans (Homo sapiens) belong to the genus ‘Homo’ and the species ‘sapiens’


HVAC – Heating, Ventilating, and Air-Conditioning

HEPA filter – High Efficiency Particulate Air filters that have been tested to assure removal of 99.9% of particles 0.3 µm in size. Another benefit of a HEPA air filtration system is that it can remove harmful V.O.C.’s (Volatile Organic Compounds) which are gases that come from house-hold chemicals and synthetic materials.
HEPA filters are highly recommended for allergy sufferers. HEPA filters collect the airborne dust and dander including dust mites rather than just pushing the air around the room as an ionizer does. Many filtration systems that don’t have HEPA filters leave the toxic elements trapped in the room and eventually they become airborne again. The idea is to remove the dust from your home, not simply move it from here to there.

hepatotoxin – a chemical compound that is poisonous to the liver

hepatitis – hepatitis is an inflammation of the liver usually caused by an acute viral infection. Yellow jaundice is one symptom of hepatitis.

heterotrophic microorganisms – microorganisms that use organic matter synthesized by other organisms for energy and growth

heterotrophic plate count (HPC) – the number of colonies of heterotrophic bacteria grown on selected solid media at a given temperature and incubation period, usually expressed in number of bacteria per milliliter of sample

histamine – a chemical present in cells throughout the body that is released during an allergic reaction. Histamine is one of the substances responsible for the symptoms of inflammation and is the major reason for running of the nose, sneezing, and itching in allergic rhinitis. It also stimulates production of acid by the stomach and narrows the bronchii or airways in the lungs.

histoplasmosis – a disease caused by the fungus Histoplasma capsulatum; may infect lungs, skin, mucous membranes, bones, skin, and eyes

host – an individual who is parasitized or infected by a parasite or pathogen

human health risk – the likelihood (or probability) that a given exposure or series of exposures may have or will damage the health of individuals experiencing the exposures

human immunodeficiency virus (HIV) – the virus that causes AIDS

humus – organic portion of the soil remaining after prolonged microbial decomposition

hypersensitivity – an allergy; an exaggerated or inappropriate immune response categorized based on which part of the immune system that is involved and the onset of response (i.e. Types I, II, III, IV)

hypha – (pl. hyphae) a branching tubular structure that forms the vegetative body of a growing filamentous fungus

hypochlorite – chemical compounds containing available chlorine; used for disinfection. They are available as liquids (bleach) or solids (powder, granules and pellets). Salts of hypochlorous acid.


immune system – a complex network of specialized cells, tissues, and organs that defends the body against attacks by disease-causing microbes

immunization – vaccination or other process that induces protection (immunity) against infection or disease caused by a microbe

immunocompromised – any condition in which the immune system functions in a abnormal or incomplete manner; such conditions are more frequent in the young, the elderly, and individuals undergoing extensive drug or radiation therapy

immunoglobulins – proteins in the blood that are generated in reaction to foreign proteins or polysaccharides; also called “antibodies” 

immunosuppression – suppression of the natural immune response (see immunocompromised)

immunotherapy – (“allergy shots”) is a form of preventive and anti-inflamamatory treatment of allergy to substances such as pollens, house dust mites, fungi, and stinging insect venom. Immunotherapy involves giving gradually increasing doses of the substance, or allergen, to which the person is allergic. The incremental increases of the allergen cause the immune system to become less sensitive to the substance, perhaps by causing production of a particular “blocking” antibody, which reduces the symptoms of allergy when the substances is encountered in the future.

impermeable – not easily penetrated. The property of a material that des not allow, or allows only with great difficulty, the movement or passage of water.

infection – a state in which disease-causing microbes have invaded or multiplied in body tissues

infectious diseases – diseases caused by microbes that can be passed to or among humans by several methods

inflammation – an immune system process that stops the progression of disease-causing microbes, often seen at the site of an injury like a cut. Signs include redness, swelling, pain, and heat

ingestion – type of exposure that occurs through the mouth

inhalation – type of exposure that occurs through the lungs

intrinsic asthma – asthma that has no apparent external cause

ion – an electrically charged atom, radical (such as SO 4 2- ), or molecule formed by the loss or gain of one or more electrons

ionization – the splitting or dissociation (separation) of molecules into negatively and positively charged ions



keratitis – microbial infections of the cornea (eye); when caused by a fungus, it is referred to as mycotic keratitis


latent – present but not seen; a latent viral infection is one in which no virus can be found in the blood cells but in which those virus-infected cells can produce virus under certain circumstances

Legionnaires’ Disease (Legionellosis) – a form of pneumonia caused by the bacterium Legionellae ; first discovered in 1976 from infected persons attending the Legionnairs meeting in Philadelphia  

lymphocyte – any of a group of white blood cells of crucial importance to the adaptive (humoral) part of the body’s immune system. The adaptive portion of the immune system mounts a tailor-made defense when dangerous invading organisms penetrate the body’s general defenses.


malignant – very dangerous or virulent, causing or likely to cause death

mast cells – cells that play an important role in the body’s allergic response. Mast cells are present in most body tissues, but are particularly numerous in connective tissue, such as the dermis (innermost layer) of skin. In an allergic response, an allergen stimulates the release of antibodies, which attach themselves to mast cells. Following subsequent allergen exposure, the mast cells release substances such as histamine (a chemical responsible for allergic symptoms) into the tissue.

meningitis – inflammation of the meninges, the membranes that surround the brain and spinal cord

microbe – a general or non-specific term for any microorganism such as bacteria, fungi (molds), algae, or protozoa

microgram (µg) – one-millionth of a gram (3.5 x 10-8 oz. 0.000000035 oz.)

micrometer (µm) or micron – a unit of length. One millionth of a meter or one thousandth of a millimeter. One micron equals 0.00004 of an inch.

microscopic – too small to be seen with the naked eye

milligrams per liter (mg/L ) – a measure of concentration of a dissolved substance. A concentration of one mg/L means that one milligram of a substance is dissolved in each liter of water. For practical purposes, this unit is equal to parts per million (ppm) since one liter of water is equal in weight to one million milligrams. Thus a liter of water containing 10 milligrams of calcium has 10 parts of calcium per one million parts of water, or 10 parts per million (10 ppm).

mildew – a common name for mold or fungi; often used in reference to fungal growth on bathroom tiles and fixtures 

mixotroph – an organism capable of producing its own food from inorganic molecules and sunlight as well as feeding directly on other organisms as well

molar or molarity – a molar solution consists of one gram molecular weight of a compound dissolved in enough water to make one liter of solution. A gram molecular weight is the molecular weight of a compound in grains. For ex- ample, the molecular weight of sulfuric acid (H2SO4) is 98. A one M solution of sulfuric acid would consist of 98 grains of H2SO4 dissolved in enough distilled water to make one liter of solution.

mold – a common name for fungi that grow in a filamentous fashion and reproduce by means of spores; all molds are fungi, but not all fungi are considered ‘molds’  

molecules – the smallest physical units of a substance that still retain the chemical properties of that chemical substance; molecules are the building blocks of a cell. Some examples are proteins, fats, carbohydrates, and nucleic acids.

most probable number (MPN) – MPN is the Most Probable Number of coliform-group organisms per unit volume of sample water. Expressed as the number of organisms per 100 mL off sample water.

motile – capable of self-propelled movement. A term that is sometimes used to distinguish between certain types of organisms found in water.

mucormycosis – a group of disease caused by the fungi belonging to the group Mucorales (Class Zygomycetes); such fungi may infect lungs, sinuses, mucous membranes, central nervous system, internal organs, and eyes  

mulch – any substance spread or allowed to remain on the soil surface to conserve soil moisture and shield soil particles from the erosive forces of raindrops and runoff

mutagenicity – the capacity of a chemical or physical agent to cause permanent alteration of the genetic material within living cells

mycellium – the collective mass of hyphae (filamentous cells) comprising the body of most fungi and molds  

mycetoma – invasive fungal infection of subcutaneous tissues (under the skin)

mycology – the scientific study of fungi (Kingdom Fungi or Mycota)    

mycosis – an infection caused by fungi (mold) (pl. mycoses)  

mycotoxicosis – any disease caused by fungal toxins (mycotoxins)  

mycotoxins – a diverse class of poisonous compounds produced by certain mushrooms and other fungi; mycotoxins are produced on the surface of mold spores and remain toxic even after the spore is dead


necrosis – death of cells or tissue

neoplasm – an abnormal growth or tissue, as a tumor

neurotoxin – a chemical compound that is poisonous to the nervous system

nitrification – the biological or chemical transformation of ammonium nitrogen to nitrate nitrogen

nitrogen fixation – the biological or chemical process by which elemental nitrogen, from the air, is converted to organic or available nitrogen

non-point source – pollution sources which are diffuse and do not have a single point of origin or are not introduced into a receiving stream from a specific outlet. The pollutants are generally carried off the land by storm water runoff. The commonly used categories for non-point sources are: agriculture. forestry, urban, mining, construction, dams and channels, land disposal, and saltwater intrusion.

nutrient – any substance that is assimilated (taken in) by organisms and promotes growth. For example, nitrogen and phosphorous are nutrients which promote the growth of algae. There are other essential and trace elements which are also considered nutrients.

nutrient pollution – contamination of water resources by excessive inputs of nutrients; in surface waters, excess algal production is a major concern


odor threshold – the minimum odor of a water sample that can just be detected after successive dilutions with odorless water. Also called THRESHOLD ODOR.

olfactory fatigue – a condition in which a person’s nose, after exposure to certain odors, is no longer able to detect the odor

oligotrophic – reservoirs and lakes which are nutrient poor and contain little aquatic plant or animal life

onychomycosis – invasive fungal infections of the nail

organic – substances that come from animal or plant sources. Organic substances always contain carbon. (Inorganic materials are chemical substances of mineral origin.)

otomycosis – a superficial fungal infection of the outer ear canal

oxidation – oxidation is the addition of oxygen, removal of hydrogen, or the removal of electrons from an element or compound. In the environment, organic matter is oxidized to more stable substances. The opposite of reduction.

oxidation-reduction potential – the electrical potential required to transfer electrons from one compound or element (the oxidant) to another compound or element (the reductant); used as a qualitative measure of the state of oxidation in water treatment systems.

oxidizing agent – any substance, such as oxygen (O 2 ) or chlorine (Cl 2 ), that will readily add (take on) electrons. The opposite is a reducing agent.

ozonation – the application of ozone to water for disinfection or for taste and odor control


pandemics – diseases that affect many people in different regions around the world

parasites – plants or animals that live, grow, and feed on or within another living organism

particle count – the results of a microscopic examination of treated water with a special “particle counter” which classifies suspended particles by number and size

particulate – a very small solid suspended in air or water which can vary widely in size, shape, density, and electrical charge

pathogen – a microorganism that causes a disease response

periphyton – microscopic plants and animals that are firmly attached to solid surfaces under water such as rocks, logs, pilings and other structures

peak flow – the fastest rate of air (airflow) that you can blow out of your lungs. Its recorded in liters per minute (l/min).

PEF – the fastest speed a person can blow air out of their lungs.

pH – an expression of the intensity of the basic or acid condition of a liquid. Mathematically, pH is the logarithm (base 10) of the reciprocal of the hydrogen ion concentration, [H+]. pH= Log (I/[H+]) The pH may range from 0 to 14, where 0 is most acid, 14 most basic, and 7 neutral. Natural waters usually have a pH between 6.5 and 8.5.

photosynthesis – a process in which organisms, with the aid of chlorophyll (green plant enzyme), convert carbon dioxide and inorganic substances into oxygen and additional plant material, using sunlight for energy. All green plants and many microorganisms (such as algae) grow by this process.

phytoplankton – small, usually microscopic plants (such as algae), found in lakes, reservoirs, and other bodies of water

piedra – fungal infection of hair shafts resulting in the formation of dark (black piedra) or white (white piedra) nodules within the hair shaft 

plankton -1) Small, usually microscopic, plants (phytoplankton) and animals (zooplankton) in aquatic systems. 2) All of the smaller floating, suspended or self-propelled organisms in a body of water.

pneumonia – a disease characterized by the inflammation of the lungs; often caused by bacteria or certain species of fungi 

point source – a stationery location or fixed facility from which pollutants are discharged or emitted. Also, any single identifiable source of pollution, e.g., a pipe, ditch, ship, ore pit, factory smokestack.

ppb – parts per billion. Also µg/L or micrograms per liter.

ppm – parts per million. Also mg/L or milligrams per liter.

propagule – any disseminable microbial element that can give rise to new growth (e.g. spores, hyphal fragments, cells) 

pulmonary hemorrhage – a condition characterized by bleeding in the lungs caused by weakening of the lung vessels

putrefaction – biological decom- position of organic matter, with the production of ill- smelling and tasting products, associated with anaerobic (no oxygen present) conditions


qualitative – descriptive of kind, type or direction, as opposed to size, magnitude or degree

quantitative – descriptive of size, magnitude or degree


RNA (ribonucleic acid) – a complex molecule that is found in the cell cytoplasm and nucleus. One function of RNA is to direct the building of proteins.

RAST testing – radioallergosorbent test; a blood test for measuring antigen specific antibodies (allergic reactions).  Used primarily where skin testing is impractical or unreliable (i.e. extreme sensitivity, dermatitis, children).     

reducing agent – any substance, such as base metal (iron) or the sulfide ion (S2-), that will readily donate (give up) electrons. The opposite is an oxidizing agent.

reduction – reduction is the addition of hydrogen, removal of oxygen, or the addition of electrons to an element or compound. Under anaerobic conditions (no dissolved oxygen present), sulfur compounds are reduced to odor-producing hydrogen sulfide (H 2 S and other com- pounds. The opposite of oxidation.

relative humidity – an expression of how much moisture is in the air as a percentage of the total moisture the air can contain at the current temperature. For example, if the air has all the water vapor that it can contain at a given temperature, the relative humidity is 100%; if the air has only half of the vapor that it can contain at a given temperature, the relative humidity is 50%.

representative sample – a portion of material or water that is as nearly identical in content and consistency as possible to that in the larger body of material or water being sampled

residual chlorine – the amount of free and/or available chlorine remaining after a given contact time under specified conditions

respiration – the process in which an organism uses oxygen for its life processes and gives off carbon dioxide

rhinitis – an inflammation of the mucous membrane that lines the nose, often due to an allergy to pollen, dust or other airborne substances. Seasonal allergic rhinitis also is known as “hay fever,” a disorder which causes sneezing, itching, a runny nose and nasal congestion.

ringworm – fungal infections of the skin resulting in raised red swellings or lines that resemble burrowing worms; includes the diseases known as athlete’s foot, jock itch, and ringworm or the scalp

risk – the potential for realization of unwanted adverse consequences or events

risk assessment – a qualitative or quantitative evaluation of the environmental and/or health risk resulting from exposure to a chemical or microorganism; combines exposure assessment results with toxicity assessment results to estimate risk.

risk characterization – final component of risk assessment that involves integration of the data and analysis involved in hazard evaluation, dose-response evaluation, and human exposure evaluation to determine the likelihood that humans will experience any of the various forms of toxicity associated with a substance.

risk estimate – a description of the probability that organisms exposed to a specified dose of chemical will develop an adverse response (e.g., cancer).

risk factor – characteristic (e.g., race, sex, age, obesity) or variable (e.g., smoking, occupational exposure level) associated with increased probability of a toxic or adverse effect

risk management – decisions about whether an assessed risk is sufficiently high to present a public health concern and about the appropriate means for control of a risk judged to be significant

rotavirus – a group of viruses that can cause digestive problems and diarrhea in young children

route of exposure – the avenue by which a chemical comes into contact with an organism (e.g., inhalation, ingestion, dermal contact, injection)


safe – condition of exposure under which there is a “practical certainty” that no harm will result in exposed individuals

saprobe – any microorganism capable of obtaining nutrients from dead or non-living organic matter  

serology – the medical science of serum; or the technique of determining antigens or antibodies in serum

serum – the clear or slightly yellowish liquid that remains after the plasma portion is allowed to clot; blood is comprised of a plasma portion (55%) and a cellular portion (45%); plasma contains water, salts, and plasma proteins (albumin, fibrinogen, antibodies) whereas the cellular portion contains red blood cells (erythrocytes), platelets, and white blood cells (leukocytes)

Sick Building Syndrome (SBS) – a set of symptoms associated with indoor exposure to chemicals or microorganisms characterized by headaches; eye, nose and throat irritations; fatigue; and skin disorders 

sinusitis – inflammation of the membrane lining the facial sinuses (air cavities within facial bones), often caused by bacterial, fungal, or viral infection.

skin tests – tests for an allergy or infectious disease performed by a patch test, scratch test, or an intracutaneous injection of an allergen or extract of the disease-causing organism

soft-rot fungi: fungi that are capable of decomposing the cellulose and hemicellulose portions of wood; most soft-rot also partially degrade lignin; these species are most common in moist hardwoods

species – the most specific taxonomic classification; an interbreeding population of individual organisms; often abbreviated as ‘sp.’ in reference to a single species or ‘spp.’ when referencing several species

spores – reproductive units or specialized cells that provide the primary means for dispersal and survival; many fungal (mold) spores are capable of long term dormancy and are therefore referred to as resistant spores or resting spores

sterilization – the removal or destruction of all microorganisms, including pathogenic and other bacteria, vegetative forms and spores

substrate – substance on or in which a microorganism is living

surface water – all water naturally open to the atmosphere (rivers, lakes. reservoirs, streams, impoundments, seas, estuaries, etc.) and all springs. wells, or other collectors which are directly influenced by surface water

synergism – an interaction of two or more chemicals which results in an effect that is greater than the sum of their effects taken independently


T cells – small white blood cells (also known as T lymphocytes) that direct or directly participate in immune defenses

teratogenesis – the induction of nonhereditary congenital malformations (birth defects) in a developing fetus by exogenous factors acting in the womb; interference with normal embryonic development

teratogenicity – the capacity of a physical or chemical agent to cause teratogenesis in offspring

tissues – groups of similar cells joined to perform the same function

toxigenic –  a substance or biological entity that has the property itself or can produce one or more compounds that have the property to harm humans or other animals

total residual chlorine – the amount of available chlorine remaining after a given contact time. The sum of the combined available residual chlorine and the free available residual chlorine. Also see residual chlorine

Type I Hypersensitivity (anaphylactic reactions) – an immediate, usually localized response to allergens such as fungi, pollen, dust mites, or animal dander; examples of this type of disorder include insect stings, asthma, food allergies, drug reactions, and hives;  type of antibodies involved: IgE 

Type II Hypersensitivity (cytotoxic reactions) – a delayed response (usually within hours or days) involving reactions against antigens located on target cells which are then destroyed; examples of this type of disorder include blood transfusions reactions and hemolytic disease of newborns (involving Rh factors); type of antibodies involved: IgG, IgM

Type III Hypersensitivity (immune-complex reactions) – a delayed response (usually within hours or days) involving insoluble antigen-antibody complexes which cause tissue necrosis (death) and acute inflammation; examples of this type of disorder include Farmer’s Lung (caused by fungi and other microorganisms), serum sickness, and malaria; type of antibodies involved IgG, IgM 

Type IV Hypersensitivity (cell-mediated response) – a delayed response to microorganisms, tissue transplants, or chemicals that cause cellular inflammation; examples of this type of disorder include contact dermatitis, and Tuberculosis reactions (Mantoux test); type of antibodies involved: none


U.S. Electrical Standard – a standard for electrical current voltage and frequency used within the United States. These values are different for every country – in the U.S. they are 120 V for voltage and 60 Hz for frequency. This means that you will not be able to use an electrical appliance made for the U.S. in a country with a different electrical standard. Also, U.S. appliances use the so-called Type A (non-polarized, with two parallel flat prongs) and Type B (polarized, with two flat parallel prongs and a round grounding pin directly above them) plugs, which will not fit into, for example, European power outlets (where the Type C plugs with two round prongs are usually used).

urticaria – a skin condition, commonly known as hives, characterized by the development of itchy, raised white lumps surrounded by an area of red inflammation


VOCs – volatile organic compounds; some VOCs are of industrial origin whereas others are produced by microorganisms

vaccines – substances that contain parts of antigens from an infectious organism. By stimulating an immune response (but not disease), they protect the body against subsequent infection by that organism.

viable – capable of living, developing, or germinating under favorable conditions; capable of success or ongoing effectiveness

volatile – readily vaporizable at a relatively low temperature


water activity  – the water activity of a solution is equal to 1/100th the relative humidity when expressed as a percent. Water activity is also equivalent to the ratio of the solution’s vapor pressure to the vapor pressure of pure water.  

white-rot fungi: fungi that are capable of utilizing lignin as well as cellulose and hemicellulose; most wood-decay fungi (especially many mushrooms) are of this type; these species are often associated with rot of building lumber

wood-decay fungi – fungi that are capable of decomposing various components of wood; categorized as either soft-rot fungi, brown-rot fungi, or white-rot fungi



yeast – a group of single-celled fungi characterized by the ability to reproduce by budding